JoNel Aleccia/AP
New tests confirm that animals can be infected by raw milk containing the H5N1 virus, known as bird flu, suggesting humans could also be at risk.
CNN
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New laboratory experiments with milk from cows infected with H5N1 influenza, known as avian flu, confirm that it is contagious, particularly when left raw or untreated, and potentially even when East Flash pasteurized.
The researchers, from the University of Wisconsin School of Veterinary Medicine, are part of a federally funded program called the Centers of Excellence for Influenza Research and Response, or CEIRR. This network conducted rapid research to answer pressing questions related to the H5N1 outbreak in dairy cattle.
In a research letter published online Friday in the New England Journal of Medicine, researchers describe the results of experiments using milk from four infected cows — two from New Mexico and two from Kansas.
Because the H5N1 virus is considered a select agent, it was handled in a high-security Biosafety Level 3 laboratory at the University of Wisconsin, using strict safety protocols.
First, they confirmed that raw milk was full of H5N1 virus. Then they stored some of the raw milk at refrigerator temperature to see if virus levels in the milk would decrease over time. Over 5 weeks, virus levels in raw milk decreased slightly, but not much.
“The fact that it doesn’t degrade over time is concerning,” said Dr. Seema Lakdawala, an associate professor of immunology and microbiology at Emory University who is also part of the CEIRR network but did not participate. in the study.
In another round of tests, researchers checked which types of pasteurization might be most effective at inactivating the virus.
They heated small samples of milk to times and temperatures used in two types of pasteurization: low-temperature, long-term or in-tank pasteurization; and high-temperature, short-term flash pasteurization, which is the most commonly used method in the United States today, according to the International Dairy Foods Association.
Heating milk to 63 degrees Celsius, or 145 degrees Fahrenheit, for intervals of between 5 and 30 minutes — the vat pasteurization method — reduced the virus to undetectable levels.
Heating milk to 72 degrees Celsius, or 181 degrees Fahrenheit, for 15 or 20 seconds — conditions that approximate flash pasteurization — significantly reduced virus levels in the milk, but it didn’t completely inactivate it.
Milk samples heated for 15 or 20 seconds were still able to infect incubated chicken eggs, a test the U.S. Food and Drug Administration called the gold standard for determining whether viruses remain infectious in milk.
“But we emphasize that the conditions used in our laboratory study are not identical to large-scale industrial processing of raw milk,” said the study’s lead author, Dr. Yoshihiro Kawaoka, a virologist specializing in the study. flu and Ebola. an email.
That’s a good reason not to panic about the study’s results, Lakdawala said.
Lakdawala said commercial flash pasteurization involves a preheating step, which was not done here. It also involves homogenization, a process that emulsifies milk fat globules so that the cream does not separate. These two steps would likely make it more difficult for the virus to survive, but she adds that the results of this study suggest that the entire commercial flash pasteurization process should be carried out “with all the steps in place.”
Recent FDA testing of 297 dairy products purchased in retail stores revealed traces of genetic material from the H5N1 virus in about 1 in 5 milk samples, and further testing confirmed that the viral fragments were inert and could not make anyone sick.
The U.S. Centers for Disease Control and Prevention says the risk to the general public is low, but people should not eat or drink raw milk or products made from it.
To date, H5N1 has been detected in 58 dairy herds across nine states. Michigan has now surpassed Texas as the state with the largest number of infected herds.
To test whether raw milk could infect other animals, the researchers also injected some of the milk in the mouths of mice. The animals showed signs of illness the next day.
By day four, the mice had not died from their infections, but they were euthanized so the researchers could see which parts of their bodies had been infected. Scientists found the virus all over their bodies, with high viral loads in the lungs and respiratory tract. They also found virus in the mammary glands of the mice, even though they were not producing milk at the time.
Taken together, their results confirm that raw milk can infect susceptible animals, the researchers said – and this could also indicate a risk to humans.
At a recent news conference, U.S. Department of Agriculture officials said that to their knowledge, no raw milk from farms known to be infected with the H5N1 virus was being sold to consumers.
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However, not all dairy farms test their cows and some of the cows infected in the current outbreak have shown no symptoms.
“Raw milk is dangerous at any time, and the idea that you can protect yourself from H5 infection by consuming it is wrong. There are much safer ways to protect yourself, including avoiding raw milk,” CDC Principal Deputy Director Dr. Nirav Shah said in a briefing.
When asked if the raw milk in the new experiments appeared different from normal, Kawaoka said the researchers only obtained a small number of samples, but some contained more debris than milk from healthy cows. This would be filtered before the sale, he said. Some of the milk looked yellowish, but he points out that milk from healthy and infected cows would likely be mixed in a large vat, making it look normal – and it would be impossible to know whether the milk was safe to drink just by ‘looking at him. .