Onchocerciasis (river blindness)
Onchocerciasis, also called river blindness, is a filarial nematode infection caused by Onchocerca volvulus and transmitted by the bite of the female black fly, producing chronic pruritic skin disease (onchodermatitis with skin atrophy and depigmentation) and subcutaneous nodules containing adult worms, and standing as a major cause of blindness in endemic rural communities; treatment is ivermectin, repeated every 6-12 months because it kills microfilariae but not adult worms, with careful screening for coendemic Loa loa before dosing.
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What this article covers
- Overview
A filarial nematode infection of rural endemic communities: onchocerciasis is caused by Onchocerca volvulus, transmitted to humans through the bite of the female black fly, and is a major cause of…
- Epidemiology
A disease of rural communities in the range of its black fly vector, reflecting the vector-restricted transmission pattern shared with other fly-borne filarial infections.
- Risk factors
Residence in a rural endemic community within the range of the Simulium black fly vector.
- Pathophysiology
Inoculation by black fly bite: infective larvae are deposited in the skin during a blood meal by the female black fly.
- Clinical features
Generalized pruritus, often the earliest and most disabling symptom, reflecting the dermal inflammatory response to microfilariae.
- Differential diagnosis
Loiasis (Loa loa infection): another filarial nematode infection of overlapping African geography, but transmitted by the Chrysops (deer/horse/mango) fly rather than the black fly, producing…
- Diagnosis
Onchocerciasis is confirmed by identifying the parasite: microfilariae recovered from the skin, or adult worms identified within an excised subcutaneous nodule, in a patient with a compatible…
- Management
First, screen for coendemic Loa loa exposure and, where relevant, quantify the Loa loa microfilarial load, because ivermectin at any dose carries the same encephalopathy risk in a heavily Loa…
- Complications
Blindness, the most severe complication and the origin of the disease's common name, resulting from progressive ocular involvement in long-standing or heavy infection.
- Prognosis
Skin and systemic symptoms respond well to regularly repeated ivermectin, with reduction in pruritus and a halt in progression of dermatitis while treatment is maintained.
- Prevention
Avoid black fly bites near fast-flowing rivers and streams in endemic areas: use insect repellent and protective clothing (long sleeves and pants) during activity near these breeding habitats.
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