Ivermectin prophylaxis against experimental Onchocerca volvulus infection in chimpanzees

Ivermectin was tested for possible prophylactic action against the third and fourth larval stages (L₃ and L₄) of Onchocerca volvulus inoculated into chimpanzees. The infective larvae (L₃) were obtained from laboratory-raised black flies. Eighteen chimpanzees were inoculated, each with approximately 250 L₃. Six were treated with ivermectin (200 μg/kg) on the day of inoculation, 6 were treated with ivermectin on day 28, and 6 were not treated. Monthly skin snips were taken for the next 30 months to detect patent infection. One of the chimpanzees treated with ivermectin on the day of infection developed a patent infection as did 4 of the 6 treated at day 28 and 4 of the 6 control animals. The results suggest that ivermectin may have a partial in vivo effect against the L₃ of O. volvulus but has no effect against later larval stages of the parasite.