May 27, 2021 — Wild Chinook salmon are more likely to be infected with Piscine orthoreovirus (PRV) the closer they are to salmon farms. This finding indicates that farms are spreading the virus to wild salmon – a theory that is further supported by the results of a recent genomic analysis.
Dr. Gideon Mordecai is a viral ecologist at the University of British Columbia who led the study.
“Both our genomic and epidemiological methods independently came to the same conclusion, that salmon farms act as a source and amplifier of PRV transmission,” said Dr. Mordecai. “Because separate lines of independent evidence all point to the same answer, we’re confident in our finding.”
In collaboration with researchers from the Strategic Salmon Health Initiative, the UBC team traced the origins of PRV to Atlantic salmon farms in Norway and found that the virus is now widespread across salmon farms in British Columbia.
After sequencing 86 PRV genomes, the researchers estimated that the lineage of the virus that is now present in the Northeast Pacific diverged from the virus in the Atlantic Ocean approximately 30 years ago. This suggests that the introduction of PRV to British Columbia, and the infection of wild Pacific salmon, is a relatively recent phenomenon.