Description

Onchocerciasis is caused by the prelarval (microfilaria) and adult stages of the nematode Onchocerca volvulus and can result in dermatitis; subcutaneous nodules; lymphadenitis; and visual impairment, including blindness. The disease is transmitted by the bite of female Simulium flies (black flies) that bite by day and are found near rapidly flowing rivers and streams.

Occurrence

Onchocerciasis is endemic in more than 25 nations located in a broad band across the central part of Africa. Small endemic foci are also present in the Arabian peninsula (Yemen) and in South and Central America (Brazil, Colombia, Ecuador, Guatemala, southern Mexico, and Venezuela).

Risk for Travelers

Those traveling for less than 3 months in onchocerciasis-endemic regions appear to be at low risk for acquiring this condition. However, temporary residents and others who visit endemic regions for longer than 3 months and live or work near black fly habitats are at greater risk for infection. Infections tend to occur in expatriate groups such as missionaries, field scientists, and Peace Corps volunteers.

Preventive Measures

No vaccine and no effective chemoprophylaxis are available. Protective measures include avoidance of black fly habitats and the use of personal protection measures against biting insects such as those outlined in Insect Protection.

Treatment

Ivermectin is the drug of choice for onchocerciasis. Repeat (that is, annual) doses are required because the drug kills the microfilaria, but not the adult worm. Travelers should be advised to consult with a specialist in infectious diseases or tropical medicine.

© Center for Disease Control

Credits: National Center of Infectious Diseases