GENETIC STABILITY AMONG TEMPORALLY AND GEOGRAPHICALLY DIVERSE ISOLATES OF BARMAH-FOREST-VIRUS

An increase in the incidence of polyarthritis caused by Barmah Forest (BF) virus, and its recent emergence into Western Australia, prompted a study of the molecular epidemiology of this Australian mosquito-born e alphavirus. The nucleotide sequence of a 500-basepair region of the 3' end of the envelope (E2) gene of the prototype BF virus strain (BH2 193) was compared with other members of the alphavirus genus, and to a panel of isolates of BF virus collected more for than 20 years from d ifferent geographic regions of Australia. The BF virus was shown to be genetically distinct from other members of the alphavirus genus. A hi gh degree of sequence homology (98-100%) was found between the BF isol ates, with no evidence of geographic or temporal divergence. This nucl eotide homogeneity was similar to that observed with other Australian mosquito-borne viruses with avian vertebrate hosts, such as Sindbis, M urray Valley, and Kunjin viruses, but it contrasts to the heterogeneit y reported for Ross River virus, an alphavirus with mammalian vertebra te hosts.