Guinea worm disease is a painful, incapacitating affliction caused by the parasite Dracunculus medinensis. About one year after a person has drunk contaminated water, one or more adult female worms - each up to 1 metre long - emerge through the skin, usually of the lower limbs. When the affected part is immersed in water, the worm expels hundreds of thousands of tiny larvae, which are then ingested by cyclops (an aquatic crustacean) to continue the cycle. The adult worm emerges slowly over several weeks. The irritation from the emerging worm and from secondary infection of the site is so painful that victims are often unable to walk or work, depending on which part of their body is affected. Sometimes the ulcer which surrounds the emerging worm is secondarily infected by tetanus, and the victim dies. Victims do not become immune. The overwhelming majority, who do not contract tetanus, live to suffer the infection year after year.
The disease probably affects an estimated 10-50 million people in poor, rural areas of Africa and Asia. In some villages of west Africa, the disease may affect up to 40% of farm workers and, because the transmission cycle is often confined to the rainy season, the victims are put out of action during the very time of year when they must plant or harvest their crops. Therein lies much of the disease's economic and social significance. Among schoolchildren, guineaworm is one of the major reasons for absenteeism. Dracunculiasis still afflicts millions of rural villagers in India and Pakistan and in a broad band of African countries from Mauritania and Senegal in the west, through Mali, Niger, Burkina Faso (formerly Upper Volta), Ivory Coast, Ghana, Togo, Benin, Nigeria, Cameroon, and Chad, to Sudan, Uganda and Ethiopia. Fewer than five percent of the cases are routinely reported.
A group of Nigerian villagers questioned about their priorities for outside assistance, listed electrification first, and elimination of guinea worm disease second; ahead of roads, hospitals, jobs, water, and several other critical needs.