A community trial of ivermectin for onchocerciasis in Sierra Leone: clinical and parasitological responses to the initial dose

Abstract

A double-blind placebo-controlled trial of ivermectin was started in 1987 in 6 villages in southern Sierra Leone. 1625 villagers, 93% of the total population, were surveyed before treatment and allocated at random to the trial. Onchocerciasis was hyperendemic and of moderate intensity in the area. Typical onchocerciasis skin lesions were seen in most cases; the blindness rate was 1.5% and a further 4.3% had visual impairment. Six months after treatment 988 subjects (80%) were reassessed and microfilarial loads in the ivermectin group were found to be 10% of control levels. Additionally, blood eosinophil concentrations were reduced by one-quarter. The severity, but not the prevalence, of skin lesions was significantly reduced in the ivermectin group, with a particularly marked effect on papular eruptions. There had been no reduction in the prevalence of itching, nor had markers of general health shown improvement after ivermectin. Ivermectin is an effective microfilaricidal agent and may improve Onchocerca-related skin lesions after a single dose. However, the lack of obvious benefit to a target population after the first dose of ivermectin may reduce compliance with subsequent doses. This has implications for planned mass treatment initiatives in onchocerciasis endemic regions.