April 30 - Coxiella burnetii

Previously we met Quahog Parasite Unknown or QPX. Today’s parasite also had a mystery name for a while. In the 1930’s slaughterhouse workers in Australia began to come down with a combination of many symptoms that resembled flu, but sometimes progressed to pneumonia and if still left untreated, went on to induce endocarditis – an inflammation around the heart. At first it was unknown what the etiological agent was, so they simply called it “Q fever” with the “Q” standing for “query.” The actual pathogen, a bacterium that was isolated and pegged as the guilty party. The history of its naming is rather convoluted as well. A Japanese researcher in the 1920’s had found a bacterium in ticks that was capable of passing through filters and he published it, but since his samples did not survive, when the Australians Derrick and Burnet and Americans Cox and Davis found similar organisms, they could not be sure if it was the same organism or not (this is why one must have type species for new descriptions!) Thinking it was a close relative of Rickettsia, the Americans proposed the name Rickettsia daiporica, because if they named it after either of the discoverers, that name would be sunk if the Japanese one were to be found to be the same species. The Australians, not so worried about losing out on having their names on a bacterial species, proposed Rickettsia burnetii. More investigation revealed that this bug was not a Rickettsia and so first a subgenus and then a whole new genus, Coxiella, came into play, honoring one American and one Australian microbiologist.

C. burnetii can be found just about everywhere in the world, but the symptoms can differ geographically. Livestock animals are believed to serve as reservoirs and it has been demonstrated that several species of ticks can transmit the bacteria from one animal to another. Humans can become infected when they inhale the bacteria in dust, ingest meat or milk from infected animals or come into contact with blood or other fluids.

In the 1950’s, the U.S. developed weaponized C. burnetii , partly because it takes such a small inoculum to begin an infection and because it is extremely resistant to heat, dessication, and even disinfectants. (The U.S. ended this bioweapons program in 1969.)

April 29 - Angiostrongylus costaricensis

This parasite is a good example of how being in an abnormal host can sometimes do much more damage than being in a normal host. Angiostrongylus costaricensis is a nematode which is usually found in cotton rats (Sigmodon hispidus) and other small rodents where it dwells in the mesenteric veins lining the intestines. Eggs are deposited into the tissues and hatch into first stage larvae which penetrate the intestinal wall and pass out in the feces. When the larvae are ingested by snails or slugs, they again penetrate the tissues and molt twice to infective third stage larvae. If the gastropods are ingested by a cotton rat, the larvae migrate to the veins and the cycle is complete. But if the gastropods are ingested by a primate, such as a person, the consequences can be severe. The first stage larvae in the intestinal wall can trigger a massive inflammatory reaction, resulting in the thickening of the wall and even intestinal blockage. The symptoms can mimic intestinal problems such as appendicitis and occasionally even lead to surgical removal of part of the intestine. Although the distribution of this nematode is primarily in Central and South America, an infection was recently found in primates in two zoos in Miami and opossums and raccoons were also found infected on the zoo grounds.

The photo shows the tail end of a male nematode with a bursa supported by small rays and two chitinized copulatory spicules.

See Miller, C. L., J. M. Kinsella, M. M. Garner, S. Evans, P. A. Gullett and R. E. Schmidt. 2006. Endemic infections of Parastrongylus (=Angiostrongylus) costaricensis in two species of non-human primates, raccoons, and an opossum from Miami, Florida. Journal of Parasitology 92:406-408 for more information.

Contributed by Mike Kinsella.

April 28 - Melophagus ovinus

What do you call a fly that doesn't fly? In this case, you call it a sheep ked. Melophagus ovinus is a very common ectoparasite of sheep. The adults feed off the blood of the sheep, hiding easily in the wool. The females will give "birth" to well-developed larvae, which actually feed off "milk" that is secreted by specialized glands of their mother. They then pupate, cementing the pupal case to the wool. The pupal stage will last for about a month and this stage is unfortunately resistant to any insecticides, making keds difficult to eradicate if the population is firmly established. Keds are distressing to the sheep and as they attempt to itch them, they will rub off or thin out their wool. thus pose economic threats to shepherds who find themselves struck with these pesky insects.

April 27 - Crepidostomum cooperi

Trematodes frequently have complex life cycles involving many hosts and Crepidostomum cooperi is no exception. The adults parasitize fish and lay eggs into the gut, where they pass out with the host's feces. The miracidia then invade tiny little pea- or fingernail clams (Pisidium spp.) The next stage goes on to infect mayflies, which then get eaten by fish to start the whole life cycle over again. A few years ago, I co-authored a paper with University of Colorado at Boulder biologists Rob Guralnick and Gene Hall where we looked at the relationship of the size of the molluscan hosts to parasitism by C. cooperi and other allocreadiid trematodes. Larger clam species (and this is relative - all of these clams are tiny!) were 12 times more likely to be infected with the trematodes than smaller species. We argued that these changes in body size over evolutionary time were a trade-off to balance the fact that the trematodes sterilize these clams.

The photo is actually of a related species, Crepidostomum opeongoensis and comes from this paper.

April 26 - Haemoproteus cyanomitrae

Yesterday was World Malaria Day and since whales do not get malaria, I held off on this parasite until today. This is a very recently described species of blood parasite from the African Olive Sunbird, named Haemoproteus cyanomitrae. Parasites in this genus are frequently called "malaria parasites" because they also belong to the order Haemosporida along with Plasmodium, which includes the causative agents of the disease malaria in humans. Unlike Plasmodium, though, these parasites do not asexually divide in their host's red blood cells - instead they use other tissues. There has been recent discussion about the possibility of splitting Haemoproteus into two genera because molecular data show that they fall into distinct clades and it appears that different lineages use different insects as their vectors.

April 25 - Cryptococcus gattii

The last parasite from "Whale Week" is Cryptococcus gattii, which both infects whales and dolphins, but also has been all over the news lately because it has been spreading across the Pacific Northwest and killing people as well. Thought to be native to the tropical regions of Australia, South America, and Africa the fungus invaded western North America (perhaps via a eucalyptus?) in the mid- to late-1990's and has worked its way as far south as Oregon now. Several whales and porpoises have been found to be infected, though how the fungal spores make their way to those marine creatures remains a mystery. Other animals such as dogs, cats, ferrets, llamas, and alpacas have also tested positive for the fungus. The recent deaths of 5 people in the Pacific Northwest have been creating a bit of a panic, but doctors and news agencies have been warning people to relax and not change their habits. Like other fungal infections, C. gattii cannot be spread from person to person.

A good paper on the recent outbreak in the U.S./Canada can be found here and if you'd rather listen than read, the CDC has a podcast here.

Photo is from this site.

April 24 - Halocercus delphini

Living in the respiratory tract of a whale presents certain challenges that are not faced by those inhabiting the respiratory tract of a terrestrial mammal. Whales and other cetaceans are well-known for their dramatic expiration when they surface to take take a breath, so if you are going to be a parasite that lives in the respiratory tract of a cetacean, you better have a way to hold on tight! Fortunately for the whale lungworms (and unfortunately for the whales), there are some parasites that can do just that. Halocercus delphini is a parasitic nematode which lives in the lung of dolphins. To ensure that it won't be dislodged and expelled when its host takes a breath, the worm plunges its anterior end into the host tissue, forming a capsule which acts an anchor that holds the worm firmly in place. Halocercus delphini is just one species of many from a family of parasitic nematodes (Pseudaliidae) that infect the respiratory, circulatory, and auditory systems of cetaceans.

Contributed by Tommy Leung.

April 23 - Osedax roseus

The genus Osedax is commonly known as the "bone worms", although some endearingly call them "zombie worms" as well. These marine polychaete worms were discovered only in 2002 in the deepest parts of Monterey Bay, California. What were they doing? If you guessed "parasitizing zombies", you'd be sadly wrong. You should put down your comic book and pick up Greg Rouse's paper here. If you guessed eating bones from dead whales, you'd be correct (you should continue reading also in case there are more gratifying questions to come). The animals were "rooted" (like tiny trees) into the bones and a large "trunk" of the animal above the bone waving in the current.

So at this point you've figured out that they're not a whale parasite because the whale is seriously 'belly-up' at this point. So Osedax is in fact a decomposer. But when Rouse took a close look at these worms, he found that they appeared to have no guts whatsoever. So where were they getting their nutrients? Being an expert on marine polychaetes he knew that some deep sea worms had the ability to garner bacteria that derive nutrients from geochemical vents or seeps. As it turns out Osedax was doing something very similar. Inside the "roots" of the animal, which are inside the whale bone, the bacteria are helping to digest the yummy fats left by the whale.

Oddly, Rouse was only seeing female Osedax in his collections. Where are they males? If you answered, "out for a cold one at the Mos Eisley Cantina" you'd need to turn off the television and pick up a book. If you guessed, "living as a harem inside the body of the female" you'd be correct! Rouse initially thought these microscopic "bags of sperm" were parasitic (yeah!) inside the females, surviving on the nutrients she and her endosymbiont bacteria were producing. However, at closer examination they appear to actually be larvae that never develop feeding structures at all, just living off the yolk for the egg sac. Never the less, they are able to provide sperm to fertilize the female's eggs!

Ok, I know what you're thinking, "its icky and it not even a parasite, why am I still reading?” Because it's fascinating! Survival in a VAST ocean where there are relatively few dead whales on which to live is a tricky thing; reproduction is even trickier. The "dwarf males" can disperse over large distances, because the only part of the life cycle that isn't attached to a whale bone is the larva. Rouse thinks that the sex is environmentally determined: if larvae land on a bone, they become a female, if they land on a female, they become male. If this species only relied on a male settling next to a female to breed, it would seriously diminish the gene pool.

So Osedax is icky and but it's not a whale parasite, though the males are sort of parasites of the females... so it is completely fascinating! Osedax has evolved surprising and strange means to eke out an existence at the bottom of the sea where few organisms (even zombies) fear to tread.

See also: Rouse et al, 2008. Acquisition of Dwarf Male "Harems" by Recently Settled Females of Osedax roseus. Biol Bull. 214, 67-82.

Contributed by Matt Leslie.

April 22 - Anisakis nascettii

Anisakid nematodes are well-known as gastrointestinal parasites of various marine mammals. They utilise crustaceans like krill and amphipods as intermediate hosts, and when these crustaceans are eaten by fish or squid, they migrate into the muscle tissue where they await ingestion by a marine mammals. Humans can become accidental host of anisakids when they eat raw or undercooked fish or squid. While the worm cannot survive in humans, they can induce a severe allergic reaction.

There are many species of anisakid nematode and recently a new species, Anisakis nascettii, was found in an Andrews' Beak Whale (Mesoplodon bowdoini) stranded off the east coast of South Island, New Zealand. Using morphological and molecular identification, a team of researchers was able to match the worms found in the New Zealand-stranded whale to specimen found in beaked whales on the coast of South Africa and Australia. They also found that those worms actually belong to an undescribed species that has only ever been recorded as larval stages in squid. This goes to shows that while these days, the prospect of discovering a new species of large vertebrates is very unlikely, new species of parasites are being uncovered literally everyday!



Reference:
Mattiucci, S., Paoletti, M., Webb, S.C. (2009). Anisakis nascettii n. sp. (Nematoda: Anisakidae) from beaked whales of the southern hemisphere: morphological description, genetic relationships between congeners and ecological data. Systematic Parasitology, 74:199-217.

Contributed by Tommy Leung.

April 21 - Cyamus ovalis

Some of you might be familiar with the New Zealand movie "Whale Rider" - well, the parasite featured today is a real whale rider.

Cyamus ovalis belongs to a family of crustaceans call Cyamidae that specialize as ectoparasites of cetaceans. Despite being called "lice", whale lice are actually amphipods, and unlike most amphipods (such as sand hoppers or "scuds") which have bodies that are laterally flattened (narrower when viewed from top), the whale lice have dorsally flattened bodies, like a crab, better suited to the life-style of clinging onto the surface of an oceanic behemoth. Because of their lack of free-swimming stages, whale lice can only be transferred from whale to whale on contact. As a result, they have a very close co-evolutionary relationship with their host, and different species of cetaceans have different species of whale lice

Whale lice have been used to track the population genetic structure of their whale hosts. In the case of Cyamus ovalis, their hosts are the right whales Eubalaena spp. Swarms of C. ovalis cover the raised pieces of roughened skin (call callosities) on the head of the whale. Studies into their population genetic structure have revealed that, just like their whale hosts, the Northern and Southern Hemisphere populations of lice have been isolated from each other for several million years.

For more information, on the coevolution of whale lice with their host, see this link . The photograph for Cyamus ovalis was taken from the same webpage as the one above - Photo Credit: Vicky Rowntree, University of Utah.

There is also a trailer on YouTube for an upcoming documentary about researching whale lice. If this doesn't make being a parasitologist look like the most exciting career out there, what will?

Thanks to Tommy Leung for all of this.

April 20 - Nasitrema globicephalae

Helpless whales and dolphins stranded on a beach are always a dismaying sight for any animal lover, and the causes of stranding can often be varied and mysterious, but who would have thought a little worm, hidden from view could be a contributing factor?

Nasitrema globicephalae and other species of that genus are trematodes that inhabit the heads and air sinuses of small cetaceans such as dolphins and pilot whales. It is unclear how dolphins become infected by these endoparasitic flukes, though seeing how it is a trematode, it is quite likely the host become infected through eating prey items which contain the larval stages. Nasitrema is definitely not a very well-behaved parasite because once it is inside the host, it tends to roam around a lot, ending up in all kinds of organs it is not supposed to and causing terrible damage in its path. Sometimes Nasitrema ends up in the brain tissue causing massive necrotic lesion and inflammation that can lead to secondary infections.

It is unknown why Nasitrema would migrate to the brain, and even though the worm can develop to full maturity and even produce eggs within the brain (see picture) this does not benefit the parasite in any way as the eggs have no way of leaving the host through the brain tissue. A study found that high percentage of the cetaceans stranded along the Southern Californian coastline were found to harbour massive infestation of Nasitrema, with mature, gravid (egg-bearing) worms in the brain tissue. Because of the injuries this parasite can cause to its host, it has been suggested as a contributing factor to the stranding of small cetaceans.

It must be noted that Nasitrema is not responsible for all or even most strandings. While they are frequently found associated with stranded dolphins and porpoises, the actual role they play in contributing to that outcome is still uncertain within the context of other factors. And fortunately, at least for dolphins in captivity, it has been found that the same anthelminthic drugs used for treating human lung fluke infection can also be use to treat bottlenose dolphins with Nasitrema infection.

References:

Dailey, M.D. and Walker, W. A. (1978). Parasitism as a factor (?) in single strandings of southern California cetaceans. Journal of Parasitology, 64: 593-596.

O'Shea, T.J., Homer, B.L., Greiner, E.C. and Layton, AW (1991). Nasitrema sp.-associated encephalitis in a striped dolphin (Stenella coeruleoalba) stranded in the Gulf of Mexico. Journal of Wildlife Diseases, 27: 706-709.

Contributed by Tommy Leung.
Photo by William Walker, from "Diseases of Marine Animals" Volume 4 edited by Otto Kinne.

April 19 - Placentanema gigantissma

The parasite featured today is the longest known parasitic nematode, appropriately, its host is also one of the largest known living animal - the sperm whale (Physeter macrocephalus). The name of this parasite is Placentanema gigantissma, and it is indeed a gigantic worm. The female worm can reach up to 8.4 m long, while the smaller male reach "only" 3.75 m in length.

Its scientific name also indicates its peculiar microhabitat - this nematode has only ever been found in the uterus and placenta of female sperm whales. Even though they are relatively common, very little is known about this species. How this parasite transmit from host to host is currently unknown, though it is likely that this is facilitated by the expulsion of the placenta (with the female worm within) at birth, and eggs are released as the female worm decomposes. It has been suggested that larval worms infect the female whale prior to sexual maturity and remain dormant until the whale becomes pregnant.

The photo is of the host, in this case a young sperm whale.
For further details, see p. 839 of Diseases of Marine Animals Vol 4 Part 2 (free to download from here)

Contributed by Tommy Leung.

April 18 - Demodex folliculorum

One of the things that grosses non-parasitologists out (and probably many parasitologists!) is the fact that little tiny mites live on our eyelashes. These are Demodex folliculorum, and they can actually inhabit many different follicles on humans' faces. In fact, they're a bit social - as many as 10 of them can co-exist in a single follicle (party on the forehead - spread the word!) There are no known pathogens that they spread, but they can cause people to lose hair and they can make pores larger. They don't bite people and instead they mostly just munch up the secretions from our sebaceous glands. One of the coolest things is that they seem to be so incredibly efficient at digestion that they don't produce waste - so much so that they don't even have an excretory pore for defecation. So, if you have to deal with the fact that right now there are potentially a bunch of tiny spider-like things living on your face, at least you can take a little comfort from the knowledge that they are clean house guests.

April 17 - Haematomyzus elephantis

The same species of louse, known as Haematomyzus elephantis, is found on both Asian and African elephants. Although it seems like a bizarre coincidence that this parasite should have a long “proboscis” like its host, the length of its mouthparts is an adaptation to penetrate the thick skin of the elephant. And although the ”proboscis” might also look like a giant straw to suck blood, these are not sucking lice (Anoplura) but chewing lice (Mallophaga), which feed on the epidermis. They are so highly evolved that an entire suborder (Rhynchophthirina) was created for only 3 species (the other 2 are found on warthogs).

Contributed by Mike Kinsella.

April 16 - Tyrranobdella rex

A new genus and species of leech, Tyrranobdella rex Phillips et al. 2010 with enormous teeth was described in the journal PLoS ONE on Wednesday of this week. Found feeding from the nose of a 9 yr old child in the upper Amazon by Renzo Arouco-Brown of the School of Medicine at the Universidad Peruana Cayetano Heredia, this new T. rex is known from 3 nasopharyngeal cases, and may well be the first leech species for which Homo sapiens is the type-host.

Phylogenetic work in the publication demonstrates that T. rex is part of a larger evolutionary group of mammal-specific endoparasites, the Praobdellidae, which includes the terrible ferocious leech (Dinobdella ferox) from Asia as well as African and Mexican pests. Mucosal leech infestations by members of this family typically involve the naries, pharynx and hypopharynx, though more alarming mucosal infestation sites are noted by Anna Phillips of the American Museum of Natural History and her co-authors. While leeches are not typically thought to be significant parasites of humans, praobdellid leeches like T. rex have been known to cause life-threatening conditions that range from choking to severe anemia and even death.

In addition to Phillips and Arauco-Brown, authors of this new and formidable T. rex include Mark Siddall and Alejandro Oceguera-Figueroa, also of the American Museum of Natural History, Gloria P.Gomez of the Department of Microbiology at the Universidad Peruana Cayetano Heredia in Lima, María Beltrán of the Enteroparasitology Laboratory at the Peruvian Public Health Center, and Lai Y-Te of the National Taiwan University in Taipei.

Contributed by Mark Siddall.

April 15 - Enterobius vermicularis

Got kids? Then, perhaps you also have Enterobius vermicularis, pinworms. These are oxyurid nematodes and one of the most prevalent diseases of children in the developed world - and the most common nematode infection in the U.S. Adult worms mate in the small intestine, after which the males promptly die and pass out of the host's bodies. Females then settle down in the large intestine and begin to fill their bodies with large numbers of eggs - more than 15,000 of them. She's not content to just pop out those eggs - no, she actually takes an active role in the process. She emerges from the anus and then does one of three things - she either expels them herself, or sometimes she just dies and her body dissolves, or sometimes, the host helps when they itch and kill her and break her open and release the eggs. Then the real fun begins - because those 15,000 eggs are sticky and can go everywhere, especially when little hands touch their bums and then touch, well, everything! Infection occurs when the eggs are ingested. The eggs are very resistant and can even be found in dust that can become airborne and inhaled, to be swallowed later. The photo is of a piece of Scotch tape with eggs attached - this is a common means of diagnosis. The tape is placed over the child's anus over the course of several mornings and then examined for the eggs under a microscope.

April 14 - Mesocestoides variabilis

Yesterday, we saw a brand new species of parasite. Today's parasite has been known to science for almost 100 years, but it still a bit of a mystery. Mesocestoides variabilis is a species of cestode, or tapeworm, that was first described in 1927. It has been reported from a wide variety of hosts - adults in foxes, cats, skunks and other carnivores and larval worms in smaller critters like lizards, birds, and small mammals, but it seems likely that what is commonly identified as Mesocestoides variabilis is actually a group of different species and genetic evidence seems to corroborate this. Although these tapeworms seem to primarily be found in wild hosts and occasionally domestic carnivores, there was one case a few years ago of an infection in a child. It appeared that the 19-month old boy had consumed Cajun sausage made of "wild animal viscera"!

This image is from the CDC Public Health Image Library.

April 13 - Isospora motmotana

One of the highlights of my recent trip to Africa was getting to see some really neat birds in the order Coraciiformes, including hornbills, rollers, and the extremely charismatic hoopoe. This order has a few representatives in the New World, including the kingfishers, the todies, and motmots, colorful birds that are prevalent in Central America and northern South America. Recently, Yabsley et al. described a new species of parasite found in blue-crowned motmots in Costa Rica, which they named Isospora motmotana. This was the first coccidian parasite described from this bird species - as always, further proof that so much of the diversity of life out there is left to be discovered!

April 12 - Delia radicum

Maybe you were scared off the pork roast last night after reading about Taenia solium and opted for a veggie stirfry instead. Although there aren't any parasites that specifically use a vegetable as an intermediate host to get into humans, that doesn't mean those broccoli and cauliflower florets didn't face the possibility of being infected with something. One parasite of the Brassica plants (the aforementioned, plus cabbage, brussel sprouts, etc) is the cabbage fly or turnip fly, Delia radicum. Adults, which look a lot like houseflies (see image here), feed on nectar of flowers, but then lay their eggs next to Brassica plants. The larvae feed on the roots and stems of the plants and can greatly harm the plant by weakening it and can also leave the plant vulnerable to secondary infections by fungi or bacteria. Eating infected broccoli won't give you any parasites - just a little extra protein.

April 11 - Taenia solium

Having a pork roast for Sunday dinner? Then, you probably don't want to think about today's parasite, Taenia solium, the pork tapeworm. Humans can acquire these worms by eating undercooked pork and if so, then the tapeworms mature into adults and take up residence in the intestine, where they can grow up to 7 meters long and will release eggs in shed proglottids. However, sometimes humans are infected after ingesting eggs directly, which means the human turns into the intermediate host. In these cases, cysticerci or bladder worms can infect other tissues, including the brain, producing a very serious and potentially even fatal disease and sometimes must be surgically removed. A recent study has suggested that humans have been hosts to T. solium for 10,000 years and picked up the tapeworms from scavenging on ungulates, passing it on to pigs when they later domesticated these animals.

April 10 - Cuscuta europaea

Cuscuta europaea, is a parasitic plant commonly known as European dodder. These insidious plants twirl around the stems of their hosts and probe into their vascular systems, stealing their water and nutrients. The leaves of dodder are virtually non-existent, reduced to just tiny scales, and many species, including this one, do not engage in photosynthesis any longer and once they are wrapped around their host and soaking up its nutrients, dodder even loses its roots. Dodder may be the most reviled plant parasite as it can infest a huge variety of hosts including both agricultural plants and horticulture species. These plants were originally in their own family, the Cuscutaceae , but new phylogenetic work has placed them in Convolvulaceae, the same family as morning glories. What might be the coolest thing about the dodder? It finds its host plant by "smell"! See this site for more info.

April 9 - Pneumocystis jirovecii

Pneumocystis jirovecii is a fungus that can be an opportunistic pathogen and produce pneumonia in humans. This species was previously known as Pneumocystis carinii, thus these pneumonias are still usually called "PCP." These infections principally infect immunocompromised people and have become associated with AIDS. These fungi are geographically widespread and most people are exposed to them by a young age. In addition to the change in the species name, these pathogens were also previously classified as protozoa since they are single-celled, however genetic and biochemical evidence all places them in with fungi.

April 8 - Maritrema novaezealandensis

The parasite Maritrema novaezealandensis is commonly found on the coast of South Island, New Zealand. It is a trematode with a typical three host life-cycle, using a snail as a first host intermediate host where clonal multiplication occurs, a crustacean as a second intermediate host where it form a cyst-like waiting stage, and gulls as the definitive host where it matures into a hermaphroditic adults and sexually reproduces.

This trematode parasite uses the New Zealand mudsnail (Zeacumantus subcarinatus) to asexually multiply, and in certain areas, more than 60% of the snails found are infected with this parasite. The parasite takes over the most of the innard of the snail, filling it up with clones of itself and diverting resources from its reproductive organs, thus castrating it. The snail is essentially a zombie under the control of the parasite. Maritrema then use the snail as a kind of "parasite factory" producing free-living swimming larval stages (also clones) call cercariae (pictured) which are released into the environment to infect the next host in the cycle which are crustaceans such small crabs and amphipods (tiny beachhopper-type animals). The cercariae penerate weak spots in the cuticle using a specialised structure known as a stylet which functions rather like a cross between a scalpel and a saw. The little cercariae (which are less than 0.15 mm long) use the stylet to cut their way into the crustacean. Once inside, they grow over the course of a few weeks and develop into a cyst. There, they wait to be eaten by a sea gull to complete their life-cycle.

The cue for the infected snails to release the free-swimming cercariae stage is an increase in temperature, and when that happens, hundreds of cercariae swarm out of an infected snail. The hotter it gets, the more parasites are released. In the summer during low tide, pools or puddles gathered on the mudflat can get quite warm in the glare of the afternoon sun. Trapped within those tide pools are various crustaceans and many, many infected snails. Triggered by the heat, each infected snail releases hundreds of cercariae into the water, turning the water into a swarming "cercariae soup" and rendering any crustaceans in the area into hapless parasite pin-cushions. For tiny crustaceans like amphipods, the experience of being penetrated simultaneously by multiple cercariae can be quite traumatic (imagine being stabbed multiple times by scalpels) and the experience can often be lethal. While killing the intermediate host before it can be passed on to the next host is not good for the parasite either, it demonstrates one of the ways that parasites can regulate the population of its host.


Some relevant papers on this parasite are:

Fredensborg, B.L., K.N. Mouritsen, and R. Poulin. 2004. Intensity-dependent mortality of Paracalliope novizealandiae (Amphipoda: Crustacea) infected by a trematode: experimental infections and field observations. Journal of Experimental Marine Biology and Ecology 311: 253-265.

Fredensborg, B.L., K.N. Mouritsen, and R. Poulin. 2005. Impact of trematodes on host survival and population density in the intertidal gastropod Zeacumantus subcarinatus. Marine Ecology Progress Series 290: 109-117.

Keeney, D.B., J.M. Waters, and R. Poulin. 2007. Clonal diversity of the marine trematode Maritrema novaezealandensis within intermediate hosts: the molecular ecology of parasite life cycles. Molecular Ecology 16: 431-439.

Martorelli, S.R., B.L. Fredensborg, K.N. Mouritsen, and R. Poulin. 2004. Description and proposed life cycle of Maritrema novaezealandensis n.sp. (Microphallidae) parasitic in red-billed gulls Larus novaehollandiae scopulinus from Otago Harbor, South Island, New Zealand. Journal of Parasitology 90: 272-277.

Contributed by Tommy Leung.

April 7 - Brucella abortus

Brucella abortus is a gram-negative bacterium that uses cattle and other ruminants as its primary host. It can however, also be transmitted to humans and will produce a disease known as "Malta fever" or "undulant fever", characterized by sweating and joint pain and the latter name specifically referring to the waves of fever that a patient can show. Brucellosis is a major health threat to cattle because it causes a high degree of spontaneous abortions, thus all cattle in the U.S. (and many other countries, for that matter) must be vaccinated against this pathogen. Recently farmers in the U.S. West have become worried that wild ungulates such as elk and bison might transfer the bacteria to their herds. Humans can acquire the bacteria either from coming into physical contact with infected cattle or even by drinking milk or eating meat from infected animals. The genomes of two strains of B. abortus have been completely sequenced and these bacteria are somewhat unusual in having two separate chromosomes.

Image from this page.

April 6 - Plasmodium ovale

Plasmodium ovale is one of the two rare species of human malaria parasites, usually present in fewer than 5% of people in any region where it is present. Although probably native to West Africa, P. ovale has now spread into several parts of Southeastern Asia and Papua New Guinea. P. ovale is commonly called tertian malaria because it produces fever cycles every two days (note that the Romans had no zero, thus the term) and very often is difficult to diagnose in a bloodsmear from Plasmodium vivax. P. ovale can relapse for several years as well, via dormant stages in the liver known as hypnozoites. Like the other mammalian Plasmodium species, P. ovale is vectored by Anopheles mosquitoes. The taxonomy of P. ovale has been somewhat troublesome as this parasite seems to be genetically quite different from other species. Some studies have placed it as closely related to Hepatocystis parasites in bats and baboons, but a recent paper reported parasites in wild chimpanzees that were closely related to P. ovale.

April 5 - Cimex lectularius

Ask any New Yorker what their greatest fear is and what do you think it will be? Runaway subway? Nah. Shoddy cranes? Well, maybe. But, my guess is that most will say bed bugs. These insects hatch from eggs into nymphs which are quite small and hard to see, but go through repeated moltings until they are about 5 mm in length and darker brown. They live in mattresses, bedding, and furniture and emerge at night to take a blood meal from a sleeping human, which they are attracted to because of the body heat and carbon dioxide. To get the blood, they insert their proboscis, and pump saliva and anticoagulants into the wound (shown in purple in the colorized micrograph). With the other part of their mouthparts (in red), they suck blood up. In recent times, bedbugs have become something of an epidemic, both in New York and globally as well. This is likely due to a decrease use in pesticides (for fighting cockroaches) and the fact the travelers spread them so easily in bedding (do *not* bring your favorite pillow to hotels!), luggage, or sometimes clothing or pets. They are extremely hard to get rid of because they are so good at hiding in very small, tight spots. Recently, dogs have been trained to sniff them out in apartments and hotels, which is helping with their extermination.

There is lots more info on bedbugs, including their historical association with humans and the best methods for detecting them and getting rid of them on their Wikipedia page.

Ok, I'm itchy now.

Image is from the CDC Public Health Image Library.

April 4 - Synodontis multipunctatus

Well, we've had cuckoo birds on this blog before, which most people would at least have heard of, but what about the cuckoo catfish? The cuckoo catfish, Synodontis multipunctatus, a popular ornamental fish that is somewhat well-known amongst aquarium enthusiasts. It is originally from Lake Tanganyika in Africa which is hotspot of cichlid fish biodiversity. The cuckoo catfish has a rather unusual breeding habit, it is a brood parasite of mouthbrooding cichlids found in Lake Tanganyika. Just like their bird namesake, the cuckoo catfish displaces the legitimate offspring of its host, forcing the cichlid to rear its young, and they have a rather clever way of accomplishing this. The catfish is attracted by the scent of the brooding cichlids, and as soon as they detect any such brooding cichlid in the vicinity, they race to the scene of the coupling. The catfish mob the pair of spawning cichlids and as soon as their eggs are fertilised, a mating pair of cuckoo catfish dash in, the female laying her own eggs amidst the brood, with the male following closely behind to fertilise them. When the brooding cichlid scoop up the clutch of eggs to brood them in its mouth, it's a mixed-bag of cichlid and catfish eggs. The catfish fry hatch a few days earlier than the cichlid fry and proceed to feed on the host's eggs with which they are sharing the brood chamber. So the cichlid is unknowingly and unwittingly carry a brood composed of juvenile catfish - imagine seeing a mouthbrooding cichlid open its mouth and out swim a swarm of splotchy little catfish!


The paper that originally described this fishy brood parasite is:
Sato, T. 1986. A brood parasitic catfish of mouthbrooding cichlid fishes in Lake Tanganyika. Nature 323:58-59

Contributed by Tommy Leung.

April 3 - Santalum spp.

Parasites often exact a heavy toll on their hosts in ways that we are all familiar with. For example, in a recent video, New York Times columnist Nicholas Kristof marveled at the crushing physical labor performed by Congolese women with heavy parasite loads. Malaria is among the deadliest diseases, infecting up to 500 million people each year, causing untold suffering and millions of deaths.

In a twist on this theme, a much-beloved parasitic plant, sandalwood, has played an important and unexpected role in human suffering. I know a native Hawaiian woman whose grandmother ripped young shoots of native sandalwood out of the ground whenever she encountered them. That plant had caused her own grandparents so much pain that she never wanted her people to experience it again.

The name sandalwood refers to any of the 15 extant described members of the genus Santalum L. of the Santalaceae, a large family of parasitic plants that includes mistletoe. Santalum has a distribution ranging from India through Southeast Asia, Australia, and across the islands of the Pacific. It is a culturally and economically important group, and its members are hemiparasitic root parasites. This means that they use a modified root called a haustorium to physically penetrate the roots of neighboring plants, thus diverting water, inorganic, and organic nutrients to themselves. Hemiparasitic means that these plants are also capable of photosynthesis themselves, unlike holoparasitic plants that mostly lack chlorophyll.

The natural oils of sandalwood bear odors that are among the most sought-after in human history. The scent is distinctive and soothing, and items carved from sandalwood can perfume a room for decades. Many ancient texts mention sandalwood, and it has been an important trade item for millennia.

Hawaii has four endemic species of sandalwood that have important traditional uses in native culture. When Europeans recognized the value of these trees (called `iliahi in the native Hawaiian language) in the late 18th century, a massive deforestation program began, fueled in large part by labor forced on native Hawaiians by their chiefs and king, who enriched themselves in the process. The ecological effects linger: sandalwood is rare in Hawaii. The social effects are made clear in this passage:

Within a few years the supply of ‘iliahi began to dwindle. This contributed to the decline of the Hawaiian population. The work in the damp uplands combined with near starvation conditions and the scourge of the white man's diseases wiped out large numbers of the native Hawaiians.

In 1827 the first written tax law in Hawaii imposed a sandalwood levy.

Every man is required to deliver a half picul of good sandalwood [a picul being 133 lbs.] to the governor of the district to which he belongs, … No person, except those who are infirm, or too advanced an age to go to the mountains, will be exempted from this law.

And so it is easier to understand the visceral reaction of my friend’s grandmother, trying to eradicate this hated plant that she thought had harmed her ancestors. The Hawaiian sandalwoods have never regained their former abundance, with one variety federally listed as endangered and two as threatened. Recent molecular work has shown that these four species are likely the result of two separate colonization events of Hawaii 1 to 1.5 million years ago from the original Santalum homeland in Australia.

If you are a fan of essential oils, remember that the soothing scent of sandalwood has a fascinating natural and cultural history, and is a lovely product of parasitism.

April 2 - Dolops sp.

Dolops lacks the stalked suckers that Argulus uses for running around on the surfaces of fish. Instead it has pretty hefty hooks that it can use to dig into the skin of the fish to hang on. Just like Argulus, though, Dolops is a really fast swimmer, and if disturbed it can actively swim away with alarming speed. It will survive in the water column without a host just fine, for a while at least. That active swimming also enhances transmission, especially in schooling fish like Piranha, where the next host is just a hop, skip and swim away.

Contributed by Al Dove.

April 1 – Polypodium hydriforme

Now here's a parasite with an expensive taste - Polypodium hydriforme. The exact taxonomic affinity of this parasite is presently unclear, though it appears to be related to jellyfish. Part of the life-cycle of P. hydriforme involves the parasitic larval stage developing in sturgeon eggs - yes, the sturgeon eggs that most people are familiar with in the form of black caviar. As the parasite grows, it consumes the content of the sturgeon egg and develops into a "stolon" which is made of a chain of multiple individuals or "bud" - each bud will grow into an individual P. hydriforme. There can be as many 30-40 buds contained within each egg, with larger eggs containing up to 100 buds.

Just prior to the sturgeon spawning, the parasite prepares itself for the transition from its parasitic to its free-living stage. It accumulates all the remaining yolk within the egg into its gastric cavity, which will act as its energy reserve for the first 6-8 days of its non-parasitic life. After this reserve is depleted, P. hydriforme develops a mouth and begins feeding on various tiny benthic organisms such as Tubifex worms (what you might feed your aquarium fish), free-living turbellarian flatworms, and rotifers. Once it reaches sexual maturity, it mates to produce the next generation of larvae which will then infect the eggs of another sturgeon - however, just exactly how the larvae manage to accomplish that is still presently unclear.

The peculiar life-cycle of P. hydriforme not only makes it one of the few (if not the only) known species of parasitic cnidarian, but also one of the few multicellular organism that has evolved to be an intracellular parasite (another notable example being the nematode Trichinella spiralis which enters muscle cells and converting it into a "nurse cell").

Contributed by Tommy Leung.