Onchocerciasis Patient Information Fact Sheet

What is onchocerciasis?
Onchocerciasis is a nonfatal parasitic disease found in tropical Africa, Yemen, and Central and South America. It is also called River Blindness because the flies that transmit the disease breed near rivers, and the primary symptoms affect vision. Symptoms include the development of smooth, non-tender nodules under the skin and close to the joints. Several pairs of worms can live in each nodule. The female worm gives off “microfilariae” that migrate through the skin often causing an itchy rash. The microfilariae often reach the eyes, where they can cause visual disturbance and blindness. Long-standing infection often leads to pigment changes in the skin, loss of skin elasticity which may give skin a “cigarette paper” appearance and also result in “hanging groin.”

How do you contract onchocerciasis?
Onchocerciasis is transmitted via the bite of an infected black fly (these are 1.5–4mm long). Black flies breed in swift-flowing streams and rivers; most bites will occur within 1km of a breeding site. The black fly bites during the daytime or at dusk and the bites are often painful. It may be a year or more after the infected black fly bite before microfilariae are found in the skin.

Onchocerciasis is diagnosed examining a small biopsy of skin under a microscope for microfilariae.

How is onchocerciasis treated and prevented?
According to the Centers for Disease Control, ivermectin (Stromectol) should be administered every 6 months for the life span of the adult worms or for as long as the infected person has evidence of skin or eye infection. Ivermectin kills the larvae and prevents them from causing damage, but it does not kill the adults.

Risk of being infected can be reduced by using repellents and bed nets. Avoid camping on the banks of rivers in endemic areas when possible.

Further information
Centers for Disease Control and Prevention: wwwnc.cdc.gov/travel/yellowbook/2010/chapter-5/onchocerciasis.aspx

Last Reviewed: June 2013