Counting Down to an Extinction

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On Exhibit posts

Mark Siddall, curator of the new exhibition Countdown to Zero, explains why the Guinea worm’s extinction would bring about tremendous social benefits.

The life cycle of a Guinea worm, Dracunculus medinensis, is deviously simple. 

Guinea Worm Specimens
The Guinea worm (Dracunculus medinensis) is a type of nematode or roundworm. The samples here were drawn out of patients in Africa and saved for the purposes of research.
© AMNH/D. Finnin

Cool water teems with life, much of it microscopic crustaceans; this is normal, and typically without consequences. But sometimes, resident water fleas host larvae of a rapacious, fiery serpent. When ingested, the water flea hosts dissolve in stomach acid, allowing the larval worms to move through the human body, where they mature and mate. 

A person seated near water’s edge washing clothes in a large vessel. Nearby is a poster on a tree depicting two people infected with Guinea worm.
A woman does her washing near a dam in the country now known as South Sudan. Nearby, a sign cautions against entering the water while infected with Guinea worm.
© The Carter Center/L. Gubb

As the females of the next generation grow, they pack their own bodies with live young. During this period, the victim suffers no immediate symptoms. A year later, the 3-foot-long mother awakens deep in her host’s leg. She rises to the surface and induces a blister on her victim’s skin that is so fierce, and of such searing agony, that the afflicted seek relief in the coolness of water.

Here, the mother dumps her offspring, completing the life cycle for another generation. The Guinea worm has repeated this process for hundreds of thousands of years. 

The Guinea worm can only reproduce at the expense of those it infects. Adult worms only infect humans, while the larvae only invade water fleas. It is also the only human parasite that must cause pain in order to successfully reproduce.

In addition to deeply wounding and torturing its victims for weeks on end, dracunculiasis is a disease of starvation. It leaves families in affected areas incapacitated and unable to reap the crops they have sown. 

Hands wearing disposable gloves are removing a long thin Guinea worm protruding from a human foot by winding it around a gauze-covered stick.
Extracting a Guinea worm is a slow and painful process. Some historians believe the medical symbol known 
as the Staff of Asclepius was inspired by the age-old method of Guinea worm extraction.
© The Carter Center/L. Gubb

There is no vaccine for Guinea worm, and there are no drugs that can cure those who are infected. The pest once afflicted hundreds of millions of people from Gambia to India. But the worm is now gone from Guinea, and from almost everywhere else. At last count (2014), there were only 126 people infected, down from an estimated 3.5 million in 1986. Of the remaining cases, 70 are in South Sudan.

We know these numbers with precision because of a campaign that former President Jimmy Carter began leading in 1986 to destroy the worm. That community-driven process, coordinated by The Carter Center and executed by the South Sudan Ministry of Health, village volunteers, and trained technical advisors, is driving the parasite out of its last remaining human hosts. Each person known to be infected with the worm, along with every village in which outbreaks have occurred or are occurring, is tracked. 

Countdown to Zero_comic book
An educational comic book captures the attention
of Guinea worm patients Sadia Mesuna (right) and Fatawu Yakubu at a case containment center in Ghana.
© The Carter Center/L. Gubb

Intervention is multi-pronged: the infected are voluntarily quarantined, since patients with emergent worms must be kept away from water sources; containment-care facilities welcome not just the victims but their dependents, too; local education programs focus on water filtration.

Two young African men standing in a lake and drinking lake water through large straws.
A small piece of steel mesh inside a plastic drinking tube offers a low-tech way to filter water on the go, preventing the small crustaceans that carry Guinea worm larvae from being consumed.
© The Carter Center/L. Gubb

Many years ago, when I was beginning a career in parasitology, I was told about the “parasitologists’ dilemma,” a spin on the Malthusian catastrophe. The premise was that, should parasitologists actually manage to eradicate infectious diseases caused by parasites, we’d be morally responsible for thrusting millions of people into the inevitable conflict and poverty that would result from population growth and increased pressures on a limited food supply. 

Poster warning against water contamination by guinea worm
Flip books, painted signs like this one from Ghana, and wall murals have helped encourage safe practices and interventions—especially in areas where few people can read.
© AMNH/D. Finnin

But in every place where the Guinea worm has been eliminated, the very opposite is true. Just a couple of decades ago, Ghana and Mauritania had thousands of cases. Now, both countries are free not only of Guinea worm but, increasingly, of the shackles of extreme poverty: per capita G.D.P. has tripled, the number of people living on less than a dollar a day has been halved, and the birth rate has plummeted. This, obviously, is the result of many factors besides Guinea worms. But I can say this: so much for Malthus. 

Most conservation efforts, like those for spotted owls and pandas, are proxies for threatened ecosystems, or seek to preserve “keystone species,” like sharks. Few focus on the despised and downtrodden species that crawl beneath our feet. As a leech expert, “save the maggots” has always been my rallying cry, but let no one mourn this extinction.

Mark Siddall is a curator in the Division of Invertebrate Zoology and curator of the exhibition Countdown to Zero: Defeating Disease, now on view in the Akeley Gallery.

This essay is adapted from a story in the Winter 2015 issue of Rotunda, the Member magazine, and was originally published in The New Yorker’s Elements blog as “An Extinction to Celebrate.”