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PRV is not the only cause of death in Pacific salmon

Wild sockeye salmon swimming in Canadian waters. Image DFO/Canada
Wild sockeye salmon swimming in Canadian waters. Image DFO/Canada

Frontiers in Physiology has released a journal that suggests Piscine Orthoreovirus(PRV) is not the only reason salmon are dying on the west coast of Canada.

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PRV  was originally detected in Canadian waters in 2011.

The virus causes heart and skeletal muscle inflammation in salmon but does not effect humans. The virus has been blamed for the decline of wild salmon populations in British Columbia. Some evidence suggested that wild salmon pick up the virus when travelling past Atlantic salmon farms located in Pacific waters.

"This study provides strong empirical evidence that a host with an extremely high-load PRV infection can sustain its respiratory functions."

"The global concern about the negative impact of this virus to salmon should be reassessed. Indeed, while several studies have associated PRV with diseased salmon in Pacific Canada, current experimental evidence does not suggest that PRV is the only factor for initiating these disease conditions which may have a more complex etiology,” said the study.

Red blood cells

Scientists injected healthy fish with PRV collected from infected fish that also had heart lesions that were consistent with muscle inflammation. PRV  impacts red blood cells that carry oxygen so impairment to this system would kill the fish. However, Canadian salmon infected with PRV did just as well as healthy fish in laboratory tests that focused on the respiratory system. 

Scientists in Norway are studying the virus which has devastated salmon farmers in that country. However, research shows that the virus acts differently in fish located in Norway and in Canada. The reason for the difference is unknown and could be due to genetic differences in the fish. 

The Canadian federal government announced earlier this week that it will not appeal a Federal Court decision ordering it to review a policy not to test young salmon for PRV before being transferred to open net sea farms  located along the west coast of British Columbia.

The journal can be read here https://www.frontiersin.org/articles/10.3389/fphys.2019.00114/full

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