Geographic distribution and evolution of Sindbis virus in Australia

The molecular epidemiology and evolution of Sindbis (SIN) virus in Australi a was examined, Several SIN virus strains isolated from other countries wer e also included in the analysis. Two regions of the virus genome were seque nced including a 418 bp region of the E2 gene and a 484 bp region containin g part of the junction region and the 5' end of the C gene. Analysis of the nucleotide and deduced amino acid sequence data from 40 SIN virus isolates clearly separated the Paleoarctic/ Ethiopian and Oriental/Australian genet ic types of SIN virus. Examination of the Australian strains showed a tempo ral rather than geographic relationship. This is consistent with the virus having migratory birds as the major vertebrate host, as it allows for movem ent of virus over vast areas of the continent over a relatively short perio d of time. The results suggest that the virus is being periodically redistr ibuted over the continent from an enzootic focus of evolving SIN virus. How ever, SIN virus strains isolated from mosquitoes collected in the south-wes t of Australia appear to represent a new SIN virus lineage, which is distin ct from the Paleoarctic/Ethiopian and Oriental/Australian lineages. Given t he widespread geographic dispersal of the Paleoarctic/Ethiopian and Orienta l/Australian lineages, it is surprising that the South-west genetic type is so restricted in its area of circulation. Nucleotide sequence data from th e C gene of the prototype strain of the alphavirus Whataroa were also deter mined. This virus was found to be genetically distinct from the SIN virus i solates included in the present study; however, it is clearly SIN-like and appears to have evolved from a SIN-like ancestral virus.