Salmonid alphavirus replicon is functional in fish, mammalian and insect cells and in vivo in shrimps (Litopenaeus vannamei)

The Salmonid alphavirus (SAV) is the etiological agent of pancreas disease in Atlantic salmon (Salmo salar) and Sleeping disease in rainbow trout (Oncorhynchus mykiss). SAV differs from alphaviruses infecting terrestrial animals in that it infects salmonid fish at low temperatures and does not use an arthropod vector for transmission. In this study we have shown that a SAVbased replicon could express proteins when driven by the subgenomic promoter in vitro in cells from fish, mammals and insects, as well as in vivo in shrimps (Litopanaeus vannamei). The SAV-replicon was found to be functional at temperatures ranging from 4 to 37 °C. Protein expression was slow and moderate compared to that reported from terrestrial alphavirus replicons or from vectors where protein expression was under control of the immediate early CMV-promoter. No cytopathic effect was visually observable in cells transfected with SAV-replicon vectors. Double stranded RNA was present for several days after transfection of the SAV-replicon in fish cell lines and its presence was indicated also in shrimp. The combination of prolonged dsRNA production, low toxicity, and wide temperature range for expression, may potentially be advantageous for the use of the SAV replicon to induce immune responses in aquaculture of fish and shrimp.