A semi-automated system of intrathoracic injection for the large-scale production of Onchocerca lienalis infective larvae.

Intrathoracic injection of Onchocerca lienalis microfilariae (mf) into Simulium ornatum sl. is a highly efficient procedure for routine production of infective stage larvae (L3). This bovine parasite provides a useful analogue of Onchocerca volvulus from man, which presents far greater difficulties for L3 production outside endemic areas of onchocerciasis. Using novel systems for the infection and caging of adult blackflies in the laboratory, mean yields of 10.1-38.6 L3 per fly have been regularly obtained. Cyclical maintenance of either the parasite or vector is not a requirement for the success of this approach. An automated device has been developed to control deliveries of mf inoculations, that permits an experienced operator to perform injections at a rate of approximately 200 flies an hour. Mass recoveries of larvae by Baermann extraction appeared to be highly efficient, contrasting an earlier report on the application of this method to Onchocerca L3. Typical performance of these techniques in routine use over a period of time is illustrated with data on 18,000 inoculated blackflies, which yielded over 100,000 L3. Viability of the L3 obtained by the procedures described was confirmed by successful transmission of patent infections to laboratory-reared calves.