Bluetongue disease and the molecular epidemiology of viruses from the western United States.

Prototype and field isolates of United States bluetongue viruses were evaluated for genetic heterogeneity by sequence analyses. Prototype viruses BTV 2, 10, 11, 13 and 17 from the United States, BTV 10 vaccine virus, and field isolates of BTV 10 and 17 from California were analyzed. Gene segment 2 from BTV 10 and 17 isolated in 1980-81 and 1990 was sequenced along with gene segment 9 from BTV 10 isolates. The Wisconsin Package was used to analyze nucleotide sequences and to predict amino acid composition of the putative proteins. Phylogenetic analyses were done using DNADIST and FITCH programs of the PHYLIP Package, v. 3.4. Gene segment 2 segregated into two monophyletic groups of BTV 2 and 13 and BTV 10, 11 and 17. BTV prototype 10, isolated in 1953 and field isolates through 1980 were similar, whereas the 1990 isolates differed by 4.5%, indicating two BTV 10 monophyletic groups over 37 years. Gene segment 2 of BTV 17 prototype virus differed from the California isolates. Gene segment 9 of BTV 10 field isolates formed into two monophyletic groups. This gene segment reassorted with all serotypes. Gene segment 9 of the 1953 BTV 10 vaccine virus was essentially the same as gene segment 9 of the BTV 13 prototype virus, isolated in Idaho in 1967. This suggested that prototype BTV 13 is a reassortant virus with gene segment 9 derived from a vaccine virus parent.