Study on the activity of antiparasitic agents against Onchocerca lienalis third stage larvae in vitro.

The in vitro drug response of third stage larvae of the cattle filarial worm Onchocerca lienalis has been studied. Larvae were maintained in Minimum Essential Eagles medium supplemented with 10% inactivated foetal calf serum and exposed to the following drugs: Mel W, caparsolate sodium, suramin, ivermectin, flubendazole, levamisole and amoscanate plus 3 novel melaminylthioarsenites. Antiparasitic activity of these compounds has been assessed on their killing effects and their ability to totally inhibit the moult from the third to the fourth stage. Unfortunately, moulting occurred at a low rate in the culture system used and was not suitable as a quantitative parameter for describing drug activity. However, the results indicated that if the rate of ecdysis could be increased by improving the culture conditions, moulting could be used in this manner since exsheathment has inhibited by certain compounds at concentrations where killing effects were less than 50%. Of the compounds evaluated ivermectin demonstrated good activity, totally preventing ecdysis at 0.001 microgram/ml. The drug assay system used in this study may offer a starting point for the eventual development of a meaningful and specific in vitro screen for new anti-Onchocerca agents.