Onchocerciasis (River Blindness) is a disease that causes blindness, second only to trachoma worldwide. It is caused by bites of the black fly(genus Simulium), which resides along rivers and streams. One must be bitten several times to acquire the disease. When the fly bites human, it releases the larvae of the nematodes (roundworms) that inhabit subcutaneous tissues. Symptom include visual impairment, nodules under the skin, and intense itching.
CDC.Parasites - Onchocerciasis (also known as River Blindness) <http://www.cdc.gov/parasites/onchocerciasis/>. retrieved 30 May 2012