Fragments of bird flu virus discovered in milk

Federal regulators Tuesday said samples of pasteurized milk from around the country had tested positive for inactive remnants of the bird flu virus that has been infecting dairy cows.

The viral fragments do not pose a threat to consumers, officials said. "To date, we have seen nothing that would change our assessment that the commercial milk supply is safe," the Food and Drug Administration said in a statement.

Over the past month, a bird flu virus known as H5N1 has been detected in more than 30 dairy herds in eight states. The virus is also known to have infected one farmworker, whose only symptom was pink eye.

Scientists have been critical of the federal response, saying that the Agriculture Department has been too slow to share important data and has not adequately pursued the testing of cattle for the infection.

Finding viral fragments in milk from the commercial supply chain is not ideal, but the genetic material poses little risk to consumers who drink milk, David O'Connor, a virus expert at the University of Wisconsin-Madison, said.

"The risk of getting infected from milk that has viral fragments in it should be nil," he said. "The genetic material can't replicate on its own."

Officials did not say how many samples of pasteurized milk had tested positive for viral fragments or where those samples had come from. Those are key questions, experts said. Roughly one-third of the samples tested positive, according to two people with knowledge of the data who were not authorized to speak publicly.

If the fragments are present in many samples throughout the commercial milk supply, it would suggest that the outbreak is likely to be far more widespread than has been believed.

The FDA said that it was studying milk samples from several sources, including infected cows, the milk processing chain and grocery store shelves. Federal officials are waiting for results from experiments designed to determine whether the milk samples might contain active virus, according to two people familiar with ongoing federal reviews.

Those tests take much longer than so-called PCR tests that determine whether there is viral material in the milk supply.

Nearly all milk produced on U.S. farms is pasteurized, a process designed to kill viruses with heat. Pasteurization should also inactivate flu viruses, which are known to be fragile and heat-sensitive, experts said.

This article originally appeared in The New York Times.