By Sarah Boden
More than 80 domestic cats, among many other types of mammals, have been confirmed to have had bird flu since 2022 — generally barn cats that lived on dairy farms, as well as feral cats and pets that spend time outdoors and likely caught it by hunting diseased rodents or wild birds.
Now, a small but growing number of house cats have gotten sick from H5N1, the bird flu strain driving the current U.S. outbreak, after eating raw food or drinking unpasteurized milk. Some of those cats died.
There have been no known cases of cat-to-human transmission during the current outbreak of H5N1.
Still, there’s always been the risk that cats, which are arguably only semi-domesticated, could bring home a disease from a midnight prowl.
“Companion animals, and especially cats, are 100% a public health risk in terms of the risk of zoonotic transmission to people,” said virologist Angela Rasmussen, who studies disease progression in emerging viruses at the University of Saskatchewan’s Vaccine and Infectious Disease Organization.
This is because we snuggle with and sleep in bed with our cats. When we’re not looking, cats drink from our water glasses and walk on kitchen counters.
So, cat owners should be aware of the ongoing spread of bird flu.
Rasmussen doesn’t think pet owners should be afraid their cats will give them bird flu but said taking precautions is good for pets, and for public health.
Signs of bird flu in cats include runny nose and discharge around the eyes, explained Michael Q. Bailey, president-elect of the American Veterinary Medical Association. Bailey encourages people to ensure pets are up to date on their vaccinations.
Veterinarian Jane Sykes, who specializes in infectious diseases in cats and dogs at the University of California-Davis School of Veterinary Medicine, said people should not assume it’s bird flu if their cat is sick — even if their animal spends time outdoors or eats a raw diet. Upper-respiratory illnesses are common in cats, while H5N1 is “still pretty rare.”
Sykes gives her indoor cat, Freckles, regular kibble exclusively. She has no concerns about Freckles getting H5N1
because the heating process of making dry or canned pet food kills viruses.
More Cases in Cats, More Risk to Humans
Some people feed their pets raw meat or unpasteurized milk because they think it’s a more nutritious or natural diet. The American Veterinary Medical Association’s website discourages this due to foodborne pathogens like salmonella and listeria, and now the highly pathogenic H5N1.
By keeping pets healthy, veterinarians play an essential role in protecting humans from zoonotic diseases. The American Veterinary Medical Association says the risk of H5N1 spilling over from a pet to a person is “considered extremely low, but not zero.”
Concerns for human health are partly why the FDA announced last month it is now requiring cat and dog food companies to update their safety plans to protect against bird flu.
This came after the Oregon Department of Agriculture discovered a cat that was “strictly an indoor cat” had contracted H5N1 and died after consuming a frozen turkey product made by the raw pet food brand Northwest Naturals. It stated that “tests confirmed a genetic match between the virus in the raw and frozen pet food and the infected cat.”
Los Angeles County’s public health department said five cats from two households tested positive for bird flu after drinking unpasteurized raw milk from the Raw Farm dairy in California’s Central Valley. Raw Farm voluntarily recalled its milk and cream after retail products tested positive for H5N1,
Veterinarians also warn pet owners not to allow cats unsupervised time outside as there’s the risk of them getting H5N1 by interacting with other animals that might carry the disease.
There isn’t a lot of research on transmission of bird flu from companion animals like cats or dogs to humans, though Rasmussen agreed it’s definitely a concern:
Most people who have caught H5N1 are agricultural workers who had direct contact with infected poultry or cattle. Of at least 67 confirmed human cases of H5N1 in the U.S., there’s been one fatality in an immunocompromised person who had contact with birds.
Chances for Mutation
Part of the concern with this H5N1 outbreak is that bird flu viruses change. Just a few mutations could make this strain adept at spreading between people.
Another concern is something called reassortment. If an animal or person is infected with two viruses at once, the viruses can trade genetic material, creating something new. This is common in influenza, so virologists are on the lookout for a case in which the bird flu reassorts to make a virus that’s far more contagious, and potentially more virulent.
Virologist Rasmussen is way more worried about this happening in pigs. Human respiratory physiology is more like that of swine than felines. So far, the current outbreak of H5N1 has not reached commercial hog operations.
Reassortments are relatively rare events, but the outcome is completely unpredictable. Sometimes the results are benign, though it was likely a reassortment that involved an avian virus that led to the 1918 flu pandemic, which killed an estimated 50 million people. In the century since, virologists have established a global surveillance network to monitor influenza viruses.
Winter is “reassortment season” because of all the influenza viruses circulating, Rasmussen said. A reassortment in cats could technically be possible since these pets occasionally get seasonal flu, but it’s highly unlikely. Rather, Rasmussen said, it’s more likely that a cat would pass H5N1 to a human who already has seasonal flu, and then a reassortment happens in the sick person.
“Unless the cat is really shedding a ton of virus, and you’re kind of making out with the cat, I think it would be hard,” she said.
Rasmussen caution there isn’t enough research to know for sure how much virus cats shed, or even how they shed the virus.
The Centers for Disease Control and Prevention was poised to release a new study about H5N1 in cats, but that was delayed when the Trump administration paused the Morbidity and Mortality Weekly Report.
Dogs Seem To Fare Better
The FDA says other domesticated animals, including dogs, can get bird flu infections. There are no confirmed cases of H5N1 among dogs in the U.S., though in other countries they have died from the virus.
There’s some disagreement and an overall lack of research on whether cat biology makes them more susceptible to H5N1 than other mammals, including humans, pigs, or dogs.
Sarah Boden contributor to KFF Health News, is a magazine writer who specializes in health care coverage. Her reporting examines how social, environmental, and economic forces shape public health in the U.S. She has won numerous awards for her health care coverage, including a 2023 Keystone Media Award for her series “The expense of forgetting: Dementia’s tax on financial health”
