PRV poses 'minimal risk' to sockeye: science panel

Review of science on PRV finds little to no risk to salmon, but timing of announcement questioned

Alexandra Morton used underwater cameras to capture images of sickly salmon at B.C. salmon farms. It's not clear what disease may cause such emaciation.| BIV archives

Is piscine reovirus the salmon killer that independent researcher Alexandra Morton insists it is?

In Norway, perhaps, but the strain of PRV found in the Pacific Ocean in farmed and wild salmon, as well as other species, appears to be a less virulent strain, according to a special panel assembled for the Canadian Science Advisory Secretariat (CSAS).

"Certainly we seem to have a virus that is different than what is present in Norway," said Gilles Olivier, co-chaiman of a special panel assembled to study the peer reviewed science on PRV.

"All the evidence that we have so far is that it doesn't cause mortality in sockeye salmon, nor Atlantic salmon, even when it's injected in high doses. So there are differences in the virus present here and the virus present in Norway."

Olivier, who is a retired former manager of DFO's Aquatic Health Division, was speaking at a press conference Thursday, February 7.

The timing of the press conference was questioned by media, since it took place just three days after the Federal Court ruled that the Department of Fisheries and Oceans must start testing smolts for PRV before it allows them to be transferred to the ocean.

John Werring, science advisor for the David Suzuki Foundation, who was one of the panel members, also questioned the timing.

"I was beside myself that this press conference even took place," Werring said.

He said the panelists were told that the findings were to be confidential until the study had been peer-reviewed and the documents published.

"For them to take that information and just throw it out there and say here's what the findings are, before we've even concluded what that is, is unprecedented," Werring said.

It was explained that the exercise was one of six risk assessments that have been done so far, at the request of DFO, as per the recommendations of the 2010 Cohen Commission report. And since there is such high public interest in PRV, DFO decided to have the panel speak to their recent findings.

Thursday's release of the panel's consensus findings was unusual, however, in that none of documentation on which the panel’s conclusions were based have been published yet. It may be some weeks before all of the scientific documentation is published and subject to scrutiny.

The PRV virus was in headlines this week, after a Federal Court judge ruled in favour of independent researcher Alexandra Morton and the Namgis First Nation and against the Department of Fisheries and Oceans (DFO).

Morton challenged DFO’s policy of not requiring salmon smolts to be tested for PRV before issuing licences that allow them to then be transferred to the ocean.

The court gave DFO four months to amend its policy. The ruling could have an impact on both fish farms and hatcheries that produce salmon for wild salmon enhancement.

Research in Norway has shown strong evidence that PRV either causes or contributes to the development of a disease called heart and skeletal muscle inflammation (HSMI).

Morton’s own research suggested that PRV found in B.C. may also cause disease in farmed and wild salmon in B.C., and at least two studies funded by the Strategic Salmon Health Initiative (involving DFO scientists) appear to bolster her findings.

One of them found a high statistical correlation between PRV and heart and skeletal muscle inflamation (HSMI). The other suggested a casual link between PRV and a type of jaundice in farmed salmon. The federal Centre for Science Advice found the latter wanting, in that "deficiencies with the data" rendered the conclusions "unsupported.”

The 33-member panel of scientists conducted their assessment of the peer reviewed science on PRV from January 28 to 30. It’s not clear why the panel wasn’t assembled earlier, as its findings might have been germane to the recently concluded Federal Court case.

Olivier said the objective was to understand the current state of scientific knowledge of PRV. He said a lot of the current science pertains to PRV in Norway, where it has been demonstrated to cause disease in Atlantic salmon.

“But it was also established that in British Columbia the strain of PRV that is present here is of lower genetic variability and of lower virulence in Atlantic salmon relative to PRV infected Atlantic salmon in Norway," Olivier said. "So it means that it doesn’t seem to have the same effect in our Atlantic salmon here in B.C. than it does in Norway.”

The panel also concluded that PRV is “ubiquitous or highly prevalent” in farmed Atlantic and Chinook salmon in B.C. Olivier said high viral loads of PRV can cause “minor to moderate lesions but no fish mortalities, nor clinical signs, nor anemia has been observed.”

“There is currently no evidence to suggest that PRV-1 causes disease or mortality in sockeye salmon,” Olivier said.

But because no documentation was provided, it’s not clear what studies Olivier was referencing.

He may have been referring to a study by a team of scientists from DFO’s Pacific Biological Research Station, which tried to induce HSMI in healthy fish by exposing them to it.

In that study, led by Kyle Garver, who heads DFO’s Virology Research Program, tissue from Chinook that had been diagnosed with HSMI was homogenized and injected into healthy Chinook, Atlantic and sockeye salmon in an attempt to induce the disease. Healthy fish were also exposed to HSMI through co-habitation with fish exhibiting HSMI symptoms.

After more than 20 weeks, none of fish exposed to HSMI infected tissue developed any symptoms of HSMI, despite having high viral loads of PRV.

Morton’s research suggests the PRV virus was introduced to B.C. from Norway via Atlantic salmon. Other research suggests the virus predates fish farms and may be endemic.

In this week's ruling, the Federal Court acknowledged that the science to date is unsettled. But until it is settled, the court ruled the precautionary principle should apply, and ordered DFO to amend policies so that smolts raised in hatcheries must be tested for PRV before they can be transferred to the ocean.