Contamination, bioaccumulation mechanism, detection, and control of human norovirus in bivalve shellfish: A review

Seasonal Variability of Human Enteric Viruses Discovered in Food Production Mussels (Mytilus galloprovincialis) Farmed in the Central Adriatic Sea (Italy)

Among the different naked and quasi-enveloped viruses, the hepatitis A virus (HAV), hepatitis E virus (HEV), and norovirus genogroups I and II (NoV GI and NoV GII) are considered the main microbiological noxae involved in foodborne outbreaks. Mussels can harbor pathogens in their tissues. In addition to epidemiological attention, marine water temperature changes are considered a crucial variable influencing viral loads. This study aimed to biomolecularly screen 1775 farmed mussels (Mytilus galloprovincialis) for viral ribonucleic acid (RNA) sequence detection (belonging to the HAV, HEV, and NoV GI and GII genogroups) in three different sampling periods (spring, summer, and winter), with the mussels collected from three farms located in the Central Adriatic Sea (Italy). The results showed that 10.42% of the screened animals harbored at least one type of pathogen RNA, more specifically, 5.35% HEV, 4.51% NoV GI, and 0.56% HAV. The highest genetic equivalent (GE) amounts were majorly observed in the winter season (NoV GI 1.0 × 103 GE/g and HEV 1.0 × 102 GE/g), resulting in statistical differences when compared to summer and spring (p-value: <0.001). The original data obtained serve to bring scientific attention to the possible influence of environmental and climatic aspects on viral loads, highlighting the crucial role played by biomolecular assays as preventive medicine tools.

Microplastics and viruses in the aquatic environment: a mini review

Microplastics (MPs) have been widely found in the environment and have exerted non-negligible impacts on the environment and human health. Extensive research has shown that MPs can act as carriers for viruses and interacts with them in various ways. Whether MPs influence the persistence, transmission and infectivity of virus has attracted global concern in the context of increasing MPs contamination. This review paper provides an overview of the current state of knowledge regarding the interactions between MPs and viruses in aquatic environments. Latest progress and research trends in this field are summarized based on literature analysis. Additionally, we discuss the potential risks posed by microplastic-associated viruses to human health and the environmental safety, highlighting that MPs can affect viral transmission and infectivity through various pathways. Finally, we underscores the need for further research to address key knowledge gaps, such as elucidating synergistic effects between MPs and viruses, understanding interactions under real environmental conditions, and exploring the role of biofilms in virus-MPs interactions. This review aims to contribute to a deeper understanding on the transmission of viruses in the context of increasing MPs pollution in water, and promote actions to reduce the potential risks.

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.

The variation of antigenic and histo-blood group binding sites synergistically drive the evolution among chronologically emerging GII.4 noroviruses

Norovirus, commonly found on shellfish and vegetables, is a foodborne virus with GII.4 as the dominant genotype responsible for widespread outbreaks since 1995. Continuous variation of major capsid protein VP1 can lead to changes in the immunogenicity and host receptor binding ability of norovirus, which is an important evolutionary mechanism. Therefore, analyzing the immunogenicity of VP1 and its binding ability to various HBGAs in GII.4 variants could improve our understanding of the persistent prevalence of GII.4. Here, the results suggest that GII.4 has gradually enhanced its HBGAs binding ability over time for various types of receptors. Variants exhibit significantly stronger immune response to homologous mouse antiserum than heterologous ones, highlighting the importance of variation of antigenic and histo-blood group binding sites in driving the evolution of GII.4. These synergistic forces constantly lead to antigenic drift and changes in receptor binding, resulting in continuous emergence of new variant strains and sustained prevalence.

Assessment of Gastroenteric Viruses in Marketed Bivalve Mollusks in the Tourist Cities of Rio de Janeiro, Brazil, 2022

This study investigated the prevalence and genetic diversity of gastroenteric viruses in mussels and oysters in Rio de Janeiro, Brazil. One hundred and thirty-four marketed bivalve samples were obtained between January and December 2022. The viral analysis was performed according to ISO/TS 15216, and the screening revealed the detection of norovirus GII/GI (40.3%), sapovirus (SaV; 12.7%), human mastadenovirus (7.5%), and rotavirus A (RVA; 5.9%). In total, 44.8% (60) of shellfish samples tested positive for one or more viruses, 46.7% (28/60) of the positive samples tested positive for a single viral agent, 26.7% (16) tested positive for two viral agents, 8.3% (5) for three viral agents, and 13.3% (8) for four viral agents. Additionally, three mussel samples were contaminated with the five investigated viruses (5%, 3/60). Norovirus GII showed the highest mean viral load (3.4 × 105 GC/g), followed by SaV (1.4 × 104 GC/g), RVA (1.1 × 104 GC/g), human mastadenovirus (3.9 × 103 GC/g), and norovirus GI (6.7 × 102 GC/g). Molecular characterization revealed that the recovered norovirus strains belonged to genotypes GII.2, GII.6, GII.9, GII.17, and GII.27; SaV belonged to genotypes GI.1 and GIV.1; RVA to genotypes G6, G8, P[8]-III, and human mastadenovirus to types F40 and F41. The GII.27 norovirus characterized in this study is the only strain of this genotype reported in Brazil. This study highlights the dissemination and diversity of gastroenteric viruses present in commercialized bivalves in a touristic area, indicating the potential risk to human health and the contribution of bivalves in the propagation of emerging pathogens.

Inactivation of Human Norovirus GII.4's Infectivity in Fresh Oysters (Crassostrea gigas) through Thermal Treatment in Association with Propidium Monoazide

The current study investigated the effects of heat treatment (85 °C or 100 °C for 5-20 min) on human norovirus (HuNoV) GII.4's capsid stability in fresh oysters. In addition, propidium monoazide (PMA) was used in viral samples to distinguish infectious viruses and evaluated using real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Further, we explored the effect of the heat treatment on oyster quality (Hunter color and hardness). The titer of HuNoV for oysters significantly (p < 0.05) decreased to 0.39-1.32 and 0.93-2.27 log10 copy number/μL in the non-PMA and PMA-treated groups, respectively, after heat treatment. HuNoV in oysters not treated with PMA showed a decrease of <1.5 - log10, whereas in PMA-treated oysters, a decrease of >1 - log10 was observed after treatment at 85 °C for 10 min. Treatments for both 15 min and 20 min at 100 °C showed a >99% log10 reduction using PMA/RT-qPCR. In the Hunter color, an increase in heat temperature and duration was associated with a significant decrease in 'L' (brightness+, darkness-) and an increase in 'a' (redness+, greenness-) and 'b' (yellowness+, blueness-) (p < 0.05). Our findings confirmed that the hardness of oyster meat significantly increased with increasing temperature and time (p < 0.05). This study demonstrated that PMA/RT-qPCR was effective in distinguishing HuNoV viability in heat-treated oysters. The optimal heat treatment for oysters was 10 min at 85 °C and 5 min at 100 °C.

Asymptomatic norovirus infection during outbreaks in China: A systematic review and meta-analysis

Acute gastroenteritis outbreaks may be caused by the excretion of norovirus (NoV) from asymptomatic individuals. Despite numerous studies involving asymptomatic NoV infection during outbreaks in China, a comprehensive assessment of its role has not been conducted, which is critical for emergency management. Our objective was to assess the prevalence of asymptomatic NoV infection during outbreaks in China. We conducted a comprehensive search of multiple databases, including PubMed, Web of Science, Cochrane Library, China National Knowledge Infrastructure, China Wanfang, and China Weipu, between January 1, 1997 and June 19, 2023. The retrieved articles and their references underwent screening, which utilized polymerase chain reaction-based assays for the detection of NoV in asymptomatic individuals during outbreaks that occurred in China. The primary summary data were the prevalence of asymptomatic NoV infection in outbreaks. We generated pooled estimates of asymptomatic prevalence in the population as a whole and in subgroups by using random-effect models. Of the 97 articles included, the pooled asymptomatic prevalence of NoV among 5117 individuals in outbreaks was 17.6% (95% confidence interval [CI]: 14.1-21.3). The asymptomatic prevalence of NoV GII (17.1%, 95% CI: 12.9-21.5) was similar to that of NoV GI (22.0%, 95% CI: 12.8-32.4). However, the proportion of asymptomatic individuals involved in NoV GII (57.44%) was significantly higher than that of NoV GI (5.12%), and NoV GII (75.26%) was reported much more frequently than NoV GI (14.43%) in the included articles. Meta-regression analysis of 11 possible influencing factors (geographic region, setting, season, sample type, genotype, transmission route, occupation, age, per capita income, study quality, and cases definition) showed that the source of heterogeneity might be related to the outbreak settings, per capita income, and study quality (p = 0.037, 0.058, and 0.026, respectively). Of particular note was the asymptomatic prevalence peaked in preschoolers (27.8%), afterward, it fell into trough in elementary and junior school children (10.5%), before the second peak located in adults (17.8%), and the elderly (25.2%). Prevalent genotypes reported include GII.4, followed by GII.17, GII.2, GII.3, GII.6, and so forth. The estimated asymptomatic prevalence of NoV during outbreaks in China was as high as 17.6%, with NoV GII dominating. In addition, genetic subtypes of NoV in outbreaks should be detected whenever possible. The role of asymptomatic individuals in NoV outbreaks cannot be ignored. This knowledge will help governments develop public health policies and emergency response strategies for outbreaks, assess the burden, and develop vaccines.

Research Progress on Biological Accumulation, Detection and Inactivation Technologies of Norovirus in Oysters

Noroviruses (NoVs) are major foodborne pathogens that cause acute gastroenteritis. Oysters are significant carriers of this pathogen, and disease transmission from the consumption of NoVs-infected oysters occurs worldwide. The review discusses the mechanism of NoVs bioaccumulation in oysters, particularly the binding of histo-blood group antigen-like (HBGA-like) molecules to NoVs in oysters. The review explores the factors that influence NoVs bioaccumulation in oysters, including temperature, precipitation and water contamination. The review also discusses the detection methods of NoVs in live oysters and analyzes the inactivation effects of high hydrostatic pressure, irradiation treatment and plasma treatment on NoVs. These non-thermal processing treatments can remove NoVs efficiently while retaining the original flavor of oysters. However, further research is needed to reduce the cost of these technologies to achieve large-scale commercial applications. The review aims to provide novel insights to reduce the bioaccumulation of NoVs in oysters and serve as a reference for the development of new, rapid and effective methods for detecting and inactivating NoVs in live oysters.

Global prevalence of asymptomatic norovirus infection in outbreaks: a systematic review and meta-analysis

BACKGROUND

Although many studies on asymptomatic norovirus infection in outbreaks have been conducted globally, structured data (important for emergency management of outbreaks) on the prevalence of this epidemic are still not available. This study assessed the global prevalence of asymptomatic norovirus infection in outbreaks.

METHODS

We identified publications on asymptomatic infections from norovirus outbreaks by searching the PubMed, Embase, Cochrane Library, Medline, and Web of Science databases and screening references from the articles reviewed. Prevalence of asymptomatic norovirus infection in outbreaks was employed as the primary summary data. The random-effects model of the meta-analysis was fitted to generate estimates of the prevalence in the overall and subgroup populations.

RESULTS

In total, 44 articles with a sample size of 8,115 asymptomatic individuals were included. The estimated pooled prevalence of asymptomatic norovirus infection in outbreaks was 21.8% (95%CI, 17.4-27.3). The asymptomatic prevalence of norovirus GII (20.1%) was similar to that of GI (19.8%); however, the proportion prevalence of asymptomatic individuals involved in the former (33.36%) was significantly higher than that of in the latter (0.92%) and the former (93.18%) was reported much more frequently than the latter (15.91%) in the included articles. These studies had significant heterogeneity (I2 = 92%, τ2 = 0.4021, P < 0.01). However, the source of heterogeneity could not be identified even after subgroup analysis of 10 possible influencing factors (geographical area, outbreak settings, outbreak seasons, sample types, norovirus genotypes, transmission routes, subjects' occupations, subjects' age, per capita national income, and clear case definition). Meta-regression analysis of these 10 factors demonstrated that the geographical area could be partly responsible for this heterogeneity (P = 0.012).

CONCLUSIONS

The overall pooled asymptomatic prevalence of norovirus in outbreaks was high, with genome II dominating. Asymptomatic individuals may play an important role in norovirus outbreaks. This knowledge could help in developing control strategies and public health policies for norovirus outbreaks.

Gut Microbiota and Transcriptomics Reveal the Effect of Human Norovirus Bioaccumulation on Oysters (Crassostrea gigas)

Human norovirus (HuNoV) is a major foodborne pathogen that causes acute viral gastroenteritis, and oysters are one of the main carriers of HuNoV transmission. While progress has been made toward understanding the pattern of oyster-bioaccumulated HuNoV, the response of oysters to HuNoV bioaccumulation, including changes in gene expression and gut microbiota, is unclear. In this study, histo-blood group antigen (HBGA)-like molecule expression and gene regulation features and the HuNoV-microbiome interactions of oysters during HuNoV bioaccumulation were characterized. With the prolongation of bioaccumulation time, the HuNoV content and expression of type A HBGA-like molecules in oysters increased and stabilized. HuNoV also altered the expression of immunity- and glycosphingolipid biosynthesis-related genes. Prolonged bioaccumulation of HuNoV can reduce the abundance and change the composition of the oyster gut microbiota. In particular, with the extension of bioaccumulation time, the abundance of Blautia, Agathobacter, Faecalibacterium, Terrisporobacter, Bifidobacterium, Lactobacillus, and Ruminococcus decreased, while the abundance of Vibrio and Alphaproteobacteria increased. This study provides potential candidates for identifying functional genes involved in the bioaccumulation of HuNoV in oysters. More importantly, it provides the first description of the changes in gut microbiota during HuNoV bioaccumulation in oysters. IMPORTANCE The role of the oyster gut microbiota in HuNoV bioaccumulation is poorly understood. This study revealed, for the first time, the changes in gut microbiota and gene expression of oysters with HuNoV bioaccumulation. This study enriches the understanding of the impact of HuNoV bioaccumulation on oysters and provides a new direction for the study of the molecular mechanism of HuNoV bioaccumulation in oysters.