Viral Protein Kinetics of Piscine Orthoreovirus Infection in Atlantic Salmon Blood Cells

Piscine orthoreovirus (PRV) is ubiquitous in farmed Atlantic salmon (Salmo salar) and the cause of heart and skeletal muscle inflammation. Erythrocytes are important target cells for PRV. We have investigated the kinetics of PRV infection in salmon blood cells. The findings indicate that PRV causes an acute infection of blood cells lasting 1-2 weeks, before it subsides into persistence. A high production of viral proteins occurred initially in the acute phase which significantly correlated with antiviral gene transcription. Globular viral factories organized by the non-structural protein µNS were also observed initially, but were not evident at later stages. Interactions between µNS and the PRV structural proteins λ1, µ1, σ1 and σ3 were demonstrated. Different size variants of µNS and the outer capsid protein µ1 appeared at specific time points during infection. Maximal viral protein load was observed five weeks post cohabitant challenge and was undetectable from seven weeks post challenge. In contrast, viral RNA at a high level could be detected throughout the eight-week trial. A proteolytic cleavage fragment of the µ1 protein was the only viral protein detectable after seven weeks post challenge, indicating that this µ1 fragment may be involved in the mechanisms of persistent infection.