A community trial of ivermectin for onchocerciasis in Sierra Leone: compliance and parasitological profiles after three and a half years of intervention

Summary We have studied the compliance patterns and the long‐term effects of repeated ivermectin at various dosing intervals in a randomized controlled trial. The setting for the trial was six neighbouring communities hyperendemic for onchocerciasis in southern Sierra Leone. A total of 335 subjects attended a survey 18 months after the fifth treatment round. Of those randomized to ivermectin, over 85 % had received at least three doses. There was no evidence that women of childbearing age were consistently under‐treated, despite the criteria for exclusion from treatment. An intention‐to‐treat analysis showed that a 6‐monthly ivermectin treatment regime satisfactorily suppressed microfilarial loads. Microfilarial repopulation was significantly slower over an 18‐month period after multiple doses compared to a single dose. Further analysis of microfilarial repopulation suggests that there is a cumulative suppressive effect after at least the first three doses of ivermectin, and that an annual treatment interval is as effective for short‐term microfilarial suppression as a 6‐monthly interval.