Last updated on February 22nd, 2025 at 10:58 am

Recent reports have established that the H5N1 form of bird flu may be infecting your domestic cat and may pose a large risk to public health. A small but growing number of house cats (those cats that do not go outside) have gotten sick from H5N1 after eating raw food or drinking unpasteurized milk. Some of these cats have died.

Since 2022, more than 80 domestic cats and many other mammals have been confirmed to have contracted bird flu. Most of these cats lived on dairy farms, although there were feral cats that spent time outdoors and probably caught the disease by hunting diseased rodents or wild birds.

Although this is concerning, the strain of H5N1 that is currently circulating has not adapted to spread efficiently between people. Moreover, there have been no known cases of cat-to-human transmission of H5N1 during the current outbreak. However, viruses that circulate widely in other mammals can mutate to become highly infectious in humans, so it bears watching.

What is H5N1 bird flu?

Avian influenza, or what everyone is now calling “bird flu,” is a type A influenza subtype designated as A(H5N1). The designation is based on antigens common to this influenza subtype.

Avian influenza viruses are classified into subtypes, which are named according to subtle variations in the structure of two key proteins on the virus surface — hemagglutinin (H) and neuraminidase (N). The hemagglutinin protein is what allows the virus to attach to the cell surface of the host, and then infect the cells. In general, H1 and H3 are best able to attach to human cells, while H5 is best at attaching to bird cells. However, H5 could mutate to a form that makes it better at attaching to human cells, and that would lead to human-to-human transmission of the disease.

Another avian influenza is designated as A(H5N9), but the current bird flu outbreak appears to be the H5N1 subtype. Thus, H5N9 and H5N1 have the same hemagglutinin protein, but a different neuraminidase protein.

As the name implies, these viruses usually affect birds but can occasionally pass from birds to humans, cattle, pigs, and other animals. The H5N1 subtype arose in Asia a few years ago and has spread worldwide. It is highly pathogenic (meaning it can cause disease in humans) and has passed to humans several times.

Infected birds shed the virus through their saliva, mucous, and feces. Human infections with bird flu viruses can happen when the virus gets into a person’s eyes, nose, or mouth, or is inhaled. This can happen when the virus is in the air (in droplets or possibly dust) and a person breathes it in, or possibly when a person touches something that has the virus on it and then touches their mouth, eyes, or nose. Human infections with bird flu viruses have occurred most often after unprotected contact with infected birds or surfaces contaminated with bird flu viruses. However, some infections have been identified where direct contact with infected birds or their environment was unknown.

There are numerous cases where bird flu has been transmitted between humans, but most infections of humans are from constant contact with infected birds. Human infection with avian influenza A virus poses pandemic potential, so CDC and other public health agencies investigate every case to assess whether human-to-human transmission might have occurred. Detailed public health investigations can help determine whether person-to-person spread of an avian influenza A virus occurred.

The signs and symptoms of bird flu infections in humans can range from nothing to severe. The infections are similar to other flu infections including fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, and shortness of breath.

According to data collected by the WHO, there have been 954 documented cases between 2003 and 2024. Of those, 464 were fatal, leading to a fatality rate of about 49 percent among the documented cases.

Domestic cats and H5N1

As I wrote above, there are not a lot of cases of domestic, house-bound cats contracting H5N1. Usually, that is from uncooked food and unpasteurized milk. Most cat food (whether wet or dry) is heated which kills these viruses, and there is no evidence that raw food or unpasteurized milk is healthier for your cat.

Most importantly, there are no known cases of cat-to-human transmission of H5N1.

Unfortunately, cats that are allowed outside, even for short periods, could bring home H5N1 from a prowl in the yard. Cats are a public health risk of zoonotic transmission to people. Cats love to snuggle us (mostly) and sleep in our beds. They also drink and eat from our food surfaces when we’re not watching. All of these are an excellent pathway for diseases to move from cats to humans.

In cats, H5N1 may cause a runny nose and discharge around the eyes in early stages. However, cats often have upper respiratory tract infections, so it probably isn’t H5N1. Unfortunately, H5N1 can lead to neurological problems like dizziness and seizures similar to rabies, but a good cat owner will have their pet up-to-date with appropriate vaccinations. Sadly, some cats that contract H5N1 will die.

If your cat is sick, don’t assume it’s bird flu.

The Oregon Department of Agriculture discovered a cat that “strictly an indoor cat” had contracted H5N1 and died after consuming a frozen turkey product made by one of those raw pet food companies that advertise as being healthier. The Department stated that “tests confirmed a genetic match between the virus in the raw and frozen pet food and the infected cat.”

The Los Angeles County Department of Health reported a case where five indoor cats were fed raw food. Four of the cats developed severe diseases, and two died. In another case, one cat developed an “acute onset of disease” after consuming three different brands of raw food. Five other cats from two different LA County households have also been confirmed with H5N1 after drinking raw milk for human consumption — all five of those cats died from H5N1.

If you’re reading this, please stop giving your cats raw food and milk. It can kill them.

What’s the risk to humans?

Most people who have contracted H5N1 bird flu have been agricultural workers who have direct contact with infected cattle and poultry. So it does move from animals to humans, and it probably is only a matter of time before it moves from companion animals, like cats, to humans.

One of the major concerns with this H5N1 outbreak is that the virus can mutate. Just a few mutations could make H5N1 better adapted to spreading to and between people. Moreover, the more people who catch H5N1, the more likely it will adapt to being more efficient.

Another huge concern is that if an animal or person is infected with two viruses at the same time, the viruses can trade genetic material, in a process called reassortment, creating a new, more dangerous virus. Reassortment is common in influenza, so scientists are watching carefully if and when H5N1 reassorts to create a virus that is more contagious and virulent.

Winter is the “reassortment season” because a lot of viruses are circulating. A person could have a different strain of flu and contract H5N1 from their cat — those two types of flu could reassort into a more powerful and dangerous strain.

Admittedly, most of these scenarios are not likely. Cats and humans have very different respiratory systems. Still, there is a non-zero chance that H5N1 passes from cats to humans, then reassorting into something more dangerous. It just takes one time for an outbreak to happen.

Just because this reassortment is very rare, and it is probably (but not guaranteed) to not happen, why are we worried? The 1918 flu pandemic, which killed 50 million people worldwide, was caused by an H1N1 avian flu virus that had probably been reassorted in some animals and jumped to humans. That’s why we watch these new strains of flu very carefully.

One more thing, the FDA states that dogs can get bird flu infections. However, there have been no confirmed cases of H5N1 in dogs in the USA, but there have been reports of dogs that have died from the virus in other countries. However, if you feed your dog raw food or unpasteurized milk, the risk of H5N1 becomes greater.

Summary

Right now, we have a few facts. First, domestic cats that roam outside may be able to pick up H5N1 from other animals, especially birds. Second, domestic, house-bound cats may contract the disease from raw foods and unpasteurized milk. Third, there have been no cases, so far, of cat-to-human transmission of H5N1. Fourth, many cats that do catch H5N1 die from the disease.

Despite the low risk, I need to remind people that it is not a zero risk. Eventually, just the right mutation could make cat-to-human transmission a reality.

It appears that a lot of scientists are monitoring the situation. I just hope the CDC can put resources into this situation, but it bears watching.

Citations

• Burrough ER, Magstadt DR, Petersen B, Timmermans SJ, Gauger PC, Zhang J, Siepker C, Mainenti M, Li G, Thompson AC, Gorden PJ, Plummer PJ, Main R. Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus Infection in Domestic Dairy Cattle and Cats, United States, 2024. Emerg Infect Dis. 2024 Jul;30(7):1335-1343. doi: 10.3201/eid3007.240508. Epub 2024 Apr 29. PMID: 38683888; PMCID: PMC11210653.
• Chothe SK, Srinivas S, Misra S, Nallipogu NC, Gilbride E, LaBella L, Mukherjee S, Gauthier CH, Pecoraro HL, Webb BT, Pipas JM, Ramasamy S, Kuchipudi SV. Marked neurotropism and potential adaptation of H5N1 clade 2.3.4.4.b virus in naturally infected domestic cats. Emerg Microbes Infect. 2025 Dec;14(1):2440498. doi: 10.1080/22221751.2024.2440498. Epub 2024 Dec 17. PMID: 39648950; PMCID: PMC11654043.