The spatial and temporal spread of highly pathogenic avian influenza in North America: Newton’s Cradle hypothesis

Abstract The recent emergence of highly pathogenic H5N1—especially clade 2.3.4.4b has led to widespread mortality in poultry and wild birds and has raised significant concerns for the dairy industry and human health. Migratory waterfowl are considered the main source of infection, and we used publicly available surveillance data and bird observation data from continental North America to show clear seasonal signals correlated with waterfowl movement, both on the continental scale and in three of the four flyways. In early 2024, the virus expanded its host range, and we observed a phase transition with the loss of the seasonal signal coupled with a concomitant increase in the proportion of mammalian cases. We also identified a second harmonic, with a regional east-to-west movement with infections spreading between regional flyways, followed by local viral amplification. We likened this to the movement of balls in a Newton’s Cradle with an analogy between potential and viral energy. We used bird data to identify bird species associated with viral cases and identified specific waterfowl species and highlighted the importance of predatory and scavenging birds, specifically raptors and gulls, in local amplification. These findings will help to focus surveillance strategies both at local and regional levels.