A Gnotobiotic Pig Model for Determining Human Norovirus Inactivation by High-Pressure Processing

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.

Ultralow temperature high pressure processing enhances inactivation of norovirus surrogates

High pressure processing (HPP) is a powerful non-thermal method for inactivating pathogens. Human norovirus and genetically-related caliciviruses are moderately sensitive to temperatures above 0 °C with >400 MPa (MPa) or higher required to inactivate multiple logs of virus. Sensitivity of murine norovirus (MNV) and Tulane virus (TV) to ice phase transitions was evaluated using ultra low temperature HPP. Identical samples containing MNV or TV were either equilibrated to +1.5 °C (thawed) or -40 °C (frozen) 24 h prior to pressurization. All samples (thawed and frozen) were then placed in a pre-chilled chamber which was then rapidly filled with -40 °C chamber fluid. Samples were immediately pressurized for 5 min at 200, 250 or 300 MPa. Controls were not pressurized. For samples that were thawed and then pressurized in 40 °C chamber fluid, the MNV average log reduction at 200 MPa was 4.4, while >6.1 log reduction (non-detectable) was achieved at 250 and 300 MPa. TV samples averaged 2.3, 5 and 4.3 log reduction at 200, 250, and 300 MPa respectively. For samples that were frozen and then pressurized in 40 °C chamber fluid, the MNV average log reductions were 2.3, 3.2 and 4.2 at 200 MPa, 250 MPa and 300 MPa, respectively, while TV samples averaged 0.81, 2.3 and 1.7 log reductions at 200, 250, and 300 MPa, respectively. Inactivation of TV within oysters at these pressures was also demonstrated. Overall, results indicate that in addition to enhancing inactivation of norovirus surrogates compared to higher temperatures, ultra-cold HPP performed on thawed samples especially enhances inactivation.

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.

Reduction of Norovirus in Foods by Nonthermal Treatments: A Review

ABSTRACT

Human noroviruses are enteric pathogens that cause a substantial proportion of acute gastroenteritis cases worldwide regardless of background variables such as age, ethnicity, and gender. Although person-to-person contact is the general route of transmission, foodborne infections are also common. Thorough cooking eliminates noroviruses, but several food products such as berries, leafy vegetables, and mollusks undergo only limited heat treatment, if any, before consumption. Novel applications of nonthermal processing technologies are currently being vigorously researched because they can be used to inactivate pathogens and extend product shelf life with limited effects on nutrient content and perceived quality. These technologies, adopted from several industrial fields, include some methods already approved for food processing that have been applied in the food industry for years. However, a majority of the research has been conducted with bacteria and simple matrixes or surfaces. This review focuses on elimination of norovirus in food matrixes by use of nonthermal technologies in four categories: high hydrostatic pressure, light, irradiation, and cold atmospheric plasma. We discuss the properties of noroviruses, principles and inactivation mechanisms of select technologies, and main findings of relevant studies. We also provide an overview of the current status of the research and propose future directions for related work.

HIGHLIGHTS

Evaluation of High-Pressure Processing in Inactivation of the Hepatitis E Virus

Hepatitis E virus (HEV) causes acute hepatitis with approximately 20 million cases per year globally. Based on genetic diversity, HEV is classified into different genotypes, with genotype 3 (HEV-3) being most prevalent in Europe and North America. The transmission of HEV-3 has been shown to be zoonotic and mainly associated with the consumption of raw or undercooked pork products. Herein, we investigated the efficacy of high-pressure processing (HPP) in inactivation of HEV-3 using a cell culture system. HPP has been indicated as a promising non-thermal pathogen inactivation strategy for treatment of certain high-risk food commodities, without any noticeable changes in their nature. For this purpose, we treated HEV-3 in media with different conditions of HPP: 400 MPa for 1 and 5 min, as well as 600 MPa for 1 and 5 min, at ambient temperature. All four HPP treatments of HEV in media were observed to result in a 2-log reduction in HEV load, as determined by the amounts of extracellular HEV RNA produced at 14-day post-infection, using the A549/D3 cell culture system. However, application of the same treatments to artificially contaminated pork pâté resulted in 0.5 log reduction in viral load. These results indicate that the efficacy of HPP treatment in the inactivation of HEV-3 is matrix-dependent, and independent of maximum pressure between 400 and 600 MPa and hold time between 1 and 5 min. Based on the obtained results, although the HPP treatment of pork pâté reduces the HEV-3 load, it might not be sufficient to fully mitigate the risk.

Animals as Reservoir for Human Norovirus

Norovirus is the most common cause of non-bacterial gastroenteritis and is a burden worldwide. The increasing norovirus diversity is currently categorized into at least 10 genogroups which are further classified into more than 40 genotypes. In addition to humans, norovirus can infect a broad range of hosts including livestock, pets, and wild animals, e.g., marine mammals and bats. Little is known about norovirus infections in most non-human hosts, but the close genetic relatedness between some animal and human noroviruses coupled with lack of understanding where newly appearing human norovirus genotypes and variants are emerging from has led to the hypothesis that norovirus may not be host restricted and might be able to jump the species barrier. We have systematically reviewed the literature to describe the diversity, prevalence, and geographic distribution of noroviruses found in animals, and the pathology associated with infection. We further discuss the evidence that exists for or against interspecies transmission including surveillance data and data from in vitro and in vivo experiments.

A Lactic Acid Bacteria (LAB)-Based Vaccine Candidate for Human Norovirus

Human noroviruses (HuNoVs) are responsible for more than 95% of the non-bacterial acute gastroenteritis epidemics in the world. The CDC estimates that every year 21 million individuals suffer from HuNoV-induced gastroenteritis in the United States. Currently, there is no FDA-approved vaccine for HuNoVs. Development of an effective vaccine has been hampered by the lack of an efficient cell culture system for HuNoVs and a suitable small animal model for pathogenesis study. In this study, we developed lactic acid bacteria (LAB) as a vector to deliver HuNoV antigen. A LAB strain (Lactococcus lactis) carrying VP1 gene of a HuNoV GII.4 virus (LAB-VP1) was constructed. It was found that HuNoV VP1 protein was highly expressed by LAB vector and was secreted into media supernatants. To test whether LAB-based HuNoV vaccine candidate is immunogenic, 4-day-old gnotobiotic piglets were orally inoculated with various doses of LAB-VP1. It was found that LABs were persistent in the small intestine of piglets and shed in pig feces for at least 25 days post inoculation. LAB DNA and VP1 were detected in mesenteric lymph nodes and spleen tissue in LAB-VP1 inoculated groups. HuNoV-specific IgG and IgA were detectable in serum and feces respectively at day 13 post-inoculation, and further increased at later time points. After being challenged with HuNoV GII.4 strain, a large amount of HuNoV antigens were observed in the duodenum, jejunum, and ileum sections of the intestine in the LAB control group. In contrast, significantly less, or no, HuNoV antigens were detected in the LAB-VP1 immunized groups. Collectively, these results demonstrate that a LAB-based HuNoV vaccine induces protective immunity in gnotobiotic piglets.

Human Norovirus: Experimental Models of Infection

Human noroviruses (HuNoVs) are a leading cause of acute gastroenteritis worldwide. HuNoV infections lead to substantial societal and economic burdens. There are currently no licensed vaccines or therapeutics for the prevention or treatment of HuNoVs. A lack of well-characterized in vitro and in vivo infection models has limited the development of HuNoV countermeasures. Experimental infection of human volunteers and the use of related viruses such as murine NoV have provided helpful insights into HuNoV biology and vaccine and therapeutic development. There remains a need for robust animal models and reverse genetic systems to further HuNoV research. This review summarizes available HuNoV animal models and reverse genetic systems, while providing insight into their usefulness for vaccine and therapeutic development.

Evaluation of Chlorine Treatment Levels for Inactivation of Human Norovirus and MS2 Bacteriophage during Sewage Treatment

This study examined the inactivation of human norovirus (HuNoV) GI.1 and GII.4 by chlorine under conditions mimicking sewage treatment. Using a porcine gastric mucin-magnetic bead (PGM-MB) assay, no statistically significant loss in HuNoV binding (inactivation) was observed for secondary effluent treatments of ≤25 ppm total chlorine; for both strains, 50 and 100 ppm treatments resulted in ≤0.8-log₁₀ unit and ≥3.9-log₁₀ unit reductions, respectively. Treatments of 10, 25, 50, and 100 ppm chlorine inactivated 0.31, 1.35, >5, and >5 log₁₀ units, respectively, of the norovirus indicator MS2 bacteriophage. Evaluation of treatment time indicated that the vast majority of MS2 and HuNoV inactivation occurred in the first 5 min for 0.2-μm-filtered, prechlorinated secondary effluent. Free chlorine measurements of secondary effluent seeded with MS2 and HuNoV demonstrated substantial oxidative burdens. With 25, 50, and 100 ppm treatments, free chlorine levels after 5 min of exposure ranged from 0.21 to 0.58 ppm, from 0.28 to 16.7 ppm, and from 11.6 to 53 ppm, respectively. At chlorine treatment levels of >50 ppm, statistically significant differences were observed between reductions for PGM-MB-bound HuNoV (potentially infectious) particles and those for unbound (noninfectious) HuNoV particles or total norovirus particles. While results suggested that MS2 and HuNoV (measured as PGM-MB binding) behave similarly, although not identically, both have limited susceptibility to chlorine treatments of ≤25 ppm total chlorine. Since sewage treatment is performed at ≤25 ppm total chlorine, targeting free chlorine levels of 0.5 to 1.0 ppm, these results suggest that traditional chlorine-based sewage treatment does not inactivate HuNoV efficiently.IMPORTANCE HuNoV is ubiquitous in sewage. A receptor binding assay was used to assess inactivation of HuNoV by chlorine-based sewage treatment, given that the virus cannot be routinely propagated in vitro Results reported here indicate that chlorine treatment of sewage is not effective for inactivating HuNoV unless chlorine levels are above those routinely used for sewage treatment.

Capturing norovirus transmission

Human norovirus is a leading cause of gastroenteritis and is efficiently transmitted between humans and around the globe. The burden of norovirus infections in the global community and in health-care settings warrant the availability of outbreak prevention strategies and control measures that are tailored to the pathogen, outbreak setting and population at risk. A better understanding of viral and host determinants of transmission would aid in developing and fine-tuning such efforts. Here, we describe mechanisms of transmission, available model systems for studying norovirus transmission and their strengths and weaknesses as well as future research strategies.

Persistence and Elimination of Human Norovirus in Food and on Food Contact Surfaces: A Critical Review

This critical review addresses the persistence of human norovirus (NoV) in water, shellfish, and processed meats; on berries, herbs, vegetables, fruits, and salads; and on food contact surfaces. The review focuses on studies using NoV; information from studies involving only surrogates is not included. It also addresses NoV elimination or inactivation by various chemical, physical, or processing treatments. In most studies, persistence or elimination was determined by detection and quantification of the viral genome, although improved methods for determining infectivity have been proposed. NoV persisted for 60 to 728 days in water, depending on water source. It also persisted on berries, vegetables, and fruit, often showing <1-log reduction within 1 to 2 weeks. NoV was resilient on carpets, Formica, stainless steel, polyvinyl chloride, and ceramic surfaces; during shellfish depuration; and to repeated freeze-thaw cycles. Copper alloy surfaces may inactivate NoV by damaging viral capsids. Disinfection was achieved for some foods or food contact surfaces using chlorine, calcium or sodium hypochlorite, chlorine dioxide, high hydrostatic pressure, high temperatures, pH values >8.0, freeze-drying, and UV radiation. Ineffective disinfectants included hydrogen peroxide, quaternary ammonium compounds, most ethanol-based disinfectants, and antiseptics at normally used concentrations. Thorough washing of herbs and produce was effective in reducing, but not eliminating, NoV in most products. Washing hands with soap generally reduced NoV by <2 log. Recommendations for future research needs are provided.

Evaluation of high hydrostatic pressure inactivation of human norovirus on strawberries, blueberries, raspberries and in their purees

Human norovirus (HuNoV) has been an increasing concern of foodborne illness related to fresh and frozen berries. In this study, high hydrostatic pressure (HHP) inactivation of HuNoV on fresh strawberries, blueberries, and raspberries and in their purees was investigated. Porcine gastric mucin (PGM)-conjugated magnetic beads (PGM-MBs) and real-time reverse transcriptional polymerase chain reaction (RT-qPCR) were utilized for infectious HuNoV discrimination and quantification. Strawberry puree inoculated with HuNoV genogroup I.1 (GI.1) strain was HHP-treated at 450, 500 and 550 MPa for 2 min each at initial sample temperatures of 0, 4 and 20 °C. HuNoV GI.1 strain became more sensitive to HHP treatment as the temperature decreased from 20 to 0 °C. HuNoV GI.1 or genogroup II.4 (GII.4) strains were inoculated into three types of berries and their purees and treated at pressure levels from 250 to 650 MPa for 2 min at initial sample temperature of 0 °C. For the purees, the HHP condition needed to achieve >2.9 log reduction of HuNoV GI.1 strain and >4.0 log reduction of HuNoV GII.4 strain was found to be ≥ 550 MPa for 2 min at 0 °C. HHP treatment showed better inactivation effect of HuNoV on blueberries than on strawberry quarters and raspberries. HuNoV GI.1 strain was more resistant to HHP treatment than HuNoV GII.4 strain under different temperatures and environment. The physical properties and sensory qualities of HHP-treated and untreated blueberries and the three types of berry purees were evaluated. Color, pH and viscosity of blueberries and three berry purees showed no or slight changes after HHP treatment. Sensory evaluation demonstrated that HHP treatment of 550 MPa for 2 min at 0 °C did not significantly reduced the sensory qualities of three berry purees. The results demonstrated that the HHP treatment of 550 MPa for 2 min at 0 °C could be a potential nonthermal intervention for HuNoV in berry purees without adversely affecting their sensory qualities and physical properties.