May 2015

O n c h o c e r c i a s i s

Vector – Simulium spp. (black flies)

These biting insects that develop in oxygenated, flowing waters are known primarily as a nuisance pest in the U.S., but pose significant health risks in other parts of the world. Essentially diurnal, black flies will feed in open, sunny situations or retreat to shaded areas during the hottest part of the day. Females will feed on humans and livestock to acquire the blood meal necessary to develop eggs.

Larval Habitat

Fast-running (highly oxygenated) waters


Commonly known as “river blindness,” onchocerciasis is a form of subcutaneous filariasis caused by the filarial worm Onchocerca volvulus. It is transmitted from human to human through the bites of black flies, which become infected with the larval stage of the parasite. As the filarial nematodes mature, spread through the body, and eventually die, they cause a variety of conditions, including skin rashes, skin depigmentation, lesions, itching, and blindness.


Black fly
Simulium spp. (black flies)