Electron Microscopic Analysis of Infection Patterns for Venezuelan Equine Encephalomyelitis Virus in the Vector Mosquito, Culex (Melanoconion) Taeniopus

S. C. Weaver Kalvin Electron Microscope Laboratory, Department of Pathology, Lenox Hill Hospital, 100 East 77th Street, New York, New York 10021

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The infectious process for Venezuelan equine encephalomyelitis virus in an enzootic vector mosquito, Culex (Melanoconion) taeniopus, was examined by transmission electron microscopy. Following large dose oral infection, virus was seen in the abdominal fat body and epidermis within 1 hr of engorgement. Replicated virus appeared to leave the mesenteron 3–4 hr post-infection. Dissemination to other organs occurred between days 1 and 2 of extrinsic incubation, when the hindgut and abdominal nerve ganglia were found to be infected. Virus reached the thoracic nerve ganglia, brain and salivary glands by 4 days post-infection, and flight muscles contained virus by day 6. Virus was never detected in the malphigian tubules or ovaries of infected mosquitoes within 21 days of extrinsic incubation. These results suggest that virus particles penetrate the mesenteron and accumulate in the abdominal fat body prior to replication within the vector. This pattern differs from that reported for other arbovirus-vector pairs.