It’s “the epidemic [de grippe aviaire] the largest observed in Europe to date”. In a report published on Monday 3 October, the European Food Safety Authority (EFSA) confirms that the 2021-2022 season has been exceptional in several respects. Over the period from June to September, EFSA reports an “unprecedented number of detections of the highly pathogenic avian influenza virus in wild and domestic birds”. The summer was notably marked by an “unusual persistence of the virus in wild birds” observed in fifteen European countries. Fatal outbreaks have been observed among breeding colonies of seabirds (gulls, gulls, gannets, etc.) on European coasts, particularly in France, the Netherlands and the United Kingdom.
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However, summertime is usually the quiet time for the circulation of the avian influenza virus, which traditionally spreads from north to south during migratory periods of wild birds. Consequence of this disrupted seasonality and the persistence of the virus in the sedentary fauna: Farms were not spared in the summer when they experienced a particularly virulent epidemic in the first half of 2022. A total of 47 million poultry had to be slaughtered in Europe this year, including 16 million in France. After a black winter and spring, in the June-September period, “the number of disease outbreaks in domestic birds was down compared to previous months, but more than five times higher than in the same period last year,” EFSA said.
Mammalian transmissions monitored
Another notable fact, according to the European agency: “The geographical scale of this year’s epidemic is unprecedented, with reported cases ranging from Svalbard, Norway, southern Portugal to Portugal and Ukraine, affecting a total of thirty-seven countries on the European continent. The same H5N1 virus also crossed the Atlantic in the fall of 2021, causing unprecedented contamination in North America. In France, relatively spared areas so far this year are on the front lines, notably Brittany, which has a high risk of farm-to-farm spread due to its high density.
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Finally, the peculiarity of this year’s epidemic is that it is dominated by a subgroup of H5N1 viruses, clade 2.3.4.4b, first identified in October 2020 in the Netherlands. Since these viruses are very conducive to reassortment, several genotypes are circulating, some of which have only appeared since June. The adaptability of these viruses is thus one of the explanations for their persistence in summer. Health authorities are particularly monitoring transmission to mammals, with the virus being detected in many species this year (fox, badger, polecat, lynx, porpoise, otter, seal, dolphin, brown bear, etc.). However, no diffusion between mammals was observed. The risk of transmission to humans is classified by EFSA as low in the general population and low to medium for those employed on farms.
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