Vector capability of Aedes aegypti mosquitoes for California encephalitis and dengue viruses at various temperatures

A Yukon strain of California encephalitis virus (snowshoe hare subtype) was transmitted by bites of laboratory-bred Aedes aegypti mosquitoes after 3 weeks of extrinsic incubation at 80°F and after 4 weeks at 55°F after intrathoracic injection. Transmission first occurred after 4 weeks incubation at 80 or 55°F when mosquitoes were infected by feeding. Zero-passage strains of dengue-2 virus were transmitted after 6 days of extrinsic incubation at 90°F after feeding or intrathoracic injection, after 6 to 13 days incubation at 75°F following injection, after 13 days at 80°F following feeding, and after 13 to 27 days at 55°F following injection. Although virtually all mosquitoes were infected at the time transmission occurred, California encephalitis virus was transmitted by less than 50% of mosquitoes, but 80% or more of mosquitoes infected with the dengue-2 strains transmitted virus. Enveloped virions about 35 nm diameter were observed in the cytoplasm of acini of salivary glands of mosquitoes infected with dengue-2 virus.