Detection of piscine orthoreovirus in farmed rainbow trout from Chile

Abstract

The Piscine orthoreovirus (PRV), a recent member of the Reoviridae family, is an emerging marine pathogen in Salmonids. Two different strains have been described, one of them PRV-Ss is associated with the highly prevalent disease in Atlantic salmon (Salmo salar) known as Heart and Skeletal Muscle Inflammation (HSMI), while the other, PRV-Om, is associated to HSMI-like disease originally described in farmed Rainbow trout from Norway. Genetically, PRV can be classified in the genotypes Ia, Ib and II, being the genotype Ia and Ib associated to PRV-Ss and genotype II to PRV-Om. In Chile, PRV is considered as high-risk marine pathogen but its prevalence on Rainbow trout (wild or farmed) has not been deeply studied. In our lab, heart tissue samples from farmed Rainbow trout mortalities with undefined diagnosis were analyzed in search of viral pathogens. The presence of both PRV-Ss and PRV-Om and absent of other fish viruses was confirmed by RT-qPCR. PRV segment S1 sequences from PRV-Ss and PRV-Om from some representative positive samples were sequenced to determine the genotype and the phylogenetic relationship to PRV strains from different countries and salmonids. The sequences identified in this work are closely related to PRV strains grouped in sub-genotype Ia (Present in Norway – Canada), and the Genotype II. We identifying also one sequence not grouped in any previously described cluster, but close to PRV-Ss from genotype Ib suggesting the presence of a new branch in Genotype I. This analysis also shows that the PRV sequences identified in Rainbow trout are closed related to sequences previously reported in Coho salmon from in Chilean farming centers. Our results suggest that in Chile, Rainbow trout can be infected by different PRVs strains (PRV-Ss and PRV-Om) related mainly to the PRV strains present in Coho salmon. This study is at our knowledge the first description of PRV-Ss and PRV-Om sequences in farmed Rainbow trout from Chile.