Bird flu highlights concerns about raw milk

While bird flu remains a low risk to the general public, health officials again warned on Wednesday about the potential risk of unpasteurized milk.

“We continue to strongly advise against consuming raw milk,” said Dr. Donald Prater, acting director of the Center for Food Safety and Applied Nutrition at the Food and Drug Administration, at a news conference.

Even in the best of times, raw milk is “one of the riskiest foods we have,” said Benjamin Chapman, a professor and food safety specialist at North Carolina State University. But health experts warn that cases of avian influenza, or bird flu, found in dairy cows may become even riskier.

Almost all milk sold in stores is pasteurized, and FDA testing so far has shown that this process inactivates the H5N1 bird flu virus.

If you consume pasteurized milk or dairy products, “I'm confident that the risk is extremely low right now,” Dr. Dean Blumberg, chief of the Division of Pediatric Infectious Diseases at UC Davis Health.

Raw milk, on the other hand, is not pasteurized and can contain dangerous germs. While the Food and Drug Administration has long recommended that consumers not drink it, more than two dozen states have legalized the sale of raw milk.

The same bacteria that commonly cause foodborne illnesses, such as salmonella, E. coli and listeria, can fester in raw milk. Between 1998 and 2018, researchers linked over 200 outbreaks that sickened 2,645 people and resulted in 228 hospitalizations to raw milk. People who are very young or very old, pregnant or have weakened immune systems are particularly likely to become seriously ill from the pathogens in raw milk, said Darin Detwiler, a food safety expert and professor at Northeastern University's College of Professional Studies.

Can you get bird flu from raw milk?

Dr. Rosemary Sifford, deputy administrator for veterinary services at the Department of Agriculture, said in Wednesday's news conference that testing had found a “high viral load” in raw cow's milk and that federal officials believe the virus spreads primarily between the types of milk produced by the cows Contact with milk. According to the FDA, government agencies continue to test samples from affected herds

Researchers and health authorities are unsure whether bird flu can be transmitted to humans from raw milk.

“There are not many studies showing the infectivity of this virus and raw milk products,” said Dr. Prater. However, he said authorities continue to monitor the problem as new research emerges.

On Wednesday, the FDA said it “recommends that the industry not manufacture or sell raw milk or raw milk products.” The agency has also recommended that producers discard milk from affected cows and pasteurize raw milk from exposed cattle before feeding it to animals.

Some researchers consider it unlikely that bird flu can be transmitted to humans through raw milk, but Dr. Meghan Davis, a veterinarian and environmental epidemiologist at the Johns Hopkins Bloomberg School of Public Health, said she is concerned about this possibility, in part because cats on dairy farms have become ill with the virus.

In a study published Monday, researchers described a group of about two dozen cats fed raw milk from cows with bird flu on a Texas dairy farm. More than half of the cats became sick and died; Two of the deceased cats were tested and found to be infected with the virus. It's possible they got sick from eating wild birds, but raw milk was “a likely route of exposure,” the researchers wrote.

Dr. Blumberg pointed out that other influenza viruses that typically affect people can spread when people touch surfaces contaminated with the virus and then touch their mouths, noses or eyes. Bird flu can spread in similar ways, he said, including through handling or consuming contaminated raw milk or cheese.

Since 2022, only two human cases of bird flu have been reported in the United States; Both people were exposed to infected animals and suffered from minor illnesses. But the virus has caused serious illness in humans in the past, Dr. Blumberg.

How about cheese made from raw milk? Or goat's milk?

Some cheesemaking processes can involve higher temperatures and pressures that could inactivate the virus in raw milk, Dr. Davis. Other steps, such as aging, could also impact the survival of the virus. But at this point, said Dr. Davis, it's hard to say how risky a particular raw milk cheese might be.

Caution should also be exercised with raw milk products from goats or sheep, said Dr. Davis. In March, avian influenza was detected in young goats on a Minnesota farm; And while no cases have yet been reported in sheep, it is plausible that they too could become infected with the virus, she added.

How widespread is the virus?

As of April 27, the U.S. Department of Agriculture had confirmed cases of avian influenza in dairy cows in nine states. But just because the virus hasn't been reported in a state doesn't mean it isn't there, Dr. Davis. The FDA has reported finding inactive fragments of the virus in about 20 percent of pasteurized milk samples across the country, suggesting the virus has spread more widely than animal tests suggested, she said.

“We don’t yet know exactly how widespread it is,” said Dr. Davis.

Because wild birds can spread the virus, both small and large farms could be affected, she said.

“The precautionary approach would be to avoid raw milk products altogether for the time being,” said Dr. Davis. “We have so many unknowns.”