Forsøksdyr: Establishing an ISAV HPR0 challenge model

Godkjenningsdato 08.07.2020

Godkjenningsperiode 10.08.2020-31.07.2021

The overarching goal of the study is to establish an experimental challenge model for ISAV HPR0 and Atlantic salmon (Salmo salar)

ISAV HPR0 is the 'avirulent' form of ISAV, that cannot be cultured in vitro, and for which there exist no challenge model. Attempts to establish an HPR0 challenge model have hitherto been unsuccessful, and we therefore suggest a new approach that mainly employs a particularly susceptible developmental stage of salmon - the fry.

The application includes two separate trials.

Trial 1 will be a challenge study on salmon fry from different fish strains, including wildtype fish and three strains that have been genetically modified to increase their susceptibility to (viral) infection. The main challenge inoculate will clearly be ISAV HPR0, but will also include the virulent ISAV HPRdelta (positive control) and genetically attenuated strains of SAV3 (to gauge the actual susceptibility of the genetically modified salmon strains). There are two important reasons for choosing salmon fry: 1) fry are more susceptible to viral infections than older stages, 2) infectious material of ISAV HPR0 is very scarce and so it is beneficial to work with small fish in small volumes.

Trial 2 will be performed after trial 1 has been completed and its exact design will depend on results from the first experiment. But differently from trial 1, it will employ post-smolt salmon in seawater. The main point of trial 2 is to examine if findings demonstrated in trial 1 can be applied to the seawater phase.

Harmfulness: the positive control groups that are challenged with ISAV HPRdelta or wildtype/partially attenuated SAV3, will experience severe disease and mortality. The groups challenged with HPR0 or highly attenuated SAV3 will experience little or no symptoms.

Utility value: a functional challenge model for HPR0 will be instrumental for work to understand the role of HPR0 in the epidemics of ISAV HPRdelta infections in Norwegian aquaculture.

Species: Atlantic salmon (Salmo salar)
Number of animals: 1650

Compliance with 3R principles: optimization of design to ensure that enough, but not too many, fish are used to obtain the goals of the experiment