Milk contaminated with the H5N1 bird flu virus, which has been found in dairy cattle in nine states, can rapidly sicken mice and affect multiple organs, according to a study published Friday.
The finding isn’t entirely surprising: at least six cats already dead Drinking raw milk containing the virus may present a risk of infection, but the new data adds to evidence that raw milk containing the virus may not be safe for other mammals, including humans.
“Don’t drink raw milk — that’s the message,” said Yoshihiro Kawaoka, a virologist at the University of Wisconsin-Madison who led the study.
Most commercially available milk in the United States is pasteurized. The U.S. Food and Drug Administration has found traces of the virus 20% Officials found no signs of the infectious virus in samples of dairy products on supermarket shelves nationwide and said pasteurised milk was safe to consume.
But Dr. Nahid Badria, director of Boston University’s Center for Emerging Infectious Diseases, who was not involved in the research, said the findings have global implications.
“If this outbreak becomes more widespread in dairy cows, other places that don’t have centralized pasteurization will also be affected,” she warned, “and there are a lot of rural communities that drink milk.”
In the study, Dr. Kawaoka and his colleagues analyzed the virus in milk samples from an infected dairy herd in New Mexico. The researchers found that virus levels slowly declined in milk samples stored at 4 degrees Celsius, suggesting that H5N1 virus in refrigerated raw milk may remain infectious for weeks. The findings were published in the New England Journal of Medicine.
Flu viruses survive well at refrigerator temperatures, and proteins in milk also help stabilize the virus, said Richard Webby, a flu expert at St. Jude Children’s Research Hospital in Memphis who was not involved in the study.
If people who drink raw milk think refrigeration kills the virus, “this clearly shows that’s not the case,” Dr. Webby said.
Mice fed the contaminated milk quickly became ill, with matted fur and listlessness. On the fourth day, the mice were euthanized and the researchers found high levels of the virus in their respiratory systems and moderate levels in several other organs. Like the infected cows, the mice contained the virus in their mammary glands—an unexpected finding.
“These mice are not lactating, but the virus is still found in the mammary glands,” Dr. Kawaoka said. “This is very interesting.”
It is not yet clear whether the presence of the virus in the mammary glands is a feature of this virus or of avian influenza viruses in general. “We’re learning new things every day,” Dr. Webby said. Rats are common pests on farms, providing another potential host for the virus. Cats and birds that feed on infected rats may also become sick.
Cat that died after drinking contaminated milk showed alarming results Neurological symptomsThese included stiff limb movements, blindness, a tendency to walk in circles and weak blinking responses. Dr. Webby said that if the mice were allowed to live longer, they would probably develop similar symptoms.
It is also unclear what the finding means for the course of infection in humans. Second dairy farm worker tests positive A nasal swab of the person tested negative for the virus, but an eye swab tested positive for the virus.
Pasteurization kills bacteria by heating milk to high temperatures. In the new study, when the researchers heated milk at temperatures and times typically used for pasteurization, the viruses were either undetectable or greatly reduced, but not completely inactivated.
Dr. Kawaoka cautioned that laboratory conditions are different from those used for commercial pasteurization, so the results do not mean that milk on grocery store shelves contains active virus.
By contrast, the finding that raw milk contained high levels of the virus was “conclusive,” he said.
Raw milk has become increasingly popular in recent years as health experts and right-wing commentators tout its alleged benefits, especially since the bird flu outbreak. Tastes better and is more nutritious than pasteurized milk. Others believe it can boost immunity.
In contrast, pasteurization preserves key nutrients in milk, calcium, and adds vitamin D to aid absorption. The Centers for Disease Control and Prevention says drinking raw milk can lead to serious complications and even death from various pathogens, especially for people with weakened immune systems.
From 1998 to 2018, the outbreak can be traced back to Raw milk consumption It resulted in 228 hospitalizations, three deaths, and more than 2,600 illnesses.
