Seroprevalence of Influenza A(H5N1) Virus in Domestic Cats at Epicenter of Dairy Cattle Outbreaks, California, 2024–2026
A study in Tulare County suggests that proximity to dairy farms is a significant risk factor for domestic cats contracting highly pathogenic avian influenza.
A team of researchers led by experts from the University of Maryland and the University of Texas Medical Branch conducted a serological study of domestic cats near the epicenter of influenza A(H5N1) outbreaks in the California dairy industry. Between December 2024 and March 2026, scientists analyzed 73 serum samples collected from cats living within a 9.7 km radius of dairy farms. The findings highlight an increasing public health threat associated with the emergence of highly pathogenic avian influenza virus clade 2.3.4.4b.
The study results indicated that three out of 73 tested cats possessed neutralizing antibodies to the H5N1 virus. Two cats showed antibody titers of 1:160, and one exhibited a titer of 1:640. Notably, the seropositive group included both indoor-only and outdoor-roaming cats, suggesting diverse transmission pathways. Statistical analysis confirmed that proximity to dairy farms is a key risk factor for seropositivity in domestic pets.
Influenza A(H5N1) clade 2.3.4.4b poses a severe threat to felids, with case-fatality rates estimated as high as 90%. Historically, cats were not considered significant influenza hosts, but recent events have challenged this assumption. Transmission through raw dairy milk, meat-based diets, or close contact with infected animals on farms poses risks not only to the cats themselves but also to personnel working in the dairy industry.
Biological characteristics, including the presence of both α-2,6- and α-2,3-linked sialic acid receptors, make cats potential "mixing vessels" for genetic material exchange between avian and human influenza viruses. There is a documented risk of viral reassortment, which could lead to novel strains adapted for human infection. Previously documented cases in the United States have included transmission of avian influenza from cats to veterinarians and shelter workers.
This study, conducted in California’s Central Valley, provides critical insights into the 2024–2025 epizootic. Researchers emphasize that monitoring the health of domestic animals in regions with active farm outbreaks is now a priority. Continued investigation into H5N1 transmission mechanisms is vital to developing effective protection strategies for both domestic animals and the agricultural workforce.