Bird Flu in Cattle: Is Cow's Milk Safe to Drink?

U.S. Food and Drug Administration (FDA) testing found that one in five pasteurized milk samples contained fragments of H5N1, a bird flu virus currently infecting dairy cattle across the nation.

As of Friday, April 26, U.S. Department of Agriculture (USDA) data shows that over 30 dairy cattle herds in eight states have confirmed cases of H5N1, a highly pathogenic avian influenza (HPAI) virus known to infect wild birds and poultry.

The USDA's Animal and Plant Health Inspection Service (APHIS) has taken several steps to combat the spread of H5N1 among cattle, including enacting mandatory testing for cattle moving between states.

However, on April 16, APHIS microbiologists found small changes in the H5N1 virus taken from a cow in Kansas that may indicate the virus has adapted to be more infectious to mammals. Still, a Centers for Disease Control and Prevention (CDC) analysis showed that these changes have previously occurred in other bird flu cases in mammals and do not impact viral transmission.

On April 21, APHIS released data showing 239 genetic sequences from the H5N1 bird flu virus infecting wild birds, poultry, and cattle to help scientists understand the disease and it's potential to spread to humans.

Earlier this month, the CDC reported that two people have tested positive for H5N1. The first case occurred in 2022 and was related to exposure to infected poultry, while the most recent case of bird flu involved an individual in Texas who had exposure to infected dairy cattle. In both cases, symptoms were mild, and the individuals recovered without incident.

Health officials say there is currently no evidence of human-to-human transmission of bird flu.

Bird flu in the U.S. milk supply

Amid concerns that H5N1 infections in dairy cattle could impact the milk supply, the FDA is conducting ongoing evaluations of milk from infected animals, processing plants, and store shelves.

In an updated safety advisory, the FDA reports that initial results of commercial milk testing found that one in five pasteurized milk samples sold in stores contained fragments of the H5N1 virus — likely remnants leftover after pasteurization.

Pasteurization is a process that destroys harmful bacteria and viruses by heating milk to a specific temperature for a set period.

While the agency asserts that viral fragments pose no risk to consumers, it says additional testing is required to determine whether store-bought milk samples contain intact versions of the H5N1 virus. If intact versions are found, the agency will then identify whether they could be infectious.

So far, National Institutes of Health (NIH)-funded investigations have found no infectious forms of H5N1 in pasteurized milk sold in retail stores.

However, raw, unpasteurized milk can contain potentially harmful pathogens, and according to the FDA, H5N1 has been detected in raw milk samples. With the unknowns surrounding the virus, the agency urges consumers to be wary of the potential risks associated with unpasteurized milk products.

To further investigate the safety of the U.S. milk supply, federal agencies are testing milk samples in supply-chain systems that gather and pool large amounts of milk from numerous farms for processing. Moreover, additional investigations are underway to evaluate other milk products, including cream and whole milk.

On May 1, the FDA, the CDC, and the U.S. Department of Agriculture held a joint press conference and announced that pasteurized dairy products like cottage cheese, sour cream, and powdered infant formula did not contain a virus.

Dr. Donald Prater, acting director of the Center for Food Safety and Applied Nutrition for the FDA, said, "These samples underwent acute qPCR (quantitative polymerase chain reaction) testing, as well as the same egg inoculation test, and we're encouraged that this preliminary testing also did not detect any viable virus."

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