“As companion animals, domestic cats provide a potential pathway for avian influenza viruses to spillover into humans,” said Kristen Coleman, an assistant professor in the UMD School of Public Health, and an affiliate professor in the University of Maryland Department of Veterinary Medicine.

“We looked at the global distribution and spread of bird flu infections in feline species between 2004 and 2024 and found a drastic rise in reports of feline infections starting in 2023, with a spike in infections reported among domestic cats, as opposed to wild or zoo-kept animals. This increase coincides with the rapid spread of the current strain of H5N1 among mammals.”

Bird flu is not currently reported to be contagious between humans, and it is not guaranteed to evolve in that direction, but the disease is clearly changing. The current strain of the H5N1 has been spreading to animals that have never been affected before, and pets that can pass it to people could play a role in how it evolves.

Coleman’s study, currently in preliminary form without peer review on MedRxiv, found that cat owners, veterinarians, zookeepers, and cat shelter volunteers may be at greater risk of contracting the H5N1 infection if the virus continues to circulate unabated. The CDC, which provides guidance for veterinarians working with potentially infected animals, says the risk of contracting the disease from pets is low, but Coleman suggests pet owners should still take precautions to protect their cats and themselves.

“Don't feed your cat raw meat or raw dairy milk and limit their unsupervised time outdoors,” she said. “Cats prey on wild birds that could be infected, and they could get into raw dairy milk on a farm if it is not securely stored.”

In addition, the virus has been reported in house mice, which cats also prey on, so it appears the opportunities for cross-species transmission are increasing, and pet cats may be at increased risk.

Pet owners should be watching for respiratory and neurological symptoms. If your cat seems to have trouble breathing or is acting unusual, you should consider taking them to the vet. The current H5N1 strain has also reportedly caused blindness in cats.

Since the emergence of H5N1 in U.S. dairy cattle, 21 domestic cats have been reported to be infected to date. Full genetic sequences of the viral strains infecting 2 of these cats have been reported in the scientific literature. Coleman said sequencing and demographic data for the other cat cases are urgently needed.

Why Cats?

Avian influenza, or bird flu, was once a finicky disease, infecting mostly migratory waterfowl and farmed poultry. But since 2020, the highly infectious strain known as H5N1 began spreading among a wider variety of birds. It has recently been appearing in a growing number of mammals, even decimating whole colonies of sea lions throughout South America. In April 2024, it appeared for the first time in dairy cattle in Texas, and a farm worker contracted the disease after interacting with sick animals. Two farm cats that were fed unpasteurized milk also became infected.

Although the disease is new among many animals, cats have been occasional victims of avian influenza for decades, most likely because they eat birds and are exposed through sick or dead prey carrying the virus.

Coleman reports that the fatality rate for the current strain of H5N1 in cats has been around 67%, which in itself is a good reason for pet owners to keep their cats inside and away from wild birds. She found a number of other worrying aspects of the disease in cats.

• There have been multiple reports of cats contracting bird flu from other cats, both in zoos and animal shelters, suggesting the disease could cause repeated outbreaks among these animals.

• Both zookeepers and animal shelter workers have contracted bird flu from cats in their care.  Although not the current H5N1 strain, these cases reveal cats as potential vectors for the disease in humans.

• In April, 2024, two farm cats got H5N1 from drinking raw milk from an infected dairy cow in Texas, showing that cats can contract this new variety from other mammals.

These factors, along with the rise in frequency of feline infections, the severity of disease and the close proximity of cats to their human companions, suggest that public health officials should consider a One Health approach to mitigating the disease beyond dairy cattle and humans. A One Health approach suggests cats and other animals should be monitored for the disease not only for their sake, but for the protection of human health as well.

“The virus is going to sneak up in more places, just like it did in dairy farms. We know cats are being infected, so let’s get ahead of it,” Coleman states.