Researchers with the University of British Columbia (UBC) have discovered three new viruses – including a virus from a group of viruses that have never been shown to infect fish before – in Chinook and sockeye salmon populations in the Pacific Northwest.
The new viruses were discovered in both wild and farmed species of Chinook salmon over the course of a series of tests performed by the UBC. The tests used DNA sequencing specific to each virus to screen more than 6,000 salmon along the coast – including wild, hatchery, and aquaculture fish – according to a release from the UBC.
“We were surprised to find viruses which had never before been shown to infect fish,” Gideon Mordecai, researcher at UBC’s department of earth, ocean, and atmospheric sciences, said in the release. “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.”
The viruses, while newly discovered, may not necessarily be new to salmon, Mordecai told SeafoodSource.
“I was careful in the paper to say that these are newly discovered viruses, that doesn’t mean that they’re new to salmon,” he said. “These are newly discovered viruses, chances are these have been around in salmon for a long time.”
The viruses were discovered distributed throughout dead and dying populations of salmon in British Columbia spawning grounds. One of the new viruses was detected most commonly in salmon hatcheries, and infected more than 15 percent of all the Chinook tested. Another was detected in 20 percent of Chinook from fish farms, but only found in adult or sub-adult salmon. All the new viruses were more prevalent in cultured fish populations than in the wild.
The reason the viruses were discovered recently, Mordecai said, is the new techniques used to find them. Historically, most virus discovery was done using cell culture methods utilizing cell lines – an established culture of cells that will proliferate indefinitely – a technique which has been used for decades. However, not all viruses can be discovered through those means, he said.
“We know that there’s lots of viruses that can’t be cultured in cell lines,” Mordecai said.
Whether or not the viruses will develop into more serious pathogens for salmon remains to be seen, but is the next target of the research, according to Mordecai.
“It’s essential that we determine whether these viruses are important factors in the decline of Chinook and sockeye salmon stocks,” said UBC virologist Curtis Suttle. “The research highlights the need for robust surveillance to improve our understanding of how viruses might impact the health of wild Pacific salmon populations.”
The study, published in eLIFE, suggests that virus discovered in fish species for the first time be given the new genus Pescarenavirus, with the subset infecting Chinook and sockeye assigned to the species Salmon pescarenavirus (SPAV) strains 1 and 2. According to the study, farmed Chinook salmon infected with SPAV-1 “displayed pathology and symptoms consistent with disease including inflammation of the spleen and liver, as well as tubule necrosis and hyperplasia in the kidney.”
Another of the newly discovered viruses, named Chinook aquareovirus (CAV), was detected solely in farmed fish on both the west and east coasts of Vancouver island. All three viruses were discovered in higher concentrations in farmed Chinook salmon than in wild or hatchery salmon.
“We found the new viruses widely distributed in dead and dying farmed salmon and in wild salmon,” Suttle said. “It emphasizes the potential role that viral disease may play in the population dynamics of wild fish stocks, and the threat that these viruses may pose to aquaculture.”
Whether the viruses result in a disease that is problematic for wild or farmed salmon populations remains to be determined.
“The next step of the research is, do we call these viruses disease?” said Mordecai. He predicts that there’s a whole range of viruses that infect salmon that researchers simply haven’t discovered yet. “I could tell you with high confidence, there’s a whole range, probably hundreds, if not thousands, that we have no idea about.”
Photo courtesy of Bill Perry/Shutterstock
