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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.