Three cases in two months alarm avian flu observers: three people who had no contact with infected livestock. Including a teenager in whom the virus shows signs of adaptation to humans.
That doesn’t mean the worst-case scenario is happening. “This is not, in any way, day 1 of a pandemic,” said microbiologist Scott Hensley of the University of Pennsylvania on November 18 in an interview with the medical magazine STAT. “There is no indication of human-to-human transmission, which is good. But this is the scenario we fear. »
His remarks are a reference to the fact that, whenever a virus succeeds in transmitting from an animal to a human, this does not mean that it has acquired the necessary mutations to then be transmitted between humans. Except that since it was identified in Hong Kong in 1997, H5N1 avian influenza has shown an ability to first infect all kinds of bird species, then increasingly mammal species including, more recently, cows.
Dozens of cases
Since this spring, 52 agricultural workers in the United States have been diagnosed as having been infected with this H5N1 virus, due to exposure to infected poultry or cows. We suspect that this figure is an underestimate, as many breeders have been reluctant to authorize systematic screening of their flocks. The medical authorities, in Washington and in the various affected regions, have also been criticized for not having tightened the screws more on breeders.
Of the three cases that are not linked to farms, two are in the United States. The first was reported in September in Missouri. The second is a child in California, who was reported on November 19. None required hospitalization. The third is a teenager in British Columbia, who had to be hospitalized on November 8 and was described at that time as being “in critical condition.”
It is in this adolescent that the sequencing of the virus’s genes, deposited by Canadian researchers in a public database, reveals three differences described as “keys” for possible transmission between humans.
More precisely, these are mutations in hemagglutinin, a protein which, present on the surface of the virus, attaches to the cells that the virus tries to “invade”. In other words, these mutations would, in theory, enhance the ability of the virus to “attach” to human cells.
Not all viruses identified in adolescents contain these mutations, which suggests that researchers were dealing with a “mixture” of two types of virus, the first, which is similar to the one currently found in poultry – and not cows, unlike the two American cases – and a second, who would be the newcomer. The British Columbia Ministry of Health said on November 26 that follow-up with relatives had revealed no other infections.
Just as the 52 farm workers might be an underestimate, so too might these three cases be an underestimate: so far, the vast majority of these human cases have not resulted in serious symptoms, so which means many others may have slipped under the radar. This is precisely what worries observers: “the thing to remember is that there is more transmission in the community than what is detected”, recalls November 26 in the magazine Salon Dr. Abraar Karan, infectious disease researcher at Stanford University.
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