Parasite of the Day

Pasteuria ramosa

2012-01-28T01:12:00.003-05:00

Parasitic infections can severely debilitate the host in many ways, sometimes this manifest itself as the loss of some or even all of the host's reproductive ability. Evolutionary speaking, an organism that cannot reproduce is as good as dead. However, it's not entirely clear who (if anyone) is benefiting from this outcome - is it; (1) a survival strategy by the host to temporarily free up resource to compensate for the parasite's presence? Or is it (2) an adaptive strategy by the parasites to divert as much resources as possible to itself without compromising the host's ability for self-maintenance and survival? Or is it (3) merely an unintended side-effect of infection? Of course, (1) and (2) are not mutually exclusive, and in the case of (3), even if it had started out as an unintended side-effect of infection, if host castration result in higher reproductive fitness for the parasite, then that trait will be positively selected for and become part of the its repertoire of host-exploitation strategies.

Waterfleas (Daphnia) are infected by all manner of parasites (we featured one of them during the early days of the blog: Caullerya mesnili) , most of them are pretty nasty - they often end up castrating and/or killing the host. Pasteuria ramosa is no different - it is a spore-forming bacteria which infects waterfleas, makes them bloated, darkening their body (see the right waterflea in the photo) and castrates them in the process. While it was previously thought that any waterfleas infected by P. ramosa are permanently castrated, it turns out that some lucky Daphnia can actually recover from their infection.

So do these little crustacean adjust their reproductive output in respond to parasites, and is castration a way for them to compensate for a (potentially) temporary hiccup in their baby-making ability? To find out, a team of scientists from Norway set out to see just who benefits the most from host castration. Their logic is that if it is an adaptive strategy by the parasite, then we should see higher spore output from permanently castrated host. Whereas if castration is an adaptive coping mechanism by the waterflea, then there should be a jump in reproduction upon the onset of infection as the waterflea tries to make as many baby Daphnia as possible before P. ramosa put a stop to it, then store up reserves during the infection to "wait it out".

To correct for any potential sex differences (there are many documented case of sex-bias in parasitism), these scientists used only female waterfleas for the experiment. During the course of the study, about half the waterfleas they infected with P. ramosa managed to regain their reproductive capacity. In those lucky ones, the parasite produced much less spores than in waterfleas which had been permanently castrated. So evidently, P. ramosa benefits from having permanently castrated hosts. But what about the waterfleas themselves? Were they able to compensate by adjusting their reproductive output in the parasite's presence?

The scientists found that by far, the strongest predictor for the lifetime reproductive output of a parasitised waterflea is the age at which it becomes infected - the later that it became infected, the more time it had to churn out babies before it came down with a severe case of P. ramosa. So it's pretty much a case of "use it or lose it". They did not find evidence to suggest the waterfleas made any effort to increase their reproductive output before they are castrated by their parasites. This is unlike other systems where parasite-castration occurs - in trematode-snail systems, the infected snails are less likely to recover from their infection. The strategy which has evolved among snails in areas with high parasite prevalence is to reach sexual maturity as quickly as possible (For example: see this study) so they can eek as many baby snails as they can before they inevitably become infected and have their bodies taken over by squirming body snatchers.

It should be noted that the waterfleas used in the experiment were from Southern Finland, whereas the parasites were isolated from a pond in Northern Germany. So perhaps the reproductive strategy of the Daphnia population used in that experiment have evolved in response to their local parasite(s) population instead. Other studies have found waterfleas to be locked in a close evolutionary race with their parasites across space and time, so the outcome of any host-parasite interaction will be dependent on the genetic identity of both host and parasite.

Image credit: Jensen et al./PLoS Biology

Reference:
Magerøy, J.H., Grepperud, E.J. and Jensen, K.H. (2011) Who benefits from reduced reproduction in parasitized hosts? An experimental test using the Pasteuria ramosa-Daphnia magna system. Parasitology 138: 1910-1915

Spauligodon atlanticus

2012-01-15T07:42:00.004-05:00

Today, we look at a paper showing how data from DNA sequences can help resolve the evolutionary relationship of different parasite species, and even find new species where we least expected it. Traditionally, parasites - like other organisms - are classified based on key characteristics of their anatomy. However, many parasites have simplified morphology (an extreme example is the parasitic snail which has evolved into nothing but a bag of genitalia) and often the few key characters that can be examined are heavily reduced. Therefore, any conclusions about relationships between different parasite species that are based upon anatomical characteristics can lead to misleading or, at best, incomplete conclusions.

Spauligodon atlanticus is a species of nematode that parasitises Gallotia, a genus of lizards living on the Canary Islands (see image). Spauligodon atlanticus was initially described in 1987 using traditional methods, i.e. based solely on its anatomical features. In the case of parasitic nematodes, the key characteristic for distinguishing different species is the shape of the genitalia and tail appendages of the male specimen (such features are too indistinct in the females across different species).

For this particular study, a group of biologist from Portugal and Spain went to the Canary Islands to collect S. atlanticus from Gallotia lizards, as well as sampling for other species of Spauligodon from lizards of southern Spain, Morocco, and Armenia. They compared the DNA sequences of the worms and found that nematodes that had been identified as S. atlanticus (based on their anatomy) actually consisted of two distinct species. While they looked the same, their molecular signature revealed two separate lineages; an eastern lineage that is specific to the lizard species Gallotia atlanticus, and the western lineage that is found in 4 different Gallotia species. They also differ in their evolutionary relationships with other nematodes in the Spauligodon genus. The eastern lineage is more closely related to nematodes in wall lizards (Podacris spp.) from southern Spain and Morocco while the western lineage is more related to worms in green lizards (Lacerta spp.) from Armenia.

These two genetically separate lineages of S. atlanticus are what are known as a cryptic species complex (something that we have previously covered on this blog). Recent studies in the last ten years have shown that some parasite species which had previously been thought to be a single generalist species infecting multiple hosts, are in fact composed of multiple specialised species in disguise.

Meanwhile, this study raises another question - how did these two genetically separate lineages, living in different lizards, evolve such similar anatomical characteristics? The authors of the paper raised the possibility that the anatomy of the two lineages had evolved to convergence due to similar conditions they encounter inside the gut of their respective lizard hosts, or that even sexual selection was responsible, since the key anatomical difference use to distinguish these nematode species is the shape of the male genitalia. But this is a question that will only be resolved with further analyses of related Spauligodon species. As the authors wrote in the title of their paper, there are "no simple answers".

Image from the Wikipedia.

Reference:
Jorge, F., Roca, V., Perera, A., Harris, D.J. and Carretero, A. (2011) A phylogenetic assessment of the colonisation patterns in Spauligodon atlanticus Astasio-Arbiza et al., 1987 (Nematoda: Oxyurida: Pharyngodonidae), a parasite of lizards of the genus Gallotia Boulenger: no simple answer. Systematic Parasitology 80:53-66

Apocephalus borealis

2012-01-03T21:40:00.009-05:00

Many of you have heard of the very scary phenomenon called "Colony Collapse Disorder" - and if you haven't, you should, because it could be a major threat to the food we eat. CCD is when the worker honey bees abandon their hives and die, which, if widespread, can mean drastic decreases in pollination of crops. This phenomenon was first reported in the U.S. in 2006 and ever since that time, scientists have struggled to uncover what was responsible. Everything from cell phone radiation to genetically modified crops to a variety of parasites of honey bees were suggested to be the cause. Then, today, a new paper in PLoS One showed data suggesting that another kind of parasite is linked to CCD. Apocephalus borealis is a parasitoid fly that was known to attack bumblebees and paper wasps, but now has been demonstrated to also attack honeybees in the U.S. - in fact, 77% of the colonies sampled near San Francisco were parasitized by A. borealis. The authors used DNA barcoding to confirm that the flies in the honey bees were genetically indistinguishable from those parasitizing bumble bees.

The authors of the new study also found that bees that were found flying around at night (something honey bees don't normally do) were significantly more likely to be parasitized by the fly and furthermore, the sick bees also seemed disoriented. It is not currently known whether or not the tendency for the parasitized bees to fly at night away from their colonies is another example of manipulation of the host by a parasite or whether this might be an act of altruism by the bee, carrying its parasite away from its colony and thus protecting the others.

Although these new results are very exciting, many questions remain to be answered about the history and impact of A. borealis. First, when did the switch into honey bees occur? Honey bees are not native to the U.S., but since they are so well monitored and studied, the authors believe that the switch must have happened recently - otherwise it would have been noticed by apiculturists. Second, could these flies also be serving as vectors for other bee pathogens? Two known bee pathogens, Deformed Wing Virus and Nosema ceranae, a microsporidian were found in the A. borealis flies. And finally, could the invasion of honey bees by this parasite mean that CCD is going to increase? The natural hosts of A. borealis are bumble bees, which live in small colonies where only the queen herself survives the winter, but honey bee colonies have thousands of bees and their activity maintains some amount of heat, even in colder winter months. This increase in host resources and more generations per year could spell a population explosion of A. borealis...and that won't be good for those of us who depend on pollination - like all of us.

The image is from the paper. Look closely at the abdomen of the bee - that's a little parasitic fly laying eggs into it. Soon the larvae will emerge from the dead host. (You can see a photo of this in the original paper as well.)

Source: Core A, Runckel C, Ivers J, Quock C, Siapno T, et al. (2012) A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis. PLoS ONE 7(1): e29639. doi:10.1371/journal.pone.0029639.

Chipping away at the tip of the iceberg

2011-12-31T16:41:00.010-05:00

Through out 2011, we have been featuring more weird and wonderful parasites as we have done in 2010, but on top of that we have also been featuring some of the latest pieces of research being published on all manners of parasitic and infectious organisms which may not have been covered elsewhere in the blogosphere.

Just this year we saw a molecular study that revealed the transmission pathway of a great white shark tapeworm via dolphin blubber, a koala blood parasite named after Steve Irwin, a nematode which infiltrate pine trees via borrowed genes from fungi, a parasitic plant which disperse its seeds via beetles, and a little digenean fluke which changed the face of an entire mudflat, just to name a handful out of dozens that we have featured.

So in 2011, we have gone beyond merely showing you the parasites, but also told you about the research which are being conducted behind the scene to work out how they live. At the same time, you also got a bit of insight into the scientific process, and how knowledge accumulate and grow over time.

In 2012, we will continue to bring you new and exciting research on parasites and parasitism - publications which we found interesting but might not have received their share of fanfare and press releases (as I type this up, I have at least another 4 paper waiting in line to write up. And no doubt I'll find another 4 to write about by the time I'm done with those).

Of course, research on a particular host-parasite system does not simply enter suspended animation after a single study has been published. For many lab groups, the parasite we have featured on this blog form the basis of their scientific research, and the newly published paper we have chosen to feature here merely represents a thin cross-section of their ongoing research program. So in 2012 we might also be revisiting some of the parasites that we have previously featured on the blog, and fill you in on the latest updates as they hit the press.

Of course, you can now also find us on other forms of social media where we will be posting about updates to the blog. Susan is on Twitter , and you can find myself on Google Plus.

Here's to another year of parasitism - the most common way of life on this planet!

Hematodinium sp.

2011-12-17T07:18:00.009-05:00

Today's parasite, Hematodinium sp., infects blue crabs and causes a disease known as "bitter crab". While the name may sound just slightly nauseating for your palate, for the afflicted crabs, its symptom is down right horrific. The parasite causes the crab's hepatopancreas (equivalent of our liver and pancreas) to malfunction, it starts suffocating, and its muscles eventually dissolve within its exoskeleton. Crabs that are experimentally infected start dying about 2 weeks after initial exposure, and this deadly parasite may have even contributed to the recent decline of blue crabs in Chesapeake Bay.

Hematodinium and related species are dinoflagellates, and while most dinoflagellate are free-living, this species belongs to a group which have evolved to be parasites, with many different species infecting a wide variety of hosts. While, several different stages of the parasite have been isolated from the blood of infected crabs, little is known about how they are transmitted between hosts, nor the inner life of those different stages in the hosts. Because many parasites live enclosed within the body of their hosts, it is almost impossible to directly observe how they live and grow the way you might be able to observe a fish or a bird. Ideally, if you can isolate a parasite out of its host, put in it a clear container which closely mimics the conditions found within its host, and still have it complete its life-cycle, then you can find out a lot more about how it lives.

Recently, a group of researchers from Virginia were able to successfully complete the life-cycle of Hematodinium in vitro - which means they were able to grow it in a culture of chemical broth that sustained the parasite's every need, without any host animals involved. This was accomplished through a painstaking series of transfers, starting with isolating the parasite from infected crabs, then moving each stage into different culture mixes as it grew, all while keeping the conditions as sterile as possible. Out of the 10 isolates they attempted to grow, only 4 successfully completed their life-cycle in vitro. The researchers also found out that the parasite grows best in the dark, and indeed light exposure kills them within weeks, which makes sense given that it is pretty dark inside a crab (a variation on the Marx Brother joke).

Through this in vitro technique, they were able observe the different parasitic stages of Hematodinium directly, and view them as they would have been while floating in the blood and organs of a blue crab. They noted that when Hematodinium cells first enter the crab as "dinospores," they turn into a worm-shaped form called a "filamentous trophont" (see the accompanying photo which was from a figure in the paper). About a month after that, the cells begin transforming into clumps that are composed of multiple clones of the original infection stage. These clumps then grow into a stage called an "arachnoid trophont," which resembles a blob with numerous tendrils around its fringe (which would be embedded in the hepatopancreas of the crab). These clumps tend to merge and form larger blobs as they come into contact with each other. When those "arachnoid trophonts" fully develop, the cells in the middle of the blob start producing spores that eventually turn into the infective dinospores that escape from the crab to infect new hosts, starting the life-cycle anew.

Reference:
Li, C., Miller, T.L., Small, H.J. and Shields, J.D. (2011) In vitro culture and developmental cycle of the parasitic dinoflagellate Hematodinium sp. from the blue crab Callinectes sapidus. Parasitology 138:1924-1934.

Postscript: Three days after this post went up, I was contacted by Peter Coffey, who used to work on this species of parasite with a bit of additional information/correction: I just have one quick comment on the first sentence in your post. In blue crabs we don't see the same bitter flavor that we do in Alaskan Tanner and Snow Crabs, so we haven't been calling infections in blue crabs BCD.
Thanks Peter!

Lepeophtheirus acutus

2011-12-08T23:06:00.006-05:00

Today, we are featuring a paper which reported on a grey reef shark (Carcharhinus amblyrhynchos) at Burger's Zoo in the Netherlands thar had to be euthanized. "Wait a sec!" you think, "Isn't this supposed to be a blog about parasites? I didn't come here for dead sharks!" Well, just calm down before you close your browser tab in outrage. This particular shark actually succumbed due to a heavy infection of today's parasite - Lepeophtheirus acutus. This parasite is in the same genus as other fish lice that we have previously featured on this blog, but very little is known about this particular species. Prior to this incident, it has only been reported once from the wild, and it was found on the back of a ribbon-tailed stingray (Taeniura lymma), not a shark and certainly nothing was known about how harmful it can be to its host.

From what the staff at the aquarium could work out, this deadly little crustacean was introduced to the facility by an infected male zebra shark (Stegostoma fasciatum) collected off Cairns, Australia on the Great Barrier Reef, which appeared perfectly healthy at the time and passed quarantine. However, about 2 weeks after he was introduced into the aquaria with the other fishes, he started acting weird. At the same time, the grey reef shark mentioned at the start of this post became lethargic and ceased to eat regularly, and about a month after that, both sharks were afflicted with swollen and opaque eyes. Despite the best efforts of the staff to put the infected sharks in quarantine, filter the water with activated carbon, and give them anti-parasite drugs, they were unable to save the grey reef shark, by which time it was swimming with its mouth wide open, not eating at all, and its eyes had deteriorated even further, so the decision was made to euthanize the long-suffering shark.

A necropsy revealed the identity of the killer - a parasitic copepod - most of which were found around the shark's eyes which caused them to become swollen and covered in mucus, and the mouth which led to bleeding gums. The parasite was also found on a female zebra shark and a shovelnose ray (Glaucostegus typus) which shared the aquaria with the deceased grey reef shark. Notably, the blacktip reef shark (Carcharhinus melanopterus) and blacktip sharks (Carcharhinus limbatus) which swam in the same water alongside those infected sharks did not become infected, nor did the many different species bony fishes sharing the same tanks and water. This indicates that L. acutus does display some selectivity in the type of host it infects, with a particular preference for elasmobranchs (sharks and rays), and even then only certain species within that group.

Other than the dead grey reef shark, the other infected sharks survived and recovered fully after treatment. However, this incident shows how outbreaks of infectious diseases can be a big problem for animals in the confined conditions of captivity. In the case of L. acutus, its small size, semi-transparent body, its tendency to infect parts of the host that are difficult to inspect (for example, inside the mouth), and the fact that nothing is know about its ecology meant that the staff had not anticipated such an outbreak. It was the first documented case of infection by a parasitic copepod that led to a shark dying in captivity. This case also illustrates the importance of thorough quarantine procedures, especially when introducing new animals into any facility, as captive conditions can seriously alter the transmission dynamics and pathology of relatively harmless parasites.

Image from figure in the paper.

Reference:

Kik, M.J.L., Janse, M., Benz, G.W. (2011) The sea louse Lepeophtheirus acutus (Caligidae, Siphonostomatoida, Copepoda) as a pathogen of aquarium-held elasmobranchs. Journal of Fish Diseases 34: 793-799,

Rhinanthus minor

2011-12-01T20:21:00.005-05:00

Many parasites can have substantial effects on their hosts, but their impact can often extend to other organisms in the environment. Today's parasite is one of the more pretty-looking ones which we have featured in a while - as opposed to the usual worms and lice, today we are featuring a flowering plant - the yellow rattle. But don't let its pretty yellow flowers fool you, Rhinanthus minor is a ruthless parasite.

It is a hemiparasite (like the mistletoe , which becomes rather popular during this time of the year). The plant overwinters as seed in the soil and germinates during spring, penetrating into the roots of its host plants where it can suck out nutrients and water from the plant's xylem tissue. The yellow rattle is a fast growing plant - it flowers 12 weeks after germination and 3 weeks after that it produces seeds that are loosely held in dry capsules, which gives the plant its name. The yellow rattle often share its host plants with a range of insects, so a group of researchers in the UK decided to look at how this hemiparasite can affect those insects. Specifically, they looked at the effects of R. minor on insects that exploit plants in different ways; the aphid that feeds on the sugary sap flowing in the plant's phloem, the spittle bug, which taps into the xylem that transports water and other nutrients, and the grasshopper, which simply chews on leaves.

The researchers predicted that the over the course of its growth, the yellow rattle would affect those insects differently. They were expecting that it would negatively impact on the spittle bug, because that insect and the hemiparasite both draw their nutrients from the host's xylem. But as is often the case in science, they found something unexpected.

First of all, they found that the effect R. minor had on those insects depended upon the parasite's growth stage, and it becomes most pronounced when the yellow rattle reaches its peak biomass and begins setting seeds. However in contrast to what they were expecting, spittle bugs actually preferred plants parasitised by R. minor. But the insect that benefited the most from the hemiparasite's presence were the aphids. Not only did they prefer sharing a host plant with the yellow rattle (there were three times as many aphids on plants with R. minor compared to uninfected plants), they also tend to breed more on infected plants. What about the grasshoppers? Grasshoppers were not all that affected by the presence of the yellow rattle either way.

The mechanism behind why the yellow rattle makes its host more attractive to plant-feeding insects is currently unknown. However, it may have something to do with the hemiparasite altering the water content of the host plant, or changing the composition of the phloem sap, which makes it more nutritious to aphids. Either way, it seems that at least for some insects, sharing a plant with a hemiparasite might actually be a good thing.

Image from the Wikipedia.

Reference:

Ewald, N.C., John, E.A. and Hartley, S. (2011) Responses of insect herbivores to sharing a host plant with a hemiparasite: impacts on preference and performance differe with feeding guild. Ecological Entomology 36: 596-604.

Ophiocordyceps unilateralis

2011-11-22T19:17:00.008-05:00

Have you ever been so intoxicated that you start walking erratically, stumble away from your friends, stagger around in circles, clamber onto things that you wouldn't normally be seen near, and the next thing you know, you are strapped down in unfamiliar surroundings, unable to extricate yourself? Well, that pretty much describe what happens to ants which become infected with the famous "zombie ant" fungus - Ophiocordyceps unilateralis.

Much has been written about this famous which turns ants into zombies - it is a parasite which captures the same part of our psyche as the monstrosities of horror movies, and there is evidence to suggest that these fungi have been tormenting ants for at least tens of millions of years. But despite all that attention, few people have actually witnessed or documented the sequence of behaviour leading up to the infected ant's paralysis and death. But in a paper published this year, a group of researchers followed the behaviour of ants infected with the famous "zombie"-inducing fungus and compare them to their uninfected brethren.

They noticed a few peculiarities with the behavioural repertoire of infected ants which stood out. While healthy ants studiously stick to the usual lanes of ant traffic, climbing into the canopy to forage with all the other busy worker ants, "zombie ants" are loners which meander around in the understory by themselves, are unresponsive to most stimuli, and frequently stumble and fall from the branches they are walking on. Essentially, the ants act absolutely drunk, indeed, the researchers described the behaviour of the "zombie ants" as a "drunkard's walk" in their paper. Another weird thing that infected ants start doing is their tendency to crawl all over and bite into leaves - something which healthy ants don't tend to do. There's a good reason why the fungus steers the ant towards leaves and afflict it with this oral fixation - it is preparing it for the next step in the fungus' development.

For the fungus to successfully reproduce, the ant must die - but it must die in a particular position to maximise the viability and dispersal of the fungal spores, specifically in the humid understory, hanging from the underside of a leaf, about 25 cm (about 10 inches) above the ground. But once the fungus maneuver the ant into position, how does it get the host to comply and stay there? The researchers made fine histological cross-section of the infected ant's head and found that once the fungus has made the ant locks its mandible in place, it busily gets to work dissolving the muscles which control those mandibles, ensuring that the ant will be locked in a death grip forevermore. A few days after the ant dies while gripping onto, the fungal stalk emerges from the head of the ant, ready to spray its spores down to the soil below to create more drunken "zombie ants".

Image from the Wikipedia.

Reference:

Hughes DP, Andersen SB, Hywel-Jones NL, Himaman W, Billen J, Boomsma JJ. (2011) Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection. BMC Ecology 11:13

Postscript: A few hours after I wrote this post, I found out that Carl Zimmer has already written about this study (why, of course! *facepalm*), so if you want to read his version instead, you can see it here.

Polypocephalus sp.

2011-11-11T11:30:00.006-05:00

Today's parasite might be thought of as an "aquatic Toxoplasma" in that it also induces behavioral changes in its hosts. Polypocephalus is a genus of tapeworms that infects both shrimp (Litopenaeus setiferus) and then likely rays such as the Atlantic stingray, (Dasyatis sabina). The larvae of the cestode invade the neural tissue of the shrimp hosts, particularly in the abdominal ganglia. Studies recently showed that the more larval tapeworms a shrimp had, the more time these hosts spent walking on the substrate, as opposed to sitting still or swimming. Although the authors had predicted that they would see an increase in swimming behavior because that might expose them to predation more readily, perhaps just the increased activity in general is enough to promote transmission. Nonetheless, this was an exciting insight into a potentially new system for studying parasite manipulation of their hosts.

Source: Carreon, N., Z. Faulkes, and B. L. Fredensborg. 2011. Polypocephalus sp. infects the nervous system and increases activity of commercially harvested shrimp. Journal of Parasitology 97:755-759

Image from figure of that paper.

Bursaphelenchus xylophilus

2011-11-03T21:45:00.009-04:00

Today's parasite is the nematode Bursaphelenchus xylophilus, a well-known tree-killer responsible for the devastating plant disease known as pine wilt. Originating in North America, it has since been spread over much of Asia, and has recently been introduced to Europe. This nematode is transported by longhorn beetles known as "pine swayers", and gain initial access to the tree through the feeding wound created by that insect. So the arrival of a B. xylophilus-laden beetle pretty much amounts to a death sentence for a pine tree. While pine trees in North America have coevolved with B. xylophilus and developed resistance or tolerance for the parasite, it has caused widespread wilting and death to the pine trees of Japan. So how can such a tiny worm bring down an entire pine forest?

For B. xylophilus, or any other plant parasites for that matter, a tree is a formidable fortress - protected by walls and scaffolding of tough cellulose, and canals of deadly resin. Plant cell wall presents the main barrier to any plant parasites - it is a tough material to break down, and most animals are incapable of doing so without the aid of symbiotic microbes. In addition, the vascular tissue of many coniferous plants like pine are saturated with resin - a thick, sticky cocktail of aromatic chemicals (from which we derive many useful substances including solvents, varnishes, adhesive and perfume) which would overwhelm and kill most invaders. Yet none of those defenses seem to deter B. xylophilus - not only can it break through the thick cellulose barrier of the pine tree, it actually lives within the resin canals of its host, which is practically the most lethal place within the tree. It would be akin to living in a moat of toxic tar.

A recent study published in PLoS Pathogens on the genome of B. xylophilus offers vital clues to how this nematode exploits its pine tree host. One of the most important enzymes for plant exploitation is cellulase - it is used to break down cellulose structures and allow potential parasites to enter and navigate through the host. Bursaphelenchus xylophilus is able to produce a unique combination of 34 enzymes for breaking down cellulose and carries a diverse suite of genes for producing enzymes that detoxify the aromatic compounds found in resin. So how did this tree killer acquire the necessary molecular machinery to invade and disarm its host?

The wide range of detoxifying genes in the B. xylophilus genome appear to be multiple duplication of pre-existing genes which are also found in other nematodes, such as the well-known standard lab worm Caenorhabditis elegans - B. xylophilus just happen to have more of copies of those genes to cope with the wider array of toxins it encounters. However, the cellulase genes have a much more unusual origin. Out of the 34 cellulase enzymes produced by B. xylophilus, 11 of those enzymes are not found in any other nematode, but are most similar to those produced by fungi. So how does a nematode end up producing fungal enzymes?

The answer might be through horizontal gene transfer (HGT). The closest living relatives of B. xylophilus are fungi-eating worms which are transported by beetles to dead and dying trees. Once they reach their destination, they disembark from their beetle vectors and feed on the fungi which have colonised the dead trees. In a case of you are what you eat, the ancestors of B. xylophilus appeared to have incorporated a whole suite of useful genes from their food, allowing them to bypass the process of feeding on fungi which are growing on dead trees and just go straight to breaking down live plant tissue.

Image from figure of the paper.

Reference:

Kikuchi T, Cotton JA, Dalzell JJ, Hasegawa K, Kanzaki N, et al. (2011) Genomic Insights into the Origin of Parasitism in the Emerging Plant Pathogen Bursaphelenchus xylophilus. PLoS Pathog 7(9): e1002219. doi:10.1371/journal.ppat.1002219

Nicothoë astaci

2011-10-23T01:49:00.008-04:00

The parasite we are featuring today is Nicothoë astaci, the "lobster louse." Despite its name, it is not a "louse" (true lice are insects) as such, but rather a copepod (a type of crustacean), just like the salmon lice we have previously featured on this blog. But whereas salmon lice are well-studied due to their economic impact on salmonid fisheries (especially on farmed fishes), far less is know about the lobster louse. Despite having been recorded on the European lobster (Homarus gammarus) since the 1950s, to this day there is very little known about this parasite, including the type of pathology it causes, its complete life-cycle, or even what the male of the species looks like (parasitic copepods often have cryptic or dwarf males which are very elusive).

The paper we are looking at today is taking the first step to rectifying that situation. The photo (from the paper itself) depicts larval stages of N. astraci, with the arrows indicating the oral cone,the structure this parasite uses (along with its front pairs of legs) to attach itself to the host's gill filament and feed on its blood. While the larval stage looks like a rather ordinary copepod, as it matures into an adult, it morphs into what looks like a miniature boomerang with a pair of stretched out "wings" on either side, and a pair of bulbous egg sacs dangling from its rear end. The attachment and feeding activity of the lobster louse can cause pronounced physical damage to the lobster's gill filaments.

As with any kind of infection, you would expect to see some kind of cellular response. While the innate immune systems of invertebrates like lobsters are not as sophisticated as the adaptive immune system of vertebrate animals such as ourselves, they can present a formidable challenge to any would-be intruder (to see an example of what the cellular defence of a crustacean can do to a parasite, click here). Basically, the crustacean's equivalent of blood cells wrap themselves around the parasite or pathogen and initiate the process of melanization, where the intruder becomes entombed in a hardened capsule of melanin (the pigment which determines our skin colour). The researcher did find signs of melanization and other cellular disruption throughout the gills of infected lobsters, but none of it was near the lobster louse's attachment point.

So the lobster's immune system recognizes the presence of an intruder, but is unable to pinpoint and focus its wrath on the parasite. The authors of this paper suggest that this indicates the lobster louse is able to somehow interfere with the lobster's defensive mechanism so that it can blood-feed in peace. The mechanism through which the lobster louse disrupts this particular aspect of host physiology is yet to be uncovered, along with much of the parasite's ecology and life-cycle. Hopefully, with further research on this host-parasite system, this situation will change in the future.

Image from the paper.

Reference:

Wootton EC, Pope EC, Vogan CL, Roberts EC, Davies CE, Rowley AF. (2011) Morphology and pathology of the ectoparasitic copepod, Nicothoë astaci ('lobster louse') in the European lobster, Homarus gammarus. Parasitology 138:1285-1295.

Maritrema subdolum

2011-10-12T21:19:00.005-04:00

This is a story about two little crustaceans and a parasitic fluke. Corophium volutator and Corophium arenarium are amphipods that make a living tunneling in the mudflats on the coast of the Danish Wadden Sea. They are also host to many species of parasitic flukes, and one of them is the parasite we are featuring today - Maritrema subdolum. Last year, we featured a related species from New Zealand - M. novaezealandensis - and much like its Kiwi cousin, M. subdolum is the bane of the local crustacean population. However, M. subdolum does not affect all of its crustacean hosts equally and this has some important ecological consequences.

Out on the Danish mudflats, C. volutator is king. Of the two Corophium species, it is the stronger competitor, reaching much higher abundances and generally making life difficult for C. arenarium. But along comes M. subdolum, which evens out the playing field. Living alongside those little crustaceans are mud snails, and during early spring they can become extremely abundant, with over 25000 snails per square metre. By summer, almost half of those snails are infected with M. subdolum, which turn them into little parasite factories, each cloning a massive reserve of parasite larval stages call cercariae that are then unleashed into the environment to infect the amphipods. The main trigger for releasing these cercariae is high temperature, and during 1990 there was a bout of unusually high temperature during summer that has been linked to North Atlantic Oscillation (NAO), a phenomenon that plays a major role in determining climatic conditions in the northern hemisphere.

All of this combined into a perfect storm that devastated the C. volutator population. Triggered by high temperature, all the infected snails released their payload of parasites into the surrounding waters. Each infected snail can release hundreds of cercariae, and with thousands of snails per square metre, the shallow waters of the mudflats turned into a seething parasite soup. To the amphipod, this amounted to being in a shooting range, as each cercaria is armed with glands of digestive enzymes and a scalpel-like organ call a stylet with that they use to puncture the amphipod's exoskeleton. For many C. volutator, the outcome of being attacked by a swarm of these little horrors was terminal, and this resulted in a dramatic decline in their population. However, for some reason we still don't know, the C. arenarium population was able to weather the M. subdolum storm unscathed, either because they tolerated the parasite swarm, or because they were simply not the preferred target. Either way, with the collapse of the C. volutator population, in the next season, C. arenarium was able to succeed them and become the dominant amphipod species on the Danish mudflat.

And this dramatic ecological change was ultimately brought about by a little parasite.

Photo by Kim Mouritsen

Reference:

Larsen, M.H., Jensen, K.T. and Mouritsen, K.M. (2011) Climate influences parasite-mediated competitive release. Parasitology 138: 1436-1441

Metarhizium acridum

2011-10-03T00:39:00.005-04:00

The locust in the photo is covered in a fine layer of green mold - that is because it was killed by the parasite we're featuring today, Metarhizium acridum. Metarhizium acridum is a pathogenic fungus which specifically infects and kills grasshoppers, locust and other insects in the Orthoptera order. Because of the pest status of some orthopterans (think locust plagues), M. acridum is mass-produced as type of environmentally-friendly, biological alternative to most insecticide. But while M. acridum only targets locust and grasshoppers, its close relative, M. robertsii, is far less picky, capable of infecting hundreds of different insect species.

So why is M. acridum so picky while its close relative is so indiscriminate? Amazingly, it appears to come down to a single gene call Mest1 - a gene present in M. robertsii, but is absent in M. acridum. To find out the function of this gene, a group of researchers in China created a mutant M. robertsii strain which has a non-functioning copy of Mest1. This mutant lost its ability to infect most insects - except grasshoppers and locusts - which happens to be the speciality of M. acridium. In parallel, the researchers also inserted functional copies of Mest1 into M. acridum. The insertion of this single gene allowed M. acridium to infect a wider range of insects.

What is so special about Mest1? In M. robertsii, Mest1 is expressed during spore germination, and plays an important role in initiating the infection process. Mest1 expression can be triggered by a range of stimuli including nutrient poor conditions or contact with insect cuticle. Metarhizium acridium has other genes playing the role of Mest1, but they are triggered by substances which are present only in the waxy coating of grasshoppers and locusts. So if its spores land on other insects such as caterpillars which have a different type of coating, M. acridum fails to germinate because the appropriate stimuli are absent. Thus, the insertion of Mest1 into M. acridium allows the fungus to bypass those usual stimuli and begin germinating under a wider range of conditions

Host specificity is one of the central question in the evolutionary biology of parasitic organisms. In this case, we can see how a single gene can changed this otherwise specialist pathogen into a broad-spectrum generalist.

Image from the Wikipedia.

Wang S, Fang W, Wang C, St. Leger RJ (2011) Insertion of an Esterase Gene into a Specific Locust Pathogen (Metarhizium acridum) Enables It to Infect Caterpillars. PLoS Pathog 7(6): e1002097. doi:10.1371/journal.ppat.1002097

Parvilucifera sinerae

2011-09-26T02:05:00.005-04:00

Phytoplankton are microscopic single-celled "plants" which float in the upper surfaces of the ocean, and their photosynthetic action is responsible for generating most of the oxygen in our atmosphere. While you might think that something so tiny would not be host to anything, there are in fact a myriad array of viruses, bacteria, and flagellate organisms that infect and exploit phytoplankton, and the parasite for today is one of them. Parvilucifera sinerae is a single-celled, flagellated organism which infects dinoflagellate algae such as Alexandrium minutum. The photo shows an infected A. minutum cell. While earlier in this post we extolled the virtue of phytoplankton, dinoflagellate algae are also known to be responsible for harmful algal bloom events such as "Red Tides", so there is a lot of interest in their ecology and the factors that can influence their likelihood of blooming.

For P. sinerae, infecting its host is not an easy task - not only does it have to find a swarm of its tiny host in the vast ocean, it also needs to make contact and accomplish what amounts to a cellular heist - the parasite needs to break through the protective shell of the alga in order to steal its valuable content. As you can imagine, during such an intense operation, being jostled around will probably throw you off your game. And indeed that is what a group of scientists in Spain have found. It appears that even a slight turbulence is enough to reduce the infection success of P. sinerae and that it performs best under calm, still conditions. These researchers suggested that turbulence would erode the zone of chemical emission around the dinoflagellate, making them more difficult to detect. Turbulence would also shorten the period of time which P. sinerae are in constant contact with the host cell - which is a necessary precondition for the parasite to perform its little cellular heist.

While both P. sinerae and its host are tiny, their interactions can have far-reaching ecological consequences, and as explained earlier they are among the most important organisms on the planet. In addition, parasitic killers, such as today's parasite, have been suggested as a possible biological control for harmful algal blooms, but it is like that the effectiveness of any such control would be at the mercy of environmental factors such as small-scale marine turbulence.

Image from figure of the paper.

Reference:
Llaveria, G., Garcés, E., Ross, O.N., Figueroa, R.I., Sampedro, N. and Berdalet, E. (2010) Small-scale turbulence can reduce parasite infectivity to dinoflagellates. Marine Ecology Progress Series 412: 45-56.

Sphaeromyxa cannolii

2011-09-16T14:53:00.005-04:00

We've met other myxozoan parasites before, including the very well-known causative agent of whirling disease in salmonid fishes, Myxobolus cerebralis. Today, meet a newly described species of myxozoan that was found infecting seahorses collected from the Gulf of Mexico. Not only was this the first such species described from this seahorse, but this is also the first time that any pathology attributable to a species in this genus has been recorded. The abundance of the parasites in the liver was observed to obstruct the bile ducts of the fish, which caused noticeable accumulation of bile in the diseased hosts. The intermediate hosts are presumed to be some kind of annelid worm, but remain unknown for this species. And in case you were wondering, yes, the species name for this parasite comes from the fact that it looks like a cannoli.

Image from the paper.

Reference: Sears, B.F., P. Anderson, and E.C. Greiner. 2011. A new species of myxosporean (Sphaeromyxidae), a parasite of lined seahorses, Hippocampus erectus, from the Gulf of Mexico. Journal of Parasitology 97:713-716.

Cardicola forsteri

2011-09-12T03:33:00.003-04:00

Today's parasite is a blood fluke that has been turning up in tuna ranches in South Australia. The blood fluke lives the tuna's circulatory system, and lays eggs that can become lodged in the fish's gills or other organs such the heart, and cause significant lesions in those tissues. This is obviously of great concern to the tuna ranchers, so they set out to find a way of alleviating their fish from infection.

Being a trematode, Cardicola fosteri must have an invertebrate host that is the source infection for the tuna. In their search for the first host of C. forsteri, researchers undertook a a truly heroic effort - sampling over 9000 (!) invertebrates, including all kinds of bivalves, snails, and polychaete worms from the pontoons on the tuna ranch and nearby areas, then meticulously dissected and examined every single one of them for parasitic infections. Those who have been following this blog would know that trematodes usually have a mollusc host in which they undergo asexual multiplication - usually a snail, but C. forsteri is very unusual - it turns out that it uses a polychaete worm, specifically tube-dwelling terebellids - also known as spaghetti worms - for asexual multiplication. Infected worms were packed with hundreds of sac-like sporocysts which continuously churn out the free-living cercarial stages that go on to infect the tuna.

The researchers then used specific sections of the DNA obtained from the parasites to match up the sac-like sporocyst stage in the worms with the adult stage in the tuna, and they were able to confirm that the blood flukes in the tuna were indeed originating from those infected tube-dwelling worms. As those sedentary worms usually live on the seafloor, researchers recommended that simply by moving them to deeper waters, the tuna would be infected by far fewer blood flukes. This study shows how understanding the ecology and life-cycle of a parasite can help us take straightforward measures that can mitigate their impact.

Photo by Robert Adlard

Reference:
Cribb TH, Adlard RD, Hayward CJ, Bott NJ, Ellis D, Evans D, Nowak BF. (2011) The life cycle of Cardicola forsteri (Trematoda: Aporocotylidae), a pathogen of ranched southern bluefin tuna, Thunnus maccoyii. International Journal for Parasitology 41:861-70.

Skrjabinoptera phrynosoma

2011-08-30T03:43:00.008-04:00

Life isn't easy as a parasite with a complex life-cycle. In order to grow up and reproduce, you often need to make your way through the bodies of at least two very different host animals - a very haphazard process that depends largely on timing and luck. In the case of today's parasite - a nematode worm called Skrjabinoptera phrynosoma - it has to make its way between a lizard and an ant. The adult S. phrynosoma lives inside the stomach of the desert horned lizard Phrynosoma platyrhinos. However, when the female becomes filled with mature eggs, she migrates to the lizard's cloaca (a nice, technical way of describing a lizard's butt).

Unlike most parasitic nematodes, which often lay eggs that are cast out of their host and left exposed to the elements, S. phrynosoma is a very maternal parasite - in a slightly morbid way. The female S. phrynosoma makes the ultimate sacrifice by casting her egg-filled body out of the lizard via the host's feces. She will die outside of the host - but in addition to protecting her eggs by doing so, it is also her strategy for helping her eggs reach the next host. For some reason, ants find the shriveled, egg-filled cadavers of female S. phrynosoma to be a tasty treat, a meal fit to feed to their brood of growing ant larvae - which then become infected with the parasite's own larvae. The life-cycle is complete when the infected larvae mature into workers, emerge from the colony, and become lizard food - horned lizards are specialists on ants.

Researchers at Georgia Southern University discovered that to ensure that this sequence of events occurs, S. phrynosoma has evolved to synchronise its life-cycle with the seasonal behaviour of both its lizard and ant hosts. They found that the number of egg-filled females (all ready to evacuate) reach peak abundance during the middle of the lizard's mating season. This is also the period when there are the greatest number of ants out busily foraging and when the colonies are packed to capacity with broods of growing ant larvae. By timing its life-cycle in such a manner, S. phrynosoma ensures that when next season rolls around, when those broods of larvae are ready to emerge as a new generation of workers ants, they will be doing so pre-infected with nematodes and just in time to welcome the hungry lizards coming out of hibernation.

Reference:
Hilsing, K.C., Anderson, R.A. and Nayduch, D. (2011) Seasonal dynamics of Skrjabinoptera phrynosoma (Nematoda) infection in horned lizards from the Alvord Basin: temporal components of a unique life-cycle. Journal of Parasitology 97: 559-564.

Caenorhabditis briggsae (KT0001)

2011-08-21T20:35:00.007-04:00

Today's parasite is in the same genus as the famous and well-studied model lab nematode worm Caenorhabditis elegans. Caenorhabditis briggsae is a relative of C. elegans and is often used in comparative studies with its more famous counterpart because many of the tools developed for C. elegans can also be used on C. briggsae. While C. elegans is the darling lab worm due to its usefulness in studying genetics and developmental biology, until very recently, very little is known about its natural ecology.

Worms in the genus Caenorhabditis are often associated with invertebrates, hitching a ride on them as a way of traveling between food sources, or even opportunistically feeding on their ride if it happens to drop dead for whatever reason. In a paper published last year, a group of researchers reported on a strain of C. briggsae (KT0001) from South Africa displaying an ability not previously known for any Caenorhabditis species - it is capable of infecting and killing wax moth larvae. This strain of C. briggsae was found to be in a symbiosis with the pathogenic bacteria Serratia which presumably allows C. briggsae (KT0001) to become a parasitic killer.

Furthermore, when the researchers tested 10 wild strains of Caenorhabditis species which had not previously displayed any ability to infect insects - including a strain of C. elegans - and cultured them with Serratia, all but one strain gained the ability to infect, kill, and reproduce in insects, including the famous C. elegans. It seems that Serratia gives Caenorhabditis a license to kill - upon forming a partnership with the bacteria, these worms turn from mere passengers into deadly killers.

Reference:
Abebe, E., Jumba, M., Bonner, K., Gray, V., Morris, K., Thomas, W.K. (2010) An entomopathogenic Caenorhabditis briggsae. Journal of Experimental Biology 213: 3223-3229.

Cytinus hypocistis

2011-08-10T02:06:00.004-04:00

For a change of pace today the blog is going to feature a parasitic plant. Cytinus hypocistis is a holoparasitic plant, which means that unlike ordinary plants it does not perform photosynthesis, but obtains all the nutrients that it needs from its host. Cytinus hypocistis is embedded entirely within the the root of its host plant, but in spring, it pokes flowers out of the ground, which are then pollinated by ants and ripen into berry-like fruits. Each of these fruits contains thousands of tiny seeds, each about 0.2 mm in length.

What makes C. hypocistis unusual is that while most fruit-bearing plants rely upon vertebrate animals to disperse their seeds, C. hypocistis mainly uses a beetle. Researchers found that the seeds collected from beetle frass (fancy name for insect poop) are just as viable as seeds which are collected directly from the fruit. While rodents and rabbits also frequently consume C. hypocistis fruits, because they have a tendency to eat immature fruits and deposit their dung (with any viable seeds) at ground level, they are not as effective as the beetles. Not only do the beetles consume only fully-ripened fruits, they also have a tendency to bury themselves into the sand during midday, which can bring the seeds closer to the roots of the host plant.

This is one of the few known case of endozoochory (where the seed is consumed and pass through the gut of an animal) which involves an insect. The researchers of this study pointed out that this type of ecological interaction may in fact be quite widespread and common, especially for plants with very small seeds. However, they have simply been overlooked because all those involved were, quite literally, lurking meekly underneath our feet.

Reference:
de Vega C, Arista M, Ortiz PL, Herrera CM, Talavera S (2011) Endozoochory by beetles: a novel seed dispersal mechanism. Annals of Botany 107: 629-637.

Isospora plectrophenaxia

2011-08-04T21:08:00.005-04:00

Today's parasite is Isospora plectrophenaxia. A few weeks ago, you met a related species - Isospora lesouefi - the coccidian parasite found in the Regent Honeyeater which keeps a daily timetable, shedding most of its oocysts (the parasite's infective stage) in the afternoon. This is a well-described phenomenon among different species of Isospora - the parasite's shedding schedule appears to be calibrated by the light-dark cycle experienced by the bird host throughout the day. Indeed, experiments conducted on Isospora in house sparrow shows that if you disrupt the circadian rhythm of the host, you also mess up the parasite's shedding schedule.

Under natural condition, the usual light-dark cycle works just fine for most species of Isospora. But I. plectrophenaxia is found in the Snow Bunting (Plectrophenax nivalis) - a bird living in the High Arctic where there is perpetual sunlight during summer. So you'd think the shedding schedule of I. plectrophenaxia would be all messed up, right? Not so, researchers found that the parasite continues to stick to its regular regime of late afternoon shedding, just like all the other Isospora. At the moment researchers are unsure how I. plectrophenaxia is able to perform this feat. Perhaps this species is more sensitive to very low concentration of melatonin - the chemical secreted by the pineal organ which coordinates the bird's circadian rhythm, or perhaps it sets its timetable on different level of UV (ultraviolet) radiation exposure, which still varies throughout the Arctic summer day. Hopefully, ongoing research on this host-parasite system will shed further light on this little mystery, so watch this space!

Reference:
Dolnik O.V., Metzger B.J., Loonen M.J. (2011) Keeping the clock set under the midnight sun: diurnal periodicity and synchrony of avian Isospora parasites cycle in the High Arctic. Parasitology 138:1077-1081.

Acanthocephalus galaxii

2011-07-28T22:45:00.006-04:00

The brown trout (Salmo trutta), a popular angling species, was introduced to the waters of New Zealand in 1867 and has become very well established in the local freshwater system. The trout have made New Zealand their own all-you-can-eat buffet, feeding on many of New Zealand's native freshwater fishes. But other native fauna have also been getting intimate with the trout in a different way. It turns out that during its time in Aotearoa, the brown trout has also picking up a new parasite - Acanthocephalus galaxii, which normally infects a little native fish call the roundhead galaxias (Galaxias anomalus).

Furthermore, the parasitic worm has actually become more abundant in the introduced trout than in the native galaxids - presumably because when compared with the tiny native fish, the much larger trout gobbles up more amphipods (the crustacean which carries the larval stage of A. galaxii). But this isn't necessarily good news for the parasite. Once they get into the trout, because of physiological incompatibility with the introduced host, the parasites are unable to reach maturity. So the trout actually acts as a kind of dead-end sink for the worm, which in turn reduces parasite burden on the native fishes.

So even while the trout might be chomping up native galaxids by the mouthful, they also are inadvertently reducing their parasite burden - though I doubt that would give much comfort to the little galaxids fleeing from a hungry trout!

References:
Paterson, R.A., Townsend, C.R., Poulin, R. and Tompkins, D.M. (2011) Introduced brown trout alter native acanthocephalan infections in native fish. Journal of Animal Ecology 88: 990-998.

Isospora lesouefi

2011-07-18T20:54:00.004-04:00

Isospora lesouefi is a coccidian parasite which infects the Regent Honeyeater (Xanthomyza phrygia), an endangered species of bird found in Australia. This parasite was found and described during a parasitological survey conducted on a group of honeyeaters at Taronga Zoo as a part of their captive breeding programme.

Before the birds can be released into the wild, their health needs to be assessed and a part of that procedure involves determining their parasite load. For animals that you want to keep alive, this usually involves counting the number of parasite eggs or spores found in their faeces. But here's the tricky bit - it turns out that I. lesouefi keeps to a daily timetable. The researchers in this study found that bird faeces collected in the afternoon contained about 200 times more oocysts (the parasite's infective stage) than those collected in the morning. Other species of Isospora also keep similar shedding schedules, and it is likely to be an adaptive trait which minimise the oocysts' exposure to desiccation and ultraviolet radiation.

This study illustrates the importance of taking multiple samples, as well as understanding the life history of the parasites when you want to obtain an accurate picture of parasite burden, and its actual impact on the health of an animal.

Reference:
Morin-Adeline, V., Vogelnest, L. Dhand, N.K., Shiels, M., Angus, W. and Šlapeta, J. (2011) Afternoon shedding of a new species of Isospora (Apicomplexa) in the endangered Regent Honeyeater (Xanthomyza phrygia). Parasitology 138: 713-724

Myxidium sp.

2011-07-04T02:00:00.005-04:00

When species of plants and animals are introduced to a new environment, this can often lead to some unexpected consequences. The parasite for today is Myxidium sp. - a myxosporean that lives in the liver and brain of native frogs in Australia. But in addition to the native amphibians, this parasite is also found in the invasive cane toad. The cane toad was introduced into Australia to control cane beetles, but has since become one of the most famous posterchildren of invasive species. While Myxidium was originally thought to have been a "present" brought to Australia by the cane toad, recent research indicates that it might actually be native to Australia.

The infamous cane toad does play a role in the story of Myxidium, but in a different manner to what was originally suspected. A collaborative group of researchers from Australia and the Czech Republic found that instead of bringing Myxidium to Australia, the toad has become embroiled in an ecological phenomenon known as "spillback". This is when a native parasite adopts a newly introduced host, this new species turns out to be a better host for the parasite than the native species it was originally infecting, and the parasite propogates more successfully in the new host species.

This can have dire consequences for the original host because the introduced species acts as an ampilifier for the parasite. As a result, the original host become exposed to more of the parasite than ever before. Because many parasites often have dose-dependent effects, this can mean a parasite, which would otherwise be tolerated, can become debilitating or even deadly to its original host.

Reference (and photo):
Hartigan A, Fiala I, Dyková I, Jirků M, Okimoto B, et al. (2011) A Suspected Parasite Spill-Back of Two Novel Myxidium spp. (Myxosporea) Causing Disease in Australian Endemic Frogs Found in the Invasive Cane Toad. PLoS ONE 6(4): e18871. doi:10.1371/journal.pone.0018871

Trypanosoma irwini

2011-06-14T22:11:00.006-04:00

Today's parasite is about as Aussie as they come - Trypanosoma irwini - a blood parasite named in honour of the late Steve "Crocodile Hunter" Irwin. What's more, this parasite infects an iconic Australian host, none other than the Koala (Phascolarctos cinereus). While the vector host for T. irwini is currently unknown, it is likely that this parasite features a life-cycle broadly similar to other trypanosomes we have featured on this blog - that is alternating sexual and asexual stages in a vector host and a vertebrate host. Trypanosoma irwini is by no mean the only unique Trypanosoma found in Australian. Scientists have been describing many novel species of Trypanosoma from the marsupials of Australia, and no doubt there are many, many more waiting to be discovered.

In addition to T. irwini, the Koala is also infected by two other species of Trypanosoma. While on its own, T. irwini seems to be pretty benign, if it gets mixed up with the other Trypanosoma species or other infections such as chlamydia or the retrovirus which causes koala AIDS syndrome, it can lead to disease in its host. Like many other parasites, the pathogenecity of T. irwini is not so straightforward, and may only manifest itself under certain conditions.

Photo from McInnes et al. (2009)

References:

McInnes, L.M., Gillett, A., Ryan, U.M., Austen, J., Campbell, R.S.F., Hanger, J. and Reid, S.A. (2009) Tryapnosoma irwini n. sp. (Sarcomastigophora: Trypanosomatidae) from the koala (Phascolarctos cinereus). Parasitology 136: 875-885.

McInnes, L.M., Gillett, A.,Hanger, J., Reid, S.A. and Ryan, U.M. (2011) The potential impact of native Australian trypanosome infections on the health of koala (Phascolarctos cinereus). Parasitology 138: 873-883

Gnathia auresmaculosa

2011-06-04T02:14:00.007-04:00

The harmfulness of parasites to their host is not always so straightforward, there are often many factors which contribute to the pathology of an infection. The parasite we are looking at today is Gnathia auresmaculosa - a type of blood-sucking crustacean with an interesting life cycle (which you can read about in this post from last year). These little gnathiids are like ticks of the sea, clinging onto passing fish and gorging themselves on blood before dropping off to continue developing. For adult fish, a few gnathiid here and there is probably not a big deal, but for growing juveniles, that is another matter.

Settlement is a critical transitional stage for coral reef fishes, and that is also when they are most vulnerable to parasites like G. auresmaculosa. A recent study by the lab group of Dr. Alexandra Grutter revealed just how costly these ticks of the sea can be to juvenile fishes. Dr. Grutter and her colleagues found that juvenile damselfish which have been fed on by just one of those little blood-suckers exhibit significantly decreased swimming ability, far higher oxygen consumption rate, and are about half as likely to survive than uninfected fishes.

So if you happen to find yourself on a beautiful tropical reef, take a moment to think about all the little baby fishes which are swimming for their lives through the gauntlet of gnathiids - they never mentioned that in Finding Nemo!

Reference:
Grutter, A.S., Crean, A.J., Curtis, L.M., Kuris, A.M., Warner, R.R. and McCormick, M.I. (2011) Indirect effects of an ectoparasite reduce successful establishment of a damselfish at settlement. Functional Ecology 25: 586-594

Eustrongylides ignotus

2011-05-29T09:54:00.003-04:00

Eustrongylides ignotus is an extremely pathogenic nematode which lives in the wall of the stomach (proventriculus) of herons and egrets and has caused die-offs in nesting colonies of some birds. Its bright color has earned it the nickname of “the big red worm.” The life cycle involves oligochaetes as the first intermediate host and various fish as the infective intermediate host. If the small fish are ingested by larger fish, reptiles, or amphibians, these can act as transport hosts. The color in this larval worm in a mosquitofish has been bleached out by the preservative. If straightened out, it would be longer than the fish.

Contributed by Mike Kinsella.

Clistobothrium carcharodoni

2011-05-18T20:13:00.006-04:00

The parasite for today is found in a celebrity of sorts, the star of the film Jaws and its sequels - the famous Great White Shark. Unlike its host - which is well-known for being big in every sense - Clistobothrium carcharodoni is a tiny little worm measuring no more than a few millimeters in length. However, what they lack in size, they make up for in numbers, as over 2000 of them can be found in a single shark.

Tapeworms in general have complex life-cycles with many different hosts, and C. carcharodoni is no different. The life cycle of tapeworms which live in marine animals such as the great white shark are difficult to unravel. That is because the larvae lack many of the diagnostic characteristics which are used to identify the adult worms, so it is next to impossible to match the identity of the larvae with adults based on their morphologies. But with the advent of molecular techniques such mystery are becoming more commonly solved.

One of my former colleagues from Otago University - Haseeb Randhawa - was able to use key genetic markers to confirm that adult C. carcharodoni found in the gut of great white sharks were identical to tapeworm larvae which have previously been found in dolphins. These larval tapeworms congregate in the tail, back, belly and groin region of the dolphins - all parts preferred by the great white sharks as the finest cuts of meat from Flipper. His study confirmed the role of dolphins in completing the life-cycle of C. carcharodoni.

So while Flipper and Jaws are famous superstars which grab all the public attention, to a tapeworm like C. carcharodoni, all those aquatic celebrities simply serve as way stations in the cycle of life.

Reference:
Randhawa, H. (2011) Insights using a molecular approach into the life cycle of a tapeworm infecting great white sharks. Journal of Parasitology 97: 275-280.

Chondracanthus parvus

2011-05-15T20:56:00.006-04:00

Chondracanthus parvus is a parasitic copepod that parasitises the smooth-cheek sculpin, Eurymen hyrinus, by attaching itself to the inner side of the fish's operculum (the flap covering the fish's gills). Chondracanthus parvus belongs to a family of parasitic copepods known as the chondracanthids, which contains 160 species, all of which are parasites of marine fishes. Phylogenetic studies of the chondracanthids indicate that these copepod have consistently co-evolved with their hosts, and their phylogeny closely reflects the evolutionary history of the fish that they infect. Such parasites are like heirlooms of the evolutionary past and phylogenetic studies conducted on these living markers can in turn shed light on the evolutionary history of their hosts.

Picture from Ho et al. (2006).

References:

Paterson, A.M. and Poulin, R. (1999) Have chondracanthid copepods co-speciated with their teleost hosts? Systematic Parasitology 44:79-85.

Ho, J-s., Kim, I-H., and Nagasawa, K. (2006) Copepod parasites of the fatheads (Pisces, Psychrolutidae) and their implication on the phylogenetic relationships of Psychrolutid genera. Zoological Science 22:411-425.

Herpyllobius vanhoeffeni

2011-04-17T20:11:00.004-04:00

Regular readers of this blog will no doubt be familiar with the wonderfully weird and twisted morphology of parasitic copepods. However, this is probably the weirdest we have featured yet. Herpyllobius vanhoeffeni is a spooky-looking parasitic copepod which has all the trappings you might associate with an Lovercraftian horror tale. They are found in the Antarctic Penninsula, in waters 666-673m deep, and they parasitise a polychaete worm, Eulagisca corrientis.

The top picture shows a pair of females attached to the ventral surface of their host; note that the lower individual has a pair of lobe-shaped egg sacs extending from its side like wings. The bottom picture shows a specimen that has been dissected from the host, showing the rest of the copepod, which is usually embedded in the host. Overall, the whole parasite looks not unlike a bulbous skull resting atop a twisted stalk of a body.

Reference:
López-González, P.J. and Bresciani, J. (2001) New Antarctic records of Herpyllobius Steenstrup and Lütken, 1861 (parasitic Copepoda) from the EASIZ-III cruise, with description of two new species. Scientia Marina 65:357-366

Columbicola extinctus

2011-04-09T11:20:00.004-04:00

Speaking of co-extinctions, here's a contribution that I just got from Anya Gonchar. Columbicola extinctus is a louse that was specific to the Passenger Pigeon, the bird that forever disappeared in the early 20th century. In addition to many advantages of the narrow specialization, C. extinctus has experienced the most drastic of its drawbacks: it has followed its only host into extinction. This could have been one of the impressive examples for a discussion regarding specialist vs. generalist strategies in parasites, if the story hadn't suddenly taken a happy turn. C. extinctus was rediscovered from the Band-tailed Pigeon, while its fellow pseudo-extinct louse C. defectus was suggested to belong to a different species Campanulotes flavus that is still safe and sound. Still, parasite coextinction is documented in numerous other cases where we may not count on such good luck. Fortunately, there is now a large body of literature featuring related topics so that the problem is not neglected. The origin of this blog goes back to celebrating the year 2010 as an International Biodiversity Year. As the previous entries have shown, parasite diversity is enormous indeed. Yet, some parasite species’ existence is challenged. Further reading: Koh L. P. et al. 2004. Species coextinctions and the biodiversity crisis. Science 305, 1632. Dunn R. R. et al. 2009. The sixth mass coextinction: are most endangered species parasites and mutualists? Proc. R. Soc. B, 276, 3037-3045. Clayton D.H., Johnson K.P. 2003. Linking coevolutionary history to ecological process: doves and lice. Evolution, 57(10), 2335–2341. Johnson K.P. et al. 2003. When do parasites fail to speciate in response to host speciation? Syst. Biol. 52(1), 37–47. Johnson K.P. et al. 2009. Competition promotes the evolution of host eneralists in obligate parasites. Proc. R. Soc. B, 276, 3921–3926. Image is of Campanulotes flavus, from the paper: Price et al. 2000. Pigeon lice down under: taxonomy of Australian Campanulotes (Phthiraptera:Philopteridae), with a description of C. durdeni n. sp. Journal of Parasitology 86:948-950.

Ixodes neuquenensis

2011-04-07T03:18:00.002-04:00

Today's parasite is a tick described from an endangered marsupial. Ixodes neuquenensis is an ectoparasite of a unique little marsupial known as monito del monte or "mountain monkey" (Dromiciops gliroides).

The "mountain monkey" is the only species still alive from an ancient lineage dating back more than 40 million years. Due to habitat loss, the population of this little marsupial has declined over recent years. This is bad news for I. neuquenensis because it is a very host-specific tick. If the "mountain monkey" goes extinct, it will also spell doom for this tick, along with a whole suite of other parasites and symbionts which are dependent upon this little marsupial.

Reference:
Guglielmone AA, Venzal JM, Amico G, Mangold AJ, Keirans JE (2004) Description of the nymph and larva and redescriptions of the female of Ixodes neuquenensis Ringuelet, 1947 (Acari: Ixodidae), a parasite of the endangered Neotropical marsupial Dromiciops gliroides Thomas (Microbiotheria: Microbiotheriidae). Systematic Parasitology 57:211–219

Philophthalmus gralli - update on the "Parasite of 2010"

2011-04-02T21:01:00.004-04:00

Last year the most “yuck” votes were cast for a photo of Philophthalmus gralli in the eyes of a rhea at the Phoenix Zoo. Melanie Church, the vet who treated the rheas, gave me a back-door tour of the zoo in January. The three rheas are doing fine. She removed most of the flukes manually, treated the eyes with an anthelmintic ointment, and the birds are now virtually parasite-free. The rheas have been moved to a pen where the snail intermediate hosts are not present to prevent re-infection.

Contributed by Mike Kinsella.

Rugogaster hydrolagi

2011-03-23T19:59:00.010-04:00

Today's parasite is a strange worm found in a habitat that may shock and bewilder many readers on multiple levels. It's a worm that lives in the rectal gland of the spotted ratfish (Hydrolagus colliei). The spotted ratfish belongs to an enigmatic group known as the chimaera, an ancient group of cartilaginous fish that branched off from sharks almost 400 million years ago. The parasite itself is just as mysterious - it belongs to a group call Aspidogastrea (we have featured other species from this group on the blog before - Lobatostoma manteri and Aspidogaster conchicola), which made the evolutionary split with the far more diverse digenean trematodes probably also a few hundred million years ago (unfortunately, most parasites don't leave fossils). Rugogaster hydrolagi can grow up to 15 mm long (a bit over half an inch), and is so-called due its "rugae", which are the ridges on its body that give it a corrugated, accordion-like appearance. The life-cycle (like most aspecst of its ecology) is unknown, though like other aspidogastreans, it most likely features a mollusc intermediate host.

Photograph by Klaus Rohde

Pygidiopsis macrostomum

2011-03-17T11:29:00.004-04:00

Pygidiopsis macrostomum is a freshwater digenean from Brazil. Like most otherdigenean trematodes, it has a three-host life-cycle. It asexually multiplies in its first intermediate host, the snail Heleobia australis, producing cercariae (pictured) which are released into the surrounding water. The cercaria swims in an series of small, stepped leaps, and then spins rapidly on its own axis once it sinks to the substrate, almost like a tiny aquatic ballerina.

All this dance-like motion attracts the attention of guppies, the parasite's second intermediate hosts, which ingest the parasite and become infected. The parasites burrow into the mesentery tissue of the fish, where they form a cyst and await ingestion by the definitive host where the worm will mature into its adult stage. While the adult specimen of P. macrostomum were first described from a rat, a subsequent study have also found it in the piscivorous bat Noctilio leporinus which, given its diet, is more likely to be the parasite's usual definitive host.

Reference:
Simões et al. (2009) The life history of Pygidiopsis macrostomum Travassos, 1928 (Digenea: Heterophyidae). Mem Inst Oswaldo Cruz 104:106-111.

Contributed by Tommy Leung.

Opechona sp.

2011-02-20T19:01:00.005-05:00

Today's parasite hails from the San José Gulf of Argentina. Opechona sp. is a digenean trematode which uses the intertidal snail Buccinanops cochlidium as a first intermediate host. The parasite sets up shop within the snail's gonads where it starts cloning itself, eventually castrating the snail through physical destruction of the gonad tissue. These clonal stages (known as rediae) produce free-living larvae called cercariae (pictured) that are released from the snail into the surrounding water, where they infect the next host in the life-cycle. This parasite reaches its peak prevalence during summer when water temperature is at its highest. While the life-cycle of Opechona is not fully known, related species have been recorded to infect jellyfishes as the second intermediate host in their life-cycle, and the period of highest cercariae emission for Opechona during summer may possibly coincide with the high abundance of jellyfishes during that season.

References:
Averbuj, A. and Cremonte, F. (2010) Parasitic castration of Buccinanops cochlidium (Gastropoda: Nassariidae) caused by a lepocreadiid digenean in San José Gulf, Argentina. Journal of Helminthology 84: 381–389.

Contributed by Tommy Leung.

Colobomatus sillaginis

2011-02-05T16:26:00.003-05:00

Colobomatus sillaginis is a parasitic copepod that lives in the head of two species of fish (commonly known in Australia as "whiting") in the genus Sillago (Sillago maculata and Sillago analis). This copepod dwells in the system of cephalic canals in the head of the fish. Interestingly, while the gut tracts of males and juvenile females are bright green, the gut of mature female copepods are usually coloured red or black. Living in the cephalic canal alongside C. sillaginis are small ciliates that are bright green due to the symbiotic algae living within them. These ciliates can be so numerous that some fish have a greenish tinge around front of the head. The male and juvenile female copepods graze upon this turf of abundant food. However, once they become mature, the female takes to feeding on blood, probably due to the physiological demand of egg production, rather like a female mosquito which normally feeds on nectar, but needs to obtain a blood meal for egg development.

Reference:
West, G.A. (1983) A new philichthyid copepod parasitic in whiting (Sillago spp.) from Australian waters. Journal of Crustacean Biology 3: 622-628.

Contributed by Tommy Leung.

Allomermis solenopsi

2011-01-30T10:59:00.006-05:00

It seems that ants just can't get a break when it comes to parasites. When they are not being persuaded to clamp themsleves to the top of a grass blade for a nightly sacrificial ritual (Dicrocoelium dendriticum), they are doing impersonations of a juicy berry thanks to some worms in their gut (Myrmeconema neotropicum). Today's parasite adds to the insult and takes its ant host for an impromptu swim, then leaves it to drown. Allomermis solenopsi is a nematode from the Mermithidae family, a group of nematodes which have plagued insects for at least 40 million years. While they superficially resemble nematomorph hairworm (e.g. Spinochordodes tellinii) and have a similar life-cycle, these worms actually belong in a separate phylum. However, the mermithid nematodes have convergently evolved the same ability as the hairworms to manipulate their hosts - namely, taking the host for a suicidal trip to the pool. Allomermis solenopsis develops inside the gaster (abdomen) of the ant and when it reaches maturity, it needs to exit into a body of water to mate and lay eggs. Other species of mermithids are well-known for inducing water-seeking behaviour in their hosts, so given that the nematode would dry out very quickly if it becomes exposed to the outside environment, it is likely that when the time comes, A. solenopsi just takes its ant for a terminal dunk.

Image from figure of the paper.

Reference:
Poinar Jr, G.O., Porter, S.D., Tang, S. and Hyman, B.C. (2007) Allomermis solenopsi n. sp. (Nematoda: Mermithidae) parasitising the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) in Argentina. Systematic Parasitology 68: 115-128.

Contributed by Tommy Leung.

Nearctopsylla brooksi

2011-01-24T17:41:00.001-05:00

Many fleas are quite host specific, although rodent and shrew fleas are occasionally also found on their predators, probably hopping on the nearest warm body when their host is killed. Fleas of the genus Nearctopsylla are primarily found on shrews and moles, but N. brooksi has so far only been reported from weasels (Mustela spp.). It is unlikely to be a weasel parasite so the true host has yet to be discovered. The flea in the photo was found on…you guessed it…a long-tailed weasel.

Contributed by Mike Kinsella.

Arthurhumesia canadiensis

2011-01-14T21:00:00.003-05:00

Parasites come in all kinds of bizarre shapes and you don't get much more bizarre than today's parasite - Arthurhumesia canadiensis. This species is a parasitic copepod that lives inside the intestine of the compound ascidian (sea squirt) Aplidium solidum. The diagram shows a female specimen, with a pair of lobe-like egg sacs attached. And if you are wondering "what's the weird little blob the arrow is pointing at?", well that's the male copepod. This weird little crustacean is named after Arthur Humes - a very prolific taxonomist. Over the course of 60 years, he was responsible for describing over 700 new species of parasitic copepods. So it's only right that a copepod named after him would appear on a blog which is about parasite biodiversity!

Reference:
Bresciani, J. and López-González, P.J. 2001. Arthurhumesia canadiensis, new genus and species of a highly transformed parasitic copepod (Crustacea) associated with an ascidian from British Columbia. Journal of Crustacean Biology 21(1): 90-95.

Contributed by Tommy Leung.

Alaria marcianae

2011-01-10T06:37:00.001-05:00

This horned little devil is the mesocercaria of the trematode, Alaria marcianae, which has a very unusual life cycle. When the metacercariae of this species are ingested by a lactating carnivore such as a Florida panther, they migrate to the tissues instead of developing in their normal site, the small intestine, and develop to this stage. They can then be passed in the milk to the kittens, where they develop normally in the intestine to the adult stage. Females can continue to transmit mesocercariae to future litters until exhausted of their infections.

Contributed by Mike Kinsella.

After One Year, Just the Tip of the Iceberg

2011-01-01T06:00:00.012-05:00

Throughout this year we've met blood-feeders, mind-benders, parasitic castrators, brood usurpers, outrageous shape-shifters, skin-clingers, eye-invaders and deadly plagues, but this is only a minuscule fraction of the true biodiversity of parasites. For some perspective let's calculate the number of years it would take to feature all the known metazoan parasites (such as worms, lice, and other multicellular animals) at a rate of one per day:

Myxozoa >1350 = 3.70
Trematoda >18000 = 49.30
Monogenea >20000 = 54.95
Cestoidea >5000 = 13.67
Acanthocephala >1200 = 3.29
Nematoda >10500 = 28.77
Mollusca >5600 = 15.34
Arachnida >30800 = 84.38
Crustacea >5360 = 14.68
Insecta >9400 = 25.75

Even without the odds and ends with less speciose groups like the Nematomorpha and Pentastomida, it would take us a little over 295 years just to feature every known and described species of metazoan parasites. This number does not include the multitude of undescribed species out there; a recent study (Randhawa and Poulin 2010) estimate that 3600 species of tapeworms are yet to be described from elasmobranchs (sharks and rays) alone - so that's another 10 years worth of tapeworms, all undescribed. The number of species of monogenean yet to be described is greater still, with 21000 - 22000 species yet to be described (Whittington 1998) - that's more than another 57 years' worth. For the digeneans, parasitic flukes, in Australia alone, over 5500 species are yet to be described (Cribb 1998) - 15 years worth of worms. All undescribed and unknown to science.

And that is just from the flatworms, which form one phylum out of many. What about the arthropods? And the nematodes? There is no reasons to think why there would be any fewer undescribed parasitic arthropods and nematodes than there are undescribed parasitic flatworms, and if such trend holds, it is likely that it would take an entire millennium to feature all described and undescribed species of metazoan parasites.

But that in itself is merely the tip of a very, very large iceberg. Moving away from the animals, what about the many parasitic fungi and plants? Parasitism as a life-style is just as common in fungi and plants as they are in animals. What about the eukaryotic single-cell parasites? This include the apicomplexans and the trypanosomes, which include parasites which cause diseases like malaria and sleeping sickness.

On top of that, throughout the year, we also featured many pathogenic bacteria and virus, and their diversity readily dwarfs the diversity found in the eukaryotes. With the use of new technology such as metagenomics, we have only begun to scratch the surface of their mind-boggling diversity. For this blog, we have looked beyond the traditional definition of a "parasite" to also included phytophagous insects (which technically are merely insects that are parasitic on plants rather than animals), and animals which have some aspect of "parasitism" to their life-style, such as brood parasites and kleptoparasites.

The Year 2010 was named as the "International Year of Biodiversity" and this blog was our attempt at showing the amazing, cool, and sometimes gross diversity just in parasitic organisms. But, we have barely scratched the tip of the iceberg with this blog and this if this iceberg represents all the species which have been described, then it is merely a small chunk from a much greater ice sheet. Any study of biodiversity that does not take parasites into account will be ignoring the elephant in the room...or should I say the lively colony of critters living in and on the elephant?

We hope that you have enjoyed your daily dose of parasites throughout 2010. We'll continue to add other posts on cool and new and interesting parasites, so please follow the blog if you want to be alerted when these are added.

Finally, a big thank you to the more than two dozen people who contributed over the year and a HUGE thank you to all of you for reading this, sharing this, and giving us your comments and questions.

References:

Cribb, T. H. 1998. The diversity of the Digenea of Australian animals. International Journal for Parasitology 28: 899-911.

Randhawa, H.S. and Poulin, R. 2010. Determinants of tapeworm species richness in elasmobranch fishes: untangling environmental and phylogenetic influences. Ecography 33: 866-877.

Whittington, I.D. 1998. Diversity "down under": monogeneans in the Antipodes (Australia) wih a prediction of monogenean biodiversity worldwide. International Journal for Parasitology 28: 1481-1493.

-- By Tommy Leung and Susan Perkins

December 31 - Guignardia bidwellii

2010-12-31T06:00:00.000-05:00

As you raise your glass of champagne tonight and toast this wonderful year of biodiversity, don't forget the parasites. And, to help you remember, today's parasite is after the grapes cultivated for wine. Guignardia bidwellii is a species of ascomycetous fungus that causes a disease called "Black rot" in many varieties of grapes in North America and now Europe, South America, and Asia as well. The vectors of this disease are not mosquitoes nor plant bugs, but rather raindrops, which splash the infective spores onto uninfected plants. Infection of the fruits will cause the grapes to shrivel up into what are known in the industry as "mummies" and these can serve as a good place for the fungus to overwinter.

December 30 - Bunocotyle progenetica

2010-12-30T06:00:00.002-05:00

Bunocotyle progenetica is another parasite (see also Parvatrema margaritense) that has been thoroughly studied in the White Sea. Being a hemiurid trematode, it possesses all the typical life cycle stages. But when it comes to hosts, we see something entirely different. Hydrobia snails serve as an “all-in-one” habitat throughout the parasite's life. That is, cercariae don't leave the rediae but instead continue their development, up to an adult stage, still inside the same mollusc. The photo shows a redia with adults inside, with visible eggs inside them. The eggs are transferred to neighboring Hydrobia molluscs after the host's death. This favours increased snail exploitation by B. progenetica, since it doesn't require the host to live long. Thus the entire life of B. progenetica passes inside its host, with no free-living stage at all. This phenomemon is not uncommon among parasites as it provides maximum protection against a potentially hostile environment. The serious drawback of such a strategy, though, is lack of dispersal opportunities. It's possible to overcome this by using mobile hosts, however, not the case here, thus B. progenetica is a good example of just how odd parasites can sometimes be.

The PhD thesis referenced is entirely dedicated to this parasite, while the second paper only has certain comments on it.
Levakin I.A. Realization of a one-host life cycle of Bunocotyle progenetica (Trematoda: Hemiuroidea: Bunocotylinae) at the White Sea intertidal zone. PhD thesis manuscript, 2007. (In Russian)

Gorbushin, AM, 1997: Field evidence of trematode-induced gigantism in Hydrobia spp. (Gastropoda: Prosobranchia). J. Mar. Biol. Ass. UK 77 , 785–800.

Contributed by Anya Gonchar, photo by Ivan Levakin.

December 29 - Eremitilla mexicana

2010-12-29T06:00:00.000-05:00

Back in 1985, Wayt Thomas, a scientist from the New York Botanical Garden discovered an unusual plant in Mexico. It had a little bloom of dense flowers that kind of looked like a pinecone and nothing else but a thick stalk - no leaves or chlorophyll anywhere. It was so unusual that Thomas did not know what it was and could only speculate as to even what family it might be in. The strange plant eventually made its way to George Yatskievych at the Missouri Botanical Garden and twenty years after it was first discovered, he traveled back to Mexico in search of more. He went to the same location - and even employed the very same guide that Thomas had - and finally, after several days of hunting through stream beds in the Sierra Madre del Sur, they found a small population and took a few samples and many photographs. They did not collect very many because it is believed to only occur in this one small region - it has never been observed elsewhere. A second trip allowed Yatskievych to identify the host plants as Hedyosmum mexicanum and it has now been named Eremitilla mexicana, which means "little Mexican hermit."

Photo by George Yatskievych.

December 28 - Hyalomma dromedarii

2010-12-28T06:00:00.002-05:00

The three wise men are said to have brought three gifts, but perhaps they brought four. The tick, Hyalomma dromedarii, is the most common ectoparasite of camels found in the Middle East. Because of the high temperatures, the females need to burrow down into the sand to lay their eggs. The larvae find a host and feed, but unlike ticks in more temperate climates that usually then drop off to molt, the larvae of H. dromedarii stay put on their host, molt, and feed again. The first host may be a rabbit, hedgehog, bird, or other small livestock, however if the first host that they feed from is a camel itself, they will sometimes stay right there and complete their entire life cycle on the same host. Dropping off into the hot sand is just far too risky, it seems.

Image is from this site.

December 27 - Macrophomina phaseolina

2010-12-27T06:00:00.002-05:00

One of the gifts that the Three Wise Men brought was frankincense, which is derived from the resin of the tree Boswellia serrata. While frankincense has been considered as a remedy for many different types of infectious diseases, B. serrata itself is by no means free from the scourge of infection itself and is plagued by the fungus Macrophomina phaseolina, which causes the disease known as Charcoal Root Rot. This fungus infects more than 300 species of plants, and can cause high mortality among tree seedlings. Macrophomina phaseolina survives and overwinters as small, black spores (call microsclerotia), hidden in the soil or debris from previously infected plants. When a growing root of a plant encounters a dormant spore, it germinates and begins growing all over the root and penetrating into the root cortex. From there, the fungus penetrates through the cortex and inner bark and into the taproot. The infected seedling eventually dies from the gradual destruction of its root system. Just prior to the death of the host, the M. phaseolina produces spores that are deposited in the inner bark of the lower stem and roots. When the host eventually dies and decays, the spores are released into the soil where they wait for an encounter with yet another growing seedling.

Contributed by Tommy Leung.

December 26 - Plasmodium vivax

2010-12-26T06:00:00.001-05:00

In Christian lore, three wise men, the magi, traveled from the East bearing gifts for the baby Jesus. These gifts were gold, myrrh and frankincense, a resin made from trees in the genus Boswellia. The reason for the gold seems obvious, myrrh was used as an incense, which had to have made the stable smell better, and frankincense was used for many things, several related to improving ones health, including ingesting the resin to combat arthritis and other ailments. Frankincense was also burned to ward off mosquitoes and thus the diseases that they carry. One of the most important mosquito-borne diseases at that point in time in that region was malaria, in this case caused by the parasite, Plasmodium vivax. Unlike it's cousin, Plasmodium falciparum, which kills many of the people it infects, P. vivax produces a milder form of the disease, though still with the classic symptoms of profound fever and chills. P. vivax has cycles every 48 hours and is sometimes thus known as "tertian malaria." (See the entry for Plasmodium malariae if that's confusing to you.) This species has a very widespread distribution and, in fact, used to cause early Americans as far north as Philadelphia and New York City to get sick every summer. Though it may kill fewer people, this parasite maintains stages in the liver of its host and can cause relapses of the disease for decades after the initial infection.

December 25 - Trypanosoma lewisi

2010-12-25T06:00:00.002-05:00

On December 25, 1643, Captain William Mynors and his crew aboard the ship the Royal Mary, sailed past a small island in the Malaysian archipelago and dubbed it "Christmas Island." More than 300 kilometers away from the nearest other piece of dry land and uninhabitated by humans or their animals until the 1890's, many of the animals and plants found here were unique to this island. These species included two endemic species of rats, Rattus macleari and Rattus nativitatis. Despite the fact that the first settlers found them to be abundant, within a very short time, i.e. by 1908, the two species had gone extinct. Why? In the early 1900's, a tropical parasitologist had noticed several Rattus macleari individuals acting sickly and he speculated that they had been infected with trypanosomes. This was nothing but a hunch for almost exactly a century at which point molecular diagnostic techniques were brought into the picture. Scientists, including some of my colleagues at the American Museum of Natural History, took rats that had been collected from Christmas Island and deposited as specimens into natural history museums, extracted DNA from them and tested them for trypanosomes. Sure enough, many of the rats collected after humans arrived on the island showed evidence for infection with the parasite, Trypanosoma lewisi. The scientists also tested three rats collected prior to any settlements and none of those tested positive. Thus, it appears that fleas bearing T. lewisi hopped off the black rats (Rattus rattus) on the ship, bit the island's endemic rats and transmitted the parasite. The naïve hosts were likely killed by these parasites and went extinct.

You can read the whole paper here. Image is from this site.

December 24 - Cephenemyia trompe

2010-12-24T06:00:00.001-05:00

Why is Rudolph's nose red, you might wonder? Could it be that he is infected with Cephenemyia trompe, the reindeer nose bot fly? Like the warble fly, that you met two days ago, these flies lay their eggs on the skin, only in this case, the females seem to prefer the muzzle and nostrils of the reindeer. The larvae typically infect the throat of the deer, growing and developing over the cold winter months. In the spring, the reindeer cough them up and then they pupate and mature into adult flies. The flies seek out new hosts using olfactory cues from reindeer urine and pheromone glands. These are just three of the couple of dozen parasites known to infect reindeer.

Photo by Arne Nilssen.

December 23 - Elaphostrongylus rangiferi

2010-12-23T06:00:00.002-05:00

Because Santa's reindeer need to travel at a speed of 650 miles per second in order to deliver all the presents to good little boys and girls, they're going to need to be in peak physical condition. That means that they'd better not be infected with Elaphostrongylus rangiferi, a nematode parasite of reindeer (and also other cervids as well as sheep and goats), commonly known as reindeer brainworm, and closely related to the parasite that causes a similar condition in North American deer, Paraelephaostrongylus tenuis. The eggs of the parasite pass out in the host's feces where they hatch into larvae that either pass into their intermediate hosts, gastropod snails or slugs, or which can remain frozen for periods of up to one year. The worms can cause either a pneumonia-like condition with weakness and coughing or a more serious form of illness that involves neurological symptoms such as confusion and a lack of coordination. This parasite remains a major concern for those raising semi-domesticated reindeer, so Santa better give all of his a thorough physical before he heads out tomorrow night.

December 22 - Hypoderma tarandi

2010-12-22T06:00:00.002-05:00

The warble fly is a nasty parasite which really gets under the skin of Santa's reindeer. Hypoderma tarandi is a pest known to afflict most reindeer populations and it has a life cycle rather similar to the human bot fly. The adult flies lay eggs on the skin of reindeer, and hundreds of eggs can be found in the hide of a single deer. When the egg hatches, the maggot penetrates the skin and burrows under the subcutaneous layer where it proceeds to grow by feeding on host tissue. The maggot can grow up to 2.5 cm long (about an inch) and each deer can be infected with anything from 50 to 300 of such maggots, with some less fortunate individuals hosting 1000 fat maggots under their skin! Ouch -that's going to hurt when Santa hooks them up to their harnesses.

Contributed by Tommy Leung. Photo by Arne Nilssen.

December 21 - Nuytsia floribunda

2010-12-21T06:00:00.003-05:00

During Christmas time in Western Australia, Nuytsia floribunda begins to flower, displaying bright orange flowers and earning itself the name "Australian Christmas Tree". Despite its name, it does not resemble the typical image of a Christmas Trees from the Northern Hemisphere. In fact, N. floribunda actually more closely resembles another Christmas-themed plant - the mistletoe - for N. floribunda is also a hemiparasite. Like other parasitic plants, they have a modified root structure call a haustorium which penetrates the roots of their host plant. The haustorium of the Australian Christmas Tree is armed with sickle-like "horns" with which it to cut its way into the root segments, allowing the Christmas Tree to tap into the flow of water and other chemicals. Interestingly, unlike most other parasites, an individual Australian Christmas Tree can actually exploit multiple hosts at the same time, spreading out a network which is linked to the roots of multiple host trees. And they are certainly not discriminating about whom they network with - most species of trees are vulnerable to invasion by their haustroia, and even underground cables have been found to have the haustoria of N. floribunda attached to them!

Contributed by Tommy Leung.

December 20 - Philotrypesis caricae

2010-12-20T06:00:00.003-05:00

In the "We Wish You a Merry Christmas" carol, there's a line in there demanding that the host bring out some figgy pudding. But there won't be much of that going around if a wasp like Philotrypesis caricae gets involved. Figs rely upon fig wasps for pollination and the close coevolutionary relationship between figs and fig wasps is one of the best examples of an animal-plant mutualism. The wasps pollinate the fig and in return, the fig wasp is provided with a secure location and an ample supply of food to raise its larvae. However, not all fig wasps are so charitable. The "grinches" in this system are parasitic, non-pollinating fig wasps that try to receive the benefits of a fig to raise their young, without paying the "admission fee" of pollinating the fig in the first place. Philotrypesis caricae is one of many hundreds of species of non-pollinator wasps which take advantage of the fig and fig wasp mutualism. The female P. carciae has a long ovipositor that allows her to penetrate through the wall of the fig to deposit her eggs directly into its interior. Furthermore the larvae of P. caricae actually outcompete the larvae of the "honest" pollinator, in this case, Blastophaga psenes. This "grinch" might not have stolen Christmas, but it sure ruined Christmas (or every other day) for many fig wasp larvae!

Contributed by Tommy Leung, with image from this site.

December 19 - Sparassis crispa

2010-12-19T06:00:00.001-05:00

Are the lights on your Christmas tree twinkling? Beautiful ornaments hung in just the perfect spots? Tinsel icicles hanging temptingly to felines (which, should Kitty eat them, will soon result in you harkening back to some worm posts of the past year!) Well, if it's a real tree, be glad that your coniferous companion escaped parasitism by Sparassis crispa. This parasitic fungus, known as the cauliflower mushroom because of its appearance, parasitizes the roots of popular species of evergreens that are used as Christmas trees - pines, firs, and spruces. This parasite may not be so great for the tree, but they're quite nice for humans - they are edible and tasty and even now cultivated and some studies suggest that they might even be capable of stimulating the immune system.

December 18 - Haemoproteus turtur

2010-12-18T06:00:00.001-05:00

On the second day of Christmas, my true love gave to me, two turtledoves (Streptopelia turtur)...and their blood parasite, Haemoproteus turtur? These parasites have a life cycle similar to the malaria parasites in the genus Plasmodium, but do not asexually divide in the host's blood cells, and only invade the erythrocytes as the transmission stages, the gametocytes (shown in photo). H. turtur has been shown to be vectored by the hippoboscid fly, Pseudolynchia canariensis. So, enjoy those turtledoves, true love - you're going to have 22 of them by the time the song is over - but if they get a little lethargic and don't want to "turrrr" (which is how they got their name - it doesn't have anything to do with turtles), it just might be a blood parasite to blame!

Photo by Vaidas Palinauskas.

December 17 - Viscum album

2010-12-17T06:00:00.001-05:00

A cozy fire burning in the hearth, carols tinkling in the background, a glass of spiked eggnog in your bellies...what could be more romantic than finding yourself underneath a sprig of mistletoe hung in the archway with a sweetie, right? That is, if you don't mind kissing under a parasite. Viscum album, the European mistletoe is a parasite of more than 200 different trees and shrubs. It is hemiparasitic in that it still possesses chlorophyll but relies on its host plant for both water and other nutrients. Birds eat the juicy berries and then the seeds pass out in their feces and stick to the branch that they happen to land on, where they will germinate and set up a new parasitic plant. Mistletoe can severely damage or even kill their hosts if the infection is intense enough. The connection to Christmas is fairly recent, thought to have begun in the 18th century, and has evolved from a symbol that protected the home from fire to the more amorous excuse to kiss a pretty girl who happens to walk under it. This species, with its white berries, is more popular in Europe (and in plastic varieties everywhere); other mistletoe species (all also parasites) are used in other parts of the world.

December 16 - Desmozoon lepeophtherii

2010-12-16T06:00:00.001-05:00

Back in July, you met Lepeophtheirus salmonis, now meet Desmozoon lepeophtherii the hyperparasite that makes a living by infecting that particular parasitic copepod. Desmozoon lepeophtherii is a microsporidian, a diverse group of unicellular parasites that are the sister group to the fungi. Microsporidians infect a wide range of animal hosts, thus it is not surprising that even a parasitic copepod is not off-limits. Interestingly, genetic analyses indicate that the closest relatives of D. lepeophtherii are microsporidian in the genus Nucleospora, which are mostly parasites of salmonids. It is possible that for some reasons, the ancestor of D. lepeophtherii opportunistically made the jump from infecting its original fish host to infecting the ectoparasites which infects the said fish.

Reference:
Freeman, M. A. and Sommerville, C. 2009. Desmozoon lepeophtherii n. gen., n. sp., (Microsporidia: Enterocytozoonidae) infecting the salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae). Parasite and Vector 2:58.

Contributed by Tommy Leung.

December 15 - "Blastocystis hominis"

2010-12-15T06:00:00.002-05:00

Single-celled organisms are difficult to classify. They don't have very much when it comes to morphology and so for a long time were just put into the large, amorphous group called "Protozoa" and treated as descending from a common ancestor. We now know that they are very divergent groups and today's parasite is a perfect example of the challenges of taxonomy. Blastocystis was originally thought to be closely related to yeasts, but then was moved to a large group called Sporozoa, which includes many well known parasites. DNA sequence data have shown, though that these parasites are part of another group known as the stramenopiles, which includes the diatoms, brown algae and Phytophthora infestans, the cause of Irish potato blight. Species of Blastocystis were classified based on the host that they had been found in, hence Blastocystis hominis. However, genetic studies showed that there is not a single species that infects humans, but rather nine or ten different subtypes, which have not yet been formally described (thus the quotation marks on the name.) Even more confusing than the taxonomy is the pathology. The protists live in the GI tract and are thought to produce typical types of GI-tract symptoms (do I have to list them?), but the symptoms reported are extremely varied and not everyone that tests positive for it shows symptoms.

December 14 - Fasciola hepatica

2010-12-14T06:00:00.001-05:00

This parasite can be baaaaad, to sheep - and to humans. Fasciola hepatica, or the common liver fluke, is a trematode parasite with a typical complex life cycle like so many that we have seen here before, involving snails that are common around pastures. Metacercariae are ingested by grazing animals and then they seek out liver tissue and feed for a month or two, causing anemia and other symptoms in the animal. Eventually, they mature into adults and settle down in the bile ducts and just churn out eggs - about half a million a day! Humans can become infected with this parasite through accidental ingestion of the metacercariae in water, on water plants, through contact with livestock and perhaps from ingesting raw liver from infected animals.

December 13 - Eudynamys scolopaceus

2010-12-13T06:00:00.000-05:00

This beautiful bird, commonly known as the Asian Koel, is a brood parasite in the cuckoo family. Eudynamys scolopaceus is found in southern Asia and primarily uses crows as hosts for its young. Although the female will sometimes remove one of the host's eggs when she lays hers, unlike many other brood parasites, the Asian Koel young usually do not kill or evict their nest mates, but rather beg their host parents in calls resembling those of baby crows. Their common name comes from the calls that the adults make, though their Sanskrit name, seen in literature that is more than 4000 years old, is Anya-Vapa which translates to "that was raised by others". Thus, the Asian Koel may be the first documented brood parasite known.

December 12 - Balamuthia mandrillaris

2010-12-12T06:00:00.000-05:00

Normally, Balamuthia mandrillaris is a free-living amoeba, but on rare occasions, it has opportunistically become a parasite, with almost always fatal results. These single-celled organisms are thought to enter the body through either open wounds or perhaps inhalation and then they make their way to the brain, where they cause a disease condition called granulomatous amoebic encephalitis. Luckily cases of B. mandrillaris are extremely rare, but on the other hand, because they are rare, not much is known about their biology.

Image is from the CDC image library.

December 11 - Pelecitus fulicaeatrae

2010-12-11T08:07:00.003-05:00

Filarial worms are nematodes that typically inhabit the body cavities and subcutaneous spaces of vertebrates. Most are viviparous (live-bearing) and their larvae, called microfilariae are found in the blood stream or subcutaneous space, where they are drawn up by biting insects when they feed. When the insects feed on a second host, the microfilariae are transferred and the life cycle starts again. Pelecitus fulicaeatrae is found in the leg joints of waster birds (coots and grebes) and its intermediate host is a louse, one more case of a parasite being the intermediate host of another parasite.

Contributed by Mike Kinsella and photo by Julia Diaz.

December 10 - Parvatrema margaritense

2010-12-10T06:00:00.002-05:00

Trematodes are famous for the complexity of their life cycles, but some species demonstrate something beyond all expectations. A good example is Parvatrema margaritense which belongs to Gymnophallidae, a relatively small family of trematodes circulating in coastal ecosystems. As studied in the Bartents and White Seas in Russia, sexual reproduction of this parasite occurs in the digestive tract of the common eider duck (Somateria mollissima). Eggs containing miracidia disperse into the water and the bivalves Turtonia minuta get infected. The cercaria develop in sporocysts, are shed and then seek out and penetrate into the second intermediate host, the gastropod Margarites helicinus. The cercariae occupy the extrapallial cavity of their hosts, lose their tails and form metacercariae. For the majority of trematodes, the latter would eventually be infective for the definitive hosts. However, P. margaritense’s metacercariae are parthenogenetic; they produce the next generation of metacercariae, also parthenogenetic. These subsequently yield mature metacercariae that can continue the cycle inside the eiders. (In addition to these findings, other gymnophallid metacercariae from Sakhalin and the Kuril Islands in Russia were shown to produce cercariae which are capable of re-infecting the host species they originate from, so creating a peculiar sub-cycle).

One cercaria established in M. helicinus can thus give rise to as many as 1.5 – 2 thousand invasive metacercariae (clones). This is about 100 times as many as the number of cercariae shed by a single T. minuta a day, providing a significant multiplication of a parasite. Another curious observation is that metacercariae in the extrapallial cavity of M. helicinus don’t cause any of the common parasite-related troubles and might better be call commensals. The broader exciting discussion on these topics as well as on their evolutionary implications can be found in the referred papers.

References

Galaktionov K. V. An experimental study of the unusual life cycle of Parvatrema sp. (Trematoda: Gymnophallidae). Parazitologiya (1996), 30, 487–494 (in Russian).

Galaktionov K.V. Phenomenon of parthenogenetic metacercariae in gymnophallids and aspects of trematode evolution. Proc. Zool. Inst. Russ. Acad. Sci, 310. 2006: 51-58.

Galaktionov K.V., Irwin S.W.B., Saville D.H. One of the most complex life-cycles among trematodes: a description of Parvatrema margaritense (Ching, 1982) n. comb. (Gymnophallidae) possessing parthenogenetic metacercariae. Parasitology (2006), 132: 733-746.

Galaktionov K. V. A description of the parthenogenetic metacercaria and cercaria of Cercaria falsicingulae I larva nov. (Digenea: Gymnophallidae) from the snails Falsicingula spp. (Gastropoda), with speculation on an unusual life-cycle. Systematic Parasitology (2007), 68 (2), 137-146.

Contributed by Anya Gonchar.

December 9 - Cancellaria cooperi

2010-12-09T06:00:00.001-05:00

On this blog, we've had all kinds of blood-suckers - leeches, bats, ticks, and lice. But when it comes to vampirism, a snail doesn't usually come to mind, but that's exactly what today's parasite is - a blood-sucking snail. Cancellaria cooperi is a snail that appears to have specialised to feed on the blood of the Californian Torpedo Ray, Torpedo californica. These snails spend most of their time inactive, buried in the sand and waiting for the next potential victim. But when a torpedo ray comes along, this mollusc springs into action. Equipped with an extremely keen sense of smell, C. cooperi is capable of detecting the slightest trace of ray mucus, and observations of trails left by these blood-thirsty snails indicate that they can sniff out a ray from as much as 24 metres (about 80 feet) away. Upon making contact, the snail begin touching and exploring the dorsal surface of the ray with extended tentacles, before extending its proboscis and making a small incision with its scalpel-like radular teeth. It then insert its proboscis into the wound and begin its blood-sucking session, which can last for up to 40 minutes. This snail appears to be a specialised parasite of the California torpedo ray, and has no interest in approaching other benthic fishes which are common in its local area, though they have been observed to feed on the Angel Shark (Squantina californica) in laboratory settings. Surprisingly, the torpedo ray seems unperturbed by the experience of being felt up by a snail before getting cut and probed and having its blood-sucked by the vampiric mollusc. But then, torpedo rays seems to be generally unresponsive to most forms of prodding and mechanical stimuli.

Source: O'Sullivan, J.B., McConnaughey, R.R. and Huber, M.E. (1987) A blood-sucking snail: the Cooper's Nutmeg, Cancellaria cooperi Gabb, parasitizes the California Electric Ray, Torpedo californica Ayre. Biological Bulletin 172: 362-366.

Post by Tommy Leung and photo by Lovell & Libby Langstroth.

December 8 - Sarcotaces arcticus

2010-12-08T06:00:00.000-05:00

Scarcely resembling a crustacean so much as some bloated, otherworldly maggot, Sarcotaces arcticus is virtually invisible when it swims up the backdoor of its preferred host, the rockfish. Attaching like a tick to the delicate membranes of the rectum, it begins to gorge on blood and releases an enzyme that causes the host's own body to grow a protective bag or "gall" around the intruder. A bag made of anus. Now impossible to dislodge, the parasite freely grows to around the size of a golf ball, which would be bad enough if the host were our size, but we're talking about a somewhat smaller fish here. Not only does the parasite make a sleeping bag out of rectum skin, it grows too large to ever fit back out either way. All the while, the parasite reproduces and releases its microscopic young, making it not only rude for the host to break wind at social gatherings, but positively terrifying.

Post by Jonathan Wojcik (of BogLeech fame - check out his cool parasite gear) and photo by Jonathan Martin (and if you're brave, check out the video that he took as well!).

December 7 - Trypanosoma cruzi

2010-12-07T06:00:00.000-05:00

Years after returning from the long voyage of the Beagle, Charles Darwin started to feel not-so-well - dizziness, muscle spasms, fatigue and other symptoms. Some speculate that the naturalist may have acquired Chagas Disease while he was traveling in South America. This malady is caused by a single-celled parasite known as Trypanosoma cruzi. These parasites are transmitted by triatomine bugs such as Rhodnius prolixus, commonly called "assassin bugs" or "kissing bugs", the latter because of their tendency to take blood meals around the mouth. The parasites are passed out in the bug's feces and enter the bite wound where they travel through the blood and can take up residence in numerous organs. The acute form may go unnoticed and the chronic form can take decades to set in. Infected people often die of heart failure, due to the damage done to this organ. Animals such as opossums, bats, and livestock serve as reservoirs for the parasites. In 2009, a paper documented transfer of genes from the trypanosome to humans followed by inheritance in the children of these Chagas Disease patients!

December 6 - Scaphanocephalus expansus

2010-12-06T06:00:00.001-05:00

One way to look at parasites is as generalists or specialists. Generalists are non-host specific and while some infect a group of related hosts, others may infect completely unrelated hosts. Specialists infect only one species of host. This strange-looking trematode with wing-like expansions on the anterior end is an intestinal parasite of the osprey, Pandion haliaetus. The osprey is so highly evolved that it is the only species in its own family, Pandionidae. Perhaps because of its evolutionary isolation, the osprey has an unusual number of helminth specialists, and because its diet is 99% fish, almost all of them probably use fish as an intermediate host.

Contributed by Mike Kinsella.

December 5 - Haemophilus influenzae

2010-12-05T06:00:00.000-05:00

Did you get a flu shot this year? Good. But, it's not going to protect you against this pathogen, Haemophilus influenzae. This gamma proteobacterium, a member of the Pasteurellaceae, was mistakenly thought to be the agent responsible for influenza until the 1930's when the actual culprit, viruses, were found. That said, these bacteria can still cause a whole slew of illnesses such as lower respiratory tract infections, pneumonia, ear infections, and meningitis. H. influenzae also holds another important distinction - it was the first bacterium to have its entire genome sequenced - this was published in 1995.

December 4 - Megarhyssa macrurus

2010-12-04T06:00:00.000-05:00

Megarhyssa macrurus is a species of parasitoid wasp. These insects seek out their hosts - larval horntail wasps - by tapping trees with their antennae until they sense their vibrations and scent. The females then bore into the wood with enormous ovipositors (now thought to be tipped with metals such as zinc!) and then she injects an egg into the larvae. Her offspring will hatch out and consume the body of its host and then use similarly metal-laden mandibles to emerge from the wood. Male M. macrurus are wandering around trees listening as well - they seek out newly emerging females to mate with.

December 3 - Schistosoma mansoni

2010-12-03T06:00:00.001-05:00

Schistosoma mansoni is an unusual parasitic trematode of humans. Unusual, because unlike most other trematodes, schistosomes are dioecious, i.e. have separate sexes and also unusual in that they are longer and more worm-like than most other flukes. Eggs are released in the host's feces and hatch into miracidia, which go on to infect freshwater snails and reproduce to form cercaria. The cercaria then seek out human hosts and penetrate their skin and make their way to the blood stream. The worms seek out a member of the opposite sex and if one is found, the pair will settle down in mesenteric blood vessels and begin to start a family. The couple is monogamous - the female actually lives within a groove in the male's body called the gynaecophoric canal (as shown in photo) and there she will churn out more than 300 eggs a day. S. mansoni is a major public health threat in parts of Africa, Asia, and South America where is causes a chronic disease known as either schistosomiasis or bilharzia.

December 2 - Myleusnema bicornis

2010-12-02T06:00:00.002-05:00

Myleusnema bicornis is a species of parasitic nematode belonging to the family Kathlaniidae which is found in the intestine of a small herbivorous freshwater fish call Pacoucine (Myleus ternetzi). This nematode has a few morphology features which are rather unusual. Firstly, while most nematodes have a relatively straightforward-looking anterior end, M. bicornis has a separate, narrow cephalic region that can be extended or retracted (see photo), superficially resembling the proboscis of acanthocephalans such as Profilicollis altmani and Echinorhynchus salmonis. Additionally, male M. bicornis worms have a pair of postcloacal horns located at the posterior end, a feature that is absent in all other species of nematode in the kathlaniid family.

Source: Moravec, F. and Thatcher, V.E. 1996. Myleusnema bicornis gen. et sp. n. (Nematoda: Kathlaniidae), an intestinal parasite of a freshwater serrasalmid fish, Myleus ternetzi, from French Guiana. Folia Parasitologica 43:53-59.

Contributed by Tommy Leung.

December 1 - Crossobothrium antonioi

2010-12-01T06:00:00.001-05:00

Crossobothrium antonioi is a species of tapeworm that was just described last year after finding it in the broadnose sevengill shark (Notorynchus cepedianus), off the coast of Argentina. This tapeworm may win the worldwide contest for having the most "cojones" as the colloquial saying goes - A mature worm can have over 60 segments or proglottids, and in every single one of them, C. antonioi has over 700 testes! That sounds rather formidable - until you realize that the entire tapeworm is only about 50 mm long.

November 30 - Pneunonema tiliquae

2010-11-30T06:00:00.000-05:00

Our parasite for today is a nematode called Pneunonema tiliquae and it is the only species within its genus. It is found in the lungs of the Eastern blue-tongue lizard (Tiliqua scincoides), a cute-looking skink from Australia which can grow to 30 cm (about a foot) long or more. Nothing is known about this parasite's life-cycle or how it enters the host. Based on what is known about other species of lung-dwelling nematodes in reptiles, it is likely that the blue-tongue lizard becomes infected through the oral route, when infective larvae in the environment are accidentally ingested by the lizard alongside its food.

A second parasite found by Tommy Leung in a roadkill skink he found. Click here to see the first.

November 29 - Equinurbia blakei

2010-11-29T06:00:00.000-05:00

The scanning electron microscope has allowed us to see the awesome symmetry of some nematodes up close and personal. Equinurbia blakei is an intestinal parasite of African elephants and one of a group called “large strongyles.” This group is characterized by complicated mouthparts called the corona radiata (radial crown) seen here. The four structures outside the crown are called amphids and are sensory organs. Large strongyles are characteristic of ruminants and some hosts, such as zebras, can harbor up to 20 species and over a million total worms per animal.

Contributed by Mike Kinsella.

November 28 - Halipegus eccentricus

2010-11-28T06:00:00.001-05:00

Halipegus eccentricus is a trematode parasite of North American frogs such as the bullfrog, Rana catesbeiana. Like many of the other trematodes we have met, H. eccentricus has a complex life cycle involving many different hosts. The first intermediate host is a snail of the genera Physa or Planorbella. The cercariae are then ingested by the second intermediate host, a small crustacean, such as a copepod or an ostracod. The metacercariae were then thought to be ingested by tadpoles where they waited for the amphibian to develop into a mature frog, at which point, the parasite would migrate to the frog's eustachian tubes (yes, these worms live in frog ears.) A recent study, however, showed that odonate insects (damselflies, dragonflies) serve as paratenic hosts for the trematodes and that only adult frogs are becoming infected. We are always learning more about parasites!

The image comes from the paper above and shows a redia of H. eccentricus, with the minute cercaria developing inside.

November 27 - Fregata minor

2010-11-27T06:00:00.001-05:00

Imagine someone waiting until just after you've swallowed your last bite of Aunt Tillie's famous pumpkin pie this Thanksgiving, and then forcing you to run a marathon until the inevitable gastric upheaval. Then, without as much as a "thank you", they catch the product of your upheaval, eat it, and run away. Shamelessly disgusting! This is how the Great Frigatebird (Fregata minor) makes a portion of its living, as an "on-the-wing" kleptoparasite. This Blog has featured "kleptos" before, but none as disgustingly brash and acrobatic as the Frigatebird. This enormous (2 meter wingspan) iridescent black seabird literally harasses (often at breakneck speeds) other self-respecting piscivorous birds until they "toss their fish-sticks". It doesn't stop here; because this bird cannot take off without a freefall (an evolutionary compromise of having the highest wing-size to body-size ratio of any bird) it cannot land on the water to eat its meal. Instead it has to perform amazing acrobatics to "catch the retch" before splashdown. When not "downing up-chuck" it feeds on flying fish caught "on-the-wing". Frigatebirds are also interesting in many less vile ways, not the least of which is the fact that they look a little like pterodactyls!

Post and photo by Matt Leslie.

November 26 - Genarchella astyanactis

2010-11-26T06:00:00.001-05:00

Today's parasite - Genarchella astyanactis - belongs to family of digenean trematodes called the Derogenidae, which have evolved a unique way of infecting their second intermediate hosts. They use copepods and other small crustaceans as second intermediate hosts, and their strangely-shaped cercariae are propelled from the snail first intermediate host by a forked appendage. The cercariae are also armed with a coiled structure call a "delivery tube" (shown extended in the drawing) that they use to gain access to the copepod host. For some reason, copepods identify the strange cercaria as a food item and avidly seize any that they encounter. However, as the crustacean manipulates the parasite with its mouth parts, the delivery tube of the cercaria rapidly extends and penetrates the coepod's gut wall. At the same time the cercaria body is propelled through the delivery tube into the body cavity. Imagine eating a muffin which stabs the back of your throat the moment that you bite it, and then injects a squirming parasite into your body!

Reference:
Ditrich, O., Scholz, T., Aguirre-Macedo, L. and Vargas-Vázquez, J. 1997. Larval stages of trematodes from freshwater mollusc of the Yucatan Peninsula, Mexico. Folia Parasitologica 44:109-127.

Contributed by Tommy Leung.

November 25 - Chelopistes meleagridis

2010-11-25T06:00:00.001-05:00

Happy Thanksgiving to all the U.S. readers out there! Seemed appropriate to feature another turkey parasite today (we've had two others recently, i.e. Syngamus trachaea and Trichomonas gallinae ), but this one is something that anyone whose exposure to turkeys is limited to defrosting a Butterball will have no opportunity to come into contact with: the Large Turkey Louse, Chelopistes meleagridis. These lice are very common, especially on wild turkeys and have been introduced to many places via transport of their avian hosts.

November 24 - Lemurpediculus verruculosus

2010-11-24T06:00:00.000-05:00

Lemurpediculus verruculosus is a species of louse that infects Microcebus rufus, commonly known as the Eastern Rufous Lemur or the Brown Mouse Lemur. L. verruculosus has a penchant for areas of its host where the skin is thin, the peripheral blood supply is good and where the animal cannot easily groom - thus the ears and, if it is on a male, the testes. This species was originally discovered back in 1951 as part of a collecting expedition by the famous medical entomologist Harry Hoogstraal, but the species description was based only on a single female that had been collected. Recent work on mouse lemurs yielded many more specimens of these lice, allowing the description to be expanded to include males and instar stages as well.

Photo contributed by Lance Durden, one of the authors of the new paper.

November 23 - Transvena annulospinosa

2010-11-23T06:00:00.001-05:00

Today's parasite is an acanthocephalan (thorny-headed worm) which lives in the Blackback Wrasse (Anampses neoguinaicus), a species of fish found on the Great Barrier Reef of Australia. The picture shows the anterior hook-lined proboscis that the worm uses to anchor itself firmly in the intestinal wall of the host. The photo is actually that of a male worm, and interestingly the males of this species have a pair of paddle-like protrusions at the posterior end of the body. The function of the protrusions are completely unknown. Because it is a purely male characteristic, it is possible that they play a role in sexual competition, though that is purely speculative. However, it has been well established that sexual competition is particularly fierce among the thorny-head worms - male acanthocephalans (including the species in today's post) are armed with a "cement gland" that secretes a substance that they use to block up the female's reproductive tract post-mating. This ensures that she cannot receive future sperm from rival males.

Reference:
Pichelin, S. and Cribb, T.H. (2001) The status of the Diplosentidae (Acanthocephala: Palaeacanthocephala) and a new family of acanthocephalan from Australian wrasses (Pisces: Labridae). Folia Parasitologica 48: 289-303.

Contributed by Tommy Leung.

November 22 - Trichomonas gallinae

2010-11-22T06:00:00.003-05:00

There's certainly no doubt that dinosaurs had parasites. The problem is, soft-bodied things like tapeworms and nematodes, let alone smaller things like trypanosomes or malaria parasites just don't fossilize well, so actually being able to say which species of parasites the "terrible lizards" might have been infected with is close to impossible. Recently, though, jaw bones from Tyrannosaurus rex specimens were re-examined and lesions in them were attributed to a parasite that continues to plague modern-day birds, Trichomonas gallinae. These single-celled parasites, closely related to the human STD, Trichomonas vaginalis, produce "cheesy" lesions in the mouth, pharynx and crop of birds such as pigeons, chickens, and your soon-to-be Thanksgiving turkey, causing a disease that is sometimes called "canker". These birds acquire the infection through consumption of contaminated water, but avian predators, such as falcons, can also be infected from eating parasitized prey. The authors of the paper that makes this link between lesions and T. gallinae hypothesize that even the Field Museum's famous "Sue" may have died of starvation as a result of this parasite damaging its mouth so badly. The image is an artist's vision of what the parasitized dino may have looked like. (Click on the thumbnail to get a better look and see the "cheesy" lesions in its mouth and check out this site for pictures of the parasite in pigeons.)

November 21 - Tetracladium sternae

2010-11-21T06:00:00.000-05:00

Although most digenetic trematodes (except for schistosomes) are hermaphroditic and thus, by definition, capable of self-fertilization, there is some evidence that cross-fertilization may be quite common and maybe even the norm. But it is unusual to catch trematodes in the act of fertilization. There is one exception - Tetracladium sternae is a trematode found in shorebirds such as terns and shearwaters and it is often found in copulating pairs.

Post and image by Mike Kinsella.

November 20 - Pedicularis groenlandica

2010-11-20T06:00:00.000-05:00

Pedicularis groenlandica, or as it is commonly known as because of the shape of its flowers (see insert), Elephant's Head or Elephanthead Lousewort (a big handle for a little flower!) is a parasitic plant in the broomrape family (see also Boschniakia hookeri and Orobranche californica). These plants can be found in - you guessed it - Greenland, but also across Canada and into western North America. P. groenlandica uses haustoria to penetrate the roots of other plants and then suck their water and nutrients out.

November 19 - Asymphylodora tincae

2010-11-19T06:00:00.003-05:00

Today's parasite is commonly found in freshwater fishes of the Palaearctic region. This particular worm has evolved to skip a few steps to the usual three-host life-cycle of most digeneans. Asymphylodora tincae uses a snails as a first intermediate host, where larval stages known as cercariae are produced through asexual multiplication - so far so usual for digeneans. However, instead of leaving the snail like most digeneans, the tailless cercariae stay inside the snail. Additionally, instead of then developing into the cyst-like metacercariae stage as a prelude to infecting the definitive host, this species has done away with that altogether. The cercariae of A. tincae can directly infect the fish definitive host, which occurs when the fish consumes an parasitised snail.

Reference and photo source:
Našincová, V. and Scholz, T. (1994) The life cycle of Asymphylodora tincae (Modeer 1790) (Trematoda: Monorchiidae): a unique development in monorchiid trematodes. Parasitology Research 80:192-197.

Contributed by Tommy Leung.

November 18 - Clinostomum sp.

2010-11-18T06:00:00.000-05:00

This is a metacercarium of a Clinostomum species that was found encysted in the fin of Perca flavescens, the yellow perch. The definitive hosts of these trematodes are fish-eating birds and reptiles, and adult clinostomes are commonly found in the mouth and esophagus. Eggs of Clinostomum are shed in the feces, hopefully in the water. Miricidia then infect planorbid snails. Cercariae released from the snails penetrate the skin fish and amphibians (the second intermediate hosts), encysting as metacercariae throughout the body. Definitive hosts become infected when feeding on infected fish. Clinstomum metacercaria are often large and yellow in appearance, thus their presence is often called “yellow grub disease”.

Contributed by Jessica Light.

November 17 - Tetrabothrius sp.

2010-11-17T06:00:00.001-05:00

The parasite for today is a tapeworm recovered from the intestine of an Andrews' Beak Whale (Mesoplodon bowdoini). This worm belongs to the genus Tetrabothrius, and while this particular species infects beaked whales (obviously), other species of Tetrabothrius have been found in a range of dissimilar marine hosts ranging from baleen whales to fish-eating birds such as albatross and penguins. Tapeworms like Tetrabothrius often have species-specific morphology of their scolex (which is the organ they use to attach themselves to the intestinal wall), and such features can be used to distinguish different species. Larval stages of tapeworm often lack such distinguishing characteristics, making their identification practically impossible. However, the advent of molecular biology technique has enable scientists to use DNA sequences from the larval stages and match them up to those taken from adult worms, allowing their full life-cycle to be mapped out.

Contributed by Tommy Leung.

November 16 - Opisthorchis viverrini

2010-11-16T06:00:00.000-05:00

Stay out of the sun to avoid skin cancer. Don't smoke to avoid lung cancer. Don't eat raw fish to avoid liver cancer? It sounds a little strange, but in fact, the liver flukes Clonorchis sinensis and Opisthorchis viverrini have been found to be carcinogenic, inducing a cancer of the bile ducts that is very often fatal. The life cycle of O. viverrini is very similar to C. sinensis - they first pass through snails, then fish, and then finally the adults inhabit mammals that like to eat fish, including cats, dogs, and humans. The region of Khon Kaen, in northeast Thailand, has the highest incidence of these bile-duct cancers in the world - and 70% of the people in this region are infected with O. viverrini. A recent study produced large libraries of sequences of the transcriptomes - the genes that are transcribed at various stages - of these two important parasites, thus it is hopeful that new drug targets can be identified.

You can read more about the fluke/cancer link here.

November 15 - Pharyngodon australis

2010-11-15T06:00:00.000-05:00

I was on my way home from grocery shopping when I spotted something in the middle of the road near where I live. As I got closer I saw that it was a dead lizard. So like any good parasitologist, I quickly got home, parked my car, grabbed some plastic bags and dashed across the road, scooping up the lizard in the process. It must have only just been recently killed because rigor mortis hasn't even set in. So I thought I'd make something worthwhile out of an otherwise senseless death, drove to work and started dissecting the dead lizard, and sure enough, found this parasite! Pharyngodon australis is a species of nematode found in the large intestine of Eastern blue-tongue lizard (Tiliqua scincoides), a large ominvorous skink from Australia. Thousands of nematodes live in the gastrointestinal tract of skinks and other lizards. Stable isotope studies have indicate that some of these nematodes might be consuming microbes living in the host's gut, while other experiments showed that they might even contribute to gut fermentation. So this might be a case of what would normally be assumed to be a parasitic organism actually being a welcome guest!

Contributed by Tommy Leung.

November 14 - Pseudolynchia canariensis

2010-11-14T06:00:00.000-05:00

Pseudolynchia canariensis is a hippoboscid or louse fly that feeds on pigeons and doves and can transmit the blood parasite Haemoproteus columbae. This species is primarily found in Africa and Asia. If you click on this photo of a P. canariensis fly and look at it carefully, you can see tiny little pink dots near the back of its abdomen. These even smaller things are mites, though in this case they are not really parasitic, but rather phoretic, a phenomenon whereby one kind of organism uses another as a means of transportation. All aboard! This fly is now departing...

November 13 - Brugia malayi

2010-11-13T06:00:00.001-05:00

Like Wuchereria bancrofti, Brugia malayi is another type of filarial nematode that is responsible for the disease known as lymphatic filariasis or, as it is better known, elephantiasis. The name comes from the fact that the adults inhabit the lymphatic system and their presence induces intense swelling, such that the skin resembles that of a saggy elephants. This species is found in Southeast Asia, including Vietnam, China, India, and other neighboring countries. It's estimated to infect over 13 million people in this part of the world. Prevention and treatment strategies include vector control and drugs, some of which are being newly developed thanks to the availability of a complete genome sequence.

November 12 - Amphibiocystidium ranae

2010-11-12T06:00:00.001-05:00

Today we are featuring a fungal parasite of frogs. This parasite is former known as Dermocystidium ranae and was classified within a genus which also included a number of fungal parasites of fishes. However, further research on D. ranae found that it has a number of life-cycle and morphological features which separate this parasite from others within the Dermocystidium genus. Because of those distinguishing characteristics, it has now been reclassified and placed in a genus of its own - Amphibiocystidium - to reflect its unique status. While the parasite in the fish-infecting sister genus, Dermocystidium, has recieved much scientific interest over the last 50 or so years, far less research has been conducted on Amphibiocystidium ranae and it is not clear if it cause any actual harm to its amphibian host or if it is more of a benign parasite.

Reference:
Pascolini, R., Daszak, P., Cunningham, A.A., Tei, S., Vagnetti, D., Bucci, S., Fagotti, A. and Di Rosa, I. (2003) Parasitism by Dermocystidium ranae in a population of Rana esculenta complex in Central Italy and descriptiion of Amphibiocystidium n. gen. Diseases of Aquatic Organisms 56: 65-74

Contributed by Tommy Leung.

November 11 - Sanguilevator yearsleyi

2010-11-11T06:00:00.000-05:00

This parasite was almost one that was featured for Halloween - you'll see why soon - before worms in the eyes of giant birds and blood-lapping/swapping bats took over. But, this tapeworm is really fascinating, so I wanted to feature it now. Sanguilevator yearsleyi was recently discovered in the spiral intestine of a broadfin shark (Lamiopsis temmincki), in Sarawak, Borneo. Histological examination of the tapeworms' scoleces (plural of scolex) revealed spherical and transverse channels that were then found to contain white and red blood cells, respectively, suggesting that the tapeworm sorts and stores these host cells. Why it does this, though, is a bit of a mystery, as tapeworms lack a digestive system per se, and typically just absorb simple nutrients from their hosts.

Nominated by Joanna Cielocha and image comes from the paper describing the species.

November 10 - Holobomolochus confusus

2010-11-10T06:00:00.000-05:00

Here’s another ectoparasite of the European flounder, Platichthys flesus (Linnaeus, 1758) (Teleostei: Pleuronectidae). This time, it is Holobomolochus confusus (Stock, 1959) (Copepoda: Bomolochidae). The photo shows an adult female with 2 egg sacs. This specimen was isolated from the fish’s nasal cavity, which is the typical infection site. In comparison with other ectoparasitic copepods of the European flounder, i.e., Acanthochondria cornuta and Lepeophtheirus pectoralis, it is remarkably smaller, occurring less frequently and in lower numbers. This parasite is commonly found infecting the cod, Gadus morhua (Linnaeus, 1758) (Teleostei: Gadidae), and has also been reported from other species of fish.

For details, see the papers below:
1. Cavaleiro, F. I. & Santos, M. J. (2007) Survey of the metazoan ectoparasites of the European flounder Platichthys flesus (Linnaeus, 1758) along the north-central Portuguese coast. Journal of Parasitology 93, 1218-1222.
2. Cavaleiro, F. I. & Santos, M. J. (2009) Seasonality of metazoan ectoparasites in marine European flounder Platichthys flesus (Teleostei: Pleuronectidae). Parasitology 136, 855-865.

Contributed by Francisca I. Cavaleiro & Maria J. Santos, Universidade do Porto, Faculdade de Ciências, Departamento de Biologia, Rua do Campo Alegre, s/n, FC4, 4169-007 Porto, Portugal.

November 9 - Meloe franciscanus

2010-11-09T06:00:00.001-05:00

Today's parasite is the larval stage of the blister beetle Meloe franciscanus. The beetle larvae are brood parasites that feed on eggs and the young of the solitary bee Habropoda pallida. The problem is, how do they get into the nest of a female bee on the first place? Well they do it by imitating the real thing. They gather into a swarm and climb to the tip of a grass stem. Once there, they clump together to form a small brown blob. While it might not look like much to you, but beetles give off a smell and produce vibrations that fool a male beetle into thinking that the blob is one fine hottie. For the beetle larvae, it's a collective effort - the more of them there are in the blob, the more attractive they appear to a male bee. As soon as the bee comes into range expecting to get lucky, all the beetle larvae jump onboard. The experience leaves the bee slightly shaken, but unstirred, and he continue on his quest to find a female bee. However, once he does find a real female, he also ends up passing on his sticky hitch-hikers as a sexually transmitted infection. Once the beetles are all onboard the poor female, they cling on for dear life, eventually disembarking at her nest where they will be surrounded by all the food they'll ever need to grow up.

Photo credit: SFSU

Contributed by Tommy Leung.

November 8 - Baylisascaris procyonis

2010-11-08T06:00:00.000-05:00

Baylisascaris procyonis is a nematode parasite, related to Toxocara canis. The adults live in the intestine of their hosts and lay eggs that pass out with the feces. If an animal swallows these eggs, the larvae hatch out in the intestine of this host and then one of two things can happen. If they find themselves in their final, i.e. definitive, host, then they will basically stay put - maturing into adults and beginning the cycle all over again. But, if the animal that swallowed them is not the definitive host, then well, things get a little messy. In these cases, the larvae leave the intestine and travel through the bloodstream, invading other tissues and usually making temporary homes in the central nervous system. If that host is a mouse, they can kill it or at the least cause it to act strangely, which can increase the chances of it being consumed by the definitive host. B. procyonis is a parasite of raccoons, and is very common in them (prevalence >70%). Recently, with raccoon populations expanding and coming into closer and closer contact with humans, people, especially children, are increasingly becoming accidentally infected with this parasite. Since we're not the definitive hosts, the larvae undergo visceral migrans and can cause very serious disease and even kill the human. There have been at least four reported deaths due to this parasite in the U.S. since 1980 and there is not currently an effective treatment.

You can read more about the human cases of B. procyonis here.

November 7 - Syngamus trachea

2010-11-07T06:00:00.000-05:00

Syngamus trachea is a nematode known as the gapeworm, which infects birds such as chickens and turkeys. The name comes from the fact that they live in the birds' trachea and, when there are enough of them, they can cut off the airways, causing the bird to gape open their mouths. Females live in permanent conjoinment with males. When they lay eggs, the bird will cough them up and swallow them, and then they will pass out with its feces. Another bird may come along and ingest them or a snail or a worm may serve as an intermediate host.

November 6 - Otodectes cynotis

2010-11-06T06:00:00.000-04:00

Many people who have had a dog or a cat as a pet are probably familiar with ear mites - infections that can cause your pet to have brown, cruddy material in their ears, shake their heads, and even itch frantically at their ears. Here's a close-up look at the culprits - Otodectes cynotis. These tiny arachnids are spread from animal to animal via direct contact and then take up residence in the ear canal. The adults lay eggs in the ears and then the mites hatch out and go through a larval stage and two nymphal stage before becoming mature. If left untreated, the mites can induce secondary bacterial or yeast infections, and, in rare severe cases, even deafness in the ear as well.

November 5 - Armillaria ostoyae

2010-11-05T06:00:00.003-04:00

Yesterday, you met the smallest wasp known. Today meet one of the largest fungi known. Armillaria ostoyae is a species of parasitic fungus that is commonly known by the pleasant name of "Honey mushroom", but which causes the disease of both hardwood and coniferous trees called "Shoestring Rot." That latter name come from the appearance of rhizomorphs that the fungus can use to move between trees and infect them. Although relatives are edible and this fungus may be fine for most people to eat, others have experienced poisoning-type symptoms, thus you should probably avoid this one unless you really know what it is and that you are tolerant of it. This particular species is found in the Pacific Northwest and a few years ago, a colony of A. ostoyae in the Strawberry Mountains of Oregon was measured to be 2200 acres (8.9 square kilometers!) in size and was estimated to be over 2000 years old. That's one humongous fungus!
Photo from biopix.dk

November 4 - Camptopteroides verrucosa

2010-11-04T06:00:00.002-04:00

Camptopteroides verrucosa is a species of fairyfly (family Mymaridae) - which is to say that it's not a fly at all, but rather a tiny little wasp. The very largest of these wasps only has a wingspan of 3 millimeters, so we are definitely talking tiny! Although not much is known about them, it has been observed that they can move and even mate underwater. The females inject their eggs into those of other insects and use an enormous variety of different hosts. These little parasitoids have recently been used in biocontrol efforts.

November 3 - Telogaster opisthorchis

2010-11-03T06:00:00.001-04:00

Previously, we met Ribeiroia ondatrae, the trematode parasite which causes limb malformation in frogs. Now meet Telogaster opisthorchis, a trematode that causes malformation in fishes, specifically the larvae of Galaxias anomalus, a freshwater fish native to New Zealand which is only found in two catchment in the Otago region. If the metacercariae of T. opisthorchis happens to lodge themselves in the right spot, they can induce spinal deformities, resulting in "kinky" fish (see photo - the top fish is normal for comparison) that, like malformed frogs, are more susceptible to predation. As you can easily imagine, even without predation pressure, the survival of such malformed fish would be heavily compromised.

Interestingly, it has been found that the parasite combined with herbicide run-off has a synergistic effect on the fish larvae. While the trematode infection alone can induce the spinal deformities, exposure to the herbicide increases the severity of malformation. In addition, snail hosts that produce the cercariae - the infective stage of T. opisthorchis which infects the fish - also release more cercariae after exposure to moderate level of herbicide. Such an example illustrates how human activities can severely alter the dynamics of pre-existing ecological processes in the environment, such as those relating to the transmission of infectious diseases.

Reference:
Kelly, D.W., R. Poulin, D.M. Tompkins, and C.R. Townsend. 2010. Synergistic effects of glyphosate formulation and parasite infection on fish malformations and survival. Journal of Applied Ecology 47: 498-504.

Contributed by Tommy Leung.