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Research Project: Genetic Improvement of North American Atlantic Salmon and the Eastern Oyster for Aquaculture Production

Location: National Cold Water Marine Aquaculture Center

Title: Piscine orthoreovirus (PRV) detection, distribution and transmission in the Northeastern Pacific

Author
item Polinski, Mark
item JOHNSON, STEWART - Department Of Fisheries And Oceans Canada
item GARVER, KYLE - Department Of Fisheries And Oceans Canada

Submitted to: American Fisheries Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/16/2022
Publication Date: 5/16/2022
Citation: Polinski, M.P., Johnson, S.C., Garver, K.A. 2022. Piscine orthoreovirus (PRV) detection, distribution and transmission in the Northeastern Pacific. American Fisheries Society Annual Meeting. https://doi.org/10.3390/fishes8050252.
DOI: https://doi.org/10.3390/fishes8050252

Interpretive Summary: Piscine orthoreovirus (PRV) is a common virus of salmon with global variability in prevalence and association with disease. We describe the development, optimization, and validation of molecular assay that can detect all known genetic variants of PRV with high sensitivity and specificity. Testing of more than 5,500 salmon from Pacific enhancement and commercial freshwater hatcheries identified extremely low (0.08%) prevalence of on one PRV genotype endemic to the region (PRV-1 ) but did not detect any non-endemic forms. Screening of more than 2,000 seawater transitioned farmed Atlantic salmon in net-pen sites from coastal British Columbia identified that nearly all farmed populations and cohorts developed PRV infections (of the endemic genotype; PRV-1) at sea irrespective of location, time of stocking, or producer. Testing of more than 4,000 wild Pacific salmon from British Columbia caught in marine waters identified moderate (0-7%) infection prevelence of the endemic genotype of PRV-1 confirming seawater-specific transmission of this virus. Controlled studies involving saltwater adapted Atlantic, Chinook, Sockeye and Pink salmon in laboratory environments revealed that PRV shedding mirrored infection intensity, whereas the initial ability of the virus to infect fish did not correlate with the viruses ability to replicate once inside the host. Cumulatively, these data provide a foundation for understanding transmission and conductivity of PRV-1 within the Northeastern Pacific.

Technical Abstract: Piscine orthoreovirus (PRV) is a common virus of salmon with global variability in prevalence and association with disease. We describe the development, optimization, and validation of a real-time reverse transcription quantitative PCR Pan-PRV assay that can detect all three known PRV genotypes with high sensitivity and specificity. Diagnostic testing of more than 5,500 juvenile salmon from Pacific enhancement and commercial hatcheries from 2019 to 2021 for PRV-1 in British Columbia (more than 2,200 of these were also screened for PRV-2 and -3 using the new Pan-PRV assay) identified extremely low (0.08%) prevalence of PRV-1 in freshwater facilities without detection of PRV-2 or -3 genotypes. PRV-1 diagnostic testing of more than 2,000 seawater transitioned Atlantic salmon in net-pen sites from coastal British Columbia between 2016 and 2019 further identified that nearly all farmed populations and cohorts developed PRV-1 infections at sea irrespective of location, time of stocking, or producer - typically between 100-300 days at sea. PRV-1 diagnostic testing of more than 4,000 wild Pacific salmon from British Columbia collected between 2011 and 2020 found PRV-1 only in juvenile (7% prevalence) and adult (3%) Chinook; and juvenile (2%) and adult (2%) Coho Salmon caught in marine waters, confirming seawater-specific transmission of this virus. As seen in Atlantic salmon farm populations, the prevalence of PRV-1 in juvenile Chinook Salmon increased with time at sea. Controlled laboratory studies involving saltwater adapted Atlantic, Chinook, Sockeye and Pink salmon revealed that PRV-1 shedding mirrored replicative ability, whereas species-specific infectivity substantially differed from replicative ability once inside the host. Cumulatively, these data provide a foundation for understanding transmission and conductivity of PRV-1 within the Northeastern Pacific.