Host Species Contribution to the Spatiotemporal Dynamics of the 2024-2025 H5N1 Epidemic in Italy.

This study uses a phylodynamic approach to investigate host species contribution in the spatiotemporal dynamics of the highly pathogenic avian influenza A(H5N1) viruses of clade 2.3.4.4b identified during the 2024-2025 epidemic in Italy. Our findings revealed the key role of swans in the initial virus incursions, the central role of synanthropic bird species as the bridge hosts at the wild-domestic interface, and provided evidence of sustained circulation in both wild and domestic birds of viruses carrying mammalian-adaptive mutations. Overall, our results highlight a complex, multi-host transmission dynamic at the wildlife-domestic interface and underscore the value of a One Health, genomics-informed surveillance approach, explicitly including synanthropic species, to reconstruct transmission pathways and refine control strategies.