river blindness

river blindness or onchocerciasis, disease caused by the parasitic nematode worm Onchocerca volvulus. The worm larvae are transmitted by the bites of blackflies (genus Simulium) that live in fast moving streams. Inside the body the worms form disfiguring skin nodules, where they mate. Their tiny larvae, or microfilariae, migrate through the skin, causing severe itching. If the infection reaches the area of the eye, allergic reaction to the microfilariae can cause blindness.

Tests can now detect infestation before the disease has progressed, and the new drugs ivermectin, which kills the larvae, and amocarzine, which kills adult forms, have begun to help control the disease. Blackfly eradication programs have had limited success because the flies can quickly develop resistance to pesticides.

River blindness, which occurs primarily in Africa, Central and South America, and Yemen, affects an estimated 18 million people. In Africa, two strains have been identified, a savanna strain and a forest strain. The forest strain does not usually lead to blindness, but it does cause severe skin symptoms (lesions, itching, discoloration, change in texture) that can result in social ostracism.

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river blindness

 or onchocerciasis

Human disease caused by a filarial worm native to Africa but also found in parts of tropical America and transmitted by several blackflies. It is so called because the flies that transmit the disease breed on rivers and mostly affect riverine populations. Blindness is caused by dead microfilariae—the larvae that can be produced for some 15–18 years by adult worms—inside the eye. River blindness is common in savannah areas of Africa and in Guatemala and Mexico. In 1987 the World Health Organization began to distribute the drug ivermectin (originally developed for use against livestock parasites), which eliminates the microfilariae, though it does not kill the adult parasite.