Federal regulators announced Tuesday that samples of pasteurized milk from around the country have tested positive for inactive remnants of the avian influenza virus that is infecting dairy cows.
Officials said the virus fragments pose no threat to consumers. “To date, we have not seen anything that would change our assessment that the commercial milk supply is safe,” the Food and Drug Administration said in a statement.
Last month, the avian influenza virus known as H5N1 was detected on more than 30 dairy farms in eight states. The virus is also known to have infected one farm worker, whose only symptom was conjunctivitis.
Scientists have criticized the federal government's response, saying the USDA has been too slow to share critical data and not adequately testing cattle for infection.
David O'Connor, a virologist at the University of Wisconsin-Madison, said that while finding virus fragments in milk in the commercial supply chain is not ideal, this genetic material poses little risk to consumers who drink the milk. .
“The risk of getting infected from milk that contains fragments of the virus should be zero,” he said. “Genetic material cannot reproduce by itself.”
Officials did not say how many samples of pasteurized milk tested positive for virus fragments or where those samples came from. These are important questions, experts say.
If this fragment is present in many samples across the commercial milk supply, it would suggest that the outbreak is likely much more widespread than reported.
Last week, the New York Times reported that the virus had been detected in a herd of dairy cows in North Carolina that had no symptoms of the disease.
“The problem with dairy cows may be much bigger than we know,” Dr O'Connor says. “That would be a concern. It's not that the milk itself is a risk.”
Federal officials have repeatedly reassured consumers that the commercial milk supply is safe, noting that dairy producers must keep milk from sick animals out of the human food supply.
And nearly all milk produced on U.S. farms is pasteurized, a process designed to kill pathogens with heat. Experts say pasteurization should also inactivate the influenza virus, which is known to be fragile and heat-sensitive. It was only recently that the FDA tested the effectiveness of his pasteurization against H5N1.
The discovery of virus fragments in milk raised significant concerns within the White House about how to avoid undue alarm over the dairy supply, according to people familiar with internal deliberations.
Federal officials are expected to address the findings at a news conference in the coming days.
This development story will be updated.