Liver involvement in post‐smolt Atlantic salmon, Salmo salar L., infected with infectious pancreatic necrosis virus (IPNV): a retrospective histopathological study

Abstract

Histological changes associated with infectious pancreatic necrosis virus (IPNV) infection have historically been described for the pancreas and gut, but any involvement of the liver was poorly acknowledged or described. The aims of this study were to find robust evidence that the reported increase in liver pathology in Atlantic salmon post-smolts in natural outbreaks was effectively related to IPNV infection and retrospectively to report when such a shift in the involvement of the liver had taken place, supported by a histopathological description for a differential diagnosis. The study reports new findings concerning the dynamics of liver pathology development, with apoptosis, demonstrated by histological and immunological techniques, described as the most relevant and particular feature. Immunohistochemical examination of affected liver suggests apoptosis is not only the result of the virus infection itself but triggered through the action of the host's innate immune response. Liver involvement contributes to the nature of infection and becomes an important factor in the disease process. Additionally, it was established that the increase in infectious pancreatic necrosis prevalence is correlated with a new distinct pattern of outbreak distribution throughout the year. The role of smolt category (i.e. S1, S1/2 or S0), hence timing of seawater transfer as a strong correlating factor, is discussed.

Histology, immunocytochemistry and qRT‐PCR analysis of Atlantic salmon, Salmo salar L., post‐smolts following infection with infectious pancreatic necrosis virus (IPNV)

“…It is interesting to combine the results from the present experimental infection with the study by Noguera & Bruno (in press) presented in this issue where liver pathology is described as the main characteristic of IPN in a recent histological survey.…”

Impact of Salmonid alphavirus infection in diploid and triploid Atlantic salmon (Salmo salar L.) fry

“…Hepatic pathology is often associated with primary pancreatic disease in humans and animals [ 33 , 34 ], and it has also been described in association with other viral infections in salmon [ 35 ]. Ferguson et al .…”