Piscine orthoreovirus (PRV) is a double-stranded RNA virus responsible for heart and skeletal muscle inflammation (HSMI), an emerging disease in Atlantic salmon ( Salmo salar ) in aquaculture . PRV is highly prevalent in Chile, and it is common to find phenotypes with asymptomatic infection with out associated lesions. PRV’s persistence can involve the release of anti-inflammatory cytokines and reduced cell populations associated with the Th1 response. T he persistence phenotype of PRV in Atlantic salmon under productive conditions has not been evaluated. Also, it has been shown in fish that water temperature significantly impacts the immune response of fish to viral infection, which could modify the response of salmon to PRV in the different seasons .
This work analyzed the cell populations of 15 salmon from a culture center in the Magallanes Region, Chile. Blood samples were collected in autumn, winter, and spring. The diagnosis by qPCR of several pathogens (including PRV) was ruled out. Peripheral blood lymphocyte populations were characterized by flow cytometry based on the expression of IgM, CD4, and CD8 surface markers in PRV (-) and PRV (+) fish. In the case of the PRV (-) fish, a significant decrease in IgM-/CD4- cells along with a significant increase in CD8+ cells was detected in autumn (Fig. 1A). In winter, an increase in IgM-/CD4- cells and a decrease in CD8+ cells were observed (Fig. 1B). No PRV (-) fish were detected in spring (Fig. 1C). By contrast, PRV (+) fish showed in autumn a significant increase in IgM-/CD4- cells and a significant decrease in CD8+ cells. Importantly, these patterns were consistent in all the seasons evaluated . No IgM+, IgM+/CD4 + cells were detected in the PRV (+) fish in spring (Fig. 1C). These results contribute to the knowledge of fish immunity to PRV infection and how temperature may compromise its modulation in a marine productive environment .
Funding : Fondecyt Iniciacion 11221308, Fondecyt Regular 1211841 (ANID; Chile), becas DICYT-USACH (082344RL_Postdoc; 082344RL_Ayudante) y Proyecto Regular UDLA (DI-14/23)..