Murine norovirus infection in Brazilian animal facilities

Detection and whole genome sequencing of murine norovirus in animal facility in Italy

Viruses belonging to the genus Norovirus (NoV) of the family Caliciviridae are the major cause of acute viral gastroenteritis worldwide. NoVs are classified into 10 genogroups (GI-GX), and those belonging to the genogroup GV are able to infect several species of rodents. To evaluate the circulation of MNV among mice housed in an Italian facility, sampling was performed over two separate periods, in 2011, and 3 years later in 2014. During the two samplings, 75 fecal samples were collected from healthy mice housed in the animal facility and subjected to RT-PCR for viral detection. After the analysis, 41/75 animals (54.6%) resulted positive for the presence of MNV in feces. Nucleotide sequencing revealed the presence of two MNV variants co-circulating in both 2011 and 2014. One MNV strain was isolated on RAW264.7 cell line, and subjected to full genome sequencing. Our study showed that the murine noroviruses are widespread in the investigated animal facility, despite guidelines for animal care and maintenance. Full genome sequence analysis of the MNV strain described in this study showed a correlation with other strains circulating in Europe. Understanding the molecular epidemiology of this virus should give insight into its natural history and evolution in mice.

Preventing the Transmission of Murine Norovirus to Mice (Mus musculus) by Using Dry-heat Sterilization

A critical component of an animal care biosecurity plan includes the sterilization of materials that come into direct contact with the animals. Dry-heat sterilization is gaining popularity in animal research facilities due to lower cost, less space utilization, no water usage, and the ability to sterilize water-sensitive materials. Currently, dry-heat sterilization ovens are validated against Bacillus atropheus spore strips with the assumption that a lack of sporulation is equivalent to successful sterilization. However, no published studies describe sterilization of rodent cages that contain relevant rodent pathogens by using this method. To determine if a dry-heat sterilizer can sterilize rodent cages and bedding against relevant rodent pathogens, we created murine norovirus (MNV)-contaminated cages by using mice with known MNV infection and shedding. The contaminated cages were either sterilized with the dry-heat sterilizer or not sterilized. Naïve, 4-wk-old, CD-1 mice were placed in the dry-heat-sterilized cages, contaminated unsterilized cages, or standard autoclaved cages for 2 wk. The mice were subsequently placed into clean, autoclaved cages for the remainder of the study. Fresh fecal pellets were collected at weeks 0, 12, and 16 and submitted for MNV PCR. Whole blood was collected for MNV serology at weeks 0, 8, 12, and 16. At week 16, all mice that had been in the unsterilized contaminated cages were positive for MNV by both fecal PCR and serology, whereas the mice in the dry-heat-sterilized and autoclaved cages were negative for MNV by both methods at all time points. Our study supports the use of dry heat sterilization as a viable sterilization method for rodent cages and bedding.

Isolation and Identification of a Murine Norovirus Persistent Infection Strain in China

Murine Norovirus (MNV) is one of the most known viruses among viruses in mice. Because of the high prevalence of MNV in frequently used laboratory animals in biomedical researches, there is a significant impact of MNV. There may be different prevalence degrees and molecular characteristics of MNV in different regions around the world. Here, we reported an MNV strain "designated HBTS-1806" isolation from commercial mice's feces that caused a detectable cytopathic effect (CPE) in RAW264.7 cells. According to electron microscopy, the virus was 50-70 nm in diameter. The complete genome of HBTS-1806 is 7383 nucleotides with a structure similar to that of MNV reference strains. According to phylogenetic analysis on the basis of the whole genome, HBTS-1806 shared nucleotide sequence identities of 90.2-95.4% with other Chinese isolates reported. Analysis of amino acid sequence on the basis of ORF1 and ORF2 suggested that the isolated strain may be derived from recombination. Although no gross lesions or histopathological changes were found from mice infected with 5 × 105 TCLD50 of MNV by oral gavage inoculation, the intestinal virus loads lasted 12 weeks, suggesting a persistent infection strain of MNV isolate in China.

A semi-nested RT-PCR assay for detection of norovirus in rat fecal samples

Norovirus is a highly prevalent pathogen that can infect a wide range of host species. Thus far, there have only been two reports of norovirus infection in rats. Diagnostic assays for the detection of norovirus are well established, but a specific molecular assay for the diagnosis of norovirus infection in laboratory rats has not yet been reported. In this study, we describe the development of a sensitive, semi-nested RT-PCR assay for detection of norovirus in fecal samples from Rattus norvegicus, reared in animal facilities under different sanitary barrier conditions. Additionally, we describe the first report of the presence of norovirus in rat colonies from Brazilian animal facilities.