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 ha ve documented reduction in itching, but a less than clear benefit on reacti ve skin lesions. It has been suggested that one of the positive effects mig ht be the prevention of new lesions. A study among a rural adult farming po pulation in southwestern Nigeria provided ivermectin in three treatment gro ups and a placebo to community members who were examined and treated at 3-m onthly intervals over a 15-month period. Among the 1206 people recruited fo r the study, 627 (52%) had no lesions at baseline examination. A total of 2 91 participants without baseline lesions attended all five follow-up examin ations, and only their results were analysed. Members of all four groups de veloped new lesions, but those receiving ivermectin had a consistently towe r proportion of lesions than the placebo group. This difference reached sta tistical 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 b eginning of a community treatment programme, and justify community treatmen t as a way of limiting morbidity and social stigma associated with these le sions.