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Emergence of D1.1 reassortant H5N1 avian influenza viruses in North America
View ORCID ProfileAlvin Crespo-Bellido, View ORCID ProfileNídia S. Trovão, Wendy Puryear, Alexander Maksiaev, View ORCID ProfileJonathan E. Pekar, View ORCID ProfileGuy Baele, View ORCID ProfileSimon Dellicour, View ORCID ProfileMartha I. Nelson
doi: https://doi.org/10.64898/2025.12.19.695329
This article is a preprint and has not been certified by peer review [what does this mean?].
Abstract
Since 2021, highly pathogenic avian influenza viruses (HPAIVs) belonging to H5N1 clade 2.3.4.4b have circulated widely in North American wild birds and repeatedly spilled over into mammals. In 2025, the first H5N1-associated deaths in humans were recorded in the Western hemisphere, raising questions about how the ongoing evolution of the virus in wild birds impacts spillover risk. Here, our analysis of 21,471 H5N1 genomes identified an evolutionary shift in mid-2024, driven by interhemispheric migration from Asia and reassortment with new antigens. The genotypes that dominated the early years of North America's H5N1 epizootic traced their ancestry back to Europe, but Asia was the source of new "D1.1" genotype viruses that (a) spread faster, (b) have higher reassortment potential, (c) a broader host range, (d) repeatedly spill over to bovines, and (e) cause severe disease in humans, including non-farm workers.
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https://www.biorxiv.org/content/10.64898/2025.12.19.695329v2
...
https://www.biorxiv.org/content/10.64898/2025.12.19.695329v2
View ORCID ProfileAlvin Crespo-Bellido, View ORCID ProfileNídia S. Trovão, Wendy Puryear, Alexander Maksiaev, View ORCID ProfileJonathan E. Pekar, View ORCID ProfileGuy Baele, View ORCID ProfileSimon Dellicour, View ORCID ProfileMartha I. Nelson
doi: https://doi.org/10.64898/2025.12.19.695329
This article is a preprint and has not been certified by peer review [what does this mean?].
Abstract
Since 2021, highly pathogenic avian influenza viruses (HPAIVs) belonging to H5N1 clade 2.3.4.4b have circulated widely in North American wild birds and repeatedly spilled over into mammals. In 2025, the first H5N1-associated deaths in humans were recorded in the Western hemisphere, raising questions about how the ongoing evolution of the virus in wild birds impacts spillover risk. Here, our analysis of 21,471 H5N1 genomes identified an evolutionary shift in mid-2024, driven by interhemispheric migration from Asia and reassortment with new antigens. The genotypes that dominated the early years of North America's H5N1 epizootic traced their ancestry back to Europe, but Asia was the source of new "D1.1" genotype viruses that (a) spread faster, (b) have higher reassortment potential, (c) a broader host range, (d) repeatedly spill over to bovines, and (e) cause severe disease in humans, including non-farm workers.
...
https://www.biorxiv.org/content/10.64898/2025.12.19.695329v2
...
https://www.biorxiv.org/content/10.64898/2025.12.19.695329v2