️ Episode 206: Wild Birds and the North American H5N1 Epizootic
In this episode of PaperCast Base by Base, we explore how wild migratory birds have shaped the ecology and spread of the 2021–2023 highly pathogenic H5N1 epizootic across North America, and what this means for wildlife conservation and poultry health.

Study Highlights:
Using 1,818 haemagglutinin gene sequences from wild birds, domestic birds, and mammals collected across North America, the authors reconstruct the timing and routes of highly pathogenic H5N1 spread using Bayesian phylogeographical and phylodynamic models. They show that North America experienced around nine separate virus introductions, mainly via the Atlantic and Pacific migratory flyways, and that wild migratory Anseriformes sustained long-distance transmission across flyways. Non-canonical hosts such as raptors, songbirds, owls, and mammals were often infected but rarely acted as sources for onward transmission, functioning largely as dead-end hosts. In agriculture, the study estimates at least 46 and up to 113 independent introductions from wild birds into domestic poultry, with viral lineages persisting on farms for several months but rarely spilling back into wildlife. Comparisons between backyard and commercial flocks suggest that backyard birds tend to be infected slightly earlier and more frequently than commercial poultry, highlighting their potential value as early sentinels of increased viral circulation.

Conclusion:
Together, these findings indicate that managing future H5N1 waves in North America will require sustained surveillance in wild migratory birds and stronger measures at the wild–agriculture interface, rather than relying solely on rapid culling of infected farms.

Music:
Enjoy the music based on this article at the end of the episode.

Reference:
Damodaran L, Jaeger AS, Moncla LH. Ecology and spread of the North American H5N1 epizootic. Nature. 2025. https://doi.org/10.1038/s41586-025-09737-x

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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