Scientists Say: Guinea worm

This parasite invades people’s bodies through their drinking water, and leaves through their skin


This Guinea worm is wound around a matchstick as it is pulled out from a person’s leg. The worm has to be pulled out very slowly, and the process is very painful. 


Guinea worm (noun, “GIH-knee worm”)

The Guinea worm (Dracunculus medinensis — “drah-CUN-cue-lus MED-in-EN- is) is a parasite — an animal that lives off a host, without giving anything in return. If this worm gets inside a person’s body, it causes a painful infection called Guinea worm disease, or Dracunculiasis (drah-CUN-due-LIE-ah-sis). In fact, Dracunculiasis means “infection with little dragons” in Latin, a sign of just how much it can hurt.

Guinea worms begin their lives as larvae in the bellies of tiny water fleas. When a person drinks water and swallows the water fleas, the fleas get digested in the person’s stomach. But the Guinea worm larvae survive. They take up residence inside the unfortunate person’s body.

Over the next 100 days, those larvae grow into long, thin, white worms. Then the males and females find each other and mate. The male dies, but the female, loaded with eggs, begins moving through the person’s muscles. This can be intensely painful. Usually, the female heads toward the person’s foot. Then, she pokes through the skin of the foot. This hurts so much that the infected person often sticks their foot in water to relieve the pain. When the worm senses water, she releases her eggs. Water fleas swallow those eggs, and the cycle begins again. The whole process takes between 10 and 14 months.

After releasing her eggs, the female worm remains dangling out of the person’s foot. Often, the worm needs to be pulled out by slowly winding it around a thin stick a few centimeters (inches) at a time. Because Guinea worms can be up to one meter (3.3 feet) long, this painful process can take weeks.

Most cases of Guinea worm disease are found in a handful of countries in Africa. Luckily, people can prevent Guinea worm disease by filtering their water. This removes the water fleas that are full of Guinea worm larvae.

Scientists and doctors have worked very hard to get rid of Guinea worm disease. In the 1980s, there were 3.5 million cases of the painful infection each year. But by 2018, there were only 28 worldwide. Now, most infections are in dogs and cats, but doctors hope to get rid of the worm entirely in a few more years.  

In a sentence

Former president Jimmy Carter founded an organization to get rid of the Guinea worm.

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Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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