Raw milk from cows with bird flu contains viruses that can transmit the disease | The science

A team of scientists has for the first time detected infectious, highly pathogenic avian influenza viruses in the raw milk of cows affected by the disease, researchers from the University of Wisconsin-Madison in the US announced this Friday. This subtype of the virus has been responsible for the deaths of hundreds of millions of birds worldwide since 2021 and was first detected two months ago in cows with mild symptoms on American farms. New work has shown that drinking this milk with viral particles causes illness in mice.

The authors warn that avian influenza viruses can remain infectious for “several weeks” in raw milk stored in the refrigerator. The representative of the National Dairy Federation (Spain’s employers’ association) reminds that, despite these new data, raw milk is “a product that poses a possible risk to human health” because it causes microbial infections such as salmonellosis and listeriosis. , so its consumption is not recommended in any case. In Spain, sellers are required to include a label that reads “Raw milk without heat treatment: consume only after boiling for at least one minute.”

Virologist Inmaculada Casas notes the effectiveness of the global surveillance system, which made it possible to identify the pathogen in cows for the first time and to detect many transitions to other species. “People who drink milk without any heat treatment may be at risk if it is contaminated with a virus,” says Casas, head of the influenza and respiratory viruses laboratory at the National Center for Microbiology in Madrid’s Majadahonda.

The expert emphasizes that so far only two cases of bird flu infection from cows to humans have been identified – on a farm in Texas and another in Michigan, both with very mild symptoms, such as conjunctivitis. “The mice in the new experiment did experience a systemic infection. This is very rare in humans. Among the millions of birds, seals and sea lions infected in South America, there have been only two serious human cases: one in Ecuador and the other in Chile. This is extremely worrying for the animal kingdom because many animals are dying,” warns Casas.

According to the World Health Organization (WHO), only about 30 cases of the disease have been reported in humans worldwide since 2021, most of them mild or asymptomatic, after contact with infected animals. No person-to-person transmission of the virus has been detected. The WHO considers the risk to public health to be “low,” but US epidemiologist Maria van Kerkhove, director of the organization’s emerging diseases division, warned this Friday: “We are almost certain to face another influenza pandemic.” throughout our lives.”

“Worrying because this is a transmission route for influenza that has never been described before”

Angela Vasquez, CSIC

Virologist Elisa Perez from the Animal Health Research Center expresses her concern. “The risk is increasing more and more, and there are already at least two cases of people becoming infected through contact with infected cows. Until now, all H5N1 cases have resulted from close contact with sick or dead birds. “We are therefore faced with a situation of extremely high uncertainty: a virus that historically only affected poultry is reproducing massively in wild birds on every continent except Oceania, and is increasingly spreading to mammals,” he explains. “We are not only talking about wild mammals (sea lions, foxes, bears…) that have little contact with humans, we are already talking about minks on fur farms in Spain and Finland, domestic cats in Poland, South Korea and the USA. USA and finally thousands of cows in the United States,” he warns.

Perez emphasizes that raw milk consumption is not unusual among the American population. According to a study published in 2022 by the US Food and Drug Administration, 4.4% of adults say they have taken it at least once in the past year. 1.6% said they took it in 2022. Consume raw milk at least once a month. “I think we now have enough information for health authorities to ban the consumption of raw milk in the United States, at least until the current situation is under control,” says a virologist at the Animal Health Research Center.

In just two months, avian influenza was detected on 58 dairy farms in the United States. On April 29, the nation’s Centers for Disease Control and Prevention reported the discovery of two dead cats on a Texas farm with widespread exposure to the virus after consuming raw milk.

“We now have enough information for health authorities to ban the consumption of raw milk in the United States.”

Elisa Perez, Animal Health Research Center

The results of the new experiment were published in a specialized journal New England Journal of Medicine, show that mice that drank 50 microliters of contaminated raw milk began to show symptoms such as lethargy and bristly fur the next day. On the fourth day they were euthanized so that their organs could be examined. The infection was systemic in nature, including in the mammary glands.

Two Spanish virologists, Angela Vazquez and Antonio Alcamy, first confirmed the presence of the virus in Antarctica on February 24 in two dead skuas (gull-like seabirds) found by Argentine scientists and analyzed at the Spanish Antarctic base Gabriel Castilla. Vasquez reflects on the discovery of infectious viruses in raw milk. “This is concerning because this is a transmission route for influenza that has never been described before. Amazingly, the virus was found in the mammary glands of mice. If this happened to a woman who was breastfeeding, she would have to consider stopping breastfeeding,” he notes.

Vázquez of the Severo Ochoa Center for Molecular Biology (CSIC) is warning global authorities. “The more people who are infected with the virus, even if it’s just conjunctivitis, the easier it is eventually to adapt and spread between people. I think there is no need to worry, but either they will begin to introduce additional control measures, or perhaps this will be the next pandemic. Indeed, the cases observed in humans are not very lethal, but the collapse of the system could be similar to the collapse of Covid,” he warns.

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