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Raw milk containing H5N1 can infect mice

By Vaseline May27,2024

Consuming raw cow’s milk containing the H5N1 bird flu virus carries a risk of infection, but a laboratory process that simulates pasteurization at high temperatures reduces the virus in infected milk by more than 99.99%. That’s according to a team led by scientists from the University of Wisconsin-Madison, who reported their findings in a letter on May 24 published in the New England Journal of Medicine.

The group, which also included researchers from Texas A&M University, found that mice that consumed untreated milk contaminated with H5N1 subsequently developed influenza and that small amounts of virus remained in untreated milk for weeks when stored at standard refrigeration temperatures. The research took place as the avian flu virus H5N1 continued its spread from birds to mammals infections reported this spring in dairy herds in the United States.

Yoshihiro Kawaoka, professor in the UW-Madison Department of Pathobiological Sciences, and Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory, led the work. The researchers tested two heat inactivation methods on four H5N1-positive milk samples taken from infected cows in New Mexico and Kansas. Both methods were intended to simulate common pasteurization techniques, although the equipment and exact processes the researchers used differed from standard industry practices.

In the first case, they heated infected raw milk to 145.4 F for a minimum of five minutes and a maximum of 30 minutes. This method reduced virus levels by more than 99.999%.

The second method involved heating raw milk to 161.6 F for up to 30 seconds. This method inactivated more than 99.99% of the virus in the samples, although it did not completely inactivate the virus.

“We must emphasize that the conditions used in our laboratory research are not identical to the large-scale industrial treatment of raw milk,” says Kawaoka. “It is important to remember that our heat treatment findings may not translate perfectly to real-world conditions.”

Meanwhile, the team orally vaccinated mice with untreated milk samples to assess the potential risk of consuming raw milk carrying the H5N1 virus. The mice started showing symptoms of illness after one day.

Although no mice died due to infection within the four days of the experiment, subsequent analyzes showed high levels of virus in their respiratory tracts, indicating that the infections originated in their throats. Some mice also had significant amounts of virus in their mammary glands, consistent with the high levels of virus found in infected cow’s milk.

To date, only two people in the US have had confirmed H5N1 infections, one in Texas and one another, reported May 22 in Michigan. Both cases occurred in farm workers who worked closely with dairy cattle, and the main symptom in both cases was eye inflammation. Although epidemiologists have not confirmed the mode of transmission, the Centers for Disease Control and Prevention cited the most likely routes came from contaminated milk splashing into workers’ eyes or from workers touching their eyes with hands contaminated with the virus.

The latest findings suggest that people could also risk a possible H5N1 infection if they consume raw milk from an infected cow.

“Don’t drink raw milk,” says Kawaoka.

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