January 31 - Cryptosporidium parvum

In 1993, almost 25% of the residents of Milwaukee, Wisconsin came down with severe stomach cramps, fever, and diarrhea. Over 100, mostly elderly or immunocompromised residents, died. The cause? The most common water-borne disease in the developed world: Cryptosporidium. Cryptosporidium parvum is one of many species of this group of apicomplexan parasites, distant relatives to those that cause malaria and toxoplasmosis. Water supplies may be tainted with the oocysts of these parasites, which are then consumed by people. In the small intestine, the parasites attach to the villi and begin to asexually divide. Eventually they will produce gametocytes - macrogametocytes are female, microgametocytes are male. These stages fuse and then produce two types of zygotes. Some have thin walls only - these serve to keep the infection going in the same host. Others, though, develop thicker walls and are released into the environment to infect new hosts. There isn't a very good treatment for those that become infected except for supportive therapy (fluids, etc) until the immune system can get it under control. The complete genome of C. parvum was completed in 2004 and it is unusual among apicomplexans in that neither its mitochondria nor its plastid organelles contain DNA.

January 30 - Dermacentor variabilis

Ticks are small, blood-feeding arachnids, relatives of spiders and mites. The American dog tick, Dermacentor variabilis has three life stages: larvae (which are 6-legged not 8!), nymphs, and adults. As the ticks pass from each life stage to the next, they require a bloodmeal from a vertebrate. Larvae and nymphs will usually obtain this bloodmeal from rodents, but adults, as their name suggests will seek out larger mammals, particularly dogs, and sometimes humans. These ticks find their hosts using a behavior known as “questing”. They crawl to the top of a blade of grass or other variation and extend their front two legs until a host brushes past, at which point they grab on. The life cycle can take two years to complete, with the ticks overwintering in the soil. D. variabilis is another example of an ectoparasite that can vector other diseases, in this case, Rocky Mountain Spotted fever, tularemia, and ehrlichiosis, which are all bacterial zoonotic diseases.

Image from Insect Images (but remember that ticks are not insects!)

January 29 - Batrachochytrium dendrobatidis

This chytrid fungus (Chytriodiomycota: Chytridiales) is the causative agent of chytridiomycosis, an emerging infectious disease of amphibians. This fungus has been implicated as the cause of amphibian declines and extinctions of more than 250 species of frogs across six continents (the widespread distribution of this disease the likely consequence of anthropogenic effects). B. dendrobatidis can infect both larval and adult amphibians. Infections in larvae cause a reduction in grazing efficiency, food intake, and survival. Infections in adults cause thickening of the skin which might interfere with osmoregulation or ion balance. This fungus has two parts of its life cycle: one part in the host and one part outside of the host (a motile zoospore stage). Recent studies have shown that B. dendrobatidis can survive for long periods of time outside of the host, increasing its ability to drive host populations extinct. Although this fungus is believed to have originated in Africa, B. dendrobatidis was first reported in North and Central America and Australia in 1998, coinciding with massive amphibian declines. However, this fungus has been around since at least 1938 (documented in museum specimens), therefore researchers are trying to determine if B. dendrobatidis is truly a novel emerging disease or a long-term endemic pathogen (where population declines are the result of changes in pathogen virulence, host susceptibility, environmental change, or a combination of these factors). What kind of disease B. dentrobatidis actually is may help to determine how to stop the rampant spread of this devastating fungus, if possible. Findings currently point to B. dendrobatidis being a novel pathogen (laboratory experiments, wave-like declines of amphibians, etc), however much more work needs to be done to be sure.

Contributed by Jessica Light.
See this paper or this one (which just came out today) for more information.

January 28 - Vandellia cirrhosa

Seems like everyone's been kind of gaga over vampires lately, so thought I would use a vampire as today's parasite. Vandellia cirrhosa is a relatively small catfish that lives in the murky waters of the Amazon river basin. It swims into the gills of a fish, slices open a wound with its teeth and engorges itself with fish blood. It then drops off, hides out, and waits until it's hungry again to go seek out a new victim. These little fish also have another sinister reputation - there has been one documented report of a candiru, as they are commonly called, mistaking the human urethra for a fish gill where it became lodged in the man's penis and had to be removed via surgery. Although fairly widespread in the folklore of the region, these invasions of man appear to be rare and their primary targets are indeed fish. My favorite quote about these parasitic fish was stumbled upon on a website devoted to aquarium lovers who keep catfish. Under "husbandry", the description says, "For obvious reasons this fish should be kept alone; smaller fish are not ignored by this fish and can be killed outright by one parasitic visitation."

January 27 - Borrelia burgdorferi

Blame Borrelia burgdorferi for one of the most common vector-borne diseases in the United States: Lyme disease. Discovered in 1982 by NIAID zoologist Willy Burgdorfer, this species belongs to a phylum of corkscrew-shaped bacteria known as spirochetes. Spirochetes are quite at home in the guts of humans and other mammals, bivalves, and insects. In the United States, black-legged ticks (also known as deer ticks) ingest Borrelia burgdorferi from an infected animal during a blood meal. When the ticks bite other suitable hosts, they pass along the spirochete through their saliva.

Learn more about wildlife hosts of B. burgdorferi in this new Science Bulletins video from the American Museum of Natural History. A second video highlights new imaging techniques that can detect B. burgdorferi's influences on the human brain.

Contributed by Laura Allen at Science Bulletins, AMNH

Image by Jeffrey Nelson, North Park University

January 26 - Cymothoa exigua

Cymothoa exigua is a parasitic isopod with a very odd and gruesome life cycle. Juveniles first attach to the gills of a fish and become males. As they mature, they become females, with mating likely occurring on the gills. The female then makes its way to the fish’s mouth where it uses its front claws to attach to the fish’s tongue. It begins to feed on the blood in the tongue until the tongue eventually atrophies completely. The isopod then takes the place of the tongue in the mouth, attaching to the floor of the mouth and the stub of what is left of the tongue with its hind pereopods. There it lives out the rest of its life – even letting the fish use it like its old tongue, holding prey against its teeth. Although these parasites were long thought to be restricted to the Gulf of California and environs, recently one turned up in the mouth of a fish that was caught off the coast of the U.K.

January 25 - Branchellion torpedinis

Leeches are a class of annelids that has many members that feed exclusively on blood and are often found ectoparasitic on their hosts. Branchellion torpedinis is a piscicolid leech that infects a wide range of elasmobranchs (sharks, rays and skates). The individual shown here came from The Georgia Aquarium collection, but they can be found on cownose rays and sawfish along the Atlantic coast. The frilly gills on the side help with respiration. Unlike many leeches, which glue a handful of cocoons containing eggs to the substrate, this species is a supreme egg layer and instead casts large quantities of eggs into the water, more like a monogenean parasite.

Contributed by Alistair Dove.

January 24 - Enteroxenos oestergreni

Let's say you are dissecting some sea cucumbers and you come across this thing (see photo) - what do you think it is? Is it a worm? No - In fact, it is a snail! You have just found Enteroxenos oestergreni - a species of parasitic gastropod that lives inside the body cavity of sea cucumbers. Evolution has done away with all its apparently superfluous organs like its digestive system, gills, heart, nervous system, and reducing it down to just the bare essentials of a parasite - reproductive organs. The only morphological clue that this organism is a gastropod are its larval stages (veligers), which look like tiny, delicate snails - just like that of many other marine snails. However, after it enters the sea cucumber host, it eventually transforms into the worm-like adult form. An adult E. oestergreni is essentially a long stringy sac of eggs, just floating in the coelomic fluid of its host.

See the original paper here.

Contribution by Tommy Leung.

January 23 - Rafflesia arnoldii

Plants can be parasitic, too and some of the best known are in the genus Rafflesia. These really unusual plants don’t have stems or leaves or even proper roots. Instead, they have structures known as haustoria, which penetrate the cells of their hosts, Tetrastigma vines, and steal their nutrients and water. The only part of the plant that ever is visible is the flower – and it’s a doozy! The flowers of Rafflesia arnoldii can be almost a meter in diameter, making them the largest in the world. And if the size wasn’t enough to get it noticed, it also has a very distinctive smell – like rotting flesh - that attracts the insects that pollinate it. Despite these factors, Rafflesia is very hard to find. Part of this is because the flowers are very short-lived, but sadly the other reason is that they are restricted to forests of Borneo, Malaysia, and the Philippines, which are disappearing.

January 22 - Pediculus humanus capitis

What do parents dread their children bringing home from school more than a bad report card? Pediculus humanus capitis, better known as head lice. These wingless insects, also called sucking lice, have parasitized humans for thousands of years and are now are common worldwide, infesting millions of school children every year. Head lice are entirely dependent on their hosts for their survival (there are no free-living stages), are found on the head and attach their eggs to the base of hair shafts. These parasites are surprisingly nimble, moving quickly among the hairs and can transfer quickly to a new host should the opportunity present itself. Head lice reproduce rapidly and treatment can be expensive and time consuming. Many common colloquialisms resulting from human parasitism of lice include “nit-picking”, “going over with a fine-toothed comb”, “nitwit”, and “lousy”.

Contribution by Jessica Light.