Histological examination of onchocercomata after therapy with ivermectin.

During chemotherapy trials in hyperendemic onchocerciasis areas in West Africa 15 adult nodule carriers in Liberia and 24 patients in Mali received single doses of ivermectin (150 or 200 micrograms/kg). Nodules were extirpated two, six and ten months after therapy and examined histologically. No macrofilaricidal effect of ivermectin was observed. Two months after therapy, in 93% of all female worms with intrauterine stretched microfilariae nearly all microfilariae were degenerated. The percentage was lower after ten months but still significantly higher than in untreated control groups. Ivermectin did not cause degeneration of the intrauterine coiled microfilariae. But the percentage of the female worms with coiled microfilariae was significantly lower two and ten months after therapy than that in the placebo or untreated control groups. Correspondingly, the percentage of nodules with intact microfilariae in the nodule tissue was also significantly lower throughout the examination period than that of the untreated control groups. There was not observed any effect on the spermatogenesis and spermatozoa were found frequently in the uteri of female worms. Using the method of histology, the long lasting inhibitory effect of a single dose of ivermectin on the intrauterine production of microfilariae could clearly be demonstrated. This proves the value of histology for the assessment of drug effects on adult O. volvulus.