HSMI and CMS - basic studies of the viral aetiology and pathogenesis in Atlantic salmon

Several achievements have been made over the last 10 years in understanding the pathology of HSMI and CMS. The inflammatory nature of the disease has been studied and the cells involved are characterised. The viruses causing HSMI and CMS can be grown in c ell culture and experimentally induce changes in the heart typical of the two disease entities. Yet there is a lot to be done to characterise the viral aetiologies. The major challenge has been to obtain a sufficiently high concentration of virus in cell culture. Our approach is to focus on detecting the peak virus titre in infected organs and in infected cell cultures. Since virus replication cannot be assessed, we will focus on detecting the host response to virus infection by monitoring interferon (IFN ) responses and related IFN pathways. This will include studies in vivo and in vitro and since changes in the heart take 2 months to develop virus replication potentially occurs in other organs prior to development of heart changes. Similar studies will b e performed in cell culture where CPE also develop long after inoculation. Monitoring of cellular responses to infection will provide information as to the peak virus replication in infected cells, not easily identified as CPE is slowly developing. This i nformation will be used for different purposes; i) identify virus specific genome sequences (subtractive hybridization), ii) search for protein signatures of virus replication in vitro (proteomics), or iii) silence or down-regulate the cellular responses to infection. We will employ the modulating effects of cortisol in down-regulating immune responses. Parr of salmon will be put in a chronic stress condition (cortisol implants) and infected with HSMIV or CMSV. Yet another ambitious approach will be to si lence the innate immune responses of infected cell cultures by use of RNAi. Our hypothesis is that we need to silence temporarily or permanently the IFN responses and shRNA is the most attractive alternative.