Abstract
Piscine orthoreovirus (PRV-1) causes heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar). Recently, a novel PRV (formerly PRV-Om, here called PRV-3), was found in rainbow trout (Oncorhynchus mykiss) with HSMI-like disease. PRV is considered to be an emerging pathogen in farmed salmonids. In this study, molecular and antigenic characterization of PRV-3 was performed. Erythrocytes are the main target cells for PRV, and blood samples that were collected from experimentally challenged fish were used as source of virus. Virus particles were purified by gradient ultracentrifugation and the complete coding sequences of PRV-3 were obtained by Illumina sequencing. When compared to PRV-1, the nucleotide identity of the coding regions was 80.1%, and the amino acid identities of the predicted PRV-3 proteins varied from 96.7% (λ1) to 79.1% (σ3). Phylogenetic analysis showed that PRV-3 belongs to a separate cluster. The region encoding σ3 were sequenced from PRV-3 isolates collected from rainbow trout in Europe. These sequences clustered together, but were distant from PRV-3 that was isolated from rainbow trout in Norway. Bioinformatic analyses of PRV-3 proteins revealed that predicted secondary structures and functional domains were conserved between PRV-3 and PRV-1. Rabbit antisera raised against purified virus or various recombinant virus proteins from PRV-1 all cross-reacted with PRV-3. Our findings indicate that despite different species preferences of the PRV subtypes, several genetic, antigenic, and structural properties are conserved between PRV-1 and-3.
Highlights
Rainbow trout (Oncorhynchus mykiss) is farmed in a variety of aquaculture systems in many countries [1]
The disease occurred in freshwater hatcheries lasting until after sea transfer, and was characterized by lesions resembling those of heart and skeletal muscle inflammation (HSMI) in Atlantic salmon (Salmo salar), and by anemia [3]
Rainbow trout eyed eggs were provided by a commercial Danish fish farm that is officially free of infectious pancreatic necrosis virus (IPNV), infectious hematopoietic necrosis virus (IHNV), viral hemorrhagic septicemia virus (VHSV), and bacterial kidney disease (BKD)
Summary
Rainbow trout (Oncorhynchus mykiss) is farmed in a variety of aquaculture systems in many countries [1]. Rainbow trout is farmed in freshwater systems for production of portion size fish (300 g), while larger fish (3–5 kg) can be produced when fish are kept in seawater for the major grow-out period. In Norway, rainbow trout is primarily produced in seawater, and the loss of fish through the seawater stage has been estimated to 19% of the fish, mostly linked to infectious diseases [2]. In 2013, a new infectious disease was reported in rainbow trout in Norway. A PRV that was genetically similar to the rainbow trout PRV was reported in Coho salmon (Oncorhynchus kisutch) in Chile, suffering from an HSMI-like disease [7]
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