Assessing HPAI-H5 transmission risk across wild bird migratory flyways in the United States

As natural hosts of avian influenza viruses, wild birds pose an increasing threat to public health. Here, using surveillance data from wild bird infections across the United States (2022-2025), we show that HPAI-H5 transmission exhibits strong interspecific variation, seasonality, and spatial heterogeneity linked to migratory flyways. Phylogeographic analysis reveals that viral genotypes evolve from early, limited transmission along single migratory routes to a nationwide dispersal pattern spanning multiple migratory flyways. Anseriformes exhibits the highest number of infections but the lowest transmission risk, whereas Strigiformes demonstrates the greatest transmission risk. The HPAI-H5 transmission in wild birds along migratory flyways exhibits significant spatial heterogeneity and is associated with bird migration. Meteorological conditions are correlated with outbreak timing and may inform early warning efforts; however, these relationships are nonlinear. These findings provide a foundation for risk assessment, early warning systems, and integrated management of avian influenza in wild bird populations. In this study, the authors use surveillance data and phylogeographic analysis to estimate HPAI H5 transmission risk in U.S. wild birds and show strong seasonality patterns, spatial hotspots, and viral spread expanding across multiple migratory flyways.