Black Flies and Onchocerciasis

Jerome Goddard, PhD, University of Mississippi School of Medicine, Jackson.


Infect Med. 2001;18(6) 

In This Article

Abstract and Introduction

Onchocerciasis, a form of which causes river blindness, is an infection with a filarial worm that is characterized by dermal nodules and ocular disease. It is transmitted by certain species of black flies and occurs in populations in sub-Saharan Africa and parts of Mexico and Central and South America as well as in travelers to those areas. Intensive vector-control programs and the use of the antifilarial drug, ivermectin, have greatly reduced the incidence of onchocerciasis in 11 countries in West Africa.

Onchocerciasis, caused by the filarial worm Onchocerca volvulus, is a nonfatal illness that produces dermal nodules and ocular disease. Eye involvement may lead to blindness ("river blindness"). The disease, which occurs in sub-Saharan Africa and parts of Mexico and Central and South America, is transmitted to humans through the bite of black flies (genus Simulium) (Figure 1).

Typical black fly. (From Mississippi Department of Health Publication "The Mosquito Book," by E. Bowles.)

In 1987, the World Health Organization estimated that at least 17.5 million people were infected with the disease and 340,000 were blind as a result.[1] Fortunately, since that time, the number of cases of onchocerciasis has been effectively reduced in 11 countries in West Africa by means of intensive vector-control programs and the use of the antiparasitic drug, ivermectin. Until 1987, suramin and diethylcarbamazine were the only drugs available for the treatment of onchocerciasis, but they could not be used for community therapy because of their toxicity and required dosing schedules.[2] The registration of ivermectin for treatment of human onchocerciasis in 1987 and the donation of this drug by Merck and Company for as long as needed provided a new opportunity for the control of this disease.[2] Ivermectin-based control through community-directed treatment is now being introduced through the African Program for Onchocerciasis Control in 19 other African countries where the disease is endemic and through the Program for the Elimination of Onchocerciasis in the Americas, in Yemen and South and Central America.[3] While onchocerciasis does not occur in the United States, international travel has created a "global village" in which tropical maladies are easily imported. Most recently, increases in "adventure vacations" and ecotourism have contributed to the spread of tropical infections.