New experiments confirm milk from H5N1-infected cows can make other animals sick — and raise questions about flash pasteurization | CNN (2024)

New experiments confirm milk from H5N1-infected cows can make other animals sick —and raise questions about flash pasteurization | CNN (1)

New tests confirm animals can be infected by raw milk containing the H5N1 virus, known as bird flu — suggesting humans may be at risk, too.


New lab experiments with milk from cows infected by H5N1 influenza,known asbird flu, confirm that it is infectious, especially when left raw, or untreated, andpotentially even whenflash 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 has been conducting rapid research to answer pressing questions in the H5N1 outbreak in dairy cattle.

In a research letter posted online on Friday in the New England Journal of Medicine, the researchers describe the results of experiments using milk from four infected cows — two from New Mexico and two from Kansas.

Because H5N1 virus is considered a select agent, it was handled in a high-security Biosafety Level 3 lab at the University of Wisconsin, using strict safety protocols.

First, they confirmed the raw milk was chock-full of H5N1 virus. Then, they stored some of the raw milk at refrigerator temperature to see if levels of the virus in milk would drop off over time. Over 5 weeks, viral levels in raw milk dropped a bit, but not much.

“That it wasn’t decaying 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 was not involved in the study.

WHITE OAK, MD - JULY 20: A sign for the Food And Drug Administration is seen outside of the headquarters on July 20, 2020 in White Oak, Maryland. (Photo by Sarah Silbiger/Getty Images) Sarah Silbiger/Getty Images Related article Early test results show pasteurized milk with traces of H5N1 virus isn’t infectious, FDA says

In another series of tests, the researchers checked to see what types of pasteurization might work best for inactivating the virus.

They heated small samples of the milk at times and temperatures used in two types of pasteurization: low-temperature, long-time, or vat pasteurization; and high-temperature short-time, or flash pasteurization, which is the most common method used in the US today,according tothe International Dairy Foods Association.

Heating the milk to 63 degrees Celsius, or 145 degrees Fahrenheit, for intervals between 5 and 30 minutes — the vat pasteurization method — reduced the virus to undetectable levels.

Heating the milk to 72 degrees Celsius, or 181 degrees Fahrenheit, for 15 or 20 seconds — conditions that approximated flash pasteurization — greatly reduced levels of the virus in the milk, but it didn’t inactivate it completely.

Milk samples heated for 15 or 20 seconds were still able to infect incubated chicken eggs, a test the US Food and Drug Administration has 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 the large-scale industrial treatment of raw milk,” senior study author Dr. Yoshihiro Kawaoka, a virologist who specializes in the study of flu and Ebola, said in an email.

That’s a good reason not to panic over the study findings, said Lakdawala.

Lakdawala said that commercial flash pasteurization involves a preheating step, which wasn’t done here.It also involves hom*ogenization, a process that emulsifies the fat globules in milk so the cream won’t separate.Both of those steps would probably make it harder for the virus to survive, but she adds that the results of this study suggest full process of commercial flash pasteurization should be done “with all the steps in place.”

Livestock - Curious Holstein dairy cows feed on silage in a freestall barn at a large California dairy / San Joaquin Valley, California, USA. (Photo by: Ed Young /Design Pics Editorial/Universal Images Group via Getty Images) Ed Young/Design Pics Editorial/Universal Images Group/Getty Images Related article Cows have human flu receptors, study shows, raising stakes on bird flu outbreak in dairy cattle

Recent tests of297 dairy productspurchased at retail stores by the FDA found tracesofgenetic material from the H5N1 virus in about 1 of 5 milk samples, and further testing confirmed the viral fragments were inert and couldn’t make anyone sick.

The US Centers for Disease Control and Prevention says the risk to the general public is low, but peopleshould not eat or drinkraw milk or products made from it.

To date, H5N1 influenza has been found in58 dairy herds in nine states. Michigan has now surpassed Texas as the state with the greatest number of infected herds.

To test whether the raw milk could infect other animals, researchers also squirtedsome of the milkinto the mouths of mice. The animals showed signs of illness the next day.

On day four, the mice hadn’t died of their infections, but they were euthanized so that researchers could see what parts of their bodies had become 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 weren’t producing milk at the time.

Taken together, their findings confirm that raw milk can infect susceptible animals, the researchers said—and that could also indicate a risk to humans.

In a recent news briefing, officials with the US Department of Agriculture said that to their knowledge, none of the raw milk from farms known to have H5N1 infections was being sold to consumers.

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    Not all dairy farms are testing their cows, however, and some of the infected cows in the current outbreak have not shown any symptoms.

    “Raw milk is unsafe at any speed, and the notion that you could protect yourself against H5 infection by consuming it is erroneous. There are there are much safer ways to protect oneself namely avoiding raw milk,” CDC Principal Deputy Director Dr. Nirav Shah said in a briefing.

    Asked if therawmilkin the new experimentslooked different than normal, Kawaoka said the researchers only got a small number of samples but some had more debris than milk from healthy cows. That would get filtered out prior to sale, he said.Some of the milk looked yellow-ish, but he points out that milk from healthy and infected cows would likely be mixed together in a big vat, making it look normal — andimpossible to tell whether milk is safe to drink just by looking at it.

    “This is good quality research with conclusions backed up by solid data,” said Dr. Ruth Harvey, deputy director of the Worldwide Influenza Center at the Francis Crick Institute in London, in a comment on the study given to the nonprofit Science Media Centre.

    “The limitations of the experimental set-up for the heat inactivation part of the research are clearly stated: that the conditions used are not identical to large-scale industrial treatment of raw milk,” Harvey said.

    “The findings that viable virus was found in the milk samples after 5 weeks of storage at (4 degrees Celsius), and that mice could be infected through drinking milk containing the virus, back up the conclusions that drinking raw milk could pose a risk,” Harvey added.

    New experiments confirm milk from H5N1-infected cows can make other animals sick — and raise questions about flash pasteurization | CNN (2024)


    New experiments confirm milk from H5N1-infected cows can make other animals sick — and raise questions about flash pasteurization | CNN? ›

    New lab experiments with milk from cows infected by H5N1 influenza, known as bird flu, confirm that it is infectious, especially when left raw, or untreated, and potentially even when flash pasteurized.

    What animals are affected by H5N1? ›

    HPAI A(H5N1) virus infection has been reported in wild mammals such as foxes, bears, seals, and sea lions, and in domesticated animals, including pets such as cats and dogs, farmed mink and foxes, and livestock such as goats and cows.

    Is it safe to drink raw milk? ›

    Raw milk can carry dangerous germs such as Salmonella, E. coli, Listeria, Campylobacter, and others that cause foodborne illness, often called “food poisoning.” These germs can seriously injure the health of anyone who drinks raw milk or eats products made from raw milk.

    Has H5N1 infected humans? ›

    From 2003 to 1 April 2024, a total of 889 cases and 463 deaths (CFR 52%) caused by influenza A(H5N1) virus have been reported worldwide from 23 countries. The most recently reported case in humans prior to the current case, was in March 2024 in Viet Nam (11).

    What is the cow disease in 2024? ›

    [1] first human case of A(H5N1) bird flu in the United States linked to an outbreak in dairy cows was also the first likely case of human infection with A(H5N1) from a cow globally. This was reported on April 1, 2024.

    Is raw milk actually illegal? ›

    In California, although the sale of raw milk and raw dairy products is legal, all such products are required to include this warning on their labels: "WARNING: Raw (unpasteurized) milk and raw milk dairy products may contain disease-causing microorganisms.

    Why is raw milk illegal in Canada? ›

    Canada prohibits the sale of raw milk due to public health threats; however, increased consumer interest in unpasteurized dairy has renewed discussions on a range of issues linked to its benefits, challenges and risks. Through regulations enacted federally in 1991, selling raw milk in Canada is illegal.

    Did humans used to drink raw milk? ›

    Raw milk, which had been safely consumed by humans for nearly 10,000 years, had become a source of deadly diseases such as tuberculosis, typhoid, diphtheria, and scarlet fever. In the late 1800's, it was recognized that raw milk being produced in these conditions was dangerous, and two solutions were proposed.

    Does H5N1 affect dogs? ›

    H5N1 bird flu viruses have been detected sporadically in some domestic animals, including cats during outbreaks in Thailand in 2004, Northern Germany in 2006, and Poland and South Korea in 2023. Additionally, cases have been reported in cats, dogs, goat kids (juvenile goats), and dairy cows in North America.

    Can H5N1 infect pigs? ›

    In conclusion, only 1 of 8 pigs inoculated intranasally with HPAI virus H5N1 underwent transient, low-level infection that resulted in the presence of viral RNA in several tissue specimens and seroconversion at 14 dpi. In naturally infected wild mammals, this virus was prominently detected in the brain (2).

    Does H5N1 affect cats? ›

    They are one of the few species that can get avian influenza. The viruses cats may get include H5N1 or H7N2, which are subtypes of avian influenza. In order to get the virus, cats need to be in contact with waterfowl, poultry, or uncooked poultry that are infected.

    Does H5N1 affect ducks? ›

    The available evidence shows that H5N1 infection is widespread among domestic ducks in southern China (2) and may therefore be endemic in domestic ducks throughout southeast Asia.

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