Bird flu wasn’t on Tim Hanson’s mind when he fed his cats specialty pet food containing raw chicken. “You go to the pet shop and it was the premium raw food,” he said. “It was finely ground to a consistency that I thought was beneficial to my cats.” But in early February, one of hi s cats, Kira, developed a fever and stopped eating. A test ordered by a veterinarian came back positive for bird flu. Within days, Kira’s condition had deteriorated — she became lethargic and had trouble breathing. After several trips to the vet and emergency room in Portland, Oregon, where Hanson lives, he made the painful decision to put Kira down.  “She was the happiest cat I’ve ever had,” he said. “You’d walk past her and she’d do a little back flip and get on her back so you could rub her belly. She did that in the hospital the last night… She just very lethargically flopped on her back so we could rub her belly.” The manufacturer of the pet food, Wild Coast Pet Foods, subsequently recalled lots of the formula Kira had consumed due to potential bird flu contamination.  Hanson filed a lawsuit against the company earlier this month, alleging that it had failed to disclose the risk of bird flu in its raw pet food. He is seeking roughly $8,000 to cover the cost of Kira’s veterinary bills. Wild Coast did not respond to a request for comment. In a letter to customers, the company said it had “transitioned to fully cooked poultry recipes to eliminate any potential risk.” Tim Hanson’s cat Kira in the hospital. (Tim Hanson) According to the U.S. Agriculture Department, 126 domestic cats in the U.S. have been infected with bird flu since 2022. Around half of those cases were recorded this year, and many were exposed through food or milk.   “We see continued reports of cats with bird flu infection from across the country, and it’s kept increasing in the past months,” said Suresh Kuchipudi, professor of infectious diseases and microbiology at University of Pittsburgh School of Public Health. In cats, bird flu tends to be swift and lethal. Although the overall risk to indoor cats is low, Kuchipudi and other experts who study or diagnose the infections say the threat is mounting. With bird flu spreading rampantly among poultry and cattle, there is a constant opportunity for the virus to enter the raw food supply. And while there’s no evidence yet that cats can transmit bird flu to people, the potential increases as more cats get sick. “We don’t have the evidence, but it doesn’t mean that it may not have happened, or it can’t happen,” Kuchipudi said. At least 3 pet food recalls in 4 months Most pet food is heated to a high enough temperature to kill pathogens before it’s packaged, but bird flu can linger in raw food if it’s sourced from infected poultry — for instance, from chickens that were culled due to an outbreak.  “The animals that were depopulated could potentially have ended up in the food chain for pets,” said Laura Goodman, an assistant professor at Cornell University’s Baker Institute for Animal Health. “It’s not uncommon for substandard meat to end up in the pet food chain.” In the last four months, at least three pet food manufacturers have recalled batches containing raw poultry. The Food and Drug Administration in January warned manufacturers using uncooked meat to reassess their food safety plans in light of the recent cat illnesses and deaths. Other cats have been exposed to bird flu on dairy farms, likely from drinking raw milk from infected cows. And in some instances, outdoor cats have picked up the virus directly from dead birds.  A Centers for Disease Control and Prevention report in February also described two indoor cats that lived with dairy farm workers and contracted bird flu. The research suggests that “individuals who are working on dairies or hauling milk have the potential to carry virus into their house on their clothing or on their shoes, and in turn the cats then are exposed,” said Kimberly Dodd, dean of the Michigan State University College of Veterinary Medicine, who coauthored the report. There is no active surveillance for bird flu in healthy cats, so cases could be underreported. A study of stray cats in the Netherlands found that nearly 12% were positive for bird flu antibodies. “We may be only testing the sickest cats or one cat from a household. It’s very likely that there have been many cases out there that the cat was not brought to a veterinarian or testing wasn’t done,” said Kristy Pabilonia, director of veterinary diagnostic laboratories at Colorado State University. Pabilonia oversaw the diagnostic testing for a hairless cat named Leonardo DiCaprio, who was found to have bird flu in January. Leo’s owner, Steve Werfelmann, said his cat had eaten chicken-based raw pet food from the company Savage Pet, which recalled dozens of batches earlier this month. Steve Werfelmann’s cat Leo. (Steve Werfelmann) “When we adopted him, that was the recommended food” for his skin, Werfelmann said. “But then talking to the vet and going through this process, they actually told us there’s no real scientific evidence to back up raw food being better.” Savage Pet referred NBC News to an online statement, which says “all of our poultry ingredients are USDA inspected and passed for human consumption.” The current bird flu strain, which began spreading among wild birds and poultry in the U.S. in 2022, often causes severe neurological symptoms in cats, such as seizures and blindness, as well as difficulty breathing and discharge from the eyes and nose. “Cats may be seen circling or having a head tilt or just acting very abnormally. Some of those clinical signs are very similar to what we see in rabies,” Dodd said. Leo didn’t show neurological symptoms, aside from wobbliness in his back legs, Werfelmann said. Instead, his main symptoms were fever, lethargy and not eating. “We thought he was going to die,” Werfelmann said. The Colorado Department of Agriculture announced this month that 11 domestic cats there had gotten bird flu from raw poultry or pet food. Leo was the only one to survive.  ‘It’s the milk’ Scientists are still trying to understand what makes bird flu so deadly in cats. The virus is highly fatal to birds but seems to affect cats more severely than some other mammals. Far fewer cases have been recorded in dogs, and though nearly 1,000 dairy herds have been affected, the disease tends to be milder in cows. In people, only one of the 70 cases recorded in the U.S. has been fatal. Kuchipudi’s research has identified receptors throughout cats’ bodies that allow them to be infected by a broad range of flu viruses, including H5N1. “When you examine these animals, the virus is everywhere in the body,” he said. “It causes a systemic infection that is potentially very severe.” Joseph Journell lost two of his cats, Alexander and Tuxedo, to bird flu just days apart in November. He had been giving them raw milk, believing it to contain extra nutrients. A third cat, Big Boy, also got sick after drinking the milk and wound up in critical condition.  Joseph Journell’s cats, including Big Boy, left. (Joseph Journell) “I said, ‘Whatever’s wrong with Big Boy is the same thing wrong with Tuxsie and then obviously the same thing wrong with Alexander,’” said Journell, who lives in San Bernardino, California. “It’s the milk.” Big Boy tested positive for bird flu via a urine sample in December. He has since recovered. The milk the three cats consumed came from a California dairy farm called Raw Farm LLC, according to Journell’s lawyer. The farm issued a recall after California health officials said samples were positive for bird flu. The farm did not respond to NBC News’ request for comment, but in an online statement last month, it said the recall had been “unfounded” and that there was “no evidence of adulterated product connecting to any consumer illness.”  Big Boy and Alexander drink raw milk. (Joseph Journell) Like Hanson in Oregon, Journell decided to pursue legal action. His lawyer sent a letter in January to the owner of Raw Farm, indicating Journell’s intent to recoup more than $16,000 in veterinary expenses, lost wages and caretaker fees for Big Boy. They hope to mediate the situation with the company outside of court but plan to file suit if that’s not possible. A threat to humans? When the veterinary office learned about Kira’s raw food diet, Hanson said, they suspected bird flu right away. “They immediately put on their PPE,” Hanson said. “I was taken aback.” Although there’s some evidence that cats can pass bird flu to each other, there’s no evidence so far that they have transmitted the virus to people. However, the more the virus spreads in cats, the more opportunities it has to mutate and get better at spreading to humans. Outdoor cats, in particular, could serve as a transmission “bridge” between wild animals and domestic pets or humans, Kuchipudi said.  In 2016, a veterinarian at a New York City animal shelter tested positive for a different strain of bird flu, H7N2, after contact with sick cats.  “We need to be aware of these ongoing circulations that could potentially complicate the disease transmission and also [pose] a risk to human health,” Kuchipudi said. Hanson said he was tested for bird flu after Kira died and was negative. In his cat’s final days, he said, he wore an N95 mask around her and washed his clothes upon returning home from the animal hospital.  He hopes his story will serve as a warning to other cat owners. “I don’t want any more cats dying,” he said. “Hopefully people can learn from Kira’s passing.” This story first appeared on NBCNews.com. More from NBC News: One dose of experimental drug nearly wipes out stealthy cholesterol in ‘remarkable’ trial New blood pressure drug helps people with uncontrolled hypertension in trial What should you do if you think you have the measles? ...read more read less