Federal regulators said Tuesday that samples of pasteurized milk from across the country tested positive for inactive remnants of the avian flu virus that infects dairy cows.
The viral fragments do not pose a threat to consumers, officials said. “So far, 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.
Over the past month, an avian flu virus known as H5N1 has been detected in more than 30 dairy herds across eight states. The virus is also known to have infected a farm worker, whose only symptom was conjunctivitis.
Scientists have criticized the federal response, saying the Agriculture Department has been too slow to share important data and has not adequately tested cattle for 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 the milk, said David O’Connor, a virologist at the University of Wisconsin-Madison.
“The risk of being infected by milk containing viral fragments should be zero,” he said. “Genetic material cannot replicate itself.”
Authorities did not say how many samples of pasteurized milk tested positive for the presence of viral fragments or where those samples came from. These are key questions, experts say. About a third of the samples tested positive, according to two people familiar with the data who were not authorized to speak publicly.
If the fragments are present in many samples throughout the commercial milk supply, this suggests that the outbreak is likely much more widespread than previously thought.
Last week, The New York Times reported that the virus had also been detected in a herd of North Carolina dairy cows that showed no symptoms of illness.
“The problem in dairy cows could be much bigger than we think,” Dr O’Connor said. “That would be our concern – not that the milk itself poses a risk. »
The FDA said it is studying milk samples from several sources, including infected cows, the milk processing line and grocery store shelves. Federal officials are still awaiting the results of experiments to determine whether the milk samples might contain an active virus, according to two people familiar with the ongoing federal reviews.
These tests take much longer than so-called PCR tests which determine the presence of viral material in milk.
Federal officials have repeatedly reassured consumers that the commercial milk supply is safe, emphasizing that dairy producers are required to keep milk from sick animals out of the human food supply.
Almost all milk produced on American farms is pasteurized, a process designed to kill pathogens with heat. Pasteurization should also inactivate flu viruses, which are known to be fragile and sensitive to heat, experts say.
Only recently has the FDA tested the effectiveness of pasteurization on H5N1. The risk of contracting the virus from unpasteurized dairy products remains unknown, but regulators have long warned consumers that raw milk poses various illness risks.
The Centers for Disease Control and Prevention monitors flu testing data and flu-related emergency room visits. “We haven’t seen anything high so far at the local, state or national level,” said Dr. Nirav Shah, the agency’s principal deputy director.
The discovery of viral fragments in milk has raised serious concerns at the White House about how to avoid triggering unwarranted alarm over the dairy supply, according to people familiar with the internal deliberations who were not authorized to speak publicly.
Federal officials are expected to revisit these findings at a news conference in the coming days.
Brian Ronholm, director of food policy at Consumer Reports, an advocacy organization, said it would be “very critical” for officials to clearly communicate the findings and educate consumers about what they mean.
Milk from farms is already pooled in thousands of gallons, which would significantly dilute any virus present. Pasteurization further reduces the levels of viruses present.
Shortly after the September 11 attacks, Michael Osterholm, an infectious disease expert at the University of Minnesota, helped the federal government plan a possible bioterrorism attack that could use botulinum neurotoxin, a highly deadly pathogen, to contaminate the milk.
Working with the dairy industry, he and others identified pasteurization conditions that could inactivate the neurotoxin. This experience reassures him that H5N1 is very unlikely to cause problems, Dr. Osterholm said.
“With a virus like this, I would have to believe that even if you had the highest levels of viral activity you could imagine in milk from the udder of an infected cow, it would be diluted millions of times at course of pasteurization. »
Ingested milk is also broken down by the body’s digestive and immune systems, so “I wouldn’t worry about leftovers,” said Dr. Nahid Bhadelia, director of the Center for Emerging Infectious Diseases at Boston University.
“As long as it’s not a live virus, it’s unlikely there will be a health risk,” she said.
Infected people – and cows – can carry remnants of viral genetic material long after the active infection has resolved. This is why PCR tests for Covid sometimes produce positive results once a person has recovered from the illness.
Affected cows appear to have large amounts of virus in their milk, suggesting it may take some time to get rid of the virus, Dr. Bhadelia said.
“But what’s interesting is we have no idea how long it takes for cows to clear the virus,” she said.
News Source : www.nytimes.com
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