The ability of Simulium mexicanum and Simulium metallicum to serve as biological or mechanical vectors of an enzootic and an epizootic strain of Venezuelan equine encephalitis (VEE) virus was examined. Guinea pigs were inoculated with the epizootic Cordoba strain or the enzootic RPVP407 strain of VEE virus. Wild-caught adult Simuliidae were fed on the viremic guinea pigs and the virus content of groups of flies was determined at daily intervals post-engorgement to test for viral replication. Flies were refed on suckling mice at ≥8 days post-engorgement to test for biological transmission. Other flies were interrupted while feeding on viremic guinea pigs and refed on suckling mice to test for mechanical transmission.
Neither S. mexicanum nor S. metallicum appear to be efficient vectors of either strain of VEE virus, although occasional mechanical transmission was obtained. Titers of virus in flies decreased rapidly after engorgement and from 3–12 days post-engorgement virus was detected only in 5%–25% of both species of flies. Although earlier field evidence implicated both S. mexicanum and S. metallicum as vectors of epizootic VEE, we conclude that it is highly unlikely that they play an important role as vectors of the virus in nature.