What is "onchocerca"

Onchocerca is a genus of parasitic roundworm. It contains one human parasite - Onchocerca volvulus - which is responsible for the neglected disease Onchocerciasis, also known as "River Blindness" because the infected humans tend to live near rivers where host black flies live. Over 40 million people are infected in Africa, Central America, and South America. Other species affect cattle, horses, etc.