Bluetongue virus serotype 8 (BTV-8) in Serbia, 2025.

Bluetongue (BT) is a vector-borne disease of ruminants caused by bluetongue virus (BTV). After more than a decade without reported cases, BT re-emerged in Serbia in 2025. In August 2025, clinical signs consistent with BT were observed in a sheep flock in western Serbia, including fever, submandibular and head oedema, oral haemorrhages, and cyanosis of the tongue. Real-time RT-PCR targeting segment 10 confirmed BTV infection, and serotyping identified BTV-8. Virus isolation in embryonated chicken eggs yielded multiple BTV-8 isolates, which underwent whole-genome sequencing using Oxford Nanopore and Illumina platforms. Complete or near-complete sequences of all ten genomic segments were obtained. Phylogenetic analysis of segment 2 showed close clustering with recent BTV-8 strains from France, Italy, and Spain (2023-2025), with no evidence of reassortment. The data indicate a likely transboundary introduction of BTV-8 from Western Europe and its rapid spread in Serbia.