Raw milk fans plan to drink up as experts warn of high levels of H5N1 virus

Enlarge / A glass of fresh raw milk in a farmer’s hand.

Drinking raw milk at any time means flirting with dangerous germs. But, against the backdrop of an unprecedented outbreak of H5N1 avian influenza among dairy cows in the United States, the risks have increased significantly. Health experts have increased warnings against consuming raw milk during the epidemic, the extent of which is still unknown.

Still, raw milk fans aren’t intimidated by the increased risk. The California-based Raw Milk Institute called the warnings “clearly alarmist.” The institute’s founder, Mark McAfee, told the Los Angeles Times over the weekend that his clients were in fact specifically requesting raw milk from cows infected with H5N1. According to McAfee, his customers believe, without evidence, that directly drinking high levels of the bird flu virus will give them immunity to the deadly pathogen.

Expert Michael Payne told the LA Times that the idea is like “playing Russian roulette with your health.” Payne, a researcher and dairy awareness coordinator at UC Davis’ Western Institute for Food Safety and Security, added that “deliberately attempting to infect oneself with a known pathogen flies in the face of all medical knowledge and common sense.

There is still much unknown about the biology of avian influenza in cattle. Until March 25, when the U.S. Department of Agriculture confirmed the presence of the virus in a Texas dairy herd, cattle were generally considered virtually resistant to H5N1. But since then, the USDA has identified 42 herds in nine states that have contracted the virus. Epidemiological data so far suggests that there has been cow-to-cow transmission following a single spread event and that the 42 herds affected by the outbreak are connected by the movement of cattle between farms.

The limited data available so far on cows suggest that the animals largely develop mild illness from the infection and recover within a few weeks. Their mammary glands are the main target of the virus. A preprint published earlier this month revealed that cows’ udders are teeming with molecular receptors that avian flu viruses latch onto to trigger infection. Additionally, the glands contain multiple types of receptors, including those targeted by human influenza viruses as well as those targeted by avian influenza viruses. So dairy cows could potentially serve as a mixing vessel for different types of flu viruses to reassemble into new variants that trigger outbreaks.

While the virus seems to have a field day in cows’ udders, researchers have found that raw milk is teeming with high levels of H5N1 virus particles, and these particles appear readily capable of spreading to other mammals. In a case study last month, researchers reported that a group of about two dozen farm cats developed severe illness after drinking milk from cows infected with H5N1. Some developed serious neurological symptoms. More than half of the cats died within a few days.

Deadly virus

Data on flu receptors in the two animals could explain the difference between cows and cats. While the cow’s mammary gland contained many types of flu receptors, these receptors were less common in other parts of the cow, including the respiratory tract and the brain. This may explain why they tend to have a mild infection. Cats, on the other hand, appear to have more widely distributed receptors, with infected cats showing viral invasion of the lungs, heart, eyes and brain.

Raw milk proponents – who claim without evidence that drinking raw milk has health benefits over drinking pasteurized milk – reject the risk of exposure to H5N1. They confidently claim – even without proof – that the human digestive system will destroy the virus. And they point out that there is no documented evidence that a human being has ever been infected with H5N1 after drinking contaminated milk.

This last point regarding the lack of evidence of transmission of H5N1 through dairy is true. However, the current outbreak is the first known spread of highly pathogenic avian influenza (HPAI) to the mammary glands of dairy cows. As such, it represents the first known opportunity for such transmission through milk.

Before pasteurization became common in commercial dairy production, raw milk was a common source of infections, containing a cornucopia of germs. According to the FDA, in 1938, dairy outbreaks accounted for 25 percent of all foodborne illness outbreaks. More recently, milk has been linked to less than 1 percent of these outbreaks. The Centers for Disease Control and Prevention notes that areas where raw milk was sold legally between 1998 and 2018 experienced 3.2 times more outbreaks than areas where the sale of raw milk was illegal.

In a question-and-answer document, the Food and Drug Administration notes that “we do not currently know whether HPAI A (H5N1) viruses can be transmitted through the consumption of unpasteurized (raw) milk and products (such as cheese) made from raw milk from infected cows. However, the agency continues, due to this lack of data and the potential for infection, the FDA recommends stopping all sales of raw milk and raw milk products from cattle infected with or exposed to H5N1 . In general, the agency does not recommend consuming raw milk.

Globally, as of March 28, 888 cases of H5N1 have been reported in humans in 23 countries. Of these 888 cases, 463 were fatal. This represents a mortality rate of 52%, but it is possible that there are asymptomatic or undiagnosed cases that could change this rate. In the United States, so far, only one human has been infected with the H5N1 virus in connection with the outbreak in dairy cows: a farm worker who developed conjunctivitis. The man had no respiratory symptoms and recovered. He did not consent to further follow-up, and researchers did not obtain consent to test the man’s household contacts to see if they too were infected.

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Gn Health

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