Transmission of Rift Valley fever virus by adult mosquitoes after ingestion of virus as larvae.

We studied the ability of Culex pipiens, Aedes circumluteolus, and Ae. mcintoshi, exposed as larvae to liver tissue from a Rift Valley fever (RVF) virus-infected hamster, to become infected and transstadially transmit virus to the adult and for the adults to transmit virus by bite to hamsters. After exposure as larvae, 9% (5/54) of adult Cx. pipiens and 8% (38/505) of the adult Ae. (Neomelaniconion) species were infected. All of the infected Cx. pipiens and about half of the infected Ae. circumluteolus and Ae. mcintoshi tested transmitted RVF virus by bite to hamsters. Transmission rates for mosquitoes orally infected as larvae were higher than those for mosquitoes orally infected as adults. Animals infected with RVF virus may abort or die in the vicinity of mosquito larvae breeding habitats and infected tissue from these animals may contaminate the water.