Vector Competence of Australian Mosquitoes (Diptera: Culicidae) for Japanese Encephalitis Virus

Australian mosquitoes were evaluated for their ability to become infected with and transmit a Torres Strait strain of Japanese encephalitis virus. Mosquitoes, which were obtained from either laboratory colonies and collected using Centers for Disease Control and Prevention light traps baited with CO<inf>2</inf> and octenol or reared from larvae, were infected by feeding on a blood/sucrose solution containing 104.5±0.1 porcine stable-equine kidney (PS-EK) tissue culture infectious dose<inf>50</inf>/mosquito of the TS3306 virus strain. After 14 d, infection and transmission rates of 100% and 81%, respectively, were obtained for a southeast Queensland strain of Culex annulirostris</it> Skuse, and 93% and 61%, respectively, for a far north Queensland strain. After 13 or more days, infection and transmission rates of >90% and =50%, respectively, were obtained for southeast Queensland strains of Culex sitiens</it> Wiedemann and Culex quinquefasciatus</it> Say, and a far north Queensland strain of Culex gelidus</it> Theobald. Although infection rates were >55%, only 17% of Ochlerotatus vigilax</it> (Skuse) and no Cx. quinquefasciatus</it>, collected from far north Queensland, transmitted virus. North Queensland strains of Aedes aegypti</it> L., Ochlerotatus kochi</it> (Dönitz), and Verrallina funerea</it> (Theobald) were relatively refractory to infection. Vertical transmission was not detected among 673 F<inf>1</inf> progeny of Oc. vigilax</it>. Results of the current vector competence study, coupled with high field isolation rates, host feeding patterns and widespread distribution, confirm the status of Cx. annulirostris</it> as the major vector of Japanese encephalitis virus in northern Australia. The relative roles of other species in potential Japanese encephalitis virus transmission cycles in northern Australia are discussed.