Experimental studies on the transmission of Guatemalan and West African strains of Onchocerca volvulus by Simulium ochraceum, S. metallicum and S. callidum

Abstract

The distribution of O. volvulus microfilariae in the skin of Guatemalan patients is described, and compared with the distribution of the bites of S. ochraceum, S. metallicum and S. callidum. Full development of the microfilariae of the Guatemalan strain of O. volvulus was recorded on a quantitative basis in large numbers of S. ochraceum, S. metallicum and S. callidum from the Finca El Amparo in an endemic onchocerciasis zone; and similar development in the same species was observed at the Finca El Faro in a zone where no endemic onchocerciasis has been reported. S. ochraceum, S. metallicum and S. callidum are compared in regard to (a) the ingestion of microfilariae, (b) survival after infected blood meals, (c) development of infective larvae, and (d) probable potentialities as vectors in the field. A 10–25-fold concentration of microfilariae of the Guatemalan strain of O. volvulus was observed in feeding S. ochraceum, S. metallicum and S. callidum, and it is suggested that this phenomenon might make possible the use of a xenodiagnostic test. Quantitative observations were made on the intake and development of West African forest and sudan savanna strains of O. volvulus in Guatemalan simuliids, and comparison is made with those seen in S. damnosum. Central American onchocerciasis is considered to be an indigenous infection differing in many respects from the African disease.