Infectious Pancreatic Necrosis (IPN)
Cause of the Disease
Infectious pancreatic necrosis (also known as Acute catarrhal enteritis) is one of the first described and most extensively studied diseases of fish. There are strains and substrains of IPN virus that can be differentiated by serological, biochemical and genetic means. The VR-299 (type 1) strain was originally isolated in North America and has since been found almost worldwide. The Ab (type 2) and Sp (type 3) strains were originally isolated in Europe, have been widely disseminated but have not yet been isolated in North America. Relative virulence and host specificity can var from one isolate or strain to another.
Host range, distribution, and occurrenceIPN is a highly contagious disease of trout and salmon. High mortality is typically experienced, especially in fry and fingerling rainbow, brook and brown trout. No species of salmonid fish is completely resistant to the virus. IPN virus also causes mortality in striped bass, sea bass, menhaden, halibut, yellowtail and eel. IPN and IPNlike viruses have been isolated from over 65 species of aquatic vertebrates and invertebrates in both freshwater and marine environments. IPN virus occurs in many parts of the world including North, Central and South America, Europe (including the UK), Scandinavia, Japan and Southeast Asia. It has not yet been described in Africa, Australia and New Zealand. The virus tends to become endemic to most watersheds in which it is found.
IPN virus can infect fish at all stages in the life cycle. Smaller fish tend to be more sensitive to the virus and mortality is rarely seen in fish over 5 g. (90 fish per pound). The one exception is Atlantic salmon, where IPN virus can cause significant chronic mortality in larger fish, particularly after the stress of smoltification and saltwater introduction. The disease can occur over a wide temperature range but tends to be most acute at 10 to 15 C. Mortality typically begins 3 to 10 days following infection and peaks in 10 to 20 days. Total mortality from acute infection may reach 70% or more over 2 to 4 weeks. Under certain conditions the course of the disease may be more chronic with lower mortality. Up to 90% of survivors carry the virus and shed it in their feces for the remainder of their life.