Federal regulators found fragments of the avian flu virus in about 20 percent of retail milk samples tested in a nationally representative study, the Food and Drug Administration said in a statement Thursday. up to date online.
Samples from areas of the country where dairy herds are known to be infected with the virus were more likely to test positive, the agency said. Regulators have said there is no evidence that this milk poses a danger to consumers or that live viruses are present in milk on store shelves, an assessment that public health experts agree with. ‘agreement.
But finding traces of the virus in such a high proportion of samples from across the country is the strongest signal yet that the outbreak of bird flu in dairy cows is wider than the official tally of 33 infected herds in eight states .
“This suggests that there is a large amount of this virus out there,” said Richard Webby, a virologist and flu expert at St. Jude Children’s Research Hospital.
Dr Webby said he believed it was still possible to eradicate the virus, known as H5N1, from the country’s dairy farms. But it will be difficult to design effective control measures without knowing the scale of the outbreak, he said.
The findings also raise questions about how the virus escaped detection and where else it might be spreading silently. Some scientists have criticized the federal testing strategy, calling it too limited to reveal the true extent of viral spread.
Until Wednesday, when the Department of Agriculture announced mandatory testing of dairy cows moving across state lines, cow testing was voluntary and primarily focused on cows with obvious symptoms.
As of Wednesday, only 23 people had been tested for the virus, while 44 people were being monitored after being exposed to it, according to the Centers for Disease Control and Prevention.
A widespread outbreak in cows would pose a higher risk to farm workers, the dairy industry and public health in general. Sustained spread among cows would give the virus more opportunities to acquire mutations that would make it more transmissible between humans.
The FDA did not provide details Thursday regarding the number or sources of the samples.
“You wouldn’t just want to go to places where you knew there was activity and cows – you want to go to places where at least there is no bird flu reported,” said the Dr. Webby.
Experts believe the pasteurization process, during which milk is briefly heated, should inactivate this avian flu virus, known as H5N1.
“And when you destroy the virus, it releases genetic material,” said Samuel Alcaine, a microbiologist and food scientist at Cornell University. Genetic fragments left behind are not capable of causing infection.
“It’s not surprising” to find them in milk, he added. “That doesn’t mean milk isn’t safe.”
Federal authorities still conduct the tedious testing necessary to determine whether viable virus remains in milk after pasteurization. Scientists believe this prospect is very unlikely.
Dr. Jeanne Marrazzo, director of the National Institute of Allergy and Infectious Diseases, said at a news briefing Wednesday that some federally funded researchers have tested for live viruses in retail milk but found none, a sign that pasteurization had killed the virus. before the milk hits grocery store shelves.
Dr Marrazzo warned that although the results were from a small sample, they were “good news”.
“To really understand the scope here, we have to wait for the FDA’s efforts,” she said.
Finding traces of the virus in 20 percent of commercial milk samples does not mean 20 percent of the country’s dairy herds are infected, experts warn. “It’s too early to try to do these kinds of superficial calculations,” Dr. Alcaine said.
Milk from several farms is generally pooled. If the virus shows up in many milk samples from the same pool, it could mean that many cows are infected – or that a smaller number of infected cows are shedding large amounts of virus, Dr. Alcaine said.
However, even in the latter case, a positivity rate of 20 percent would suggest that well over 33 herds are infected, he noted.
At Wednesday’s press conference, Dr. Donald A. Prater, acting director of the FDA’s Center for Food Safety and Applied Nutrition, noted the novelty of the research effort. No studies have ever been done on the effects of pasteurization on the avian flu virus in milk, he said.
Regulators are examining milk at different stages of the commercial supply chain, he added, including milk on grocery store shelves, and are also studying potential differences between dairy products, such as those between whole milk and cream, Dr. Prater said.
News Source : www.nytimes.com
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