Journal
PLoS One
Volume 11, Issue 10, Pages -Publisher
PUBLIC LIBRARY SCIENCE
DOI: 10.1371/journal.pone.0165424
Keywords
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Funding
- Agriculture Forestry and Fisheries Research Council Japan
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Erythrocytic inclusion body syndrome (EIBS) causes mass mortality in farmed salmonid fish, including the coho salmon, Onchorhynchus kisutchi, and chinook salmon, 0. tshawytscha. The causative agent of the disease is a virus with an icosahedral virion structure, but this virus has not been characterized at the molecular level. In this study, we sequenced the genome of a virus purified from EIBS-affected coho salmon. The virus has 10 dsRNA genomic segments (L1, L2, L3, Ml, M2, M3, Si, S2, S3, and S4), which closely resembles the genomic organization of piscine orthoreovirus (PRV), the causative agent of heart and skeletal inflammation (HSMI) in Atlantic salmon and HSMI-like disease in coho salmon. The genomic segments of the novel virus contain at least 10 open reading frames (ORFs): lambda 1 (lambda 1), lambda 2, lambda 3, mu 1 (mu 1), mu 2, mu NS, sigma 1 (sigma 1), sigma 2, sigma 3, and sigma NS. An additional ORF encoding a 12.6-kDa protein (homologue of PRV p13) occurs in the same genomic segment as sigma 3. Phylogenetic analyses based on S1 and lambda 3 suggest that this novel virus is closely related to PRV, but distinctly different. Therefore, we designated the new virus `piscine orthoreovirus 2' (PRV-2). Reverse transcription quantitative real-time PCR revealed a significant increase in PRV-2 RNA in fish blood after the artificial infection of EIBS-naive fish but not in that of fish that had recovered from EIBS. The degree of anemia in each fish increased as the PRV-2 RNA increased during an epizootic season of EIBS on an inland coho salmon farm. These results indicate that PRV-2 is the probable causative agent of EIBS in coho salmon, and that the host acquires immunity to reinfection with this virus. Further research is required to determine the host range of PRV species and the relationship between EIBS and HSMI in salmonid fish.
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