Use of Human Intestinal Enteroids to Evaluate Persistence of Infectious Human Norovirus in Seawater

The use of human intestinal enteroid cell cultures for detection of multiple gastroenteric viruses

Human norovirus (HuNoV) and human astrovirus (HAstV) are viral enteric pathogens and known causative agents of acute gastroenteritis. Identifying the presence of these viruses in environmental samples such as irrigation water, or foods exposed to virus contaminated water (e.g., shellfish, agricultural crops), remains an important goal in the field of food safety. Determining if a virus species present in a sample is infectious is complicated by the recalcitrance of many enteric virus species to grow in culture, and/or the lack of a common cell culture system(s). Human intestinal enteroids (HIEs) can support the replication of HuNoV and HAstV, and thus hold promise as a platform for demonstrating the replication of multiple enteric virus species within a single sample. The objective of this study was to determine if HIEs can support co-replication of two genetically distinct human enteric viruses, HAstV3 and HuNoV GII.4[P16]. In single virus infections, HuNoV GII.4[P16] RNA levels were highest at 48-72 hpi (6.3-9.1 x 106 genome copy equivalents [gce]/well) and HAstV3 RNA levels were highest at 24 hpi (3.4 ×108 gce/well). HAstV3-infected cells stained positive for viral capsid protein at 24 hpi and induced the synthesis of RNA and protein expression of interferon (IFN)-beta, -lambda 1 and 2/3, peaking at 24 hpi and 48 hpi respectively. HuNoV GII.4[P16] replication was negatively impacted by HAstV3 co-infection, but HAstV3 was unaffected by HuNoV. A reduction in HuNoV GII.4[P16] RNA during co-infections was observed at 72 hpi, with partial restoration achieved using neutralizing anti-IFN-antibodies. Human intestinal enteroids can support the co-infection and replication of HuNoVGII.4[P16] and HAstV3, even at more than 100-fold excess in one virus over the other, and compounds (e.g., anti-IFN antibodies) that interfere with HIE antiviral mechanism(s) can aid in maximizing HuNoV replication during co-infection.

Human intestinal enteroids for evaluating the persistence of infectious human norovirus in raw surface freshwater

Globally, human norovirus (HuNoV) is the leading cause of foodborne illnesses. Norovirus transmission to fresh produce can occur via several sources, including contaminated irrigation water. HuNoV RNA has been detected in freshwater resources, but knowledge about virus infectivity is limited due to a historical lack of a HuNoV cell culture. Recently, HuNoV was shown to replicate in human intestinal enteroids (HIE). The objective of this study was to use HIE to evaluate the persistence of infectious HuNoV in raw (i.e. biologically active) surface freshwater. The virus was spiked into freshwater microcosms sampled from three freshwater ponds and then incubated inside an environmental chamber at 20-15 °C and 50-80 % relative humidity (day-night) and 12 h photoperiod. The water was tested for infectious HuNoV, intact HuNoV capsids, indigenous bacteria, and other water quality parameters over a period of 2 weeks. The persistence of infectious HuNoV in the three freshwater microcosms ranged from ≤1 day to ≥7 days. Decay rates for RNA from intact HuNoV capsids ranged from 0.04 to 0.54/day, predicting a 4.2 to 57.5 days, respectively for 1 log reduction. The intact virus showed a significant negative and positive linear relationship with indigenous bacteria and dissolved oxygen, respectively. Using multiple logistic regression, HuNoV RNA >4.4 log genomic equivalent/ml (Cycle threshold values <32) predicted higher probability of detecting infectious HuNoV in contaminated raw freshwater using HIE. Overall, our results provide valuable insights for enhancing quantitative microbial risk assessment models for pre-harvest agricultural water to understand the public health risks associated with the detection of HuNoV RNA in freshwater.

Comparing Two Seawater Temperatures For Human Norovirus Depuration From Oysters

Despite regulations set up to monitor the microbiological quality of shellfish in producing areas, shellfish-borne gastroenteritis outbreaks still occur. Indeed, oyster depuration practices that are efficient to eliminate bacteria, fail to eliminate human norovirus from oyster flesh. In order to evaluate the impact of seawater temperature on the elimination of norovirus particles from oysters, large batches of oysters were contaminated using raw sewage containing norovirus and subjected to depuration at 8 °C or 18 °C. Over the experiment, quantitative RT-qPCR showed a one-log decrease of norovirus (both genogroups combined) genome copies per gram of digestive tissue after 41 days for oysters depurated at 8 °C and 24 days at 18 °C. The decrease of norovirus (both genogroups combined) in two batches of field-contaminated oysters depurated for two weeks at 18 °C was in the same range (21 and 23 days, respectively). All experiments showed a difference in genomic decay between the two norovirus genogroups, with norovirus genogroup I being more persistent in March/April compared to April/May.

Utilizing Zebrafish Embryos for Replication of Tulane Virus: A Human Norovirus Surrogate

The zebrafish larvae/embryo model has been shown to support the replication of seven strains (G1.7[P7], GII.2[P16], GII.3[P16], GII.4[P4], GII.4[P16], GII.6[P7], and GII.17[P13]) of human norovirus (HuNoV). However, due to challenges in consistently obtaining HuNoV-positive stool samples from clinical sources, evaluating HuNoV surrogates in this model is highly valuable. This study assesses the potential of zebrafish embryos and larvae as a model for Tulane virus (TuV) replication. Three infection methods were examined: microinjection, immersion, and feeding. Droplet digital PCR was used to quantify viral RNA across all three infection methods. Microinjection of 3 nL of TuV into zebrafish embryos (< 6-h post-fertilization) resulted in significant replication, with viral RNA levels reaching 6.22 logs at 4-day post-infection. In contrast, the immersion method showed no replication after immersing 4-day post-fertilization (dpf) larvae in TuV suspension for 6 h. Similarly, no replication was observed with the feeding method, where Paramecium caudatum loaded with TuV were fed to 4 dpf larvae. The findings indicate that the zebrafish embryo model supports TuV replication through the microinjection method, suggesting that TuV may serve as a useful surrogate for studying HuNoV pathogenesis. Additionally, TuV can be utilized in place of HuNoV in method optimization studies using the zebrafish embryo model, circumventing the limited availability of HuNoV.

Human norovirus cultivation models, immune response and vaccine landscape

Norovirus infections are a leading cause of gastroenteritis worldwide. Despite the substantial global health burden and economic impact, there are currently no approved antiviral therapeutics or vaccines. Additionally, much of our knowledge of norovirus comes from experiments using surrogate viruses, such as murine norovirus and feline calicivirus. The challenge surrounding human norovirus research arises from a lack of robust cell culture systems and efficient animal models. In this review, we explore recent advances in the in vitro cultivation of human norovirus and reverse genetics systems and discuss commonly used in vivo models. We summarize the current understanding of both innate and adaptive immune responses to norovirus infection and provide an overview of vaccine strategies and the current clinical trial landscape, with a focus on the only vaccine candidate that has reached phase III clinical development stage.

Assessing infectivity of emerging enveloped viruses in wastewater and sewage sludge: Relevance and procedures

The emergence of SARS-CoV-2 has heightened the need to evaluate the detection of enveloped viruses in the environment, particularly in wastewater, within the context of wastewater-based epidemiology. The studies published over the past 80 years focused primarily on non-enveloped viruses due to their ability to survive longer in environmental matrices such as wastewater or sludge compared to enveloped viruses. However, different enveloped viruses survive in the environment for different lengths of time. Therefore, it is crucial to be prepared to assess the potential infectious risk that may arise from future emerging enveloped viruses. This will require appropriate tools, notably suitable viral concentration methods that do not compromise virus infectivity. This review has a dual purpose: first, to gather all the available literature on the survival of infectious enveloped viruses, specifically at different pH and temperature conditions, and in contact with detergents; second, to select suitable concentration methods for evaluating the infectivity of these viruses in wastewater and sludge. The methodology used in this data collection review followed the systematic approach outlined in the PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) guidelines. Concentration methods cited in the data gathered are more tailored towards detecting the enveloped viruses' genome. There is a lack of suitable methods for detecting infectious enveloped viruses in wastewater and sludge. Ultrafiltration, ultracentrifugation, and polyethylene glycol precipitation methods, under specific/defined conditions, appear to be relevant approaches. Further studies are necessary to validate reliable concentration methods for detecting infectious enveloped viruses. The choice of culture system is also crucial for detection sensitivity. The data also show that the survival of infectious enveloped viruses, though lower than that of non-enveloped ones, may enable environmental transmission. Experimental data on a wide range of enveloped viruses is required due to the variability in virus persistence in the environment.

Hydroponic Nutrient Solution Temperature Impacts Tulane Virus Persistence over Time

Controlled environment agriculture (CEA), or indoor agriculture, encompasses non-traditional farming methods that occur inside climate-controlled structures (e.g., greenhouses, warehouses, high tunnels) allowing for year-round production of fresh produce such as leaf lettuce. However, recent outbreaks and recalls associated with hydroponically grown lettuce contaminated with human pathogens have raised concerns. Few studies exist on the food safety risks during hydroponic cultivation of leaf lettuce; thus, it is important to identify contributing risk factors and potential mitigation strategies to prevent foodborne transmission via hydroponically grown produce. In this study, the concentration of infectious Tulane virus (TV), a human norovirus surrogate, in hydroponic nutrient solution at 15 °C, 25 °C, 30 °C, and 37 °C was determined over a duration of 21 days to mimic the time from seedling to mature lettuce. The mean log PFU reduction for TV was 0.86, 1.80, 2.87, and ≥ 3.77 log10 at 15 °C, 25 °C, 30 °C, and 37 °C, respectively, at the end of the 21-day period. Similarly, average decimal reduction values (D-values) of TV at 15 °C, 25 °C, 30 °C, and 37 °C were 48.0, 11.3, 8.57, and 7.02 days, respectively. This study aids in the (i) identification of possible food safety risks associated with hydroponic systems specifically related to nutrient solution temperature and (ii) generation of data to perform risk assessments within CEA leaf lettuce operations to inform risk management strategies for the reduction of foodborne outbreaks, fresh produce recalls, and economic losses.

Human intestinal enteroids platform to assess the infectivity of gastroenteritis viruses in wastewater

Fecal-orally transmitted gastroenteritis viruses, particularly human noroviruses (HuNoVs), are a public health concern. Viral transmission risk through contaminated water results underexplored as they have remained largely unculturable until recently and the robust measuring of gastroenteritis viruses infectivity in a single cell line is challenging. This study primarily aimed to test the feasibility of the human intestinal enteroids (HIE) model to demonstrate the infectivity of multiple gastroenteritis viruses in wastewater. Initially, key factors affecting viral replication in HIE model were assessed, and results demonstrated that the reagent-assisted disruption of 3D HIE represents an efficient alternative to syringe pass-through, and the filtering of HuNoV stool suspensions could be avoided. Moreover, comparable replication yields of clinical strains of HuNoV genogroup I (GI), HuNoV GII, rotavirus (RV), astrovirus (HAstV), and adenoviruses (HAdV) were obtained in single and multiple co-infections. Then, the optimized HIE model was used to demonstrate the infectivity of multiple naturally occurring gastroenteritis viruses from wastewater. Thus, a total of 28 wastewater samples were subjected to (RT)-qPCR for each virus, with subsequent testing on HIE. Among these, 16 samples (57 %) showed replication of HuNoVs (n = 3), RV (n = 5), HAstV (n = 8), and/or HAdV (n = 5). Three samples showed HuNoV replication, and sequences assigned to HuNoV GI.3[P13] and HuNoV GII.4[P16] genotypes. Concurrent replication of multiple gastroenteritis viruses occurred in 4 wastewater samples. By comparing wastewater concentrate and HIE supernatant sequences, diverse HAstV and HAdV genotypes were identified in 4 samples. In summary, we successfully employed HIE to demonstrate the presence of multiple infectious human gastroenteritis viruses, including HuNoV, in naturally contaminated wastewater samples.

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 cultivation systems and their use in antiviral research

Human norovirus (HuNoV) is a major cause of acute gastroenteritis and foodborne diseases, affecting all age groups. Despite its clinical needs, no approved antiviral therapies are available. Since the discovery of HuNoV in 1972, studies on anti-norovirals, mechanism of HuNoV infection, viral inactivation, etc., have been hampered by the lack of a robust laboratory-based cultivation system for HuNoV. A recent breakthrough in the development of HuNoV cultivation systems has opened opportunities for researchers to investigate HuNoV biology in the context of de novo HuNoV infections. A tissue stem cell-derived human intestinal organoid/enteroid (HIO) culture system is one of those that supports HuNoV replication reproducibly and, to our knowledge, is most widely distributed to laboratories worldwide to study HuNoV and develop therapeutic strategies. This review summarizes recently developed HuNoV cultivation systems, including HIO, and their use in antiviral studies.

Leveraging Plasma-Activated Seawater for the Control of Human Norovirus and Bacterial Pathogens in Shellfish Depuration

Cold plasma is a promising alternative for water treatment owing to pathogen control and a plethora of issues in the agriculture and food sectors. Shellfish pose a serious risk to public health and are linked to large viral and bacterial outbreaks. Hence, current European regulations mandate a depuration step for shellfish on the basis of their geographical growth area. This study investigated the inactivation of relevant viral and bacterial pathogens of three plasma-activated seawaters (PASWs), and their reactive oxygen and nitrogen species (RONS) composition, as being primarily responsible for microbial inactivation. Specifically, F-specific (MS2) and somatic (φ174) bacteriophage, cultivable surrogate (murine norovirus, MNV, and Tulane virus, TV), and human norovirus (HuNoV GII.4) inactivation was determined using plaque counts and infectivity assays, including the novel human intestinal enteroid (HIE) model for HuNoV. Moreover, the kinetic decay of Escherichia coli, Salmonella spp., and Vibrio parahaemolyticus was characterized. The results showed the complete inactivation of phages (6-8 log), surrogates (5-6 log), HuNoV (6 log), and bacterial (6-7 log) pathogens within 24 h while preventing cytotoxicity effects and preserving mussel viability. Nitrites (NO2-) were found to be mostly correlated with microbial decay. This research shows that PASWs are a suitable option to depurate bivalve mollusks and control the biohazard risk linked to their microbiological contamination, either viral or bacterial.

Persistence of Infectious Human Norovirus in Estuarine Water

Norovirus is the predominant cause of viral acute gastroenteritis globally. While person-to-person is the most reported transmission route, norovirus is also associated with waterborne and foodborne illness, including from the consumption of contaminated bivalve molluscan shellfish. The main cause of shellfish contamination is via the bioaccumulation of norovirus from growing waters impacted by human wastewater. However, data on the persistence of infectious norovirus in the environment are limited due to a lack of a human norovirus culture method in the past. In this study, we applied the recently established method of norovirus replication in human intestinal enteroids to determine the persistence of norovirus in artificial estuarine water at 25 ppt for up to 21 days at 4 °C and 16 °C in the dark. Infectious norovirus was detected for up to 21 days. The relative infectivity declined from 100 to 3% at day 21, with decay rate constants of 0.07 day-1 at 4 °C and 0.17 day-1 at 16 °C. There was no decrease in norovirus titres as measured by reverse transcription-droplet digital PCR (RT-ddPCR), confirming the lack of the relationship between norovirus infectivity and direct detection by PCR. The results confirm that norovirus can remain infectious for at least 3 weeks in an estuarine water environment, presenting associated health risks.

Retention of Virus Versus Surrogate, by Ultrafiltration in Seawater: Case Study of Norovirus Versus Tulane

In the field of chemical engineering and water treatment, the study of viruses, included surrogates, is well documented. Often, surrogates are used to study viruses and their behavior because they can be produced in larger quantities in safer conditions and are easier to handle. In fact, surrogates allow studying microorganisms which are non-infectious to humans but share some properties similar to pathogenic viruses: structure, composition, morphology, and size. Human noroviruses, recognized as the leading cause of epidemics and sporadic cases of gastroenteritis across all age groups, may be mimicked by the Tulane virus. The objectives of this work were to study (i) the ultrafiltration of Tulane virus and norovirus to validate that Tulane virus can be used as a surrogate for norovirus in water treatment process and (ii) the retention of norovirus and the surrogate as a function of water quality to better understand the use of the latter pathogenic viruses. Ultrafiltration tests showed significant logarithmic reduction values (LRV) in viral RNA: around 2.5 for global LRV (i.e., based on the initial and permeate average concentrations) and between 2 and 6 for average LRV (i.e., retention rate considering the increase of viral concentration in the retentate), both for norovirus and the surrogate Tulane virus. Higher reduction rates (from 2 to 6 log genome copies) are obtained for higher initial concentrations (from 101 to 107 genome copies per mL) due to virus aggregation in membrane lumen. Tulane virus appears to be a good surrogate for norovirus retention by membrane processes.

Challenges for estimating human norovirus infectivity by viability RT-qPCR as compared to replication in human intestinal enteroids

Viability RT-qPCR, a molecular detection method combining viability marker pre-treatment with RT-qPCR, has been proposed to infer infectivity of viruses which is particularly relevant for non-culturable viruses or sophisticated cell culture systems. Being human noroviruses (HuNoV) most frequently associated with foodborne outbreaks, this study compared different viability techniques and infectivity in human intestinal enteroids (HIE) to ultimately determine whether the molecular approaches could serve as rapid assays to predict HuNoV inactivation in high-risk food. To this end, the performance of three viability RT-qPCR assays with different intercalating markers ((Viability PCR Crosslinker Kit (CL), propidium monoazide (PMAxx™), and platinum chloride (PtCl4)) in estimating survival of HuNoV exposed to thermal and high pressure (HPP) treatments was compared to replication tested in the HIE cell culture model. A nearly full-length genomic molecular assay coupled with PMAxx™ to infer HuNoV thermal inactivation was also assessed. The experimental design included HuNoV genogroup I.3 [P13], GII.4 Sydney [P16], GII.6 [P7], along with Tulane virus (TV) serving as surrogate. Finally, viability RT-qPCR was tested in HPP-treated strawberry puree, selected as a food matrix with high viral contamination risk. PMAxx™ and CL performed evenly, while PtCl4 affected HuNoV infectivity. Taking all experimental data together, viability RT-qPCR was demonstrated to be an improved method over direct RT-qPCR to estimate viral inactivation at extreme thermal (95 °C) and HPP (450 MPa) exposures, but not under milder conditions as amplification signals were detected. Despite its complexity and limitations, the HIE demonstrated a more robust model than viability RT-qPCR to assess HuNoV infectivity.

Temperature and particles interact to affect human norovirus and MS2 persistence in surface water

Modeling the fate and transport of viruses and their genetic material in surface water is necessary to assess risks associated with contaminated surface waters and to inform environmental surveillance efforts. Temperature has been identified as a key variable affecting virus persistence in surface waters, but the effects of the presence of biological and inert particles and of their interaction with temperature have not been well characterized. We assessed these effects on the persistence of human norovirus (HuNoV) genotype II.4 purified from stool and MS2 in surface water. Raw or filter-sterilized creek water microcosms were inoculated and incubated in the dark at 10 °C, 15 °C, and 20 °C. HuNoV (i.e., genome segments and intact capsids) and MS2 (i.e., infectious MS2, genome segments, and intact capsids) concentrations were followed over 36 days. The range in positive, significant first-order decay rate constants for HuNoV in this study was 0.14 to 0.69 day-1 compared with 0.026 to 0.71 day-1 for that of MS2. Decay rate constants for HuNoV genome segments and infectious MS2 were largest in creek water that included biological and inert particles and incubated at higher temperatures. In addition, for HuNoV and MS2 incubated in raw or filter-sterilized creek water at 15 °C, capsid damage was not identified as a dominant inactivation mechanism. Environmental processes and events that affect surface water biological and inert particles, temperature, or both could lead to variable virus decay rate constants. Incorporating the effects of particles, temperature, and their interaction could enhance models of virus fate and transport in surface water.

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.

Standardization of an antiviral pipeline for human norovirus in human intestinal enteroids demonstrates nitazoxanide has no to weak antiviral activity

Human noroviruses (HuNoVs) are the leading cause of acute gastroenteritis. In immunocompetent hosts, symptoms usually resolve within 3 days; however, in immunocompromised persons, HuNoV infection can become persistent, debilitating, and sometimes life-threatening. There are no licensed therapeutics for HuNoV due to a near half-century delay in its cultivation. Treatment for chronic HuNoV infection in immunosuppressed patients anecdotally includes nitazoxanide, a broad-spectrum antimicrobial licensed for treatment of parasite-induced gastroenteritis. Despite its off-label use for chronic HuNoV infection, nitazoxanide has not been clearly demonstrated to be an effective treatment. In this study, we standardized a pipeline for antiviral testing using multiple human small intestinal enteroid lines representing different intestinal segments and evaluated whether nitazoxanide inhibits replication of five HuNoV strains in vitro. Nitazoxanide did not exhibit high selective antiviral activity against any HuNoV strain tested, indicating it is not an effective antiviral for HuNoV infection. Human intestinal enteroids are further demonstrated as a model to serve as a preclinical platform to test antivirals against HuNoVs to treat gastrointestinal disease. Abstr.

Toward better monitoring of human noroviruses and F-specific RNA bacteriophages in aquatic environments using bivalve mollusks and passive samplers: A case study

Monitoring pathogenic enteric viruses in continental and marine water bodies is essential to control the viral contamination of human populations. Human Noroviruses (NoV) are the main enteric viruses present in surface waters and foodstuff. In a context of global change, it is currently a challenge to improve the management of viral pollutions in aquatic environments and thereby limit the contamination of vulnerable water bodies or foodstuffs. The aim of this study is to evaluate the potential of specific accumulation systems for improving the detection of NoV in water bodies, compared to direct water analyses. Passive samplers (Zetapor filters) and three species of bivalve molluscan shellfish (BMS) (Dreissena polymorpha, Mytilus edulis and Crassostreas gigas) were used as accumulation systems to determine their performance in monitoring continental and marine waters for viruses. F-specific RNA bacteriophages (FRNAPH) were also analyzed since they are described as indicators of NoV hazard in many studies. During a one-year study in a specific area frequently affected by fecal pollution, twelve campaigns of exposure of passive samplers and BMS in continental and coastal waters were conducted. Using suitable methods, NoV (genome) and FRNAPH (infectious and genome) were detected in these accumulation systems and in water at the same time points to determine the frequency of detection but also to gain a better understanding of viral pollution in this area. The reliability of FRNAPH as a NoV indicator was also investigated. Our results clearly showed that BMS were significantly better than passive samplers and direct water analyses for monitoring NoV and FRNAPH contamination in water bodies. A dilution of viral pollution between the continental and the coastal area was observed and can be explained by the distance from the source of the pollution. Viral pollution is clearly greater during the winter period, and stakeholders should take this into consideration in their attempts to limit the contamination of food and water. A significant correlation was once again shown between NoV and FRNAPH genomes in BMS, confirming the reliability of FRNAPH as a NoV indicator. Moreover, a strong correlation was observed between NoV genomes and infectious FRNAPH, suggesting recent viral pollution since infectious particles had not been inactivated at sufficient levels in the environment. More generally, this study shows the value of using BMS as an active method for improving knowledge on the behavior of viral contamination in water bodies, the ranking of the contamination sources, and the vulnerability of downstream water bodies.

A Comprehensive Review for the Surveillance of Human Pathogenic Microorganisms in Shellfish

Bivalve molluscan shellfish have been consumed for centuries. Being filter feeders, they may bioaccumulate some microorganisms present in coastal water, either naturally or through the discharge of human or animal sewage. Despite regulations set up to avoid microbiological contamination in shellfish, human outbreaks still occur. After providing an overview showing their implication in disease, this review aims to highlight the diversity of the bacteria or enteric viruses detected in shellfish species, including emerging pathogens. After a critical discussion of the available methods and their limitations, we address the interest of technological developments using genomics to anticipate the emergence of pathogens. In the coming years, further research needs to be performed and methods need to be developed in order to design the future of surveillance and to help risk assessment studies, with the ultimate objective of protecting consumers and enhancing the microbial safety of bivalve molluscan shellfish as a healthy food.

Human Sapovirus Replication in Human Intestinal Enteroids

Human sapoviruses (HuSaVs), like human noroviruses (HuNoV), belong to the Caliciviridae family and cause acute gastroenteritis in humans. Since their discovery in 1976, numerous attempts to grow HuSaVs in vitro were unsuccessful until 2020, when these viruses were reported to replicate in a duodenal cancer cell-derived line. Physiological cellular models allowing viral replication are essential to investigate HuSaV biology and replication mechanisms such as genetic susceptibility, restriction factors, and immune responses to infection. In this study, we demonstrate replication of two HuSaV strains in human intestinal enteroids (HIEs) known to support the replication of HuNoV and other human enteric viruses. HuSaVs replicated in differentiated HIEs originating from jejunum, duodenum and ileum, but not from the colon, and bile acids were required. Between 2h and 3 to 6 days postinfection, viral RNA levels increased up from 0.5 to 1.8 log10-fold. Importantly, HuSaVs were able to replicate in HIEs independent of their secretor status and histo-blood group antigen expression. The HIE model supports HuSaV replication and allows a better understanding of host-pathogen mechanisms such as cellular tropism and mechanisms of viral replication. IMPORTANCE Human sapoviruses (HuSaVs) are a frequent but overlooked cause of acute gastroenteritis, especially in children. Little is known about this pathogen, whose successful in vitro cultivation was reported only recently, in a cancer cell-derived line. Here, we assessed the replication of HuSaV in human intestinal enteroids (HIEs), which are nontransformed cultures originally derived from human intestinal stem cells that can be grown in vitro and are known to allow the replication of other enteric viruses. Successful infection of HIEs with two strains belonging to different genotypes of the virus allowed discovery that the tropism of these HuSaVs is restricted to the small intestine, does not occur in the colon, and replication requires bile acid but is independent of the expression of histo-blood group antigens. Thus, HIEs represent a physiologically relevant model to further investigate HuSaV biology and a suitable platform for the future development of vaccines and antivirals.

Persistence of Human Norovirus (GII) in Surface Water: Decay Rate Constants and Inactivation Mechanisms

Human norovirus (HuNoV) is an important cause of acute gastroenteritis and can be transmitted by water exposures, but its persistence in water is not well understood. Loss of HuNoV infectivity in surface water was compared with persistence of intact HuNoV capsids and genome segments. Surface water from a freshwater creek was filter-sterilized, inoculated with HuNoV (GII.4) purified from stool, and incubated at 15 or 20 °C. We measured HuNoV infectivity via the human intestinal enteroid system and HuNoV persistence via reverse transcription-quantitative polymerase chain reaction assays without (genome segment persistence) or with (intact viral capsid persistence) enzymatic pretreatment to digest naked RNA. For infectious HuNoV, results ranged from no significant decay to a decay rate constant ("k") of 2.2 day-1. In one creek water sample, genome damage was likely a dominant inactivation mechanism. In other samples from the same creek, loss of HuNoV infectivity could not be attributed to genome damage or capsid cleavage. The range in k and the difference in the inactivation mechanism observed in water from the same site could not be explained, but variable constituents in the environmental matrix could have contributed. Thus, a single k may be insufficient for modeling virus inactivation in surface waters.