Germany as a key transit hub for the emergence and spread of high pathogenicity avian influenza H5 clade 2.3.4.4b reassortants in Europe

High pathogenicity avian influenza (HPAI) H5 viruses of the Goose/Guangdong lineage continue to diversify through recurrent reassortment, sustaining an evolving threat to animal health and transboundary disease control in Europe. While multiple incursions of HPAI H5 clade 2.3.4.4b viruses have been documented, the regional and ecological contexts that facilitate reassortment during ongoing circulation remain insufficiently characterized. In this study, we combined nationwide avian influenza surveillance in Germany with whole-genome sequencing and Bayesian phylogeographic reconstruction to investigate virus evolution during the 2024–2025 season. Phylogenetic analyses identified multiple genetically distinct HPAI H5 clade 2.3.4.4b genotypes, including several reassortants that emerged during the observation period. The inferred evolutionary histories indicate repeated virus introductions into Germany, followed by local diversification and onward dissemination across Europe. Spatio-temporal reconstruction consistently highlighted coastal regions along the North Sea and Baltic Sea as major interfaces of viral exchange, in line with their role as convergence zones of migratory bird flyways. Rather than representing a primary source of viral lineages, phylogeographic analyses identified Germany as prominent node within the European HPAI network, consistent with a central role in virus movement and mixing. This pattern was observed across multiple genotypes, supporting a generalized role of this region in HPAI evolution. Together, these findings provide a continental-scale perspective on HPAI virus dynamics and emphasize the value of integrated surveillance approaches combining wild bird monitoring and whole-genome sequencing. From an epidemiological standpoint, expanding surveillance frameworks to include low pathogenic avian influenza viruses is likely to improve early detection of reassortment events and enhance preparedness for the emergence of novel HPAI variants.