Infectious pancreatic necrosis in Atlantic salmon, Salmo salar L

Area of Science:

• Aquaculture
• Fish Pathology
• Veterinary Virology

Background:

• Infectious pancreatic necrosis (IPN) is a significant disease affecting farmed Atlantic salmon (Salmo salar L.).
• Historically, IPN was characterized by pancreatic and intestinal lesions.

Purpose of the Study:

• To review clinical and histopathological findings of 21 IPN outbreaks in Scottish salmon farms (1991-2004).
• To describe novel pathological changes and disease progression in freshwater and marine environments.

Main Methods:

• Clinical and histopathological review of 21 IPN outbreaks.
• Analysis of viral strains from affected freshwater and marine salmon.
• Observation of disease progression and secondary complications.

Main Results:

• A distinctive syndrome with consistent liver lesions, previously unassociated with IPN, was observed in both freshwater fry and saltwater post-smolts.
• The pathology extended geographically from Shetland down the West coast of Scotland and into Ireland.
• Viral strain analysis indicated similarities between freshwater and saltwater isolates, differing from rainbow trout strains.
• Freshwater survivors developed distended intestines; saltwater survivors exhibited poor growth and susceptibility to sea lice.
• Significant economic losses were reported, with initial mortality rates exceeding 50% in some marine outbreaks.

Conclusions:

• IPN in Scottish salmon presents with novel liver lesions and has expanded its geographical range.
• Similar viral strains appear responsible for IPN in both freshwater and marine environments.
• Despite mitigation efforts, IPN continues to be a major economic threat to salmon aquaculture.