Relationships amongst bluetongue viruses revealed by comparisons of capsid and outer coat protein nucleotide sequences.

Sequence data from the gene segments coding for the capsid protein. VP3, of all eight Australian bluetongue virus serotypes were compared. The high degree of nucleotide sequence homology for VP3 genes amongst BTV isolates from the same geographic region supported previous studies (Gould, 1987; 1988b, c; Gould et al., 1988b) and was proposed as a basis for "topotyping" a bluetongue virus isolate (Gould et al., 1989). The complete nucleotide sequences which coded for the VP2 outer coat proteins of South African BTV serotypes 1 and 3 (vaccine strains) were determined and compared to cognate gene sequences from North American and Australian BTVs. These VP2 comparisons demonstrated that BTVs of the same serotype, but from different geographical regions, were closely related at the nucleotide and amino acid levels. However, close inter-relationships were also demonstrated amongst other BTVs irrespective of serotype or geographic origin. These data enabled phylogenic relationships of the BTV serotypes to be analysed using VP2 nucleotide sequences as a determinant.