A team of scientists has discovered for the first time infectious highly pathogenic avian flu viruses in the raw milk of cows affected by the disease, according to have announced this Friday the researchers, from the University of Wisconsin-Madison, in the United States. This subtype of the virus has caused the death of hundreds of millions of birds worldwide since 2021 and was first detected two months ago in cows, with mild symptoms, on American farms. The new work has shown that ingesting this milk with viral particles causes the disease in mice.
The authors warn that avian flu viruses can remain infective for “several weeks” in raw milk stored in the refrigerator. A spokesperson for the National Federation of Dairy Industries—the Spanish employers’ association—recalls that, regardless of this new data, raw milk is “a food of possible risk to people’s health,” by causing microbial infections, such as salmonellosis and the listeriosis, so its consumption is discouraged in any case. In Spain, sellers are obligated to include a label with the indication “Raw milk without heat treatment: Consume only after boiling for at least one minute.”
The virologist Immaculate Houses celebrates the effectiveness of the global surveillance system, which has made it possible to identify the pathogen in cows for the first time and detect a multitude of jumps to other species. “People who drink milk without any type of heat treatment may be at risk if it is infected by the virus,” says Casas, head of the Influenza and Respiratory Viruses Laboratory of the National Center for Microbiology, in the Madrid town of Majadahonda.
The expert emphasizes that, for the moment, only two cases of contagion of avian flu from cows to humans have been detected, in a Texas farm and in another from Michigan, in both with very mild symptoms, such as conjunctivitis. “In the mice in the new experiment, a systemic infection did occur. In people, this is very rare. With all the millions of birds, seals and sea lions infected in South America, there have only been two serious human cases, one in Ecuador and the other in Chile. For the animal world, it is extremely worrying, because many animals are dying,” Casas warns.
Only about 30 cases have been recorded in humans worldwide since 2021, most of them mild or asymptomatic, after contact with infected animals, according to the World Health Organization (WHO) count. No human-to-human transmission has been detected. The WHO considers that the risk to public health It is low”but the American epidemiologist Maria van Kerkhovedirector of the organization’s emerging diseases unit, has launched an advert this Friday: “We will almost certainly have another flu pandemic in our lifetime.”
“Disturbing because it is a transmission route that had never been described until now for influenza”
Angela Vazquez, CSIC
The virologist Elisa Perez, from the Animal Health Research Center, shows his concern. “The risk is increasing more and more and there are already at least two cases of contagion in people through contact with infected cows. Until now all H5N1 cases have occurred through close contact with sick or dead birds. Therefore, we are facing a situation of extremely high uncertainty, with a virus that historically only affected poultry, replicating massively in wild birds on all continents, except Oceania, and jumping increasingly frequently to mammals,” he explains. . “We are not just talking about wild mammals (sea lions, foxes, bears…) with 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 United States and Finally, thousands of cows in the United States,” he warns.
Pérez emphasizes that the consumption of raw milk is not that uncommon in the American population. 4.4% of adults claim to have taken it at least once in the last year, according to A study published in 2022 by the United States Food and Drug Administration, with data from surveys conducted between 2016 and 2019. 1.6% reported consuming raw milk at least once a month. “I think we now have enough information for health authorities to prohibit the consumption of raw milk in the United States, at least until the current situation is controlled,” says the virologist from the Animal Health Research Center.
In just two months, avian flu has been detected in 58 farms of dairy cows in the United States. On April 29, the country’s Centers for Disease Control and Prevention reported the discovery of two dead cats on a Texas farm, with widespread infection with the virus, after ingesting raw milk.
“We now have enough information for health authorities to prohibit the consumption of raw milk in the United States”
Elisa Pérez, Animal Health Research Center
The results of the new experiment, published in the specialized magazine New England Journal of Medicine, show that the mice, after drinking 50 microliters of infected raw milk, began to have symptoms the next day, such as lethargy and bristly fur. On the fourth day they were euthanized, so their organs could be studied. The infection was systemic, including in her mammary glands.
Two Spanish virologists, Angela Vazquez and Antonio Alcamí, confirmed for the first time the presence of the virus in Antarctica, on February 24, in two dead skuas (seabirds similar to seagulls) found by Argentine scientists and analyzed at the Spanish Antarctic base Gabriel de Castilla. Vázquez reflects on the discovery of infectious viruses in raw milk. “It is worrying because it is a transmission route that had never been described until now for influenza. He draws attention that the virus has been detected in the mammary glands of mice. If this were the case for a woman who is breastfeeding, she would have to consider stopping,” he points out.
Vázquez, from the Severo Ochoa Molecular Biology Center (CSIC), issues a warning to world authorities. “The more humans have the virus, even if it is only with conjunctivitis, the easier it is for it to end up adapting and transmission between people to occur. I think there is no need to be alarmed, but either more controls begin to be put in place, or possibly it will be the next pandemic. It is true that the cases observed in humans are not very lethal, but the collapse in the system could be similar to that of covid,” he warns.
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