Circulation of influenza D virus in Ukraine: A multi-species serological study

• A total of 363 serum samples from different animal species were collected in 2021, 2023 and 2024 in Ukraine, including clinically healthy domestic animals (pigs and horses), wild animals (moufflon, deer, saiga) and pet animals (guinea pig, rabbit, chinchilla, ferret). • The highest seroprevalence for the D/660 lineage was detected in horses (57%), followed by swine (10%), with sporadic positivity observed in wild and companion animals. • These findings underscore the importance of coordinated monitoring of livestock, wildlife, and at-risk human populations to fully assess the public health significance of influenza D virus. Influenza viruses infect a wide range of animal species and continue to pose a significant threat to global health. Influenza D virus (IDV), first identified in 2011, has emerged as a new pathogen with a broad host range and remains poorly understood. This seroepidemiological study aimed to investigate the circulation of IDVs in Ukraine by analysing serum samples from domestic, wild and pet animals collected between 2021 and 2024. All samples tested negative for influenza A viruses. The highest seroprevalence for the D/660 lineage was detected in horses (57%), followed by swine (10%), with sporadic positivity observed in wild and companion animals. Positivity for the D/OK lineage was lower across all species. Overall, these finding provide evidence of the circulation and predominance of the D/660 lineage as the major IDV circulating in Ukraine and underscore the importance of coordinated surveillance in livestock, wildlife, and at-risk human populations to fully evaluate the public health implications of this emerging pathogen.