Infectious Pancreatic Necrosis (IPN)

Overview

What is Infectious Pancreatic Necrosis (IPN)?

Infectious Pancreatic Necrosis (IPN) is a highly contagious viral disease affecting various fish species in aquaculture, including Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), and other salmonids. It is caused by the Infectious Pancreatic Necrosis Virus (IPNV), a member of the genus Aquabirnavirus within the family Birnaviridae. It can cause high mortality rates, especially in young fish, and significant economic losses 1 7. The disease can occur in both freshwater and seawater production: it is particularly associated with fry and juvenile salmonids in freshwater hatcheries and post-smolts after transfer to seawater, but can also infect adult fish asymptomatically 1 7.

Clinical Signs of Infectious Pancreatic Necrosis

Common Signs

Physical Signs:
- Abdominal Swelling: Distended abdomen due to fluid accumulation 1 4.
- Pale inner organs: Typically pale gills and liver in affected fish, indicating anaemia. In seawater the liver tends to get more yellowish 4 8.
- Internal haemorrhages: Small "pinpoint" (petechial) bleeding spots in adipose tissue between the pyloric caeca 8.
- Outer haemorrhages: Bleeding can occur ventral areas and fins 4.
- Darkening of the Skin: Affected fish may exhibit darkened coloration 1 4.
- Exophthalmos (popeye): Protruding eyes.
- Empty intestine or filled with clear mucus 4
- Emaciation: Affected or surviving fish may become markedly thin, with poor body condition 7.
- Faecal casts: White, string-like casts of faeces and sloughed intestinal tissue may hang from the vent as a result of inflammation in the intestine 4.
Behavioural Changes:
- Lethargy: Fish lying still on the bottom of tanks or ponds 4.
- Loss of Appetite: Anorexia and significant weight loss 2.
- Abnormal Swimming Patterns: Fish may swim in a corkscrew or spiral motion 1 4.

Progression of Symptoms

Early Stages: Sudden and progressive increase in mortality at first feeding of fry, particularly in faster-growing individuals 4.
Advanced Stages: Pronounced physical symptoms such as abdominal swelling, haemorrhages, and darkened skin, leading to high mortality rates of 10% to 90% 1 4.
Carrier state: Fish may survive IPNV infection and become asymptomatic carriers. Carrier fish can harbour and intermittently shed the virus without obvious clinical signs, particularly during periods of stress, creating a potential source of infection for susceptible fish 7.
Impact on Fish Health: IPN can cause substantial tissue damage in several organs, particularly the pancreas. Pancreatic necrosis can impair the production of enzymes needed for digestion and nutrient absorption. Consequently, affected fish may show poor feed utilisation, reduced growth, and poor body condition. Mortality varies among outbreaks and may be very high, particularly in susceptible fry and post-smolts. IPN severely compromises immune function and overall vitality, making fish susceptible to secondary infections 3 8.

Causes of Infectious Pancreatic Necrosis

Etiology

Causative Agent: Infectious Pancreatic Necrosis Virus (IPNV), in the genus Aquabirnavirus (family Birnaviridae) 1 2.
Transmission Methods:
- Horizontal Transmission: Spread between fish through contaminated water and equipment 1. The virus is environmentally robust and may persist outside the host, making eradication difficult 7.
- Vertical Transmission: IPNV may be transmitted from parent to progeny through infected eggs 1 7. Vertical transmission has been demonstrated in brook trout and rainbow trout, while its role in Atlantic salmon remains uncertain 9.

Risk Factors

Environmental Factors: Outbreaks can occur at water temperatures between 4°C and 18°C, with stress factors such as high stocking densities, handling, fluctuations in water temperature and salinity increasing susceptibility 4.
Host factors: Young fish—particularly fry and fish at first feeding—are most susceptible; Atlantic salmon post-smolts may also be at increased risk shortly after seawater transfer 7.
Farm Management Practices: Movement of equipment from infected sites and improper handling of mortalities and wastes can facilitate the spread of the virus 1.

Diagnosis

Diagnostic Methods

Clinical Examination: Observation of physical and behavioural symptoms; susceptible fish, especially fry or post-smolts, show an acute increase in mortality together with compatible clinical signs. Clinical findings alone are not specific and require laboratory confirmation. 1 2.
Laboratory Tests:
- Histopathology and immunohistochemistry: A diagnosis of clinical IPN is supported by histopathological detection of characteristic necrosis in the exocrine pancreas and/or liver in formalin-fixed tissues, together with immunohistochemical detection of IPNV antigen in affected lesions 7.
- Real-time PCR (Polymerase Chain Reaction): Detects IPNV genetic material in fish tissues 3. Head kidney or mid-kidney are commonly sampled; however, a positive result alone does not confirm clinical IPN because healthy fish can be carriers 7.
- Virus Isolation: IPNV can be isolated from fish tissues using susceptible cell lines, such as CHSE-214 cells, and subsequently identified by molecular or immunological methods 1. Virus isolation demonstrates the presence of replication-competent infectious virus, and can be used to estimate infectious virus titre.
- ELISA and Antibody Neutralization: For identification of the virus 1.

Differential Diagnosis

Distinguishing IPN from Other Diseases: It is crucial to differentiate IPN from diseases with similar symptoms, such as infectious salmon anaemia (ISA), infection with salmonid alphavirus (SAV), infectious haematopoietic necrosis (IHN), and viral haemorrhagic septicaemia (VHS) 4. In fry, Flavobacterium psychrophilum and Yersinia ruckeri infections may produce similar signs or lesions 7.

Treatment and Prevention

Treatment Options

Current Treatments: There are no specific antiviral treatments for IPN. Management focuses on preventing the spread and mitigating the impact through biosecurity measures 1 3.

Preventive Measures

Biosecurity Protocols:
- Testing of broodstock and eggs for IPNV, and destruction of eggs from infected parents 1.
- Desinfection of eggs to reduce virus contamination on the egg surface.
- Maintain strict hygiene, cleaning, and disinfection procedures in hatcheries and smolt facilities 7. Efforts to eliminate site-specific (“house”) IPNV strains during the freshwater phase have been associated with fewer IPN outbreaks in fry and post-smolts after seawater transfer 7.
- IPNV is highly resistant to low pH, elevated temperatures and UV-radiation, which contributes to its persistence in the environment. However, it can be inactivated by validated disinfection procedures using agents such as ozone, formalin, or iodine 7.
- Restricting movement of fish and equipment between sites 1.
Vaccination Strategies: A provisional marketing authorization has been granted for a vaccine against IPN for Atlantic salmon, but protection may be incomplete and outbreaks can still occur 1 7.
Farm Management Practices:
- Reduce factors that promote clinical disease by minimising handling stress, avoiding excessive stocking density, maintaining stable environmental conditions, and applying sound water-quality and fish-health monitoring practices 2.
- Implementing strict protocols regarding movement, water sources, and stock replacement 2.
- Ensure fish have robust smolt quality and documented seawater tolerance before transfer - close health monitoring during and after transfer is important.
Selective breeding:
- Selective breeding for IPNV resistance, including use of quantitative trait loci (QTL)-associated resistance, has also contributed to the long-term reduction in IPN outbreaks in farmed Atlantic salmon in Norway 7.

Case Studies

Real-World Examples

Notable Outbreaks:
- Scotland: High prevalence of IPNV infection in farmed Atlantic salmon in seawater, with increasing incidence in freshwater salmon farms in recent years 1.
- Norway: Considerable mortalities from IPN in Atlantic salmon post-smolts 1.

Data Insights

Disease Impact by Country

Canada

IPN Incidence in Canada:
- IPN is considered one of the major fish disease problems in Canada 6.

Norway

IPN Incidence in Norway:
- IPN has been a significant problem in Norwegian salmon farming, particularly affecting fry, smolts, and post-smolts after seawater transfer 3 5.
- The number of outbreaks declined markedly from around 2010, largely alongside the use of genetically resistant fish and strengthened IPNV control in hatcheries and smolt facilities 10 11.
- After several years of low outbreak numbers, IPN increased in 2025, with 40 reported cases—nearly three times the number reported in 2024 10. Recent outbreaks in QTL-selected fish have been associated with a potentially new IPNV variant with genetic changes in the region used for viral characterisation 11.
Geographical Spread:
- IPN is widespread in Norwegian salmon farms, affecting both freshwater and seawater environments 3 5.
- Recent reports from 2026 indicate a relative concentration of reported cases from central Norway northwards to Troms 11.
Economic Impact:
- IPN has caused considerable mortalities in Atlantic salmon post-smolts, leading to significant economic losses for the Norwegian salmon industry 3 5.
Treatment & Management:
- There is no specific treatment for IPN. Prevention has relied on a combination of genetic selection for IPN resistance (QTL-selected fish), control of IPNV in hatcheries and smolt facilities, biosecurity, good smolt quality, and stress reduction 7 3.
- Vaccination is commonly used in Norwegian Atlantic salmon and may reduce losses during outbreaks, but it does not reliably prevent infection, carrier status, or virus shedding 7 11.

Scotland

IPN Incidence in Scotland:
- The prevalence of IPNV infection is very high in farmed Atlantic salmon in sea water 3
- In freshwater salmon farms, the prevalence of infection and incidence of disease is lower but has increased in recent years 3
Geographical Spread:
- IPN affects salmon farms across Scotland, in both freshwater and marine environments 3

Research and References

Latest Research Findings

Recent studies on Infectious Pancreatic Necrosis (IPN) in salmonids have focused on various aspects of the disease, including its prevention, control, and molecular characteristics. Here are some notable recent research findings:

"The Infectious Pancreatic Necrosis Virus (IPNV) and its Virulence Determinants"
Authors: Jurado, C., et al.
Reference: Jurado, C., et al. (2020). The Infectious Pancreatic Necrosis Virus (IPNV) and its Virulence Determinants. Viruses, 12(2), 152.
Link to study
"Susceptibility of rainbow trout to three different genogroups of infectious pancreatic necrosis virus"
Authors: Mutoloki, S., et al.
Reference: Mutoloki, S., et al. (2020). Susceptibility of rainbow trout to three different genogroups of infectious pancreatic necrosis virus. Diseases of Aquatic Organisms, 141, 103-116.
Link to study

These studies represent advancements in understanding the molecular characteristics, prevention, and control of IPN in various regions with significant salmon farming industries.

Conclusion

Infectious Pancreatic Necrosis (IPN) remains a significant threat to aquaculture, necessitating diligent management and preventive measures. By implementing robust biosecurity protocols, investing in ongoing research, and fostering industry-wide cooperation, fish health managers and veterinarians can mitigate the impact of IPN and ensure the sustainability of aquaculture operations. This comprehensive guide aims to provide the necessary information and resources to effectively manage IPN and support the health and welfare of farmed fish.

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Last Modified: 2026-10-04

Tags: #InfectiousPancreaticNecrosis, #IPN, #IPNV, #InfectiousPancreaticNecrosisVirus #Birnaviridae, #Salmonids, #Salmon, #AtlanticSalmon, #Trout, #RainbowTrout, #ViralDisease, #Virus