Federal officials who spent the last year grappling with a surge of bird flu infections in cows and people are now confronting a spate of new cases in cats, some of which have died after eating contaminated, uncooked pet food.

Since early December, more than two dozen cases have been confirmed in domestic cats in the United States. Officials have linked some of the cases to virus-laden raw milk, which is known to pose a serious risk to cats. But other cats fell ill after eating commercially available raw pet food — the first known cases in the country linked to pet food.

The cases have already prompted one pet food manufacturer to recall some of its products. And last week, federal officials announced new pet food safety rules and poultry surveillance efforts.

Bird flu “is an emerging contaminant in animal food,” Dr. Steve Grube, a chief medical officer at the U.S. Food and Drug Administration, said at a briefing last week.

Still, experts and officials said that there was no need for pet owners to panic. There is no evidence that infected cats have passed the virus on to people, and the cases have been linked specifically to unpasteurized milk and uncooked meat or poultry products.

Most commercial pet foods are cooked or heat-treated. “The heat of processing should be enough to inactivate the virus,” said Phyllis Entis, a food safety microbiologist who worked for Canada’s food safety agency.

But the cat cases highlight the risk of raw food products and raise questions about safety and surveillance gaps in parts of the food supply chain.

“We really don’t have a sense of how widespread this virus is, and we’ve already seen several cases of it sneaking up in the pet food supply,” said Kristen Coleman, an infectious disease researcher at the University of Maryland who is studying bird flu in cats. “It’s a really big vulnerability.”

Although dogs appear to be less susceptible to the virus than cats, and generally experience milder symptoms, contaminated food products pose risks to canines, too.

Here’s what to know.

How are cats getting infected?

Experts have long known that cats are susceptible to the virus, which is called H5N1 and is often fatal in felines. There have been sporadic deaths in cats that preyed on wild birds, and there was a spike in cat cases after bird flu began circulating in dairy farms about a year ago. Raw milk from infected cows often contains very high levels of the virus; farm cats that died after lapping up raw milk often served as an early sign of an outbreak.

(Pasteurization, a process in which milk is rapidly heated and then cooled, inactivates the virus and makes milk safe to drink, according to the F.D.A.)

Many of the recent infections occurred in indoor cats that had no known contact with wild birds or dairy farms.

In December, Oregon officials announced that a pet cat had contracted bird flu and died after eating raw, frozen pet food from Northwest Naturals. Samples of the food — the company’s Feline Turkey Recipe — tested positive for H5N1 and the virus was a genetic match for the one found in the cat, officials said.

In an emailed statement, Northwest Naturals said that the company had “deep concern about the accuracy of testing an open bag of pet food, which can contribute to cross-contamination and the introduction of external contaminants that could lead to false positive or inaccurate test results.”

Nevertheless, the company decided to issue a voluntary recall.

California has also reported bird flu infections in cats fed raw milk or pet food. In one Los Angeles household, five cats got sick — and two died — after eating two kinds of raw pet food. Samples from one of the two brands, Monarch Raw Pet Food, tested positive for the virus, officials said.

“Monarch is complying with outreach from local agencies; however, they are not asking for a recall, and to the best of our knowledge there have been no other cases that involve Monarch,” Stephanie Greene, a spokesperson for the company, said in an email.

How is the virus getting into pet food?

It’s not entirely clear, and there could be different sources for different cases.

But in an email on Wednesday, an F.D.A. spokesman said that some viral samples from infected cats were closely related, genetically, to samples from turkey farms in Minnesota.

When bird flu is detected in a farmed turkey or chicken, federal regulations require that all birds in that flock be killed. Those birds “are not permitted in any food product at all,” Dr. Eric Deeble, an official at the U.S. Department of Agriculture, said at the briefing last week.

Turkeys and chickens typically become severely ill and die soon after they are infected. But if a bird picked up the virus right before it was slaughtered, or somehow had a very mild infection, it could potentially slip into the food supply undetected, experts said.

The F.D.A., which regulates commercial pet food, requires animal food manufacturers to develop written safety plans, outlining the steps they are taking to ensure that their products are safe for consumption.

The agency “has zero tolerance for pathogens like salmonella or listeria or E. coli or any other potential pathogen in ready-to-eat pet food, and that includes raw pet foods,” said Ms. Entis, who is the author of the book “Toxic: From Factory to Food Bowl, Pet Food Is a Risky Business.”

(The F.D.A. does not have a formal definition for raw pet food, but in general, products marketed as “raw” have not undergone any kind of heat treatment, such as cooking or pasteurization.)

But in practice, Mr. Entis said, the agency does not have a lot of resources for pet food regulation and oversight. “So there’s a lot that doesn’t get caught, or only gets caught when there are illness reports,” she said.

Northwest Naturals said that its pet food was processed at a facility that had a U.S.D.A. inspector on site and also produced food for human consumption. “We remain fully confident in our rigorous quality control and its ability to ensure that our customers’ pets are being served safe and nutritious food,” the company said.

What are officials doing about it?

Last Friday, the F.D.A. announced new rules that require companies making pet food containing certain uncooked or unpasteurized ingredients to update their food safety plans to account for the potential hazards of bird flu.

Whether that will result in meaningful safety reforms remains to be seen, Ms. Entis said. Some companies may decide to implement new precautions, such as buying ingredients only from suppliers that regularly test their animals for the virus. But others could say that they’ve reviewed their existing safety plans and determined that no new safeguards are necessary, Ms. Entis said.

Northwest Naturals said it was working to “reanalyze and strengthen our already stringent food safety plan.”

The U.S.D.A. also announced new bird flu surveillance guidelines for large, commercial turkey farms in Minnesota and South Dakota. The guidelines, which could be expanded to other states in the future, call for turkeys to be isolated, monitored and tested for the virus 72 hours before they are sent to slaughter.

What can pet owners do?

The easiest way to protect your pets is to avoid feeding them raw milk, meat or poultry, experts agreed. Those products, which can harbor an array of food-borne pathogens, have always posed health risks, and bird flu ratchets them up. “It’s just not safe right now,” Dr. Coleman said.

Owners whose pets are doing well on a particular raw pet food — and don’t want to or can’t suddenly switch to a new product — can significantly reduce the risks by cooking the food before serving it.

Pet owners should also use this as an opportunity to become more familiar with what’s in the food that they are serving their pets and how it’s processed, Dr. Coleman said. People who have questions or concerns can reach out to the pet food companies directly to ask where they source their ingredients and what food safety measures are in place. “And if they can’t give you an answer to those just very simple questions, then there’s your answer — stop buying their product,” Dr. Coleman said.

People should also try to limit their pets’ contact with birds — and wild animals in general — and report sick and dead birds to local officials.