ARI SHAPIRO, HOST:
For the past few years, the world has been on the edge of one of the biggest medical triumphs of modern history. A global effort has nearly wiped out the Guinea worm, a horrific parasite. Where there were millions of cases in the 1980s, there were only seven this year. If those cases dropped to zero, Guinea worm would become only the second human disease ever eradicated. But a surprising wrinkle has cropped up. Guinea worm, it seems, has found a new way to hide and thrive. NPR's Michaeleen Doucleff reports.
MICHAELEEN DOUCLEFF, BYLINE: The last remaining cases are in Africa. If you have Guinea worm, it's excruciatingly painful. The worm can be three feet long, and it slowly emerges from your skin. Sometimes it can take weeks for the worm to come out. David Molyneux is at the Liverpool School of Tropical Medicine. He's been working on eradicating Guinea worm for more than 40 years. He says for decades, things were going swimmingly. Cases had fallen off drastically from millions to just a handful. Then, in 2013...
DAVID MOLYNEUX: Something strange was happening.
DOUCLEFF: In rural parts of Chad, dogs started showing up with worms coming out of their legs - many dogs with many, many worms.
MOLYNEUX: A female dog had a record 62 Guinea worms emerge from it.
DOUCLEFF: Most infections only involve one worm, maybe two or three - but 62?
MOLYNEUX: Now, I mean, that's a huge infection in an animal. I mean, I've never heard of that before. That's extraordinary.
DOUCLEFF: Molyneux says such a huge infection means one thing.
MOLYNEUX: It means there's an awful lot of Guinea worm out there.
DOUCLEFF: An awful lot of Guinea worm spreading across Chad. This year, there have been more than 600 dogs infected, spread over a huge part of the country.
MOLYNEUX: My concern is that it's going to be a longer haul, I think, than we anticipated, and it's a massive challenge.
DOUCLEFF: You see, for more than 100 years, scientists thought they had the Guinea worm figured out. They thought the critter needed people to survive. So if you got rid of it in people, poof, the worm is gone, extinct. But now it looks like Guinea worm can also live in dogs. Dr. Don Hopkins is with the Carter Center, which has led the eradication effort. He says to wipe Guinea worm off the planet...
DON HOPKINS: We have to get rid of this worm in dogs, as well as the few remaining worms in humans before you can safely say that this disease has been eradicated.
DOUCLEFF: And stopping Guinea worm in dogs isn't easy. Hopkins says it's actually harder than with people. To keep dogs from spreading Guinea worm, they have to be tied up for two weeks while the worms come out of their legs. And dogs in Chad aren't like dogs here in the U.S. They're not pets. They don't come inside or sleep on the bed.
HOPKINS: People use them in households to help protect their crops from baboons and things like that.
DOUCLEFF: So they roam free day and night. The Carter Center has started paying people $20 to tie up their infected dogs. But there's another problem - no one knows how the dogs are getting infected. At first, they thought dogs were eating infected fish guts. Now they think it might be frogs. Scientists at the Centers for Disease Control and Prevention have started using GPS collars to track the dogs and radio isotope labeling to figure out what food is left on their whiskers. Despite all of this, Hopkins isn't deterred about eradication.
HOPKINS: I'm confident we're going to do it and we'll see. But we have seen already 17 of these 21 countries get rid of Guinea worm and have it stay away.
DOUCLEFF: And that confidence comes with some serious credentials. Dr. Hopkins knows a thing or two about ending diseases. He was key in eradicating smallpox, so far the only human disease to be wiped out. Michaeleen Doucleff, NPR News.
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