Review: Norovirus prevalence in Belgian, Canadian and French fresh produce: A threat to human health?

Improving the Detection and Understanding of Infectious Human Norovirus in Food and Water Matrices: A Review of Methods and Emerging Models

Human norovirus (HuNoV) is a leading global cause of viral gastroenteritis, contributing to numerous outbreaks and illnesses annually. However, conventional cell culture systems cannot support the cultivation of infectious HuNoV, making its detection and study in food and water matrices particularly challenging. Recent advancements in HuNoV research, including the emergence of models such as human intestinal enteroids (HIEs) and zebrafish larvae/embryo, have significantly enhanced our understanding of HuNoV pathogenesis. This review provides an overview of current methods employed for HuNoV detection in food and water, along with their associated limitations. Furthermore, it explores the potential applications of the HIE and zebrafish larvae/embryo models in detecting infectious HuNoV within food and water matrices. Finally, this review also highlights the need for further optimization and exploration of these models and detection methods to improve our understanding of HuNoV and its presence in different matrices, ultimately contributing to improved intervention strategies and public health outcomes.

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.

Evaluation of crAssphages as a potential marker of human viral contamination in environmental water and fresh leafy greens

CrAssphages are human gut bacteriophages with potential use as an indicator of human fecal contamination in water and other environmental systems. We determined the prevalence and abundance of crAssphages in water, food, and fecal samples and compared these estimates with the prevalence of norovirus. Samples were tested using two crAssphage-specific qPCR assays (CPQ056 and TN201-203) and for norovirus using TaqMan realtime RT-PCR. CrAssphage was detected in 40% of human fecal specimens, 61% of irrigation water samples, 58.5% of stream water samples, and 68.5% of fresh leafy greens samples. Interestingly, across all sample categories, crAssphage concentrations were 2-3 log10 higher than norovirus concentrations. The correlation of detection of crAssphage and norovirus was significant for the irrigation water samples (r = 0.74, p = 7.4e-06). Sequences obtained from crAssphage positive samples from human fecal and stream water samples phylogenetically clustered with genotype I crAssphages, whereas sequences derived from irrigation water samples clustered differently from other genotypes. Our data show that crAssphages were prevalent in norovirus-positive water samples and in fresh leafy green samples, there was a strong correlation between the presence of crAssphage and norovirus. CrAssphage genomic copies were consistently higher than norovirus copies in all sample types. Overall, our findings suggest that crAssphages could be used as reliable indicators to monitor fecal-borne virus contamination within the food safety chain.

Application of combined treatment of peracetic acid and ultraviolet-C for inactivating pathogens in water and on surface of apples

In this study, a combined treatment of peracetic acid (PAA) and 280 nm Ultraviolet-C (UVC) - Light emitting diode (LED) was applied for inactivating foodborne pathogens in water and apples. The combined treatment of PAA (50 ppm) and UVC-LED showed synergistic inactivation effects against Escherichia coli O157:H7 and Listeria monocytogenes in water. In mechanism analysis, PAA/UVC-LED treatment induced more lipid peroxidation, intracellular ROS, membrane, and DNA damage than a single treatment. Among them, membrane damage was the main synergistic inactivation mechanism of combination treatment. Cell rupture and shrink of both pathogens after PAA/UVC-LED treatment were also identified through scanning electron microscope (SEM) analysis. To examine inactivation of pathogens on the surface of apples by PAA, UVC-LED, and their combined treatment, a washing system (WS) was developed and used. Through applying the WS, PAA/UVC-LED treatment effectively inactivated two pathogens in washing solution and on the surface of apples below the detection limit (3.30 log CFU/2000 mL and 2.0 log CFU/apple) within 5 min. In addition, there was no significant difference in color or firmness of apples after PAA/UVC-LED treatment (p > 0.05).

Simulation of contamination and elimination of Escherichia coli, Listeria monocytogenes, and Murine norovirus 1 (MNV-1) from the washing process when handling of potatoes

Root vegetables, which are in close contact with soil, are particularly vulnerable to soil contamination or decay as they can be contaminated from multiple sources, including primary production and processing. This study investigated effective washing conditions to reduce the microbial contamination of potatoes by using soaking and shaking in the washing process. The reduction of Escherichia coli, Listeria monocytogenes, and Murine norovirus 1 (MNV-1) in four washing processes (soaking only, shaking only, combined soaking-shaking I, and combined soaking-shaking I-shaking II) were compared. The numbers of E. coli and L. monocytogenes decreased by 0.55 and 0.49 log CFU/g after shaking only, 1.96 and 1.80 log CFU/g after soaking, 2.07 and 1.67 log CFU/g after soaking-shaking I, and 2.42 and 1.90 log CFU/g after soaking-shaking I-shaking II, respectively. The combined process reduced the microbial contamination more efficiently than shaking only. The reduction of E. coli in the washing process was higher than that of L. monocytogenes by approximately 0.5 logs. MNV-1 showed a reduction in the soaking and shaking steps by 1.34 and 1.98 log GC/100 g, with no significant reduction observed after the combination process. A combined process of soaking-shaking I-shaking II was effective to eliminate E. coli, L. monocytogenes, and MNV-1 from potatoes during the handling and washing process.

Prevalence of Foodborne Viruses in Berries Harvested in Canada

It is known that the transmission of different foodborne viruses can occur either via discharge of contaminated water close to the production environment or via close contact with animal feces. Cranberries are intimately associated with water throughout their production cycle, and blueberries grow close to the ground which could lead to contact with wildlife. The aim of this study was to evaluate the prevalence of human norovirus (HuNoV GI and GII), hepatitis A virus (HAV) and hepatitis E virus (HEV) in two berries produced commercially in Canada. The detection of HuNoV and HAV on RTE cranberries and of HEV on wild blueberries was evaluated using the ISO method 15216-1:2017. Only 3 of 234 cranberry samples tested positive for HuNoV GI (3.6, 7.4, 5.3 genome copies/g, respectively) and all were negative for HuNoV GII and HAV. PMA pre-treatment and sequencing confirmed the absence of potential intact HuNoV GI particles on cranberries. None of the 150 blueberry samples tested positive for HEV. Overall, the prevalence of foodborne viruses in RTE cranberries and wild blueberries harvested in Canada is low, making these products relatively safe for consumers.

Recent trends and developments of PCR-based methods for the detection of food-borne Salmonella bacteria and Norovirus

In recent years, rapid detection methods such as polymerase chain reaction (PCR) and quantitative real-time PCR (qPCR) have been continuously developed to improve the detection of food-borne pathogens in food samples. The recent developments of PCR and qPCR in the detection and identification of these food-borne pathogens are described and elaborated throughout this review. Specifically, further developments and improvements of qPCR are discussed in detecting Salmonella and norovirus. Promising advances in these molecular detection methods have been widely used to prevent human food-borne illnesses and death caused by the food-borne pathogens. In addition, this review presents the limitations and challenges of the detection methods which include conventional culture method and conventional PCR method in detecting Salmonella and norovirus. Furthermore, several advances of qPCR such as viability PCR (vPCR) and digital PCR (dPCR) have been discussed in the detection of Salmonella and norovirus. Good practice of analysis of the food-borne pathogens and other contaminants in the food industry as well as the advancement of molecular detection methods will help improve and ensure food safety and food quality.

Evaluation of water-assisted UV-C light and its additive effect with peracetic acid for the inactivation of Listeria monocytogenes, Salmonella enterica and murine norovirus on whole and fresh-cut strawberries during shelf-life

BACKGROUND

The purpose of the present study was to examine the inactivation of Salmonella enterica (50 μL; 10⁹  CFU g^-1 ), Listeria monocytogenes (50 μL; 10⁹  CFU g^-1 ), and murine norovirus (MNV-1; 50 μL; 10⁷ 50% tissue culture infectious dose (TCID₅₀ ) mL^-1 ) on whole and fresh-cut strawberries after 2 min disinfection treatments (water (H₂ O), chlorine 200 mg L^-1 (NaClO), water-assisted ultraviolet-C (UV-C) (WUV), and the combination WUV and 40 mg L^-1 of PA (WUV + PA)) in a water tank (15 L) equipped with 4 UV-C lamps (17.2 W each), and after 7 days of cold storage (4 and 10 °C). For MNV-1, dry UV-C treatment (DUV) was also tested. For all UV-C treatments, an irradiation dose of 1.3 kJ m^-2 was used.

RESULTS

When strawberries were washed with WUV, L. monocytogenes and S. enterica were reduced by 2.8 and 2.2 log CFU g^-1 , respectively. The addition of 40 mg L^-1 of PA to WUV (WUV + PA) increased the reduction range of L. monocytogenes and S. enterica by 1.9 and 0.8 log, respectively. Regarding the wash water, no pathogens were recovered after the WUV + PA treatment (detection limit 50 CFU mL^-1 ). Depending on storage conditions (7 days at 4 or 10 °C), reductions observed were 0.5 to 2.0 log for S. enterica and 0.5 to 3.0 log for L. monocytogenes. The reductions in MNV-1 titer after disinfection treatments ranged from 1.3 to 1.7 log. No significant differences between storage conditions were observed for MNV-1: titers did not decline or were reduced up to 0.3 log after 7 days of cold storage.

CONCLUSION

The three-way action for disinfecting strawberries by UV-C irradiation and PA, plus the physical removal of the microorganisms by agitated water, are effective against foodborne pathogens on strawberries and water wash. During storage, WUV had a larger impact on the inactivation kinetics of S. enterica. Storage had little impact on MNV-1 inactivation. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Detection of Norovirus and Hepatitis A Virus in Strawberry and Green Leafy Vegetables by Using RT-qPCR in Egypt

There is an upward trend of consumption of organic fresh vegetables due to consumer demand for healthy foods without chemical additives. On the other hand, the number of food borne outbreaks associated with contaminated fresh produce has raised, being human norovirus genogroup I (GI), GII and hepatitis A virus (HAV) the most commonly reported causative agents. This study aimed to detect the presence of these viruses in green leafy vegetables (watercress, leek, coriander, and parsley) and strawberry using quantitative reverse transcription polymerase chain reaction (RT-qPCR). Samples were collected from the Egyptian regions of Kalubia, Giza, and Mansoura. Overall HAV average occurrence in fresh strawberry was 48% with a mean concentration of 6.1 × 10³ GC/g; Also NoV GI overall average occurrence was 25% with a mean concentration of 9.7 × 10² genome copies (GC)/g, while NoV GII was 40% with a mean concentration of 2.4 × 10³ GC/g. For strawberry collected directly from Kalubia farms, neither HAV nor HNoV GI & GII were detected. In green leafy vegetable samples, the occurrence of HAV was 31.2% with a mean concentration of 9.2 × 10⁴ GC/g, while occurrence of NoV GI and NoV GII were 20% and 30% with a mean concentrations of 1.1 × 10⁴ and 2.03 × 10³ GC/g, respectively. In conclusion, the importance of a virus surveillance program for soft fruits and fresh vegetables is highlighted by the outcomes of this study. Our findings should help with the management and control of microbial concerns in fresh foods, reducing the danger of consuming contaminated foods.

Occurrence of Norovirus, Rotavirus, Hepatitis a Virus, and Enterovirus in Berries in Argentina

Berries have been implicated as the probable vehicle of infection in multiple outbreaks of norovirus and hepatitis A virus (HAV). These foods often receive minimal or no processing and may be exposed to virus contamination at each stage of production. In an increasingly globalized world, berries have a wide distribution and can give rise to the spread of diseases in distant parts of the world. With the aim of describing the virological quality of the berries cultivated in Argentina, a total of 184 soft fruits of different varieties (strawberries, blueberries, raspberries, blackberries, currants, pomegranate arils, cassis, and elder) were collected during the periods 2016-2018 and 2020. Viral particles were eluted and concentrated by polyethylene glycol precipitation according to ISO 15216-2:2019 guidelines. Genome detection of norovirus (NoV) genogroups I (GI) and II (GII), HAV, rotavirus, and enterovirus was performed by real-time RT-PCR with TaqMan probes. Positive samples were amplified by conventional RT-PCR and the amplicons were purified and sequenced in both directions. Phylogenetic analysis was performed using the Neighbor-Joining method based on the evolutionary model Kimura-2-parameters. NoV GII.6 was detected in 1/184 (0.5%) of the soft fruits, corresponding to a raspberry sample obtained during the fall of 2017. No presence of other human enteric viruses was found in the other berries analyzed. The collected data are the first in Argentina in relation to the prevalence of enteric viruses in berries and is useful as reference data for a risk assessment of soft fruits as vehicles of foodborne pathogenic viruses.

Quantitative RT-PCR detection of human noroviruses and hepatitis A virus in fresh produce and surface water used for irrigation in the Mansoura and Giza regions, Egypt

Surface water used as an irrigation source can be a significant source of viral contamination of fresh produce. Enteric viruses such as hepatitis A virus (HAV) and human norovirus genogroup I (HNoV GI) and genogroup II (HNoV GII) can be transmitted to human via fresh produce when irrigated with contaminated water or when prepared by infected food handlers. In the current study, we investigated the presence of HAV, HNoV GI and GII in fresh produce and surface water used in cultivation of this produce using real-time PCR. Samples were collected from six different points in the Mansoura and Giza regions, Egypt. Our analysis showed that at least one virus was found in 41.6% (30/72) of surface water samples and 27% (13/48) of fresh produce samples. HAV (23/72) with a mean viral concentration = 4 × 10⁶ genome copies/litre (GC/L) was the most frequently identified virus in surface water samples, followed by human norovirus genogroup II (HNoV GII) (15/72, with a mean concentration = 1.2 × 10⁶ GC/L, and human noroviruses genogroup I (HNoV GI) (12/72, with a mean concentration = 1.4 × 10⁴ GC/L). Additionally, HAV (10/48) with a mean concentration = 5.2 × 10⁵ genome copies/gram (GC/g) was also the most frequently detected virus in the fresh produce samples, followed by HNoV GII (8/48, with a mean concentration = 1.7 × 10⁴ GC/g); meanwhile, HNoV GI (6/48) was less detected virus with a mean concentration = 3 × 10³ GC/g. This work suggests a wide prevalence of human enteric viruses in surface waters and fresh produce, which is of concern when the fresh produce is eaten raw. Thus, additional monitoring for viral pathogens in irrigation water and food is needed to increase the awareness of this issue to rise the control measures to reduce illness from contaminated food.

Detection and Sequencing of Multiple Human Norovirus Genotypes from Imported Frozen Raspberries Linked to Outbreaks in the Province of Quebec, Canada, in 2017

Human noroviruses are among the main causes of acute gastroenteritis worldwide. Frozen raspberries have been linked to several norovirus food-related outbreaks. However, the extraction of norovirus RNA from frozen raspberries remains challenging. Recovery yields are low and PCR inhibitors limit the sensitivity of the detection methodologies. In 2017, 724 people from various regions of the Province of Quebec, Canada, were infected by noroviruses and the outbreak investigation pointed to frozen raspberries as a putative source. A new magnetic silica bead approach was used for the extraction of viruses from different outbreak samples. The RNA extracts were tested by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and five samples were confirmed positive for norovirus by RT-qPCR amplicon sequencing. A multiplex long-range two-step RT-PCR approach was developed to amplify norovirus ORF2 and ORF3 capsid genes from the positive frozen raspberry RNA extracts and other sequencing strategies were also explored. These capsid genes were sequenced by Next-Generation Sequencing. Phylogenetic analyses confirmed the presence of multiple genotypes (GI.3, GI.6, and GII.17) and intra-genotype variants in some of the frozen raspberry samples. Variants of genotype GI.3 and GI.6 had 100% homology with sequences from patient samples. Similar strains were also reported in previous outbreaks. Confirmation approaches based on sequencing the norovirus capsid genes using Next-Generation Sequencing can be applied at trace level contaminations and could be useful to assess risk and assist in source tracking.

Optimizing Human Intestinal Enteroids for Environmental Monitoring of Human Norovirus

Human noroviruses (HuNoV) are the leading cause of gastrointestinal illness and environmental monitoring is crucial to prevent HuNoV outbreaks. The recent development of a HuNoV cell culture assay in human intestinal enteroids (HIEs) has enabled detection of infectious HuNoV. However, this complex approach requires adaptation of HIEs to facilitate HuNoV replication from environmental matrixes. Integrating data from 200 experiments, we examined six variables: HIE age, HIE basement membrane compounds (BMC), HuNoV inoculum processing, HuNoV inoculum volume, treatment of data below limit of detection (LOD), and cutoff criteria for determining positive HuNoV growth. We infected HIEs with HuNoV GII.4 Sydney positive stool and determined 1.4 × 103 genome equivalents per HIE well were required for HuNoV replication. HIE age had minimal effect on assay outcomes. LOD replacement and cutoff affected data interpretation, with lower values resulting in higher estimated HuNoV detection. Higher inoculum volumes lead to minimal decreases in HuNoV growth, with an optimal volume of 250uL facilitating capture of low concentrations of HuNoVs present in environmental isolates. Processing of HuNoV inoculum is valuable for disinfection studies and concentrating samples but is not necessary for all HIE applications. This work enhances the HuNoV HIE cell culture approach for environmental monitoring. Future HIE research should report cell age as days of growth and should clearly describe BMC choice, LOD handling, and positive cutoff.

Assessment of the Impact on Human Health of the Presence of Norovirus in Bivalve Molluscs: What Data Do We Miss?

In the latest One Health ECDC EFSA technical report, Norovirus in fish and fishery products have been listed as the agent/food pair causing the highest number of strong-evidence outbreaks in the EU in 2019. This review aims to identify data gaps that must be filled in order to increase knowledge on Norovirus in bivalve molluscs, perform a risk assessment and rank the key mitigation strategies for this biological hazard, which is relevant to public health. Virologic determinations are not included in any of the food safety and process hygiene microbiologic criteria reflected in the current European regulations. In addition, the Escherichia coli-based indices of acceptable faecal contamination for primary production, as well as the food safety criteria, do not appear sufficient to indicate the extent of Norovirus contamination. The qualitative risk assessment data collected in this review suggests that bivalve molluscs present a high risk to human health for Norovirus only when consumed raw or when insufficiently cooked. On the contrary, the risk can be considered negligible when they are cooked at a high temperature, while information is still scarce for non-thermal treatments.

NGS Techniques Reveal a High Diversity of RNA Viral Pathogens and Papillomaviruses in Fresh Produce and Irrigation Water

Fresh fruits and vegetables are susceptible to microbial contamination at every stage of the food production chain, and as a potential source of pathogens, irrigation water quality is a critical factor. Next-generation sequencing (NGS) techniques have been flourishing and expanding to a wide variety of fields. However, their application in food safety remains insufficiently explored, and their sensitivity requires improvement. In this study, quantitative polymerase chain reaction (qPCR) assays showed low but frequent contamination of common circulating viral pathogens, which were found in 46.9% of samples of fresh produce: 6/12 lettuce samples, 4/12 strawberries samples, and 5/8 parsley samples. Furthermore, the application of two different NGS approaches, target enrichment sequencing (TES) for detecting viruses that infect vertebrates and amplicon deep sequencing (ADS), revealed a high diversity of viral pathogens, especially Norovirus (NoV) and Human Papillomavirus (HPV), in fresh produce and irrigation water. All NoV and HPV types found in fresh fruit and vegetable samples were also detected in irrigation water sources, indicating that these viruses are common circulating pathogens in the population and that irrigation water may be the most probable source of viral pathogens in food samples.

In the landscape of SARS-CoV-2 and fresh fruits and vegetables: The fake and hidden transmission risks

From the first notification reporting to the WHO a cluster of coronavirus in Wuhan City (China), over 114 million cases of SARS-CoV-2 have been confirmed, with more than 2,530,000 deaths, and over 400,000 new cases and 10,000 deaths daily. Numerous viruses are susceptible to contaminate crops during growth, harvesting, handling, marketing and minimally processing, and these steps share one common factor which is human. Different studies showed that viruses might persist on different crops for periods of 2 to 14 days under different conditions such as refrigeration, household and freezing. Little is known on SARS-CoV-2, but preliminary studies showed that this virus might survive 24 hr on cardboard and 72 hr on plastic, materials used in fruits and vegetables packaging. Based on preliminary data, there is no evidence of food or food packaging being associated with transmission of SARS-CoV-2. Certainly, to date there is no scientific evidence that SARS-CoV-2 might be transmitted by a contact with, or the ingestion of contaminated fresh or minimally processed fruits and vegetables. However, this risk even though being considered improbable, it cannot be "completely and definitely" discarded or ignored, particularly where the virus is spreading in the word. Some agencies indicated that in case some commodities and handlers are contaminated among the multiple people involved from the farm to the table, a cross-contamination may occur, and the risk of the contamination of food, food contact materials, and packaging from infected but asymptomatic workers should not be discarded even though considered "Very Low = meaning very rare but cannot be excluded."

Investigating awareness, fear and control associated with norovirus and other pathogens and pollutants using best-worst scaling

Pollutants found in the water and air environment represent an ever-growing threat to human health. Contact with some air-, water- and foodborne pathogens (e.g. norovirus) results in gastrointestinal diseases and outbreaks. For future risk mitigation, we aimed to measure people's awareness of waterborne and foodborne norovirus relative to other environment-associated pollutants (e.g. pesticides, bioaerosols, antibiotic resistant bacteria) and well-known risks (e.g. diabetes, dementia, terrorist attack). We used an online survey, which included a best-worst scaling component to elicit personal levels of control and fear prompted by norovirus relative to 15 other risks. There was a negative correlation between levels of fear vs. control for all 16 measured risks. Perceived infection control levels were higher amongst women compared to men and correlated with age and the level of qualification in both groups. Participants who had sought advice regarding the symptoms caused by norovirus appeared to have more control over the risks. Norovirus is associated with high levels of fear, however, the levels of control over it is low compared to other foodborne illnesses, e.g. Salmonella. Addressing this deficit in the public's understanding of how to control exposure to the pathogen in an important health need.

SARS-CoV-2 transmission via aquatic food animal species or their products: A review

Outbreaks of COVID-19 (coronavirus disease 2019) have been reported in workers in fish farms and fish processing plants arising from person-to-person transmission, raising concerns about aquatic animal food products' safety. A better understanding of such incidents is important for the aquaculture industry's sustainability, particularly with the global trade in fresh and frozen aquatic animal food products where contaminating virus could survive for some time. Despite a plethora of COVID-19-related scientific publications, there is a lack of reports on the risk of contact with aquatic food animal species or their products. This review aimed to examine the potential for Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) contamination and the potential transmission via aquatic food animals or their products and wastewater effluents. The extracellular viability of SARS-CoV-2 and how the virus is spread are reviewed, supporting the understanding that contaminated cold-chain food sources may introduce SAR-CoV-2 via food imports although the virus is unlikely to infect humans through consumption of aquatic food animals or their products or drinking water; i.e., SARS-CoV-2 is not a foodborne virus and should not be managed as such but instead through strong, multifaceted public health interventions including physical distancing, rapid contact tracing, and testing, enhanced hand and respiratory hygiene, frequent disinfection of high-touch surfaces, isolation of infected workers and their contacts, as well as enhanced screening protocols for international seafood trade.

Occurrence of Human Enteric Viruses in Water Sources and Shellfish: A Focus on Africa

Enteric viruses are a diverse group of human pathogens which are primarily transmitted by the faecal-oral route and are a major cause of non-bacterial diarrhoeal disease in both developed and developing countries. Because they are shed in high numbers by infected individuals and can persist for a long time in the environment, they pose a serious threat to human health globally. Enteric viruses end up in the environment mainly through discharge or leakage of raw or inadequately treated sewage into water sources such as springs, rivers, dams, or marine estuaries. Human exposure then follows when contaminated water is used for drinking, cooking, or recreation and, importantly, when filter-feeding bivalve shellfish are consumed. The human health hazard posed by enteric viruses is particularly serious in Africa where rapid urbanisation in a relatively short period of time has led to the expansion of informal settlements with poor sanitation and failing or non-existent wastewater treatment infrastructure, and where rural communities with limited or no access to municipal water are dependent on nearby open water sources for their subsistence. The role of sewage-contaminated water and bivalve shellfish as vehicles for transmission of enteric viruses is well documented but, to our knowledge, has not been comprehensively reviewed in the African context. Here we provide an overview of enteric viruses and then review the growing body of research where these viruses have been detected in association with sewage-contaminated water or food in several African countries. These studies highlight the need for more research into the prevalence, molecular epidemiology and circulation of these viruses in Africa, as well as for development and application of innovative wastewater treatment approaches to reduce environmental pollution and its impact on human health on the continent.

Molecular Detection of Norwalk Virus in Carp Fish and Shrimp Ponds in Khuzestan Province, Iran by RT-PCR Method

Background: Norwalk virus is one of the most common causes of viral gastroenteritis. The aquatic products are potential sources of contamination with this virus. Objectives: The main objective of the study was to investigate the presence of the Norwalk virus in different aquatic animals in Khuzestan provinces, Iran. Materials and Methods: A total of 40 pieces of fish (silver carp, common carp, big head, and grass carp species) and 10 pieces of shrimps were caught from ponds, and the samples were transferred to the laboratory in ice bags. After the separation of the intestine, the content of the intestine was extracted using two sterile filters. Then, the supernatant was used for reverse transcription polymerase chain reaction (RT-PCR) using Calicivirus-specific primers (p289/ p290). Then, Norwalk virus-specific primers (NVp36/NVp35) were detected in Calicivirus positive samples. Results: The results showed 8% (4 samples) and 6% (3 samples) of the samples were infected with Calicivirus (p289/p290 genes) and Norwalk virus (NVp36/NVp35 genes), respectively. Calicivirus positive samples included 2 common carp, 1 silver carp, and 1 shrimp. Norwalk virus-positive samples included 2 common carp and 1 shrimp. In other words, the highest prevalence of virus was observed in aquatic fish feeding from the bottom of the pool. Due to the fact that this species is bred with other species and considering that this virus lives in the gastrointestinal tract, the ingestion of feces of other infected organisms can lead to the increase of this virus in the digestive system of carp. Conclusion: Therefore, due to the importance of Norwalk as a zoonotic agent and the possibility of human infection through consumption of aquatic products, preventive measures such as not using animal manure for fertilization and preventing the growth of phytoplankton in aquaculture ponds and cooking meat properly are suggested.

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.

Transmission routes of rare seasonal diseases: the case of norovirus infections

Norovirus (NoV) is the most commonly recognized cause of acute gastroenteritis, with over a million cases globally per year. While usually self-limiting, NoV poses a substantial economic burden because it is highly contagious and there are multiple transmission routes. Infection occurs through inhalation of vomitus; faecal-oral spread; and food, water and environmental contamination. While the incidence of the disease is predictably seasonal, much less is known about the relative contribution of the various exposure pathways in causing disease. Additionally, asymptomatic excretion and viral shedding make forecasting disease burden difficult. We develop a novel stochastic dynamic network model to investigate the contributions of different transmission pathways in multiple coupled social networks representing schools, hospitals, care-homes and family households in a community setting. We analyse how the networks impact on transmission. We used ward-level demographic data from Northumberland, UK to create a simulation cohort. We compared the results with extant data on NoV cases from the IID2 study. Connectivity across the simulated cohort was high. Cases of NoV showed marked seasonality, peaking in early winter and declining through the summer. For the first time, we show that fomites and food appear to be the most important exposure routes in determining the population burden of disease. This article is part of the theme issue 'Modelling infectious disease outbreaks in humans, animals and plants: epidemic forecasting and control'. This theme issue is linked with the earlier issue 'Modelling infectious disease outbreaks in humans, animals and plants: approaches and important themes'.

Survival of Human Norovirus Surrogates in Water upon Exposure to Thermal and Non-Thermal Antiviral Treatments

Human noroviruses are the leading cause of foodborne gastroenteritis worldwide and disease outbreaks have been linked to contaminated surface waters as well as to produce consumption. Noroviruses are extremely stable in water and their presence is being detected with increasing frequency, yet there are no viable methods for reducing norovirus contamination in environmental water. Despite this, there is little knowledge regarding the physical and chemical factors that influence the environmental persistence of this pathogen. This study evaluated the impact of common chemical and physical properties of surface water on the stability of murine norovirus and examined the effect of food-safe chitosan microparticles on infectivity of two human norovirus surrogates. While chemical additives had a minor impact on virus survival, chitosan microparticles significantly reduced infectious titers of both murine norovirus and MS2 bacteriophage.

Occurrence of selected viral and bacterial pathogens and microbiological quality of fresh and frozen strawberries sold in Spain

Strawberry production and exports have been increasing in Spain in recent decades. However, little information is available about their microbiological quality. Due to the growing concern about the microbial safety of these fruits, the objective of this investigation was to study the microbiological quality and the prevalence of the main foodborne pathogens on strawberries sold in Spain. Fresh (n = 152) and frozen (n = 31) samples were obtained from marketplaces and fields in 2017 and 2018. The samples were assayed for total aerobic mesophilic microorganisms (TAM), moulds and yeasts (M&Y), total coliforms (TC), Escherichia coli, Salmonella spp., Listeria monocytogenes as well as Norovirus (NoV) GI and GII. The microbiological counts ranged from <1.70 (detection limit, dl) - 5.89 log₁₀ CFU/g (mean 3.78 log₁₀ CFU/g) for TAM; 2.10-5.86 log₁₀ CFU/g (mean 3.80 log₁₀ CFU/g) for M&Y; and <0.70 (dl) - 4.91 log₁₀ CFU/g (mean 2.15 log₁₀ CFU/g) for TC in fresh strawberries. In frozen strawberries, the counts were <1.70 (dl) - 3.66 log₁₀ CFU/g (mean 2.30 log₁₀ CFU/g) for TAM; <1.70 (dl) - 2.76 log₁₀ CFU/g (mean 1.82 log₁₀ CFU/g) for M&Y; and <0.70(dl) - 1.74 log₁₀ CFU/g (mean 0.77 log₁₀ CFU/g) for TC. All the samples in this study tested negative for Salmonella spp., L. monocytogenes. E. coli and NoV GI and GII genome. A global overview of all the data was executed using Principal Component Analysis (PCA), and the results showed that the scores and loadings according to principal components 1 (PC1) and 2 (PC2) accounted for 75.9% of the total variance, allowing a distinction between fresh and frozen samples. The presence of moulds was significantly higher in the supermarket samples whereas the presence of total coliforms was significantly higher in the field samples (p < 0.05). Although pathogenic microorganisms were not found, preventative measures and prerequisites in the strawberry production chain must be considered in order to avoid possible foodborne diseases related to the microbiological quality of the fruit.

Co-contamination of food products from family farms in an environmental disaster area in Southeast Brazil with pathogenic bacteria and enteric viruses

In the present study, we evaluated the degree of contamination of fresh vegetables, cheeses and jellies from disaster area in Brazil with bacteria and enteric viruses. Food samples (n = 350) were tested for Escherichia coli, Salmonella spp., Listeria monocytogenes, Staphylococcus spp., and enteric viruses (rotavirus A (RVA), human adenovirus (HAdV), hepatitis A virus (HAV), and human norovirus (HNoV). E. coli was present in 56% of the samples, Salmonella spp. was present in 14% of the samples, L. monocytogenes and Staphylococcus spp. (coagulase-positive) were present in 36% of the samples. The enteric viruses RVA and HAdV were detected in cheeses and vegetables.

Effectiveness of Consumers Washing with Sanitizers to Reduce Human Norovirus on Mixed Salad

Human norovirus (HuNoV) is a foremost cause of domestically acquired foodborne acute gastroenteritis and outbreaks. Despite industrial efforts to control HuNoV contamination of foods, its prevalence in foodstuffs at retail is significant. HuNoV infections are often associated with the consumption of contaminated produce, including ready-to-eat (RTE) salads. Decontamination of produce by washing with disinfectants is a consumer habit which could significantly contribute to mitigate the risk of infection. The aim of our study was to measure the effectiveness of chemical sanitizers in inactivating genogroup I and II HuNoV strains on mixed salads using a propidium monoazide (PMAxx)-viability RTqPCR assay. Addition of sodium hypochlorite, peracetic acid, or chlorine dioxide significantly enhanced viral removal as compared with water alone. Peracetic acid provided the highest effectiveness, with log10 reductions on virus levels of 3.66 ± 0.40 and 3.33 ± 0.19 for genogroup I and II, respectively. Chlorine dioxide showed lower disinfection efficiency. Our results provide information useful to the food industry and final consumers for improving the microbiological safety of fresh products in relation to foodborne viruses.

Norovirus Detection at Oualidia Lagoon, a Moroccan Shellfish Harvesting Area, by Reverse Transcription PCR Analysis

Norovirus (NoV) is the leading cause of acute viral gastroenteritis outbreaks in the world. These outbreaks are frequently associated with bivalve shellfish consumption, particularly because these products are often eaten raw or only slightly cooked. In Morocco, regulations concerning the acceptable levels of enteric bacteria indicator organisms in these products have been put in place. However, these regulations do not take into account the risk of viral contamination, and many gastroenteritis outbreaks have been linked to the ingestion of bivalve shellfish from areas that comply with the current food safety criteria. The aim of this study was to investigate NoV presence in shellfish samples (n = 104) collected at four sites owcff Oualidia lagoon (Moroccan Atlantic coast) from November 2015 to February 2017. Samples were analysed using real-time RT-PCR in accordance with the ISO 15216-2 method. NoVs of the genogroup II were detected in 7% of samples that were all collected during the winter months. Moreover, 71% of NoV-positive samples were harvested at sites upstream of the lagoon. These results highlight the need of regularly monitoring viral contamination in bivalve shellfish to limit the risk of viral gastroenteritis outbreaks.

Prevalence of Norovirus in produce sold at retail in the United Kingdom

To acquire data on contamination with Norovirus in berry fruit and salad vegetables in the United Kingdom, one thousand one hundred and fifty two samples of fresh produce sold at retail in the UK were analysed for Norovirus. Of 568 samples of lettuce, 30 (5.3%) were Norovirus-positive. Most (24/30) lettuce samples which tested positive for Norovirus were grown in the UK and 19 of those 24 samples contained NoV GI. Seven/310 (2.3%) samples of fresh raspberries were Norovirus-positive. Most (6/7) of the positively-testing fresh raspberry samples were imported, but no predominance of a genogroup, or any seasonality, was observed. Ten/274 (3.6%) samples of frozen raspberries were Norovirus-positive. The country of origin of the positively-testing frozen raspberry samples was not identified in most (7/10) instances. The collected data add to the currently limited body of prevalence information on Norovirus in fresh produce, and indicate the need for implementation of effective food safety management of foodborne viruses.

Final Consumer Options to Control and Prevent Foodborne Norovirus Infections

Norovirus (NoV) causes about one-fifth of all cases of foodborne diseases and is a foremost cause of domestically acquired foodborne acute gastroenteritis and outbreaks. NoV infections are often associated with the consumption of contaminated fresh and ready-to-eat produce, fresh and frozen berries, raw/undercooked bivalve mollusks and products which become contaminated during handling. Despite many industrial efforts to control and prevent NoV contamination of foods, the prevalence of NoV in high-risk foodstuffs at retail is still significant. Although certain consumer behaviors may even increase the risk of virus transmission, interventions aiming at changing/implementing consumer habits may be considered as opportunities for risk mitigation. This review aims at providing an update on the progress made in characterizing the effect that consumer habits, which are most critical to prevent NoV transmission (food choice and hygiene, disinfection and cooking during food preparation), may have on reducing the risk of NoV infection. A better understanding of the options for NoV control and prevention may be translated into innovative educational, social or even technological tools targeting consumers with the objective of mitigating the risk of NoV transmission.

An outbreak of norovirus infection caused by ice cubes and a leaking air ventilation valve

A gastrointestinal outbreak was reported among 154 diners who attended a Christmas buffet on the 9 and 10 December 2016. A retrospective cohort study was undertaken. Faecal samples, water, ice and an air ventilation device were tested for indicators and routine pathogens. Altogether 26% (24/91) fulfilled the case definition of having typical viral gastrointestinal symptoms. Norovirus genogroup I was detected in faecal samples from three cases. One of these cases tested positive also for sapovirus and had a family member testing positive for both norovirus and sapovirus. A diner who drank water or drinks with ice cubes (risk ratios (RR) 6.5, 95% confidence intervals (CI) 1.5–113.0) or both (RR 8.2, 95% CI 1.7–145.5) had an increased risk in a dose-response manner. Ice cubes from three vending machines had high levels of heterotrophic bacteria. A faulty air ventilation valve in the space where the ice cube machine was located was considered a likely cause of this outbreak. Leaking air ventilation valves may represent a neglected route of transmission in viral gastrointestinal outbreaks.

Tracing of Selected Viral, Bacterial, and Parasitic Agents on Vegetables and Herbs Originating from Farms and Markets

Fresh vegetables and herbs are usually prepared and eaten raw without cooking or heating, which leads to a high risk of foodborne infection. The aim of the present study was to assess the contamination of raw vegetables, herbs, and the environment of food chains. Vegetable and herb samples originating both from the Czech Republic as well as from other countries were examined. The work was focused on the detection of commonly found, but also less frequently monitored foodborne pathogens, including viruses of the genus Norovirus (NoVs), hepatitis A virus (HAV), Listeria monocytogenes and Cronobacter spp. bacteria, and the parasites Cryptosporidium spp. and Giardia intestinalis. All samples were analyzed using individual RT-qPCR/qPCR assays; bacterial pathogens were also simultaneously detected using culture methods. The prevalence of the studied microorganisms in 623 samples ranged from 0.6% to 44.3% for individual pathogens. None of the samples were positive for the presence of HAV. Analysis of 157 environmental samples from 12 farms revealed the presence of NoVs in the environment of four farms. NoVs were detected in water samples as well as on the hands and gloves of workers. Escherichia coli was detected in all farms in the environmental samples and in eight farms in water samples. However, no sample of water exceeded the level of 100 CFU/mL for E. coli. None of the samples of water were positive for the presence of the studied parasites. Vegetables and herbs available from Czech markets and farms may pose a certain risk of foodborne disease, especially in the case of NoVs and parasites. PRACTICAL APPLICATION: This study provides valuable information on the microbiological quality of raw vegetables and herbs available from Czech markets and farms. Good hygienic practices aimed at reducing the incidence of pathogenic agents on fresh produce should not be neglected. Emphasis should be placed on the control of irrigation water, especially with respect to norovirus contamination. It is appropriate to combine culture methods and qPCR methods for the detection of bacterial agents.

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.

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.

Irrigating Lettuce with Wastewater Effluent: Does Disinfection with Chlorine Dioxide Inactivate Viruses?

Reclaimed water obtained from urban wastewater is currently being used as irrigation water in water-scarce regions in Spain. However, wastewater can contain enteric viruses that water reclamation treatment cannot remove or inactivate completely. In the present study, greenhouse-grown baby lettuce ( L.) was irrigated with secondary treatment effluent from a wastewater treatment plant untreated and treated using chlorine dioxide (ClO). The effect of ClO treatment on the physicochemical characteristics and the presence of enteric viruses in irrigation water and lettuce was assessed. The presence of human noroviruses genogroups I and II (NoV GI and NoV GII), and human astroviruses (HAstV), was analyzed by real-time polymerase chain reaction (RT-qPCR). Additionally, to check for the loss of infectivity induced by the disinfection treatment, positive samples were re-analyzed after pretreatment with the intercalating dye PMAxx before RNA extraction and RT-qPCR. There were no significant differences in the proportion of positive samples and the concentration of enteric viruses between treated and untreated reclaimed water without PMAxx pretreatment ( > 0.05). A significantly lower concentration of NoV GI was detected in ClO-treated water when samples were pretreated with PMAxx ( < 0.05), indicating that inactivation was due to the disinfection treatment. Laboratory-scale validation tests indicated the suitability of PMAxx-RT-qPCR for discrimination between potentially infectious and ClO-damaged viruses. Although the applied ClO treatment was not able to significantly reduce the enteric virus load of the secondary effluent from the wastewater treatment plant, none of the lettuce samples analyzed ( = 36) was positive for the presence of NoV or HAstV.

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.

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.