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After mice drink raw H5N1 milk, bird flu virus riddles their organs

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Deadly dairy —

No, really, drinking raw milk during the H5N1 outbreak is a bad idea.

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Fresh raw milk being poured into a container on a dairy farm on July 29, 2023, in De Lutte, Netherlands.

Enlarge / Fresh raw milk being poured into a container on a dairy farm on July 29, 2023, in De Lutte, Netherlands.

Despite the delusions of the raw milk crowd, drinking unpasteurized milk brimming with infectious avian H5N1 influenza virus is a very bad idea, according to freshly squeezed data published Friday in the New England Journal of Medicine.

Researchers at the University of Wisconsin-Madison squirted raw H5N1-containing milk from infected cows into the throats of anesthetized laboratory mice, finding that the virus caused systemic infections after the mice were observed swallowing the dose. The illnesses began quickly, with symptoms of lethargy and ruffled fur starting on day 1. On day 4, the animals were euthanized to prevent extended suffering. Subsequent analysis found that the mice had high levels of H5N1 bird flu virus in their respiratory tracts, as well their hearts, kidneys, spleens, livers, mammary glands, and brains.

“Collectively, our data indicate that HPAI [Highly Pathogenic Avian Influenza] A(H5N1) virus in untreated milk can infect susceptible animals that consume it,” the researchers concluded. The researchers also found that raw milk containing H5N1 can remain infectious for weeks when stored at refrigerator temperatures.

Bird flu has not historically been considered a foodborne pathogen, but prior to the unexpected outbreak of H5N1 in US dairy cows discovered in March, it had never been found at high levels in a food product like milk before. While experts have stepped up warnings against drinking raw milk amid the outbreak, the mouse experiment offers some of the first data on the risks of H5N1 from drinking unpasteurized dairy.

Before the mouse data, numerous reports have noted carnivores falling ill with H5N1 after eating infected wild birds. And a study from March in the journal Emerging Infectious Diseases reported that over half of the 24 or so cats on an H5N1-infected dairy farm in Texas died after drinking raw milk from the sick cows. Before their deaths, the cats displayed distressing neurological symptoms, and studies found the virus had invaded their lungs, brains, hearts, and eyes.

While the data cannot definitely determine if humans who drink H5N1-contaminated raw milk will suffer the same fate as the mice and cats, it highlights the very real risk. Still, raw milk enthusiasts have disregarded the concerns. PBS NewsHour reported last week that since March 25, when the H5N1 outbreak in US dairy cows was announced, weekly sales of raw cow’s milk have ticked up 21 percent, to as much as 65 percent compared with the same periods a year ago, according to data shared by market research firm NielsenIQ. Moreover, the founder of California-based Raw Milk Institute, Mark McAfee, told the Los Angeles Times this month that his customers baselessly believe drinking H5N1 will give them immunity to the deadly pathogen.

In normal times, the Centers for Disease Control and Prevention and the Food and Drug Administration strongly discourage drinking raw milk. Without pasteurization, it can easily be contaminated with a wide variety of pathogens, including Campylobacter, Cryptosporidium, E. coli, Listeria, Brucella, and Salmonella.

Fortunately, for the bulk of Americans who heed germ theory, pasteurization appears completely effective at deactivating the virus in milk, according to thorough testing by the FDA. Pasteurized milk is considered safe during the outbreak. The US Department of Agriculture, meanwhile, reports finding no H5N1 in retail beef so far and, in laboratory experiments, beef patties purposefully inoculated with H5N1 had no viable virus in them after the patties were cooked to 145°F (medium) or 160°F (well done).

To date, the USDA has reported that H5N1 has infected at least 58 dairy herds in nine states.

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Fragments of bird flu virus genome found in pasteurized milk, FDA says

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Milk testing —

The test cannot tell if the virus is live. The FDA still assess milk supply as safe.

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Cows being milked

Enlarge / Cows being milked

The Food and Drug Administration on Tuesday announced that genetic fragments from the highly-pathogenic avian influenza virus H5N1 have been detected in the pasteurized, commercial milk supply. However, the testing completed so far—using quantitative polymerase chain reaction (qPCR)—only detects the presence of viral genetic material and cannot tell whether the genetic material is from live and infectious viral particles or merely remnants of dead ones killed by the pasteurization process.

Testing is now ongoing to see if viable, infectious H5N1 can be identified in milk samples.

So far, the FDA still believes that the milk supply is safe. “To date, we have seen nothing that would change our assessment that the commercial milk supply is safe,” the agency said in a lengthy explanation of the finding and ongoing testing.

H5N1 made its startling jump to US dairy cows recently, with the first ever documented cases in a Texas herd confirmed on March 25. It has spread widely since then with at least 32 herds in eight states now known to be infected. The unexpected spread to bovines has raised fears that the virus is evolving to infect mammals more efficiently, and so poses a heightened risk of spread to and among humans.

But amid the alarming outbreak among the country’s dairy herds, federal agencies have appeared confident that the virus poses little risk to no risk to the safety of the milk supply.

“At this time, there continues to be no concern that this circumstance poses a risk to consumer health, or that it affects the safety of the interstate commercial milk supply because products are pasteurized before entering the market” the FDA wrote in an FAQ published Friday. “Pasteurization has continually proven to inactivate bacteria and viruses, like influenza, in milk.”

In the announcement Tuesday, the FDA also highlighted that multiple studies have shown that the pasteurization process for eggs, which uses lower temperatures than what is used for milk, is effective at inactivating H5N1.

Nevertheless, the FDA, along with the Centers for Disease Control and Prevention and the US Department of Agriculture, have continued to investigate potential risks, including establishing whether pasteurization can inactivate this specific virus. The FDA noted in its announcement Tuesday that, while pasteurization is expected to kill the virus, pasteurization is “different than complete sterilization.”

As such, it carried out the qPCR tests, expecting it might find some genetic fragments in the pasteurized milk because virus has been detected in raw milk. “Based on available information, pasteurization is likely to inactivate the virus, however the process is not expected to remove the presence of viral particles,” the FDA explained. “Therefore, some of the samples collected have indicated the presence of HPAI [Highly Pathogenic Avian Influenza] using quantitative polymerase chain reaction (qPCR) testing.”

The FDA did not indicate how many samples it has tested, where the samples were collected from, or the level of viral genetic material the samples contained.

The agency is now working on assessing whether it can identify if any virus particles are infectious using egg inoculation tests, which are considered a gold-standard for determining viral viability. It added that it will release results from those tests and others in “the next few days to weeks.”

“[W]e take this current situation and the safety of the milk supply very seriously. We recognize the importance of releasing further, actionable information,” the FDA said.

Meanwhile, the agency reported that the CDC’s food safety group has been closely monitoring emergency department data and flu testing data for any unusual trends in flu-like illness, flu, or conjunctivitis, which could indicate spread of H5N1 to people. “To date, surveillance systems do not show any unusual trends or activity,” the FDA said.

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