Cats Near Dairy Farms Have High H5N1
A study shows 25% of cats near H5N1-infected California dairy farms have virus antibodies, indicating their potential role in spreading the disease.
One in four cats living near active H5N1 dairy cattle outbreaks in California tested positive for antibodies against the virus. The research 2026 in the CDC's Emerging Infectious Diseases journal, was led by scientists from the University of Maryland School of Public Health and the University of Texas Medical Branch.
Scientists collected serum samples from 73 cats in Tulare County, California, between December 2024 and March 2026. This period coincided with the peak of the H5N1 dairy cattle crisis in the state's Central Valley. three cats tested positive for both influenza A nucleoprotein antibodies and neutralizing antibodies against the H5N1 clade 2.3.4.4b virus, resulting in a total seropositivity rate of 4.1%.
Proximity Drives Exposure
The risk was not evenly distributed. When researchers focused only on cats living within 2 kilometers of a dairy farm, the seropositivity rate jumped dramatically to 25%. This proximity signal is the study's most significant finding.
On average, cats that tested positive lived 1.34 kilometers from the nearest dairy farm. Seronegative cats lived an average of 4.83 kilometers away. The exposure pattern held across different types of cats, including one outdoor feral cat and two indoor-only cats. Both indoor cats lived in the household of a dairy industry worker.
A Biologically Concerning Position
Cats occupy a worrying position in the H5N1 risk landscape. Like pigs, they carry receptors that bind both human and avian influenza strains. The study authors state this biological fact makes cats "a candidate mixing vessel for viral reassortment." In theory, a cat co-infected with avian and human flu strains could generate new variants with enhanced ability to spread among people.
This concern is not purely theoretical. Documented cat-to-human influenza transmission has occurred three times in the United States. One case involved a veterinary professional in Los Angeles exposed to an H5N1-infected cat in 2024.
The estimated case-fatality rate for cats with confirmed H5N1 infection is about 90%. This high mortality rate means the seroprevalence figures reported in the study likely underestimate true infection rates. Cats that survive a mild infection contribute to the antibody count. Those that die from severe symptoms like acute encephalitis, paralysis, or blindness do not.
Study Limitations and Sentinel Potential
The study's authors acknowledge important limitations. With only three seropositive animals, the findings are suggestive rather than conclusive. The small sample size limits statistical power. Samples came from routine veterinary blood draws at a single animal welfare organization, so the population studied may not represent all cats in the region. The exact source of transmission for the three positive cats could not be confirmed.
Despite these limits, the research highlights a surveillance gap. Monitoring of companion animals has lagged far behind livestock and wildlife monitoring during the H5N1 dairy cattle crisis. The authors argue that cat surveillance could serve as an early warning system. It could flag nearby H5N1 activity in cattle or poultry that has not yet been detected through conventional channels.
The authors point to vaccinating dairy cattle as a structural solution that could reduce spillover risk to cats and, by extension, to the humans living and working near them. Until such protection is widespread, guidance for farm workers, veterinarians, and pet owners near affected farms remains a critical and underdeveloped part of the public health response. The research was sourced and reported by Global Biodefense.
