Part of their job is to fight folk-medicine habits that sometimes die harder than any disease.

In a village north of Ogi, a traditional healer, Yahaya Sarki, demonstrated his own "worm treatment." Plucking a short iron blade from his straw roof, he whetted it on his stone doorstep and heated it on a hot coal. Then he mimed how he would plunge it into the emerging worm's head.

"The idea is to burn the worm to death," Dr. Ityonzughul explained, "but as soon as you touch it, it recoils and tries to find an exit elsewhere. It's very brutal, and it frequently causes tetanus. In 2002, we lost two volunteers to it. But in northern Nigeria, it's used in almost all cases. I've given up fighting it. No matter what I say, they do it anyway."

"Besides," he added of the victims, "it incapacitates them. They can't walk, so they don't put it in the water."

People also pick off their dressings, saying "the worm must breathe," he said. He has tried paying them a few cents to keep wounds bandaged, but it rarely works.

Still, he is not easily put off his mission, though tactics are not always as public and confrontational as they were in Ogi.

"We have paid people to put Abate in the sacred ponds secretly," he admitted.

He described a northern village that practiced both ancestor worship and Islam, which considers dogs unclean.

"They refused the Abate," he said, adding with a grin: "But someone killed a dog and threw it in their sacred pond. People stopped drinking the water -- and Guinea worm cases went down."

On the Brink

This is the second in a series of articles about five diseases -- polio, Guinea worm, measles, blinding trachoma and lymphatic filariasis -- that are extinct in the developed world but stubbornly persistent in some poor nations. As the diseases hover on the brink of eradication, doctors and scientists face daunting obstacles as they struggle to finish the job. The articles in the series will be online, along with multimedia presentations, including a video on the effort to wipe out Guinea worm disease, at nytimes.com/health.