A patient will develop a painful skin blister, through which a worm will emerge about 10 to 14 months after infection. The worm can be up to three feet long, and looks like a very long spaghetti noodle.
When the patient heads to a body of water to try to soothe the fiery pain, the worm deposits more larvae in the water, and the cycle starts over.
No vaccines or treatments are available for Guinea worm, but the international effort has made significant strides with health education and encouraging behavior changes.
Prevention strategies include filtering drinking water and discouraging people with Guinea worm from wading in water. Water can also be chemically treated with larvicide.
While Guinea worm disease does not usually result in death, it is associated with incapacitating pain and secondary bacterial infections. Patients find it difficult to work, farm and function. In a household where a parent has had Guinea worm, toddlers will be less well nourished because the infected parent will have difficulty farming, Hopkins said.
Carter recalled Thursday that he first saw people living with Guinea worm in Ghana. He saw a young woman, about 20, who appeared to be holding a baby. But he discovered that it was not a baby; it was her right breast, which was swollen because of the disease.
The international effort is monitoring about 7,000 villages, Carter said. "We need to find anyone who has Guinea worm" and "prevent them from going back to the water source," he said.
In terms of government support from individual countries, South Sudan is most strongly behind the eradication efforts, Hopkins said. In that country, there are about 110 workers on payroll, and some 12,000 unpaid volunteers, Carter said.
The program in Mali, however, has not been able to operate fully, or at all, in areas occupied by rebel groups, said Ernesto Ruiz-Tiben, director of the Guinea Worm Eradication Program at the Carter Center. The unrest there has made efforts to stop Guinea worm more difficult.
Educating people about Guinea worm has other benefits besides preventing this specific disease, Hopkins said, such as helping people to think more carefully about the water they drink. A clean water supply can help prevent other diseases.