Human norovirus detection in bivalve shellfish in Brazil and evaluation of viral infectivity using PMA treatment

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.

Assessment of wastewater derived pollution using viral monitoring in two estuaries

Human wastewater-derived pollution of the environment is an emerging health risk that increases the number of waterborne and foodborne illnesses globally. To better understand and mitigate such health risks, we investigated the prevalence of faecal indicator bacteria, Escherichia coli, and indicator virus (crAssphage) along with human and animal enteric viruses (adenoviruses, noroviruses, sapoviruses, hepatitis E virus) in shellfish and water samples collected from two shellfish harvesting areas in the UK. Human noroviruses were detected at higher detection rates in oyster and water samples compared to mussels with peaks during the autumn-winter seasons. Human enteric viruses were sporadically detected during the warmer months, suggesting potential introduction by tourists following the relaxation of COVID-19 lockdown measures. Our results suggest that viral indicators are more suitable for risk assessment and source tracking than E. coli. The detection of emerging hepatitis and sapoviruses, support the need for comprehensive viral monitoring in shellfish harvesting areas.

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.

Monitoring and Genotyping of Norovirus in Bivalve Molluscan Shellfish from Northern Italian Seas (2018-2020)

Norovirus (NoV) is an enteric virus with foodborne transmission. Bivalve shellfish are a main source of infections and outbreaks. In Italy a voluntary based monitoring plan to check the safety of bivalve shellfish was set up at provincial level. This study describes the occurrence and distribution of NoV in the Northern Adriatic Sea and in the Ligurian Sea. From October 2018 to September 2020, 807 bivalve shellfish samples (n = 205 oysters, n = 182 mussels, n = 348 clams, n = 72 other bivalve shellfish) were tested by One-Step Retrotranscription Real-time polymerase chain reaction for NoV GI and GII and quantified according to the ISO 15216-2:2013 and ISO 15216-1:2017. Positive samples were further analyzed to determine genotype by sequencing of the ORF1/ORF2 junction of the viral genome. A total of 126 samples were positive for NoV, mussels, and oysters had the highest probability of being positive and positive samples were found mainly in the colder season. Of these samples, 46% were NoV GII, 13% NoV GI, and 40% carried both genogroups. Thirty-seven samples were typeable (GI n = 12 and GII n = 25) with GI samples belonging to four genotypes and GII samples belonging to five genotypes. GII.3 genotype was the most prevalent, followed by GII.4, particularly Sydney 2012 subtype, a leading cause of infections worldwide, was found in three oysters' and three clams' samples. The phylogenetic analysis revealed a high heterogeneity among the species that are scattered in several clusters. Considering the low infectious dose the overall presence of NoV in edible shellfish, particular those to be eaten raw or undercooked, is moderately high. The presence of genotypes frequently involved in human infections strengthens the need for ongoing monitoring, which should be extended at national level.

A review of nucleic acid-based detection methods for foodborne viruses: Sample pretreatment and detection techniques

Viruses are major pathogens that cause food poisoning when ingested via contaminated food and water. Therefore, the development of foodborne virus detection technologies that can be applied throughout the food distribution chain is essential for food safety. A common nucleic acid-based detection method is polymerase chain reaction (PCR), which has become the gold standard for monitoring food contamination by viruses due to its high sensitivity, and availability of commercial kits. However, PCR-based methods are labor intensive and time consuming, and are vulnerable to inhibitors that may be present in food samples. In addition, the methods are restricted with regard to site of analysis due to the requirement of expensive and large equipment for sophisticated temperature regulation and signal analysis procedures. To overcome these limitations, optical and electrical readout biosensors based on nucleic acid isothermal amplification technology and nanomaterials have emerged as alternatives for nucleic acid-based detection of foodborne viruses. Biosensors are promising portable detection tools owing to their easy integration into compact platforms and ability to be operated on-site. However, the complexity of food components necessitates the inclusion of tedious preprocessing steps, and the lack of stability studies on residual food components further restricts the practical application of biosensors as a universal detection method. Here, we summarize the latest advances in nucleic acid-based strategies for the detection of foodborne viruses, including PCR-based and isothermal amplification-based methods, gene amplification-free methods, as well as food pretreatment methods. The principles, strengths/disadvantages, and performance of each method, problems to be solved, and future prospects for the development of a universal detection method are discussed.

Acute gastroenteritis outbreak associated with multiple and rare norovirus genotypes after storm events in Santa Catarina, Brazil

Norovirus is a major cause of acute diarrheal disease (ADD) outbreaks worldwide. In the present study, we investigated an ADD outbreak caused by norovirus in several municipalities of Santa Catarina state during the summer season, southern Brazil in 2023. As of the 10th epidemiological week of 2023, approximately 87 000 ADD cases were reported, with the capital, Florianópolis, recording the highest number of cases throughout the weeks. By using RT-qPCR and sequencing, we detected 10 different genotypes, from both genogroups (G) I and II. Some rare genotypes were also identified. Additionally, rotavirus and human adenovirus were sporadically detected among the ADD cases. Several features of the outbreak suggest that sewage-contaminated water could played a role in the surge of ADD cases. Storm events in Santa Catarina state that preceded the outbreak likely increased the discharge of contaminated wastewater and stormwater into water bodies, such as rivers and beaches during a high touristic season in the state. Climate change-induced extreme weather events, including intensified rainfall and frequent floods, can disturb healthcare and sanitation systems. Implementing public policies for effective sanitation, particularly during peak times, is crucial to maintain environmental equilibrium and counter marine pollution.

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.

The impact of climate change and pollution on trematode-bivalve dynamics

Coastal ecosystems and their marine populations are increasingly threatened by global environmental changes. Bivalves have emerged as crucial bioindicators within these ecosystems, offering valuable insights into biodiversity and overall ecosystem health. In particular, bivalves serve as hosts to trematode parasites, making them a focal point of study. Trematodes, with their life cycles intricately linked to external factors, provide excellent indicators of environmental changes and exhibit a unique ability to accumulate pollutants beyond ambient levels. Thus, they act as living sentinels, reflecting the ecological condition of their habitats. This paper presents a comprehensive review of recent research on the use of bivalve species as hosts for trematodes, examining the interactions between these organisms. The study also investigates the combined impact of trematode infections and other pollutants on bivalve molluscs. Trematode infections have multifaceted consequences for bivalve species, influencing various aspects of their physiology and behavior, including population-wide mortality. Furthermore, the coexistence of trematode infections and other sources of pollution compromises host resistance, disrupts parasite transmission, and reduces the abundance of intermediate hosts for complex-living parasites. The accumulation process of these parasites is influenced not only by external factors but also by host physiology. Consequently, the implications of climate change and environmental factors, such as temperature, salinity, and ocean acidification, are critical considerations. In summary, the intricate relationship between bivalves, trematode parasites, and their surrounding environment provides valuable insights into the health and sustainability of coastal ecosystems. A comprehensive understanding of these interactions, along with the influence of climate change and environmental parameters, is essential for effective management and conservation strategies aimed at preserving these delicate ecosystems and the diverse array of species that rely on them.

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.

A triton X-100 assisted PMAxx-qPCR assay for rapid assessment of infectious African swine fever virus

Introduction

African Swine Fever (ASF) is a highly infectious disease of pigs, caused by African swine fever virus (ASFV). The lack of vaccines and drugs makes strict disinfection practices to be one of the main measurements to curb the transmission of ASF. Therefore, it is important to assess if all viruses are inactivated after disinfection or after long time exposure in their natural conditions. Currently, the infectivity of ASFV is determined by virus isolation and culture in a biosafety level 3 (BSL-3) laboratory. However, BSL-3 laboratories are not readily available, need skilled expertise and may be time consuming.

Methods

In this study, a Triton X-100 assisted PMAxx-qPCR method was developed for rapid assessment of infectious ASFV in samples. PMAxx, an improved version of propidium monoazide (PMA), can covalently cross-link with naked ASFV-DNA or DNA inside inactivated ASFV virions under assistance of 0.1% (v/v) TritonX-100, but not with ASFV-DNA inside live virions. Formation of PMAxx-DNA conjugates prevents PCR amplification, leaving only infectious virions to be detected. Under optimum conditions, the limit of detection of the PMAxx-qPCR assay was 2.32log₁₀HAD₅₀/mL of infectious ASFV. Testing different samples showed that the PMAxx-qPCR assay was effective to evaluate intact ASFV virions after treatment by heat or chemical disinfectants and in simulated samples such as swine tissue homogenate, swine saliva swabs, and environmental swabs. However, whole-blood and saliva need to be diluted before testing because they may inhibit the PCR reaction or the cross-linking of PMAxx with DNA.

Conclusion

The Triton X-100 assisted PMAxx-qPCR assay took less than 3 h from sample to result, offering an easier and faster way for assessing infectious ASFV in samples from places like pig farms and pork markets.

Detection and Molecular Characterization of Enteric Viruses in Bivalve Mollusks Collected in Arraial do Cabo, Rio de Janeiro, Brazil

Viral bivalve contamination is a recognized food safety hazard. Therefore, this study investigated the detection rates, seasonality, quantification, and genetic diversity of enteric viruses in bivalve samples (mussels and oysters). We collected 97 shellfish samples between March 2018 and February 2020. The screening of samples by qPCR or RT-qPCR revealed the detection of norovirus (42.3%), rotavirus A (RVA; 16.5%), human adenovirus (HAdV; 24.7%), and human bocavirus (HBoV; 13.4%). There was no detection of hepatitis A virus. In total, 58.8% of shellfish samples tested positive for one or more viruses, with 42.1% of positive samples contaminated with two or more viruses. Norovirus showed the highest median viral load (3.3 × 106 GC/g), followed by HAdV (median of 3.5 × 104 GC/g), RVA (median of 1.5 × 103 GC/g), and HBoV (median of 1.3 × 103 GC/g). Phylogenetic analysis revealed that norovirus strains belonged to genotype GII.12[P16], RVA to genotype I2, HAdV to types -C2, -C5, and -F40, and HBoV to genotypes -1 and -2. Our results demonstrate the viral contamination of bivalves, emphasizing the need for virological monitoring programs to ensure the quality and safety of shellfish for human consumption and as a valuable surveillance tool to monitor emerging viruses and novel variants.

Updating a New Semi-nested PCR Primer Pair for the Specific Detection of GII Norovirus in Oysters

Oysters are major transmission vectors of noroviruses (NoVs) in the environment. Outbreaks of NoVs are often associated with the consumption of NoV-contaminated oysters. Laboratory confirmation of suspected oyster samples is a critical step in the surveillance and control of NoVs. Because of non-specific amplification, false-positive results are frequently obtained by semi-nested RT-PCR with the presently widely used primer set (G2SKF/G2SKR). Here, a novel universal PCR primer set N (NG2OF/NG2OR) specific for genogroup II (GII) NoVs was designed based on all GII NoV sequences available in public databases. Specific products were obtained with the primer set N when the NoV-positive oysters, spiked with each of five representative genotypes of GII NoVs (GII.17, GII.13, GII.4, GII.3, and GII.12), were subjected to analyzing. No products were detected with the primer set N for the NoV-negative oysters, while the primer set C gave various non-specific bands. Twenty-three out of 156 fresh oyster samples were NoV-positive with both the primer set N and the classic primer set, while eight were NoV-positive solely with the primer set N. Compared with the classic primer set, the newly designed primer set N had a higher detection rate and improved specificity for GII NoVs in oyster samples. These results show that the novel PCR primer pair is specific and applicable for the detection of GII NoVs in oysters.

Detection of Norovirus Recombinant GII.2[P16] Strains in Oysters in Thailand

Human norovirus causes sporadic and epidemic acute gastroenteritis worldwide, and the predominant strains are genotype GII.4 variants. Recently, a novel GII.17[P17] and a recombinant GII.2[P16] strain have been reported as the causes of gastroenteritis outbreaks. Outbreaks of norovirus are frequently associated with foodborne illness. In this study, each of 75 oyster samples processed by a proteinase K extraction method and an adsorption-elution method were examined for noroviruses using RT-nested PCR with capsid primers. Thirteen (17.3%) samples processed by either method tested positive for norovirus genogroup II (GII). PCR amplicons were characterized by DNA sequencing and phylogenetic analysis as GII.2 (n = 6), GII.4 (n = 1), GII.17 (n = 3), and GII.unclassified (n = 3). Norovirus-positive samples were further amplified by semi-nested RT-PCR targeting the polymerase-capsid genes. One nucleotide sequence revealed GII.17[P17] Kawasaki strain. Five nucleotide sequences were identified as belonging to the recombinant GII.2[P16] strains by recombination analysis. The collected oyster samples were quantified for norovirus GII genome copy number by RT-quantitative PCR. Using the proteinase K method, GII was found in 13/75 (17.3%) of samples with a range of 8.83-1.85 × 10⁴ genome copies/g of oyster. One sample (1/75, 1.3%) processed by the adsorption-elution method was positive for GII at 5.00 × 10¹ genome copies/g. These findings indicate the circulation of a new variant GII.17 Kawasaki strain and the recombinant GII.2[P16] in oyster samples corresponding to the circulating strains reported at a global scale during the same period of time. The detection of the recombinant strains in oysters emphasizes the need for continuing systematic surveillance for control and prevention of norovirus gastroenteritis.

Norovirus Foodborne Outbreak Associated With the Consumption of Ice Pop, Southern Brazil, 2020

Norovirus is a major cause of foodborne-associated acute gastroenteritis (AGE) outbreaks worldwide. Usually, food products are contaminated either during harvesting or preparation, and the most common products associated to norovirus outbreaks are raw or undercooked bivalve shellfish, fruits (frozen berries) and ready-to-eat produce. In the present study, we investigated an AGE outbreak caused by norovirus associated with the consumption of ice pops in southern Brazil. Clinical stool samples from patients and ice pops samples were collected and analyzed for viruses' detection. By using RT-qPCR and sequencing, we detected the uncommon genotype GII.12[P16] in clinical samples and GII.12 in samples of ice pop. Strains shared identity of 100% at nucleotide level strongly suggesting the consumption of ice pops as the source of the outbreak.

Application of Lab-on-Chip for Detection of Microbial Nucleic Acid in Food and Environment

Various diseases caused by food-borne or environmental pathogenic microorganisms have been a persistent threat to public health and global economies. It is necessary to regularly detect microorganisms in food and environment to prevent infection of pathogenic microorganisms. However, most traditional detection methods are expensive, time-consuming, and unfeasible in practice in the absence of sophisticated instruments and trained operators. Point-of-care testing (POCT) can be used to detect microorganisms rapidly on site and greatly improve the efficiency of microbial detection. Lab-on-chip (LOC) is an emerging POCT technology with great potential by integrating most of the experimental steps carried out in the laboratory into a single monolithic device. This review will primarily focus on principles and techniques of LOC for detection of microbial nucleic acid in food and environment, including sample preparation, nucleic acid amplification and sample detection.

Norovirus GII and astrovirus in shellfish from a mangrove region in Cananéia, Brazil: molecular detection and characterization

In recent years, annual cases of gastroenteritis have been reported in the world at high rates, suggesting an association with the consumption of shellfish with enteric viruses in their tissues. Anthropic activities are considered a source of environmental pollution and the main responsible for contamination by pathogenic microorganisms in aquatic environments. The objective of this study was to evaluate, by RT-semi-nested PCR, the presence of astrovirus (AstV) and norovirus genogroup II (NoV GII) in mussels (Mytella falcata) and oysters (Crassostrea brasiliana) collected in two sites of the Lagunar Complex of Cananéia, State of São Paulo, Brazil. A total of 150 samples of mussels and oysters (75 samples each) were analyzed. AstV was not identified in any shellfish sample. NoV GII was detected in 21 samples (14%), 8 mussel samples (38%), and 13 oyster samples (62%). From the 21 positive samples, 16 were analyzed by nucleotide sequencing. The molecular characterization revealed that Brazilian samples were grouped into clades along with other sequences from Brazil, Japan, and Mexico. There was 93.8-100% amino acid sequence similarity among the samples in this study and > 94.9% when compared with the strains isolated from clinical cases in Brazil. The screening of shellfish for the presence of health-significant enteric viruses can help prevent outbreaks among consumers and contribute to the improvement of the estuarine environment.

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

Human norovirus (HuNoV) is a major foodborne pathogen that causes acute viral gastroenteritis, and bivalve shellfish are one of the main carriers of HuNoV transmission. A comprehensive understanding of bivalve shellfish-related HuNoV outbreaks focusing on contamination factors, bioaccumulation mechanisms, and pre- and post-harvest interventions is essential for the development of effective strategies to prevent contamination of shellfish. This review comprehensively surveys the current knowledge on global contamination and non-thermal treatment of HuNoV in bivalve shellfish. HuNoV contamination in bivalve shellfish is significantly related to the season and water. While evaluating the water quality of shellfish-inhabited waters is a key intervention, the development of non-heat treatment technology to effectively inactivate the HuNoV in bivalve shellfish while maintaining the flavor and nutrition of the shellfish is also an important direction for further research. Additionally, this review explores the bioaccumulation mechanisms of HuNoV in bivalve shellfish, especially the mechanism underlying the binding of histo-blood group antigen-like molecules and HuNoV. The detection methods for infectious HuNoV are also discussed. The establishment of effective methods to rapidly detect infectious HuNoV and development of biological components to inactivate or prevent HuNoV contamination in shellfish also need to be studied further.

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.

Optimisation of a PMAxx™-RT-qPCR Assay and the Preceding Extraction Method to Selectively Detect Infectious Murine Norovirus Particles in Mussels

Human noroviruses are a major cause for gastroenteritis outbreaks. Filter-feeding bivalve molluscs, which accumulate noroviruses in their digestive tissues, are a typical vector for human infection. RT-qPCR, the established method for human norovirus detection in food, does not allow discrimination between infectious and non-infectious viruses and can overestimate potentially infectious viral loads. To develop a more accurate method of infectious norovirus load estimation, we combined intercalating agent propidium monoazide (PMAxx™)-pre-treatment with RT-qPCR assay using in vitro-cultivable murine norovirus. Three primer sets targeting different genome regions and diverse amplicon sizes were used to compare one-step amplification of a short genome fragment to three two-step long-range RT-qPCRs (7 kbp, 3.6 kbp and 2.3 kbp amplicons). Following initial assays performed on untreated infectious, heat-, or ultraviolet-inactivated murine noroviruses in PBS suspension, PMAxx™ RT-qPCRs were implemented to detect murine noroviruses subsequent to their extraction from mussel digestive tissues; virus extraction via anionic polymer-coated magnetic beads was compared with the proteinase K-dependent ISO norm. The long-range RT-qPCR process detecting fragments of more than 2.3 kbp allowed accurate estimation of the infectivity of UV-damaged murine noroviruses. While proteinase K extraction limited later estimation of PMAxx™ pre-treatment effects and was found to be unsuited to the assay, magnetic bead-captured murine noroviruses retained their infectivity. Genome copies of heat-inactivated murine noroviruses differed by 2.3 log₁₀ between RT-qPCR and PMAxx™-RT-qPCR analysis in bivalve molluscs, the PMAxx™ pre-treatment allowing a closer approximation of infectious titres. The combination of bead-based virus extraction and PMAxx™ RT-qPCR thus provides a more accurate model for the estimation of noroviral bivalve mollusc contamination than the conjunction of proteinase K extraction and RT-qPCR and has the potential (once validated utilising infectious human norovirus) to provide an added measure of security to food safety authorities in the hazard assessment of potential bivalve mollusc contamination.