As experts continue monitoring and surveying the environment and the nation’s food supply for H5N1 bird flu, a rash of dead cats has many officials on edge.

From pet cats in Los Angeles County and Oregon to captive wild cats in Washington and Colorado, dozens of felines have died as a result of consuming H5N1-infected raw pet food and raw milk.

Although the products carrying the virus were largely marketed for animals — with the exception of raw milk — experts say the presence of the virus in commercial meat and dairy highlights the vulnerability of the U.S. food chain to this virus.

“With multiple diagnosed cases of H5N1 mortalities, can we in good conscience fail to provide widespread public warnings that raw meat… has been linked to multiple big cat mortalities,” said John Korslund, a retired U.S. Department of Agriculture veterinarian epidemiologist, in an email.

The deaths prompted policy changes announced Friday by the USDA and the Food and Drug Administration, which focus on pre-slaughter rules for select poultry farms in Minnesota and South Dakota, as well as changes in food safety risk assessments for raw pet food producers.

And they underscore the murky and largely unregulated industry of raw pet-food manufacturing.

Although the FDA offers guidance on best practices for raw pet food producers, there are few rules, if any, regarding how raw meat is sourced for pet food; industrious entrepreneurs can source meat and protein from wild game, non-USDA inspected backyard flocks and farms, as well as meat not considered fit or appetizing for human consumption — as long as “it is safe to eat, produced under sanitary conditions, contain no harmful substances, and be truthfully labeled,” according to the Federal Food, Drug, and Cosmetic Act, the law that governs pet food.

The agency will also investigate companies if animals have become sickened from eating pet food. And birds affected by the virus are not allowed to enter the food supply, per USDA regulations.

“Obviously, a great deal of protein that is produced outside of [the USDA’s] Food Safety and Inspection Services inspected facilities is never intended for human consumption,” said Eric Deeble, deputy under secretary for marketing and regulatory programs for the USDA, at a press conference on Thursday. But H5N1-infected birds “are not permitted in any food product at all. They are most frequently composted on site as part of the efforts to mitigate the spread of the virus.”

In L.A. County alone, nine cats have been sickened or died from eating raw milk, raw pet food or both containing the H5N1 bird flu. On Monday, county public health officials said five indoor cats in one household were sickened after eating Monarch Raw Pet Food (based in San Jacinto, Calif.); two died.

In December, 20 captive wild cats — including four cougars and a half-Bengal/half-Siberian tiger — died after eating H5N1-contaminated raw pet food at an animal sanctuary in Shelton, Wash. An additional five animals at a private animal sanctuary in Colorado — two tigers, one lion, a mountain lion and a fox — also perished from eating the food. So, too, did two house cats — one in Oregon, another in Colorado.

In all but nine of the Washington cats, the genetic sequencing of their H5N1 virus matched up with samples taken from frozen turkey packaged in May and June by Oregon-based Northwest Naturals pet food, according to data published by the USDA’s Animal and Plant Health Inspection Service, GISAID (a public genetic database focused on influenza viruses), the National Institutes of Health’s GenBank, and the World Organization for Animal Health, an international organization dedicated to the investigation and surveillance of animal diseases. The meat was raw when frozen.

According to evolutionary molecular biologist Henry Niman, in each case, there is a signature mutation on one segment of the virus — a switch at position 52 on the NP protein — in both the food samples and dead animals, providing an unmistakable link between them.

Only the Oregon house cat has been positively linked by state and federal agencies to the Northwest Naturals brand name. Although the other cats were killed by a virus genetically identical to the one found in the Oregon cat and the samples of Northwest Naturals food, it is possible those animals were given food sourced from the same meat or outbreak but under a different brand name.

Questions sent to Northwest Naturals went unanswered.

Northwest Naturals has voluntarily recalled the suspect batch: two-pound plastic bags with “Best if used by” dates of 05/21/26 B10 and 06/23/2026 B1. And on its website, the company suggests the sample was contaminated after packaging and production.

“Testing an open bag of pet food leaves open the possibility that the virus may have entered the bag after it was opened,” wrote the company on an FAQ page about the recall.

The change observed in the genetic sequences, said Niman, “is exceedingly rare. And other than Northwest Naturals samples and the animals that ate it,” the only three other animals to have shown that change in this latest H5N1 outbreak were three Minnesota commercial turkeys that were culled in June as a result of infection — the same month the raw pet food was processed and packaged.

Niman said there’s no way to show from the genomic sequencing that it was turkeys from that Minnesota farm that got into the pet food, but the virus was likely moving around the region at that time. And somehow, he said, infected birds must have gotten into the slaughterhouse without anyone noticing — an occurrence that most researchers say should be extremely rare. Commercial poultry generally show symptoms within hours of H5N1 infection, and die almost immediately.

Maurice Pitesky, an associate professor who researches poultry health and food safety epidemiology at UC Davis, agreed. “Not sure but maybe the birds got infected right before slaughter?,” he said in an email, adding that “he was not aware that there are companies that sell raw poultry with the intent of consumption by pets.”

But if infected turkeys made it to slaughter without being identified, it suggests there may be more infected meat out there, said Korslund, the former USDA veterinarian epidemiologist.

And that’s what has researchers and health authorities at the USDA and FDA concerned.

On Friday, the USDA announced that it was launching a new policy for turkey operations in Minnesota and South Dakota that have more than 500 birds — birds will be required to have a pre-slaughter inspection and isolation 72 hours before slaughter. The agency noted the link between the infected turkeys and the Oregon house cat as the reason for the new program.

Meanwhile, the FDA cited the “cases of H5N1 in domestic and wild cats in California, Colorado, Oregon and Washington State that are associated with eating contaminated food products” as its reason to call for raw pet food processors to reanalyze their food safety systems, and incorporate H5N1 into their analyses.

“The FDA has determined that it is necessary for cat and dog food manufacturers… who are using uncooked or unpasteurized materials derived from poultry or cattle… in cat or dog food, to reanalyze their food safety plans to include H5N1 as a new known or reasonably foreseeable hazard.”

It will likely continue to fall on cats to signal the virus’ presence in food and in the environment.

Scientists say that cats are extraordinarily susceptible to H5N1 infection. Since the outbreak was first reported in a Texas dairy herd last March, dead barn cats have served as sentinel warnings to veterinarians and investigators of the virus’ presence on a farm.

In cats, the virus can affect the brain and nervous system. Many suffer blindness, seizures and abnormal behavior. Necropsies often show large amounts of the virus in their brains.

And while the deaths of these cats are alarming in terms of conservation and protecting animals whose habitats are being destroyed and whose populations are increasingly marginalized, it’s the deaths of the captive cats, say scientists, that should concern public health authorities. It’s a sign that the virus is getting into the commercial meat and milk supply — a worrisome, but not surprising, development considering the virus’ presence in dairy cattle and commercial poultry farms.

Health officials say the best way to avoid infection is to cook meat thoroughly and consume only pasteurized dairy products — and to stop feeding raw meat and dairy — commercial or otherwise — to pets.