Pancreas Disease (PD) of Salmonids: A Disease Guide
Pancreas disease, caused by salmonid alphavirus, damages the pancreas, heart, and muscle of farmed salmon and trout. There is no cure; control relies on vaccination and biosecurity.
Overview
Pancreas disease (PD) is an important viral disease of sea-farmed salmonids. It is caused by salmonid alphavirus (SAV), also called salmon pancreas disease virus, an enveloped, positive-sense single-stranded RNA virus of the genus Alphavirus, family Togaviridae. Six genotypes have been identified, designated SAV1 to SAV6. The same virus causes 'sleeping disease' in rainbow trout. PD is a major economic problem in salmon farming in Norway, Ireland, and Scotland.
Affected species
PD affects farmed Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) in seawater. A notable feature is that infection is often subclinical: a substantial proportion of SAV-infected populations never develop clinical PD, which makes monitoring and control difficult because infected fish may show no obvious external signs.
Clinical signs
- Sudden loss of appetite and lethargy
- Faecal casts appearing in the net pen
- Difficulty maintaining position in the water due to muscle damage
- Increased mortality
- Loss of condition, with many survivors failing to grow and becoming runts
- Internally, necrosis of the exocrine pancreas and degeneration and inflammation of heart and skeletal muscle
Transmission and diagnosis
SAV spreads horizontally through seawater currents and human activities between sites, and high infection pressure from neighboring farms is a key risk for outbreaks. Diagnosis combines RT-PCR detection of the virus with histopathology of the pancreas, heart, and skeletal muscle, supported by serology such as virus neutralisation. Because many infections are subclinical, laboratory screening is important.
Treatment, control and prevention
There is no specific cure for PD. Control relies on vaccination, biosecurity, and coordinated area management. Commercial PD vaccines have been used since the late 2000s; they reduce mortality and viral shedding but do not provide complete protection.
- Vaccinate salmon before sea transfer; both inactivated whole-virus and DNA vaccines are used
- Reduce infection pressure through coordinated zone management and synchronized stocking and fallowing
- Fallow sites between production cycles to break the transmission chain
- Apply strict biosecurity to limit transfer between sites via water, equipment, and movements
- Minimize stress and handle fish gently, especially in fish with heart and muscle damage