An electron microscopical study of Rift Valley fever and Sindbis viral infection in mosquito salivary glands (Diptera: Culicidae)

Aedes aegypti Linnaeus and Culex theileri Theobald were infected by intrathoracic inoculation with Sindbis virus, while Aedes circumluteolus (Theobald) was infected with Rift Valley fever virus. After a lengthy incubation period of 45-63 days, the salivary glands were removed and studied by transmission electron microscopy. No pathological changes or damage was observed. Arrays of Sindbis virus particles were present in both Ae. aegypti and Cn. theileri, associated with distended endoplasmic reticulum but no virions were seen within vacuoles. Virions occurred freely in the cytoplasm in Cs. theileri but not in Ac. aegypti. In Aedes circumluteolus, arrays of Rift Valley fever virus that accumulated in the cytoplasm were being released into the salivary duct through microvilli. The Rift Valley fever virions measured slightly less than those cultured in mouse brain-tissue. The known degree of vector capability of each mosquito species is discussed in relation to the ultrastructural observations.