The same strain of Piscine orthoreovirus (PRV-1) is involved with the development of different, but related, diseases in Atlantic and Pacific Salmon in British Columbia

TL;DR

This study investigates how PRV-1 virus causes different diseases in Atlantic and Pacific salmon in BC, revealing similar viral strains but different pathological effects, raising concerns about risks to wild salmon populations.

Contribution

It demonstrates that PRV-1 causes distinct disease pathways in Atlantic and Chinook salmon despite genetic similarity, highlighting potential risks to wild Pacific salmon.

Findings

PRV-1 localizes within lesions in both salmon species.

Different pathological pathways observed in Atlantic and Chinook salmon.

No significant genetic differences in PRV-1 variants involved in diseases.

Abstract

Piscine orthoreovirus Strain PRV-1 is the causative agent of heart and skeletal muscle inflammation (HSMI) in Atlantic salmon (Salmo salar). Given its high prevalence in net pen salmon, debate has arisen on whether PRV poses a risk to migratory salmon, especially in British Columbia (BC) where commercially important wild Pacific salmon are in decline. Various strains of PRV have been associated with diseases in Pacific salmon, including erythrocytic inclusion body syndrome (EIBS), HSMI-like disease, and jaundice/anemia in Japan, Norway, Chile and Canada. We examine the developmental pathway of HSMI and jaundice/anemia associated with PRV-1 in farmed Atlantic and Chinook (Oncorhynchus tshawytscha) salmon in BC, respectively. In situ hybridization localized PRV-1 within developing lesions in both diseases. The two diseases showed dissimilar pathological pathways, with inflammatory lesions in heart and skeletal muscle in Atlantic salmon, and degenerative-necrotic lesions in kidney and liver in Chinook salmon, plausibly explained by differences in PRV load tolerance in red blood cells. Viral genome sequencing revealed no consistent differences in PRV-1 variants intimately involved in the development of both diseases, suggesting that migratory Chinook salmon may be at more than a minimal risk of disease from exposure to the high levels of PRV occurring on salmon farms.