Individual monitoring of immune response in Atlantic salmon salmo salar following experimental infection with piscine myocarditis virus (PMCV)

Piscine myocarditis virus (PCMV) is a double-stranded RNA virus structurally similar to the Totiviridae family. PCMV is the causative agent of cardiomyopathy syndrome (CMS), a severe cardiac disease that affects farmed Atlantic salmon (Salmo salar). A recent study characterized the host immune response in infected salmon through a transcriptome immune profiling, which confirmed a high regulation of immune and anti-viral genes throughout infection with PCMV. We developed a novel model based on repeated non-lethal blood sampling, enabling the individual monitoring of salmonids during an infection. In the present work, we used this model to describe the host immune response in Atlantic salmon after intramuscular infection with PCMV during a 77-day period. A range of key immune genes was monitored during infection by real-time PCR. Results indicated that both type I and type II interferons (IFN), IFN-Ia and IFN-γ, respectively) are up-regulated in infected blood at different-time points. Selected immune genes (e.g. Mx, CD8a and gIP) were also analysed in heart tissue, confirming an up-regulation at the terminal time point. The PCMV load and CMS pathology was verified by real-time PCR and histopathology. This study confirms the importance of using a non-lethal sampling method in order to individually monitor host response throughout infection with a chronic disease such as CMS.