In vitro cell culture infectivity assay for human noroviruses

Murine norovirus-1 entry into permissive macrophages and dendritic cells is pH-independent

Murine norovirus (MNV) is a recently discovered mouse pathogen. Unlike the fastidious human noroviruses that cause the overwhelming majority of non-bacterial gastroenteritis worldwide, MNV readily infects cells in culture. Its replication in primary murine macrophages and dendritic cells and their derived cell lines allows the study of norovirus cell entry for the first time. In this study we determined the role of pH during MNV-1 infection since the low pH environment of endosomes often triggers uncoating of viruses. We demonstrated that MNV-1 viral titers by plaque assay and expression of the non-structural protein VPg by immunofluorescence were not affected by pH in cultured and primary macrophages and dendritic cells in the presence of two known endosome acidification inhibitors, bafilomycin A1 and chloroquine. These data indicate that MNV-1 enters permissive cells in a pH-independent manner.

Evaluation of murine norovirus as a surrogate for human norovirus and hepatitis A virus in heat inactivation studies

Aims:  To determine the suitability of murine norovirus (MNV) as a surrogate for human norovirus (HuNoV) in heat inactivation studies.

Methods and Results:  MNV, hepatitis A virus (HAV) and HuNoV genogroup I and II (GI and GII) specific real‐time quantitative reverse transcription (qRT)‐PCR assays were used to determine the effects of heat exposure (63 and 72°C) for up to 10 min in water and milk. Using culture assays, MNV and HAV showed similar reductions in infectivity over time. Both HuNoV GI and GII showed lower log reductions in qRT‐PCR titre following heat exposure than either MNV or HAV. No significant protective effect of milk was observed for any virus.

Conclusions:  MNV is as suitable a surrogate for HuNoV as HAV. In heat inactivation studies at 63 and 72°C, qRT‐PCR results indicate that HuNoV is less susceptible to heat than either HAV or MNV and so neither virus may be an appropriate surrogate for HuNoV.

Significance and Impact of the Study:  Caution should be used when extrapolating surrogate virus data for HuNoV. Although not conclusive, our results suggest that HuNoV may be more resistant to heat than either HAV or MNV.

Ganglioside-linked terminal sialic acid moieties on murine macrophages function as attachment receptors for murine noroviruses

Noroviruses are the major cause of nonbacterial gastroenteritis in humans. However, little is known regarding the norovirus life cycle, including cell binding and entry. In contrast to human noroviruses, the recently discovered murine norovirus 1 (MNV-1) readily infects murine macrophages and dendritic cells in culture. Many viruses, including the related feline calicivirus, use terminal sialic acids (SA) as receptors for infection. Therefore, we tested whether SA moieties play a role during MNV-1 infection of murine macrophages. Competition with SA-binding lectins and neuraminidase treatment led to a reduction in MNV-1 binding and infection in cultured and primary murine macrophages, suggesting a role for SA during the initial steps of the MNV-1 life cycle. Because SA moieties can be attached to glycolipids (i.e., gangliosides), we next determined whether MNV-1 uses gangliosides during infection. The gangliosides GD1a, GM1, and asialo-GM1 (GA1) are natural components of murine macrophages. MNV-1 bound to ganglioside GD1a, which is characterized by an SA on the terminal galactose, but not to GM1 or asialo-GM1 in an enzyme-linked immunosorbent assay. The depletion of gangliosides using an inhibitor of glycosylceramide synthase (d-threo-P4) led to a reduction of MNV-1 binding and infection in cultured and primary murine macrophages. This defect was specifically rescued by the addition of GD1a. A similar phenotype was observed for MNV field strains WU11 (GV/WU11/2005/USA) and S99 (GV/Berlin/2006/DE). In conclusion, our data indicate that MNV can use terminal SA on gangliosides as attachment receptors during binding to murine macrophages.

Real-time molecular methods to detect infectious viruses

Waterborne transmitted viruses pose a public health threat due to their stability in aquatic environment and the easy transmission with high morbidity rates at low infectious doses. Two major challenge of virus analysis include a lack of adequate information in infectivity and the inability to cultivate certain epidemiologically important viruses in vitro. The use of fluorescent probes in conjunction with fluorescence microscopy allows us to reveal dynamic interactions of the viruses with different cellular structures in living cells that are impossible to detect by immunological or PCR-based experiments. Real-time viral detection in vivo provides sufficient information regarding multiple steps in infection process at molecular level, which will be valuable for the prevention and control of viral infection.

Laboratory efforts to eliminate contamination problems in the real-time RT-PCR detection of noroviruses

In the current study, laboratory efforts to prevent the presence of positive NTCs (no template controls) during the optimization of a quantitative real-time reverse transcriptase PCR assay for detection of Noroviruses (NoVs) are described. Two DNA types (single-stranded (ss)DNA fragments and plasmid DNA) were used to generate a real-time PCR standard and a high frequency of positive NTCs was noticed in the case of ssDNA fragments. To investigate our suspicion of well-to-well migration of DNA during real-time PCR runs as possible cause of the positive NTCs, an "evaporation-experiment" was set up in which the evaporation of water and the possible co-evaporation of DNA were measured as a function of the DNA type (ssDNA-fragments, plasmid DNA and genomic DNA), the reaction plate seal type (adhesive film or 8-cap strips) and the use of 7 microl of mineral oil as cover layer. Results of this experiment indicated that evaporation of water occurred during real-time PCR runs regardless of the DNA type, the seal type and whether or not 7 microl of mineral oil was used as cover layer. Data from this experiment also suggested co-evaporation of DNA, with an apparent negative correlation between the size of the DNA type and the extent of this co-evaporation. The use of 7 microl of mineral oil as cover layer seemed to prevent to some extent co-evaporation of DNA. The use of plasmids as standard combined with 7 microl of mineral oil as cover layer in the real-time PCR setup resulted in a complete absence of positive NTCs while only minor effects were noticed on the performance of the real-time PCR. In general, our results showed that the high sensitivity of an optimized real-time PCR assay should be considered as--besides a great advantage--a potential risk factor for obtaining false-positive results when using this technique.

Norwalk virus shedding after experimental human infection

Noroviruses are shed in feces up to 8 weeks after infection.

Noroviruses are the most common cause of viral gastroenteritis in the United States. To determine the magnitude and duration of virus shedding in feces, we evaluated persons who had been experimentally infected with Norwalk virus. Of 16 persons, clinical gastroenteritis (watery diarrhea and/or vomiting) developed in 11; symptomatic illness lasted 1–2 days. Virus shedding was first detected by reverse transcription–PCR (RT-PCR) 18 hours after participant inoculation and lasted a median of 28 days after inoculation (range 13–56 days). The median peak amount of virus shedding was 95 × 10⁹ (range 0.5–1,640 ×10⁹) genomic copies/g feces as measured by quantitative RT-PCR. Virus shedding was first detected by antigen ELISA ≈33 hours (median 42 hours) after inoculation and lasted 10 days (median 7 days) after inoculation. Understanding of the relevance of prolonged fecal norovirus excretion must await the development of sensitive methods to measure virus infectivity.

Self-assembly of the recombinant capsid protein of a swine norovirus into virus-like particles and evaluation of monoclonal antibodies cross-reactive with a human strain from genogroup II

Noroviruses (NoVs) are responsible for the majority of gastroenteritis outbreaks in humans. Recently, NoV strains which are genetically closely related to human genogroup II (GII) NoVs have been detected in fecal specimens from swine. These findings have raised concern about the possible role of pigs as reservoirs for NoVs that could infect humans. To better understand the epidemiology of swine NoVs in both the swine and the human populations, rapid immunoassays are needed. In this study, baculovirus recombinants were generated to express the capsid gene of a swine NoV GII genotype 11 (GII.11) strain which self-assembled into virus-like particles (VLPs). Subsequently, the purified VLPs were used to evoke monoclonal antibodies (MAbs) in mice. A panel of eight promising MAbs was obtained and evaluated for their ability to bind to heterologous VLPs, denaturated antigens, and truncated capsid proteins. The MAbs could be classified into two groups: two MAbs that recognized linear epitopes located at the amino-terminal half (shell domain) of the swine NoV GII.11 VLPs and that cross-reacted with human GII.4 NoV VLPs. The other six MAbs bound to conformational epitopes and did not cross-react with the human GII.4 VLPs. To our knowledge, this is the first report on the characterization of MAbs against swine NoVs. The swine NoV VLPs and the MAbs described here may be further used for the design of diagnostic reagents that could help increase our knowledge of the prevalence of NoV infections in pigs and the possible role of pigs as reservoirs for NoVs.

Torque teno virus: an improved indicator for viral pathogens in drinking waters

BACKGROUND

Currently applied indicator organism systems, such as coliforms, are not fully protective of public health from enteric viruses in water sources. Waterborne disease outbreaks have occurred in systems that tested negative for coliforms, and positive coliform results do not necessarily correlate with viral risk. It is widely recognized that bacterial indicators do not co-occur exclusively with infectious viruses, nor do they respond in the same manner to environmental or engineered stressors. Thus, a more appropriate indicator of health risks from infectious enteric viruses is needed.

PRESENTATION OF THE HYPOTHESIS

Torque teno virus is a small, non-enveloped DNA virus that likely exhibits similar transport characteristics to pathogenic enteric viruses. Torque teno virus is unique among enteric viral pathogens in that it appears to be ubiquitous in humans, elicits seemingly innocuous infections, and does not exhibit seasonal fluctuations or epidemic spikes. Torque teno virus is transmitted primarily via the fecal-oral route and can be assayed using rapid molecular techniques. We hypothesize that Torque teno virus is a more appropriate indicator of viral pathogens in drinking waters than currently used indicator systems based solely on bacteria.

TESTING THE HYPOTHESIS

To test the hypothesis, a multi-phased research approach is needed. First, a reliable Torque teno virus assay must be developed. A rapid, sensitive, and specific PCR method using established nested primer sets would be most appropriate for routine monitoring of waters. Because PCR detects both infectious and inactivated virus, an in vitro method to assess infectivity also is needed. The density and occurrence of Torque teno virus in feces, wastewater, and source waters must be established to define spatial and temporal stability of this potential indicator. Finally, Torque teno virus behavior through drinking water treatment plants must be determined with co-assessment of traditional indicators and enteric viral pathogens to assess whether correlations exist.

IMPLICATIONS OF THE HYPOTHESIS

If substantiated, Torque teno virus could provide a completely new, reliable, and efficient indicator system for viral pathogen risk. This indicator would have broad application to drinking water utilities, watershed managers, and protection agencies and would provide a better means to assess viral risk and protect public health.

A SYBR Green RT-PCR assay in single tube to detect human and bovine noroviruses and control for inhibition

Background

Noroviruses are single-stranded RNA viruses belonging to the family Caliciviridae. They are a major cause of epidemic and sporadic gastroenteritis in humans and clinical signs and lesions of gastroenteritis were reported in bovines. Due to their genetic proximity, potential zoonotic transmission or animal reservoir can be hypothesized for noroviruses. RT-PCR has become the "gold standard" for the detection of noroviruses in faecal and environmental samples. With such samples, the control for inhibition of the reaction during amplification and detection is crucial to avoid false negative results, which might otherwise not be detected. The aim of the reported method is to detect, with a SYBR Green technology, a broad range of noroviruses with a control for inhibition.

Results

A SYBR Green real-time RT-PCR assay was developed making use of a foreign internal RNA control added in the same tube. This assay is able to detect human and bovine noroviruses belonging to genogroups I, II and III and to distinguish between norovirus and internal control amplicons using melting curve analysis. A 10-fold dilution of samples appears to be the method of choice to remove inhibition. This assay was validated with human and bovine stool samples previously tested for norovirus by conventional RT-PCR.

Conclusion

This SYBR Green real-time RT-PCR assay allows the detection of the most important human and bovine noroviruses in the same assay, and avoids false negative results making use of an internal control. Melting curves allow the discrimination between the internal control and norovirus amplicons. It gives preliminary information about the species of origin. The sensitivity of the developed assay is higher than conventional RT-PCR and a 10-fold dilution of samples showed a better efficiency and reproducibility to remove RT-PCR inhibition than addition of bovine serum albumin.

Aqueous matrix compositions and pH influence feline calicivirus inactivation by high pressure processing

The individual effects of pH (pH 3 to 8), NaCl (0 to 21%), sucrose (0 to 70%), and whey protein (0 to 2%) on pressure resistance of feline calicivirus (FCV) in Dulbecco's modified Eagle medium with 10% fetal bovine serum were determined. At pH 3 through 8, the virus was more resistant to pressure at a pH of < or = 5.2. For FCV samples with sucrose (up to 40%) or NaCl (up to 12%), the amount of FCV inactivated by pressure was inversely proportional to the sucrose or NaCl concentration. For example, a treatment of 250 MPa at 20 degrees C for 5 min reduced the FCV titer by 5.1 log PFU/ml without added sucrose and by 0.9 log PFU/ml with 40% sucrose. Reduced pressure sensitivity with increasing NaCl and sucrose concentrations was not a simple function of water activity. Different PFU reductions were observed for NaCl and sucrose samples with equivalent water activity. When protein at concentrations up to 2% did not provide a protective effect. The combined effect of NaCl and sucrose at 4 and 20 degrees C on pressure resistance of FCV also was examined. When both NaCl and sucrose were added to the FCV stock, they had an additive effect on increasing the pressure resistance of FCV. The individual (6% NaCl or 20% sucrose) and combined (6% NaCl plus 20% sucrose) resistance effects did not abrogate enhanced inactivation for pressure treatments at 4 degrees C compared with those at 20 degrees C. Aqueous matrix compositions, in particular different concentrations of NaCl and sucrose or different pH values, can substantially alter the efficiency of virus inactivation by high pressure processing.

Survival and transfer of murine norovirus 1, a surrogate for human noroviruses, during the production process of deep-frozen onions and spinach

The reduction of murine norovirus 1 (MNV-1) on onions and spinach by washing was investigated as was the risk of contamination during the washing procedure. To decontaminate wash water, the industrial sanitizer peracetic acid (PAA) was added to the water, and the survival of MNV-1 was determined. In contrast to onions, spinach undergoes a heat treatment before freezing. Therefore, the resistance of MNV-1 to blanching of spinach was examined. MNV-1 genomic copies were detected with a real-time reverse transcription PCR assay in PAA-treated water and blanched spinach, and PFUs (representing infectious MNV-1 units) were determined with a plaque assay. A < or = 1-log reduction in MNV-1 PFUs was achieved by washing onion bulbs and spinach leaves. More than 3 log PFU of MNV-1 was transmitted to onion bulbs and spinach leaves when these vegetables were washed in water containing approximately 5 log PFU/ml. No decline of MNV-1 occurred in used industrial spinach wash water after 6 days at room temperature. A concentration of 20 ppm of PAA in demineralized water (pH 4.13) and in potable water (pH 7.70) resulted in reductions of 2.88 +/- 0.25 and 2.41 +/- 0.18 log PFU, respectively, after 5 min of exposure, but no decrease in number of genomic copies was observed. No reduction of MNV-1 PFUs was observed on frozen onions or spinach during storage for 6 months. Blanching spinach (80 degrees C for 1 min) resulted in at least 2.44-log reductions of infectious MNV-1, but many genomic copies were still present.

Leader of the capsid protein in feline calicivirus promotes replication of Norwalk virus in cell culture

The inability to grow human noroviruses in cell culture has greatly impeded the studies of their pathogenesis and immunity. Vesiviruses, in the family Caliciviridae, grow efficiently in cell culture and encode a unique protein in the subgenomic region designated as leader of the capsid protein (LC). We hypothesized that LC might be associated with the efficient replication of vesiviruses in cell culture and promote the replication of human norovirus in cells. To test this hypothesis, a recombinant plasmid was engineered in which the LC region of feline calicivirus (FCV) was placed under the control of the cytomegalovirus promoter (pCI-LC) so that the LC protein could be provided in trans to replicating calicivirus genomes bearing a reporter gene. We constructed pNV-GFP, a recombinant plasmid containing a full-length NV genome with a green fluorescent protein (GFP) in the place of VP1. The transfection of pNV-GFP in MVA-T7-infected cells produced few GFP-positive cells detected by fluorescence microscopy and flow cytometry analysis. When pNV-GFP was cotransfected with pCI-LC in MVA-T7-infected cells, we observed an increase in the number of GFP-positive cells (ca. 3% of the whole-cell population). Using this cotransfection method with mutagenesis study, we identified potential cis-acting elements at the start of subgenomic RNA and the 3' end of NV genome for the virus replication. We conclude that LC may be a viral factor which promotes the replication of NV in cells, which could provide a clue to growing the fastidious human noroviruses in cell culture.

Closing the phenotypic gap between transformed neuronal cell lines in culture and untransformed neurons

Studies of neuronal dysfunction in the central nervous system (CNS) are frequently limited by the failure of primary neurons to propagate in vitro. Neuronal cell lines can be substituted for primary cells but they often misrepresent normal conditions. We hypothesized that a three-dimensional (3D) cell culture system would drive the phenotype of transformed neurons closer to that of untransformed cells, as has been demonstrated in non-neuronal cell lines. In our studies comparing 3D versus two-dimensional (2D) culture, neuronal SH-SY5Y (SY) cells underwent distinct morphological changes combined with a significant drop in their rate of cell division. Expression of the proto-oncogene N-myc and the RNA-binding protein HuD was decreased in 3D culture as compared to standard 2D conditions. We observed a decline in the anti-apoptotic protein Bcl-2 in 3D culture, coupled with increased expression of the pro-apoptotic proteins Bax and Bak. Moreover, thapsigargin (TG)-induced apoptosis was enhanced in the 3D cells. Microarray analysis demonstrated significantly differing mRNA levels for over 700 genes in the cells of the two culture types, and indicated that alterations in the G1/S cell-cycle progression contributed to the diminished doubling rate in the 3D-cultured SY cells. These results demonstrate that a 3D culture approach narrows the phenotypic gap between neuronal cell lines and primary neurons. The resulting cells may readily be used for in vitro research of neuronal pathogenesis.

Development of a DNA microarray for the simultaneous detection and genotyping of noroviruses

Current methods for detecting and genotyping noroviruses focus on the use of reverse transcriptase (RT)-mediated PCR. A major drawback of this approach is that short target RT-PCR products do not always encompass sequences that can be compared among research laboratories, resulting in difficulties for molecular epidemiology. We describe the use of a microarray-based system for simultaneous detection and molecular characterization of noroviruses. The protocol generates a 917-bp RT-PCR product that encompasses two major regions currently used for detection and analysis of norovirus genomes. The PCR products are then hybridized to an oligonucleotide array (NoroChip) based on 50-mer features, which allows for both confirmation of reaction specificity and molecular characterization of the amplified genome. Parallel sequence analyses of amplicons revealed that our microarray data were robust in separating genogroups I and II, and further subtyping to the cluster level was possible. This approach, combining detection and characterization, overcomes the need for expensive and time-consuming sequence analysis of amplified genome targets for molecular epidemiology.

Reducing absenteeism from gastrointestinal and respiratory illness in elementary school students: a randomized, controlled trial of an infection-control intervention

BACKGROUND

Students often miss school because of gastrointestinal and respiratory illnesses. We assessed the effectiveness of a multifactorial intervention, including alcohol-based hand-sanitizer and surface disinfection, in reducing absenteeism caused by gastrointestinal and respiratory illnesses in elementary school students.

METHODS

We performed a school-based cluster-randomized, controlled trial at a single elementary school. Eligible students in third to fifth grade were enrolled. Intervention classrooms received alcohol-based hand sanitizer to use at school and quaternary ammonium wipes to disinfect classroom surfaces daily for 8 weeks; control classrooms followed usual hand-washing and cleaning practices. Parents completed a preintervention demographic survey. Absences were recorded along with the reason for absence. Swabs of environmental surfaces were evaluated by bacterial culture and polymerase chain reaction for norovirus, respiratory syncytial virus, influenza, and parainfluenza 3. The primary outcomes were rates of absenteeism caused by gastrointestinal or respiratory illness. Days absent were modeled as correlated Poisson variables and compared between groups by using generalized estimating equations. Analyses were adjusted for family size, race, health status, and home sanitizer use. We also compared the presence of viruses and the total bacterial colony counts on several classroom surfaces.

RESULTS

A total of 285 students were randomly assigned; baseline demographics were similar in the 2 groups. The adjusted absenteeism rate for gastrointestinal illness was significantly lower in the intervention-group subjects compared with control subjects. The adjusted absenteeism rate for respiratory illness was not significantly different between groups. Norovirus was the only virus detected and was found less frequently on surfaces in intervention classrooms compared with control classrooms (9% vs 29%).

CONCLUSIONS

A multifactorial intervention including hand sanitizer and surface disinfection reduced absenteeism caused by gastrointestinal illness in elementary school students. Norovirus was found less often on classroom surfaces in the intervention group. Schools should consider adopting these practices to reduce days lost to common illnesses.

New tools for the study and direct surveillance of viral pathogens in water

Half a century ago scientists attempted the detection of poliovirus in water. Since then other enteric viruses responsible for gastroenteritis and hepatitis have replaced enteroviruses as the main target for detection. However, most viral outbreaks are restricted to norovirus and hepatitis A virus, making them the main targets in water. The inclusion of virus analysis in regulatory standards for viruses in water samples must overcome several shortcomings such as the technical difficulties and high costs of virus monitoring, the lack of harmonised and standardised assays and the challenge posed by the ever-changing nature of viruses. However, new tools are nowadays available for the study and direct surveillance of viral pathogens in water that may contribute to fulfil these requirements.

Evaluation of the persistence of infectious human noroviruses on food surfaces by using real-time nucleic acid sequence-based amplification

Noroviruses (NoV) are the major cause of nonbacterial gastroenteritis. However, there is no published study to ascertain their survival on foodstuffs which are directly related to human health risk. In the present study, we developed a rapid, simple, and sensitive real-time nucleic acid sequence-based amplification (NASBA) combined with an enzymatic treatment for distinguishing infectious from noninfectious human NoV. The developed method was validated using spiked ready-to-eat food samples. When feline calicivirus (FCV) was used as a NoV surrogate in the preliminary assays, it appeared more sensitive to heat inactivation and enzymatic pretreatment than the human NoV. This suggests that FCV may not be an ideal model for studying NoV. Our results reveal clearly that the developed enzymatic pretreatment/real-time NASBA combination successfully distinguished the infectious from heat-inactivated NoV. Moreover, we demonstrate that NoV survived for at least 10 days on refrigerated ready-to-eat foods, such as lettuce and turkey. However, the survival rate was higher on turkey than on lettuce, probably because of their different surface natures. The approach developed in this study may be suitable for more in-depth studies of the persistence and inactivation of human NoV and may be applied to other nonculturable RNA viruses. Moreover, the evaluation of infectious NoV survival provided valuable information concerning its persistence on ready-to-eat food.

UV light inactivation of hepatitis A virus, Aichi virus, and feline calicivirus on strawberries, green onions, and lettuce

A majority of illnesses caused by foodborne viruses are associated with fresh produce. Fruits and vegetables may be considered high-risk foods, as they are often consumed raw without a specific inactivation step. Therefore, there is a need to evaluate nonthermal treatments for the inactivation of foodborne pathogens. This study investigates the UV inactivation of three viruses: feline calicivirus (a surrogate for norovirus), and two picornaviruses, hepatitis A virus and Aichi virus. Three produce types were selected for their different surface topographies and association with outbreaks. Green onions, lettuce, and strawberries were individually spot inoculated with 10(7) to 10(9) 50% tissue culture infective doses (TCID50) of each virus per ml and exposed to UV light at various doses (< or = 240 mW s/cm2), and viruses were eluted using an optimized recovery strategy. Virus infection was quantified by TCID50 in mammalian cell culture and compared with untreated recovered virus. UV light applied to contaminated lettuce resulted in inactivation of 4.5 to 4.6 log TCID50/ml; for contaminated green onions, inactivation ranged from 2.5 to 5.6 log TCID50/ml; and for contaminated strawberries, inactivation ranged from 1.9 to 2.6 log TCID50/ml for the three viruses tested. UV light inactivation on the surface of lettuce is more effective than inactivation on the other two produce items. Consistently, the lowest results were observed in the inactivation of viruses on strawberries. No significant differences (P > 0.05) for virus inactivation were observed among the three doses applied (40, 120, and 240 mW s/cm2) on the produce, with the exception of hepatitis A virus and Aichi virus inactivation on green onions, where inactivation continued at 120 mW s/cm2 (P < 0.05).

Bioinformatic and functional analysis of RNA secondary structure elements among different genera of human and animal caliciviruses

The mechanism and role of RNA structure elements in the replication and translation of Caliciviridae remains poorly understood. Several algorithmically independent methods were used to predict secondary structures within the Norovirus, Sapovirus, Vesivirus and Lagovirus genera. All showed profound suppression of synonymous site variability (SSSV) at genomic 5' ends and the start of the sub-genomic (sg) transcript, consistent with evolutionary constraints from underlying RNA structure. A newly developed thermodynamic scanning method predicted RNA folding mapping precisely to regions of SSSV and at the genomic 3' end. These regions contained several evolutionarily conserved RNA secondary structures, of variable size and positions. However, all caliciviruses contained 3' terminal hairpins, and stem-loops in the anti-genomic strand invariably six bases upstream of the sg transcript, indicating putative roles as sg promoters. Using the murine norovirus (MNV) reverse-genetics system, disruption of 5' end stem-loops produced approximately 15- to 20-fold infectivity reductions, while disruption of the RNA structure in the sg promoter region and at the 3' end entirely destroyed replication ability. Restoration of infectivity by repair mutations in the sg promoter region confirmed a functional role for the RNA secondary structure, not the sequence. This study provides comprehensive bioinformatic resources for future functional studies of MNV and other caliciviruses.

In-vivo efficacy of hand sanitisers against feline calicivirus: a surrogate for norovirus

Hand disinfection is considered important in preventing the transmission of viruses, including norovirus. We investigated the virucidal efficacy of nine hand sanitisers (four alcohol-based sanitisers, three non-alcoholic sanitisers and two triclosan-containing antimicrobial liquid soaps) against feline calicivirus, a surrogate for norovirus, on artificially contaminated fingertips for 30 s and 2 min contact periods. Among alcohol-based sanitisers, a product containing 99.5% ethanol was more effective than those containing 62% ethanol, 70% isopropanol or 91% isopropanol. A log(10) virus reduction factor of 1.00-1.30 was achieved with 99.5% ethanol but those containing a lower alcohol concentration only achieved a log(10) reduction factor of <or=0.67. Antiseptics containing 10% povidone-iodine (equivalent to 1% available iodine) reduced virus titre by a log(10) reduction factor of 2.67 within 30s contact time. This viral reduction rate was higher than that achieved with any of the alcohol-based sanitisers, non-alcoholic sanitisers or antimicrobial soaps. The two antimicrobial soaps tested showed minimal virus reduction (a log(10) reduction factor of 0.17-0.50), which is similar to that obtained by washing hands without any soap (a log(10) reduction factor of 0.33-0.42). These results indicate that triclosan-containing antimicrobial soaps or alcohol-based hand rubs may be inadequate for preventing norovirus transmission. Further research on alternative hand sanitisers should continue for effective control of norovirus infections.

Immunology of Norovirus Infection

Noroviruses are the leading cause of epidemic non-bacterial gastroenteritis worldwide. Despite their discovery over three decades ago, little is known about the host immune response to norovirus infection. The purpose of this chapter is to review the field of norovirus immunology and discuss the contributions of outbreak investigations, human and animal challenge studies and population-based studies. This chapter will survey both humoral and cellular immunity as well as recent advances in norovirus vaccine development.

Enteric Viruses

Many viruses use the enteric tract as a route of entry to the human, animal, or avian host. The onset of acute enteritis is associated with infection by viruses that replicate at or near the site of entry into the intestinal mucosa, including caliciviruses, rotaviruses, adenoviruses, astroviruses, and coronaviruses. These ‘enteric’ viruses occur globally and share similar features. Most are RNA viruses that replicate in the cytoplasm of mature absorptive epithelial cells lining the villi of the small intestine, leading to inflammation and villus atrophy. Vomiting and diarrhea can result in dehydration and death if untreated. Despite abundant growth in vivo, they initially proved difficult or impossible to grow in vitro. Most are genetically diverse, species specific, highly infectious within species and transmitted by the fecal–oral route. Severe symptoms are most commonly associated with primary infections of young animals, and are followed by short-lived immunity. Reinfections are common throughout life, but are often only mildly symptomatic. Safe and effective vaccines have been developed to prevent severe rotavirus disease in young children. In addition to these enterotropic viruses, enteric disease can also result from spread to the intestine of HIV or cytomegaloviruses during the later stages of systemic disease in immunocompromised hosts.

The application of low shear modeled microgravity to 3-D cell biology and tissue engineering

The practice of cell culture has been virtually unchanged for 100 years. Until recently, life scientists have had to content themselves with two-dimensional cell culture technology. Clearly, living creatures are not constructed in two dimensions and thus it has become widely recognized that in vitro culture systems must become three dimensional to correctly model in vivo biology. Attempts to modify conventional 2-D culture technology to accommodate 3-D cell growth such as embedding cells in extracellular matrix have demonstrated the superiority of concept. Nevertheless, there are serious drawbacks to this approach including limited mass transport and lack of scalability. Recently, a new cell culture technology developed at NASA to study the effects of microgravity on cells has emerged to solve many of the problems of 3-D cell culture. The technology, the Rotating Wall Vessel (RWV) is a single axis clinostat consisting of a fluid-filled, cylindrical, horizontally rotating culture vessel. Cells placed in this environment are suspended by the resolution of the gravitational, centrifugal and Coriolis forces with extremely low mechanical shear. These conditions, which have been called "low shear modeled microgravity", enable cells to assemble into tissue-like aggregates with high mass transport of nutrients, oxygen and wastes. Examples of the use of the RWV for basic cell biology research and tissue engineering applications are discussed.

Pathogenesis and immune responses in gnotobiotic calves after infection with the genogroup II.4-HS66 strain of human norovirus

We previously characterized the pathogenesis of two host-specific bovine enteric caliciviruses (BEC), the GIII.2 norovirus (NoV) strain CV186-OH and the phylogenetically unassigned NB strain, in gnotobiotic (Gn) calves. In this study we evaluated the Gn calf as an alternative animal model to study the pathogenesis and host immune responses to the human norovirus (HuNoV) strain GII.4-HS66. The HuNoV HS66 strain caused diarrhea (five/five calves) and intestinal lesions (one/two calves tested) in the proximal small intestine (duodenum and jejunum) of Gn calves, with lesions similar to, but less severe than, those described for the Newbury agent 2 (NA-2) and NB BEC. Viral capsid antigen was also detected in the jejunum of the proximal small intestine of one of two calves tested by immunohistochemistry. All inoculated calves shed virus in feces (five/five calves), and one/five had viremia. Antibodies and cytokine (proinflammatory, tumor necrosis factor alpha [TNF-alpha]; Th1, interleukin-12 [IL-12] and gamma interferon [IFN-gamma]; Th2, IL-4; Th2/T-regulatory, IL-10) profiles were determined in serum, feces, and intestinal contents (IC) of the HuNoV-HS66-inoculated calves (n = 5) and controls (n = 4) by enzyme-linked immunosorbent assay in the acute (postinoculation day 3 [PID 3]) and convalescent (PID 28) stages of infection. The HuNoV-HS66-specific antibody and cytokine-secreting cells (CSCs) were quantitated by ELISPOT in mononuclear cells of local and systemic tissues at PID 28. Sixty-seven percent of the HuNoV-HS66-inoculated calves seroconverted, and 100% coproconverted with immunoglobulin A (IgA) and/or IgG antibodies to HuNoV-HS66, at low titers. The highest numbers of antibody-secreting cells (ASC), both IgA and IgG, were detected locally in intestine, but systemic IgA and IgG ASC responses also occurred in the HuNoV-HS66-inoculated calves. In serum, HuNoV-HS66 induced higher peaks of TNF-alpha and IFN-gamma at PIDs 2, 7, and 10; of IL-4 and IL-10 at PID 4; and of IL-12 at PIDs 7 and 10, compared to controls. In feces, cytokines increased earlier (PID 1) than in serum and TNF-alpha and IL-10 were elevated acutely in the IC of the HS66-inoculated calves. Compared to controls, at PID 28 higher numbers of IFN-gamma and TNF-alpha CSCs were detected in mesenteric lymph nodes (MLN) or spleen and Th2 (IL-4) CSCs were elevated in intestine; IL-10 CSCs were highest in spleen. Our study provides new data confirming HuNoV-HS66 replication and enteropathogenicity in Gn calves and reveals important and comprehensive aspects of the host's local (intestine and MLN) and systemic (spleen and blood) immune responses to HuNoV-HS66.

Detection of murine norovirus 1 by using plaque assay, transfection assay, and real-time reverse transcription-PCR before and after heat exposure

The correlation between the detection of murine norovirus 1 RNA by real-time reverse transcription-PCR and the infectivity by plaque assay before and after heat exposure (80 degrees C) was examined. No correlation was found in the current study. Moreover, heat inactivation had a much stronger detrimental effect on virus infectivity than on the integrity of the viral genome.

Norwalk virus RNA is infectious in mammalian cells

Human noroviruses are positive-sense RNA viruses and are the leading cause of epidemic acute viral gastroenteritis in developed countries. The absence of an in vitro cell culture model for human norovirus infection has limited the development of effective antivirals and vaccines. Human histo-blood group antigens have been regarded as receptors for norovirus infection, and expression of the alpha(1,2) fucosyltransferase gene (FUT2) responsible for the secretor phenotype is required for susceptibility to Norwalk virus (NV) infection. We report for the first time that transfection of NV RNA, isolated from stool samples from human volunteers, into human hepatoma Huh-7 cells leads to viral replication, with expression of viral antigens, RNA replication, and release of viral particles into the medium. Prior treatment of the RNA with proteinase K completely abolishes RNA infectivity, suggesting a key role of an RNA-protein complex. Although overexpression of the human FUT2 gene enhances virus binding to cells, it is not sufficient to allow a complete viral infection, and viral spread from NV-transfected cells to naïve cells does not occur. Finally, no differences in NV RNA replication are observed between Huh-7 and Huh-7.5.1 cells, which contain an inactivating mutation in retinoic acid-inducible gene I (RIG-I), suggesting that the RIG-I pathway does not play a role in limiting NV replication. Our results strongly suggest that the block(s) to NV replication in vitro is at the stage of receptor and/or coreceptor binding and/or uncoating, either because cells lack some specific factor or activation of cellular antiviral responses independent of RIG-I inhibits virus replication.

Comparison of the sensitivities of noroviruses and feline calicivirus to chemical disinfection under field-like conditions

Noroviruses (NV), in the family Caliciviridae, are an important cause of gastroenteritis in humans worldwide. Measures for prevention and control of NV dissemination are therefore necessary to ensure public safety. The abilities of an organic acid (Venno Vet 1 Super), an aldehyde (Venno FF Super), a halogen compound (sodium hypochlorite solution), and a peroxide (Oxystrong FG) to inactivate feline calicivirus (FCV), a cultivable virus surrogate for NV, were studied. Molecular protocols were then used for the comparative evaluation of disinfectant efficacies against NV and FCV, which were tested by reproducing NV field conditions, using human fecal material as a protein load. Generally, disinfectant efficacy was strongly reduced by the organic impurities (feces) used during tests. All disinfectants, except the aldehyde, were effective on FCV, as measured by cell culture and reverse transcription-PCR (RT-PCR), with inactivation levels of >or=99.9%. The glutaraldehyde-based compound failed to adequately inactivate FCV according to RT-PCR results, although the infectivity in cell culture was completely abolished. Similar inactivation levels were achieved with NV, but generally NV appeared more resistant than FCV, and consequently, the suitability of FCV as a model for NV should be considered with caution. In conclusion, according to RT-PCR results, 5% Venno Vet 1 Super, 1% Oxystrong FG, and not less than 2% Venno FF Super, with a contact time of 1 h, and 1% sodium hypochlorite, with 6,000 ppm of free chlorine and a contact time of 15 min, are required for safe disinfection when a calicivirus-related outbreak is suspected.

Sensitive multiplex real-time reverse transcription-PCR assay for the detection of human and animal noroviruses in clinical and environmental samples

In this study, we developed a triplex real-time reverse transcription-PCR (RT-PCR)-based method that detects and distinguishes between noroviruses belonging to genogroups I, II, and III and that targets the junction between the regions of open reading frame 1 (ORF1) and ORF2. This is the first assay to include all three genogroups and the first real-time RT-PCR-based method developed for the detection of bovine noroviruses. The assay was shown to be broadly reactive against a wide spectrum of norovirus genotypes, including GI/1 through GI/7, GII/1 through GII/8, GII/10, GII/12, and GII/17, in different matrices (including fecal specimens, treated and raw sewage, source water, and treated drinking water). The assay is highly sensitive, detecting low copy numbers of plasmids that carry the target sequence. A new bovine norovirus, Bo/NLV/Norsewood/2006/NZL, was identified by this assay and was further genetically characterized. The results implicate a broad range of possible applications, including clinical diagnostics, tracing of fecal contaminants, and due to its sensitivity and broad reactivity, environmental studies.