VP2 gene sequence analysis of some isolates of bluetongue virus recovered in the Mediterranean Basin during the 1998-2002 outbreak

Since 1998, five serotypes of bluetongue virus (BTV), BTV-1, BTV-2, BTV-4, BTV-9 and BTV-16, have been reported in countries surrounding the Mediterranean Basin. Preliminary data on the sequencing analysis of the VP2-genes of BTV isolates recovered during the 1998-2002 epizootic of BT in Italy, Greece and Israel were studied. The VP2-genes of the Italian BTV-2 and BTV-9, Greek BTV-4 and BTV-9, Israeli BTV-4 and BTV-16 and South African BTV-2, BTV-4, BTV-9 and BTV-16, together with those of their corresponding South African serotype reference and vaccine strains, were cloned and the sequences of their terminal ends determined. These sequences, as well as those of all BTV VP2-gene sequences currently available on GenBank, were used to compile a phylogenetic tree to determine the probable geographic origins of the BTV incursions into Europe. The Italian isolates included in this study were from different regions, animal hosts and years (2000-2002). The results demonstrated that sequencing of the terminal end of the VP2-gene of BTV can be used for topotyping. According to the phylogenetic analysis, the Italian BTV-2 and BTV-9 isolates were stable across all species, irrespective of geographic origin and year of isolation. The sequencing data of the Italian isolates were identical to those of a BTV-2 isolate from Corsica. There was 97% homology between the Italian and Corsican BTV-2 isolates and the BTV-2 vaccine and reference isolates from South Africa. Italian BTV-9 isolates were also identical to the Greek BTV-9 isolates (99% homology). Surprisingly these BTV-9 isolates had only 67% homology with the reference BTV-9 isolate from South Africa. Conversely, BTV-9 field isolates from Australia and elsewhere in Europe had 89% homology with the Italian isolate at the nucleic acid level. Greek and Israeli BTV-4 isolates were almost identical (98% homology) and shared a 90% homology with the BTV-4 South African reference and vaccine strains. Israeli BTV-16 and South African BTV-16 reference strains were also similar. From these results, it may be concluded that Italian and Corsican BTV-2, Israeli and Greek BTV-4, and South African and Israeli BTV-16 had a common origin. The Greek BTV-9 isolate had more than 99% homology with the isolates from Italy, indicating these isolates to have had a common origin. The European BTV-9 isolates, grouped as ‘eastern isolates’, were more similar to the Australian isolates than to the South African reference strains