The World Health Organization (WHO) this Monday expressed its concern about the outbreaks of avian flu detected in recent weeks on dairy cow farms in the United States. “It is a cause for concern that the virus infects new species [de animales] and, with this, the number of people exposed to the pathogen increases,” said the agency’s director for epidemics and pandemics, Maria Van Kerkhove.
A total of 36 farms in nine US states have so far detected cases of avian flu in their flocks. The outbreaks were discovered in March after investigations began in January, when several farms noticed a drop in milk production. The symptoms presented by the animals are very mild or almost undetectable. Although investigations are still open, they suggest that the origin of the infections would be wild birds that came into contact with livestock.
How the virus is transmitted between cows remains a mystery. “It does not appear that the transmission is [directa entre animales] through the usual forms of respiratory infections. Rather, it seems that some element used in milking the animals is what facilitates the spread of the virus, although for now these are hypotheses under investigation,” said the director of the WHO Research Center on Avian Pathologies, Richard Webby. The movement of livestock between farms would explain why the virus has been detected in dozens of farms. “It is very likely that the number of farms with cases is greater than the [36] officially detected,” this expert added.
So far, only one worker has been infected in connection with these outbreaks. This is a man from Texas who has developed mild conjunctivitis-type symptoms, but not respiratory ones. The suspicion is that the virus got into his eyes when he scratched them with his infected hand after touching an infected cow.
The information offered at a meeting with experts and journalists this Monday reveals that the milk of affected animals has a high viral load, although the pathogens with the capacity to infect disappear with the pasteurization process. The WHO, like the US authorities, recommends not consuming milk or products made with it that have not been subjected to this thermal process, a minority but widespread practice in the country.
Available data also shows that up to 20% of tested milk on sale in affected States contains viral particles, although these are not infectious. The investigations carried out to date have not found viruses with the capacity to infect other products of animal origin such as meat and eggs in food sales circuits.
For now, the WHO continues to consider the risk that these episodes pose to the general population “low” and “low to moderate” for farm workers and other people exposed to livestock. Cats and raccoons infected with the virus have also been detected in the farm environment.
No apparent risk to people
Despite this, those responsible for the organization do not hide their concern about the danger posed by the presence of the virus in livestock, since although for now no data points to a greater risk for people, the fact that the pathogen circulates and spreads Replication in mammals close to humans increases the likelihood that it will develop mutations that allow it to adapt.
The virus causing the outbreaks is clade (variant) 2.3.4.4b, which emerged in 2020 and quickly spread throughout most of the world through migratory birds, causing the death of hundreds of millions of birds since then. In these four years, viruses have also infected other mammalian species, which has increased concern among experts as to whether the mutations that make this possible could bring the pathogen closer to adapting to humans. For now, however, this clade has had almost no impact on people. The WHO only has 13 documented infections in humans, almost all of them mild, or very mild.
In a risk report published on April 23 together with the Food and Agriculture Organization of the United Nations (FAO) and the World Organization for Animal Health (WHO), the WHO warned that “avian influenza A(H5N1) viruses, especially those of the clade 2.3.4.4b, they continue to diversify genetically and spread geographically”, which together with the jump to mammals gives the pathogen “greater opportunities for viral rearrangement, generating new genotypes”. An example of this has been the “detection of a new form of influenza A(H5N1) virus in poultry in Cambodia, Laos and Vietnam” that contains “the surface proteins of clade 2.3.2.1c that have circulated locally, but internal genes from clade 2.3.4.4b.”
The document recalled that “to date, there have been limited reports of transmission between mammals despite the increase in infections” and maintained that, “although direct evidence is lacking, the large mortalities of marine mammals caused, the infection in multiple animal farms fur in Finland and mink in Spain are consistent with mammal-to-mammal spread in these cases.”
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