Genomic Divergence among Sindbis Virus Strains

Antigenic variants of the alphavirus Sindbis strains have been isolated from the Paleartic, Ethiopian, Oriental, and Australian zoogeographic regions. The genome of these variants were analyzed for homology by hybridization of virion RNAs to double-stranded RNAs isolated from infected cells. Under nonstringent conditions (Tm-55°) the RNA of Oriental-Australian strains showed only 35 to 51% nucleotide sequence homology with the RNAs of the Paleartic-Ethiopian strains although homology was essentially complete among isolates within the Oriental and Australian regions and among isolates within the Paleartic and Ethiopian regions. Under more stringent conditions (Tm-26°), nucleotide sequence differences of 2 to 45% were detected among the RNAs of virus strains from geographically distant localities within each of these two major zoogeographic subdivisions. Year of isolation, passage histoty and vertebrate or invertebrate host of origin were not major determinants of sequence heterology. The hypothesis that ancestral Sindbis virus became separated by geographic barriers and evolved into two distinct types is presented. Further divergent evolution has obviously occurred wihin each of these types.