In the Arbovirology Group we are using molecular biological approaches to study the proteins and genes of bluetongue virus (BTV). BTV exists as 24 serotypes. The practical significance of this is that infection/vaccination of an animal with one serotype does not confer immunity to any of the other serotypes. It is virus protein 2 (VP2), located at the surface of the virus, that is the major inducer of protective immune responses and, indeed, determines the serotype. Vaccines exist for just a few of the 24 serotypes. Knowing the serotype of BTV associated with a given outbreak is important in relation to the possibility that an appropriate BT vaccine might be available, and in working out from where the virus came from which also gives clues as to by what mechanism and route the virus had spread. We have sequenced the gene that encodes VP2 of all 24 serotypes, and have developed polymerase chain reaction tests to identify them. These tests are much more rapid (results within day) than conventional virus neutralisation tests (three weeks or so)
When northern European countries experienced their first bluetongue outbreak, in the summer of 2006, we first used a polymerase chain reaction (PCR) test based on the gene encoding virus protein 7, able to detect any and all of the 24 serotypes of BTV, to confirm the presence of the virus. Subsequently we used our VP2-based PCR to demonstrate that the virus was serotype 8 ? which had never previously been identified in Europe.
We then sequenced the whole of the VP2 gene and compared it with other VP2 gene sequences of BTV-8 viruses that had been previously isolated in Africa. This indicated that the BTV-8 virus of northern Europe had originated in sub-Saharan Africa, being most similar to BTV-8 in Nigeria.
The distance from this region to northern Europe is too great for the BTV-8 to have been spread by winds bearing infected midges. How the virus got to northern Europe remains a mystery. In September 2007 samples from British animals suspected as having bluetongue were tested at Pirbright using the PCR tests described above, plus tests for antibody to the virus. These tests confirmed that BTV-8 had been spread to Britain.