Raw milk could carry deadly flu viruses for days

Raw milk, often valued for being natural and nutritious, is gaining popularity among health-conscious individuals. But a recent study from Stanford University brings up serious concerns about the safety of this product.

The research reveals that the flu virus can survive in refrigerated raw milk for up to five days. This discovery comes as outbreaks of bird flu in dairy cattle spark fears about a potential pandemic.

“This work highlights the potential risk of avian influenza transmission through consumption of raw milk and the importance of milk pasteurization,” said Professor Alexandria Boehm, the study’s senior author.

Raw milk: A risky trend

More than 14 million Americans consume raw milk each year. Unlike pasteurized milk, raw milk isn’t heated to kill harmful pathogens.

Advocates believe raw milk retains more nutrients, enzymes, and probiotics, which may boost immune and gut health. However, health agencies strongly warn against drinking raw milk.

The FDA has linked raw milk to over 200 outbreaks of illnesses. Along with the CDC, the agency emphasizes that raw milk can harbor dangerous pathogens like E. coli and Salmonella.

Such pathogens pose severe risks to children, pregnant women, the elderly, and people with weakened immune systems.

Flu virus in cow’s milk

The Stanford researchers studied how long the H1N1 PR8 flu virus can stay infectious in raw cow’s milk at typical refrigeration temperatures. They discovered that the virus remained infectious for up to five days.

“The persistence of infectious influenza virus in raw milk for days raises concerns about potential transmission pathways,” said Mengyang Zhang, co-lead author of the study.

“The virus could contaminate surfaces and other materials in dairy facilities, posing risks to both animals and humans.”

Prolonged persistence of viral RNA

Additionally, viral RNA – the virus’s genetic material – stayed detectable in raw milk for at least 57 days. While RNA itself isn’t harmful, it complicates food safety assessments and environmental surveillance.

Pasteurization completely destroyed infectious flu viruses in raw milk and reduced viral RNA by 90%, but traces of RNA still lingered.

“The prolonged persistence of viral RNA in both raw and pasteurized milk has implications for food safety assessments and environmental surveillance,” explained Alessandro Zulli, co-lead author of the study.

This study builds on earlier research, funded by the Stanford Woods Institute for the Environment, which was focused on human norovirus and the subfamily of viruses responsible for the COVID-19 pandemic.

The team’s work was also focused on zoonotic pathogens – viruses that jump from animals to humans.

The need for better monitoring systems

Each year, flu viruses infect over 40 million people and cause more than 50,000 deaths in the U.S. alone. These viruses can move from animals to humans, as seen in the 2009-2010 swine flu pandemic, which caused up to 1.4 billion infections worldwide.

While bird flu hasn’t posed the same threat yet, recent cases in cattle raise serious concerns about its transmission through raw milk and other dairy products.

This study highlights the need for better monitoring systems, especially as bird flu spreads among livestock. Improved surveillance could help public health officials respond faster and reduce risks to people and animals.

Earlier research by the team showed how wastewater analysis could detect flu activity in nearby cattle populations.

“We never thought wastewater could be used to detect and respond to zoonotic pathogens in the community,” said Professor Boehm. “It has been amazing to see our wastewater detection work scale across the U.S. and globally.”

Destroying flu virus in raw milk

The findings emphasize the critical role of pasteurization in ensuring milk safety. Policymakers and health officials should consider these results if they wish to strengthen food safety protocols and surveillance systems.

As zoonotic diseases become more common, proactive measures will help prevent outbreaks and protect public health.

Raw milk may appeal to some for its natural benefits, but science shows that its risks far outweigh its rewards. By understanding these dangers and sticking to pasteurized products, we can make safer choices for ourselves and our families.

The project received funding from the Stanford Woods Institute for the Environment and the Sergey Brin Family Foundation.

The study is published in the journal Environmental Science & Technology Letters.

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