A “small but detectable quantity” of infectious virus H5N1 avian flu The virus was able to survive a common approach to pasteurizing milk, according to new research co-authored by scientists at the National Institutes of Health.
The findings, published Friday in the New England Journal of Medicine, were based on experiments conducted in the agency’s laboratory. The researchers note that this is not the same as finding the infectious H5N1 virus in grocery store milk.
So far, authorities have not detected any infectious viruses in supermarket milk samples.
The discovery comes as authorities continue to identify new infected herds during this year’s unprecedented outbreak of H5N1 avian flu in dairy cattle.
Infections have been detected in cows on farms in at least a dozen states, with most positive tests coming from raw milk samples that were full of the virus. The authorities called on states to curb sales of raw milk who could spread the virus and have warned consumers against consuming raw milk.
“The study reflects experimental conditions and should not be used to draw conclusions about the safety of the milk supply in the United States,” a Food and Drug Administration spokesperson said in a statement.
In the real world of commercial dairy processing, milk from infectious cows is likely mixed with milk from healthy cows, diluting the virus and making it less likely that there will be enough of it to survive. The technical details of how the milk is pasteurized, as well as the additional steps to process the milk, also reduce the risk. Pasteurization involves treating milk at high temperatures for a period of time to remove contamination.
Results from previous FDA studies of 297 samples of retail dairy products like milk and yogurt found no infectious viruses. Previous tests found only a few harmless fragments of the remaining virus pasteurization.
Laboratory experimental conditions
“These are more or less experimental laboratory conditions. And we think that mechanical pasteurization in dairy farming will probably be more effective than what we are doing,” said Vincent Munster, head of the virus ecology unit at the National Institute of Allergy and Infectious Diseases.
The Munster, Mont., lab has for years studied the ability of viruses to remain infectious under a variety of conditions, including previous work on pasteurizing pathogens in milk, such as during a coronavirus outbreak in camels from Jordan.
In this study, they looked at two pasteurization approaches, tested on milk with concentrations of H5N1 added at levels similar to those seen in some highly infectious cows.
One pasteurization method involved heating milk to 72 degrees Celsius (about 161 degrees Fahrenheit) for 15 seconds, similar to the “high heat, short time” method widely used in the dairy industry. This resulted in milk containing what Munster said still contained “trace amounts of infectious virus.”
“You’re really talking about 10 virus particles, whereas the initial starting dose would be about 10 or 100 million virus particles,” Munster said.
He also highlighted the differences between the lab study and actual industry practices, which give commercial milk pasteurization a step forward against the virus.
“There is an initial period in the pasteurization of cow’s milk where the milk has to go from, say, 4 degrees to 72 degrees (Celsius). And obviously, once it starts to reach around 56 degrees, it starts already to inactivate the virus,” he said.
The second pasteurization approach – half an hour at 63 degrees Celsius – was found to be more effective. The infectious virus was undetectable within minutes, well before pasteurization was complete.
“Pasteurization methods were developed to reduce the amount of viable bacteria in milk to extend refrigerator life, so to speak. And they’re not necessarily initially designed to inactivate viruses,” Munster said.
Pasteurize milk for longer or at warmer temperatures
Munster believes that even adding an extra 5 to 10 seconds of pasteurization could offer the dairy industry a “safety buffer”, ensuring that no active viruses remain in the milk, even if their raw milk supply is appears to contain greater concentrations of infectious virus than that in the laboratory. .
“If you really want to be 100% sure that there is no active virus, increasing the pasteurization time, even by 5 to 10 seconds, would allow you to really increase that margin of safety,” Munster said .
But an FDA spokesperson said its test results so far show that the pasteurization processes used by U.S. dairy companies are effective at killing H5N1. Many companies are “using higher temperatures, often well above minimum standards,” the spokesperson said, as well as equipment to heat milk more consistently.
“(T)he United States would be hesitant to change pasteurization parameters without data demonstrating a public health need,” the spokesperson said, warning that changing the standards would affect the flavor of dairy products.
The agency has so far not released the results of its own study to validate pasteurization of raw milk for H5N1, first announced earlier this year. Last month, he cited “the totality of evidence” in reiterating that “the commercial milk supply is safe.”
The spokesperson said the FDA study “is a top priority for the agency” and that it was working to share the results in the near future. The agency seeks to validate “real-world processing conditions” with equipment used in commercial facilities.
“Sound scientific data is essential to inform public health decisions such as those made by the FDA regarding food safety and we take the current situation and the safety of the milk supply very seriously,” the spokesperson said. -speech.
Munster said the FDA and U.S. Department of Agriculture have also conducted studies on pasteurization, among a number of groups that have confirmed that warming milk is often able to completely inactivate the threat of the H5N1 virus.
“Fortunately, they inactivate viruses very well. But I think the focus should be twofold: making sure that pasteurization is up to the task that we ask of it, and the data suggests that it is, but also that we should minimize any H5N1 positive milk entering these dairy pasteurizations,” he said.