An established IPN virus bath challenge model available in Tromsø.
In Norway, the virus disease infectious pancreatic necrosis (IPN) is a major problem for the Atlantic salmon farmers. Earlier, it was known as a disease on fry, but now increasing numbers of disease outbreaks are registered on smolts in seawater.
An important measure against disease is vaccines. To develop effective vaccines, one has to have the opportunity to test both experimental- and established products under controlled conditions in a laboratory.
Testing of experimental IPN vaccines using an IPN virus challenge model
Eight weeks after Atlantic salmon had been vaccinated with IPN vaccines, they were bath challenged with IPN virus. The vaccinated fish were well protected against the viral disease, while fish given a vaccine without IPN virus antigen (vaccine C) and fish given saline were not protected. (Sommer, Knappskog and Rødseth, Norsk Fiskeoppdrett nr. 18, p. 30-32,1998).
Outbreak of IPN in Atlantic salmon smolts subjected to intensive rearing conditions
Atlantic salmon smolts subjected to intensive rearing conditions, with high density, low water flow and oxygenation in fresh water (treated), had a much higher mortality than the control fish when they were bath challenged with IPN virus in sea water.
Developing a challenge model
Since 1998, an IPN virus bath challenge model for salmon smolts developed at Fiskeriforskning has given the vaccine producers this opportunity. The model has so far produced mortality in every experiment, and is therefore both well established and reliable. However, there are still parameters we know have an impact on the mortality level which we are not able to fully control.
Several experiments from 1998 until today show that the vaccines sold in Norway have a protective effect against IPN under controlled conditions. The fish feed companies have also tested their special feeds in the challenge model with a positive result.
The increasing number of IPN outbreaks in Atlantic salmon after seawater transfer has been connected to the intensive rearing conditions in freshwater. It has been discussed whether high density, low water flow and oxygenation to save freshwater can lead to increased susceptibility to IPN virus. Experiments at Fiskeriforskning confirm that this is the case.
Research is now in progress to further clarify the cause of this increased susceptibility to IPN virus. The IPN virus bath challenge model is an important tool in this research.
