Genetic description of a new Sockeye Salmon virus and its association with a previously discovered signal of premature death (mortality-related signature or MRS)
Description
A primary goal of this research has been to identify conditional states in wild migrating salmon that may be associated with poor performance as smolts transition to the ocean and adults migrate into freshwater to spawn. Following that theme, in-house large-scale genomics research has led to the discovery of a widespread and powerful genomic signature (mortality related signature or MRS) among adult Sockeye Salmon in the Fraser River. This signature occurs in salmon that display a viral infection response and accumulated data thus far have been consistent with a negative impact on survival of salmon carrying this signature. Perhaps coincidentally, a novel parvovirus in liver tissue from smolts and adults carrying this signature has recently been identified. Application of molecular markers to this virus has shown that it is not native to Sockeye populations and its presence reflects those observed of the genomic signature. This project sought to characterize this virus and its association with the genomic signature, establish infectivity and transmission, to assess its frequency and distribution over life-history stages, stocks, species, and years, and to determine its potential role on salmon declines.
Researchers identified several project objectives related to describing the newly discovered parvovirus and its relationship to the “mortality-related signature”. First, the team tested the theory that the MRS signature is being caused by a new, unidentified virus. Second, researchers attempted to fully describe the genetic code of the new parvovirus and its potential to work in conjunction with helper viruses. The third objective was to determine the natural distribution of the salmon parvovirus (and/or other viruses uncovered in the analysis) across multiple salmonid species and stocks to gain information on potential origins of the virus. Fourth, determine whether, and under what conditions, the virus may cause disease and mortality in wild salmon. Finally, determine the potential role of the parvovirus (and/or other novel viruses identified in the study) and MRS on salmon declines in multiple species.
Results: A virus challenge study of Sockeye Salmon parr (juveniles) was completed to establish whether the virus was infective. After three months, no mortality was observed but it was noted that the virus may not have gone through a full infection cycle which may occur when the salmon smolts (grows to next life cycle stage) and migrates out to sea. The liver appeared to be the tissue that was primarily infected, showed the earliest detection, and displayed the highest amount of virus among all tissues.
Other results of significance:
- The full genetic sequence of the virus was obtained from two samples of the parr challenge study. The structure of the virus was similar to other parvoviruses that infect mammals and birds.
- In attempting to correlate the existence of the parvovirus with the genomic signature in multiple tissues, the liver showed positive but not perfect correlation upon initial analyses. No significant correlation was observed in brain and gill tissues. The theory right now is that this new parvovirus does not cause the MRS.
- The research has shown that this parvovirus is almost exclusively a virus of Sockeye Salmon. A sample of both Atlantic Salmon and Chinook Salmon were challenged with the virus and data suggest that neither species is highly susceptible to the parvovirus.
- In a survey of Sockeye Salmon returns in the Fraser River, parvovirus was among the most prevalent microbe infecting liver tissue.
- The study has not been able to show a direct link between the presence of the parvovirus and disease in Sockeye Salmon.
- It has been found that the amount of virus in gill tissues can vary but it does not actively replicate.
Scientific title for this project:
Genomic Characterization of Physiologically Compromised Wild Salmon
Program Name
Genomics Research and Development Initiative (GRDI)
Year(s)
2011 - 2014
Principal Investigator(s)
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