Feline Calicivirus, Murine Norovirus, Porcine Sapovirus, and Tulane Virus Survival on Postharvest Lettuce

Human Norovirus Surrogate Is Highly Stable in Berry Smoothies and under In Vitro Simulated Digestion

Human noroviruses are major causes of foodborne outbreaks linked to berries. The overall goal of this study was to investigate the persistence of a human norovirus surrogate, Tulane virus (TV), in berry smoothies and under simulated digestion through the gastrointestinal track. Two types of smoothies were prepared from blueberries and strawberries. Tulane virus was spiked into each smoothie and incubated either at 37 or 4 °C for 2, 60, and 120 min. Furthermore, the virus-spiked smoothies were subjected to sequential oral (2 min), gastric (10 and 60 min), and intestinal (15 and 120 min) digestion according to the standardized INFOGEST model. Quantification of infectious TV was carried out using the TCID50 assay. At 4 °C, in both berry smoothies, TV infectivity did not show significant changes throughout the 120 min period. At 37 °C, TV infectivity showed significant reduction (~0.5 log TCID50/mL) only in blueberry smoothies starting at 60 min. During the oral, gastric, and intestinal digestion phases, the mean log reduction in TV infectivity in blueberry did not exceed ~0.5 log, while infectious TV in strawberry smoothies under all phases was stable. Given the notable stability of infectious viruses in berry smoothies and the gastrointestinal tract, prevention of norovirus contamination of berries is paramount to reduce virus outbreaks linked to berries.

Common and Potential Emerging Foodborne Viruses: A Comprehensive Review

Human viruses and viruses from animals can cause illnesses in humans after the consumption of contaminated food or water. Contamination may occur during preparation by infected food handlers, during food production because of unsuitably controlled working conditions, or following the consumption of animal-based foods contaminated by a zoonotic virus. This review discussed the recent information available on the general and clinical characteristics of viruses, viral foodborne outbreaks and control strategies to prevent the viral contamination of food products and water. Viruses are responsible for the greatest number of illnesses from outbreaks caused by food, and risk assessment experts regard them as a high food safety priority. This concern is well founded, since a significant increase in viral foodborne outbreaks has occurred over the past 20 years. Norovirus, hepatitis A and E viruses, rotavirus, astrovirus, adenovirus, and sapovirus are the major common viruses associated with water or foodborne illness outbreaks. It is also suspected that many human viruses including Aichi virus, Nipah virus, tick-borne encephalitis virus, H5N1 avian influenza viruses, and coronaviruses (SARS-CoV-1, SARS-CoV-2 and MERS-CoV) also have the potential to be transmitted via food products. It is evident that the adoption of strict hygienic food processing measures from farm to table is required to prevent viruses from contaminating our food.

Use of Human Intestinal Enteroids for Recovery of Infectious Human Norovirus from Berries and Lettuce

Norovirus (NoV) is the leading cause of viral foodborne gastroenteritis globally. Currently, the gold standard for detecting NoV in clinical, food, and environmental samples is via molecular-based methods, primarily RT-PCR. Nevertheless, there is a great need for confirmatory assays that can determine the infectivity of viral particles recovered from contaminated matrices. The use of the human intestinal enteroids system (HIEs) has allowed for the expansion of norovirus replication, although it still suffers from limitations of strain preferences and the requirement of high titer stocks for infection. In this study, we wanted to explore the feasibility of using the HIEs to support the replication of NoV that had been recovered from representative food matrices that have been associated with foodborne illness. We first confirmed that HIEs can support the replication of several strains of NoV as measured by RT-qPCR. We subsequently chose two of those strains that reproducibly replicated, GII.4 and GII.6, to evaluate in a TCID50 assay and for future experiments. Infectious NoV could be recovered and quantified in the HIEs from lettuce, frozen raspberries, or frozen strawberries seeded with high titers of either of these strains. While many experimental challenges still remain to be overcome, the results of this study represent an important step toward the detection of infectious norovirus from representative produce items.

The Effect of Water Hardness and pH on the Efficacy of Peracetic Acid and Sodium Hypochlorite against SARS-CoV-2 on Food-Contact Surfaces

Sodium hypochlorite (NaOCl) and peracetic acid (PAA) are commonly used disinfectants with a maximum recommended concentration of 200 ppm for food-contact surfaces. The objectives of this study were to assess the effect of pH and water hardness on NaOCl and PAA efficacy against SARS-CoV-2 on stainless steel (SS). The two disinfectants were prepared at 200 ppm in water of hardness 150 or 300 ppm with the final pH adjusted to 5, 6, 7, or 8. Disinfectants were applied to virus-contaminated SS for one minute at room temperature following the ASTM E2197 standard assay. SARS-CoV-2 infectivity was quantified using TCID50 assay on Vero-E6 cells. In general, increasingly hard water decreased the efficacy of NaOCl while increasing the efficacy of PAA. Hard water at 300 ppm significantly increased virus log reduction with PAA at pH 8 by ~1.5 log. The maximum virus log reductions were observed at pH 5 for both NaOCl (~1.2 log) and PAA (~2 log) at 150 and 300 ppm hard water, respectively. In conclusion, PAA performed significantly better than NaOCl with harder water. However, both disinfectants at 200 ppm and one minute were not effective (≤3 log) against SARS-CoV-2 on contaminated food-contact surfaces, which may facilitate the role of these surfaces in virus transmission.

Soluble extracellular polymeric substance (SEPS) of histo-blood group antigen (HBGA) expressing bacterium Sphingobacterium sp. SC015 influences the survival and persistence of norovirus on lettuce

Foodborne norovirus (NoV) outbreaks linked to leafy greens are common due to a lack of efficient strategies to prevent NoV spread from contaminated surfaces. We previously found that Sphingobacterium sp. SC015 in lettuce phyllosphere expresses histo-blood group antigen (HBGA)-like substances in soluble extracellular polymeric substances (SEPS) that contribute to NoV adherence on lettuce. Here, we extracted SEPS from bacterium SC015 (SEPS-SC015), analyzed their chemical composition, and examined their roles in the survival and protection of NoV and surrogates [murine norovirus (MNV-1) and Tulane virus (TuV)] on lettuce. Presence of SEPS-SC015 significantly increased survival and persistence of human NoV (HuNoV), MNV-1, and TuV at days 7 and 14, compared with virus alone. HuNoV, TuV, and MNV-1 seeded with SEPS-SC015 were more resistant to heat (70 °C, 2 min) than these viruses alone. SEPS-SC015 also increased viral resistance to sodium hypochlorite inactivation by treatment with 30 and 300 ppm bleach at 26 °C for 10 min. However, SEPS-SC015 was not effective at protecting these viruses under UV inactivation. Binding of TuV to SC015 bacteria and SEPS-SC015, visualized using transmission electron microscopy, suggests that protection might be related to direct interaction between SEPS-SC015 and viral particles. This study provides important insights that will help inform strategies to improve food safety.

SARS-CoV-2 remains infectious for at least a month on artificially-contaminated frozen berries

The potential transmission of SARS-CoV-2 via food has been controversial since the beginning of the COVID-19 pandemic. To investigate these concerns, reliable detection methods and data on virus die-off rates in various foods are needed. Here, an FDA-standard method for the detection of enteric viruses’ RNA from soft fruits was modified for the recovery of infectious SARS-CoV-2. Then, the survival of SARS-CoV-2 on berries was investigated as well as the effectiveness of washing virus-contaminated berries with water. The modified method did not significantly reduced log infectivity titers of recovered viruses, but berries did. The detection limit of the method for infectious SARS-CoV-2 was ∼2.97 log TCID50/g of berries. On SARS-CoV-2-inoculated berries that were stored at 4 °C for 7 days, significant reductions in SARS-CoV-2 infectivity were observed over time. In contrast, on frozen berries, infectious SARS-CoV-2 was recovered for 28 days without significant reductions. Washing SARS-CoV-2-inoculated berries with water removed >90% of infectious viruses within 10 min; however, infectious viruses were detected in wash water. Therefore, on fresh berries infectious viruses are markedly inactivated over time and can be largely removed by washing with water. However, the prolonged survival of SARS-CoV-2 on frozen berries suggests that the virus can potentially spread through frozen fruits.

Natural Host-Environmental Media-Human: A New Potential Pathway of COVID-19 Outbreak

Identifying the first infected case (patient zero) is key in tracing the origin of a virus; however, doing so is extremely challenging. Patient zero for coronavirus disease 2019 (COVID-19) is likely to be permanently unknown. Here, we propose a new viral transmission route by focusing on the environmental media containing viruses of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or RaTG3-related bat-borne coronavirus (Bat-CoV), which we term the "environmental quasi-host." We reason that the environmental quasi-host is likely to be a key node in helping recognize the origin of SARS-CoV-2; thus, SARS-CoV-2 might be transmitted along the route of natural host-environmental media-human. Reflecting upon viral outbreaks in the history of humanity, we realize that many epidemic events are caused by direct contact between humans and environmental media containing infectious viruses. Indeed, contacts between humans and environmental quasi-hosts are greatly increasing as the space of human activity incrementally overlaps with animals' living spaces, due to the rapid development and population growth of human society. Moreover, viruses can survive for a long time in environmental media. Therefore, we propose a new potential mechanism to trace the origin of the COVID-19 outbreak.

The Basis of Peracetic Acid Inactivation Mechanisms for Rotavirus and Tulane Virus under Conditions Relevant for Vegetable Sanitation

We determined the disinfection efficacy and inactivation mechanisms of peracetic acid (PAA)-based sanitizer using pH values relevant for vegetable sanitation against rotavirus (RV) and Tulane virus (TV; a human norovirus surrogate). TV was significantly more resistant to PAA disinfection than RV: for a 2-log10 reduction of virus titer, RV required 1 mg/liter PAA for 3.5 min of exposure, while TV required 10 mg/liter PAA for 30 min. The higher resistance of TV can be explained, in part, by significantly more aggregation of TV in PAA solutions. The PAA mechanisms of virus inactivation were explored by quantifying (i) viral genome integrity and replication using reverse transcription-quantitative PCR (RT-qPCR) and (ii) virus-host receptor interactions using a cell-free binding assay with porcine gastric mucin conjugated with magnetic beads (PGM-MBs). We observed that PAA induced damage to both RV and TV genomes and also decreased virus-receptor interactions, with the latter suggesting that PAA damages viral proteins important for binding its host cell receptors. Importantly, the levels of genome-versus-protein damage induced by PAA were different for each virus. PAA inactivation correlated with higher levels of RV genome damage than of RV-receptor interactions. For PAA-treated TV, the opposite trends were observed. Thus, PAA inactivates each of these viruses via different molecular mechanisms. The findings presented here potentially contribute to the design of a robust sanitation strategy for RV and TV using PAA to prevent foodborne disease.IMPORTANCE In this study, we examined the inactivation mechanisms of peracetic acid (PAA), a sanitizer commonly used for postharvest vegetable washing, for two enteric viruses: Tulane virus (TV) as a human norovirus surrogate and rotavirus (RV). PAA disinfection mechanisms for RV were mainly due to genome damage. In contrast, PAA disinfection in TV was due to damage of the proteins important for binding to its host receptor. We also observed that PAA triggered aggregation of TV to a much greater extent than RV. These studies demonstrate that different viruses are inactivated via different PAA mechanisms. This information is important for designing an optimal sanitation practice for postharvest vegetable washing to minimize foodborne viral diseases.

Key characteristics of foods with an elevated risk for viral enteropathogen contamination

Viral enteropathogens are one of the leading causative agents of foodborne illnesses in both the United States and the European Union. While human noroviruses and hepatitis A virus cause the vast majority of outbreaks and illnesses, there are handful of human enteric viruses that contribute to sporadic outbreaks worldwide including astrovirus, sapovirus, rotavirus, enterovirus and Aichi virus. In addition, hepatitis E virus is increasingly being recognized as an emerging zoonotic threat within the food supply. This review aims to briefly describe the primary human enteric viruses of concern with respect to foodborne transmission. Next, we focus on the contamination and persistence of these viruses within three high-risk food commodities-leafy greens, soft red fruits and bivalve mollusks. As opposed to detailing the specific routes by which these foods can be contaminated with enteric viruses, we have chosen to focus on their persistence and specific interactions within the food itself. Therefore, the processes of attachment and internalization of the viruses in foods have been emphasized. Looking forward, the implications of these specific interactions of human enteric viruses with leafy greens, soft red fruits and bivalve mollusks are briefly considered within the context of future prevention and control strategies.

Tissue Distribution and Visualization of Internalized Human Norovirus in Leafy Greens

Lettuce has been implicated in human norovirus (HuNoV) outbreaks. The virus is stable on the leaf surface for at least 2 weeks; however, the dynamics of virus internalization have not been fully investigated. The purpose of this study was to assess the internalization and distribution of HuNoV and two surrogate viruses, porcine sapovirus (SaV) and Tulane virus (TV), in lettuce and spinach. Viral inoculations through the roots of seedlings and the petiole of leaves from mature plants were performed, and the viruses were tracked on days 1 and 6 post-root inoculation and at 16 h and 72 h post-petiole inoculation. Confocal microscopy was used to visualize root-internalized HuNoV. In both lettuce and spinach, (i) HuNoV was internalized into the roots and leaves at similar RNA titers, whereas surrogate viruses were more restricted to the roots, (ii) all three viruses were stable inside the roots and leaves for at least 6 days, and (iii) HuNoV disseminated similarly inside the central veins and leaf lamina, whereas surrogate viruses were more restricted to the central veins. Infectious TV, but not SaV, was detectable in all tissues, suggesting that TV has greater stability than SaV. HuNoV was visualized inside the roots' vascular bundle and the leaf mesophyll of both plants. In conclusion, using surrogate viruses may underestimate the level of HuNoV internalization into edible leaves. The internalization of HuNoV through roots and cut leaves and the dissemination into various spinach and lettuce tissues raise concerns of internal contamination through irrigation and/or wash water.IMPORTANCE Human noroviruses are the leading cause of foodborne outbreaks, with lettuce being implicated in the majority of outbreaks. The virus causes acute gastroenteritis in all age groups, with more severe symptoms in children, the elderly, and immunocompromised patients, contributing to over 200,000 deaths worldwide annually. The majority of deaths due to HuNoV occur in the developing world, where limited sanitation exists along with poor wastewater treatment facilities, resulting in the contamination of water resources that are often used for irrigation. Our study confirms the ability of lettuce and spinach to internalize HuNoV from contaminated water through the roots into the edible leaves. Since these leafy greens are consumed with minimal processing that targets only surface pathogens, the internalized HuNoV presents an added risk to consumers. Thus, preventive measures should be in place to limit the contamination of irrigation water. In addition, better processing technologies are needed to inactivate internalized viral pathogens.

New Proof-of-Concept in Viral Inactivation: Virucidal Efficacy of 405 nm Light Against Feline Calicivirus as a Model for Norovirus Decontamination

The requirement for novel decontamination technologies for use in hospitals is ever present. One such system uses 405 nm visible light to inactivate microorganisms via ROS-generated oxidative damage. Although effective for bacterial and fungal inactivation, little is known about the virucidal effects of 405 nm light. Norovirus (NoV) gastroenteritis outbreaks often occur in the clinical setting, and this study was designed to investigate potential inactivation effects of 405 nm light on the NoV surrogate, feline calicivirus (FCV). FCV was exposed to 405 nm light whilst suspended in minimal and organically-rich media to establish the virucidal efficacy and the effect biologically-relevant material may play in viral susceptibility. Antiviral activity was successfully demonstrated with a 4 Log₁₀ (99.99%) reduction in infectivity when suspended in minimal media evident after a dose of 2.8 kJ cm^-2. FCV exposed in artificial faeces, artificial saliva, blood plasma and other organically rich media exhibited an equivalent level of inactivation using between 50-85% less dose of the light, indicating enhanced inactivation when the virus is present in organically-rich biologically-relevant media. Further research in this area could aid in the development of 405 nm light technology for effective NoV decontamination within the hospital environment.

Antimicrobial effects of vinegar against norovirus and Escherichia coli in the traditional Korean vinegared green laver (Enteromorpha intestinalis) salad during refrigerated storage

In Korea, edible seaweeds are potentially regarded as high-risk foods with respect to enteric norovirus (NoV) and non-pathogenic generic Escherichia coli. This study investigated the antimicrobial effects of 5%, 10%, and 15% vinegar (6% acetic acid) on the survival of murine norovirus-1 (MNV-1), a human NoV surrogate, and E. coli, a fecal indicator in experimentally contaminated raw fresh green lavers (Enteromorpha intestinalis) during a 7-d storage period at 4°C. Both MNV-1 titers and E. coli counts significantly (p<0.05) decreased with stepwise increase in vinegar concentration and storage time, except in E. coli of the 0% vinegar-containing lavers; however, MNV-1 was more resistant to vinegar than E. coli. The overall average MNV-1 titers were significantly (p<0.05) higher in 0% vinegar-containing lavers (3.6log₁₀PFU/ml) than in 5-15% vinegar-containing lavers (3.3-3.1log₁₀PFU/ml) throughout the 7days of storage. A 1-log reduction in the MNV-1 titer was observed in 0% vinegar-containing laver samples after 5days of storage and 5-15% vinegar-containing laver samples after 3days of storage. The overall E. coli count was also significantly (p<0.05) decreased in the 15% (6.8log₁₀CFU/g) vinegar-containing lavers than in the 10% (7.3log₁₀CFU/g) and 5% (7.6log₁₀CFU/g) vinegar-containing lavers. A >1-log reduction in the E. coli count was observed in 10-15% vinegar-containing laver samples just after 1day of storage. A 2-log reduction in the E. coli count was also observed in 10-15% vinegar-containing laver samples after 5days of storage. Using the non-linear Weibull model, this study showed that the d_R-values (1-log reduction) of MNV-1 were 4.90days for 0%, 4.28days for 5%, 3.79days for 10%, and 2.88days for 15% vinegar-containing lavers, whereas those for E. coli were 1.12day for 5%, 1.03day for 10%, and 0.90day for 15% vinegar-containing lavers stored at 4°C. Vinegar with over the storage time can be used as an antimicrobial ingredient against NoV and E. coli in Korean conventional foods. Specifically, this study suggests that ~1day of storage is required for 1-log reduction in the E. coli count in the vinegar-containing (5-15%) lavers, whereas 3-5days of storage at 4°C is adequate for 1-log reduction in the MNV-1 count in the vinegar-containing and non-vinegar-containing lavers.

Comparison and optimization of detection methods for noroviruses in frozen strawberries containing different amounts of RT-PCR inhibitors

Frozen berries have been repeatedly identified as vehicles for norovirus (NoV) transmission causing large gastroenteritis outbreaks. However, virus detection in berries is often hampered by the presence of RT-PCR-inhibiting substances. Here, several virus extraction methods for subsequent real-time RT-PCR-based NoV-RNA detection in strawberries were compared and optimized. NoV recovery rates (RRs) between 0.21 ± 0.13% and 10.29 ± 6.03% were found when five different artificially contaminated strawberry batches were analyzed by the ISO/TS15216-2 method indicating the presence of different amounts of RT-PCR inhibitors. A comparison of five different virus extraction methods using artificially contaminated strawberries containing high amounts of RT-PCR inhibitors revealed the best NoV RRs for the ISO/TS15216 method. Further improvement of NoV RRs from 2.83 ± 2.92% to 15.28 ± 9.73% was achieved by the additional use of Sephacryl(®)-based columns for RNA purification. Testing of 22 frozen strawberry samples from a batch involved in a gastroenteritis outbreak resulted in 5 vs. 13 NoV GI-positive and in 9 vs. 20 NoV GII-positive samples using the original ISO/TS15216 method vs. the extended protocol, respectively. It can be concluded that the inclusion of an additional RNA purification step can increase NoV detection by the ISO/TS15216-2 method in frozen berries containing high amounts of RT-PCR inhibitors.

Abiotic Stress and Phyllosphere Bacteria Influence the Survival of Human Norovirus and Its Surrogates on Preharvest Leafy Greens

Foodborne outbreaks of human noroviruses (HuNoVs) are frequently associated with leafy greens. Because there is no effective method to eliminate HuNoV from postharvest leafy greens, understanding virus survival under preharvest conditions is crucial. The objective of this study was to evaluate the survival of HuNoV and its surrogate viruses, murine norovirus (MNV), porcine sapovirus (SaV), and Tulane virus (TV), on preharvest lettuce and spinach that were subjected to abiotic stress (physical damage, heat, or flood). We also examined the bacteria culturable from the phyllosphere in response to abiotic stress and in relation to viral persistence. Mature plants were subjected to stressors 2 days prior to inoculation of the viruses on leaves. We quantified the viral RNA, determined the infectivity of the surrogates, and performed bacterial counts on postinoculation days (PIDs) 0, 1, 7, and 14. For both plant types, time exerted significant effects on HuNoV, MNV, SaV, and TV RNA titers, with greater effects being seen for the surrogates. Infectious surrogate viruses were undetectable on PID 14. Only physical damage on PID 14 significantly enhanced HuNoV RNA persistence on lettuce, while the three stressors differentially enhanced the persistence of MNV and TV RNA. Bacterial counts were significantly affected by time and plant type but not by the stressors. However, bacterial counts correlated significantly with HuNoV RNA titers on spinach and with the presence of surrogate viruses on both plant types under various conditions. In conclusion, abiotic stressors and phyllosphere bacterial density may differentially influence the survival of HuNoV and its surrogates on lettuce and spinach, emphasizing the need for the use of preventive measures at the preharvest stage.