US regulators despite an outbreak of bird flu virus among dairy cows, no live virus had been detected in the first batch of retail milk samples they’ve tested.
In an online update, the US Food and Drug Administration said an initial set of tests looking for live virus, not just genetic fragments, suggested that the pasteurisation process was effectively neutralising the pathogen.
“These results reaffirm our assessment that the commercial milk supply is safe,” the FDA wrote in the update, adding that the testing efforts were ongoing.
The New York Times reports that officials also tested infant and toddler formula, which incorporate powdered dairy, and did not find the virus.
The FDA had embarked on a national survey of milk samples shortly after an outbreak of the bird flu virus (H5N1) was discovered among dairy cows.
Government scientists have been testing 297 samples of retail dairy products from 38 states, a swath of the country that covers regions far beyond the nine states known to have infected herds.
The first type of testing regulators conducted, a form of polymerase chain reaction, or PCR, is relatively speedy, but it picks up only genetic traces of the virus and does not tell researchers whether the live pathogen is present.
Last Thursday, the FDA said those tests showed that roughly one in five retail milk samples nationwide contained fragments of bird flu virus, suggesting it was spreading among cows much more widely than previously known.
The samples containing genetic fragments are subsequently tested for live bird flu virus, which, if present, might represent a widespread health threat.
The test for live virus – egg inoculation – is the most sensitive of its kind, but it takes time. The process involves injecting a portion of the milk product into chicken eggs, waiting for the virus to grow in the egg and then looking for signs of an infection.
Chicken eggs are efficient vessels for growing flu viruses; even scarce amounts will thrive there. For that reason, the FDA’s new results strongly suggest that the tested samples did not contain infectious virus and that pasteurisation is working, scientists said.
“The answer at this point seems pretty conclusive that pasteurised milk is safe,” said Samuel Scarpino, a professor of the practice in health sciences at Northeastern University. “The fact that it’s coming back negative is really strong evidence that, at least in the samples they tested, there’s no live virus.”
Scientists said authorities would need to test more milk samples, and keep testing them as the outbreak continues.
Some faulted officials for not acting sooner.
“The FDA should have run these tests six weeks ago, when we first heard about it,” Scarpino said, referring to the outbreak among cattle.
He also urged the government to conduct egg inoculation experiments with milk containing varying concentrations of viral genetic material. Those tests, he said, could offer reassurance that even pasteurised milk containing copious amounts of genetic fragments remained safe to drink.
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