Telltale signs of a multispecies epizootic: Spatial epidemiology of HPAI during the 2022 seabird outbreak.

Understanding an emerging epizootic is particularly challenging in wildlife. We not only need to quantify the epidemiology of an unknown disease, but we also need to do it in systems that are often already vulnerable and not amenable to direct observation and intervention. The recent outbreak of HPAI has taken a stark toll on populations of seabirds and very little is known about the large-scale patterns of its spread, or the intra-colony transmission and virulence parameters. By fitting a spatially structured (metapopulation) SIR model to sparse carcass observations of gannets across Europe, we were able to estimate all epidemiological parameters and reconstruct the distinct shape of the outbreak in a network of 43 colonies. At the metapopulation scale, the disease is driven by both intra-specific and extrinsic transmission whose relative strength varies at different time stages of the outbreak. However, sources external to the breeding population are the main driver of incoming cases into colonies. Within each colony, transmission did not deviate from perfect mixing, indicating that the finer spatial structure of nests is less important than the total cases. Overall, we estimate that between 9-20% of the European gannet population died during the outbreak. Using the gannet metapopulation as a sentinel network, we were able to reconstruct the spatiotemporal spread of the disease, indicating spatial contiguity, but also multiple spatial loci of outbreaks. We discuss possible mechanisms that may explain these patterns and implications for future outbreaks.

Jason Matthiopoulos (1), Stephen Votier (2), Emma Cunningham (3), Jude Lane (4) & Jana Jeglinski (1) (1) University of Glasgow (2) Heriot Watt University (3) University of Edinburgh (4) Royal Society for the protection of Birds

Mortality estimations, impacts on harvest, conservation considerations, and potential mitigation strategies in wild birds