Dinobdella ferox

When it comes to parasitology, sometimes you have to get really up close with your study organism, as one researcher in Taiwan did in trying to figure out the behaviour of Dinobdella ferox - a species of leech that has a habit of getting into some uncomfortable (for its host) places.

Dinobdella belongs to a family of leeches call the Praobdellidae - unlike other leeches that simply latch onto their host's skin and start sucking, Dinobdella and most other praobdellid leeches attach themselves to and feed from the host's mucous membranes - which means they either crawl up the host's nose, or occasionally even up their urethra or anus. Because of their habit of hiding themselves in parts of the host where the sun doesn't shine, it is rather difficult to figure out just what exactly what they get up to when they are attached to the host (aside from sucking blood).

Top: a D. ferox leech poking out of Dr Lai's nose., Bottom: a D. ferox leech which has emerged after the infection period
From Fig. 1. of the paper

Dr Yi-Te Lai at National Taiwan University decided to put his body on the line in the name of science, and infected himself with some D. ferox leeches, diligently documenting his own health and the leeches' behaviour throughout entire duration. He conducted three trials, each time administering himself with a different D. ferox leech - and you can see him demonstrating his procedure for self-infection in this video.

During this period, in addition to documenting the leech's behaviour based on his first hand experience, Dr Lai also took regular trips to a local clinical laboratory to examine the leech via endoscopy, and take measurements of his red and white blood cell counts to see what effects the leech's feeding might have on his blood works.

Some of the symptoms he experienced during the leeches' residency were to be expected, including nasal congestion, mild stinging sensations and some nosebleeds. But despite the leech's feeding, he found that both his red and white blood cell count held steady during the infection period, and his body was able to compensate for the blood loss. Furthermore, despite their activities in the nasal passage, they can be remarkably camera shy and were pretty good at hiding from the endoscope.

And those leeches had a ravenous appetite - during the course of their stay (which can range from 24-75 days), they grew to five to ten times their original length, and increased their body mass by up to 380 times. The juvenile leech starts out as a tiny dark mote just 3-4 millimetres long, but by the end of their stay, they were big enough to be easily noticeable when they decide to poke their head out.

Cohabiting with a bunch of nose leeches allowed Dr Lai to make round-the-clock observations and record behaviours which might not have been previously documented. After about a month into the infection period, the leeches started getting restless and were looking for a new host, and this behaviour manifested itself in some disconcerting ways.

When D. ferox starts looking for a new host, it develops an attraction to darkness and water. According to Dr Lai's account, whenever he was in a dark place such as in the middle of watching a movie at a theatre, the leeches came poking out of his nose. But this wasn't the only time when they made their presence noticeable - they also got nosy when he went about some of his daily routines like showering or washing his face. This overlapped with the ceasing of bleeding-related symptoms - which meant the leeches had finished feeding.

With their cohabitation coming to an end, Dr Lai tested out some methods for removing such leeches which have been reported in the scientific literature. His self-experimentation showed that while the leech can be coaxed out with a bowl of water, this only worked at later stages of the infection, presumably after the leech has finish feeding and was ready to move on. Once they were out, they made one final contribution to science - they were preserved in a vial of 95% ethanol and are now held at the Academia Sinica collection in Taiwan.

There is a bit of a tradition among parasitologists to infect themselves with all manners of parasites to learn more about their study organisms or test out various techniques for treatment. In this case, through self-infection, one researcher was able to shine some light on a leech which usual prefers hanging out in dark places.

Reference:
Lai, Y. T. (2019). Beyond the epistaxis: Voluntary nasal leech (Dinobdella ferox) infestation revealed the leech behaviours and the host symptoms through the parasitic period. Parasitology 11: 1477-1485

December 15 - "Blastocystis hominis"

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

December 3 - Schistosoma mansoni

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

November 13 - Brugia malayi

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

September 15 - Entamoeba histolytica

Entamoeba histolytica is one of the most common parasites of humans and apes, with some estimates going as high as 50 million people infected worldwide. These single-celled amoebae are ingested as cysts that are shed in feces of other infected hosts. The protozoa excyst in the intestines and multiply there, usually resulting in symptoms ranging from mild diarrhea to full-on amebic dysentery. Eventually, they can bore through the intestinal wall and begin to infect other tissues such as the liver, spleen and brain. The amoebae will even gobble up red blood cells as seen in the photo (the dark circles in the outer two cells). Interestingly, it is now known that many suspected cases of E. histolytica that are based on microscopic examination are actually those of Entamoeba dispar, a benign species, which is actually up to 10 times more common that it's virulent cousin.

May 30 - Ascaris suum

Although most commonly found infecting pigs, Ascaris suum, a large roundworm nematode, can also infect humans. This species has the same lifecycle as Ascaris lumbricoides, and also like its cousin, has eggs that are extremely durable in the environment. Although they were long popular in biology classes as a large, easy-to-dissect representative of Nematoda, because the eggs are so resistant and easily spread, the represent a health risk and their use has largely been discontinued. You can virtually dissect one here.

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.

March 26 - Trichuris trichiura

Trichuris trichiura is a parasite found in human intestines. Also known as the human whipworm, this parasite’s adult and larval forms can live in the large intestine for up to 5 years, feeding on intestinal tissue secretions. These roundworms are pinkish-white in color and resemble a whip in shape and movement. Females lay 2,000-10,000 larvae per day, which are shed in human feces. With the right amount of moisture and warmth, in 2-3 weeks these eggs become infectious. Humans may become infected by accidental ingestion of eggs from fecal contaminated soil. Infectious eggs are sometimes found in water or in dry foods such as rice, grains, vegetables, and beans. Once ingested, the eggs hatch and burrow into the wall of the small intestine where they grow. About 300-500 million people are infected worldwide, mostly located in tropical places. Diagnosis occurs when eggs are observed in patients’ feces. Although rare in the U.S., people who do not dispose of human waste properly, have poor hygiene, and children playing in dirt contaminated with animal feces are especially prone to the disease. Recent studies have also shown that people with trait characteristics in chromosomes 9 and 18 may also be susceptible. Humans with over 100 parasites may have symptoms associated with intestinal disease. Very serious cases may cause diarrhea, vomiting, loss of appetite, constipation, blood loss, anemia, rectal prolapse, inflammatory and toxic damage to intestines. Medication as well as anti-parasitics are effective to promote healing.

Contributed by Allison Gittings, Bucknell University.
Image from the CDC Public Health Image Library.

February 7 - Legionella pneumophila

In 1976, the nation celebrated the American bicentennial. One event, a convention of members of the American Legion in Philadelphia, had tragic results that led to the discovery of a new pathogenic bacterium. In the weeks following the convention, over 200 people became ill and 34 of them died, triggering public health officials to track down the unknown culprit. The guilty party was Legionella pneumophila, a Gram-negative, rod-shaped bacterium that is both an intracellular parasite of protists (like the ciliate shown here - the long red bits that look like yarn are chains of bacteria inside these cells), and also free-living in the environment, particularly warm, wet places like air-conditioners at convention centers and saunas. People acquire the bacteria when they breathe in vapor containing them, but the disease cannot be spread from person to person. For some, particularly elderly people, people with weak immune systems, and smokers, the bacteria can present a very serious health problem in the form of pneumonia. For others, a milder infection produces what has come to be called "Pontiac fever", named for a similar outbreak that occurred (in all places, amongst county public health department employees) in Pontiac, Michigan eight years before the Legionnaire's convention of 1976. At that point, they could not find the pathogen, but were later able to tie those cases to Legionella pneumophila.

Image from the CDC Public Health Image Library.

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 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 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.

January 19 - Trypanosoma brucei

Trypanosoma brucei is the causative agent of sleeping sickness, a disease found in sub-Saharan Africa. Trypanosomes are flagellated unicellular eukaryotes that belong to the kinetoplastids, named for their distinctive organelles called kinetoplasts. T. brucei is vectored by tsetse flies (Glossina), but can also be spread by blood transfer. Trypanosomes are masters of immune evasion due to their ability to rapidly change their coats – their variable surface glycoprotein (VSG) coats, that is. By changing the proteins on the surface of their cells, they are able to thwart the antibodies of the specific immune system from recognizing them again. Sleeping sickness is a very serious disease which progresses from infection of the blood and lymph nodes (producing characteristic swollen lymph nodes known as Winterbottom’s sign), to eventually infecting other tissues including the nervous system. At this point, in addition to confusion and loss of coordination, the sleep cycle may be disrupted, giving the disease its name.

January 9 - Toxoplasma gondii

Blame it on the cat. Or the raw meat. Exposure to either can result in infection with Toxoplasma gondii. Distant relatives of Plasmodium, the parasites that cause malaria, T. gondii often doesn't show many symptoms in its host. Immunocompromised patients and fetuses of pregnant women who become infected can be at high risk from more serious complications. Recently, data have shown that people infected with T. gondii show behavioral changes, too - with differences between sexes. Men with T. gondii are more aggressive, while women seem more intelligent! Another case of parasite manipulation?

January 4 - Taenia saginata

Did you overindulge at the holidays? Gym's been too crowded? Well, there might be another solution: infect yourself with the beef tapeworm, Taenia saginata! These cestodes can be 5 meters in length and were, in fact, marketed as weight-loss tools...though it's not recommended as they can cause malnutrition and other health problems that offset the removal of holiday pounds. Humans can become naturally infected when eating undercooked beef if it comes from unsanitary conditions.

January 1 - Plasmodium falciparum

Plasmodium falciparum Welch 1897 (Apicomplexa: Haemosporida) is one of the handful of species of malaria parasites that infect humans as their hosts. These single-celled eukaryotes are transmitted by Anopheles mosquitos. Of all of the species that infects humans, P. falciparum is the most deadly. It is thought that these parasites might kill close to two million people a year, primarily in sub-Saharan Africa. The genome of this species was completely sequenced in 2002.