Some time ago, a reader wrote to us about worms in humans in Africa. The worms were “embedding in humans” and then they would work their way out through the afflicted person’s legs – a painful experience, not surprisingly. The reader said he came across this rather horrifying human worm parasite in an article published in Smithsonian Magazine in 2011, and it seemed as though he wanted us to find out the issue of the magazine in which this article was printed. Despite a few searches, we didn’t find any specific article (at least not in 2011), but we suspect the article might have been about guinea worm disease (GMD), or dracunculiasis. Guinea worm disease is in fact caused by a worm – the Dracunculus parasite, which goes by the scientific name Dracunculus medinensis – and it does afflict humans (along with a few other animals). What are guinea worms and guinea worm disease?
Guinea worms are long and thin nematodes, which are more commonly known as “roundworms.” Guinea worms are, in fact, among the longest roundworms that infect humans. It is the female guinea worm, which is generally significantly longer than the male guinea worm, that actually causes guinea worm disease.
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People are infected with guinea worm disease by drinking contaminated water, although in very rare cases the disease can be transmitted when a person eats a paratenic host fish. (“Paratenic” simply means that host is not essential to the parasite’s development, but it can serve to maintain the parasite’s life cycle.) A person will drink water that contains small crustaceans known as copepods that are infected with guinea worm larvae (i.e., the immature form of the guinea worm), and this is what introduces the disease into the human body.
After ingestion, the copepods die, leaving the guinea worm larvae behind. The larvae will then penetrate the host’s stomach and intestinal wall and make their way into the abdominal cavity. Male guinea worms will die after they have matured, but the female worm does not, and here is where the problems start. The female worm will move to the host’s subcutaneous tissue, which is the lowermost level of one’s skin. The worm, after about a year of infection, will cause a blister on the host. This blister is generally found on the host’s foot, but it can be found on other parts of the body as well. The formation of the blister is painful to the host and causes a burning sensation, which in turn can cause the host to seek relief by placing his or her foot in water. However, when this occurs, the guinea worm will emerge and release a whole new set of larvae. These larvae are then consumed by copepods, which may later be ingested by a person.
Guinea worm disease afflicts people in Africa and India, and since it is caused by contaminated drinking water, the solution to the problem is of course providing safe drinking water to the people in these areas of the world. A net of fine mesh can be used to remove copepods from drinking water, or water can be boiled to make it safe. Insecticides can also be used to kill copepods without posing a significant risk to humans or other wildlife. Many efforts involving insecticides have been highly successful, and in general the fight against guinea worm disease has gone well. The disease has not been completely eradicated, but only thousands have been infected each year in recent years, whereas less than 20 years ago millions of people were afflicted every year.
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We can’t help our reader with the Smithsonian Magazine article, but we are fairly confident he was reading about guinea worms and guinea worm disease. Hopefully the next major article regarding guinea worm disease will be about its complete eradication.