Assessment of the Impact on Human Health of the Presence of Norovirus in Bivalve Molluscs: What Data Do We Miss?

In the latest One Health ECDC EFSA technical report, Norovirus in fish and fishery products have been listed as the agent/food pair causing the highest number of strong-evidence outbreaks in the EU in 2019. This review aims to identify data gaps that must be filled in order to increase knowledge on Norovirus in bivalve molluscs, perform a risk assessment and rank the key mitigation strategies for this biological hazard, which is relevant to public health. Virologic determinations are not included in any of the food safety and process hygiene microbiologic criteria reflected in the current European regulations. In addition, the Escherichia coli-based indices of acceptable faecal contamination for primary production, as well as the food safety criteria, do not appear sufficient to indicate the extent of Norovirus contamination. The qualitative risk assessment data collected in this review suggests that bivalve molluscs present a high risk to human health for Norovirus only when consumed raw or when insufficiently cooked. On the contrary, the risk can be considered negligible when they are cooked at a high temperature, while information is still scarce for non-thermal treatments.

Occurrence of Human Enteric Viruses in Shellfish along the Production and Distribution Chain in Sicily, Italy

Contamination of bivalve mollusks with human pathogenic viruses represents a recognized food safety risk. Thus, monitoring programs for shellfish quality along the entire food chain could help to finally preserve the health of consumers. The aim of the present study was to provide up-to-date data on the prevalence of enteric virus contamination along the shellfish production and distribution chain in Sicily. To this end, 162 batches of mollusks were collected between 2017 and 2019 from harvesting areas, depuration and dispatch centers (n = 63), restaurants (n = 6) and retail stores (n = 93) distributed all over the island. Samples were processed according to ISO 15216 standard method, and the presence of genogroup GI and GII norovirus (NoV), hepatitis A and E viruses (HAV, HEV), rotavirus and adenovirus was investigated by real-time reverse transcription polymerase chain reaction (real-time-RT PCR), nested (RT)-PCR and molecular genotyping. Our findings show that 5.56% of samples were contaminated with at least one NoV, HAV and/or HEV. Contaminated shellfish were sampled at production sites and retail stores and their origin was traced back to Spain and several municipalities in Italy. In conclusion, our study highlights the need to implement routine monitoring programs along the whole food chain as an effective measure to prevent foodborne transmission of enteric viruses.

Occurrence of Human Enteric Viruses in Water Sources and Shellfish: A Focus on Africa

Enteric viruses are a diverse group of human pathogens which are primarily transmitted by the faecal-oral route and are a major cause of non-bacterial diarrhoeal disease in both developed and developing countries. Because they are shed in high numbers by infected individuals and can persist for a long time in the environment, they pose a serious threat to human health globally. Enteric viruses end up in the environment mainly through discharge or leakage of raw or inadequately treated sewage into water sources such as springs, rivers, dams, or marine estuaries. Human exposure then follows when contaminated water is used for drinking, cooking, or recreation and, importantly, when filter-feeding bivalve shellfish are consumed. The human health hazard posed by enteric viruses is particularly serious in Africa where rapid urbanisation in a relatively short period of time has led to the expansion of informal settlements with poor sanitation and failing or non-existent wastewater treatment infrastructure, and where rural communities with limited or no access to municipal water are dependent on nearby open water sources for their subsistence. The role of sewage-contaminated water and bivalve shellfish as vehicles for transmission of enteric viruses is well documented but, to our knowledge, has not been comprehensively reviewed in the African context. Here we provide an overview of enteric viruses and then review the growing body of research where these viruses have been detected in association with sewage-contaminated water or food in several African countries. These studies highlight the need for more research into the prevalence, molecular epidemiology and circulation of these viruses in Africa, as well as for development and application of innovative wastewater treatment approaches to reduce environmental pollution and its impact on human health on the continent.

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

Noroviruses are the most common cause of gastroenteritis outbreaks in humans and bivalve shellfish consumption is a recognized route of infection. Our aim was to detect and characterize norovirus in bivalves from a coastal city of Brazil. Nucleic acid was extracted from the bivalve's digestive tissue concentrates using magnetic beads. From March 2018 to June 2019, 77 samples were screened using quantitative RT-PCR. Noroviruses were detected in 41.5%, with the GII being the most prevalent (37.7%). The highest viral load was 3.5 × 106 and 2.5 × 105 GC/g in oysters and mussels, respectively. PMA-treatment demonstrated that a large fraction of the detected norovirus corresponded to non-infectious particles. Genetic characterization showed the circulation of the GII.2[P16] and GII.4[P4] genotypes. Norovirus detection in bivalves reflects the anthropogenic impact on marine environment and serves as an early warning for the food-borne disease outbreaks resulting from the consumption of contaminated molluscs.

Analysis of the sanitary survey 2015-2017 conducted in the gulf of La Spezia (Italy): Reclassification of the areas of production of live bivalve molluscs

The sanitary survey is aimed at classifying and monitoring the production areas of live bivalve molluscs (LBM) and it is performed using standards that are provided by the Centre for Environment, Fisheries and Aquaculture Science's Guide to Good Practice. In this study, data from the sanitary survey carried out by the Asl5 Spezzino on the production areas of the gulf of La Spezia during the period 2015-2017 were analysed. The number and type of the analysis performed both on the total sampling and on the individual target species, as well as the number and type of found non-compliance (assessed on both mandatory parameters and on parameters fixed by the local monitoring plan) were considered. Data were also compared with those from the sanitary survey 2012-2014. Appropriate statistic tests were used to evaluate data from E. coli and Norovirus monitoring. Overall, 4306 analysis were performed, especially on the species M. galloprovincialis (89%) and they were mostly focused on to the search of biological agents. 160 NC were detected. Most of the NC concerns the Norovirus's positivity (93.75%) in M. galloprovincialis and C. gigas. A correlation between the levels of E. coli and rainfall/ seasonality (higher levels in the colder months) was proved, especially in the sampling points located in the inner part of the dam and in the Portovenere Bay. Class B was reconfirmed for M. galloprovincialis, the production areas of C. gigas were reclassified as A and those of V. verrucosa were definitively closed. The sanitary survey was therefore confirmed as a useful tool for reclassification and for monitoring LBM production areas.

Incidence of norovirus in tropical seafood harbouring fecal indicator bacteria

The occurrence of human norovirus (HuNoV) in fresh seafood was studied by reverse transcription-polymerase chain reaction (RT-PCR). Samples (n = 104) comprising of oysters, clams, shrimps and finfish were collected from 3 retail markets, a landing center and a rocky intertidal zone. The samples were subjected to virus concentration, followed by RNA extraction and RT-PCR. Of these, 43 (41.34%) samples were positive for HuNoV Group II (GII). The fecal contamination status of the samples was determined by the Most Probable Number (MPN) method. All (100%) the samples were fecally contaminated, with the fecal coliform counts ranging from 10 to >1400 MPN/100 g. The study shows that fresh seafood, especially the bivalve mollusks, can act as vehicles for transmission and spread of HuNoV in the community. The high level of HuNoV contamination of seafood not only constitutes a health risk to the domestic consumers, but also compromises the microbiological qualities of seafood meant for international trade.

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.

Cockles and mussels, alive, alive, oh-The role of bivalve molluscs as transmission vehicles for human norovirus infections

Human noroviruses are recognized as the leading worldwide cause of sporadic and epidemic viral gastroenteritis, causing morbidity and mortality in impoverished developing countries and engendering enormous economic losses in developed countries. Transmitted faecal-orally, either via person-to-person contact, or by consumption of contaminated foods or water, norovirus outbreaks are often reported in institutional settings or in the context of communal dining. Bivalve molluscs, which accumulate noroviruses via filter feeding and are often eaten raw or insufficiently cooked, are a common food vehicle implicated in gastroenteritis outbreaks. The involvement of bivalve molluscs in norovirus outbreaks and epidemiology over the past two decades are reviewed. The authors describe how their physiology of filter feeding can render them concentrated vehicles of norovirus contamination in polluted environments and how high viral loads persist in molluscs even after application of depuration practices and typical food preparation steps. The global prevalence of noroviruses in bivalve molluscs as detected by different monitoring efforts is determined and the various methods currently utilized for norovirus extraction and detection from bivalve matrices described. An overview of gastroenteritis outbreaks affirmatively associated with norovirus-contaminated bivalve molluscs as reported in the past 18 years is also provided. Strategies for risk reduction in shellfish contamination and subsequent human infection are discussed.

Final Consumer Options to Control and Prevent Foodborne Norovirus Infections

Norovirus (NoV) causes about one-fifth of all cases of foodborne diseases and is a foremost cause of domestically acquired foodborne acute gastroenteritis and outbreaks. NoV infections are often associated with the consumption of contaminated fresh and ready-to-eat produce, fresh and frozen berries, raw/undercooked bivalve mollusks and products which become contaminated during handling. Despite many industrial efforts to control and prevent NoV contamination of foods, the prevalence of NoV in high-risk foodstuffs at retail is still significant. Although certain consumer behaviors may even increase the risk of virus transmission, interventions aiming at changing/implementing consumer habits may be considered as opportunities for risk mitigation. This review aims at providing an update on the progress made in characterizing the effect that consumer habits, which are most critical to prevent NoV transmission (food choice and hygiene, disinfection and cooking during food preparation), may have on reducing the risk of NoV infection. A better understanding of the options for NoV control and prevention may be translated into innovative educational, social or even technological tools targeting consumers with the objective of mitigating the risk of NoV transmission.

Occurrence and Trend of Hepatitis A Virus in Bivalve Molluscs Production Areas Following a Contamination Event

The aim of this study was to assess the trend of hepatitis A virus (HAV) in a coastal zone impacted by a contamination event, providing data for the development of management strategies. A total of 352 samples, including four bivalve mollusc species (Mytilus galloprovincialis, Solen vagina, Venus gallina and Donax trunculus), were taken over a period of 6 months from 27 production areas of the coast and analysis were performed according to ISO/TS 15216-1:2013. HAV presence was detected in 77 samples from 11 production areas and all positive results were related to samples collected in the first 3 months of the surveillance, during which HAV prevalence was 39.9% and values as high as 5096 genome copies/g were detected. A progressive reduction of viral contamination was evident during the first trimester of the monitoring, with prevalence decreasing from 78.8% in the first month, to 37.8% in the second and 3.9% in the third and quantitative levels reduced from an average value of 672 genome copies/g to 255 genome copies/g over a period of 4 weeks (virus half-life: 21.5 days). A regression analysis showed that, during the decreasing phase of the contamination, the data fitted a reciprocal quadratic model (Ra² = 0.921) and, based on the model, a residual presence of HAV could be estimated after negativization of the production areas. The statistical analysis of the results per shellfish species and per production area showed that there were limited differences in contamination prevalence and levels among diverse bivalve species, while a statistically significant difference was present in quantitative levels of one production area. These data could be useful for the development of both risk assessment models and code of practice for the management of viral contamination in primary production.

Food-Borne Viruses in Shellfish: Investigation on Norovirus and HAV Presence in Apulia (SE Italy)

Shellfish are an important vehicle for transmission of food-borne pathogens including norovirus (NoV) and hepatitis A virus (HAV). The risks related with consumption of shellfish are greater if these products are eaten raw or slightly cooked. As molluscs are filter-feeding organisms, they are able to concentrate pathogens dispersed in the water. Data on shellfish viral contamination are therefore useful to obtain a background information on the presence of contamination in the environment, chiefly in shellfish production areas and to generate a picture of the epidemiology of viral pathogens in local populations. From January 2013 to July 2015, 253 samples of bivalve molluscs collected in harvesting areas from a large coastal tract (860 km) of Southern Italy were screened for HAV and NoV of genogroups GI and GII, using real-time reverse transcription qualitative PCR. The RNA of HAV was not detected in any of the analyzed samples. In contrast, the RNA of NoV was identified in 14.2% of the samples with a higher prevalence of NoVs of genogroup GII (12.2%) than genogroup GI (1.6%). Upon sequence analysis of a short diagnostic region located in capsid region, the NoV strains were characterized as GII.2, GII.4 Sydney 2012, GII.6, GII.13, GI.4, and GI.6, all which were circulating in local populations in the same time span. These data confirm that consumption of mussels can expose consumers to relevant risks of infection. Also, matching between the NoV genotypes circulating in local population and detected in molluscs confirms the diffusion in the environment of NoVs.

Norovirus and other human enteric viruses in moroccan shellfish

The aim of this study was to evaluate the presence of human enteric viruses in shellfish collected along the Mediterranean Sea and Atlantic Coast of Morocco. A total of 77 samples were collected from areas potentially contaminated by human sewage. Noroviruses were detected in 30 % of samples, with an equal representation of GI and GII strains, but were much more frequently found in cockles or clams than in oysters. The method used, including extraction efficiency controls, allowed the quantification of virus concentration. As in previous reports, results showed levels of contamination between 100 and 1,000 copies/g of digestive tissues. Sapoviruses were detected in 13 % of samples mainly in oyster and clam samples. Hepatitis A virus was detected in two samples, with concentrations around 100 RNA copies/g of digestive tissues. Only two samples were contaminated with enterovirus and none with norovirus GIV or Aichi virus. This study highlights the interest of studying shellfish samples from different countries and different production areas. A better knowledge of shellfish contamination helps us to understand virus levels in shellfish and to improve shellfish safety, thus protecting consumers.