Norovirus Detection in Shellfish Using a Rapid, Sensitive Virus Recovery and Real-Time RT-PCR Detection Protocol

Droplet Digital PCR for Precise Quantification of Human Norovirus in Shellfish Associated with Gastroenteritis Illness

Norovirus is the predominant cause of viral gastroenteritis globally with foodborne outbreaks commonly reported. Filter-feeding bivalve molluscan shellfish can become contaminated with norovirus when grown in waters impacted by inadequately treated effluent wastewater, overflows, or other human fecal sources. Contaminated shellfish pose a significant risk to consumers, because combined with a low norovirus infectious dose, oysters and mussels are often eaten raw or lightly cooked resulting in no or minimal virus inactivation, respectively. In addition, shellfish contamination has significant economic impacts on the seafood industry. To improve risk assessments, reverse transcription (RT)-digital droplet PCR (ddPCR) was used to determine the precise norovirus concentrations in 20 shellfish samples, all positive for norovirus genogroup I and/or II (GI or GII) by RT-quantitative PCR (qPCR), and associated with reported norovirus illness in New Zealand. Using RT-ddPCR, total norovirus GI and/or GII concentrations in shellfish ranged between 44 and 4,630 genome copies (GC)/g digestive tissue. Importantly, 40% (8/20) of shellfish samples contained a total norovirus concentration less than 200 GC/g digestive tissue. In parallel, RNase treatment was applied, prior to viral extraction to remove free viral RNA, which subsequently led to average reductions in norovirus GC/g concentration of 37.1% and 19.4% for GI and GII, respectively. These RT-ddPCR data provide valuable evidence for risk assessment of contaminated shellfish and evaluation of safety guidelines and highlight issues associated with setting a safe threshold of norovirus in shellfish.

Efficient capturing and sensitive detection of hepatitis A virus from solid foods (green onion, strawberry, and mussel) using protamine-coated iron oxide (Fe3O4) magnetic nanoparticles and real-time RT-PCR

Hepatitis A virus (HAV) continues to be a public health concern and has caused large foodborne outbreaks and economic losses worldwide. Rapid detection of HAV in foods can help to confirm the source of outbreaks in a timely manner and prevent more people getting infected. In order to efficiently detect HAV at low levels of contamination in foods, rapid and easy-to-use techniques are required to separate and concentrate viral particles to a small volume. In the current study, HAV particles were eluted from green onion, strawberry, and mussel using glycine buffer (0.05 M glycine, 0.14 M NaCl, 0.2% (v/v) Tween 20, pH 9.0) and suspended viral particles were captured using protamine-coated magnetic nanoparticles (PMNPs). This process caused a selective concentration of the viral particles, which could be followed by quantitative real-time RT-PCR analysis. Results showed that pH, NaCl concentration, and PMNP amount used for the capturing had significant effects on the recovery efficiency of HAV (P < 0.05). The highest recovery rate was obtained at pH 9.0, 0.14 M NaCl, and 50 μL of PMNPs. The optimized PMNP capturing method enabled the rapid capture and concentration of HAV. A sensitive real-time RT-PCR test was developed with detection limits of 8.3 × 10⁰ PFU/15 g, 8.3 × 10¹ PFU/50 g, and 8.3 × 10⁰ PFU/5 g of HAV in green onion, strawberry, and mussel, respectively. In conclusion, the PMNP method is rapid and convenient in capturing HAV from complex solid food samples and can generate concentrated HAV sample solutions suitable for high-sensitivity real time RT-PCR detection of the virus.

Evaluation of pepper mild mottle virus as an indicator of human faecal pollution in shellfish and growing waters

Bivalve molluscan shellfish grown in areas impacted by human faecal pollution are at risk of being contaminated with multiple enteric viruses. To minimise the public health risks associated with shellfish consumption, determining the presence of faecal contamination in shellfish and their growing waters is crucial. In this study, we evaluated the use of pepper mild mottle virus (PMMoV) as an indicator of human faecal contamination in oysters, mussels, cockles and shellfish growing waters in New Zealand. Using reverse transcription quantitative polymerase chain reaction (RT-qPCR) the presence, and where applicable, the concentration of PMMoV was determined in faeces from 11 different animal species, influent (untreated) wastewater, shellfish and shellfish growing waters. Non-human faecal samples (from seagull, Canada goose, black swan and dog) were RT-qPCR positive for PMMoV. The faecal source specificity of PMMoV was 0.83 (maximum value of 1) when 'detected but not quantifiable' (DNQ) values were used. However, when 'lower limit of quantification' (LLOQ) values were used, the specificity increased to 0.92. The PMMoV concentration in influent wastewater (n = 10) ranged from 6.3 to 7.7 log₁₀ genome copies (GC)/L with a mean (±standard deviation) of 7.1 ± 0.5 log₁₀ GC/L. The overall occurrence of PMMoV in shellfish and shellfish growing waters from four different areas was 46/51 (90%) and 29/52 (56%), respectively. Of the cockles collected from an area known to be impacted by effluent wastewater, 14/14 (100%) contained PMMoV concentrations above the LLOQ. In contrast, only 13/37 (35%) shellfish and 6/52 (11.5%) growing water samples collected from three areas with low anthropogenic impact contained PMMoV concentrations above the LLOQ. The high concentration of PMMoV in influent wastewater indicates that PMMoV may be a promising indicator of human faecal contamination. The presence of PMMoV in shellfish and growing waters with a low anthropogenic impact may be of avian origin, and this needs to be considered if using PMMoV for monitoring shellfish and shellfish growing water quality in New Zealand.

Detection of Human Enteric Viruses in French Polynesian Wastewaters, Environmental Waters and Giant Clams

Lack of wastewater treatment efficiency causes receiving seawaters and bivalve molluscan shellfish to become contaminated, which can lead to public health issues. Six wastewater samples, five seawater samples and three batches of giant clams from Tahiti (French Polynesia) were investigated for the presence of enteric viruses, but also if present, for the diversity, infectivity and integrity of human adenoviruses (HAdV). Enteroviruses (EV), sapoviruses (SaV) and human polyomaviruses (HPyV) were detected in all wastewater samples. In decreasing frequency, noroviruses (NoV) GII and HAdV, rotaviruses (RoV), astroviruses (AsV), NoV GI and finally hepatitis E viruses (HEV) were also observed. Nine types of infectious HAdV were identified. HPyV and EV were found in 80% of seawater samples, NoV GII in 60%, HAdV and SaV in 40% and AsV and RoV in 20%. NoV GI and HEV were not detected in seawater. Intact and infectious HAdV-41 were detected in one of the two seawater samples that gave a positive qPCR result. Hepatitis A viruses were never detected in any water types. Analysis of transcriptomic data from giant clams revealed homologues of fucosyltransferases (FUT genes) involved in ligand biosynthesis that strongly bind to certain NoV strains, supporting the giant clams ability to bioaccumulate NoV. This was confirmed by the presence of NoV GII in one of the three batches of giant clams placed in a contaminated marine area. Overall, all sample types were positive for at least one type of virus, some of which were infectious and therefore likely to cause public health concerns.

Effect of the Shellfish Proteinase K Digestion Method on Norovirus Capsid Integrity

Norovirus outbreaks are associated with the consumption of contaminated shellfish, and so efficient methods to recover and detect infectious norovirus in shellfish are important. The Proteinase K digestion method used to recover norovirus from shellfish, as described in the ISO 15216, would be a good candidate but its impact on the virus capsid integrity and thus infectivity was never examined. The aim of this study was to assess the impact of the Proteinase K digestion method, and of the heat treatment component of the method alone, on norovirus (genogroups I and II) and MS2 bacteriophage capsid integrity. A slightly modified version of the ISO method was used. RT-qPCR was used for virus detection following digestion of accessible viral RNA using RNases. MS2 phage infectivity was measured using a plaque assay. The effect of shellfish digestive glands (DG) on recovery was evaluated. In the presence of shellfish DG, a reduction in MS2 phage infectivity of about 1 log₁₀ was observed after the Proteinase K digestion method and after heat treatment component alone. For norovirus GII and MS2 phage, there was no significant loss of genome following the Proteinase K digestion method but there was a significant 0.24 log₁₀ loss of norovirus GI. In the absence of shellfish DG, the reduction in MS2 phage infectivity was about 2 log₁₀, with the addition of RNases resulting in a significant loss of genome for all tested viruses following complete Proteinase K digestion method and the heat treatment alone. While some protective effect from the shellfish DG on viruses was observed, the impact on capsid integrity and infectivity suggests that this method, while suitable for norovirus genome detection, may not completely preserve virus infectivity.

Spatial and Temporal Distribution of Norovirus and E. coli in Sydney Rock Oysters Following a Sewage Overflow into an Estuary

This paper reports a study of norovirus (NoV) GII distribution and persistence in Sydney rock oysters (SRO) (Saccostrea glomerata) located in an estuary after a pump station sewage overflow. SRO were strategically placed at six sites spanning the length of the estuary from the pump station to the sea. The spatial and temporal distribution of NoV, hepatitis A virus (HAV) and Escherichia coli (E. coli) in oysters was mapped after the contamination event. NoV GI and GII, HAV and E. coli were quantified for up to 48 days in oysters placed at six sites ranging from 0.05 to 8.20 km from the sewage overflow. NoV GII was detected up to 5.29 km downstream and persisted in oysters for 42 days at the site closest to the overflow. NoV GII concentrations decreased significantly over time; a reduction rate of 8.5% per day was observed in oysters (p < 0.001). NoV GII concentrations decreased significantly as a function of distance at a rate of 5.8% per km (p < 0.001) and the decline in E. coli concentration with distance was 20.1% per km (p < 0.001). HAV and NoV GI were not detected. A comparison of NoV GII reduction rates from oysters over time, as observed in this study and other published research, collectively suggest that GII reduction rates from oysters may be broadly similar, regardless of environmental conditions, oyster species and genotype.

Propidium Monoazide Integrated with qPCR Enables the Detection and Enumeration of Infectious Enteric RNA and DNA Viruses in Clam and Fermented Sausages

The increase of foodborne viral outbreaks highlights the need for a rapid and sensitive method for the prediction of viral infectivity in food samples. This study assesses the use of propidium monoazide (PMA) coupled with real-time PCR methods (RT-qPCR or qPCR for RNA or DNA viruses, respectively) in the determination of viral infectivity in complex animal-related food matrices. Clam and Spanish fermented sausage (“chorizo”) samples were spiked with infectious and heat-inactivated human adenovirus-2 (HAdV-2) and mengovirus (vMC₀). PMA-qPCR/RT-qPCR discriminated infective virus particles, with significant reductions (>2.7 log₁₀ or 99.7%). Additionally, infectious HAdV-2 and vMC₀ were quantified by plaque assay (in plaque forming units, PFU), and compared with those in virus genomes copies (GCs) quantified by PMA-qPCR/RT-qPCR. A consistent correlation (R² > 0.92) was showed between PFU and GCs along serial 10-fold dilutions in both DNA and RNA virus and in both food matrices. This study shows the use of PMA coupled to qPCR/RT-qPCR as a promising alternative for prediction of viral infectivity in food samples in comparison to more expensive and time-consuming methods and for those viruses that are not able to grow under available cell culture techniques.

A 1-Year Study on the Detection of Human Enteric Viruses in New Caledonia

Human enteric viruses occur in high concentrations in wastewater and can contaminate receiving environmental waters. Due to the lack of data on the prevalence of enteric viruses in New Caledonia, the presence and the concentrations of enteric viruses in wastewater and seawater were determined. Untreated wastewater and seawater samples were collected monthly for 1 year from a wastewater treatment plant (WWTP) and from the WWTP's outlet, located directly on a popular recreational beach. Samples were tested for norovirus genogroups I and II (NoV GI and GII), astroviruses (AsV), sapoviruses (SaV), enteroviruses (EV), hepatitis A viruses (HAV), rotaviruses (RoV), human adenoviruses (HAdV) and human polyomaviruses (HPyV). To support these data, faecal samples from cases of gastroenteritis were tested for the first time for NoV and detected in the population. NoV GI, NoV GII, EV, SaV, HAdV and HPyV were detected in all wastewaters, RoV in 75% and AsV in 67%. HAV were not detected in wastewater. Overall, 92% of seawater samples were positive for at least one virus. HPyV were detected most frequently in 92% of samples and at concentrations up to 7.7 × 10(3) genome copies/L. NoV GI, NoV GII, EV, SaV, RoV and HAdV were found in 33, 66, 41, 33, 16 and 66% of seawater samples, respectively. AsV were not detected in seawater. This study reports for the first time the presence of NoV and other enteric viruses in New Caledonia and highlights the year-round presence of enteric viruses in the seawater of a popular beach.

Waterborne human pathogenic viruses of public health concern

In recent years, the impending impact of waterborne pathogens on human health has become a growing concern. Drinking water and recreational exposure to polluted water have shown to be linked to viral infections, since viruses are shed in extremely high numbers in the faeces and vomit of infected individuals and are routinely introduced into the water environment. All of the identified pathogenic viruses that pose a significant public health threat in the water environment are transmitted via the faecal-oral route. This group, are collectively known as enteric viruses, and their possible health effects include gastroenteritis, paralysis, meningitis, hepatitis, respiratory illness and diarrhoea. This review addresses both past and recent investigations into viral contamination of surface waters, with emphasis on six types of potential waterborne human pathogenic viruses. In addition, the viral associated illnesses are outlined with reference to their pathogenesis and routes of transmission.

Rotavirus Occurrence in Shellfish with Low Levels of E. coli

The purpose of this study was to evaluate "in field" the accumulation of virus in shellfish and compare it with the concentration of bacterial indicators. Individuals of Mytilus galloprovincialis were placed in two sampling station located in a contaminated coastal bay and in one control station located one kilometer offshore. The presence of Rotavirus and E. coli was assessed weekly both in seawater and in shellfish samples. The Rotavirus genome was detected in water, preliminarily concentrated by tangential flow ultrafiltration method, and in hepatopancreas of mussels by Real-Time PCR. E. coli was enumerated in water matrices by a filtering method and in mussels by the MPN method. Rotaviruses were not recorded in seawater, while in mussels they were detected since third week after placement. E. coli in mussels were always below the limits set in the Regulation (EC) 854/2004. This study suggests the need for a viral indicator to insure the safety for consumption of shellfish.

Molecular detection and genotyping of noroviruses

Noroviruses (NoVs) are a major cause of gastroenteritis worldwide in humans and animals and are known as very infectious viral agents. They are spread through feces and vomit via several transmission routes involving person-to-person contact, food, and water. Investigation of these transmission routes requires sensitive methods for detection of NoVs. As NoVs cannot be cultivated to date, detection of these viruses relies on the use of molecular methods such as (real-time) reverse transcriptase polymerase chain reaction (RT-PCR). Regardless of the matrix, detection of NoVs generally requires three subsequent steps: a virus extraction step, RNA purification, and molecular detection of the purified RNA, occasionally followed by molecular genotyping. The current review mainly focused on the molecular detection and genotyping of NoVs. The most conserved region in the genome of human infective NoVs is the ORF1/ORF2 junction and has been used as a preferred target region for molecular detection of NoVs by methods such as (real-time) RT-PCR, NASBA, and LAMP. In case of animal NoVs, broad range molecular assays have most frequently been applied for molecular detection. Regarding genotyping of NoVs, five regions situated in the polymerase and capsid genes have been used for conventional RT-PCR amplification and sequencing. As the expected levels of NoVs on food and in water are very low and inhibition of molecular methods can occur in these matrices, quality control including adequate positive and negative controls is an essential part of NoV detection. Although the development of molecular methods for NoV detection has certainly aided in the understanding of NoV transmission, it has also led to new problems such as the question whether low levels of human NoV detected on fresh produce and shellfish could pose a threat to public health.

Analytical methods for the detection of viruses in food by example of CCL-3 bioagents

This critical review presents challenges and strategies in the detection of viral contaminants in food products. Adenovirus, caliciviruses, enteroviruses, and hepatitis A are emerging contaminant viruses. These viruses contaminate a variety of food products, including fruits, vegetables, shellfish, and ready-to-eat processed foods. The diversity of targets and sample matrices presents unique challenges to virus monitoring that have been addressed by a wide array of processing and detection methods. This review covers sample acquisition and handling, virus recovery/concentration, and the determination of targets using molecular biology and mass-spectrometric approaches. The concentration methods discussed include precipitation, antibody-based concentration, and filtration; the detection methods discussed include microscopy, polymerase chain reaction, nucleic acid sequence-based amplification, and mass spectrometry.

Detection and molecular characterization of enteric viruses in environmental samples in Monastir, Tunisia between January 2003 and April 2007

AIMS

A prospective study was performed to characterize the main human enteric viruses able to persist in sewage samples and in shellfish tissues, and to establish the correlation between environmental strains and viral infantile diarrhoea observed in the same area during the same period.

METHODS AND RESULTS

A total of 250 sewage (raw and treated) and 60 shellfish samples were collected between January 2003 and April 2007 in Monastir region, Tunisia. Group A rotavirus (RVA) was detected in 80 (32%) sewage samples, norovirus (NoV) in 11 (4·4%) and enteric adenovirus (AdV) in 1 (0·4%). Among 60 shellfish samples collected near sewage effluents, one was contaminated by NoV (1·6%).

CONCLUSION

Our data represent the first documentation in Tunisia, combining gastroenteritis viruses circulating in the environment and in clinical isolates. We observed a correlation between environmental strains and those found in children suffering from gastroenteritis during the same period study. This suggests the existence of a relationship between water contamination and paediatric diarrhoea.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results address the potential health risks associated with transmission of human enteric viruses through water-related environmental routes. The research findings will aid in elucidating the molecular epidemiology and circulation of enteric viruses in Tunisia and in Africa, where data are rare.

Viral multiplex quantitative PCR assays for tracking sources of fecal contamination

Human and animal fecal pollution of the environment presents a risk to human health because of the presence of pathogenic viruses and bacteria. To distinguish between human and animal sources of pollution, we designed specific real-time reverse transcription (RT)-PCR assays for human and animal enteric viruses, including norovirus genogroups I, II, and III; porcine adenovirus types 3 and 5; ovine adenovirus; atadenovirus; and human adenovirus species C and F, which are excreted by infected humans, pigs, cattle, sheep, deer, and goats, and for the detection of F+ RNA bacteriophage genogroups I to IV, which are associated with human and animal wastes. The sensitivity of this viral toolbox (VTB) was tested against 10-fold dilution series of DNA plasmids that carry the target sequences of the respective viruses and was shown to detect at least 10 plasmid copies for each assay. A panel of human and animal enteric and respiratory viruses showed these assays to be highly sensitive and specific to their respective targets. The VTB was used to detect viruses in fecal and environmental samples, including raw sewage and biosolids from municipal sewage treatment plants, abattoir sewage, and fecally contaminated shellfish and river water, which were likely to contain animal or human viruses.

Inactivation and elimination of human enteric viruses by Pacific oysters

AIMS

To investigate the comparative elimination of three different human enterically transmitted viruses [i.e. hepatitis A virus (HAV), norovirus (NoV) and poliovirus (PV)] and inactivation of HAV and PV by Pacific oysters.

METHODS AND RESULTS

New Zealand grown Pacific oysters (Crassostrea gigas) were allowed to bioaccumulate HAV, NoV and PV. Samples of oyster gut, faeces and pseudofaeces were then analysed by using real-time RT-PCR to determine the amount of viral RNA and cell culture methods to identify changes in the number of plaque forming units. The results suggest that the majority of the PV present in the oyster gut and oyster faeces is noninfectious, while in contrast, most of the HAV detected in the oyster gut are infectious. Depuration experiments identified a large drop in the count of PV in the gut over a 23-h cleansing period, whereas the levels of HAV and NoV did not significantly decrease.

CONCLUSIONS

Human enterically transmitted viruses are eliminated and inactivated at different rates by Pacific oysters.

SIGNIFICANCE AND IMPACT OF STUDY

The research presented in this article has implications for risk management techniques that are used to improve the removal of infectious human enteric viruses from bivalve molluscs.