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Bird flu makes raw milk dangerous to consume, mouse study finds

A A new study released Friday provides more evidence of the potential harm of consuming unpasteurized or raw milk containing the H5N1 avian flu virus.

The work, published in the New England Journal of Medicine, showed that mice fed milk from cows infected with the H5N1 virus became very ill.

The study cannot prove that what happened to the mice would certainly happen to people who drink raw milk containing the dangerous virus, but it highlights the likely risk, experts said. Studies like this cannot be carried out on people, for ethical reasons.

“Raw milk is clearly strongly suspected of transmitting the H5N1 virus to animals,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. “We still don’t know what the risk is to humans. But I wouldn’t want to take any risks. »

Thijs Kuiken agreed. A pathologist in the Department of Viroscience at the Erasmus Medical Center in Rotterdam, the Netherlands, Kuiken has long studied the effect of H5N1 viruses on mammals, including cats. During this outbreak in dairy cattle, many cases of farm cats died, presumably after drinking contaminated milk.

“Based on the weight of evidence from our knowledge of (this H5N1 lineage), to which this letter contributes, it is likely that people drinking raw milk from infected cows would acquire systemic disease,” Kuiken told STAT in an email.

The Food and Drug Administration has long recommended against drinking raw milk, which can contain a number of dangerous pathogens such as E. coli, Salmonella and Listeria. The agency reiterated this advice in the context of the current H5N1 outbreak in dairy cattle. As of Thursday, 58 herds in nine states have tested positive for the virus since the outbreak was first detected in late March, and two human infections in farmworkers have been detected.

Neither Kuiken nor Osterholm was involved in the research, conducted by researchers at the University of Wisconsin-Madison. The lead author was Yoshihiro Kawaoka, a prominent influenza virologist who has studied H5N1 for decades.

Kawaoka told STAT in an email that the mice were euthanized on the fourth day of the study “because we didn’t want to see the mice die before (tissue) sampling.” Studies that involve exposing animals to potentially lethal pathogens do not allow them to experience prolonged death.

The multi-part study was conducted in early April before the FDA and other academic groups announced research findings showing that active virus could not be grown from pasteurized dairy products.

In addition to the work of feeding raw milk to the mice, the team simulated different pasteurization approaches, which use heat to inactivate pathogens in milk, to see if they could grow an active virus from the heat-treated samples. One approach used killed all viruses in the milk, while another, which involved heating for a short time, only reduced the amount of active virus in the milk to low levels.

The researchers cautioned that their approaches to milk processing were not the same as those used by milk processors when they pasteurize commercial milk.

Another aspect of the study involved storing raw milk containing the virus at refrigerator temperature for several weeks to see if the amount of virus decreased over time. They found only a minor reduction in the amount of active virus in the milk, suggesting that “the virus may therefore remain infectious for several weeks in raw milk stored at 4°C.”

Keith Poulsen, one of the authors, said the finding was not a surprise. “The flu likes cold and wet,” said Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory and professor of large animal internal medicine at the University of Wisconsin-Madison.

Interestingly, the researchers also detected the H5N1 virus in the mammary glands of two of the mice while they were studying where the virus had been found in mouse tissues after euthanasia. The mammary tissues of dairy cattle appear to be very susceptible to the virus, with infected lactating cows shedding extraordinarily high levels of virus in their milk.

This article has been updated to include comments from the lead author.

News Source : www.statnews.com
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