Since the avian flu arrived en force in California’s dairy industry in 2024, not only has it sickened cows, it has killed hundreds of domestic cats. Some pet cats that live on dairy farms were infected with the H5N1 virus by drinking raw milk. Both pets and feral barn cats got sick after eating raw pet food that harbored the virus. Still others got it by eating infected wild birds, rats or mice, or from contact with dairy workers’ contaminated clothes or boots.
But a new published case suggests that death may be averted if infected cats are treated early with antiviral medications, such as Tamiflu, or oseltamivir. Once treated, these animals may carry antibodies to the virus that makes them resistant to reinfection, at least temporarily.
The discovery was made by Jake Gomez, a veterinarian who treats small animals, such as cats and dogs, as well as large ones, including dairy cows, from his clinic, Cross Street Small Animal Veterinary Hospital, in Tulare.
Last fall, Gomez worked with a team of scientists from the University of Maryland and University of Texas who were in the Central Valley collecting blood samples from outdoor cats at dairy farms, looking to see if they could find antibodies to the H5N1 flu.
Cats are exquisitely sensitive to H5N1; one of the telltale signs that a dairy herd is infected is the presence of dead barn cats.
On Oct. 31, a cat owner brought in an indoor/outdoor cat to Gomez’ clinic that was ADR — a technical veterinarian acronym that stands for “ain’t doing right.”
The cat was up-to-date on all its vaccinations and the owner reported no known exposure to toxic chemicals.
Gomez offered to do blood work and urinalysis to probe more deeply what was going on, but the owner declined. So, Gomez sent them home with an antibiotic and an appetite stimulant. Two days later, the cat died.
It turned out the family had had another cat die just a few days earlier, Gomez said, recalling the visit.
Also during that time, Gomez was treating infected dairy herds around Tulare. Thousands of cows were falling sick from the virus. The family with the sick cats, he learned, lived less than a mile from an infected dairy, and the cat owner worked delivering hay to local dairies, spending time on infected farms.
“Considering how quickly it moved from one cat to the next, it occurred to me it might be H5N1,” he said.
Gomez said he reached out to the U.S. Department of Agriculture and the California Department of Food and Agriculture to see if they would test the dead animals for the virus. The agencies, he said, gave him the runaround and he couldn’t get anyone to answer his calls — which he said was perplexing, considering the rapid response when he alerted them to infected cattle.
“If I called to tell them a dairy herd had it, within 24 hours a SWAT team from the USDA and state would be swarming the farm,” he said. But for a cat? Crickets.
On Nov. 6 and 7, the family returned with two more sick cats.
Gomez said he still didn’t know what they had, but had a suspicion they could be infected with H5N1. So, he treated them with the antiviral oseltamivir, known also as Tamiflu, and they recovered.
In March this year, blood samples collected from the two cats showed high levels of antibodies to H5N1 — suggesting the cats had been exposed.
The case was published in the journal One Health.
Kristen Coleman, an airborne infectious disease researcher at the University of Maryland School of Public Health, and an author on the paper, said the findings suggest that cats may be effectively treated and that antiviral medications could help prevent further spread of the virus among cats living in the same home and the humans who care for them.
She said there have been no known transmissions from cats to humans in this outbreak, but there have in the past — in 2005, Thai zookeepers were infected by tigers that had the virus, and in 2016, New York veterinarians at an animal shelter got it from tending to sick cats.
But Jane Sykes, a professor of medicine and epidemiology at UC Davis School of Veterinary Medicine, said she’s not convinced the cats in this case actually had H5N1 — and urged people to read the study with care and caution.
“It’s possible that the positive antibody test results were unrelated to the reasons why those two cats died,” she said. “The virus wasn’t detected in any of the four cats, so infection was not proven.”
And whether the cats recovered because they were treated with Tamiflu, or whether the medication was incidental and they’d have recovered on their own — from another virus, infection or ailment — isn’t clear.
In addition, she said, no one has researched the effects of Tamiflu on cats. And while these two cats appeared to tolerate the drug, that doesn’t mean other cats will.
“Cats metabolize some of the anti-infective compounds very differently than other animals, including people, and they’re quite susceptible to bad side effects of many of these drugs,” she said. “We have to be really careful when we start just using random antiviral drugs that haven’t been studied for safety in cats, because they are so likely to get bad side effects.”
Having said that, she said if she were faced with a similar situation, a high certainty that a cat had been exposed, whether from drinking raw milk or eating raw food that had been infected, she would consider prescribing the medication. But she’d caution her client that it was experimental, and the animal could die from the drug.
She said there are numerous labs across the country that will test blood and urine for the virus.
Sykes urged people not to feed raw food or milk to their pets.
She said she’s seeing more raw food products for pets “and people want them, and they don’t understand the harms and the fact that some of these are contaminated for a long period of time with influenza viruses, like H5N1.”
Neither freezing nor smoking meat kills the virus.
“It’s astonishing how big this industry is getting,” Sykes said. “It’s crazy.”
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