Onchocerciasis (or /ˈɒnkoʊsɜrˈkaɪ.əsɨs/), also known as river blindness,'s the world's third leading infectious cause of blindness. It's caused by Onchocerca volvulus, a nematode that can live for up to fifteen years in the human body. It's transmitted to people through the bite of a black fly. The worms spread throughout the body, and when they die, they cause intense itching and a strong immune system response that can destroy nearby tissue, such as the… (More on Onchocerciasis)