Natural infections of Simulium bidentatum (diptera: simuliidae) with larvae of Onchocerca SPP., in relation to a human zoonotic onchocerciasis in Oita, Japan.

A total of 579 wild female flies belonging to eight species of Simulium were collected on human baits, in relation to the transmission of a human zoonotic onchocerciasis found in Oita, Japan.Simulium bidentatum was the most dominant species.Natural infections with filarial larvae were found in 11 of 449 S. bidentatum (or 6.5% of the parous flies) and in 1 of 23 S. aokii (or 10% of the parous flies).All the infected flies had 1-4 either first-, second-or early third-stage larvae in the thorax.Examination of third-stage larvae shows that S. bidentatum is infected with at least two species of Onchocerca.Our result represents the first record of natural Onchocerca infections in Japanese Simuliidae, and also suggests the possibility of S. bidentatum as the potential vector of zoonotic Onchocerca spp. to humans.