Phylogenetic relationships of bluetongue viruses based on gene S7

Previous phylogenetic analyses based on bluetongue virus (BTV) gene segment L3, which encodes the inner core protein, VP3, indicated a geographical di stribution of different genotypes. The inner core protein, VP7, of BTV has been identified as a viral attachment protein for insect cell infection. Be cause the inner core proteins are involved with infectivity of insect cells , we hypothesized that certain VP7 protein sequences are preferred by the i nsect vector species present in specific geographic locations. We compared the gene segment S7, which encodes VP7, from 39 strains of BTV isolated fro m Central America, the Caribbean Basin, the United States, South Africa and Australia. For comparison, the S7 sequences from strains of the related or biviruses, epizootic hemorrhagic disease virus (EHDV) and African horse sic kness virus (AHSV) were included. The S7 gene was highly conserved among BT V strains and fairly conserved among the other orbiviruses examined. VP7 se quence alignment suggests that the BTV receptor-binding site in the insect is also conserved. Phylogenetic analyses revealed that the BTV S7 nucleotid e sequences do not unequivocally display geographic distribution. The BTV s trains can be separated into five clades based on the deduced VP7 amino aci d sequence alignment and phylogeny but evidence for preferential selection by available gnat species for a particular VP7 clade is inconclusive. Diffe rences between clades indicate allowable Variation of the VP7 binding prote in. (C) 2000 Elsevier Science B.V. All rights reserved.