In experiments, mice become ill from raw milk containing the bird flu virus

Researchers confirmed the dangers of drinking raw cow’s milk when the H5N1 bird flu virus is circulating in US dairy herds and found that mice fed the milk quickly became ill.

“Our data indicate that HPAI A[H5N1] virus in untreated milk can infect susceptible animals that consume it,” concluded a team led by virologist Yoshihiro Kawaoka of the University of Wisconsin-Madison. His team published the findings Friday in the New England Journal of Medicine.

In late March, researchers first discovered traces of H5N1 bird flu in nasal swabs and milk obtained from American dairy cows. Since then, the outbreak has been identified in many dairy herds in multiple states.

So far, H5N1 does not appear to transmit easily between animals and humans: there are only two known cases of H5N1 infection in humans linked to the dairy cow outbreak in the US. Both have occurred in dairy workers who had prolonged and close contact with the animals.

Experts also believe that the general milk supply is safe because the heating associated with pasteurization kills the virus.

However, drinking unpasteurized ‘raw’ milk – all the rage among a small group of consumers – may carry the risk of passing H5N1 to other mammals, including humans.

To find out if that’s true, Kawaoka and his team gave mice raw cow’s milk that was known to be contaminated with the H5N1 virus. The rodents ingested the milk through the mouth.

The mice showed typical signs of infection such as “ruffled fur and lethargy” just one day after being given the milk, the researchers reported.

“All animals survived until day 4, when they were euthanized to determine virus titers [levels] in multiple organs,” Kawaoka’s group said.

“We detected high virus titers in the respiratory tract [which suggests that infection may have occurred through the pharynx] and moderate virus titers in several other organs, findings consistent with the systemic infections typically caused by HPAI H5 viruses in mammals,” the team reported.

High levels of virus were also found in the mammary glands of the female mice, even though they were not breastfeeding, the researchers said.

Based on their findings, the researchers believe that infection in mammals with the bird flu virus can occur after consuming cow’s milk containing the pathogen, if the milk has not been heat treated, as occurs during pasteurization.

People who drink raw milk may think that refrigeration can kill the H5N1 virus. The researchers explored that idea by cooling the infected milk to a temperature of 39 degrees Fahrenheit.

However, virus levels in the unpasteurized milk declined only slowly while held at this temperature for five weeks, suggesting that the “virus may therefore remain infectious for several weeks under these conditions,” the researchers said.

As for pasteurization, the scientists passed raw, infected milk through heating processes similar to those used in the pasteurization process. They report that virus levels have been reduced to undetectable or barely detectable levels, but in some cases not completely eliminated.

Kawaoka’s team emphasized that “the conditions used in our laboratory research are not identical to those used in large-scale industrial studies [pasteurization] treatment of raw milk.”

Yet the research appears to confirm that the real danger of passing H5N1 to consumers lies in consuming raw milk.

“Don’t drink raw milk, that’s the message,” Kawaoka told the New York Times.

And there are more reasons than bird flu to avoid raw milk.

According to one from 2022 study According to the U.S. Centers for Disease Control and Prevention, raw milk consumption has been linked to 228 hospitalizations, three deaths and illnesses in more than 2,600 people between 1998 and 2018.

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