Survival of human norovirus surrogates in milk, orange, and pomegranate juice, and juice blends at refrigeration (4 °C)

Development of a broad-spectrum therapeutic Fc-nanobody for human noroviruses

Human norovirus was discovered more than five decades ago and is a widespread cause of outbreaks of acute gastroenteritis. There are no approved vaccines or antivirals currently available. However, norovirus inhibitors, including capsid-specific monoclonal antibodies (Mabs) and nanobodies, have recently shown promising results. Several Mabs and nanobodies were found to inhibit norovirus replication using a human intestinal enteroid (HIE) culture system and/or could block norovirus attachment to histo-blood group antigen (HBGA) co-factors. In our pursuit to develop a single broad-spectrum norovirus therapeutic, we continued our analysis and development of a cross-reactive and HBGA interfering nanobody (NB26). To improve NB26 binding capacity and therapeutic potential, we conjugated NB26 onto a human IgG Fc domain (Fc-NB26). We confirmed that Fc-NB26 cross-reacts with genetically diverse GII genotype capsid protruding (P) domains (GII.8, GII.14, GII.17, GII.24, GII.26, and GII.NA1) using a direct enzyme-linked immunosorbent assay. Furthermore, X-ray crystallography structures of these P domains and structures of other GII genotypes reveal that the NB26 binding site is largely conserved, validating its broad reactivity. We showed that Fc-NB26 has ~100-fold higher affinity toward the norovirus P domain compared to native NB26. We also found that both NB26 and Fc-NB26 neutralize human norovirus replication in the HIE culture system. Furthermore, the mode of inhibition confirmed that like NB26, Fc-NB26 caused norovirus particle disassembly and aggregation. Overall, these new findings demonstrate that structural modifications to nanobodies can improve their therapeutic potential.IMPORTANCEDeveloping vaccines and antivirals against norovirus remains a challenge, mainly due to the constant genetic and antigenic evolution. Moreover, re-infection with genetically related and/or antigenic variants is not uncommon. We further developed our leading norovirus nanobody (NB26) that indirectly interfered with norovirus binding to HBGAs, by converting NB26 into a dimeric Fc-linked Nanobody (Fc-NB26). We found that Fc-NB26 had improved binding affinity and neutralization capacity compared with native NB26. Using X-ray crystallography, we showed this nanobody engaged highly conserved capsid residues among genetically diverse noroviruses. Development of such broadly reactive potent therapeutic nanobodies delivered as a slow-releasing prophylactic could be of exceptional value for norovirus outbreaks, especially for the prevention or treatment of severe acute gastroenteritis in high-risk groups such as the young, elderly, and immunocompromised.

Antiviral Natural Products, Their Mechanisms of Action and Potential Applications as Sanitizers and Disinfectants

Plant extracts, natural products and plant oils contain natural virucidal actives that can be used to replace active ingredients in commercial sanitizers and disinfectants. This review focuses on the virucidal mechanisms of natural substances that may exhibit potential for indoor air and fomite disinfection. Review of scientific studies indicates: (1) most natural product studies use crude extracts and do not isolate or identify exact active antiviral substances; (2) many natural product studies contain unclear explanations of virucidal mechanisms of action; (3) natural product evaluations of virucidal activity should include methods that validate efficacy under standardized disinfectant testing procedures (e.g., carrier tests on applicable surfaces or activity against aerosolized viruses, etc.). The development of natural product disinfectants requires a better understanding of the mechanisms of action (MOA), chemical profiles, compound specificities, activity spectra, and the chemical formulations required for maximum activity. Combinations of natural antiviral substances and possibly the addition of synthetic compounds might be needed to increase inactivation of a broader spectrum of viruses, thereby providing the required efficacy for surface and air disinfection.

Direct Blockade of the Norovirus Histo-Blood Group Antigen Binding Pocket by Nanobodies

Noroviruses are the leading cause of outbreaks of acute gastroenteritis. These viruses usually interact with histo-blood group antigens (HBGAs), which are considered essential cofactors for norovirus infection. This study structurally characterizes nanobodies developed against the clinically important GII.4 and GII.17 noroviruses with a focus on the identification of novel nanobodies that efficiently block the HBGA binding site. Using X-ray crystallography, we have characterized nine different nanobodies that bound to the top, side, or bottom of the P domain. The eight nanobodies that bound to the top or side of the P domain were mainly genotype specific, while one nanobody that bound to the bottom cross-reacted against several genotypes and showed HBGA blocking potential. The four nanobodies that bound to the top of the P domain also inhibited HBGA binding, and structural analysis revealed that these nanobodies interacted with several GII.4 and GII.17 P domain residues that commonly engaged HBGAs. Moreover, these nanobody complementarity-determining regions (CDRs) extended completely into the cofactor pockets and would likely impede HBGA engagement. The atomic level information for these nanobodies and their corresponding binding sites provide a valuable template for the discovery of additional "designer" nanobodies. These next-generation nanobodies would be designed to target other important genotypes and variants, while maintaining cofactor interference. Finally, our results clearly demonstrate for the first time that nanobodies directly targeting the HBGA binding site can function as potent norovirus inhibitors. IMPORTANCE Human noroviruses are highly contagious and a major problem in closed institutions, such as schools, hospitals, and cruise ships. Reducing norovirus infections is challenging on multiple levels and includes the frequent emergence of antigenic variants, which complicates designing effective, broadly reactive capsid therapeutics. We successfully developed and characterized four norovirus nanobodies that bound at the HBGA pockets. Compared with previously developed norovirus nanobodies that inhibited HBGA through disrupted particle stability, these four novel nanobodies directly inhibited HBGA engagement and interacted with HBGA binding residues. Importantly, these new nanobodies specifically target two genotypes that have caused the majority of outbreaks worldwide and consequently would have an enormous benefit if they could be further developed as norovirus therapeutics. To date, we have structurally characterized 16 different GII nanobody complexes, a number of which block HBGA binding. These structural data could be used to design multivalent nanobody constructs with improved inhibition properties.

Natural extracts, honey, and propolis as human norovirus inhibitors

Norovirus is the most important cause of acute gastroenteritis, yet there are still no antivirals, vaccines, or treatments available. Several studies have shown that norovirus-specific monoclonal antibodies, Nanobodies, and natural extracts might function as inhibitors. Therefore, the objective of this study was to determine the antiviral potential of additional natural extracts, honeys, and propolis samples. Norovirus GII.4 and GII.10 virus-like particles (VLPs) were treated with different natural samples and analyzed for their ability to block VLP binding to histo-blood group antigens (HBGAs), which are important norovirus co-factors. Of the 21 natural samples screened, date syrup and one propolis sample showed promising blocking potential. Dynamic light scattering indicated that VLPs treated with the date syrup and propolis caused particle aggregation, which was confirmed using electron microscopy. Several honey samples also showed weaker HBGA blocking potential. Taken together, our results found that natural samples might function as norovirus inhibitors.

Antiviral Potential of Plants against Noroviruses

Human noroviruses, which belong to the enterovirus family, are one of the most common etiological agents of food-borne diseases. In recent years, intensive research has been carried out regarding the antiviral activity of plant metabolites that could be used for the preservation of fresh food, because they are safer for consumption when compared to synthetic chemicals. Plant preparations with proven antimicrobial activity differ in their chemical compositions, which significantly affects their biological activity. Our review aimed to present the results of research related to the characteristics, applicability, and mechanisms of the action of various plant-based preparations and metabolites against norovirus. New strategies to combat intestinal viruses are necessary, not only to ensure food safety and reduce infections in humans but also to lower the direct health costs associated with them.

What makes a foodborne virus: comparing coronaviruses with human noroviruses

In order to answer the question whether coronaviruses (CoVs) can be transmitted via foods, this review made a comparison between CoVs with the most recognized foodborne virus, human noroviruses (NoVs). As a result, although CoVs indeed have shown the possibilities to remain infectious on foods and/or food packaging materials long enough (from several days to several weeks) to potentially cause transmission, they seem to be less persistent than NoVs towards common disinfection practices with alcohols, chlorine and ultraviolet (UV). More importantly, the chance of foodborne transmission of CoVs is considered low as CoVs mainly spread through the respiratory tract and there is no clear evidence showing CoVs can follow fecal-oral routes like human NoVs and other foodborne viruses.

Foodborne viruses: Detection, risk assessment, and control options in food processing

In a recent report by risk assessment experts on the identification of food safety priorities using the Delphi technique, foodborne viruses were recognized among the top rated food safety priorities and have become a greater concern to the food industry over the past few years. Food safety experts agreed that control measures for viruses throughout the food chain are required. However, much still needs to be understood with regard to the effectiveness of these controls and how to properly validate their performance, whether it is personal hygiene of food handlers or the effects of processing of at risk foods or the interpretation and action required on positive virus test result. This manuscript provides a description of foodborne viruses and their characteristics, their responses to stress and technologies developed for viral detection and control. In addition, the gaps in knowledge and understanding, and future perspectives on the application of viral detection and control strategies for the food industry, along with suggestions on how the food industry could implement effective control strategies for viruses in foods. The current state of the science on epidemiology, public health burden, risk assessment and management options for viruses in food processing environments will be highlighted in this review.

Norovirus: The Burden of the Unknown

Human noroviruses (HNoVs) are primarily transmitted by the fecal-oral route, either by person-to-person contact, or by ingestion of contaminated food or water as well as by aerosolization. Moreover, HNoVs significantly contribute to foodborne diseases being the causative agent of one-fifth of acute gastroenteritis worldwide. As a consequence of globalization, transnational outbreaks of foodborne infections are reported with increasing frequency. Therefore, in this review, state-of-the-art information regarding molecular procedures for human norovirus detection in food as well common food processing technologies have been summarized. Besides, the purpose of this chapter is to consolidate basic information on various aspects of HNoVs and to summarize food processing technologies that can potentially be applied in the food industry.

Human norovirus inhibition by a human milk oligosaccharide

Human noroviruses are the leading cause of outbreaks of acute gastroenteritis. Norovirus interactions with histo-blood group antigens (HBGAs) are known to be important for an infection. In this study, we identified the HBGA binding pocket for an emerging GII genotype 17 (GII.17) variant using X-ray crystallography. The GII.17 variant bound the HBGA with an equivalent set of residues as the leading pandemic GII.4 variants. These structural data highlights the conserved nature of HBGA binding site between prevalent GII noroviruses. Noroviruses also interact with human milk oligosaccharides (HMOs), which mimic HBGAs and may function as receptor decoys. We previously showed that HMOs inhibited the binding of rarely detected GII.10 norovirus to HBGAs. We now found that an HMO, 2'-fucosyllactose (2'FL), additionally blocked both the GI.1 and GII.17 noroviruses from binding to HBGAs. Together, these findings provide evidence that 2'FL might function as a broadly reactive antiviral against multiple norovirus genogroups.

Reduction of Enteric Viruses by Blueberry Juice and Blueberry Proanthocyanidins

Blueberry and blueberry extracts are known for their health benefits and antimicrobial properties. Natural therapeutic or preventive options to decrease the incidences of foodborne viral illnesses are becoming popular and being researched. This study aimed to determine the antiviral effects of blueberry juice (BJ) and blueberry proanthocyanidins (BB-PAC, B-type PAC structurally different from A-type PAC found in cranberries) against the infectivity of hepatitis A virus (HAV) and human norovirus surrogates (feline calicivirus (FCV-F9) and murine norovirus (MNV-1)) at 37 °C over 24 h using standard plaque assays. Viruses at ~5 log PFU/ml were mixed with equal volumes of BJ (pH 2.8), neutralized BJ (pH 7.0), BB-PAC (1, 2, 4, and 10 mg/ml), malic acid (pH 3.0), or phosphate-buffered saline (pH 7.2) and incubated over 24 h at 37 °C. Each experiment was carried out in duplicate and replicated thrice. FCV-F9 titers were found to be reduced to undetectable levels with 1 and 2 mg/ml BB-PAC after 5 min, with 0.5 mg/ml BB-PAC after 1-h, and with BJ after 3-h. MNV-1 titers were reduced to undetectable levels after 3 h with 1, 2, and 5 mg/ml BB-PAC and after 6 h with BJ. HAV titers were reduced to undetectable levels after 30 min with 2 and 5 mg/ml BB-PAC, after 3 h with 1 mg/ml BB-PAC, and by ~2 log PFU/ml with BJ after 24-h. BB-PAC shows preventive potential against infection by the tested enteric viruses in a dose- and time-dependent manner, although further in vitro studies in model food systems and in vivo studies using animal models are warranted.

Curcumin Shows Antiviral Properties against Norovirus

Phytochemicals provide environmentally friendly and relatively inexpensive natural products, which could potentially benefit public health by controlling human norovirus (HuNoV) infection. In this study, 18 different phytochemicals were evaluated for antiviral effects against norovirus using murine norovirus (MNV) as a model for norovirus biology. Among these phytochemicals, curcumin (CCM) was the most potent anti-noroviral phytochemical, followed by resveratrol (RVT). In a cell culture infection model, exposure to CCM or RVT for 3 days reduced infectivity of norovirus by 91% and 80%, respectively. To confirm the antiviral capability of CCM, we further evaluated its antiviral efficacy at various doses (0.25, 0.5, 0.75, 1, and 2 mg/mL) and durations (short-term: 10, 30, 60, and 120 min; long-term: 1, 3, 7, and 14 days). The anti-noroviral effect of CCM was verified to occur in a dose-dependent manner. Additionally, we evaluated the inhibitory effect of each phytochemical on the replication of HuNoV using a HuNoV replicon-bearing cell line (HG23). Neither CCM nor RVT had a strong inhibitory effect on HuNoV replication, which suggests that their antiviral mechanism may involve viral entry or other life cycle stages rather than the replication of viral RNA. Our results demonstrated that CCM may be a promising candidate for development as an anti-noroviral agent to prevent outbreaks of foodborne illness.

Survival of hepatitis A virus and Aichi virus in cranberry-based juices at refrigeration (4 °C)

Viral foodborne illness continues to be a health-concern globally, with numerous fruit and juice outbreaks of Hepatitis A virus (HAV) reported worldwide. Aichi virus (AiV) is an emerging pathogen with limited epidemiological data. Both, HAV and AiV are resistant to low pH and can survive under adverse environmental conditions leading to transmission ease. The objective of this study was to evaluate the survival of HAV and AiV in commercially-available cranberry-based juices (Cranberry juice cocktail, CJ and a 100% juice with cranberry, MJ) over 21 days at refrigeration (4 °C). Equal volumes of juice was mixed with each virus individually (final titer of 6 log PFU/mL) and stored at refrigeration over 21 days. At each time interval, the inoculated juices were serially diluted in cell culture media and infectious virus survival was determined by standard plaque assays. Each experiment was carried out in duplicate and replicated thrice. Reductions of 0.72 ± 0.06 (after day 1) to 2.3 ± 0.18 log PFU/mL (after day 21) and 0.63 ± 0.02 (after day 1) to 1.84 ± 0.14 log PFU/mL (after day 21) were obtained for AiV with MJ and CJ, respectively. Reductions ranging from 0.67 ± 0.03 (after day 1) to 1.09 ± 0.1 log PFU/mL (after day 21) and 0.93 ± 0.27 (after day1) to 1.49 ± 0.18 log PFU/mL (after day 21) were obtained for HAV at refrigeration in MJ and CJ, respectively. HAV showed greater survival than AiV in these juices over refrigerated storage. These results provide survival data of HAV and AiV in cranberry-based juices that can be used in risk-modeling and risk assessment studies.

Fate of Foodborne Viruses in the "Farm to Fork" Chain of Fresh Produce

Norovirus (NoV) and hepatitis A virus (HAV) are the most important foodborne viruses. Fresh produce has been identified as an important vehicle for their transmission. In order to supply a basis to identify possible prevention and control strategies, this review intends to demonstrate the fate of foodborne viruses in the farm to fork chain of fresh produce, which include the introduction routes (contamination sources), the viral survival abilities at different stages, and the reactions of foodborne viruses towards the treatments used in food processing of fresh produce. In general, the preharvest contamination comes mainly from soli fertilizer or irrigation water, while the harvest and postharvest contaminations come mainly from food handlers, which can be both symptomatic and asymptomatic. Foodborne viruses show high stabilities in all the stages of fresh produce production and processing. Low-temperature storage and other currently used preservation techniques, as well as washing by water have shown limited added value for reducing the virus load on fresh produce. Chemical sanitizers, although with limitations, are strongly recommended to be applied in the wash water in order to minimize cross-contamination. Alternatively, radiation strategies have shown promising inactivating effects on foodborne viruses. For high-pressure processing and thermal treatment, efforts have to be made on setting up treatment parameters to induce sufficient viral inactivation within a food matrix and to protect the sensory and nutritional qualities of fresh produce to the largest extent.

Treatment of norovirus particles with citrate

Human norovirus is a dominant cause of acute gastroenteritis around the world. Several norovirus disinfectants label citric acid as an active ingredient. In this study, we showed that norovirus virus-like particles (VLPs) treated with citrate buffer caused the particles to alter their morphology, including increased diameters associated with a new ring-like structure. We also found that epitopes on the protruding (P) domain on these particles were more readily accessible to antibodies after the citrate treatment. These results suggested that citrate had a direct effect on the norovirus particles. Using X-ray crystallography, we showed that the P domain bound citrate from lemon juice and a disinfectant containing citric acid. Importantly, citrate binds at the histo-blood group antigen binding pocket, which are attachment factors for norovirus infections. Taken together, these new findings suggested that it might be possible to treat/reduce norovirus infections with citrate, although further studies are needed.

Persistence of human norovirus RT-qPCR signals in simulated gastric fluid

Human noroviruses (HuNoV) are a leading cause of foodborne disease and are known to be environmentally persistent. Foods usually become contaminated by contact with fecal material, both on hands and on surfaces. Emerging evidence suggests that HuNoVs are also shed and potentially aerosolized during projectile vomiting, resulting in another source of contamination. The purpose of this study was to compare the persistence of HuNoV in vomitus-like material (simulated gastric fluid, SGF, pH 2.5) to that in a pH neutral buffer (phosphate buffered saline, PBS, pH 7.4) in suspension and on surfaces. Human fecal suspensions containing two HuNoV strains (GI.1 and GII.4) were suspended in SGF and PBS. Suspension and surface samples were held at room temperature, and subsamples were collected from both samples for a period up to 42 days. Subsamples were subjected to RNA isolation, with and without inclusion of an RNase pre-treatment, followed by RT-qPCR amplification. In suspension assays, the genome copy number of HuNoV GII.4 decreased by ≤1.0-1.3 log10 over 42 days, irrespective of suspension buffer. On stainless steel, there was virtually no reduction in HuNoV GII.4 RT-qPCR signal over the 42-days experimental period, regardless of suspension buffer. Overall, the GI.1 RT-qPCR signal dropped more precipitously. In most cases, there were no statistically significant differences (p > 0.05) between persistence in solution or on surfaces when comparing RT-qPCR assays with and without prior RNase treatment. This study suggests that HuNoV suspended in vomitus-like material can persist for long periods, a likely contributor to foodborne transmission.

Chemical constitution and effect of extracts of tomato plants byproducts on the enteric viral surrogates

Byproducts of tomato are known to include phenolic compounds but have not been studied in depth. In this study, the phenolic compositions of (stem, leaf, root, and whole plant) of two tomato cultivars, Pitenza and Floradade, were analyzed by HPLC-DAD. In parallel, the antiviral effects of crude extracts on viral surrogates, the bacteriophages MS2 and Av-05 were evaluated. The leaf extracts from the two varieties showed the highest concentration of phenolic compounds. The compounds identified were gallic acid, chlorogenic acid, ferulic acid, cafeic acid, rutin, and quercetin, and they represented 3174.3 and 1057.9 mg/100 g dried weight of the Pitenza and Floradade cultivars, respectively. MS2 and Av-05 titers at 5 mg/mL were reduced by 3.47 and 5.78 log10 PFU/mL and 3.78 and 4.93 log10 PFU/mL by Pitenza and Floradade cultivar leaf extract, respectively. These results show that tomato extracts are natural sources of bioactive substances with antiviral activity.

Norovirus

Norovirus, an RNA virus of the family Caliciviridae, is a human enteric pathogen that causes substantial morbidity across both health care and community settings. Several factors enhance the transmissibility of norovirus, including the small inoculum required to produce infection (<100 viral particles), prolonged viral shedding, and its ability to survive in the environment. In this review, we describe the basic virology and immunology of noroviruses, the clinical disease resulting from infection and its diagnosis and management, as well as host and pathogen factors that complicate vaccine development. Additionally, we discuss overall epidemiology, infection control strategies, and global reporting efforts aimed at controlling this worldwide cause of acute gastroenteritis. Prompt implementation of infection control measures remains the mainstay of norovirus outbreak management.

Strategies to enhance high pressure inactivation of murine norovirus in strawberry puree and on strawberries

Due to the increasing concern of viral infection related to berries, this study investigated strategies to enhance high hydrostatic pressure (HHP) inactivation of murine norovirus 1 (MNV-1), a human norovirus (HuNoV) surrogate, on strawberries and in strawberry puree. Strawberry puree was inoculated with ~10(6)PFU/g of MNV-1 and treated at 350 MPa for 2 min at initial sample temperatures of 0, 5, 10 and 20°C. MNV-1 became more sensitive to HHP as initial sample temperature decreased from 20 to 0°C. To determine the effect of pressure cycling on MNV-1 inactivation, inoculated puree samples were treated at 300 MPa and 0°C with 1, 2 and 4 cycles. Pressure cycling offered no distinct advantage over continuous HHP treatment. To determine the effect of presence of water during HHP on MNV-1 inactivation, strawberries inoculated with ~ 4 × 10(5)PFU/g of MNV-1 were either pressure-treated directly (dry state) or immersed in water during pressure treatment. MNV-1 was very resistant to pressure under the dry state condition, but became sensitive to pressure under the wet state condition. The inactivation curves of MNV-1 in strawberry puree and on strawberries were obtained at 300 and 350 MPa and initial sample temperature of 0°C. Except for the curve of strawberries treated at 350 MPa which had a concave downward shape, the other three curves were almost linear with R(2) value of 0.99. The fate of MNV-1 in the un-treated and pressure-treated strawberries and strawberry puree during frozen storage was determined. The virus was relatively stable and only reduced by <1.2 log during the 28-day frozen storage. In all, this study provides practical insights of designing strategies using HHP to inactivate HuNoV on strawberries and in strawberry puree assuming that HuNoV behaved similarly to MNV-1 when treated by HHP.

Antiviral effect of korean red ginseng extract and ginsenosides on murine norovirus and feline calicivirus as surrogates for human norovirus

Korean red ginseng has been studied various biological activities such as immune, anti-oxidative, anti-microbial, and anticancer activities but antiviral mechanism needs further studies. In this study, we aimed to examine the antiviral effects of Korea red ginseng extract and ginsenosides on norovirus surrogate, including murine norovirus (MNV) and feline calicivirus (FCV). We evaluated the pre-, co-, and post-treatment effects of Korean red ginseng (KRG), ginsenosides Rb₁ and Rg₁. To measure the antiviral effect and cytotoxicity of KRG extract, and ginsenosides Rb₁ and Rg₁, we treated Crandell-Reese Feline Kidney for FCV or RAW264.7 cells for MNV with concentrations of 0, 5, 6.7, 10, 20 ug/mL total saponin. There was cytotoxic effect in the highest concentration 20 ug/mL of KRG extract so this concentration was excluded in this study. The FCV titer was significantly reduced to 0.23-0.83 log₁₀ 50% tissue culture infectious dose (TCID₅₀)/mL in groups pre-treated with red ginseng extract or ginsenosides. The titer of MNV was significantly reduced to 0.37-1.48 log₁₀ TCID₅₀/mL in groups pre-treated with red ginseng extract or ginsenosides. However, there was no observed antiviral effect in groups co-treated or post-treated with KRG and its constituents. Our data suggest that KRG extract has an antiviral effect against norovirus surrogates. The antiviral mechanisms of KRG and ginsenosides should be addressed in future studies.

Grape seed extract for foodborne virus reduction on produce

Grape seed extract (GSE) is reported to have antibacterial properties with few current studies on antiviral activity. Recently, we reported the effects of GSE against foodborne viral surrogates in vitro. This study evaluated the application of GSE (commercial Gravinol-S) against hepatitis A virus (HAV) and human norovirus surrogates, feline calicivirus (FCV-F9) and murine norovirus (MNV-1), on model produce. Washed and air-dried lettuce (3 × 3 cm(2)) and jalapeno peppers (25-30 g) were inoculated with FCV-F9, MNV-1, or HAV at high (∼7 log10 PFU/ml) or low (∼5 log10 PFU/ml) titers, and treated with 0.25, 0.5, 1 mg/ml GSE or water for 30 s to 5 min. Treatments were stopped/diluted with cell-culture media containing 10% heat-inactivated fetal bovine serum and evaluated using plaque assays. At high titers, FCV-F9 was reduced by 2.33, 2.58, and 2.71 log10 PFU on lettuce; and 2.20, 2.74, and 3.05 log10 PFU on peppers after 1 min using 0.25, 0.50, and 1 mg/ml GSE, respectively. Low FCV-F9 titers could not be detected after 1 min at all three GSE concentrations. Low titer MNV-1 was reduced by 0.2-0.3 log10 PFU on lettuce and 0.8 log10 PFU on peppers, without reduction of high titer. GSE at 0.25-1 mg/ml after 1 min caused 0.7-1.1 and 1-1.3 log10 PFU reduction for high and low HAV titers, respectively on both commodities. Instrumental color analysis showed no significant differences between treated and untreated produce. GSE shows potential for foodborne viral reduction on produce as part of hurdle technologies.

Evaluation of concentration efficiency of the Pseudomonas aeruginosa phage PP7 in various water matrixes by different methods

Enteric viruses monitoring in surface waters requires the concentration of viruses before detection assays. The aim of this study was to evaluate different methods in terms of recovery efficiencies of bacteriophage PP7 of Pseudomonas aeruginosa, measured by real-time PCR, using it as a viral control process in water analysis. Different nucleic acid extraction methods (silica-guanidinium thiocyanate, a commercial kit (Qiagen Viral RNA Kit) and phenol-chloroform with alcohol precipitation) exhibited very low recovery efficiencies (0.08-4.18 %), being the most efficient the commercial kit used for subsequent experiments. To evaluate the efficiency of three concentration methods, PBS (as model for clean water) and water samples from rivers were seeded to reach high (HC, 10(6) pfu ml(-1)) and low concentrations (LC, 10(4) pfu ml(-1)) of PP7. Tangential ultrafiltration proved to be more efficient (50.36 ± 12.91, 17.21 ± 9.22 and 12.58 ± 2.35 % for HC in PBS and two river samples, respectively) than adsorption-elution with negatively charged membranes (1.00 ± 1.34, 2.79 ± 2.62 and 0.05 ± 0.08 % for HC in PBS and two river samples, respectively) and polyethylene glycol precipitation (15.95 ± 7.43, 4.01 ± 1.12 and 3.91 ± 0.54 %, for HC in PBS and two river samples, respectively), being 3.2-50.4 times more efficient than the others for PBS and 2.7-252 times for river samples. Efficiencies also depended on the initial virus concentration and aqueous matrixes composition. In consequence, the incorporation of an internal standard like PP7 along the process is useful as a control of the water concentration procedure, the nucleic acid extraction, the presence of inhibitors and the variability of the recovery among replicas, and for the calculation of the sample limit of detection. Thus, the use of a process control, as presented here, is crucial for the accurate quantification of viral contamination.

Human norovirus surrogate reduction in milk and juice blends by high pressure homogenization

Novel processing technologies such as high pressure homogenization (HPH) for the inactivation of foodborne viruses in fluids that retain nutritional attributes are in high demand. The objectives of this research were (i) to determine the effects of HPH alone or with an emulsifier (lecithin) on human norovirus surrogates-murine norovirus (MNV-1) and feline calicivirus (FCV-F9)-in skim milk and orange juice, and (ii) to determine HPH effects on FCV-F9 and MNV-1 in orange and pomegranate juice blends. Experiments were conducted in duplicate at 0, 100, 200, 250, and 300 MPa for <2 s and plaque was assayed in duplicate. In milk, FCV-F9 was reduced by ≥4 and ∼1.3 log PFU/ml at 300 and 250 MPa, respectively, and ≥4- and ∼1-log PFU/ml reductions were obtained in orange juice at 300 and 250 MPa, respectively. In orange juice or milk combined with lecithin, FCV-F9 was reduced to nondetectable levels at 300 MPa, and by 1.77 and 0.78 log PFU/ml at 250 MPa. MNV-1 in milk was reduced by ∼1.3 log PFU/ml only at 300 MPa, and by ∼0.8 and ∼0.4 log PFU/ml in orange juice at 300 and 250 MPa, respectively. MNV-1 in milk or orange juice containing lecithin at 300 MPa showed 1.32- and 2.5-log PFU/ml reductions, respectively. In the pomegranate-orange juice blend, FCV-F9 was completely reduced, and MNV-1 was reduced by 1.04 and 1.78 log PFU/ml at 250 and 300 MPa, respectively. These results show that HPH has potential for commercial use to inactivate foodborne virus surrogates in juices.

Survival and inactivation of human norovirus surrogates in blueberry juice by high-pressure homogenization

Human noroviruses (HNoV) have been implicated in gastrointestinal outbreaks associated with fresh produce, juices, and ready-to-eat foods. In order to determine the risk of HNoV transmission by contaminated blueberry juice, survival characteristics of cultivable HNoV surrogates (murine norovirus, MNV-1; feline calicivirus, FCV-F9; and bacteriophage MS2) in blueberry juice (pH = 2.77) after 0, 1, 2, 7, 14, and 21 days at refrigeration temperatures (4°C) were studied. High-pressure homogenization (HPH) was studied as a novel processing method for noroviral surrogate inactivation in blueberry juice. Blueberry juice or phosphate-buffered saline (PBS; pH 7.2 as control) was inoculated with each virus, stored over 21 days at 4°C or subjected to HPH, and plaque assayed. FCV-F9 (∼5 log(10) PFU/mL) was undetectable after 1 day in blueberry juice at 4°C. MNV-1 (∼4 log(10) PFU/ml) showed minimal reduction (1 log(10) PFU/mL) after 14 days, with greater reduction (1.95 log(10) PFU/mL; p < 0.05) after 21 days in blueberry juice at 4°C. Bacteriophage MS2 (∼6 log(10) PFU/mL) showed significant reduction (1.93 log(10) PFU/mL; p < 0.05) after 2 days and was undetectable after 7 days in blueberry juice at 4°C. FCV-F9 remained viable in PBS for up to 21 days (2.28 log(10) PFU/mL reduction), while MNV-1 and MS2 survived after 21 days (1.08 and 0.56 log(10) PFU/mL reduction, respectively). Intriguingly, FCV-F9 and bacteriophage MS2 showed reduction after minimal homogenization pressures in blueberry juice (pH = 2.77), possibly due to the combination of juice pH, juice components, and mechanical effects. MNV-1 in blueberry juice was only slightly reduced at 250 (0.33 log(10) PFU/mL) and 300 MPa (0.71 log(10) PFU/mL). Virus surrogate survival in blueberry juice at 4°C correlates well with the ease of HNoV transmission via juices. HPH for viral inactivation in juices is dependent on virus type, and higher homogenization pressures may be needed for MNV-1 inactivation.

Survival of murine norovirus and F-RNA coliphage MS2 on pork during storage and retail display

The existence of animal strains of norovirus (NV) that are closely related to human strains raises concerns about interspecies recombination and the potential for zoonotic transmission through undercooked meat products. Contamination of meat with NV can occur both via meat processing operations and poor food handler hygiene. There is a lack of knowledge on the survival of NV on raw meat because NV cannot be effectively cultivated and its detection is limited to molecular methods. The survival of murine norovirus (MNV) and MS2, as surrogates for NV, was determined on pork chops by plaque assay and real time RT-PCR. Both MNV and MS2 displayed very high survival rates on vacuum packaged raw pork chops that were stored at 2°C for up to 7 weeks and numbers declined little during subsequent retail display for 7 days. Maximum reductions for MNV and MS2 were 1.0 log PFU/cm(2) and 0.6 log genome copies(GC)/cm(2) or 1.1 log PFU/cm(2) and 1.2 log GC/cm(2), respectively. The viability of MS2 and MNV was not affected by the proteolytic enzymes present in the meat nor by numbers of bacteria that increased with time during storage in vacuum packs and while on retail display. MNV and MS2 can be considered as good surrogates for NV on raw meat. The findings of this study indicate that potentially pathogenic NV will likely survive extremely well on fresh meat and consumers could potentially be at risk when consuming undercooked meat that is contaminated with NV.

Tannic acid inhibited norovirus binding to HBGA receptors, a study of 50 Chinese medicinal herbs

Noroviruses (NoVs) are the leading cause of viral acute gastroenteritis affecting people of all ages worldwide. The disease is difficult to control due to its widespread nature and lack of an antiviral or vaccine. NoV infection relies on the interaction of the viruses with histo-blood group antigens (HBGAs) as host receptors. Here we investigated inhibition effects of Chinese medicinal herbs against NoVs binding to HBGAs for potential antivirals against NoVs. Blocking assays was performed using the NoV protrusion (P) protein as NoV surrogate and saliva as HBGAs. Among 50 clinically effective Chinese medicinal herbs against gastroenteritis diseases, two herbs were found highly effective. Chinese Gall blocked NoV P dimer binding to type A saliva at IC(50)=5.35 μg/ml and to B saliva at IC(50)=21.7 μg/ml. Similarly, Pomegranate blocked binding of NoV P dimer to type A saliva at IC(50)=15.59 μg/ml and B saliva at IC(50)=66.67 μg/ml. Literature data on preliminary biochemistry analysis showed that tannic acid is a common composition in the extracts of the two herbs, so we speculate that it might be the effective compound and further studies using commercially available, highly purified tannic acid confirmed the tannic acid as a strong inhibitor in the binding of NoV P protein to both A and B saliva (IC(50)≈0.1 μM). In addition, we tested different forms of hydrolysable tannins with different alkyl esters, including gallic acid, ethyl gallate, lauryl gallate, octyl gallate and propyl gallate. However, none of these tannins-derivatives revealed detectable inhibiting activities. Our data suggested that tannic acid is a promising candidate antiviral against NoVs.

Structural basis for norovirus inhibition and fucose mimicry by citrate

Human noroviruses bind with their capsid-protruding domains to histo-blood-group antigens (HBGAs), an interaction thought to direct their entry into cells. Although human noroviruses are the major cause of gastroenteritis outbreaks, development of antivirals has been lacking, mainly because human noroviruses cannot be cultivated. Here we use X-ray crystallography and saturation transfer difference nuclear magnetic resonance (STD NMR) to analyze the interaction of citrate with genogroup II (GII) noroviruses. Crystals of citrate in complex with the protruding domain from norovirus GII.10 Vietnam026 diffracted to 1.4 Å and showed a single citrate bound at the site of HBGA interaction. The citrate interaction was coordinated with a set of capsid interactions almost identical to that involved in recognizing the terminal HBGA fucose, the saccharide which forms the primary conserved interaction between HBGAs and GII noroviruses. Citrate and a water molecule formed a ring-like structure that mimicked the pyranoside ring of fucose. STD NMR showed the protruding domain to have weak affinity for citrate (460 μM). This affinity, however, was similar to the affinities of the protruding domain for fucose (460 μM) and H type 2 trisaccharide (390 μM), an HBGA shown previously to be specifically recognized by human noroviruses. Importantly, competition STD NMR showed that citrate could compete with HBGA for norovirus binding. Together, the results suggest that citrate and other glycomimetics have the potential to block human noroviruses from binding to HBGAs.