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.