Eastern equine encephalomyelitis virus: an electron microscopic study of Aedes triseriatus (Say) salivary gland infection

Aedes triseriatus (Say) mosquitoes were infected with eastern equine encephalomyelitis virus from a blood meal on viremic chicks. Individual mosquitoes that transmitted virus by bite were dissected at intervals for light and thin section electron microscopy of salivary glands. Viral nucleocapsids were found in the cytoplasm of salivary gland epithelial cells from day 13 onward. Nucleocapsids envelopment occurred during passage through membranes of the acinar cells. Subsequently virus particles accumulated within cisternae of cytoplasmic organelles and in extracellular spaces. After 21 days of incubation, the endoplasmic reticulum of many cells was distended by masses of trapped virus particles. Budding from apical plasma membranes of acinar cells deposited virus directly into secretory products within gland lumina; the striking number of particles in luminal saliva was consistent with the transmission efficiency of arthropods in nature. Viral morphogenesis in mosquito salivary glands was similar in character to that in mammalian tissues and cell cultures, although tubular structures and accumulations of nucleocapsids were not found. No cytopathic effect in virus-infected salivary gland cells was observed during the 31 days of the experiment.