Facilitation of Rift Valley fever virus transmission by Plasmodium berghei sporozoites in Anopheles stephensi mosquitoes.

Certain mosquito species are susceptible to viral infection but cannot transmit the virus due to a salivary gland barrier. We hypothesized that such species could transmit virus if the mosquito were infected with both virus and malaria parasites. Malaria sporozoites disrupt the integrity of mosquito salivary glands and, in so doing, may destroy salivary gland barriers to viral transmission. To examine this postulate, the model system of Rift Valley fever (RVF) virus and a rodent parasite, Plasmodium berghei, in Anopheles stephensi mosquitoes was used. Viral transmission rates for RVF virus-inoculated anophelines that were previously fed either gametocytemic blood (malaria-infected) or normal blood (control) were compared. Viral transmission rates for anophelines having concurrent sporozoite infection of the salivary glands were 32% (n = 25). None of the RVF virus-inoculated control anophelines (n = 55) transmitted virus. These studies confirm an earlier report that malaria sporozoites can disrupt salivary gland barriers and enhance mosquito transmission of arboviruses. Taken together with similar studies using microfilarial parasites, it is increasingly apparent that mosquito-borne parasites have the potential to enhance mosquito transmission of arboviruses.