Modelling the potential exposure of Atlantic salmon post-smolts to the infectious salmon anemia virus during simulated outbreaks at salmon farms

Assessing the exposure of wild hosts to waterborne pathogens during aquaculture outbreaks is key to understand pathogen transmission between farmed and wild fish. In this study, we coupled an Atlantic salmon (Salmo salar) post-smolt migration model with an infectious salmon anemia virus (ISAV) dispersal model to simulate their potential exposure to outbreaks at 19 salmon aquaculture sites in the Quoddy region (New Brunswick, Canada, and Maine, USA). Exposure of virtual post-smolts to ISAV varied with farm location and outbreak timing. Simulations indicated that post-smolts could encounter relatively high ISAV concentrations but were unlikely to become infected from a single outbreak when applying a laboratory-derived minimum infectious dose, even under worst-case conditions. However, reliance on a strict threshold may underestimate infection probability in the wild, where host susceptibility and environmental variability can permit infection at lower doses. While this modelling framework offers a tool to evaluate potential impacts of viral outbreaks and aquaculture-related risks for wild species, validating the ISAV dispersal model with field data remains essential to strengthen predictive capacity and support evidence-based decision‑making.