Ivermectin in human onchocerciasis: a clinical-pathological study of skin lesions before and three days after treatment.

Findings are presented from an histological study of 360 skin-snips (from iliac crests, calves, ankles) taken from 30 Ivory Coast onchocerciasis patients before and three days after an oral dose of ivermectin (200 micrograms/kg). This dose causes a nearly complete disappearance of the intralymphatic microfilariae and, surprisingly, of the "extra-vascular" ones. That shows the difficulty to localize the microfilariae on histological sections; these microfilariae are in fact inside the lymphatic pre-capillaries. There was no intensification of acute skin lesions after the treatment, thus showing that, contrary to diethylcarbamazine (DEC), ivermectin does not induce an exit of microfilariae into the extralymphatic connective tissue. Under the influence of ivermectin, paralyzed microfilariae may be carried passively towards the deep sub-cutaneous lymphatics, and then destroyed inside the regional lymph nodes, without producing major changes in the skin.