Cows are seen on a dairy farm in Virginia on October 5, 2022.
Brendan Smialowski/AFP via Getty Images
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Brendan Smialowski/AFP via Getty Images
Cows are seen on a dairy farm in Virginia on October 5, 2022.
Brendan Smialowski/AFP via Getty Images
Federal officials say the risk to the public remains low after the Food and Drug Administration announced Wednesday that tests on commercially available milk detected traces of avian flu.
The announcement comes amid a national outbreak of highly pathogenic avian influenza (HPAI) among dairy cows that was first confirmed late last month. The disease, highly contagious and often fatal in avian populations, has spread to flocks in at least eight states. At least one person who had contact with presumably sick animals also contracted the virus.
But government officials and scientific experts say there is so far no evidence of infectious viruses in pasteurized milk.
National Institute of Allergy and Infectious Diseases Director Jeanne Marrazzo said on a call with reporters Wednesday that tests of retail milk showed the presence of genetic material from the virus.
Efforts to culture the virus from those samples indicated that the virus was neither infectious nor “live,” Marrazzo said, adding that testing was only done on a small set of samples.
“So far, we have not seen anything that would change our assessment that the commercial milk supply is safe,” the FDA said in a statement.
If pasteurization inactivates the virus, why does it appear in milk?
Pasteurization has been used in the United States for decades to kill harmful bacteria and viruses in milk, but pasteurization cannot erase all traces of a virus.
Some genetic material may be left behind after the pasteurization process, such as like DNA or RNA, the “instructions” that tell the virus what to do, according to Samuel Alcaine, professor of food sciences at Cornell University.
“A car has an accident. It doesn’t work anymore. You can’t drive it. It doesn’t do anything a car does. But you search the rubble and you can still find the instruction manual that tells it how to work,” he said.
Alcaine said that’s probably what’s happening with bird flu in milk: Tests show the virus was there, but it’s no longer capable of causing infection.
The FDA said no studies have been conducted specifically to determine whether pasteurization inactivates avian flu in cow’s milk because bovine infections are so new. However, he adds that previous studies have shown that pasteurization is “highly likely to effectively inactivate heat-sensitive viruses, such as H5N1” and that pasteurization has inactivated avian influenza in eggs, a process that occurs at a lower temperature than for milk.
The FDA said it detected avian flu in milk using quantitative polymerase chain reaction (qPCR) tests, which “do not represent an actual virus that could pose a risk to consumers.”
Further evaluation of milk samples will be done using egg inoculation tests, the FDA said, which it called the “gold standard for determining viable virus.” The agency said it would release the results of several studies within days or weeks.
Is it still safe to drink milk?
“There are no safety concerns,” Alcaine said of milk containing traces of bird flu. “I always buy my milk at my local grocery store.”
Federal officials emphasize that any milk from infected cows is supposed to be thrown away or destroyed and not enter the human diet.
Additionally, any milk sold via interstate commerce in the United States must be pasteurized. The FDA has encouraged consumers not to drink raw, unpasteurized milk.
But Alcaine said the flu is not typically spread through food and the most pressing concern is protecting people like farmworkers, who might come into close physical contact with infected animals.
In an attempt to further contain the outbreak, the USDA’s Animal and Plant Health Inspection Service announced an order Wednesday requiring dairy cows to test negative for avian flu before they can cross state borders. State, among other measures.
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