Gyliauchen volubilis

Fish image taken by Richard Field, found at FishBase

Today's parasite is Gyliauchen volubilis - an intestinal fluke from a family of parasites that exclusively inhabit the gut of herbivorous fishes, in this case, the rabbitfish Siganus rivulatus, (see photo) which feed mostly on seaweed. The larvae of G. volubilis infect the rabbitfish by sticking to aquatic vegetation and wrapping themselves up into little cysts, which are then swallowed by their herbivorous host alongside their food (a strategy reminiscent of Philophthalmus sp. which we featured back in May).

The number of G. volubilis that infect each individual fish varies considerably, with some host to only a dozen G. volubilis, while others may have over a hundred flukes in their gut. Today's post is based on a study that looked at how infection level (or population size from the parasite's perspective) can affect the adult life of a fluke inside the rabbitfish's gut. While you may study this simply by looking inside the intestine of naturally infected fish, the problem with this approach is that you cannot know if there were other key events in the fish's life that might have affected the parasite population that you find. What you really need in order to get a more accurate picture is to start off with a blank slate.

Gyliauchen volubilis image
modified from original by
M.O. Al-Jahdali in this paper

That was exactly what a researcher in Saudi Arabia did to find out. For this study he took 70 pre-marked rabbitfish from an area where fish were found to be free of intestinal parasites, and moved them to a netpen in a lagoon where rabbitfish are known to be infected with G. volubilis. Ten weeks later, he recaptured the marked fish and noted how many G. volubilis they picked up while they were in the lagoon, and recorded the developmental stages of the flukes he found.

He found that when a fish's gut is occupied by fewer than about 60 G. volubilis individuals, flukes that newly arrived had a good chance of settling into a nice spot within the intestine. But, as the gut gets more crowded, he started finding more and more dead flukes - most of them were young flukes which had just arrived in the fishes with a mouthful of algae and have barely exited the cyst they came in. When the population of already established G. volubilis reached above 100, these new arrivals starts dying in droves, and the number of "dead on arrival" increased almost exponentially. At high population density, the gut is littered with dozens of dead worms - most of them young, and in some cases none of the newly excysted worms survived.

Crowding also alters the mating behaviour of these flukes. Like most flukes, G. volubilis are hermaphrodites with simultaneously functional male and female sex organs. When the gut is sparsely populated, they kept mostly to themselves - being hermaphrodites they simply reproduce by mixing their own sperm and eggs together - a process also known as "selfing" (other hermaphroditic animals and some flowers do this too). But when the neighbourhood gets more crowded, they get a bit more "social" and G. volubilis become embroiled in "mating groups". For those that produce eggs via selfing, they lay many small eggs. Because it doesn't get more incestuous than mating with yourself, it pays to hedge your bets and lay a lot of eggs in case some of them turn out to be defective. In contrast, flukes that had an opportunity to mate with others tended to lay fewer eggs, but they were comparatively larger - when your eggs are likely to turn out okay and defect-free, you might as well invest more into them to give them the best start in life.

As the flukes grow in size, they also adopt different mating habits, and as hermaphrodites, they also alter how many resources are allocated to the different sex organs to suit their habits. Smaller flukes that have just recently reached sexual maturity usually assume the role of sperm acceptors, receiving them into an organ called a seminal receptacle. This organ becomes very swollen with sperm in these smaller flukes. Medium-size flukes tend to pair up with a single mating partner with which they mutually exchange both sperm and eggs. Large flukes tend have shrivelled-up seminal receptacles and assume the role of sperm donors, inseminating multiple smaller flukes and rarely if ever pair with a worm of equal size.

In short, while starting out life in a crowded fish gut could be a dead end for many, for flukes that do survive that initial gauntlet, they also end up with more mating opportunities.

Reference:
Al-Jahdali, M.O. (2012) Infrapopulations of Gyliauchen volubilis Nagaty, 1956 (Trematoda: Gyliauchenidae) in the rabbitfish Siganus rivulatus (Teleostei: Siganidae) from the Saudi coast of the Red Sea. Parasite 19:227-238.

Bolbosoma balaenae

Image from Figure 1 of the paper

Today's parasite is an acanthocephalan (also known as a thorny-headed worm) and its name should be a clue to what it infects - baleen whales. And what do most baleen whales eat? Krill - lots and LOTS of it. The authors of the study I am writing about in this post found Bolbosoma balaenae larvae infecting krill that were caught during a plankton trawl off the coast of Ría de Vigo, Spain in the NW Iberian Peninsula.

The krill serve as hosts for larval B. balanae and from there, they proceed to infect the next host of their life-cycle, which as mentioned above, are baleen whales where they develop into adult worms. Acanthocephalans as a whole generally only have two hosts in their life-cycle - a small arthropod intermediate host where the larval worm resides, and the vertebrate definitive host where the adult lives and reproduces. But many of the thorny-headed worms that infect marine mammals add another host into the life-cycle between the crustacean host and the vertebrate host - this extra host is known as a paratenic host. The paratenic host is different from the intermediate host, and here's why.

For parasites with complex, multi-host life-cycles, the intermediate host is an obligate component for successful completion of the cycle. It is where the larval parasites gather resources to undergo development into the next stage, and at the same time, the intermediate host also serves as a mean of transporting the larvae into the definitive host (usually by getting itself eaten by the said host). It is in the definitive host where the parasite reaches sexual maturity. In contrast, a paratenic host serves only as a transport, and while the parasite has to infect an intermediate host to complete its life-cycle, infecting the paratenic host is optional. Seeing how the parasite can technically go through its life without ever hopping inside the paratenic host, why do it at all?

Image from Figure 1 of the paper

In the case of other acanthocephalans that infect marine mammals (such as Corynosoma cetaceum), if they are accidentally ingested by their marine mammal hosts while still inside the tiny crustacean intermediate hosts, they will still reach adulthood. But because the chances of that happening is negligibly slim compared to the likelihood of the crustacean host being eaten by a fish, which itself is then eaten by the said marine mammal, incorporating a paratenic host greatly enhances its chances of completing its life-cycle.

However, all this is unnecessary for B. balaenae, as their next host - fin whales and minke whales - do in fact feed on those tiny crustaceans. The authors of this study found that the infection prevalence of B. balaenae in krill is very low - only one in every thousand krill was infected with B. balaenae. But considering that a fin whale gulps down about 10 kg (22 lb) worth of krill with every mouthful and eats about 1800 kg (4000 lb) of those little crustaceans each day,  they can easily pick a few hundred worms very quickly even though the infection level is relatively low in krill.

Just like another acanthocephalan we have previously featured on this blog, Acanthocephalus dirus, instead of simply shedding eggs that are released into the environment with the host's faeces, the female worm actually leaves the gut once she is filled with fertilised eggs (see this paper). So even though the whale is constantly being infected with new worms with every mouthful, there is also a constant turnover in the population in the form of mature female worms exiting the host.

Reference:
Gregori, M., Aznar, F.J., Abollo, E., Roura, Á., González, Á.F. and Pascual, S. (2012) Nyctiphanes couchii as intermediate host for the acanthocephalan Bolbosoma balaenae in temperate waters of the NE Atlantic. Diseases of Aquatic Organisms 99: 37-47.

Antricola marginatus

People usually associate bats with the image of vampires and blood feeding, even though most bats are not blood drinkers. However, bats are themselves host to all manners of blood-feeding parasites. Today, we are looking one such blood sucker - Antricola marginatus - a tick with a caring, maternal side that people don't usually associate with the word "parasite" (though we have featured a few parasites on this blog which go out of their ways to give their offspring with the best possible start to life).

Image from Figure 1 of the paper

While collecting ticks in a cave which is home to nine species of bats (if you are wondering, none of those bats are vampires) in the Yucatan, Mexico, a trio of researchers came across eight female A. marginatus that were covered in massive broods of little baby tick. Each of the female ticks carried between a hundred to four hundred nymphs on their backs. Those little nymphs are very attached to their mother - when the researchers tried to brush some nymphs off, they quickly scramble back onto mother's back at their own volition.

Over the course of its evolution, A. marginatus has almost completely given up its vampiric life-style of drinking bat blood in favour of... something less glamourous - eating bat droppings. However, they still go through a stage in their life as nymphs when they retain their taste for blood. So how are the nymphs suppose to disperse to a suitable host when their mothers are scrambling around and munching on bat poop? The researchers suggested that A. marginatus facilitates her babies by making regular visits to roosting bats, where the nymphs can disembark and drink all they want.

Indeed, when they brush a nymph-ladened mother tick onto a rabbit's ear, the nymphs quickly jump off and started gorging themselves on blood. However, after three days of chugging down rabbit blood, they died - this is not surprising because as I have discussed in a previous post, blood-feeding parasite can be remarkably picky about their hosts, and for some parasites even a slight host species difference can result in deterioration in survival, let alone the large difference between bats and rabbits. So it was no surprises that those nymphs dropped dead after a few days of imbibing rabbit blood. Back in their natural environment of the bat cave, the next warm-bodied mammal A. marginatus would have off-loaded her nymphs on to would have been roosting bat.

Maternal care has been reported for other arachnids like spiders and scorpions, but not ticks. It is unknown just how unique A. marginatus is among ticks with its maternal behaviours, or if there are many other caring, motherly ticks out there which are just waiting to be discovered.

Reference:
Labruna MB, Nava S, Guzmán-Cornejo C, Venzal JM. (2012) Maternal Care in the Soft Tick Antricola marginatus. Journal of Parasitology 98: 876-877

Metschnikowia bicuspidata

If you are a regular reader of this blog, at some point you would have read about the concept of coevolutionary arms races between hosts and parasites (see this for example). Previously, we have featured Pasteuria ramosa - a bacterial parasite of the waterflea Daphnia. Pasteuria ramosa is very picky about its host - specific strains are compatible only with specific host genetic lines, and as we have talked about in that previous post, this parasite is very harmful. Because of how virulent P. ramosa is to waterfleas and because the resistance by the host is dependent upon being the lucky genotype that is not compatible with whatever strain of the parasite which is most common at the time, this sets up an ideal situation for a Red Queen-style evolutionary arms race (and it is one that has been going on for long time).

Uninfected (top right) and
infected waterflea (lower left)
Photo by Meghan Duffy

But in some areas where P. ramosa is found, it also co-occurs with a different parasite - the one that we are featuring today: Metschnikowia bicuspidata. It is a yeast that also infects Daphnia (other fungal parasites also named Metschnikowia biscuspidata have been reported to cause disease in shrimps, crabs, even fish - but it is more likely that they are similar-looking fungi that have been lumped together). The study we are looking at today was conducted by a collaborative group of three researchers who wanted to find out what happens when waterfleas are confronted by both parasites.

Under such circumstances, will the presence of M. bicuspidata exacerbate the existing arms race between Daphnia and P. ramosa, or will it simply get in the way? If resistance for P. ramosa is also associated with resistance to M. bicuspidata, then it means Daphnia has a general mechanism for resisting both parasites. This scenario will simply select for general parasite resistance in the Daphnia population, reducing the level of genetic variation in the population (the raw material for ongoing Red Queen-style evolutionary arms race). On another hand, if Daphnia resistant to P. ramosa are negatively associated with resistance to M. bicuspidata, then it means resistance for one parasite will come at the cost to another - this trade-off in defending against two different parasites sets up an additional selective pressure that can potentially accelerate the arms race.

There are a number of key differences between the two parasites. While P. ramosa reduces the reproductive capacity of the host more than M. bicuspidata, the latter kills the host quicker. Metschnikowia bicuspidata is extremely lethal, killing infected waterfleas within 2-3 weeks of infection (whereas waterfleas can live up to 5-7 weeks after being infected by P. ramosa). The fungus releases its spores after the waterflea dies, and those infective spores can even survive passage through a fish's gut if their host Daphnia is eaten.

And unlike P. ramosa, infection success of M. bicuspidata depends not so much on encountering a host with the right genes, but through sheer persistence - the more often a waterflea is exposed to M. bicuspidata spores, the more likely that they become infected. This difference also manifests in the nature of outbreaks caused by the two parasites. Outbreaks of P. ramosa tend to be rarer and more limited, especially in genetically diverse populations, whereas M. biscuspidata is more prone to massive outbreaks that spread widely across the whole population. Even though it is not as discriminate about host genotype as P. ramosa, it is not as if M. bicuspidata does not influence the evolution of its host. But the way it affects host evolution is different to that of P. ramosa - instead of selecting for specific genotypes, it influences how much the waterfleas allocate their resources into either reproduction or parasite resistance.

In this study, the researchers found that different genetic lines of waterfleas varied considerably in their resistance to M. bicuspidata, but a waterflea's resistance to the fungal parasite did not in turn predict how well it also resisted P. ramosa. Instead, as found in previous studies, infection success of different P. ramosa strains depended upon the specific combination of host genotype and parasite genotype. This indicates that waterfleas have very different ways of resisting the two parasites, and that resistance to one does not lend protection to the other, but at the same time, nor does protection against one parasite increases a waterflea's vulnerability to the other.

Therefore, as far as the Red Queen arms race between waterfleas and P.ramosa is concerned, even though M. bicuspidata looms as a significant threat to the waterflea population, it is unlikely to significantly alter the coevolutionary dynamics between Daphnia and P. ramosa.

Reference:
Auld SKJR, Hall SR, Duffy MA (2012) Epidemiology of a Daphnia-Multiparasite System and Its Implications for the Red Queen. PLoS ONE 7(6): e39564. doi:10.1371/journal.pone.0039564

Eimeria echidnae

We have previously featured a number of coccidian parasites on this blog from birds (here and here), alligators, and groundhogs. Today's coccidian parasite lives in a strange ant-eating, egg-laying mammal from Australia - the short-beaked echidna Tachyglossus aculeatus.

photo from Figure 1 of the paper

The parasite we are featuring today is found in the gut of the echidna where it resides alongside another species of Eimeria - E. tachyglossi. Both these coccidians are found exclusively in echidna guts (generally coccidians are highly host-specific), and both are known to cause mild to severe inflammation of the small intestine, and in some cases, associated with fatality in systemic infections where the parasites have spread to the echidna's other organs. However, the exact role they might play in disease is still unclear. The study we are featuring today was conducted to establish the baseline, background level of Eimeria infection found in healthy echidnas.

The researchers of this study collected fecal sample from echidnas from various zoos and wildlife parks, and examined them for oocysts (see accompanying photo) - the infective stage of coccidia that are shed by infected animals. They found that most echidna shed between a few thousand to tens of thousands of oocysts in each gram of feces. While that may sound a like lot, all the echidnas involved in the study were clinically healthy, and the oocyst numbers were comparable to those from wild marsupials. Furthermore, infection intensity did not change over the different seasons, though oocysts (the parasite's infective stage) were more commonly shed by animals that were housed in outdoor enclosures

Additionally, they also found that while wild and short-term captive echidna shed oocyst of both E. echidnae and E. tachyglossi, echidna that have been held in captivity for an extended period of time only shed E. echidnae, indicating that captive conditions are unfavourable for E. tachyglossi transmission . Because coccidian oocysts are commonly found in the soil, presumably the echidnas become infected while feeding on ants; as they poke their snout in the dirt and use their long sticky tongue to lick up ants, they also end up ingesting a lot of soil (see this video of a hungry echidna on the prowl)

Most newborn mammals become infected with coccidia within their first week or month of life. In contrast, juvenile echidnas that have not been weaned were found to be free of coccidia. Given that echidnas become infected with E. echidnae through exposure to oocysts while feeding on ants, and young echidnas do not start feeding on ants until they are weaned at 6 months old, this age-dependent diet shift most likely explains the absence of E. echidnae infection in juvenile echidnas.

Reference:
Debenham JJ, Johnson R, Vogelnest L, Phalen DN, Whittington R, Slapeta J. (2012) Year-long presence of Eimeria echidnae and absence of Eimeria tachyglossi in captive short-beaked echidnas (Tachyglossus aculeatus). Journal of Parasitology 98:543-549

Mysidobdella californiensis

Photo taken from Figure 3 of the paper

Marine leeches are commonly known to feed on various vertebrate hosts - mainly fish and sea turtles. However, today's parasite stands out from the pack by associating itself with an arthropod. Instead of fish or turtles, Mysidobdella californiensis sticks its sucker onto mysid shrimps. Mysids are also known as opossum shrimps because the females have a little brood pouch (called a marsupium) in which they carry developing young.

The discovery of Mysidobdella californiensis actually occurred rather serendipitously. Back in the summer and fall of 2010, an unprecedentedly huge swarm of mysid shrimp appeared off the central Californian coast. Some of those shrimps got sucked into the water clarification system at the Bodega Marine Laboratory. With all this shrimp in the system, the lab staff began collecting them opportunistically for fish food. But then, they started noticing these little leeches attached to the shrimps, so they made a concerted effort to collect the shrimps directly from the water clarifier, and examine them under the microscope.

What they found were tiny leeches about 1.5 cm (a bit above half an inch) long. Approximately one in every six shrimp were found to have leeches on them, and each infected shrimp was carrying between one to three leeches. Seeing as this is a new species, at this stage very little is known about its biology except what can be inferred based on what we know of a related species - M. borealis - which has been studied in slightly more details. It is unclear whether M. californiensis (and related species) merely hitch-hike on the shrimp and use it to carry them to potential hosts, or if they in fact feed on the shrimp. In laboratory trials on M. borealis, the leeches refused to feed on any of the fishes that they were presented with, and none of the leeches were found to have fish blood cells in their gut. It is possible that Mysidobdella as a genus specialise in feeding on mysid shrimps. If that is indeed the case, then Mysidobdella would be the only marine leech known to feed on the blood of invertebrates rather than vertebrates. However, mysid blood has yet to be found in the gut of these leeches, so at least at this point, the diet of M. californiensis remains a mystery.

Reference:
Burreson, E.M., Kim, B. and Passarelli, J.K. (2012) A New Species of Mysidobdella (Hirudinida: Piscicolidae) from Mysids along the California Coast. Journal of Parasitology 98: 341-343.

Special Report: #ASP2012 (American) - Part II: 'Omics, Roasts, and Yoda

Sunday morning started off with the Associate Editor's symposium, a fairly new feature of the ASP meetings where 3 of the associate editors of the Journal of Parasitology give talks about their own research. Ramon Carreno began and talked about his work on the pinworms of arthropods - people went crazy over these beautiful worms (I know, we're weird folk). Ash Bullard then showed us the results of his recent work following up on the effects of the Deepwater Horizon oil "spill" on parasite fauna. For most types of parasites, there wasn't a significant difference, but for a few, oiled sites had more and for a few others, oiled sites had less. The symposium concluded with my AMNH colleague, Mark Siddall, up on a soapbox about doing 'omics studies of parasites and asking folks to collaborate to get more genomes and transcriptomes of parasites as they represent a lot of phyla that we don't have reference genomes for. Armand Kuris later gave his presidential address, this time talking about humans as parasites and describing patterns across the globe. I headed to the taxonomy and systematics talks for the afternoon, which included the one given by my grad student, Bryan Falk.

That evening, we had our banquet at the Lewis Ginter Botanical Garden. Though the clouds were horribly menacing, soon we were all eating and drinking merrily. As the desserts rolled out, there was suddenly a toast -- er, a roast! -- of Jerry Esch, our out-going editor.

The meeting wrapped up on Monday with another session of taxonomy and systematics for me, including several talks by folks from Gerardo Pérez-Ponce de Leon's lab from UNAM who I met while visiting last fall and then my talk, where I talked about a way to eradicate Plasmodium falciparum - taxonomically, that is. Posters were presented over lunch and then we headed into our business meeting. Lihua Xiao of CDC recapped his childhood in China and how it prompted him to have an interest in parasitology and then, as an introduction to Bill Font's acceptance of the Mentor Award, Charles Criscione and Michelle Steinauer did a little skit comparing him to Yoda - complete with voices.

Looking forward to seeing everyone in beautiful Quebec City in 2013. If you're interested in joining the American Society of Parasitologists, click here.

Special Report: #ASP2012 (American) - Part I: What's a Parasite? Zombie Ants, and Bidding Wars

The 2012 American Society of Parasitology meetings were held July 13-16 in Richmond, Virginia. There were over 150 papers presented and an additional 50 or so posters and being just one person, I obviously couldn't see all of them! Here are a few of the highlights of the meeting from the ones I did see, though. The first talk I saw was my Ron Fayer of the USDA, who studies Blastocystis in livestock. Seems that the prevalence of this parasite can be quite high, but detection methods have improved a lot, making its prevention and control more hopeful. Heather Stigge then gave a nice talk about how digeneans (like this one) choose sites in their frog hosts - apparently no one likes bullfrog mouths! This was followed by another digenean talk by Stephen Greiman, who presented data on pathogenic bacteria being transmitted by these parasites in some cases. At the end of this first afternoon, there was a new feature of the meetings - shorter talks by more junior grad students who presented their ideas and plans for Ph.D. projects in order to solicit some feedback from us sage old members. It was very impressive to me how many of the faculty forewent dinner in order to do this. The next morning started rather somberly - it was the final editorial breakfast for Jerry Esch, who has been at the helm of the Journal of Parasitology for 19 years (more on that to come). The President's Symposium followed and that was great fun. ASP President Armand Kuris kicked it off with a summary of the patterns of evolution of parasitism and a search for unifying themes in ecological modeling. His presentation began some debate in that he narrowly defined "parasite" and perhaps prompted a few later speakers to justify why they were at a Parasitology meeting! David Hughes then wowed us with his work on "zombie ants" - behaviorally modified ants who are infected with fungal parasites. It is really elegant, systems-biology-style work that looks at manipulation from many different angles, including ecological, neurological, and phylogenetic. Ryan Hechinger, a former student of Kuris's, finished up the symposium with a great talk highlighting how large a role that parasites plan in understanding energy fluxes in ecosystems. There were some other nice talks in the afternoon in the parallel sessions. A current student of Kuris, Sarah Weinstein, set the place abuzz when her analyses suggested that parasitism as a lifestyle has evolved 175 times and then a few talks on gregraines by the Clopton and Cook labs set my mind adrift to Dr. Seuss characters. That evening, we held our annual Live and Silent Auctions to raise money to support the student travel grants and once again had a slew of really fun donations by the creative community. Highlights are always paintings that Bill Campbell has done - they fetch hundreds of dollars - but Kristin Jensen's felted iPhone and iPad covers have also grown in popularity (and I was thrilled to win one again this year!). The high-drama auction item of the night turned out to be a pair of hand-painted wine glasses with snails and cercariae, done by author and artist (oh, and parasitologist), John Janovy, Jr.

Special Report: #ASP2012 (Australia) Part IV: Swimming with the Parasites

This post is part 4 (and final) of my special report on the #ASP2012 (Australia) meeting at Launceston, Tasmania - see part 1 here, part 2 here, and part 3 here.

Photo by Kate Hutson

The last day of the conference was a bumper day for marine parasitology so I will just write as briefly as I can on what I saw to cover some highlights. The day kicked off with a series of plenary lectures on; sea lice on farmed salmonids in British Columbia, the history of using parasites as biological markers to identify stock and age of orange roughy (Hoplostethus atlanticus), and an overview of the various parasitic infections that pose a threat to aquaculture by Prof. Barbara Nowak.

But out of those, the presentation which stood out as being most relevant to the original mission of this blog was a talk by Terry Miller - a research officer from the Queensland Museum. He discussed the outcome (so far) of a project to explore to categorise the diversity and genetics of parasites found in fishes of Lizard Island and Heron Island on the Great Barrier Reef, as well as Ningaloo Reef on Western Australia as a part of the Census of Marine Life project. The sheer biodiversity of parasites was the reason why this blog was started and a subject that we discussed in an essay at the end of 2010 - Terry Miller, with his many collaborators, have certainly been busy finding, describing, and classifying this overlooked wealth of biodiversity. They found all manners of myxozoans, flukes, tapeworms, and roundworms, and have already described 56 new species so far. But there are still many unanswered questions relating to biogeography, life-cycles, phylogenetics of these parasites and their significance for fisheries. With 2000 species of parasitic flukes (not counting other fish parasites) estimated to be in the fishes of Australia alone - that's a lot of species descriptions to come!

Photos and drawings used with permission from Leonie Barnett

Speaking of the weird and wonderful, Leonie Barnett from Central Queensland University presented a poster on the molecular phylogeny of a family of parasitic flukes call acanthocolpids which have very odd-looking and remarkably ornate cercariae (the free-living stage which emerge form the first host in the fluke life-cycle). Most cercariae simply look like microscopic tadpoles, with a leaf-shaped body followed by a tapered tail. Leonie has given those acanthocolpid "funky cercariae" nicknames such as "Ducks" and "Starship Enterprise"(see photo on the right). The question must be asked (which at this point can only be rhetorical) - why produce such remarkably elaborate-looking larvae when the majority of them will die after a day or two? What hosts do these parasites infect which warrant such amazing extravagance?

There were a number of presentations thorough the day which were relevant to the fisheries and aquaculture industry, including talks on the detection and treatment of blood-flukes in ranched tuna, identifying and characterising anisakid nematode larvae (which normally infect marine mammals but can cause disease in human if accidentally ingested) from fishes in Australasian waters, and a presentation by Kate Hutson on assessing risks pose to barramundi and mulloway aquaculture by various parasites.

Different Philophthalmus sp. rediae morphs
(insert: specialised morph attacking
the sporocysts of a rival species)

Ian Whittington started off the afternoon session with some videos of monogeneans and to follow that, I talked about potential caste formation and eusocial-like traits amongst the asexual stage of Philophthalmus sp. and how these specialised morphs may in fact be playing a in interspecific competition (see photo on the right or my alternative rendering here)

Sarah Catalano from the Hutson lab talked about a bizarre and little-known group of parasite called the dicyemids which are found in the kidneys of cephalopods (octopus, squid, cuttlefish). These parasites have a very simple body structure, but a very complicated life-cycle. They are astonishingly diverse and also display high levels of host specificity with each species occurs exclusively in a single host species. Because of their specificity they can also be used as a biological marker to reveal different host species where before they were simply considered as subpopulations.

Also from the Hutson lab was Alex Brazenor who presented a study looking at the effects of different water temperature and salinity levels on Neobenedenia - the little worm mentioned in the previous post which is capable of consecutive bouts of self-fertilisation and kick off an outbreak on its own. Alex found that at higher water temperature, Neobendenia lived a faster life -  whereas it took 18 days to reach sexual maturity at 22°C, it only took 10 days to reached that stage at 30°C. Their eggs are more likely to hatch successfully at the higher temperature and salinity level, although if the temperature reached beyond 32°C they start suffering detrimental effects.

Well, that does it for my reports on the #ASP2012 (Australia) conference. Overall, I had a great time - I got to catch up with some colleagues I haven't seen for a while,we talked about a lot of interesting science, and I saw some great presentations and posters - just about all that you can ask for at a conference really. So for me, it's back to writing up blog posts about new papers being published on all manners of interesting parasites - and I already have quite a few lined up...

Special Report: #ASP2012 (Australia) Part III: Sleepy Lizards, Painted Dogs

This post is part 3 of my special report on the #ASP2012 (Australia) meeting at Launceston, see part 1 here and part 2 here.

Photo by Caroline Wohlfeil

There were a number of interesting talks from the wildlife session, first up was a talk by Caroline Wohlfeil - a student from Michael Bull's lab. She gave a talk on sleepy lizards (see right) and the reptile tick, Bothriocroton hydrosauri. These ticks go through 3 stages in their life-cycle, alternating between feeding on a lizard and dropping off in a sheltered area to develop once they are fully engorged. It is in this latter stage that there ticks are transmitted - when lizards take shelter at refuges that have previously been used by infected lizards, they pick up ticks that were dropped off from the previous lizard. Using GPS loggers which continuously recorded the lizard's activity and location, Caroline was able to use that data to work out how often each of the tracked lizard had opportunities for infection. Her network analysis revealed that lizards that are highly-connected also had higher tick loads.

This was followed with a talk by Luz Botero Gomez, a student at Murdoch University, on trypanosome infections in little marsupial call the Brushed-Tail Bettong or Woylie. We have previously covered trypanosomes in another marsupials on this blog, namely the koala, but as it turns out, there is a great diversity of Trypanosoma in native marsupials - most of it still unknown. Woylie are known to be infected with 3 species - T. cruzi (the species which causes Chagas disease), T. copemani, and an as yet unnamed clade of Trypanosoma. Some of those Trypanosoma species are also found in other Australian marsupials but only the woylie is known to carry all three. Much like the koala-infecting trypanosome, T. copemani seems to only cause problem when it occurs in mixed infection with other Trypanosoma species - such co-infections can leads to inflammations and lesions in the tissue. In addition, these different trypanosomes also seem to have varying degrees of tissue specificity, with some species occurring in the blood, while other in muscle tissues, but overall mixed infections are more likely to occur in organs and muscles. Given the Woylie is currently critically endangered, it is very important to know what kind of diseases are induced by these trypanosomes and how it is affected by whether they are single or mixed infections.

Photo from Wikipedia by Helenabella

For a change of pace from parasites threatening a critically endangered mammal, Amanda Ash (also from Murdoch University) presented a talk call "Parasite: embrace not erase" which praised the important functional roles played by parasites in various ecosystems, and discussed the results of a study she conducted looking at the inestinal parasites of African Painted Dogs. She collected fecal samples from captive and wild Painted Dogs and compared the types of parasite eggs and cysts found in those sample. She found that the intestinal fauna of captive dogs was comparatively depauperated, populated only by Giardia whereas the wild dogs had a more eclectic mix of tapeworms, hookworms, and various protozoan parasites - in addition Giardia. Another stark contrast between the captive and wild dogs is that whereas parasitic infection was ubiquitous in the wild population, with 99% had some sort of parasite, only 15% of the captive dogs carried intestinal parasites of some sort.

This has enormous implications for conservation measures such as captive breeding programs - animals which have not been exposed to a wide range of parasites and pathogens can grow up to become immunologically naive so that when they are release into the wild, they may not be able to cope with the wide range of parasites they encounter. In addition, it is unknown what other physiological side-effects may result from lack of exposure to parasites. According to the hygiene hypothesis, the numerous types of allergies and auto-immune diseases which afflict some of us living in western societies have result from the lack of exposure to parasitic worms which are masters at manipulating and modulating our immune system. By limiting both the prevalence and variety of parasitic infections in those captive African Painted Dogs, are we consigning them to the same fate?

During the poster presentation, we saw some students who have come up with creative ways of presenting a 2 min talk - a student from James Cook University read a poem about whether wild dingoes pose a threat to the health of Indigenous communities in Queensland, while a student from University of Western Australia was literally singing the praises of using volatile chemicals for malaria parasite detection. Some of the most fascinating poster talks may present nightmarish scenarios to some people, but for different reasons.

Photo by Kate Hutson

For non-parasitologists, the tongue-biter seems like a one-off freak of nature. But in fact there are actually many species of tongue-biting isopods and other parasitic crustaceans which inhabit the mouth, gills, and branchial cavity of fish. One genus of tongue-biter isopod - Ceratothoa - encompasses 29 known species worldwide, 6 of which are found in Australia waters. However, a new study by Melissa Martin from University of Tasmania revealed that there at least 12 species of Ceratothoa (from 7 families of fish), and 4 of them are new to science.

Dinh Hoai Truong, a student from the Hutson lab at James Cook University presented a horror of a different kind - less visceral than having a parasite in your mouth, but more of a biosecurity nightmare to aquaculturists. He presented a poster on Neobenedenia - a hermaphroditic monogenean which infects the skin of Barramundi. His experiment showed that a single Neobenedenia is able produce eggs through self-fertilisation for consecutive generations without suffering any deleterious effects of inbreeding - each consecutive generation of inbred Neobenedenia are just as infective as the last. This means that even a single worm can start an entire sustained infestation at a fish farm. Unlike the widespread monogenean Gyrodactylus - a notorious aquacuture pest which has the viviparous "Russian Doll"-style "worm-within-a-worm" reproductive set-up (which allows them to swarm a fish like aphids on a rose bush) - Neobenedenia does what most monogeneans do and simply produce eggs. However because they are able to self-fertilise and have very short generation time, they can still become a serious pest to aquaculture.

In the next and final post on #ASP2012 (Australia), we will talk about how environmental factors can affect the generation time of Neobenedenia, and meet many other weird and wonderful marine parasites.

Next post: Swimming with the Parasites