A One Health Investigation into H5N1 Avian Influenza Virus Epizootics on Two Dairy Farms

Background: In early April 2024 we studied two Texas dairy farms which had suffered incursions of H5N1 highly pathogenic avian influenza virus (HPAIV) the previous month. Methods: We employed molecular assays, cell and egg culture, Sanger and next generation sequencing to isolate and characterize viruses from multiple farm specimens (cow nasal swab, milk specimens, fecal slurry, and a dead bird). Results: We detected H5N1 HPAIV in 64% (9/14) of milk specimens, 2.6% (1/39) of cattle nasal swab specimens, and none of 17 cattle worker nasopharyngeal swab specimens. We cultured and characterized virus from eight H5N1-positive specimens. Sanger and next-generation sequencing revealed the viruses were closely related into other recent Texas epizootic H5N1 strains of clade 2.3.4.4b. Our isolates had multiple mutations associated with increased spillover potential. Surprisingly, we detected SARS-CoV-2 in a nasal swab from a sick cow. Additionally, 14.3% (2/14) of the farm workers who donated sera were recently symptomatic and had elevated neutralizing antibodies against a related H5N1 strain. Conclusions: While our sampling was limited, these data offer additional insight into the large H5N1 HPAIV epizootic which thus far has impacted at least 96 cattle farms in twelve US states. Due to fears that research might damage dairy businesses, studies like this one have been few. We need to find ways to work with dairy farms in collecting more comprehensive epidemiological data that are necessary for the design of future interventions against H5N1 HPAIV on cattle farms.