Bluetongue virus serotype 24 (BTV-24) in Israel: phylogenetic characterization and clinical manifestation of the disease.

Bluetongue (BT), an arthropod-borne viral disease of ruminants, affects sheep most severely than other domestic animals. Bluetongue virus serotype 24 (BTV-24) is one of 26 known Bluetongue virus (BTV) serotypes. In this article, we present data of phylogenetic analysis of 9 viral genes (Seg1, Seg2, Seg3, Seg4, Seg5, Seg6, Seg8, Seg9, and Seg10) from 8 Israeli BTV-24 isolates and relate the genotype of the BTV-24 isolates to their phenotype with regard to clinical manifestations. The high level of genetic identity (> 99.6%) between Seg2, Seg4 and Seg5 in all 8 BTV-24 isolates indicated that these segments shared the same viral ancestor. Phylogenetic analysis of Seg1, Seg3, Seg5, Seg8, Seg9, and Seg10 revealed that the Israeli BTV-24 strains comprised 4 variants. Five of the viruses revealed high identity among all 9 segments, and represented variant 1. A second variant (BTV24/3027/6/10), isolated in 2010, showed significant variation from variant 1 in 3 gene segments (VP-1, VP-3, and NS-3 genes). A third variant (BTV24/3027/1/10) showed significant variation from variant 1 in 6 segments (VP-1, VP-3, VP-6 and NS-1, NS-2 and NS-3 genes), while a fourth variant (BTV24/2214/1/10) showed significant variation from variant 1 in 4 segments (VP-1, NS-1, NS-2 and NS-3 genes). These marked differences in sequence identity indicate that a high level of genetic reassortment is occurring between co-circulating BTV strains in Israel.