During field investigations of recurrent small outbreaks of epidemic polyarthritis on Port Stephens Peninsula, New South Wales, 12 strains of Ross River virus (RRV) were recovered from pools of mosquitoes collected in a small area of dry sclerophyll forest on stable sand dunes in the vicinity of the township of Nelson Bay. The viruses were recovered during April of 3 successive years. The Nelson Bay strains of RRV are antigenically indistinguishable from Queensland strains by routine serological methods, but consistent biological differences are apparent in laboratory mice. It is unlikely that the virus is annually reintroduced from northern foci. Pseudomys novaehollalldiae, the New Holland mouse, is the only vertebrate so far found in the area which fulfills the criteria for a reservoir vertebrate host, but it is not suggested that this is the only host involved. Most RRV strains were recovered from Aedes vigilax, but the highest infection rates were obtained in pools of Culex and Mansonia species. One recovery was made from Mansonia linealis, which has not previously been recorded as a vector of this virus. In addition to RRV, 9 strains of Edge Hill virus, 4 strains of a previously undescribed Mapputta group virus, 1 orbivirus related to Eubenangee, and 1 uncharacterized probable arbovirus were recovered from mosquitoes collected in the same area.
Present address: Veterinary Research Station, Glenfield, N.S.W., Australia.