Quantitative Studies of the Vector Competence of Aedes Aegypti, Culex Annulirostris and Other Mosquitoes (Diptera: Culicidae) with Murray Valley Encephalitis and Other Queensland Arboviruses1

Abstract

Ten (Getah, Ross River, Murray Valley encephalitis, Kunjin, Kokobera, Edge Hill, Alfuy, Corriparta, Belmont, Ngaingan) of 28 known or unproven Queensland arboviruses, and chikungunya, known to be transmitted naturally elsewhere, showed some evidence of multiplication in colonized Aedes aegypti after oral infection. Parameters of vector competence (i.e., infection, susceptibility and transmission rates, threshold of infection, extrinsic incubation period) were determined for the 11 viruses. Nine of these were transmitted by bite to infant suckling mice. Several patterns of response were evident which suggested loss of vector efficiency not only at the gut barrier but also in spread of virus to the salivary glands and in the salivary glands themselves. Different patterns of infection were achieved with viruses of different mouse passage level. This work provided a model on which to base studies of Culex annulirostris with Murray Valley encephalitis virus. Wild Cx. annulirostris from Brisbane were highly efficient vectors of MVE virus. This efficiency was characterized by a low threshold (ID₅₀ of 10^2.9 LD₅₀/mosquito), complete susceptibility to infection, and transmission to day-old chickens from 7 days, which reached 75–95% transmission by 10 days after ingestion of blood-virus mixture. These results were considered comparable to those for a Murray Valley strain of Cx. annulirostris studied previously by McLean. More limited investigations indicated that Aedes vigilax, Ae. lineatopennis and Ae. vittiger could also act as vectors of MVE virus.