UMD-led Study Shows Higher Rates of Bird Flu in Cats Near Infected Dairy Farms

University of Maryland researchers and their colleagues found that after an H5N1 bird flu outbreak on dairy farms, cats living closer to them were more likely to have bird flu antibodies, indicating their immune systems had fought the pathogen. 

Their study appears in the September 2026 issue of Emerging Infectious Diseases, and includes a call for greater surveillance of cats and companion animals.

“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 affiliate professor in the Department of Veterinary Medicine and an assistant professor and airborne infectious disease researcher in the School of Public Health.

The team analyzed blood serum samples collected from 73 feral cats and indoor cats during and after the 2024-25 H5N1 outbreak at dairy farms in California’s Central Valley. Its survey encompassed a six-mile radius around dairy farms. Three of the cats (4.1%) tested positive for H5N1 antibodies—all from within 1.25 miles of the farms (where the rate rose to 25%). True infection rates may be higher because some cats may have died from H5N1, which often causes death, paralysis or blindness.

The study could not determine 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 have simply shared 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.

Cats with bird flu are a concern for human health because the animals can be infected with both human- and bird-specific influenza strains, making them potential "mixing vessels" where genes from different flu viruses can recombine, possibly yielding a new bird flu strain capable of spreading between humans.