Patterns of eastern equine encephalomyelitis virus infection in Culiseta melanura (Diptera: Culicidae).

Infection of the mosquito Culiseta melanura (Coquillett) by eastern equine encephalomyelitis virus was examined using transmission electron microscopy (TEM) of whole tagmata and fluorescent antibody assay (FA) and infectious assay (IA) of dissected tissues. Following infectious blood meals from chicks circulating different virus titers, mosquitoes were examined after extrinsic incubation intervals of 1-22 d. Virus was first detected by FA and IA in midguts and nonalimentary tissues 24 h after infection. Nascent virus was first visualized by TEM in several tissues, including midgut, fat body, and salivary glands, of high-titer-infected mosquitoes 48 h after they engorged. Moderate- and low-titer blood meals resulted in slightly slower appearance and dissemination of virus. Results were consistent with dissemination of virus from the posterior midgut to salivary glands via the hemolymph. Neural tissues contained little or no virus, whereas fat body appeared to be an important organ for virus replication and dissemination. Dissemination barriers did not accompany mosquito infections.