Cat Hunting

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Cats can catch the highly pathogenic avian influenza virus, H5N1, from contact with infected birds, including through hunting.

While talking to a pet owner about their cat's diet recently, Dr. Liz Grauer was asked a question that stumped her: Is freeze-drying pet food an effective way to kill pathogens in raw food?

A practitioner in Washington state, Grauer turned to colleagues at the Veterinary Information Network, an online community for the profession, for an answer. No, she learned, freeze-drying doesn't necessarily kill germs in raw food.

For Grauer, the query wasn't just about avoiding common food-borne bacteria like Salmonella but about a pathogen she's increasingly concerned about: the avian influenza virus.

Though her clinic has not seen a case, she believes encountering a feline patient with avian flu is inevitable. "I know it's going to happen here," Grauer said. "I mean, it's happening everywhere."

The U.S. Department of Agriculture is logging a rising number of cases in domestic cats. In 2023, it reported 12 detections in cats of a highly pathogenic subtype of avian flu, known as H5N1. In 2024, the number rose to 49. This year, in January alone, there were 13. (These figures do not include seven cases in January and two cases in 2024 attributed to "H5" influenza virus but not specifically to H5N1.)

The documented cases have occurred mostly in the West and midsection of the country, including California, Oregon, Montana, South Dakota and Michigan. While some of these cases involved barn cats — animals exposed to avian flu through close contact with infected livestock — many were urban or suburban house cats that had not set foot on a farm or even outside.

This trend has effectively moved avian flu, a disease primarily of wild birds and domestic fowl raised for food, into the purview of companion animal practitioners.

H5N1 originated in and spreads widely in birds. It can infect animals besides birds but is less adapted to them, meaning it doesn't spread as effectively, according to Dr. Scott Weese,  an infectious disease veterinarian at the University of Guelph who reports on the outbreak in his Worms & Germs Blog. A virus' transmissibility depends on its ability to latch onto an animal's cell receptors to cause infection. Sometimes, when a flu virus spreads to a new species, that virus becomes particularly adapted to it and can spread effectively within that group. The canine influenza virus H3N2 began in birds but adapted to spread from dog to dog, making birds no longer part of the equation, Weese explained.

Exactly why cats are more susceptible to H5N1 than some other mammals isn't clear. Weese said it might be because the virus is better able to attach to feline cell receptors. The primary infection pathways for cats presumably are direct contact, respiratory secretions and ingestion through diet.

Cats infected with H5N1 can become very sick quickly. Initially, they may be lethargic and lose their appetite. They may develop a fever. Soon, they might cough and sneeze, with discharge from their nose and eyes. At the peak of illness, cats may develop neurological signs, such as tremors, walking in circles, losing muscle control and balance, and seizures.

Highly pathogenic avian influenza in cats often is fatal. Research at the University of Maryland, posted in December and not yet peer reviewed, found that cats with H5N1 infections had an overall mortality rate of 71%. Treating cats for the flu consists of managing their clinical signs.

Widely considered to have originated from wild birds in Europe, this outbreak of H5N1 was first detected in a United States commercial poultry flock in February 2022. Since then, the confirmed number of affected birds in commercial or backyard poultry operations has reached more than 153 million, according to figures from the U.S. Department of Agriculture. Flocks that test positive for the virus are isolated and exterminated.

Last year, H5N1 hit dairy herds in the U.S. First detected in cows in March 2024 in Texas, then Kansas, then Michigan, the virus reached cows in California, the nation's largest milk producer, in August.

People are susceptible, as well. To date, there have been 67 confirmed cases in the U.S. of H5N1 avian flu in humans, and on Jan. 6, the state of Louisiana reported the first death. As of now, the disease is not known to spread from person to person. 

"This is still a significant public health disease," said Dr. Ryan Scholz, Oregon's state veterinarian. "Allowing this disease to circulate allows it more opportunity to mutate, allows it more opportunity to affect more animals, and more opportunity to potentially affect people."

Raw food as a source for infection

In December, an Oregon house cat who died suddenly after a short illness was submitted by the cat's veterinarian to the Oregon Veterinary Diagnostic Laboratory for a necropsy, Scholz said.

The cat had become sluggish and tired, as if in a stupor, he explained. A pathologist detected encephalitis — inflammation of brain tissue — which immediately triggered tests for rabies and influenza. From a conversation with the owner, an investigator determined that while the cat occasionally took walks on leash, it hadn't been outdoors in some time due to the wet Oregon fall.

"We started digging a little deeper and found that she was feeding a raw pet food," Scholz said. "The cat food ended up being positive for virus. And more than just the cat food being positive, they were an exact whole genome sequence match."

The exact match left Scholz confident that the raw diet was the source of the infection. As a result, the pet food company, Northwest Naturals, recalled one batch of its 2 lb Feline Turkey Recipe raw frozen pet food, which was sold in 12 states and British Columbia.

Another raw food product was implicated in a separate case in late December in Los Angeles. Just days after the report of the feline case in Oregon, the Los Angeles County public health department stated that avian flu virus had been detected in a cat and in several samples of Monarch Raw Pet Food sold at farmers markets in California. The county said four other suspected, but unconfirmed, cases were linked to the same food.

"Testing confirmed that product of unopened Monarch Raw Pet food was positive with live and infective influenza A H5N1 virus," a health department representative told VIN News by email. "Sequencing performed on the Monarch Pet Food samples confirmed a direct link between the pet food and the cat." The health department added that a different brand of raw food eaten by the cat, which had been kept strictly indoors, was negative for the virus.

Following the county's press release, Monarch Raw Pet Food posted a company press release referring to the report as "misinformation" and stating that "these claims are not substantiated by any scientific evidence at this time." It did not recall the product.

Contacted for further comment, a company representative told the VIN News by email this week that local agencies "have not requested a recall. To the best of our knowledge, there have been no additional cases involving Monarch products."

Conversations with cat owners

Back in Washington, where news broke in December about 20 felines dying of avian flu at a big cat sanctuary, Grauer has been keeping H5N1 top of mind.

"I'm a big proponent of being prepared for it," she said.

Her preparations include monitoring and contributing to online discussions and advising clients to stay away from potential infection pathways such as raw food. And should she see a cat suspected of having avian flu, she'll keep it away from all other animals and clients, with only staff equipped with personal protective gear interacting with the cat until its diagnosis is confirmed. Grauer added that she'd likely call around to specialty or emergency clinics in the area that might be better equipped to isolate a patient.

"I know if I see a really sick cat with respiratory signs, I'm going to put it immediately under quarantine," she said.

In New York City, most of the feline patients seen by Dr. Ann Hohenhaus, a senior veterinarian at the Schwarzman Animal Medical Center, are apartment dwellers. But pet food isn't the only topic coming up in her conversations with clients on how to mitigate H5N1 risks.

She recalled one email from a client asking whether their cat could catch bird flu from pigeons landing on their open window.

"I have more than one time had a client come home to a big pigeon in their apartment and the cat being very proud of the pigeon that it captured inside the apartment," Hohenhaus said. She recommends that clients screen their windows.

As for the pet food risk, she advises veterinarians to inquire about patients' diets.

"They're not always going to follow it, but they want to hear from you about diet," Hohenhaus believes. "Veterinarians need to be proactive in finding out what people are feeding and then making solid recommendations. In this case, scrap the raw food, because I'm more worried than I ever was before."

Dr. Anne Kimmerlein, a veterinary epidemiologist at VCA Animal Hospitals in California, said it's important for veterinarians to ask detailed questions about a pet's diet while taking their history.

"Keep in mind that [raw] pet food and treats may be sold as freeze-dried, and clients may not know that they are feeding a raw diet," Kimmerlein said in an interview by email.

Recognizing that raw diets are an issue that some clients feel passionate about, it's important to be respectful, she said.

"People who feed raw diets to their pets are doing so because they believe it is best for their pets' health," she said. "It is imperative that we, as veterinarians, respect what our clients feel is important while also educating them about the risk of feeding raw diets to their pets. For clients who are adamant about feeding raw diets despite the associated risks, it is important to provide risk reduction methods."

Kimmerlein suggests that they avoid raw diets with poultry and monitor their pet food brand for any association with avian flu.

Some practitioners advise cooking raw food to kill the influenza virus and other pathogens, but heating a diet designed to be eaten raw could alter its nutritional profile, potentially causing other problems, experts in veterinary nutrition caution.

To owners of cats suspected of having the flu, the American Veterinary Medical Association advises calling ahead to the veterinary clinic before arriving. "Describe any clinical signs ... noticed so that the veterinary team can be ready when the patient arrives," the AVMA recommends. 

For veterinarians encountering a suspected case of avian flu in cats, Scholz, the state veterinarian in Oregon, encourages reporting the case to government authorities early, even before a diagnosis is confirmed.

"I hear it over and over from vets that they don't want to waste our time," Scholz said. "In most cases with immediate reportable diseases, we want to know before you test."