Norovirus in shellfish: An overview of post-harvest treatments and their challenges

PMAxx-RT-qPCR to Determine Human Norovirus Inactivation Following High-Pressure Processing of Oysters

Norovirus is the leading cause of viral gastroenteritis globally. While person-to-person transmission is most commonly reported route of infection, human norovirus is frequently associated with foodborne transmission, including through consumption of contaminated bivalve molluscan shellfish. Reverse transcription (RT)-qPCR is most commonly used method for detecting human norovirus detection in foods, but does not inform on its infectivity, posing challenges for assessing intervention strategies aimed at risk elimination. In this study, RT-qPCR was used in conjunction with a derivative of the photoreactive DNA binding dye propidium monoazide (PMAxx™) (PMAxx-RT-qPCR) to evaluate the viral capsid integrity of norovirus genogroup I and II (GI and GII) in shellfish following high pressure processing (HPP). Norovirus GI.3 and GII.4 bioaccumulated oysters were subjected to HPP at pressures of 300 and 450 MPa at 15 °C, and 300, 450 and 600 MPa at 20 °C. Samples were analysed using both RT-qPCR and PMAxx-RT-qPCR. For each sample, norovirus concentration (genome copies/g digestive tissue) determined by RT-qPCR was divided by the PMAxx-RT-qPCR concentration, giving the relative non-intact (RNI) ratio. The RNI ratio values relate to the amount of non-intact (non-infectious) viruses compared to fully intact (possible infectious) viruses. Our findings revealed an increasing RNI ratio value, indicating decreasing virus integrity, with increasing pressure and decreasing pressure. At 300 MPa, for norovirus GI, the median [95% confidence interval, CI] RNI ratio values were 2.6 [1.9, 3.0] at 15 °C compared to 1.1 [0.9, 1.8] at 20 °C. At 450 MPa, the RNI ratio values were 5.5 [2.9, 7.0] at 15 °C compared to 1.3 [1.0, 1.6] at 20 °C. At 600 MPa, the RNI ratio value was 5.1 [2.9, 13.4] at 20 °C. For norovirus GII, RT-qPCR and PMAxx-RT-qPCR detections were significantly reduced at 450 and 600 MPa at both 15 °C and 20 °C, with the median [95% CI] RNI ratio value at 300 MPa being 1.1 [0.8, 1.6]. Following HPP treatment, the use of PMAxx-RT-qPCR enables the selective detection of intact and potential infectious norovirus, enhancing our understanding of the inactivation profiles and supporting the development of more effective risk assessment strategies.

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.

Short Depuration of Oysters Intended for Human Consumption Is Effective at Reducing Exposure to Nanoplastics

Nanoplastics (NPs; <1 μm) have greater availability to marine organisms than microplastics (1-5000 μm). Understanding NP uptake and depuration in marine organisms intended for human consumption is imperative for food safety, but until now it has been limited due to analytical constraints. Oysters (Crassostrea gigas) were exposed to polystyrene NPs doped with palladium (Pd), allowing the measurements of their uptake into tissues by inductively coupled plasma mass spectrometry (ICP-MS) combined with electron microscopy. Oysters were exposed for 6 days (d) to "Smooth" or "Raspberry" NPs, followed by 30 d of depuration with the aim of assessing the NP concentration in C. gigas following exposure, inferring the accumulation and elimination rates, and understanding the clearance of Pd NPs during the depuration period. After 6 d, the most significant accumulation was found in the digestive gland (106.6 and 135.3 μg g^-1 dw, for Smooth and Raspberry NPs, respectively) and showed the most evident depuration (elimination rate constant K_Smooth = 2 d^-1 and K_Raspberry = 0.2 d^-1). Almost complete depuration of the Raspberry NPs occurred after 30 d. While a post-harvesting depuration period of 24-48 h for oysters could potentially reduce the NP content by 75%, more research to validate these findings, including depuration studies of oysters from the field, is required to inform practices to reduce human exposure through consumption.

Study on the Effect of Relaying on Norovirus Reduction from Crassostrea gigas Oysters

Norovirus (NoV) is the most important cause of seafood-borne gastroenteritis worldwide, mainly associated with the consumption of raw oysters. NoV is often present in oysters that comply with existing control standards for shellfish. Therefore, the improvement of post-harvest treatments and practices can represent one of the main strategies to reduce the incidence of viral diseases related to shellfish. This study aimed to investigate long-term relays for the reduction of NoV levels in live oysters, during the high-risk cold months, by transferring the oysters from a more contaminated site to two sites with lower NoV levels. The efficacy of relaying was evaluated by analyzing oyster samples collected at days 0 (T0) and 30 (T30) for NoV levels using a real-time quantitative PCR (RT-qPCR). The NoV level at the relay sites was consistently lower than at the harvest site. The relay process for 30 days in seawater with a lower NoV level resulted in a decrease in the NoV load compared to day 0 with significant reductions depending on the site and genogroup of NoV considered. These results suggest that long-term relaying of oysters to reduce NoV levels is promising and could help growers to improve oyster safety; however, further investigations are needed.

Antibacterial, Antifungal and Antiviral Polymeric Food Packaging in Post-COVID-19 Era

Consumers are now more concerned about food safety and hygiene following the COVID-19 pandemic. Antimicrobial packaging has attracted increased interest by reducing contamination of food surfaces to deliver quality and safe food while maintaining shelf life. Active packaging materials to reduce contamination or inhibit viral activity in packaged foods and on packaging surfaces are mostly prepared using solvent casting, but very few materials demonstrate antiviral activity on foods of animal origin, which are important in the human diet. Incorporation of silver nanoparticles, essential oils and natural plant extracts as antimicrobial agents in/on polymeric matrices provides improved antifungal, antibacterial and antiviral properties. This paper reviews recent developments in antifungal, antibacterial and antiviral packaging incorporating natural or synthetic compounds using preparation methods including extrusion, solvent casting and surface modification treatment for surface coating and their applications in several foods (i.e., bakery products, fruits and vegetables, meat and meat products, fish and seafood and milk and dairy foods). Findings showed that antimicrobial material as films, coated films, coating and pouches exhibited efficient antimicrobial activity in vitro but lower activity in real food systems. Antimicrobial activity depends on (i) polar or non-polar food components, (ii) interactions between antimicrobial compounds and the polymer materials and (iii) interactions between environmental conditions and active films (i.e., relative humidity, oxygen and water vapor permeability and temperature) that impact the migration or diffusion of active compounds in foods. Knowledge gained from the plethora of existing studies on antimicrobial polymers can be effectively utilized to develop multifunctional antimicrobial materials that can protect food products and packaging surfaces from SARS-CoV-2 contamination.

Advances and Future Perspective on Detection Technology of Human Norovirus

Human norovirus (HuNoV) is a food-borne pathogen that causes acute gastroenteritis in people of all ages worldwide. However, no approved vaccines and antiviral drugs are available at present. Therefore, the development of accurate and rapid detection technologies is important in controlling the outbreak of HuNoVs. This paper reviewed the research progress on HuNoV detection, including immunological methods, molecular detection and biosensor technology. Immunological methods and molecular detection technologies are still widely used for HuNoV detection. Furthermore, biosensors will become an emerging developmental direction for the rapid detection of HuNoVs because of their high sensitivity, low cost, easy operation and suitability for onsite detection.

Application of crAssphage, F-RNA phage and pepper mild mottle virus as indicators of human faecal and norovirus contamination in shellfish

Shellfish growing waters contaminated with inadequately treated human wastewater is a major source of norovirus in shellfish and poses a significant human health risk to consumers. Microbial source tracking (MST) markers have been widely used to identify the source (s) of faecal contamination in water but data are limited on their use for shellfish safety. This study evaluated the source specificity, sensitivity, occurrence and concentration of three viral MST markers i.e. cross-assembly phage (crAssphage), F-specific RNA bacteriophage genogroup II (F-RNA phage GII) and pepper mild mottle virus (PMMoV) using animal faeces (n = 119; 16 animal groups), influent wastewater (n = 12), effluent wastewater (n = 16) and shellfish (n = 33). CrAssphage, F-RNA phage GII and PMMoV had source specific values of 0.97, 0.99 and 0.91, respectively. The sensitivity of MST markers was confirmed by their 100% detection frequency in influent wastewaters. The frequency of detection in effluent wastewater ranged from 81.3% (F-RNA phage GII) to 100% (PMMoV). Concentration of F-RNA phage GII was one log₁₀ (influent wastewater) and 2-3 log₁₀ (effluent wastewater) lower than crAssphage and PMMoV, respectively. Despite lower prevalence of F-RNA phage GII in oysters and mussels compared to crAssphage and PMMoV, concentrations of the three MST markers were similar in mussels. As an indicator of norovirus contamination in shellfish, crAssphage and PMMoV had greater predictive sensitivity (100%; [95% CI; 81.5%-100%)]) and F-RNA phage GII had greater predictive specificity (93.3%; [95% CI; 68.1%-99.8%]). In contrast, crAssphage and F-RNA phage GII have similar accuracy for predicting norovirus in shellfish, however, PMMoV significantly overestimated its presence. Therefore, a combination of crAssphage and F-RNA phage GII analysis of shellfish could provide a robust estimation of the presence of human faecal and norovirus contamination.

Application of virome capture sequencing in shellfish sold at retail level in Singapore

During the period from late 2019 to early 2020, we performed a foodborne virus detection from shellfish collected in Singapore at retail level. Multiple human enteric viruses were included as our targets including human noroviruses (NoVs) GI and GII, hepatitis A virus, hepatitis E virus and rotavirus. Out of the 60 shellfish samples, 23 (38·3%) were detected to be positive by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) with human enteric viruses. Six samples were selected to proceed with virome capture sequencing with positive control samples spiked with serially diluted NoV GII clinical samples in oyster extract. As a result, the natural sample with comparable Ct values (34·0-35·0) of the spiked sample as detected by RT-qPCR generated much lower read counts (>7-log₂ cumulative sum scaling difference) and genome coverage (406 nt. vs 3715 nt.), suggesting that the RT-qPCR positive signals detected from the shellfish samples collected at the retail market were likely from degraded RNA derived from inactive virus particles.

Preliminary Quantitative Risk Assessment of Norovirus in Shellfish in the Yellow Sea and Bohai Sea of China

Norovirus (NoV) is a main foodborne pathogen of acute gastroenteritis in the world. A preliminary quantitative risk assessment (QRA) was conducted to evaluate the health risk caused by this virus in shellfish in the Yellow Sea and Bohai Sea of China. The QRA framework was established from the process of shellfish at retail through cooking at home to consumer consumption. The prevalence and quantity of NoVs in shellfish, cooking methods, internal temperature and time of shellfish in different cooking conditions, shellfish consumption frequency, and consumption amount were analyzed in the exposure assessment. The results of exposure assessment were introduced into the beta-Poisson dose-response model, and Monte Carlo analysis was used to calculate the risk of gastroenteritis caused by shellfish consumption in the cities around the Yellow Sea and Bohai Sea of China. The results showed that the probability of illness caused by NoVs due to shellfish consumption per year (P_ill,yr) was 1.86 × 10^-5. It was estimated that the annual number of patients with gastroenteritis per 1,000,000 general population (N_exp,mil) was 0.10, 1.23, 16.90, and 0.38 for population aged 0-4, 5-18, 19-64, and >65 years, respectively. This assessment provides valuable information such as the probability of illness associated with the consumption of shellfish and it also provides a reference for further in-depth QRA of NoVs in shellfish or other foods.

A multi-platform metabolomics approach to identify possible biomarkers for human faecal contamination in Greenshell™ mussels (Perna canaliculus)

Bivalve molluscs have the potential to bioaccumulate microbial pathogens including noroviruses from aquatic environments and as such, there is a need for a rapid and cheap in-situ method for their detection. Here, we characterise the tissue-specific response of New Zealand Greenshell™ mussels (Perna canaliculus) to faecal contamination from two different sources (municipal sewage and human faeces). This is done with the view to identify potential biomarkers that could be further developed into low cost, rapid and sensitive in-situ biosensors for human faecal contamination detection of mussels in growing areas. Tissue-specific metabolic profiles from gills, haemolymph and digestive glands were analysed using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). Clear differentiation of metabolic profiles was observed among treatments in each tissue type. Overall, energy pathways such as glycolysis, citrate cycle and oxidative phosphorylation were downregulated across the three mussel tissues studied following simulated contamination events. Conversely, considerable sterol upregulation in the gills was observed after exposure to contamination. Additionally, free pools of nucleotide phosphates and the antioxidant glutathione declined considerably post-exposure to contamination in gills. These results provide important insights into the tissue-specific metabolic effects of human faecal contamination in mussels. This study demonstrates the utility of metabolomics as a tool for identifying potential biomarkers in mussels.

Influence of fucosidase-producing bifidobacteria on the HBGA antigenicity of oyster digestive tissue and the associated norovirus binding

Bivalve molluscan shellfish such as oysters are filter feeders and are able to accumulate human noroviruses (NoVs) largely due to the presence of human histo-blood group antigens (HBGAs)-like carbohydrates in their intestine. Since the fucose contents play a key role in the binding of NoVs to HBGAs, this study intended to investigate the influence of fucosidase-producing bifidobacteria on the HBGA antigenicity of oyster digestive tissue and the associated NoV binding. On the contrary to the expected, after a treatment of the oyster digestive tissue extracts with Bifidobacterium bifidum strain JCM 1254, the binding of human NoV GII.4 virus like particles (VLPs) to the oyster digestive tissue extracts enhanced significantly (OD₄₅₀ from 1.15 ± 0.05 to 1.51 ± 0.02, P < 0.001) in an in vitro direct binding assay. The accumulation of human NoV GII·P16-GII.4 also enhanced significantly in the intestine of B. bifidum JCM 1254 treated oysters from 4.27 ± 0.25 log genomic copies/g oyster digestive tissue to 5.25 ± 0.29 log genomic copies/g oyster digestive tissue (P < 0.005) as observed in an in vivo test. Correspondingly, the type A antigenicity of the oyster digestive tissue extracts enhanced (OD₄₅₀ from 0.77 ± 0.04 to 1.06 ± 0.05, P < 0.01) after the treatment with B. bifidum JCM 1254. These results could be explained by the substrate specificity of the B. bifidum JCM 1254 associated fucosidases. This study identified an indirect interaction possibly happening between the bacterial microbiota with human NoVs during their transmission in the food systems. We also supplied a potential strategy to mitigate the NoV contamination from shellfish, suppose bacterial strains with specified fucosidase production could be obtained in the future.

Synergistic Antimicrobial Effectiveness of Plant Essential Oil and Its Application in Seafood Preservation: A Review

The synergistic potential of plant essential oils (EOs) with other conventional and non-conventional antimicrobial agents is a promising strategy for increasing antimicrobial efficacy and controlling foodborne pathogens. Spoilage microorganisms are one of main concerns of seafood products, while the prevention of seafood spoilage principally requires exclusion or inactivation of microbial activity. This review provides a comprehensive overview of recent studies on the synergistic antimicrobial effect of EOs combined with other available chemicals (such as antibiotics, organic acids, and plant extracts) or physical methods (such as high hydrostatic pressure, irradiation, and vacuum-packaging) utilized to reduce the growth of foodborne pathogens and/or to extend the shelf-life of seafood products. This review highlights the synergistic ability of EOs when used as a seafood preservative, discovering the possible routes of the combined techniques for the development of a novel seafood preservation strategy.

Study on norovirus contamination of live bivalve molluscs using real-time PCR

Foodborne and waterborne viruses are a major cause of human morbidity. Of them, noroviruses are recognised as the leading causative agents of sporadic infections and epidemic outbreaks of acute gastroenteritis in humans. Contaminated food products and water are the main source of infection with noroviruses. The infection of bivalve molluscs with human pathogenic viruses occurs by faecal contamination in the production coastal waters. In this study, 47 samples of live bivalve molluscs, including 15 samples of cultivated mussels (Mytilus galloprovincialis) and 32 samples of wild mussels (Tapes decussatus), collected from the Bulgarian and Mediterranean coasts, respectively, were submitted to RT-real-time TaqMan PCR to detect the presence of noroviruses genotype GI and GII. Norovirus genotype GII was found in 11 (23.4%) of all the samples tested. A single mollusc sample (2.1%) was positive for both norovirus genotypes. Our results demonstrated that shellfish intended for sale on the Bulgarian market might pose a potential risk for acquiring norovirus infection. Thus, food safety quality control of shellfish by optimised and standardised methods for detection of foodborne viruses, including noroviruses, should be urgently implemented in Bulgaria.

Evaluation of Inactivation of Murine Norovirus in Inoculated Shell Oysters by High Hydrostatic Pressure Treatment

One of the major foods causing norovirus gastroenteritis is bivalve shellfish, such as oysters. Depuration and relaying methods have been used to control norovirus. However, these methods may be inadequate to control norovirus gastroenteritis. The present study aimed to investigate the effectiveness of high hydrostatic pressure (HHP) treatment in controlling norovirus in shelled oysters, by evaluating the inactivating effect of HHP on murine norovirus strain 1 (MNV-1) inoculated into a buffer, oyster homogenate, and shelled oysters. First, MNV-1 was inoculated (infectivity of 4.5 log PFU/mL) into the buffer and oyster homogenate, with a pH of 6.3 and salinity (NaCl) of 1.5%, mimicking the habitats of the Pacific oyster (Crassostrea gigas). HHP treatment at 100, 200, 275, and 300 MPa for 2 and 5 min was conducted at an initial temperature of 0 or 5°C. The infectivity of MNV-1 in both the buffer and the oyster homogenate was lower when the initial temperature was 0°C. In the buffer, the infectivity of MNV-1 decreased to 1.8 log PFU/mL after HHP treatment (200 MPa for 5 min at 0°C), and the inactivating effect was higher in the buffer than in the oyster homogenate. MNV-1 was inoculated into shelled oysters (4.8 log PFU per oyster), and HHP treatment was done at 275, 300, and 350 MPa for 5 min at the initial temperature of 0°C. The infectivity of MNV-1 decreased to 2.8 log PFU per oyster after HHP treatment at 275 MPa for 5 min. The results indicate that the inactivating effect of HHP treatment varies, depending on the medium surrounding the viral particles. Inactivation was best in buffer, followed by oyster homogenate and shelled oysters. The data could inform the development of methods to control norovirus in oysters.