Emergence, Local Circulation, and Limited Spread of Bluetongue Virus Serotype 5 in Sardinia, Italy, 2025–2026

Bluetongue virus serotype 5 (BTV-5) was detected in Sardinia in 2025, representing the first documented occurrence of this serotype in Europe. Following the initial identification and development of BTV-5-specific diagnostic tools, we examined its epidemiological trajectory through 2026. Molecular and serological data generated within Italian bluetongue surveillance were analysed together with outbreak-level information from Sardinia and compared with the historical trajectory of BTV-3 on the island. From October 2025 to September 2026, 1310 diagnostic samples were tested for BTV-5 at the National Reference Laboratory for Bluetongue; 169 samples from Sardinia were positive in 2025 and four in 2026, whereas no positives were detected among samples referred from the rest of Italy. The 2026 transmission season is still ongoing at the time of writing, and the 2026 figures should be therefore considered preliminary. Regional molecular surveillance in Sardinia detected BTV-5 in 114 BTV-positive samples in 2025 and three in 2026. In 2025, a total of 105 BTV-5 outbreaks affecting 33 municipalities were confirmed, followed by two outbreaks in 2026. These data document substantial local transmission in 2025 and further detection in 2026, with no evidence of broad geographical expansion. The previous non-linear course of BTV-3 in Sardinia cautions against interpreting low activity in a single season as evidence of disappearance and supports continued molecular, genomic, and epidemiological surveillance.