Brugia malayi microfilariae (Nematoda : Filaridae) enhance the infectivityof Venezuelan equine encephalitis virus to Aedes mosquitoes (Diptera : Culicidae)

We examined the potentially conflicting effects that microfilarial (MF) enh ancement of viral infectivity and MF-induced mortality in mosquitoes have o n the vectorial capacity of Aedes aegypti (L.),Aedes triseriatus (Say),and Aedes taeniorhynchus (Wiedemann ) for Venezuelan equine encephalitis virus (VEE) when mosquitoes feed on gerbils co-infected with Brugia malayi (Buckl ey). Groups of mosquitoes were fed on gerbils that were either dually infec ted (VEE plus B. malayi MF) or singly infected (VEE only). Mosquito mortali ty was recorded daily, and 5-8 d later, surviving mosquitoes were assayed f or disseminated viral infection. The contrasting effects of MF enhancement and MF-induced mortality differed among mosquito species and were determine d by the nature and consequences of MF penetration through the mosquito mid gut, but not to differences in mosquito susceptibilities to parenterally in troduced virus. In As. aegypti, MF-induced mortality was high and tended to eliminate any significant effect of MF enhancement. In Ae. triseriatus, MF -induced mortality was low, and feeding on dually infected hosts resulted i n 9 times as many mosquitoes with disseminated viral infections as did feed ing on singly-infected hosts. In Ae. taeniorhynchus, MF-induced mortality w as extremely high, yet under our experimental conditions, feeding on a dual ly infected hosts resulted in nearly 30 times as many disseminated infectio ns as did feeding on singly infected hosts. The final outcome on vectorial capacity depended on the specific combination of MF. virus, and mosquito sp ecies involved. Therefore, future efforts toward understanding MF enhanceme nt should be directed toward mosquito-virus-parasite species combinations t hat occur together in nature.