New Viruses Found in Wild Pacific Salmon

University of British Columbia researchers have discovered three new viruses in endangered Chinook and sockeye salmon populations, all of which are related to other viruses known to cause serious disease in other species.

“These new viruses, whose effect on wild salmon is not yet know, have probably been circulating in salmon populations for a long time, so they are new to science, but not salmon,” said Gideon Mordecai, a researcher at UBC’s Department of Earth, Ocean and Atmospheric Sciences. “Although there’s no risk to humans, one of the viruses is evolutionarily related to respiratory coronaviruses and is localized to the gills. That suggests it has a similar infection strategy to its distant relatives that infect mammals.

“Something to bear in mind is that there are probably tens of thousands of different fish viruses, and we only know of a few hundred,” Mordecai said. “New technologies are enabling us to discover them at a faster and faster rate, but the challenge is working out if these viruses have any implications in the health of wild or cultured populations.”

Viruses are microscopic parasites that lack the capacity to thrive and reproduce outside of a host. At times they may become pathogens, viruses that can cause disease.

“In the wild, the virus wants to live lightly on its host and shed itself all over the place, but in captivity everybody dies, so suddenly everything changes,” said Alexandra Morton, a Canadian American marine biologist whose work in British Columbia since the 1990s has focused on the impact of salmon farming on Canadian wild salmon. She has been studying the piscine orthoerovirus (PRV).

Morton noted that Washington State prohibited PRV-infected farmed salmon from being transferred into fish farms. “It is almost impossible to study disease in wild salmon because predators take them out of the population almost immediately. As for the new viruses all we know is what is in the papers. What we do know is that viruses mutate to higher levels of virulence in feed lot environments. And so, we can expect a nonstop stream of new virus strains from aquaculture,” she said.

UBC and Fisheries and Oceans Canada researchers used DNA sequencing followed by tests specific to each virus to screen over 6,000 salmon from along the coast of British Columbia, including wild, hatchery and aquaculture fish. Mordecai’s research group has, for this study, cultured only Chinook, not sockeye. “I would expect to find these viruses in fish either side of the border. In fact, we have sampled Chinook which originate from the Columbia River which were positive for salmon percareavirus-1. Fish don’t respect international borders,” Mordecai said. Researchers have drawn no conclusions though on whether these viruses spread more readily from hatchery to wild stocks or vice versa.