Seroprevalence of Influenza D Virus in Cattle Workers: An Occupational Health Perspective

Influenza D virus (IDV) was first isolated in 2011 from a swine with respiratory disease symptoms in the United States. Epidemiological and serological evidence suggests that cattle are the natural reservoir of IDV, with periodic spillover events to other animal hosts. This study investigated the seroprevalence of two IDV lineages, D/660 and D/OK, among cattle workers in Southern Italy between 2023 and 2024 to better characterize the zoonotic exposure risk in this occupational setting. A control group from the same geographical area was also included. Serum samples were tested by hemagglutination inhibition and virus neutralization (VN) assays. Overall, 42.9% (60/140) of cattle workers were positive at least to one of the two IDV lineages. Moreover, 39.3% (55/140) were positive for D/660 and 34.3% (48/140) for D/OK, with all but one positive result confirmed by VN assay. In the control group, tested only for D/660, a significantly higher seroprevalence was observed, with 65.0% (39/60) testing positive. These findings suggest that IDV exposure is not restricted to occupational settings involving direct contact with cattle and underscore the importance of incorporating IDV into current influenza surveillance programs.