Development of Onchocerca volvulus in Simulium ochraceum and Simulium metallicum

The development of Onchocerca volvulus was compared in Simulium ochraceum and S. metallicum by maintaining infected flies under uniform conditions. Larval development in S. ochraceum was synchronous and orderly so that nearly all larvae reaching the thoracic muscles from a single blood meal matured to third-stage infective larvae within 192 hours. In contrast, development in S. metallicum was asynchronous, slower, and retarded. In this species many first-larvae were malformed and stunted after the 5th day of development; and microfilariae and first- and second-stage larvae were still present 8--10 days after a single infecting blood meal when third-stage larvae had developed. The development of O. volvulus in S. ochraceum is more compatible with the intense transmission associated with human disease.