Scientists find raw milk risks with limited airborne spread of H5N1 virus in mammals

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Researchers at the University of Wisconsin–Madison have found that the H5N1 avian influenza virus, present in raw milk from infected cows, can make mammals sick, but it doesn’t spread easily through the air.

This discovery provides important insights into the risks of consuming raw milk and the potential for virus transmission.

The study, published in the journal Nature, shows that the H5N1 virus from raw milk can infect mice and ferrets when introduced into their noses.

However, airborne transmission between ferrets—a common model for human flu transmission—appears to be limited.

This is reassuring news, suggesting that while raw milk infected with H5N1 poses a risk, the virus may not spread rapidly to others.

“This relatively low risk is good news,” says Yoshihiro Kawaoka, a professor at UW–Madison and lead researcher of the study. “It means the virus is unlikely to easily infect people who aren’t exposed to raw infected milk.”

However, Kawaoka cautions that these findings are based on mice and ferrets and may not fully represent how the virus behaves in humans.

In their experiments, the team found that even small amounts of raw milk from an infected cow could make mice sick.

They also tested the virus’s ability to spread through the air by placing infected ferrets near healthy ones without direct contact. Although none of the healthy ferrets got sick, one did produce antibodies against the virus, indicating some level of airborne transmission but not a significant one.

The researchers also studied how the virus binds to receptors—molecules that allow the virus to enter cells—typically recognized by avian and human influenza viruses. They found that the bovine H5N1 virus could bind to both types, showing its potential adaptability to humans. This adaptability is concerning, as past influenza pandemics in 1957 and 1968 occurred after the viruses developed the ability to bind to human receptors.

Additionally, the study found that the virus spread to the mammary glands and muscles of infected mice and from mother mice to their pups through milk. These findings highlight the dangers of consuming unpasteurized milk and possibly undercooked beef from infected cattle if the virus spreads widely among livestock.

“The H5N1 virus currently circulating in cattle has limited capacity to transmit in mammals,” Kawaoka says. “But we need to monitor and contain this virus to prevent it from evolving into a form that transmits well in humans.”

In summary, while raw milk from infected cows can make mammals sick, the risk of the H5N1 virus spreading through the air is low. However, it is crucial to avoid consuming raw milk and to monitor the virus to prevent a potential outbreak.

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