Vector competence of select black fly species for vesicular stomatitis virus (New Jersey serotype)

Black flies collected from southern Arizona were evaluated for their vector competence to the Oaxaca and Camp Verde isolates of vesicular stomatitis virus (New Jersey serotype) (VSV-NJ). The Camp Verde isolate is the index isolate of the 1982-1983 VSV-NJ epizootic that infected humans and livestock in 14 western states. Previous experiments have shown that colonized Simulium vittatum females are competent laboratory vectors of both virus isolates. However, under controlled laboratory conditions, Simulium bivittatum and S. longithallum were found to be incompetent vectors of both virus isolates. After oral infections, the Oaxaca isolate replicated in 35% and 38% of S. bivittatum and S. longithallum, respectively, but did not disseminate to the salivary glands. Thus, virus was not detected in the saliva of either black fly species with either VSV-NJ isolate, indicating the presence of a midgut barrier. Simulium notatum was found to be a competent laboratory vector of both virus isolates. Infectious virions were detected in the saliva of 23% and 26% of S. notatum infected orally with the Oaxaca and Camp Verde VSV-NJ isolates, respectively. This study suggests that the black fly identified as S. bivittatum was probably not involved in virus dissemination during the 1982-1983 epizootic in the western United States. Because the geographic distribution of S. notatum is not known, its involvement in that epizootic remains obscure.