Salmon gill poxvirus-like (SGPV-like): Characterisation, Atlantic Salmon susceptibility, and initial survey in farmed and wild salmon

Description

Poxviruses are large DNA viruses of vertebrates and insects causing disease in many animal species. In Spring 2006, a new poxvirus, the salmon gill poxvirus (SGPV), was discovered in salmon in freshwater in northern Norway. The salmon showcased proliferative gill disease (PGD) and demonstrated other clinical disease symptoms like lethargy, respiratory distress, and mortality. Later the same year, this virus was also found on salmon gills at two marine sites in western Norway where all farms suffered high losses associated with the presence of this virus.

In 2015, an unknown virus was isolated from tissues sampled from a wild Atlantic salmon caught in a river in New Brunswick. Using Next Generation sequencing, researchers found that there was an 80-90% similarity to Norwegian SGPV, hence “SGPV-like”. The significance of SGPV-like detection is unclear, although there are anecdotal reports that salmon gill diseases of unknown etiology were previously detected on the East Coast of Canada. A survey and examination of the local SGPV strains were needed to determine the extent of the virus distribution on the East Coast, and its potential to compromise the health of salmon.

Findings

SGPV was detected in various wild and farmed populations of Atlantic salmon, in both fresh and saltwater. For farmed Atlantic salmon, SGPV was detected at different life stages in hatcheries and in marine farms, suggesting that SGPV is as wide spread in Atlantic Canada as it is in Norway. However, generally, a low prevalence of SGPV was observed and infected fish had a low viral load. Detections over time were sporadic suggesting that infections are transient.

Phylogenetic analysis showed that two SGPV genogroups are present in Atlantic Canada. The predominant strain detected were related with the SGPV-like strain identified in 2015. The other was related to the Norwegian strain. While none of the usual infection methods used in in vivo challenges were successful at initiating an infection in fish, transmission to naïve salmon by cohabitation with fish that had positive PCR results for SGPV was obtained.

There have not been any reports that proliferative gill disease (PDG) is caused by the SGPV strains that are present in Eastern Canada. The SGPV-like strain identified in 2015, and in most sites tested as part of this survey, may be too different from the SGPV strain identified in Norway, which is believed to cause PDG. Through our survey, a few strains more closely related to the known Norwegian SGPV were observed in some hatcheries, and are being further examined.

Program name

Aquaculture Collaborative Research and Development Program (ACRDP)

Years

2016 - 2019

Principal investigator

Nellie Gagné
Research Scientist, Fisheries and Oceans Canada, Gulf Fisheries Centre, Gulf Region
Email: Nellie.Gagne@dfo-mpo.gc.ca

Team member(s)

Delphine Ditlecadet, Biologist, Fisheries and Oceans Canada, Gulf Fisheries Centre, Gulf Region

Valérie Godbout, Technician, Fisheries and Oceans Canada, Gulf Fisheries Centre, Gulf Region

Jean-René Arseneau, Technician, Fisheries and Oceans Canada, Gulf Fisheries Centre, Gulf Region

Francis Leblanc, Biologist, Fisheries and Oceans Canada, Gulf Fisheries Centre, Gulf Region

Steven Leadbeater, Biologist, Fisheries and Oceans Canada, St. Andrews Biological Station, Maritimes Region

Philip Byrne, Research Scientist, Fisheries and Oceans Canada, Gulf Biocontainment Unit, Gulf Region

Collaborator(s)

Keng Pee Ang, Kelly Cove Salmon Ltd.