Laboratory exposure of Chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch) and rainbow trout (O. mykiss) to a Pacific Canadian strain of piscine orthoreovirus genotype one (PRV-1)

Piscine orthoreovirus genotype one (PRV-1) is the causative agent of heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar L.). The virus has also been found in Pacific salmonids in western North America, raising concerns about the risk to native salmon and trout. Here, we report the results of laboratory challenges using juvenile Chinook salmon, coho salmon, and rainbow trout injected with tissue homogenates from Atlantic salmon testing positive for PRV-1 or with control material. Fish were sampled at intervals to assess viral RNA transcript levels, hematocrit, erythrocytic inclusions, and histopathology. While PRV-1 replicated to high loads in all species, there was negligible mortality in any group. We observed a few erythrocytic inclusion bodies in fish from PRV-1 infected groups. At a few time points, hematocrits were significantly lower in the PRV-1 infected groups relative to controls but in no case was anemia noted. The most common histopathological finding was mild, focal myocarditis in both the non-infected controls and PRV-1 infected fish. All cardiac lesions were judged mild and none were consistent with those of HSMI. Together, these results suggest all three species are relatively susceptible to PRV-1 infection, but in no case did infection cause notable disease in these experiments.