Development and application of a broadly reactive real-time reverse transcription-PCR assay for detection of murine noroviruses

Murine norovirus (MNV) is a viral agent newly identified in laboratory mice and a large number of genetically diverse MNV strains have been reported to date. A broadly reactive TaqMan-based real-time reverse transcription (RT)-polymerase chain reaction (PCR) assay was developed for MNVs. Novel primers and a TaqMan MGB probe were designed targeting highly conserved sequences among MNV strains, which are located in the open reading frames 1 (ORF1)–ORF2 junction region. The quantitative range of this assay was determined as 1.0 × 102–1.0 × 108 copies/PCR tube based on a 10-fold serial dilution of plasmid DNA containing the target sequences. Viral RNA in eight murine stool specimens positive by nested RT-PCR assay was measured, and the highest viral RNA load was calculated at 4.7 × 106 copies/g-stool. MNV was inoculated into RAW 264.7 cells, and the viral RNA was monitored to validate assay sensitivity. MNV-RNA in the supernatant was detected during in vitro replication, which increased substantially from 5 to 30 h post-infection (hpi) and reached more than 1.0 × 1010 copies/mL at 96 hpi. This real-time RT-PCR assay is a useful tool to detect and quantify MNV-RNA in in vivo and in vitro studies.