Onchocerciasis (River Blindness)
Description
Onchocerciasis is caused by the prelarval (microfilaria)
and adult stages of the nematode Onchocerca volvulus. The
disease is transmitted by the bite of certain species 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 the Americas (Brazil, Colombia, Ecuador, Guatemala, southern Mexico,
and Venezuela).
Risk for Travelers
Those traveling for short periods in onchocerciasis-endemic
regions appear to be at low risk for acquiring this condition. However,
those who visit or live in endemic regions for >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.
Clinical Presentation
Infection with O. volvulus can result in
dermatitis; subcutaneous nodules; lymphadenitis; and ocular lesions,
which can progress to blindness. Symptoms may occur months to years
after departure from endemic areas.
Prevention
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 the section on Protection
against Mosquitoes and Other Arthropods).
Treatment
Ivermectin is the drug of choice for onchocerciasis.
Repeated oral doses are required for up to several years, 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.
— Frank
O. Richards, Jr.
|