  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.
