Onchocerca /ong′kōsər′kə/ [Gk, onkos, tumor + kerkos, tail] , a genus of nematode parasites of the superfamily Filarioidea that infects humans and ruminants. The adults live and breed in subcutaneous fibroid nodules. The young (the microfilariae) are carried by the lymph and are found chiefly in the skin, subcutaneous connective tissues, and eyes. O. volvulus is a common parasite of humans that breeds in fast-flowing rivers and streams in tropical regions of the Americas and Africa, particularly West Africa. It is the cause of human onchocerciasis and is transmitted by the bites of buffalo gnats.
