Molecular Detection of Murine Norovirus from Experimentally and Spontaneously Infected Mice

The RNA polymerase gene of murine norovirus (MNV) was isolated from feces and organ samples by the reverse transcription (RT)-polymerase chain reaction (PCR). For experimental infection, homogenate of cecum obtained from an MNV-infected mouse was gavaged to 3 C.B-17-Prkdc(scid) (scid) mice and 3 ICR mice at 6 weeks of age. Sixty days after oral inoculation, MNV was isolated from the cecum (3/3 scid and 3/3 ICR), feces (3/3 scid and 3/3 ICR), duodenum (1/3 scid and 3/3 ICR), liver (1/3 scid and 1/3 ICR), and spleen (3/3 ICR) samples, but MNV was not detected in the brain, heart, kidney, lung, salivary gland, ovary, thymus, or uterus samples of any of the orally inoculated mice. Feces of males cohabiting with MNV infected dams were positive for viral RNA after 18 days of cohabitation, but 8 fetuses (embryonic day 18.0) derived from the dams were negative for the virus. The results suggest that the cecum and feces are the most suitable sample types for the detection of MNV in infected animals and that caesarean section is efficient for the elimination of the virus. In terms of spontaneous infection, the RNA polymerase gene of MNV was isolated from 33/245 (13.1%) cecum samples derived from 15/59 (25.4%) facilities, and the sequence analysis revealed that at least 5 types of the virus were prevalent. This is the first report on MNV infection in mouse colonies in Japan.