Bovine respiratory disease complex (BRDC) is a major disease problem in cattle production systems. Numerous pathogens have been implicated as causing BRDC, including the recently discovered influenza D virus (IDV). IDV has been found to be highly enzootic in cattle across multiple continents, and there is some evidence of spillover to livestock workers. In March 2024, unprecedented outbreaks of influenza A virus (IAV) H5N1 clade 2.3.4.4b were reported in the United States with occasional spillover to dairy and poultry workers. Given the occupational threats of both IDV and IAV H5N1, we sought to assess the dynamics of antibodies to IAV H5N1 and IDV in farm workers and cattle.

As part of our One Health surveillance initiative in the United States and Mexico, between April 2024 and May 2025 we enrolled a total of seven dairy and beef cattle farms in Indiana (n?=?1), Kentucky (n?=?3), and Texas (n?=?2) (Table 1). Our visits to these farms took place on four separate occasions, permitting us to prospectively follow the farms. We obtained informed consent from every farm worker who participated in the study. Based on availability, we collected 5 to 10?mL of blood from both the cattle and the farm workers through venipuncture using a plain vacutainer tube (BD, Franklin Lakes, NJ, USA). After collection, the blood samples were centrifuged at 600?g for 15?min, and the serum was harvested and stored in microtubes at ?20°C. Throughout the four visits, we collected 270 serum samples, which comprised 142 samples from cattle and 128 samples from farm workers (Table 1). Ethical approval for the study was granted by the University of Texas Medical Branch´s Institutional Review Board (23-0085).