The highly pathogenic new H5N1 avian flu virus may have gained the ability to transmit between mammals and therefore poses “a greater risk to public health” than previously thought, a study by US and Japanese scientists who analysed the variant of the pathogen found on US cow farms warned on Monday.
Last Wednesday, the authorities announced a fourth case of infection of a worker at a dairy farm in Colorado, where an outbreak had previously been detected among dairy cows. As in the three previous cases, this person had only mild symptoms — eye irritation — and these disappeared after taking the antiviral drug oseltamivir.
The United States has already detected infections in 130 livestock farms in twelve states. It is thought that cow udders and automatic milking systems may be behind the livestock epidemic and the cases of infection in workers. Despite the new contagion, the Center for Disease Control of the United States (CDC) continues to consider that the risk to the population posed by this virus is It is lowalthough it recommends close monitoring of people who are in contact with infected animals.
The world is experiencing the worst avian flu crisis ever recorded. A new subtype of the virus, called H5N1 2.3.4.4b, emerged in 2021 and has since led to the culling of hundreds of millions of farm birds and the death of millions of wild birds. These birds have infected thousands of wild marine and terrestrial mammals. The epidemic has now reached all continents, including remote Antarctica, where Spanish scientists detected a “massive outbreak” in April. This scope shows the virus’s ability to spread through wild species and its jump to domestic ones. There is a real risk that in these jumps between species and recombination of variants, the virus will gain new capabilities, especially the ability to transmit between people, something not observed until now.
The new study, which is published This Monday in the magazine Naturea leading authority in world science, has analysed the infectious capacity of a virus isolated from the milk of an infected cow in the United States. Scientists have shown that it can infect both mice and ferrets and that it is transmitted from mothers to offspring through milk. This type of analysis is only carried out in high-security laboratories.
The researchers also found the virus could be transmitted between ferrets, although with low efficiency. This is a similar conclusion to that of another CDC study that found that the virus isolated from an infected worker could be transmitted between these animals. The researchers also cite the example of the mink farm in Galicia, where an outbreak of avian flu possibly originated in dead birds, and in which there was transmission between animals. This is also the case with the thousands of sea lions and wolves that died in Peru.
The researchers have made another worrying finding. The H5N1 virus analysed has the capacity to infect both bird and mammal cells, including humans, using two different receptors. This may show the bridge of contagion between some species and others that has been observed so far.
The same team has already warned that raw milk from infected cows contains a viral load sufficient to cause infection, which has revived the call from authorities not to consume unpasteurized milk.
The big question now is whether the virus can gain the ability to transmit between people, something that has not been observed so far. “Although so far the cases of H5N1 in humans have been mild, these viruses are highly pathogenic in the animal models we have used. [ratones y hurones]. It is worrying that viruses like this are circulating in nature. And as long as they continue to infect livestock, there will continue to be more cases in humans,” the virologist explained to EL PAÍS. Yoshihiro Kawaokalead author of the study. “It is possible that H5N1 will become more virulent. We don’t want these viruses circulating on farms. The goal is to contain it. Vaccinating animals would reduce the spread, but it may not work 100%. That is why vaccination is a strategy that needs to be evaluated very carefully,” warns Kawaoka, an animal health researcher at the University of Wisconsin in Madison.
Elisa Pérez, a veterinary virologist at the CSIC Animal Health Research Centre, who was not involved in the study, believes that the new data are “very important and worrying”. “We are seeing that this virus has an increasing capacity to be transmitted between mammals, something that has never been seen before in avian influenza.” A virus of this type with an affinity for infecting both birds and mammals has never been seen before. For Pérez, all the new data on milk is especially relevant because of its repercussions on livestock farming and the food industry. “This virus shows a clear preference for the breasts and is transmitted through milk. The quantity of viruses in cow’s milk is enormous, something never seen before. That is why we assume that on farms in the United States the infections are being transmitted through mechanical milking systems and the movement of animals and workers between farms, although we really do not have data to know what is really happening. It is also a mystery why there are so many farms affected in the United States and not one in Europe. There may be more contact with wild birds there, but that is an unanswered question,” he said.
In June, researchers from the United States and Germany assured The New York Times They have found no evidence that H5N1 is transmitted through the air, which would be good news for its containment, although the results have not yet been published in a scientific journal.
Antonio Alcamí, a virologist from the Spanish National Research Council, was part of an international team that detected a massive outbreak of H5N1 in Antarctica. The researcher explains to this newspaper that “the most worrying thing” is the “double specificity of the new virus”, which allows it to bind to the receptor that human cells in the upper respiratory tract have. “It is clear that the virus is changing and this is one more step. We need to increase surveillance of this pathogen,” he believes.
So far, there have been about 30 human infections reported worldwide since 2021, mostly mild or asymptomatic, following contact with infected animals. However, of the seven cases of infection with the 2.3.4.4b variant, four developed severe illness and one died, according to the CDC. No human-to-human transmission has been detected so far. The WHO considers the risk to public health to be It is low”but in May, the American epidemiologist Maria van Kerkhovedirector of the organization’s emerging diseases unit, warned that: “We will almost certainly have another influenza pandemic in our lifetime.”
Meanwhile, in Europe, cases of avian flu in wild birds have fallen dramatically between March and June, according to data published Thursday by the European Centre for Disease Control. The risk of infection with the highly pathogenic H5N1 variant for the general population is low, and low to moderate for people exposed to infected animals, it said. the EU agency.
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