Subcutaneous nodules where Onchocerca volvulus adult worms reside. Credit: B.O.L. Duke, MD
Onchocerciasis ("river blindness") is a second leading infectious cause of blindness in the world. Although current treatments such as ivermectin can reduce transmission of the parasite by killing the microfilariae, adult worms are not affected. Thus infected people, even though treated, are not cured of disease. There is no vaccine available for this infection and more effective therapeutics are urgently needed.
What is it?
Onchocerciasis is caused by the filarial worm Onchocerca volvulus. It is transmitted through the bite of an infected blackfly, which breeds in fast-flowing streams and rivers. Microfilariae, the immature larval form that are released from adult female worms, move under the skin and throughout the human body, including the eyes. When the microfilariae die, they cause an intense inflammatory response. Over time, inflammation in the eye results in scarring of the cornea leading to impaired vision and eventually blindness, hence the name "river blindness."
Where does it occur?
The World Health Organization's (WHO) expert committee on onchocerciasis estimates that of the 37 million people who are afflicted by this parasite, about 270,000 are blind and another 500,000 have visual impairment. About 99% of infected persons are in Africa; the remainder are in Yemen and six countries in the Americas.