シロサケにおける伝染性造血器壊死症ウイルス(IHNV)M遺伝子RNAと相同のDNA型の存在

概要

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Homologous DNAs (M DNA) to the infectious hematopoietic necrosis virus (IHNV) M gene were detected in river-homing chum salmon Oncorhynchus keta sperm, eyed-egg embryos, alevins and fry collected from nine rivers and four hatcheries in Hokkaido Prefecture, Japan, in 1998-2002, although no virus titer was observed in the samples. Real-time PCR assay revealed M DNA at the highest number of 1.7 × 104 copies/mg of tissue. Nucleotide sequence similarities between the M DNA and the viral M genes were ≥97%. When CHSE-214 and RTG-2 cells were inoculated with IHNV, the cells contained 3.8 × 101 to 1.8 × 103 copies of M DNA/105 cells and showed cytopathic effects (CPE). Salmonid fish fry and yearlings infected with the virus contained 1.3 × 101 to 2.6 × 103 copies of M DNA/mg of tissue. CHSE-214 cells transfected with the viral RNA produced M DNA without showing CPE. Reverse transcriptase (RTase) activities in the fish cells and the fish tissues were equivalent to 86-578 pg HIV-1 RTase/106 cells and 2.1-12 pg HIV-1 RTase/mg of tissue, respectively. These results suggest that M DNA is produced from IHNV RNA and retained in the fish.