Development of reactive onchocercal skin lesions during a placebo-controlled trial with ivermectin among persons without lesions at baseline

Clinical trials of the effects of ivermectin on onchocercal skin disease have documented reduction in itching, but a less than clear benefit on reactive skin lesions. It has been suggested that one of the positive effects might be the prevention of new lesions. A study among a rural adult farming population in southwestern Nigeria provided ivermectin in three treatment groups and a placebo to community members who were examined and treated at 3-monthly intervals over a 15-month period. Among the 1206 people recruited for the study, 627 (52%) had no lesions at baseline examination. A total of 291 participants without baseline lesions attended all five follow-up examinations, and only their results were analysed. Members of all four groups developed new lesions, but those receiving ivermectin had a consistently lower proportion of lesions than the placebo group. This difference reached statistical significance at the 5% level in three of the five periods and was below the 10% level at the other two periods. These findings are suggestive of an inhibiting effect of ivermectin among those without lesions at the beginning of a community treatment programme, and justify community treatment as a way of limiting morbidity and social stigma associated with these lesions.