The first report of PRV was in 2010), associated with Heart and skeletal muscle inflammation HSMI in Norway. In Chile, genotypes PRV-1 and PRV-3 have been identified, affecting the three productive species: Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch). Although it is a pathogen that generates low mortality, morbidity can reach 100%. It has been established that it generates persistence, and its genome can be detected several months after the end of the clinical picture. The primary target cell is the erythrocytes, where it replicates and disseminates to other organs, accessing secondary target cells: cardiomyocytes, enterocytes, hepatocytes, macrophages, and myocytes). Recent studies establish that the virus generates modifications in the transcriptomic profile in erythrocytes, among which are genes associated with the innate immune response and antiviral response; however, the main difficulty in its study has been its in vitro propagation. In this sense, a series of cell lines had been evaluated to establish their relationship with PRV and their ability to support its replication without positive results. In this study, we showed for the first time the infection of field isolated PRV-1 in SHK-1 cells, detecting the viral transcript at 2, 4, 6, 12, 24 and 48 hours post-infection (hpi) which increased significantly at 24 hours of culture (fig1).
A differential quantification of viral ssRNA was subsequently performed, establishing the presence of viral mRNA at 24 hpi, corresponding to 49% of the total RNA . Along with the above, the abundance of immune and antiviral response mRNAs was analyzed in the infected cells, establishing a correlation between viral kinetics and the cellular response, observing an increase in the IFN I transcript at 24 hpi, together with the antiviral mRNAs of ISG15 and Mx. A similar result was observed for transcripts of MHC I and MHC II in accordance with the peak of PRV expression, suggesting that the increase PRV-1 RNA generates an important interferon-dependent response(fig2).
Once the peak of PRV expression was identified, indirect immunofluorescence of the cells infected for 24h was performed, detecting the presence of three viral proteins, two structural (σ1 and σ3) and one non-structural (σNS) in the cytoplasm of SHK-1 cells. Finally, electron microscopy (TEM) studies were performed (fig 3), detecting vesicles with viral particles inside like those previously described in erythrocytes. (Wessel et al, 2014).
These findings strongly suggest that PRV-1 chilean isolate infect and replicate in SHK-1 cells generating an early immune and antiviral response in this fish cells.
Founded by Doctoral Scholarship from the National Agency for Research and Development (ANID) 2021 21210561 and FONDAP 1523A0007