A quarter of a century after it was first observed in poultry in Hong Kong, and three years after it began infecting dozens of mammal species around the world, H5N1 influenza has indeed spread , since last March, on cattle farms in the United States, thereby increasing its daily contact with humans.
What doesn’t help matters is that since last March, American farmers have often been hostile to the idea of letting veterinarians carry out systematic screening of their animals or their employees, which has only given a partial idea of the dispersion of the virus. As of December 11, there were officially 58 cases of H5N1 in Americans, including 32 in California. Most had only mild symptoms.
In two cases, as well as another in British Columbia — who had to be hospitalized in November in critical condition — these involved young people who had had no known contact with a farm, raising fears “community” contamination – that is to say from a loved one, and not from an animal. This last detail is a reminder that a virus can be transmitted from an animal to a human and stop there, because it does not have the capacity to transmit itself in this new “species”. But the worst-case scenario feared by epidemiologists is that it would only take one mutation for H5N1 to soon be capable of being transmitted among humans. Research published at the beginning of December in the journal Science precisely identified this possible mutation, in a protein found on the surface of the virus, a mutation that would help it “cling” to human cells.
We don’t know if the mutation will actually occur one day. But it reinforces the need, in 2025, for systematic screening in cattle farms, something which, in 2024, remained theoretical.
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