Effects of multiple monthly doses of ivermectin on adult Onchocerca volvulus

Abstract This paper assesses the effects on adult Onchocerca volvulus of monthly doses of ivermectin (150 µg/kg) given over 4, 8, and 12 months to patients in Guatemala. Nodules were removed 4 months after the last dose; the adult O. volvulus were extracted by collagenase digestion, studied by histological techniques, and compared with worms from untreated patients. Twelve monthly doses killed a proportion of the adult worms (12% of males and 22% of females), leaving the remainder relatively unaffected and the females slowly resuming embryogenesis. After 8 and 12 doses, a number of female worms had resumed embryogenesis in 1 genital tract only, and in 1 female a total degeneration of 1 ovary was seen. Ivermectin also led to a marked drop in the number of male worms in nodules. No serious adverse reactions occurred and the treatment was well accepted.