Pitfalls in mouse norovirus (MNV) detection in fecal samples using RT-PCR, and construction of new MNV-specific primers

Sensitive electrochemical gold nanoparticle-based immunosensor for norovirus detection in food samples

Norovirus (NoV) infection is one of the most common non-bacterial causes of gastroenteritis among the population worldwide. From the point of view of medical diagnostics, it is important to develop a system that would sensitively and selectively detect norovirus from a patient's sample in order to control and limit its spread. In this paper, we present a stable and sensitive NoV (mouse model) detection matrix in infected food samples. The bio-platform was made of a modified gold electrode with a self-assembled l-cysteine monolayer, covered with gold nanoparticles, a linker and an antibody specific to the VP1 surface protein of the virus. Binding of the VP1 protein to the antibody caused a decrease in the current strength confirmed by electrochemical techniques - cyclic voltammetry (CV) and differential pulse voltammetry. The reduction of the current was proportional to the concentration of NoV sample. The biosensors showed high sensitivity and linearity in a range from 1 × 10-9 to 1 × 10-18 TCID50, with the detection limit of 1 × 10-18 TCID50. CV showed a diffusion-controlled process. In addition, each modification step was confirmed by scanning electron microscopy, electrochemical impedance spectroscopy, and CV. The described immunosensor showed excellent recovery values, good linearity and long-term stability, crucial parameters for biosensor construction.

Multi-phased internalization of murine norovirus (MNV) in Arabidopsis seedlings and its potential correlation with plant defensive responses

Norovirus is a highly infectious human pathogen that causes acute foodborne diseases worldwide. As global diet patterns have begun to incorporate a higher consumption of fresh agricultural products, the internalization of norovirus into plants has emerged as a potential threat to human health. Here, we demonstrated that murine norovirus (MNV1) was internalized into Arabidopsis in multiple phases, and this internalization was correlated with Arabidopsis innate immunity responses. Under hydroponic conditions, continuous treatment of MNV1 retarded root growth and facilitated flower development of Arabidopsis without causing necrotic lesions. Examination of viral titers and RNA levels revealed that MNV1 was internalized into Arabidopsis in at least three different phases. In response to MNV1 treatment, the Arabidopsis defensive marker PR1 (a salicylic acid signaling marker) was transiently up-regulated at the early stage. PDF1.2, a jasmonic acid signaling marker, exhibited a gradual induction over time. Noticeably, Arabidopsis RNS1 (T2 ribonuclease) was rapidly induced by MNV1 and exhibited anti-correlation with the internalization of MNV1. Exposure to recombinant Arabidopsis RNS1 protein reduced the viral titers and degraded MNV1 RNA in vitro. In conclusion, the internalization of MNV1 into Arabidopsis was fluctuated by mutual interactions that were potentially regulated by Arabidopsis immune systems containing RNS1.

Development and evaluation of a broadly reactive reverse transcription recombinase polymerase amplification assay for rapid detection of murine norovirus

Background

Murine norovirus (MNV) is recognized as the most prevalent viral pathogen in captive mouse colonies. The rapid detection assay for MNV would be a useful tool for monitoring and preventing MNV infection. A recombinase polymerase amplification (RPA) assay was established in this study to provide a solution for rapid and sensitive detection of MNV.

Results

The detection limit of the RT-RPA assay for the detection of MNV was 1 × 10² copies of RNA molecules per reaction. The assay was specific since there was no cross-reaction with other common murine viruses. In addition, the broad reactivity of the RT-RPA assay was validated using the synthesized template carrying seven point mutations among several MNV strains. The MNV RT-RPA assay could detect as few as 1 × 10² copies of the mutant per reaction, suggesting the assay could be broadly reactive against a large diversity of MNV strains. Forty eight clinical samples including 16 gastric tissue specimens, 16 cecal tissue specimens and 16 fecal specimens were tested for the validation of the new developed RT-RPA assay. The detection results of RT-RPA and RT-qPCR for clinical samples were very similar, except that a gastric tissue sample which was positive by RT-qPCR, with a RNA titer of 27 copies, was negative by RT-RPA.

Conclusions

A broadly reactive RT-RPA assay was successfully established for MNV detection.

An enteric virus can replace the beneficial function of commensal bacteria

Intestinal microbial communities have profound effects on host physiology¹. Whereas the symbiotic contribution of commensal bacteria is well established, the role of eukaryotic viruses that are present in the gastrointestinal tract under homeostatic conditions is undefined^2,3. Here, we demonstrate that a common enteric RNA virus can replace the beneficial function of commensal bacteria in the intestine. Murine norovirus (MNV) infection of germfree or antibiotics-treated mice restored intestinal morphology and lymphocyte function without inducing overt inflammation and disease. The presence of MNV also suppressed an expansion of group 2 innate lymphoid cells (ILCs) observed in the absence of bacteria, and induced transcriptional changes in the intestine associated with immune development and type I interferon (IFN) signaling. Consistent with this observation, the IFNα receptor was essential for the ability of MNV to compensate for bacterial depletion. Importantly, MNV infection offset the deleterious effect of antibiotics-treatment in models of intestinal injury and pathogenic bacterial infection. These data indicate that eukaryotic viruses have the capacity to support intestinal homeostasis and shape mucosal immunity akin to commensal bacteria.

MNV primarily surveillance by a recombination VP1-derived ELISA in Beijing area in China

Murine norovirus (MNV) was first found as a surrogate for human norovirus study. However, MNV infection was mostly prevalent in laboratory mice, and its immunomodulatory properties may affect the outcome of animal experiments. MNV surveillance had been performed in Europe, North America and some other countries, but not in China. Nowadays, the complete MNV virions had been used as antigen in MNV serological detection. However, the complexity in the preparation of virions might affect the antigen stability, and the virulence recovery of virion antigen had also been detected. In this study, the caspid VP1 protein was proved to be the mostly predominant antigen in MNV virions. An ELISA method using the recombination VP1 as antigen was developed (rVP1 ELISA). The rVP1 ELISA is more sensitive and less specific than the MNV virion-derived IFA method. To address the prevalence of MNV in China, a totally 600 mouse serum samples from Beijing area were tested by rVP1 ELISA and confirmed by IFA and WB. The MNV infection rate was 11.67%, but most of the MNV-positive samples were from experimental facilities (MNV rate=30.94%), not from commercial vendors (MNV rate=0.27%). Collectively, a sensitive rVP1 ELISA was developed in the current study, and the MNV investigation by rVP1 ELISA showed that MNV infection was mostly prevalent in the laboratory mice, especially the mice from experimental facilities in Beijing area in China.

A broadly reactive one-step SYBR Green I real-time RT-PCR assay for rapid detection of murine norovirus

A one-step SYBR Green I real-time RT-PCR assay was developed for the detection and quantification of a broad range of murine noroviruses (MNVs). The primer design was based on the multiple sequence alignments of 101 sequences of the open reading frame (ORF)1−ORF2 junction of MNV. The broad reactivity and quantitative capacity of the assay were validated using 7 MNV plasmids. The assay was completed within 1 h, and the reliable detection limit was 10 copies of MNV plasmid or 0.063 median tissue culture infective doses per milliliter of RAW264 cell culture-propagated viruses. The diagnostic performance of the assay was evaluated using 158 mouse fecal samples, 91 of which were confirmed to be positive. The melting curve analysis demonstrated the diversity of MNV in the samples. This is the first report of a broadly reactive one-step SYBR Green I real-time RT-PCR assay for detecting of MNVs. The rapid and sensitive performance of this assay makes it a powerful tool for diagnostic applications.

Detection of murine norovirus by reverse transcription loop-mediated isothermal amplification

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RT-LAMP method with the potential to detect a broad range of MNV was developed.

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Sensitivity of RT-LAMP was 50-fold less than that of TaqMan RT-PCR.

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In a practical diagnostic test, RT-LAMP exhibited 96.4% and 94.7% sensitivity compared with TaqMan RT-PCR and nested RT-PCR.

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In a practical diagnostic test, RT-LAMP exhibited 100% specificity compared with both TaqMan RT-PCR and nested RT-PCR.

Murine norovirus (MNV) has considerable genetical and biological diversity and is recognized worldwide as the most common contaminant in laboratory mouse colonies. This study developed a reverse transcription loop-mediated isothermal amplification (RT-LAMP) method with the potential to detect a broad range of MNV. RT-LAMP, using a set of five primers containing mixed bases, obtained results under isothermal conditions at 62 °C for 90 min. Sensitivity of RT-LAMP was 50-fold less than that of two-step TaqMan real-time reverse transcription-polymerase chain reaction (TaqMan RT-PCR). Diagnostic performance of RT-LAMP on RNA extracted from mouse fecal specimens was compared with TaqMan RT-PCR and nested RT-PCR. MNV was detected in 54 of 120 mouse fecal specimens by RT-LAMP, and RT-LAMP had an estimated sensitivity and specificity of 96.4% and 100% compared with TaqMan RT-PCR, and 94.7% and 100% compared with nested RT-PCR. RT-LAMP, which does not require expensive instruments, might be useful for the screening of mice actively or persistently infected with MNV.