Completion of the sequence analysis and comparisons of genome segment 2 (encoding outer capsid protein VP2) from...

Bluetongue (BT) is a non-contagious, arthropod-transmitted viral disease of domestic and wild ruminants. It is caused by bluetongue virus (BTV), a double-stranded (ds) RNA virus that is classified within the genus Orbivirus, family Reoviridae. There are at least twenty-four serotypes of BTV worldwide, five of which (1, 2, 4, 9 and 16) have been identified recently in Europe. BTV infects ruminants and its distribution throughout temperate and tropical regions of the world is dependent on the activity and abundance of certain vector-competent species of Culicoides midge. The outer capsid protein VP2 of BTV is a major protective antigen and the primary determinant of virus serotype. For the first time, the authors have completed the sequence analysis of full-length VP2 genes from the reference strains of each of the 24 BTV serotypes and their amino acid sequences were deduced. Multiple alignment of the VP2 gene (protein) sequences revealed that the level of nucleotide (amino acid) sequence variation between serotypes ranged from 29% (23%) to 59% (73%), confirming that segment 2/VP2 is the most variable BTV gene/protein. Phylogenetic analysis of VP2 grouped together the BTV types that are known to cross-react serologically. Low identity between types was demonstrated for specific regions within the VP2 amino acid sequences that have been shown to be antigenic and play a role in virus neutralisation. The sequence data represent the completion of an important step in the creation of a comprehensive BTV sequence database, which will support more rapid molecular methods for diagnosis and identification of BTV 'types', as well as continuing molecular epidemiology and surveillance studies of BTV.