Evaluation of Assays to Quantify Infectious Human Norovirus for Heat and High-Pressure Inactivation Studies Using Tulane Virus

Evaluating the Potential of Ozone Microbubbles for Inactivation of Tulane Virus, a Human Norovirus Surrogate

This study investigated the efficacy of low-dose ozone microbubble solution and conventional aqueous ozone as inactivation agents against Tulane virus samples in water over a short period of time. Noroviruses are the primary cause of foodborne illnesses in the US, and the development of effective inactivation agents is crucial. Ozone has a high oxidizing ability and naturally decomposes to oxygen, but it has limitations due to its low dissolution rate, solubility, and stability. Ozone microbubbles have been promising in enhancing inactivation, but little research has been done on their efficacy against noroviruses. The study examined the influence of the dissolved ozone concentration, inactivation duration, and presence of organic matter during inactivation. The results showed that ozone microbubbles had a longer half-life (14 ± 0.81 min) than aqueous ozone (3 ± 0.35 min). After 2, 10, and 20 min postgeneration, the ozone concentration of microbubbles naturally decreased from 4 ppm to 3.2 ± 0.2, 2.26 ± 0.19, and 1.49 ± 0.23 ppm and resulted in 1.43 ± 0.44, 0.88 ± 0.5, and 0.68 ± 0.53 log10 viral reductions, respectively, while the ozone concentration of aqueous ozone decreased from 4 ppm to 2.52 ± 0.07, 0.43 ± 0.05, and 0.09 ± 0.01 ppm and produced 0.8 ± 0.28, 0.29 ± 0.41, and 0.16 ± 0.21 log10 reductions against Tulane virus, respectively (p = 0.0526), suggesting that structuring of ozone in the bubbles over the applied treatment conditions did not have a significant effect, though future study with continuous generation of ozone microbubbles is needed.

Sample Processing and Concentration Methods for Viruses from Foods and the Environment Prior to Detection

Viruses are the leading cause of foodborne illness globally. Concentration of viruses from samples is important for detection because viral contamination of foods often occurs at low levels. In general, virus concentration methods can be classified as either nonspecific, exploiting the relatively homogeneous physicochemical properties of the virus to separate/concentrate it from the sample matrix, or specific, relying on recognition elements such as antibodies to specifically capture and separate viruses from foods. Numerous nonspecific and specific techniques for virus concentration have been reported, each with its own advantages and limitations. Factors to consider can include reagent and equipment costs, time-to-result, ease of use, and potential to eliminate matrix-associated inhibitors. The purpose of this review is to survey the different foodborne virus concentration techniques and their efficacy in various food and environmental matrices as well as discuss some emerging techniques for purification and concentration of viral pathogens from food samples.

PMAxx-RT-qPCR to Determine Human Norovirus Inactivation Following High-Pressure Processing of Oysters

Norovirus is the leading cause of viral gastroenteritis globally. While person-to-person transmission is most commonly reported route of infection, human norovirus is frequently associated with foodborne transmission, including through consumption of contaminated bivalve molluscan shellfish. Reverse transcription (RT)-qPCR is most commonly used method for detecting human norovirus detection in foods, but does not inform on its infectivity, posing challenges for assessing intervention strategies aimed at risk elimination. In this study, RT-qPCR was used in conjunction with a derivative of the photoreactive DNA binding dye propidium monoazide (PMAxx™) (PMAxx-RT-qPCR) to evaluate the viral capsid integrity of norovirus genogroup I and II (GI and GII) in shellfish following high pressure processing (HPP). Norovirus GI.3 and GII.4 bioaccumulated oysters were subjected to HPP at pressures of 300 and 450 MPa at 15 °C, and 300, 450 and 600 MPa at 20 °C. Samples were analysed using both RT-qPCR and PMAxx-RT-qPCR. For each sample, norovirus concentration (genome copies/g digestive tissue) determined by RT-qPCR was divided by the PMAxx-RT-qPCR concentration, giving the relative non-intact (RNI) ratio. The RNI ratio values relate to the amount of non-intact (non-infectious) viruses compared to fully intact (possible infectious) viruses. Our findings revealed an increasing RNI ratio value, indicating decreasing virus integrity, with increasing pressure and decreasing pressure. At 300 MPa, for norovirus GI, the median [95% confidence interval, CI] RNI ratio values were 2.6 [1.9, 3.0] at 15 °C compared to 1.1 [0.9, 1.8] at 20 °C. At 450 MPa, the RNI ratio values were 5.5 [2.9, 7.0] at 15 °C compared to 1.3 [1.0, 1.6] at 20 °C. At 600 MPa, the RNI ratio value was 5.1 [2.9, 13.4] at 20 °C. For norovirus GII, RT-qPCR and PMAxx-RT-qPCR detections were significantly reduced at 450 and 600 MPa at both 15 °C and 20 °C, with the median [95% CI] RNI ratio value at 300 MPa being 1.1 [0.8, 1.6]. Following HPP treatment, the use of PMAxx-RT-qPCR enables the selective detection of intact and potential infectious norovirus, enhancing our understanding of the inactivation profiles and supporting the development of more effective risk assessment strategies.

Heat stability of foodborne viruses - Findings, methodological challenges and current developments

Heat treatment of food represents an important measure to prevent pathogen transmission. Thus far, evaluation of heat treatment processes is mainly based on data from bacteria. However, foodborne viruses have gained increasing attention during the last decades. Here, the published literature on heat stability and inactivation of human norovirus (NoV), hepatitis A virus (HAV) and hepatitis E virus (HEV) was reviewed. Data for surrogate viruses were not included. As stability assessment for foodborne viruses is often hampered by missing infectivity assays, an overview of applied methods is also presented. For NoV, molecular capsid integrity assays were mainly applied, but data from initial studies utilizing novel intestinal enteroid or zebrafish larvae assays are available now. However, these methods are still limited in applicability and sensitivity. For HAV, sufficient cell culture-based inactivation data are available, but almost exclusively for one single strain, thus limiting interpretation of the data for the wide range of field strains. For HEV, data are now available from studies using pig inoculation or cell culture. The results of the reviewed studies generally indicate that NoV, HAV and HEV possess a high heat stability. Heating at 70-72 °C for 2 min significantly reduces infectious titers, but often does not result in a >4 log10 decrease. However, heat stability greatly varied dependent on virus strain, matrix and heating regime. In addition, the applied method largely influenced the result, e.g. capsid integrity assays tend to result in higher measured stabilities than cell culture approaches. It can be concluded that the investigated foodborne viruses show a high heat stability, but can be inactivated by application of appropriate heating protocols. For HAV, suggestions for safe time/temperature combinations for specific foods can be derived from the published studies, with the limitation that they are mostly based on one strain only. Although significant improvement of infectivity assays for NoV and HEV have been made during the last years, further method development regarding sensitivity, robustness and broader applicability is important to generate more reliable heat inactivation data for these foodborne viruses in future.

Capsid integrity detection of pathogenic viruses in waters: Recent progress and potential future applications

Waterborne diseases caused by pathogenic human viruses are a major public health concern. To control the potential risk of viral infection through contaminated waters, a rapid, reliable tool to assess the infectivity of pathogenic viruses is required. Recently, an advanced approach (i.e., capsid integrity (RT-)qPCR) was developed to discriminate intact viruses (potentially infectious) from inactivated viruses. In this approach, samples were pretreated with capsid integrity reagents (e.g., monoazide dyes or metal compounds) before (RT -)qPCR. These reagents can only penetrate inactivated viruses with compromised capsids to bind to viral genomes and prevent their amplification, but they cannot enter viruses with intact capsids. Therefore, only viral genomes of intact viruses were amplified or detected by (RT-)qPCR after capsid integrity treatment. In this study, we reviewed recent progress in the development and application of capsid integrity (RT-)qPCR to assess the potential infectivity of viruses (including non-enveloped and enveloped viruses with different genome structures [RNA and DNA]) in water. The efficiency of capsid integrity (RT-)qPCR has been shown to depend on various factors, such as conditions of integrity reagent treatment, types of viruses, environmental matrices, and the capsid structure of viruses after disinfection treatments (e.g., UV, heat, and chlorine). For the application of capsid integrity (RT-)qPCR in real-world samples, the use of suitable virus concentration methods and process controls is important to control the efficiency of capsid integrity (RT-)qPCR. In addition, potential future applications of capsid integrity (RT-)qPCR for determining the mechanism of disinfection treatment on viral structure (e.g., capsid or genome) and a combination of capsid integrity treatment and next-generation sequencing (NGS) (capsid integrity NGS) for monitoring the community of intact pathogenic viruses in water are also discussed. This review provides essential information on the application of capsid integrity (RT-)qPCR as an efficient tool for monitoring the presence of pathogenic viruses with intact capsids in water.

Inactivation Mechanism and Efficacy of Grape Seed Extract for Human Norovirus Surrogate

Proper disinfection of harvested food and water is critical to minimize infectious disease. Grape seed extract (GSE), a commonly used health supplement, is a mixture of plant-derived polyphenols. Polyphenols possess antimicrobial and antifungal properties, but antiviral effects are not well-known. Here we show that GSE outperformed chemical disinfectants (e.g., free chlorine and peracetic acids) in inactivating Tulane virus, a human norovirus surrogate. GSE induced virus aggregation, a process that correlated with a decrease in virus titers. This aggregation and disinfection were not reversible. Molecular docking simulations indicate that polyphenols potentially formed hydrogen bonds and strong hydrophobic interactions with specific residues in viral capsid proteins. Together, these data suggest that polyphenols physically associate with viral capsid proteins to aggregate viruses as a means to inhibit virus entry into the host cell. Plant-based polyphenols like GSE are an attractive alternative to chemical disinfectants to remove infectious viruses from water or food. IMPORTANCE Human noroviruses are major food- and waterborne pathogens, causing approximately 20% of all cases of acute gastroenteritis cases in developing and developed countries. Proper sanitation or disinfection are critical strategies to minimize human norovirus-caused disease until a reliable vaccine is created. Grape seed extract (GSE) is a mixture of plant-derived polyphenols used as a health supplement. Polyphenols are known for antimicrobial, antifungal, and antibiofilm activities, but antiviral effects are not well-known. In studies presented here, plant-derived polyphenols outperformed chemical disinfectants (i.e., free chlorine and peracetic acids) in inactivating Tulane virus, a human norovirus surrogate. Based on data from molecular assays and molecular docking simulations, the current model is that the polyphenols in GSE bind to the Tulane virus capsid, an event that triggers virion aggregation. It is thought that this aggregation prevents Tulane virus from entering host cells.

Photoinactivation of bacteriophage MS2, Tulane virus and Vibrio parahaemolyticus in oysters by microencapsulated rose bengal

Objectives

Bivalve molluscan shellfish such as oysters are important vectors for the transmission of foodborne pathogens including both viruses and bacteria. Photoinactivation provides a cold-sterilization option against the contamination as excited photosensitizers could transfer electronic energy to oxygen molecules producing reactive oxygen species such as singlet oxygen, leading to oxidative damage and death of the pathogens. However, the efficacy of photoinactivation is very often compromised by the presence of food matrix due to the non-selective reactions of short-lived singlet oxygen with the organic matters other than the target pathogens.

Materials and Methods

In order to address this issue, we encapsulated a food grade photosensitizer rose bengal (RB) in alginate microbeads. An extra coating of chitosan effectively prevented the release of RB from the microbeads in seawater, and more importantly, enhanced the selectivity of the photoinactivation via the electrostatic interactions between cationic chitosan and anionic charge of the virus particles (bacteriophage MS2 and Tulane virus) and the gram-negative bacteria Vibrio parahaemolyticus.

Results

The treatment of oysters with microencapsulated RB resulted in significantly higher reductions of MS2 phage, Tulane virus and V. parahaemolyticus than free RB and non-RB carrying microbeads (P < 0.05) tested with both in vitro and in vivo experimental set-ups. (4)

Conclusions

This study demonstrated a new strategy in delivering comprehensively formulated biochemical sanitizers in bivalve shellfish through their natural filter feeding activity and thereby enhancing the mitigation efficiency of foodborne pathogen contamination.

Inactivation of Murine Norovirus Suspended in Organic Matter Simulating Actual Conditions of Viral Contamination

Foodborne viral illnesses are frequent worldwide and costly for the society. Human norovirus is one of the most common causal agents. Although some norovirus genotypes can now be cultured, surrogates are still used for inactivation studies. The aim of this study was to evaluate the effects of different organic loads individually (artificial feces, real fecal matter, ASTM tripartite organic load, fetal bovine serum) on the efficacy of three highly used sanitization treatments (thermal inactivation, peracetic acid and sodium hypochlorite treatment) using murine norovirus 3 in solutions and surfaces. Based on plaque-forming units, we show that organic matter protects murine norovirus 3 against thermal inactivation (viral reduction of ~ 1 log compared to 2.67 with PBS). However, there was a low-level but significant protection against peracetic acid (viral reduction of ~ 2 log compared to 2.85 with PBS) and none in the presence of sodium hypochlorite. Our study showed that the tested organic matters do not behave similarly depending on the treatments, especially with heat treatments, which showed a higher protection. Furthermore, Feclone ™ artificial feces mimicked some aspect of real fecal matter and may be used instead. Our results will be helpful to researchers undertaking viral inactivation studies in which an organic matrix is used to simulate actual conditions of human norovirus environment.

The globally re-emerging norovirus GII.2 manifests higher heat resistance than norovirus GII.4 and Tulane virus

AIMS

To compare the heat stability of two globally prevalent human norovirus (HuNoV) strains (GII.2[P16] and GII.4[P16]) and a commonly used HuNoV surrogate, Tulane virus (TV).

METHODS AND RESULTS

With the use of a newly developed zebrafish larvae platform, we measured the change of infectivity of HuNoV GII.2[P16] and GII.4[P16] toward mild heat treatment at 55°C for 5 min. TV was tested with the same experimental design. As a result, the virus infectivity measurement clearly indicated the higher heat resistance of HuNoV GII.2[P16] (no reduction) than GII.4[P16] (>0.8-log TCID₅₀  ml^-1 reduction) and TV (2.5-log TCID₅₀  ml^-1 reduction). Further exploration revealed higher virus structural stability of HuNoV GII.2 than GII.4 strains by the use of different clinical samples with different evaluation methods.

CONCLUSION

The inactivation data generated from the surrogate virus TV cannot be used directly to describe the inactivation of HuNoV. The phylogenetic classification of HuNoVs may correlate with the virus stability and/or circulation dynamics.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is expected to serve as an important reference when revisiting the numerous previous data evaluating HuNoV inactivation conditions in foods with the use of TV as the cultivable surrogate or with genuine HuNoV but using molecular methods. The higher resistance of NoV GII.2 strains than GII.4 strains toward inactivation treatment supplies a possible explanation for the global re-emerging of NoV GII.2 epidemic in recent years.

Generation of Nucleic Acid Aptamer Candidates against a Novel Calicivirus Protein Target

Human norovirus is the leading cause of foodborne illness globally. One of the challenges in detecting noroviruses is the identification of a completely broadly reactive ligand; however, all detection ligands generated to date target the viral capsid, the outermost of which is the most variable region of the genome. The VPg is a protein covalently linked to the viral genome that is necessary for replication but hitherto remains underexplored as a target for detection or therapeutics. The purpose of this work was to generate nucleic acid aptamers against human norovirus (Norwalk) and cultivable surrogate (Tulane) VPgs for future use in detection and therapeutics. Eight rounds of positive-SELEX and two rounds of counter-SELEX were performed. Five and eight unique aptamer sequences were identified for Norwalk and Tulane VPg, respectively, all of which were predicted to be stable (∆G < −5.0) and one of which occurred in both pools. All candidates displayed binding to both Tulane and Norwalk VPg (positive:negative > 5.0), and all but two of the candidates displayed very strong binding (positive:negative > 10.0), significantly higher than binding to the negative control protein (p < 0.05). Overall, this work reports a number of aptamer candidates found to be broadly reactive and specific for in vitro-expressed VPgs across genus that could be used for future application in detection or therapeutics. Future work characterizing binding of the aptamer candidates against native VPgs and in therapeutic applications is needed to further evaluate their application.

Preliminary Quantitative Risk Assessment of Norovirus in Shellfish in the Yellow Sea and Bohai Sea of China

Norovirus (NoV) is a main foodborne pathogen of acute gastroenteritis in the world. A preliminary quantitative risk assessment (QRA) was conducted to evaluate the health risk caused by this virus in shellfish in the Yellow Sea and Bohai Sea of China. The QRA framework was established from the process of shellfish at retail through cooking at home to consumer consumption. The prevalence and quantity of NoVs in shellfish, cooking methods, internal temperature and time of shellfish in different cooking conditions, shellfish consumption frequency, and consumption amount were analyzed in the exposure assessment. The results of exposure assessment were introduced into the beta-Poisson dose-response model, and Monte Carlo analysis was used to calculate the risk of gastroenteritis caused by shellfish consumption in the cities around the Yellow Sea and Bohai Sea of China. The results showed that the probability of illness caused by NoVs due to shellfish consumption per year (P_ill,yr) was 1.86 × 10^-5. It was estimated that the annual number of patients with gastroenteritis per 1,000,000 general population (N_exp,mil) was 0.10, 1.23, 16.90, and 0.38 for population aged 0-4, 5-18, 19-64, and >65 years, respectively. This assessment provides valuable information such as the probability of illness associated with the consumption of shellfish and it also provides a reference for further in-depth QRA of NoVs in shellfish or other foods.

Contamination, bioaccumulation mechanism, detection, and control of human norovirus in bivalve shellfish: A review

Human norovirus (HuNoV) is a major foodborne pathogen that causes acute viral gastroenteritis, and bivalve shellfish are one of the main carriers of HuNoV transmission. A comprehensive understanding of bivalve shellfish-related HuNoV outbreaks focusing on contamination factors, bioaccumulation mechanisms, and pre- and post-harvest interventions is essential for the development of effective strategies to prevent contamination of shellfish. This review comprehensively surveys the current knowledge on global contamination and non-thermal treatment of HuNoV in bivalve shellfish. HuNoV contamination in bivalve shellfish is significantly related to the season and water. While evaluating the water quality of shellfish-inhabited waters is a key intervention, the development of non-heat treatment technology to effectively inactivate the HuNoV in bivalve shellfish while maintaining the flavor and nutrition of the shellfish is also an important direction for further research. Additionally, this review explores the bioaccumulation mechanisms of HuNoV in bivalve shellfish, especially the mechanism underlying the binding of histo-blood group antigen-like molecules and HuNoV. The detection methods for infectious HuNoV are also discussed. The establishment of effective methods to rapidly detect infectious HuNoV and development of biological components to inactivate or prevent HuNoV contamination in shellfish also need to be studied further.

Aspects of high hydrostatic pressure food processing: Perspectives on technology and food safety

The last two decades saw a steady increase of high hydrostatic pressure (HHP) used for treatment of foods. Although the science of biomaterials exposed to high pressure started more than a century ago, there still seem to be a number of unanswered questions regarding safety of foods processed using HHP. This review gives an overview on historical development and fundamental aspects of HHP, as well as on potential risks associated with HHP food applications based on available literature. Beside the combination of pressure and temperature, as major factors impacting inactivation of vegetative bacterial cells, bacterial endospores, viruses, and parasites, factors, such as food matrix, water content, presence of dissolved substances, and pH value, also have significant influence on their inactivation by pressure. As a result, pressure treatment of foods should be considered for specific food groups and in accordance with their specific chemical and physical properties. The pressure necessary for inactivation of viruses is in many instances slightly lower than that for vegetative bacterial cells; however, data for food relevant human virus types are missing due to the lack of methods for determining their infectivity. Parasites can be inactivated by comparatively lower pressure than vegetative bacterial cells. The degrees to which chemical reactions progress under pressure treatments are different to those of conventional thermal processes, for example, HHP leads to lower amounts of acrylamide and furan. Additionally, the formation of new unknown or unexpected substances has not yet been observed. To date, no safety-relevant chemical changes have been described for foods treated by HHP. Based on existing sensitization to non-HHP-treated food, the allergenic potential of HHP-treated food is more likely to be equivalent to untreated food. Initial findings on changes in packaging materials under HHP have not yet been adequately supported by scientific data.

Evaluation of Copper Alloy Surfaces for Inactivation of Tulane Virus and Human Noroviruses

ABSTRACT

This study evaluated the efficacy of copper alloy surfaces for inactivation of Tulane virus (TV), assessed by plaque assay and porcine gastric mucin-conjugated magnetic bead (PGM-MB) binding assay, followed by quantitative reverse transcription PCR (PGM-MB-RT-qPCR assay). In addition, the efficacy of a copper surface for inactivation of human norovirus (HuNoV) GII.4 Sydney and GI.3B Potsdam strains was evaluated by PGM-MB-RT-qPCR assay. Results of time-dependent inactivation of viruses on copper, bronze, and brass coupons revealed that 15 min of surface treatments of each of the copper and copper alloys achieved >4-log reduction of purified TV, as assessed by plaque assay, while up to 20 min of copper alloy surface treatments only achieved ∼2-log reduction, as assessed by PGM-MB-RT-qPCR assay. As assessed by PGM-MB-RT-qPCR assay, 10 min of copper surface treatments achieved reductions of 3 and 4 log units for HuNoVs GII.4 Sydney and GI.3B Potsdam, respectively. Results from this study suggest that even though PGM-MB-RT-qPCR assay underestimated the efficacy of copper alloy surface inactivation of TV, copper alloy surfaces were able to effectively inactivate TV and HuNoVs. Therefore, copper alloys can be used as a preventive measure to prevent HuNoV infection and are an effective surface treatment for HuNoVs.

HIGHLIGHTS

Interaction between norovirus and Histo-Blood Group Antigens: A key to understanding virus transmission and inactivation through treatments?

Human noroviruses (HuNoVs) are a main cause of acute gastroenteritis worldwide. They are frequently involved in foodborne and waterborne outbreaks. Environmental transmission of the virus depends on two main factors: the ability of viral particles to remain infectious and their adhesion capacity onto different surfaces. Until recently, adhesion of viral particles to food matrices was mainly investigated by considering non-specific interactions (e.g. electrostatic, hydrophobic) and there was only limited information about infectious HuNoVs because of the absence of a reliable in vitro HuNoV cultivation system. Many HuNoV strains have now been described as having specific binding interactions with human Histo-Blood Group Antigens (HBGAs) and non-HBGA ligands found in food and the environment. Relevant approaches to the in vitro replication of HuNoVs were also proposed recently. On the basis of the available literature data, this review discusses the opportunities to use this new knowledge to obtain a better understanding of HuNoV transmission to human populations and better evaluate the hazard posed by HuNoVs in foodstuffs and the environment.

The impact of thermal pasteurization on viral load and detectable live viruses in human milk and other matrices: a rapid review

Holder pasteurization (62.5 °C, 30 min) of human milk is thought to reduce the risk of transmitting viruses to an infant. Some viruses may be secreted into milk - others may be contaminants. The effect of thermal pasteurization on viruses in human milk has yet to be rigorously reviewed. The objective of this study is to characterize the effect of common pasteurization techniques on viruses in human milk and non-human milk matrices. Databases (MEDLINE, Embase, Web of Science) were searched from inception to April 20th, 2020, for primary research articles assessing the impact of pasteurization on viral load or detection of live virus. Reviews were excluded, as were studies lacking quantitative measurements or those assessing pasteurization as a component of a larger process. Overall, of 65 131 reports identified, 109 studies were included. Pasteurization of human milk at a minimum temperature of 56-60 °C is effective at reducing detectable live virus. In cell culture media or plasma, coronaviruses (e.g., SARS-CoV, SARS-CoV-2, MERS-CoV) are highly susceptible to heating at ≥56 °C. Although pasteurization parameters and matrices reported vary, all viruses studied, except parvoviruses, were susceptible to thermal killing. Future research important for the study of novel viruses should standardize pasteurization protocols and should test inactivation in human milk. Novelty In all matrices, including human milk, pasteurization at 62.5 °C was generally sufficient to reduce surviving viral load by several logs or to below the limit of detection. Holder pasteurization (62.5 °C, 30 min) of human milk should be sufficient to inactivate nonheat resistant viruses, including coronaviruses, if present.

Ìn situ inactivation of human norovirus GII.4 by cold plasma: Ethidium monoazide (EMA)-coupled RT-qPCR underestimates virus reduction and fecal material suppresses inactivation

Cold atmospheric-gaseous plasma (CAP) is an emerging non-thermal technology for decontamination of foodborne bacterial and viral pathogens. We obtained a >5 log10 reduction in the titer (TCID50) of feline calicivirus (FCV) on stainless steel discs and Romaine lettuce leaves after 3 min wet exposure to air plasma generated by a two-dimensional array of integrated coaxial-microhollow dielectric barrier discharge (2D-AICM-DBD). However, when human norovirus (HuNoV GII.4) was treated for 5 min under the same conditions, ~2.6 log10 (>99.5%) reduction in genome copy number was observed as measured by ethidium monoazide-coupled RT-qPCR (EMA-RT-qPCR). To assess this discrepancy, we studied CAP's effect on FCV by the cell culture method and by the EMA-coupled RT-qPCR method. It was found that the molecular titration method (EMA-RT-qPCR) underestimates the level of virus reduction by CAP. Additionally, the fecal matter present in HuNoV samples partially suppressed virucidal activity of CAP. Assuming that the lower virus reduction measured by EMA-RT-qPCR method compared to cell culture method for FCV is the same as for HuNoV, we can conclude that FCV may be used as a surrogate for HuNoV to assess the virucidal effect of CAP. CAP is able to inactivate 3.5 Log10 units of HuNoV at low titers after 2 min of exposure.

Current and Emerging Technologies for the Detection of Norovirus from Shellfish

Reports of norovirus infections associated with the consumption of contaminated bivalve molluscan shellfish negatively impact both consumers and commercial shellfish operators. Current virus recovery and PCR detection methods can be expensive and time consuming. Due to the lack of rapid, user-friendly and onsite/infield methods, it has been difficult to establish an effective virus monitoring regime that is able to identify contamination points across the production line (i.e., farm-to-plate) to ensure shellfish quality. The focus of this review is to evaluate current norovirus detection methods and discuss emerging approaches. Recent advances in omics-based detection approaches have the potential to identify novel biomarkers that can be incorporated into rapid detection kits for onsite use. Furthermore, some omics techniques have the potential to simultaneously detect multiple enteric viruses that cause human disease. Other emerging technologies discussed include microfluidic, aptamer and biosensor-based detection methods developed to detect norovirus with high sensitivity from a simple matrix. Many of these approaches have the potential to be developed as user-friendly onsite detection kits with minimal costs. However, more collaborative efforts on research and development will be required to commercialize such products. Once developed, these emerging technologies could provide a way forward that minimizes public health risks associated with shellfish consumption.

Estimation of Human Norovirus Infectivity from Environmental Water Samples by In Situ Capture RT-qPCR Method

Human noroviruses (HuNoVs) are highly infectious viruses for which water is an important medium of transmission. In this study, we explored a new in situ capture RT-qPCR (ISC-RT-qPCR) methodology to estimate the infectivity of HuNoV in environmental water samples. This assay was based on capturing encapsidated HuNoV by viral receptors, followed by in situ amplification of the captured viral genomes by RT-qPCR. We demonstrated that the ISC-RT-qPCR did not capture and enable signal amplification of heat-denatured Tulane Virus (TV) and HuNoVs. We further demonstrated that the sensitivity of ISC-RT-qPCR was equal or better than that of conventional RT-qPCR procedures for the detection of HuNoV GI and GII. We then utilized the ISC-RT-qPCR to detect HuNoV in environmental water samples for comparison against that from a conventional RT-qPCR procedure. TV was used as a process control virus. While complete inhibition of TV genomic signal was observed in 27% of samples tested by RT-qPCR, no inhibition of TV genomic signal was observed by ISC-RT-qPCR. From 72 samples tested positive for HuNoV GI signal by RT-qPCR, only 20 (27.8%) of these samples tested positive by ISC-RT-qPCR, suggesting that 72.2% of RT-qPCR-positive samples were unlikely to be infectious. From 16 samples tested positive for HuNoV GII signal by RT-qPCR, only one of these samples tested positive by ISC-RT-qPCR. Five samples that had initially tested negative for HuNoV GII signal by RT-qPCR, was tested as positive by ISC-RT-qPCR. Overall, ISC-RT-qPCR method provided an alternative assay to estimate infectivity of HuNoV in environmental samples.

Enzymatic and viability RT-qPCR assays for evaluation of enterovirus, hepatitis A virus and norovirus inactivation: Implications for public health risk assessment

AIM

To assess the potential of a viability dye and an enzymatic reverse transcription quantitative PCR (RT-qPCR) pretreatment to discriminate between infectious and noninfectious enteric viruses.

METHODS AND RESULTS

Enterovirus (EntV), norovirus (NoV) GII.4 and hepatitis A virus (HAV) were inactivated at 95°C for 10 min, and four methods were used to compare the efficiency of inactivation: (i) cell culture plaque assay for HAV and EntV, (ii) RT-qPCR alone, (iii) RT-qPCR assay preceded by RNase treatment, and (iv) pretreatment with a viability dye (reagent D (RD)) followed by RT-qPCR. In addition, heat-inactivated NoV was treated with RD coupled with surfactants to increase the efficiency of the viability dye. No treatment was able to completely discriminate infectious from noninfectious viruses. RD-RT-qPCR reduced more efficiently the detection of noninfectious viruses with little to no removal observed with RNase. RD-RT-qPCR method was the closest to cell culture assay. The combination of surfactants and RD did not show relevant improvements on the removal of inactivated viruses signal compared with viability RT-qPCR, with the exception of Triton X-100.

CONCLUSION

The use of surfactant/RD-RT-qPCR, although not being able to completely remove the signal from noninfectious viral particles, yielded a better estimation of viral infectivity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Surfactant/RD-RT-qPCR may be an advantageous tool for a better detection of infectious viruses with potential significant impact in the risk assessment of the presence of enteric viruses.