Molecular epidemiology of bluetongue viruses from disease outbreaks in the Mediterranean Basin.

Bluetongue virus (BTV) serotype is primarily controlled by the variable outer coat protein VP2, encoded by genome segment 2. Phylogenetic analyses of segment 2 show that recent Mediterranean isolates of BTV-2 have a similar genetic lineage to those from sub-Saharan Africa and North America but are distinct from Asian strains. In contrast, isolates of BTV-9, from the eastern Mediterranean, are related to a genetic lineage from Asia. BTV-1 from Greece 2001 is also more closely related to Indian isolates, suggesting (in both cases) virus movement from east to west. Recent BTV-4 field isolates from Greece and Turkey are similar to each other, but differ from the Turkish type 4 vaccine strain. These sequencing studies are being used to establish a database for molecular epidemiological studies which is available on the website of the Institute for Animal Health. This resource will support and improve BTV serotype identification methods, by using sequence comparisons (via the Web) rather than by conventional serological techniques that require standardised (and therefore expensive) serological reagents. Phylogenetic trees for BTV genome segment 2 are available on the website.