Identification of a new Infectious Pancreatic Necrosis Virus (IPNV) isolate in Atlantic salmon (Salmo salar L.) that causes mortality in resistant fish

Abstract

Infectious pancreatic necrosis (IPN) is an important viral disease of salmonids that can affect fish during various life cycles. In Atlantic salmon, selecting for genetically resistant animals against IPN has been one of the most highly praised success stories in the history of fish breeding. The findings that resistance against this disease has a significant genetic component, which is mainly controlled by variations in a single gene, has helped to reduce the IPN outbreaks over the past decade to a great extent. In this paper, we present the identification of a new isolate of the IPN virus, from a field outbreak, that had caused mortality, even in the genetically resistant animals. We recovered and assembled the full-length genome of this virus, following deep-sequencing of an infected tissue. The comparative sequence analysis revealed that for the critical amino acid motifs, previously found to be associated with the degree of virulence, the newly identified isolate is similar to the viruss avirulent form. However, we detected a set of deduced amino acid residues, particularly in the hypervariable region of the polyprotein, that collectively are unique to this strain compared to all other reference sequences assessed in this study. We suggest that these mutations have likely equipped the virus with the capacity to escape the host defence mechanism more efficiently, even in the genetically deemed IPN resistant animals.