Effect of ivermection prophylaxis on antibody responses to Onchocerca volvulus recombinant antigens in experimentally infected chimpanzees

Antibody responses to recombinant Onchocerca volvulus antigens were studied in experimentally infected chimpanzees. Sera from 3 groups of 6 animals were tested by ELISA with recombinant antigens OC 3.6 and OC 9.3. Groups I and II were treated with 200 μg/kg of ivermectin on the day of infection or on day 28, respectively. Group III were untreated controls. Antibodies to OC 3.6 developed during the prepatent period in all 3 groups. In contrast, antibodies to OC 9.3 were usually first detected around the time of onset of patency. Several animals had early antibody responses to OC 9.3, but these animals subsequently failed to develop microfilarial patency. Only 1 of 6 animals in group I produced a strong antibody response to OC 9.3 while all 12 animals in groups II and III developed antibodies to this antigen. Although there was some incomsistency in antibody responses observed in each treatment group, the results suggest that OC 9.3 may be more useful than OC 3.6 for monitoring the efficacy of prophylactic drugs or vaccines for onchocerciasis while OC 3.6 may be useful for detecting exposure to the parasite and early infection, regardless of the later outcome of the infection.