A scientific team confirmed on Wednesday the most feared scenario: the highly pathogenic avian influenza virus, which has been invading dairy farms in the United States for months, has managed to jump from cow to cow, and from cattle to cats and a raccoon. The researchers, from Cornell University, have issued an alert. “Efficient and sustained transmission from mammal to mammal is unprecedented. It is worrying because it can cause the virus to adapt, improving its infectivity and transmissibility to other species, including humans,” they warn in their study, published urgently. in the magazine NatureThe authors call for strict measures to prevent the spread of the disease to cows and “reduce the risk of a pandemic in humans.”
The planet is experiencing the worst bird flu crisis ever known. A subtype of the H5N1 virus, called 2.3.4.4b, emerged in 2021 in wild birds and has since killed hundreds of millions of birds worldwide. The World Health Organization still considers the risk to citizens to be “low,” although its records show that the H5N1 virus has jumped from birds to at least 889 people since 2003, killing 463 of them (52%). Scientists’ worst nightmare is that a virus with such lethality mutates and is capable of being transmitted from human to human, something that has not happened so far.
Cornell researchers, led by Brazilian virologist Diego Dielhave observed that this subtype of the virus has a great capacity to infect udder cells and concentrate in milk, although it also appears in the lungs of cows. Scientists speculate that the pathogen can be transmitted by respiratory or oral routes, but they also suggest that the virus enters through the nipple orifice from contaminated soil or milking machines. As for the cats and the raccoon, the hypothesis is that they were infected by drinking infected milk. Two months ago, an experiment on mice showed that raw milk can contain viruses capable of transmitting the disease.
To the virologist Elisa Perez He doesn’t like what is happening in the United States, where there are already 168 flocks affected in 13 states since the first case was detected in a cow on March 25. “It is very worrying, because it implies that cows constitute a new reservoir of avian influenza – at least of this specific genotype – and that they can act as a source of infection for other species, both birds and mammals. This is something that has never been observed before for this virus, since the only natural reservoir of avian influenza was birds,” warns the expert, from the Animal Health Research Centrein the Madrid town of Valdeolmos. Infected cows may have symptoms such as reduced appetite, digestive disorders, respiratory problems and reduced milk production. So far, there have only been outbreaks in cattle in the United States.
The nine farms analysed in the study are located in Texas, New Mexico, Ohio and Kansas. They are open-air farms where wild birds have contact with dairy cows, both directly and indirectly, through contaminated water or feed. The first farms affected are on a route commonly used by migratory birds to cross North America. On 25 January, a scientific team found in a Canadian goose found in Wyoming the B3.13 version of the 2.3.4.4b subtype of the H5N1 virus, which is the cause of unprecedented outbreaks in dairy cattle. The analysis of the complete genome of the virus in cows has not detected mutations that favour the jump to humans.
Pérez points out that cows on a farm in Ohio were infected after the arrival of asymptomatic cattle from another facility in Texas. “This confirms that apparently healthy cows can transmit the virus. In other words, not all cows develop clinical symptoms after infection. This has very important implications for surveillance systems,” explains the virologist. “With these data, it is clear that passive surveillance should not be carried out alone (analyzing only samples from cows with symptoms), but it is essential to also include active surveillance programs, such as, for example, analyzing tank milk on all beef farms, as will begin to be done.” in Coloradoone of the states most seriously affected by avian flu in cows,” adds Pérez.
The American epidemiologist Maria van Kerkhovedirector of the emerging diseases unit of the World Health Organization, declared Two months ago, “with almost total certainty, we will have another flu pandemic in our lifetime.” Virologist Diego Diel points to H5N1 from his laboratory at Cornell University. “It is difficult to predict which virus will be next, but, given the propensity of flu viruses to cause pandemics, it is very important to closely monitor the H5N1 situation in dairy cattle,” he explains to EL PAÍS.
The first outbreak that set off alarm bells around the world occurred on a mink farm in Spain. In the fall of 2022, dead seagulls and gannets appeared on Galician beaches. In early October, on a fur farm in Carral, a few minutes’ drive from A Coruña, American minks began to die from hemorrhagic pneumonia. The mortality rate of the outbreak exceeded 4% in just seven days. study The group led by biologist Montserrat Agüero of the Ministry of Agriculture’s Central Veterinary Laboratory suggested in January 2023 that the bird flu virus had jumped from wild birds to minks, mutated on farms and been transmitted from mammal to mammal. Also early last year, the mass death of sea lions from bird flu in Peru suggested that the virus could be jumping between mammals in the wild. The Dutch veterinarian Thijs Kuikenfrom the Erasmus University Medical Center in Rotterdam, then asked EL PAÍS a question: “If it occurs in minks and sea lions, why wouldn’t it occur in humans?”
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