Does infection with piscine reovirus (PRV) affect how salmon respond to challenge with and vaccination against infectious hematopoietic necrosis virus (IHNV)?

Description

Piscine Reovirus (PRV) is a double stranded ribonucleic acid (RNA) virus belonging to the family Reoviridae. PRV is common in wild and farmed salmon in BC and likely establishes long term infections in its hosts. It is inevitable that mixed infections of PRV and known pathogens will occur. In the same geographical area with PRV is the infectious hematopoietic necrosis virus (IHNV). IHNV occurs naturally in the waters of the Pacific Northwest and with the appropriate virus strain, host condition, and environmental parameters, IHNV can cause an acute disease known as infectious hematopoietic necrosis (IHN) in all five species of Pacific salmon, Atlantic Salmon, and Rainbow Trout (Oncorhynchus mykiss). Despite the widespread use of the IHNV vaccine in the BC salmon aquaculture industry, little is known concerning the effectiveness of the vaccine when administered in asymptomatic fish infected with other viruses.

This project sets out to examine the consequences of viral co-infections of Piscine Reovirus (PRV) and Infectious Hematopoietic Necrosis Virus (IHNV) in Atlantic and Sockeye salmon. The study addressed how Atlantic Salmon and Sockeye Salmon hosts, infected with a virus with no or low pathogenic effect, respond to vaccination against, and to challenge with another different virus. Challenge trials were used to examine IHN disease progression in naïve (never before infected), IHNV vaccinated non-PRV (control), and PRV-infected Atlantic Salmon. An IHNV challenge trial was also conducted with non-PRV (control), and PRV-infected Sockeye Salmon that are naïve with respect to IHNV. These challenge trials were used to determine if there are differences between groups in morbidity associated with IHNV challenge, and to generate biological samples for gene and microRNA expression studies.

This research helps to determine what, if any, additional risk is posed to wild and/or farmed fish due to changes in their ability to respond to IHNV vaccination and/or to exposure to IHNV, thereby contributing to the knowledge base important for the sustainable management of the salmon aquaculture industry.

Findings

The presence of PRV did not significantly affect IHNV viral loads or the outcome of IHNV with respect to prevalence of infection and morbidity. Prior infection with PRV appeared to have a negligible effect on the transcriptional response of Sockeye Salmon head kidney to IHNV exposure or infection. The transcriptomic responses in Atlantic Salmon kidney and blood to PRV mirrored the lack of response seen in Sockeye Salmon.

The study suggested that PRV sourced from waters of British Columbia is of low virulence to Sockeye and Atlantic salmon in western Canada and that fish carriers of PRV are not at a disadvantage when it comes to superinfection with IHNV. Whether different environments, virus strains, and/or host conditions contribute to the development of disease remains unknown.

Publications

Polinski, M. P, Bradshaw, J. C., Inkpen, S. M., Richard, J. R., Fritsvold, C., Poppe, T. T., Rise M. L., Garver, K. A. and Johnson, S. C. 2016. De novo assembly of Sockeye salmon kidney transcriptomes reveal a limited early response to piscine reovirus with or without infectious hematopoietic necrosis virus superinfection. BMC Genomics (2016) 17:848. DOI 10.1186/s12864-016-3196-y

Garver, K. A., Johnson, S. C., Polinski, M. P., Bradshaw, J. C., Marty, G. D., Snyman, H. N., Morrison, D. B. and Richard, J. 2016. Piscine Orthoreovirus from Western North America is transmissible to Atlantic Salmon and Sockeye Salmon but fails to cause Heart and Skeletal Muscle Inflammation. PLoS ONE 11(1): e0146229. doi:10.1371/journal.pone.0146229

Program Name

Program for Aquaculture Regulatory Research (PARR)

Year(s)

2014 - 2017

Principal Investigator(s)

Stewart Johnson
Research Scientist, Fisheries and Oceans Canada, Pacific Biological Station, Pacific Region
Email: Stewart.Johnson@dfo-mpo.gc.ca

Kyle Garver
Research Scientist, Fisheries and Oceans Canada, Pacific Biological Station, Pacific Region
Email: Kyle.Garver@dfo-mpo.gc.ca

Team Member(s)

Jon Richards, Technician, Fisheries and Oceans Canada, Pacific Biological Station, Pacific Region

Julia Bradshaw, Biologist, Fisheries and Oceans Canada, Pacific Biological Station, Pacific Region

Collaborator(s)

Matthew Rise, Memorial University of Newfoundland

Rune Adnreassen, Oslo and Akershus University College of Applied Sciences