Infectious Pancreatic Necrosis in Atlantic Cod (Gadus morhua): Complete Viral Genome Characterization From the First Norwegian Field Case Suggests Cross-Species Transmission.

We describe the first natural outbreak of infectious pancreatic necrosis (IPN) in farmed Atlantic cod (Gadus morhua) in Norway. IPN was originally described in young salmonids, but the greatest losses have historically occurred in Atlantic salmon (Salmo salar) following sea transfer despite high vaccination coverage. The number of cases fell drastically in Norway after the introduction of IPN virus (IPNV)-resistant QTL-roe and the reduction of 'house strains'. However, recent reports suggest that IPN is re-emerging as an important health challenge in Norwegian aquaculture. Carrier-state infection is documented in many species of fish, molluscs, and crustaceans. Previously, the disease in farmed cod has only been reported from Denmark and the Faroe Islands (1990s). The present case occurred in juveniles in 2024. The main histopathological finding was exocrine pancreatic necrosis, consistent with IPN in salmonids. Viral antigen in lesions was visualized by immunohistochemistry. IPNV infection was confirmed by real-time RT-PCR and virus isolation. Whole-genome sequencing showed that the NVI-066 isolate clustered closely with IPNV strains typically associated with Atlantic salmon, suggesting cross-species transmission, although the source of infection could not be determined. This study demonstrates that clinically relevant IPN can occur in Atlantic cod under field conditions and extends current understanding of IPNV host range, transmission, and disease expression. The findings are particularly relevant for the expanding cod aquaculture industry, highlighting the need for targeted surveillance, biosecurity, and management strategies.