Science Advisory Report 2020/049

Advice from the assessment of the risk to Fraser River Sockeye Salmon due to viral haemorrhagic septicaemia virus IVa (VHSV-IVa) transfer from Atlantic Salmon farms in the Discovery Islands area, British Columbia

Summary

Viral haemorrhagic septicaemia virus IVa (VHSV-IVa) transfer risk assessment

• Viral haemorrhagic septicaemia virus (VHSV) released from farmed Atlantic Salmon (Salmo salar) in the Discovery Islands area was assessed to pose minimal risk to Fraser River Sockeye Salmon (Oncorhynchus nerka) abundance and diversity under current farm practices.
• The overall likelihood assessment concluded that it is extremely unlikely that juvenile and adult Fraser River Sockeye Salmon would become infected with VHSV released from farmed Atlantic Salmon in the Discovery Islands area, because Sockeye Salmon are not susceptible to VHSV. The uncertainties for the different steps ranged from reasonable certainty to high certainty.
• As the consequences are dependent on the susceptibility of Sockeye Salmon, the magnitude of consequences to the abundance and diversity of Fraser River Sockeye Salmon are both estimated as negligible.
• The assessment relied on the current state of knowledge of VHSV, fish health surveillance data, experimental laboratory studies, historical wild salmon surveys for the presence of fish pathogens in British Columbia, and 2002 to 2019 fish health data on salmon farms.

This risk assessment was informed by a summary of the current state of knowledge on VHSV (Garver and Hawley, in press). The key elements of this review are summarized below.

Characterization of viral haemorrhagic septicaemia virus (VHSV) and viral haemorrhagic septicaemia (VHS)

• Globally, VHSV is the causative agent of the disease VHS, which can occur in a wide range of cultured and wild fish species in both marine and freshwater environments. There are four major genotypes of VHSV that differ in geographic distribution and host-specific virulence. Genotype IVa is the only VHSV genotype found in British Columbia (BC) and the surrounding northeastern Pacific Ocean.
• In British Columbia, VHSV-IVa is endemic in the marine environment where it causes noticeable, recurring mortality events in Pacific Herring (Clupea pallasii) and Pacific Sardine (Sardinops sagax). Less commonly, the virus has been detected in farmed and wild salmon.
• The low prevalence of VHSV infection and disease reported for farmed salmon in BC is demonstrated through routine monitoring by industry as well as active surveillance carried out by DFO under the Fish Health Audit and Surveillance Program (FHASP).
• Waterborne transmission is a likely route of VHSV infection of susceptible species of fish as consistently demonstrated in bath challenge and cohabitation laboratory studies.
• Laboratory studies exposing Pacific Herring, Atlantic Salmon, and Sockeye Salmon corroborate a gradient of VHSV susceptibility. Pacific Herring were the most susceptible. Atlantic Salmon demonstrated low to moderate susceptibility. Sockeye Salmon, regardless of whether exposed to VHSV through waterborne or cohabitation exposure, for short or long periods, proved refractory to VHSV infection. In addition, there are no confirmed reports of VHSV or VHS in Sockeye Salmon in fish health records, published studies and surveillance studies.
• Sockeye Salmon are not considered susceptible to VHSV based on the World Organisation for Animal Health (OIE) criteria for listing species as susceptible to infection with a specific pathogen.

This Science Advisory Report is from the September 15-17, 2020, National Peer Review Meeting on the Assessment of the risk to Fraser River Sockeye Salmon due to Viral Haemorrhagic Septicaemia Virus (VHSV) transfer from Atlantic Salmon farms located in the Discovery Islands area, British Columbia. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2020/049 (PDF, 1,041 KB)

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