The predictable HPAI H5 outbreaks in European wild birds

Highly pathogenic avian influenza (HPAI) H5 viruses have caused widespread mortality in wild birds and poultry, with increasing spillover risk into mammals. The recently dominant clade 2.3.4.4b has produced multiple epidemic waves, first driven by H5N8 and more recently by H5N1, which has spread more rapidly, infected a broader host range, and caused higher mortality. While earlier studies identified consistent roles of waterbird community composition in shaping HPAI outbreaks, it remains unclear whether these factors also apply to the currently circulating H5N1. We analyzed HPAI H5N1 outbreaks in European wild birds during the 2021/22 epidemic, examining the influence of waterbird communities and environmental variables, and compared these patterns with earlier epidemics, including H5N1 in 2005/06 and H5N8 in 2016/17 and 2020/21. Our results showed that waterbird abundance, species richness, and the abundance of key species were positively associated with disease occurrence, whereas phylogenetic diversity was negatively associated, suggesting greater interspecific transmission among closely related hosts. Models trained on earlier epidemics accurately predicted the H5N1 occurrence in 2021/22. These findings demonstrate consistent effects of waterbird community composition across multiple epidemics and highlight their values as predictors of HPAI risk. Integrating community metrics into surveillance and early-warning systems can strengthen our capacity to anticipate future outbreaks across clades and subtypes.