Onchocerciasis

Key facts

• Onchocerciasis, commonly called river blindness, is caused by the parasitic roundworm Onchocerca volvulus.
• Blackflies that breed near fast-flowing rivers spread the larvae through their bites; the worms then mature under the skin and release microscopic offspring called microfilariae.
• Microfilariae migrating through the skin cause intense itching and rash; when they reach the eyes and die there, the resulting inflammation can permanently damage the cornea.
• A single oral dose of ivermectin kills the microfilariae; repeat doses every six to twelve months are usually needed, and anyone with eye involvement should be assessed by a clinician first.

What the infection does to skin and eyes

The worms mature under the skin, forming nodules and producing millions of microfilariae. These migrate through the skin, causing intense itching, rashes and, over time, thickened or depigmented patches. When microfilariae reach the eyes and die there, the resulting inflammation gradually damages the cornea and can lead to permanent vision loss, which is how the disease earned its common name.

How onchocerciasis spreads

Blackflies breeding near fast-flowing rivers carry the larvae and pass them to humans through repeated bites. People who live, work or travel near affected river systems for extended periods face the highest risk, since infection typically follows years of repeated exposure rather than a single bite.

Treating onchocerciasis

The standard treatment is a single oral dose of ivermectin, an antiparasitic medicine that rapidly kills the microfilariae and suppresses new production for several months. Repeat doses at six- to twelve-month intervals are typically needed because ivermectin does not kill the adult worms, which can survive for years. Anyone with possible eye involvement or a heavy worm burden should be assessed by a clinician before treatment, since a heavy die-off of microfilariae can trigger its own inflammatory reaction.

When to see a doctor

See a doctor for persistent itching, skin nodules or any change in vision after time spent near rivers where the infection is known to occur, and seek prompt eye assessment if vision changes develop.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.