Detection of Piscine orthoreoviruses (PRV-1b AND PRV-3a) in farmed Coho salmon with jaundice syndrome from Chile

Abstract

Piscine orthoreoviruses (PRVs) represent a group of marine viruses belonging to Reoviridae family, which are associated to emerging diseases in farmed Atlantic salmon, Rainbow trout and Coho salmon around the world. In Chile, the prevalence and deleterious effects of PRV infection in farmed salmonids had been studied recently, showing the occurrence of PRV-1 (formerly PRV-Ss) in Atlantic salmon with Heart and Skeletal Muscle Inflammation (HSMI), PRV-3 (formerly PRV-Om) in Rainbow trout with HSMI-like disease, and both viruses (PRV-1 and PRV-3) in Coho salmon with HSMI-like disease. In 1997, Jaundice Syndrome in Coho salmon was first described in Chile associated to outbreaks with high mortality, which occur during autumn season. Then, it was reported in 2006 that the jaundice condition in Coho salmon is consistent with an infectious form of hemolytic anemia and probably a virus was the causative agent, however the identification of the putative virus was not possible. Currently, the etiology of this syndrome is unknown, but several of the clinical signs exhibited by diseased Coho salmon are comparable to the signs showed by salmonids affected with some disease which are caused by PRVs. Therefore, it was of interest to determine if some PRVs could be related to Jaundice Syndrome in Coho salmon. In this manner, heart and head kidney tissue samples obtained from Coho salmon mortalities were analyzed in search of viral pathogens, where the presence of both PRV-1 and PRV-3 was confirmed by RT-qPCR and Sanger sequencing. Moreover, full-length genomic segment S1 sequences were obtained to determine the phylogenetic relationship with others PRV isolates previously described in Europe, America and Japan. One group of sequences found in Coho salmon with Jaundice Syndrome clustered into Sub-genotype Ib together with PRV-1 isolate described in Coho salmon with HSMI-like condition from Chile, and other group of sequences clustered into Genotype II with the first PRV-3 detected in Rainbow trout from Norway into previously described PRV-3a clade. Our results also suggest that PRVs has developed an infection cycle, which involves to Atlantic salmon, Rainbow trout and Coho salmon.