PRJNA470897
Successful passage of PRV but not HSMI in Mowi-McConnell Atlantic salmon suggests secondary requirements for initiating PRV-associated disease
Piscine orthoreovirus (PRV) is the causative agent of Heart and Skeletal Muscle Inflammation (HSMI) – a widespread and significant disease of cultured Atlantic salmon in Norway. PRV is also widespread in farmed Atlantic salmon of Pacific Canada, but has not been a significant concern to production even in the limited instances where HSMI has been observed. This study investigated PRV infection dynamics and the potential for experimental passage of HSMI in Pacific-adapted Mowi-McConnell Atlantic salmon to better understand the mechanisms for PRV-associated pathogenesis. Regardless of the PRV source (non-diseased or HSMI-diseased fish), infections led to viremia that induced only minor focal heart inflammation without significant transcriptional induction of inflammatory cytokines. Repeated screening of PRV dsRNA/ssRNA along with histopathology and gene expression analysis of host blood and heart tissues identified three distinct phases of infection: (1) early systemic dissemination and replication without host recognition; (2) peak replication, erythrocyte inclusion body formation and load-dependent host recognition; followed by (3) long-term, high-load viral persistence with limited replication or host recognition sometimes accompanied by minor heart inflammation. These findings contrast previous PRV challenge trials that induced HSMI in multiple regards, and suggest that secondary requirements may be necessary to initiate PRV-associated disease.