Written by Ingrid R. Niesman MS, PhD

When 38 out of 40 cats die from a disease, it’s time to take notice. A 2024 report out of South Korea describes a swift wave of infections in a closed cat shelter (1). Between June and July of 2023, symptoms of high fevers, anorexia and neurological issues were evident within the shelter, ultimately killing nearly all the cats. H5N1, clade, was confirmed by a private lab in July.  As the cats were housed separately, in groups of 4-5 cats, infected poultry in the cat food is a suspected route of transmission.

What is H5N1 and clade 

H5N1, an avian-derived Influenza A strain (IAV), was initially identified in 1996 in Guangdong Province. It has flared up globally over the intervening years as migrating birds move across continents. The letters H and N are designations of two easily mutated viral proteins, hemagglutinin (H) and neuraminidase (N). The numbers designate differences between different strains of IAV. This is how the CDC tracks and identifies influenza each year.

Viruses within the Influenza A class can be further subdivided into low pathogenicity (LPIAV) or, as in the case of H5N1, highly pathogenic (HPIAV). The H5N1 virus has evolved steadily into different groupings, called clades, based on an accumulation of multiple genetic mutations. Coincidentally, at the same time as SARS-COV2 was circulating, a new and highly pathogenic clade of H5N1 emerged, clade Since its emergence, we have seen documented reports of massive cross-species transmission worldwide.

The clade and severe feline disease  

This is not what we may usually think of as “kitty flu,” which is caused by the feline calici or feline herpes virus. The disease caused by clade is a true flu infection, and worthy of intense vigilance. Typically, we associate our seasonal human flu infections with acute upper respiratory symptoms, resulting in mild yet unpleasant effects.

In stark contrast, the HPIAV H5N1 results in severe generalized systemic disease, leading to death in a high percentage of infected cats. “There is a lot of fear out there right now. We keep getting public reports of dead and dying barn cats without diagnostic testing,” says University of Wisconsin researcher Erin Lashnits, MS, DVM, PhD, DACVIM. Particularly troubling is the clear neurological component of feline infections and the swiftness of decline after only a 1–2-day incubation period. 

Pretty Litter

Disease is spreading worldwide in domestic cats 

Naturally occurring H5N1 infections in domestic and large cats were identified as early as 2006 in Iraq and Thailand, after first being experimentally demonstrated in 2004 (2). The real worry has been since 2022, when the first described feline infections and enhanced mortality popped up in France, Poland, Italy, Finland, Spain, South Korea and now in the US. Dead and sick cats have been found in Nebraska, Kansas, and Texas, with many infections associated with dairy cattle. As is evident from current transmission data, it is just as easily passed orally as respiratory. An early release article further suggests even an ocular route of transmission is possible in cats (3). 

The implications for pet cats, community cats and feral cats 

Anytime a zoonotic infection becomes widespread, the chances for genetic swapping or mutation becomes high. In the case of clade, the DNA from the HPIAV isolate of a French cat revealed a mutation in the polymerase protein known to be a major genetic change allowing mammalian adaptation.

Scary prospects, but for now, cats are a transmission dead-end. No influenza A virus has yet been shown to fully adapt to feline physiology, unlike proven zoonotic carriers and reservoirs, such as pigs and bats.

Transmission from food sources

Caution and concern are nevertheless warranted for our feline population. Influenza virus is typically killed at temperatures associated with cooking and milk pasteurization but can thrive in aquatic environments. There are limited protective options for feral cats. Eating infected wild birds is an obvious and present danger, bad for cats and sad for wild birds. Drinking from contaminated water sources is a daily possibility.

What we do have in our control is what we feed community and pet cats. As suggested from the South Korean outbreak, infected chicken and duck products can be a threat in cat food. Raw milk is considered a possible source of transmission on dairy farms. “The high viral load of H5N1 in raw milk poses a real risk to barn cats,” explains Dr. Lashnits.

Cats thrive on many commercial raw diets. After all, wild cats, big or small, eat raw prey. Given what is currently understood about the serious mortality to cats from this clade of H5N1, cat parents should carefully evaluate what they serve their cats, and where that food is sourced. Food safety in the US is a high priority, but we have been slow in recognizing the full extent of this new threat. Infections in cattle may have been smoldering for months before the first human case uncovered the sick cows.

Darwin’s Natural Pet Products, a leading manufacturer of commercial raw foods, has been watching the recent developments carefully. Their source farms are strictly US based and carefully monitored and inspected.  Brittany Rees, Associate Director of Brand Marketing, recognizes their clients’ concerns. “We are monitoring our farms closely,” she says. “Our Senior Director of Supply Chain has been keeping an active eye on the issue and ensuring our poultry farms are taking all steps needed to ensure the poultry used in our meals is safe.” This includes testing flocks for illness. Per the USDA, if any bird tests positive for H5N1, the flock will be depopulated. This prevents any poultry infected from making it on the market. “We are on top of the situation and issues,” adds Rees. “At this time, we are confident none of our farms have been impacted by this virus.”

As our cats are fully reliant on meat protein, more pet food manufacturers should follow Darwin’s lead. Using only USDA inspected human-grade meats can help prevent a tragedy like the South Korea shelter and multiple suspected cat deaths in Poland.


Follow the news, but do not panic

In an assessment of US beef, the USDA now reports that H5N1 is not found in properly cooked ground beef (CIDRAP, 5/16/24). As the virus is killed at cooking temperatures, fully cooked poultry is less of a risk. If you feed home cooked meats or fish to your cats that you source from the grocery store rather than a reputable manufacturer, cooking it well is the best advice.

Infections, nonetheless, are spreading. The CDC is tracking the virus in wastewater and is reporting more dairy outbreaks daily. As of 5/15/24, there are 39 confirmed dairy herd infections, spread across 9 states. New infections on poultry farms and backyard flocks are popping up. Keep informed of developments, but, as Dr, Lashnits explains, “If you are simply owner of a cat and not owner of a cat and dairy, chances of an infection are pretty much zero.”

Cats are loving their new Cat Box Classics Cardboard Cat Houses

Importance of individual awareness for prevention and containment

Sadly, we had to wait until there was a verified human infection before the death of two cats and reductions in milk production by cows caused concern about a possible infectious disease. What we don’t want to happen is a major spillover event that radically mutates this clade into a full mammalian adapted pathogen. Due to their quasi-domesticated status, cats provide a possible “canary in a coalmine” situation. More cats dying from this virus should be an immediate eye-opener for public health authorities.

A much better scenario is keeping our cats safe from possible infections. As cat parents, evaluate the need for your cat to wander outdoors this summer, especially if they are noted bird catchers. Provide plenty of clean fresh water if they are outdoors. Watch for pet food warnings and toss any suspected foods. Immediately isolate any cat you suspect may have encountered any infected food sources, water, or other sick cats to prevent cat-to-cat transmission. These are all common sense precautions.

Do we have to worry? 

Obviously, the threat of a deadly cat influenza strain is distressing. We are not yet at the point of declaring a reason to panic. Use the advice from your veterinarian, CDC, WHO, and One Health to make appropriate choices for you and your cats. I will be closely monitoring all incoming reports myself.  For the conceivable future, my kids are indoors and can just watch the bird feeders and drool.

Ingrid R. Niesman MS PhD is the Director of the SDSU Electron Microscope Imaging Facility at San Diego State University. She graduated from Utah State University and received her MS from the University of Illinois-Urbana-Champaign. After 30 years of technical electron microscopy, cell biology, neuroscience and infectious disease research, Dr. Niesman completed her PhD in the UK at the University of Sunderland. Her work experience includes time at LSU Medical School, Washington University, UAMS in Little Rock, UCSD, TSRI and a postdoctoral year at CALIBR in La Jolla, CA. She has worked for at least two National Academy of Science members and is credited with over 50 publications. She can be reached at [email protected]


  1. Lee, K., et al. (2024). “Characterization of highly pathogenic avian influenza A (H5N1) viruses isolated from cats in South Korea, 2023.” Emerg Microbes Infect 13(1): 2290835
  2. Kuiken, T., et al. (2004). “Avian H5N1 influenza in cats.” Science 306(5694): 241.
  3. Burrough, E. R., et al. (2024). “Highly Pathogenic Avian Influenza A(H5N1) Clade Virus Infection in Domestic Dairy Cattle and Cats, United States, 2024.” Emerg Infect Dis 30(7).

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4 Comments on H5N1 Infections in Cats: Surveillance is Warranted, Panic is Not

  1. Dear Ingrid, thank you for this very informative article. It is very important news that you have sent us. And I was particularly thankful for the report from Darwins since both Allegra and Cricket eat that. Sometimes you are interesting. And other times you are Really Important. Thanks Ingrid.

    • I’m glad this was helpful. It was important to me to get input from Darwin’s on this topic since I know many of our readers feed it.

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