Genetic and antigenic variations among geographical isolates of Sindbis virus

The genetic and antigenic variation in 12 Sindbis (SIN) virus isolates from four zoogeographic regions (Paleoarctic, Ethiopian, Oriental and Australian) has been examined at a molecular level. RNase T1 oligonucleotide fingerprinting of genomic RNA from SIN isolates revealed that the primary structure of the RNA from viruses from each zoogeographic region was unique. The E₁ and E₂ glycoproteins and the capsid protein of two isolates from each zoogeographic region were compared by tryptic peptide mapping with the Egyptian prototype strain AR-339. Tryptic peptide maps of viruses from Sicily and the Ethiopian region were similar to those of the prototype; maps of isolates from the Oriental and Australia regions were different from each other and from those of the prototype strain. Viruses from each of the four zoogeographic regions were analysed antigenically by neutralization with polyclonal serum to AR-339 and by enzyme-linked immunosorbent assay with an anti-E2 monoclonal AR-339 antibody. Clear antigenic divergence of SIN isolates into two groups, representing the Paleoarctic-Ethiopian and Oriental-Australian regions were demonstrated. These results support a hypothesis which proposes that ancestral SIN virus diverged into two distinct groups. The genetic changes have resulted in further phenotypic divergence within the geographic varieties.