British Columbia freshwater salmon hatcheries demonstrate minimal contribution to piscine orthoreovirus (PRV) regional occurrence with no evidence for nonendemic strain introductions

Piscine orthoreovirus genotype 1 (PRV-1) is a common virus in farmed and wild salmon the northeastern Pacific Ocean. Its regional occurrence freshwater far less clear. From 2019 to 2021, tissues of 5619 juvenile anadromous (primarily Atlantic, Chinook, coho) sampled from 12 commercial 27 enhancement British Columbia hatcheries during 83 sampling events were screened for PRV-1 prior seawater entry. More than 2200 (∼40%) also using Pan-PRV assay targeting all known PRV genotypes. was detected four coho at two facilities one Chinook facility. Partial (S1 segment) genome sequencing identified detections be subgenotype endemic Pacific. not (5611 individuals; 99.9%) or test results inconclusive (3 0.05%) remaining samples PRV-1. PRV-2 PRV-3 assay. It concluded that contribute minimally prevalence persistence Pacific, these appear have contracted participated distribution nonendemic forms recent years.