The Collaborative International Dictionary of English v.0.48:

onchocerciasis \onchocerciasis\ n. (Med.)
   An infection with nematodes of the genus Onchocerca,
   especially Onchocerca volvulus. Untreated, such infections
   can cause serious dermatological problems, and in advanced
   cases may lead to blindness. In certain areas of tropical
   Africa the blindness caused by onchocerciasis is called
   river blindness.
   [PJC]

WordNet (r) 3.0 (2006):

onchocerciasis
    n 1: infestation with slender threadlike roundworms (filaria)
         deposited under the skin by the bite of black fleas; when
         the eyes are involved it can result in blindness; common in
         Africa and tropical America [syn: onchocerciasis, river
         blindness]