The effects of diethylcarbamazine, mebendazole and levamisole on Onchocerca volvulus in vivo and in vitro.

The effects of mebendazole, levamisole, diethylcarbamazine citrate (DEC-C), and the combination of mebendazole and levamisole, on adult Onchocerca volvulus and on the in utero development of microfilariae was studied in nodules excised from patients in Southern Mexico. Adult worms isolated from patients treated with mebendazole showed a reduction in mobility and contained 40 times fewer developing microfilarial forms than did worms from untreated patients. Most of the developmental forms found in adult worms from mebendazole-treated patients were either oocytes or early morulae, with more mature forms being scarce or morphologically abnormal. Treatment with levamisole had a similar effect on embryogenesis, however it was much less marked. The number and distribution of developing forms in worms from patients treated with DEC-C was similar to that found in the control groups. The effect of the same three drugs on microfilariae in vitro was also tested. DEC-C at concentrations of 0.5 microgram - 2000 micrograms/ml did not have any obvious effect on motility or morphology of the worms provided the pH was maintained at physiological levels; levamisole also had no effect in vitro. Mebendazole induced the death of microfilariae when used at concentrations greater than 100 micrograms/ml, however these levels are greater than those found in the blood of patients under treatment. The optimal conditions for short-term maintenance of O. volvulus microfilariae in culture, are discussed. It is apparent from these studies that mebendazole has an effect on the maturation of microfilariae in utero and may also, at high concentrations, have a direct effect on mature microfilariae.