Vector competence of Simulium metallicum s.l. (Diptera: Simuliidae) in two endemic areas of human onchocerciasis in northern Venezuela.

Experimental infections of Simulium metallicum s.l. with Onchocerca volvulus were carried out in two onchocerciasis foci, Altamira and Trincheras, in northern Venezuela, to determine vector competence. Wild-caught flies, fed on infected volunteers, were maintained in the laboratory for 13-15 days at 27 degrees C. Parasite development was complete but asynchronous and retarded. No differences in the vector competence of the two populations of S. metallicum s.l. were found. However, a less efficient development of the parasite occurred during the dry season at both localities. The distribution of the parasite within the vector was aggregated and also displayed seasonal variation. The seasonal susceptibility may be a consequence of a density-dependence regulation mechanism of the parasite within the vector. These results indicate a relatively low vector competence for S. metallicum s.l. in northern Venezuela.