Influenza D Virus Circulation Among Bovines, Swine, Equines, and Wild Boars in Italy: A Sero-Epidemiological Study

Influenza D virus (IDV), belonging to the <i>Orthomyxoviridae</i> family, was first discovered in 2011 in pigs. Surveys in humans and animals have been carried out to decipher IDV ecology. In this seroepidemiological study, we investigated the circulation of IDV lineages across Italy in livestock and wildlife animals. A total of 1038 animal serum samples (from 246 bovines, 249 swine, 98 equines, and 445 wild boars) were tested using hemagglutination inhibition and virus neutralization assays. The results confirm bovines as the primary reservoir for IDV, with high seroprevalence for both D/660 (87%) and D/OK (80%) strains. Swine and equines demonstrated limited exposure, suggesting they are infrequent spillover hosts. Notably, wild boars showed high seroprevalence, especially for the D/660 lineage (80%), indicating their potential role in a wildlife transmission cycle. Continuous surveillance in both livestock and wildlife is essential to monitor the spread and evolution of IDV.