No Evidence of Direct Transmission of Emerging Bluetongue Virus Strains Between Israel and Europe Based on Genomic Analyses (2013-2023).

Bluetongue (BT) is an arthropod-borne viral disease primarily affecting domestic and wild ruminants. In recent years, several BTV serotypes and genotypes have been detected in Israel almost annually, raising questions about their origin and routes of introduction. Some BTV serotypes closely related to those first identified in Israel, including BTV-3, BTV-8, and BTV-12, were subsequently reported in Europe after a delay of several years. In this study, we sequenced the complete genomes of one representative strain of all newly identified Israeli BTV genotypes/serotypes-BTV-1, -4, -5, -8, and -11-first detected between 2021 and 2023. Additionally, complete sequences of enzootic Israeli BTV (2015) and eleven BTV-3 strains (2019-2023), with two representative strains for every year of isolation, except 2021 (three strains), were analyzed using phylogenetic, BLAST, and pairwise identity approaches. Genetic analyses revealed that recently identified Israeli and European BTV strains share common African ancestors, with some genomic "incursions" from Mayotte Island or the Arabian Peninsula. These incursions appeared more frequently in Israeli than in European strains. Nevertheless, nucleotide sequence differences of at least 2-3% across all genes indicate several years of independent evolution. The observed divergence suggests that no direct transmission of BTV occurred between Israel and Europe during the past decade.