Piscine Reovirus (PRV)

• Heart and Skeletal Muscle Inflammation (HSMI):
  • Inflammation: Swelling and inflammation of heart and skeletal muscles.
  • Anorexia: Loss of appetite.
  • Lethargy: Reduced activity.
  • Ascites: Accumulation of fluid in the body cavity 1.
• Jaundice Syndrome:
  • Yellowing: Jaundice observed in skin, gills, and eyes.
  • Anemia: Pale gills and organs.
  • Liver and Kidney Degeneration: Necrotic lesions in liver and kidney 2.

Early Stages: Mild signs such as reduced feed intake and slight lethargy.

Advanced Stages: More pronounced physical symptoms like inflammation and internal lesions.

Impact on Fish Health: PRV infections can compromise immune function and overall vitality, potentially increasing susceptibility to secondary infections 3.

Causative Agent: Piscine Orthoreovirus (PRV), a double-stranded RNA virus with three known genotypes: PRV-1, PRV-2, and PRV-3 3.

Transmission Methods:

• Horizontal Transmission: Spread between infected and healthy fish through water or direct contact.
• Vertical Transmission: Possible transmission from parent to offspring through eggs 3.

Environmental Factors: Stress conditions may precipitate clinical disease 1.

Farm Management Practices: High-density aquaculture settings may facilitate virus spread.

Clinical Examination: Observation of physical and behavioral symptoms indicative of PRV infection.

Laboratory Tests:

• RT-qPCR: Detects PRV genetic material in fish tissues.
• Histopathology: Microscopic examination of heart and muscle tissues to identify characteristic lesions of HSMI.
• Virus Sequencing: Molecular detection and sequencing for confirmation of virus strain13.

• Implementing strict quarantine measures for new stock to prevent the introduction of PRV.
• Regular health monitoring and early detection programs to identify and manage outbreaks promptly.

Notable Findings:

• Pacific Northwest: PRV has been detected in both wild and farmed salmonids since at least 1987, possibly as early as 1977 1.
• Canada: PRV was found in 95% or more of escaped farmed Atlantic salmon in Washington State and British Columbia 5.
• Japan: PRV-2 has been associated with EIBS and jaundice/anemia in farmed coho salmon 1.

Research Outcomes:

• Studies suggest that PRV-1 may be of low risk to wild Pacific salmon species, as it has been present in these populations for decades without clear association with disease 1.
• Experimental infections have shown that PRV can be infectious for Chinook and sockeye salmon but may not cause mortality or apparent disease 1.

PRV Incidence in Canada:

• PRV has been detected in both farmed and wild salmon populations in Canada, particularly in British Columbia 426.

Geographical Spread:

• The virus is prevalent along the Pacific coast, with widespread distribution in various salmon species 26.

Economic Impact:

• PRV outbreaks have led to economic losses in the Canadian salmon farming industry, though the impact is considered lower compared to other regions due to the lower virulence of the virus in some cases 26.

Treatment & Management:

• Canadian salmon farms have adopted biosecurity measures and treatments to manage PRV, with ongoing research into vaccine development and other preventive strategies 26.

PRV Incidence in Norway:

• PRV was first identified in Norway in the 1990s and has since been a significant concern in the aquaculture industry 41.
• Significant outbreaks of Heart and Skeletal Muscle Inflammation (HSMI) caused by PRV have been reported, impacting farmed Atlantic salmon 41.

Geographical Spread:

• PRV has been detected throughout Norway, affecting various regions where salmon farming is prevalent 12.
• The virus has been found in both farmed and wild salmon populations, indicating widespread distribution 2.

Economic Impact:

• PRV-related diseases, particularly HSMI, have led to substantial economic losses in the Norwegian salmon farming industry due to increased mortality and reduced fish health 14.
• The costs associated with managing outbreaks and implementing biosecurity measures have also added to the economic burden 1.

Treatment & Management:

• The Norwegian industry has implemented various control measures, including early detection, biosecurity protocols, and treatments such as freshwater baths and hydrogen peroxide12.
• Research is ongoing to develop vaccines and other preventive strategies to mitigate the impact of PRV 41.