The parasitic worms (Onchocerca volvulus) which cause onchocerciasis live in fibrous nodules just below the skin or close to joint and muscular tissue. They produce millions of microfilariae which cause intense itching, disfiguring skin lesions, and various lesions in the eye that can lead to river blindness (which affects around 300,000 people). Current disease control depends almost entirely on yearly treatments with the drug ivermectin. Jacques Gardon, Brian Duke, and colleagues from the River Blindness Foundation in the Republic of Cameroon aimed to compare the effect of higher doses, more frequent doses, or both, with standard therapy in treating onchocerciasis.

657 patients who had onchocerciasis were randomly assigned to:- 150 mg/kg ivermectin yearly; 150 mg/kg every 3 months; 400 then 800 mg/kg yearly; or 400 then 800 mg/kg every 3 months. Death of female worms was the indicator of successful therapy. After 3 years of treatment, around one third more female worms had died in the groups treated every 3 months than in the group given standard therapy. There was no additional benefit from high-dose ivermectin, which was associated with subjective visual disturbance in some patients.

Brian Duke comments: "Widespread yearly treatments with ivermectin lead to an important decrease in transmission of O volvulus. If our results from patients treated 3-monthly were to be extrapolated to the total population eligible to take ivermectin, the benefit in reducing both transmission and acute itching skin lesions would almost certainly be much greater than after yearly treatment."

In an accompanying Commentary (p 182), Thomas Unnasch from the University of
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Lancet
18-Jul-2002