Central America Research Station, Bureau of Tropical Diseases, Center for Disease Control, Public Health Service, U.S. Department of Health, Education, and Welfare, Arthropod-Borne Animal Disease Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, San Salvador, El Salvador, C.A.
Three strains of Culicoides variipennis (two colonized strains designated as 000 and 036 and wild flies reared from field-collected larvae) were fed on cow blood in membrane feeders containing microfilariae of Onchocerca cervicalis ranging in concentration from 5.2 to 13.0 × 104 microfilariae per ml. Flies were maintained at different temperatures during the development of parasite larvae, and infective larvae were collected by individual dissection and by feeding infective flies on horse serum. Additionally, infective flies were fed on jirds (Meriones unguiculatus). High concentrations of microfilariae (12.0 × 104 per ml blood or greater) were required to infect a high proportion of the flies and to produce many infective larvae. In the 000 and 036 strains, 5.2% and 13.2% of the flies, respectively, developed infective larvae compared to 57.1% in wild flies when fed on identical concentrations of microfilariae (12.0 × 104 per ml blood) obtained from the same horses. However, wild flies were more reluctant to feed on the membranes. Infective larvae developed 7 days after feeding in the 000 strain of flies maintained at 80 ± 2°F and 12 days after feeding in those maintained at 71 ± 2°F. In the 036 strain, 66% of infective flies fed on jirds; 86.0% of all infective larvae were shed while biting and 62.5% of the flies lost all of their larvae. Infective flies (of all strains) fed on horse serum in the membrane feeder and transmitted infective larvae into it. The application of the O. cervicalis-C. variipennis system to human onchocerciasis is discussed.