In the past four years, avian influenza (bird flu) has devastated poultry farms in most of the major poultry-producing countries and caused the largest decline in the global wild bird population in decades. It also affects numerous mammal species, and some humans. A panzootic – the animal equivalent of our pandemics – that has been made possible by the virus's adaptation to wild birds.

Farm birds – mainly hens, chickens, geese and ducks – bear the brunt of avian influenza. Partly because the global poultry population makes up 70% of the world's birds, but also due to the collective culling measures taken upon the discovery of the first infection case.

Until recently, "wild birds did not have a central role in virus perpetuation," write Marcel Klaassen and Michelle Wille, Australian researchers, in a study published in Nature Ecology & Evolution in 2023.

But the emergence in 2021 of a new viral offshoot in the large family of the H5N1 avian influenza changed the situation. Variants of this new clade 2.3.4.4b have spread worldwide, moving from continent to continent. First Asia, then Europe, North America, South America, and finally the French Southern and Antarctic Lands, north of Antarctica. The clade "has now adapted from poultry to wild birds, which explains the explosion of sustainable outbreaks in wild birds, including in remote areas without poultry," analyze Klaassen and Wille.

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