INVESTIGATION OF GRAY-HEADED FLYING FOXES (PTEROPUS-POLIOCEPHALUS) (MEGACHIROPTERA, PTEROPODIDAE) AND MOSQUITOS IN THE ECOLOGY OF ROSS RIVER VIRUS IN AUSTRALIA

Entomologic and virologic factors were investigated to determine wheth er gray-headed flying foxes (Pteropus poliocephalus) from Indooroopill y Island, Brisbane, Australia could be vertebrate hosts of Ross River (RR) virus. Aedes funereus was the most abundant mosquito species with 6,300-38,700 females per light trap night in the flying fox camp cont aining gray-headed, black (P. alecto), and little red (P. scapulatus) flying foxes. Sixteen Ae. funereus blood meals from this collection we re analyzed by hemoglobin electrophoresis and were found to be from P. alecto. From pledget feeding with RR virus, the infectious dose requi red to infect 50% of wild caught Ae. funereus was log(10) 4.2 50% tiss ue culture infectious doses per mosquito, with a transmission rate to mice of 17% at 9-10 days post infection. Experimental infection of 10 juvenile P. poliocephalus produced viremias of low titer in five anima ls. with a duration of 1-4 days and a mean of two days. Three percent of colonized Ae. vigilax that fed on the 10 animals during this period became infected. One of the five viremic flying foxes and two of the five aviremic animals produced a detectable immune response by either neutralization or hemagglutination-inhibition tests. Based on the low to moderate vector competence of Ae. funereus for RR virus, and eviden ce that P. poliocephalus is a poor vertebrate host of RR virus, it is unlikely that RR virus transmission would be maintained between these two species, but it could be maintained by other more competent vector /host pairs.