This is “the epidemic [de grippe aviaire] the largest observed to date in Europe ». In a report published Monday, October 3, the European Food Safety Authority (EFSA) confirms that the 2021-2022 season was exceptional in several respects. Over the period from June to September, the EFSA reports a “unprecedented number of highly pathogenic avian influenza virus detections in wild and domestic birds”. The summer was marked in particular by a “unusual persistence of the virus in wild birds” observed in fifteen European countries. Fatal outbreaks have been observed among breeding colonies of seabirds (seagulls, gulls, gannets, etc.) on European coasts, particularly in France, the Netherlands and the United Kingdom.
However, the summer period is normally the calm period for the circulation of the avian influenza virus, which traditionally spreads during the migration phases of wild birds from north to south. Consequence of this disrupted seasonality and the persistence of the virus among sedentary fauna: farms were not spared during the summer, when they already experienced a particularly virulent epidemic in the first half of 2022. In total, 47 million poultry had to be slaughtered in Europe this year, including 16 million in France. After a dark winter and spring, the June-September period saw “the number of epidemic outbreaks in domestic birds decreased compared to previous months, but it was more than five times higher compared to the same period the previous year”continues the EFSA.
Mammalian transmissions monitored
Another notable fact, according to the European agency: “The geographic scope of this year’s outbreak is unprecedented, with reported cases ranging from the Svalbard Islands, Norway, southern Portugal and as far east as Ukraine, affecting a total of thirty-seven countries. of the European continent. » This same H5N1 virus also crossed the Atlantic in the fall of 2021 and caused an unprecedented level of contamination in North America. In France, areas hitherto relatively spared find themselves on the front line this year, particularly Brittany, with a high risk of spread between farms, due to their high density.
Finally, the particularity of the epidemic this year is that it is dominated by a subgroup of H5N1 viruses, clade 2.3.4.4b, identified for the first time in the Netherlands in October 2020. These viruses being very conducive to reassortment , several genotypes are circulating, some of which have appeared very recently since June. The adaptation capacities of these viruses are thus one of the explanations for their persistence during the summer. Health authorities are particularly monitoring transmissions to mammals, the virus having been detected this year in many species (foxes, badgers, polecats, lynx, porpoises, otters, seals, dolphins, brown bears, etc.). However, no diffusion between mammals has been observed. As for the risk of transmission to humans, it is considered low in the general population by the EFSA, and low to medium for people working professionally on farms.
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