University of Maryland researchers and their colleagues found that after an H5N1 bird flu outbreak on dairy farms, cats were more likely to have bird flu antibodies the closer they were to the farms. Their study appears in the September 2026 issue of Emerging Infectious Diseases.
“As bird flu surges worldwide, our study—though small in geographic scale—tackles a root problem where data are scarce: increasing interspecies transmission, including spillover to cats,” said Kristen Coleman, an Assistant Professor and airborne infectious disease researcher in the School of Public Health and an affiliate professor in the Department of Veterinary Medicine. “Our epidemiological findings can help health agencies sharpen public messaging around this rapidly emerging issue and focus surveillance efforts and limited resources where they might be needed most.”
The team analyzed blood serum samples collected from feral cats and indoor cats during and after the 2024-2025 outbreak of H5N1 bird flu at dairy farms in California’s Central Valley. Their survey encompassed a six-mile radius around dairy farms. Overall, 4.1% of the cats tested positive for H5N1 antibodies, but within 1.25 miles of farms, the rate rose to 25%. What’s more, all of the cats that tested positive for H5N1 antibodies were found in that 1.25 mile radius. Infection rates may be even higher, according to the study, because some cats may have succumbed to H5N1, which often causes death, paralysis, or blindness that would have precluded them from being captured and tested during the study period.
The researchers cannot say whether the dairy herds directly infected nearby cat populations, or even whether the cats came in contact with bird flu through the farms. The cats and cattle may simply share the same source of infection, such as nearby wild birds or rodents. But Coleman said that this knowledge gap points out the importance of monitoring for infectious diseases in companion animals that can serve as conduits for emerging pathogens.
Why cats with bird flu should be a concern for humans.
Cats can be infected with both human- and bird-specific influenza strains, making them potential "mixing vessels" where genes from different flu viruses can recombine. If a bird flu virus and a human flu virus exchanged genetic material inside an infected cat, the result could be a new bird flu strain capable of spreading between humans. Currently, most documented human infections have been limited to individuals with direct exposure to infected animals, which limits transmission. But if a newly recombined virus gained the ability to spread easily person to person, it could trigger a new pandemic.
The researchers note that the total number of cats in the study was small, 73 total, with 3 testing positive for H5N1, but they say the study highlights the point that surveillance of domestic animals is an important blind spot that should be filled as health agencies seek to mitigate the threat of emerging infectious diseases such as H5N1.
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In addition to Coleman and Bemis, additional authors from the University of Maryland include Esther Fadaka and Sofia Perez from the UMD School of Public Health. Other collaborators include Ismaila Shittu and Gregory Gray from The University of Texas, Galveston, and Jacob Gomez from Cross Street Small Animal Veterinary Hospital, Tulare, CA.
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By Kimbra Cutlip
[Original article published here]