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onchocerciasis on·cho·cer·ci·a·sis (ŏng'kō-sər-kī'ə-sĭs) or on·cho·cer·co·sis (-sər-kō'sĭs)
A disease occurring in tropical Africa and Central America, transmitted by black flies and caused by infestation with filariform nematodes of the genus Onchocerca, especially O. volvulus, and characterized by nodular swellings on the skin and lesions of the eyes. Also called river blindness, volvulosis.
filarial disease caused by the helminth Onchocerca volvulus, which is transmitted to humans by the bite of the black fly Simulium. The disease is found chiefly in Mexico, Guatemala, and Venezuela in the Americas and in sub-Saharan Africa in a broad belt extending from Senegal on the west coast to Ethiopia on the east; in Africa its northern edge is about 15 N of the equator, and it extends as far south as Angola and Tanzania. It has also been reported in Colombia, northern Sudan, and Yemen.