Comparison of Norovirus RNA Levels in Outbreak-Related Oysters with Background Environmental Levels

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131

The contamination of bivalve shellfish with norovirus from human fecal sources is recognized as an important human health risk. Standardized quantitative methods for the detection of norovirus in molluscan shellfish are now available, and viral standards are being considered in the European Union and internationally. This 2-year systematic study aimed to investigate the impact of the application of these methods to the monitoring of norovirus contamination in oyster production areas in the United Kingdom. Twenty-four monthly samples of oysters from 39 United Kingdom production areas, chosen to represent a range of potential contamination risk, were tested for norovirus genogroups I and II by using a quantitative real-time reverse transcription (RT)-PCR method. Norovirus was detected in 76.2% (643/844) of samples, with all sites returning at least one positive result. Both prevalences (presence or absence) and norovirus levels varied markedly between sites. However, overall, a marked winter seasonality of contamination by both prevalence and quantity was observed. Correlations were found between norovirus contamination and potential risk indicators, including harvesting area classifications, Escherichia coli scores, and environmental temperatures. A predictive risk score for norovirus contamination was developed by using a combination of these factors. In summary, this study, the largest of its type undertaken to date, provides a systematic analysis of norovirus contamination in commercial oyster production areas in the United Kingdom. The data should assist risk managers to develop control strategies to reduce the risk of human illness resulting from norovirus contamination of bivalve molluscs.T he contamination of bivalve shellfish with norovirus from human fecal sources is recognized as a major human health risk (21). Risk assessment and management currently rely on the use of Escherichia coli as an indicator of fecal (sewage) contamination in shellfish (3). However, this approach has been repeatedly demonstrated to inadequately indicate the risk from human enteric viruses (2,8,16). Over the last decade, considerable progress has been made toward the development of sensitive quantitative detection methods for norovirus in molluscan shellfish, and there are numerous reports describing various approaches to virus testing (19,24,25). All available methods are based on the detection of virus genomes by using molecular techniques (PCR), as the successful cultivation of norovirus by conventional virological techniques has been reported only rarely (33, 34) and is not currently feasible for application to foodstuffs. At present, no internationally accepted reference method exists; however, the European Committee on Normalization (CEN) has an active working group addressing the development of an ISO standard method for the detection of norovirus and hepatitis A virus (HAV) in foodstuffs, including bivalve shellfish (22). The method is scheduled for publication in 2012, and publication will be followed by an internatio...

Section: Discussionmentioning

confidence: 99%

Two-Year Systematic Study To Assess Norovirus Contamination in Oysters from Commercial Harvesting Areas in the United Kingdom

Lowther

Gustar

Powell

et al. 2012

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131

“…The 50% infectious dose (ID 50 ) was reported as 18 NoV genome copies for a disaggregated inoculum, whereas the probability of an infected subject becoming ill (i.e., expressing NoV symptoms) ranged from 10% at a dose of 10 3 NoV genomes to 70% at a dose of 10 8 virus genomes. This dose-dependent outcome may help explain why asymptomatic NoV excretion has been observed in a substantial proportion (up to 16%) of healthy individuals (121) and also, since reporting of outbreaks depends on expression of clinical symptoms, why NoV levels seen in shellfish associated with outbreaks are generally higher than background environmental levels (122). Assuming that NoV detected in shellfish is viable, then this dose-response model can give an indication of the likely outcome following consumption of the NoV levels observed in shellfish surveillance studies.…”

Section: Accumulation and Clearance By Shellfishmentioning

confidence: 99%

Environmental Transmission of Human Noroviruses in Shellfish Waters

Campos

Lees

2014

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Human noroviruses (NoV) are the most common cause of epidemic gastroenteritis following consumption of bivalve shellfish contaminated with fecal matter. NoV levels can be effectively reduced by some sewage treatment processes such as activated sludge and membrane bioreactors. However, tertiary sewage treatment and substantial sewage dilution are usually required to achieve low concentrations of virus in shellfish. Most outbreaks have been associated with shellfish harvested from waters affected by untreated sewage from, for example, storm overflows or overboard disposal of feces from boats. In coastal waters, NoV can remain in suspension or associate with organic and inorganic matter and be accumulated by shellfish. Shellfish take considerably longer to purge NoV than fecal indicator bacteria when transferred from sewage-polluted estuarine waters to uncontaminated waters. The abundance and distribution of NoV in shellfish waters are influenced by the levels of sewage treatment, proximity of shellfish beds to sewage sources, rainfall, river flows, salinity, and water temperature. Detailed site-specific information on these factors is required to design measures to control the viral risk.

“…Consequently, laboratories sometimes fail to detect the presence of HuNoV genomes in oysters involved in global HuNoV gastroenteritis outbreaks (17). On the other hand, a very high overestimation of the infectious risk may also occur (17)(18)(19) because of the persistence of viral genomes being greater than viral infectivity (20)(21)(22)(23), especially after disinfection treatment. It has been suggested that as shellfish are not able to bioaccumulate NoV RNA fragments present in seawater (24), the genomes detected in shellfish mainly result from infectious virus accumulation.…”

mentioning

confidence: 99%

“…In this context, the 5.0% to 76.2% positive results for the detection of HuNoV genomes in shellfish intended for commercial use (17,(29)(30)(31)(32)(33)(34)(35)(36)(37) are difficult to interpret in terms of infectious risk. Although the dose-response concept is often observed (3,18), HuNoV genome levels may be sometimes low in shellfish commodities involved in HuNoV gastroenteritis outbreaks (19) and may be high in nonoutbreak-related samples (18).…”

mentioning

confidence: 99%

Relevance of F-Specific RNA Bacteriophages in Assessing Human Norovirus Risk in Shellfish and Environmental Waters

Hartard

Banas

Loutreul

et al. 2016

Human noroviruses (HuNoVs) are the main cause of shellfish-borne gastroenteritis outbreaks. In the absence of routine technical approaches allowing infectious particles to be detected, this viral pathogen is currently targeted by genome research, leading to difficult interpretations. In this study, we investigated the potential of F-specific RNA bacteriophages (FRNAPH) as fecal and viral contamination indicators in shellfish and water from a local harvesting area. FRNAPH were also used as microbial source tracking tools. Constraints imposed by detection limits are illustrated here by the detection of infectious FRNAPH in several samples in the absence of FRNAPH genomes. The opposite situation was also observed, likely explained by the persistence of the genomes being greater than infectivity. Similar considerations may be applied to HuNoVs, suggesting that HuNoV genome targeting is of limited relevance in assessing infectious risks. While FRNAPH did not provide any benefits compared to Escherichia coli as fecal pollution indicators in water, novel observations were made in shellfish: contrary to E. coli, a seasonal trend of infectious FRNAPH concentrations was observed. These concentrations were higher than those found in water, confirming bioaccumulation in shellfish. This study also underlines a relationship between the presence of HuNoV genomes and those of human- specific FRNAPH subgroup II (FRNAPH-II) in shellfish collected throughout Europe. Further research should be undertaken to evaluate FRNAPH potential as an indicator of the presence of infectious HuNoVs. To this end, shellfish involved in HuNoVcaused gastroenteritis outbreaks should be analyzed for the presence of infectious FRNAPH-II. IMPORTANCEThis work provides new data about the use of F-specific RNA phages (FRNAPH) as a tool for evaluating fecal or viral contamination, especially in shellfish. In our case study, FRNAPH did not provide any benefits compared to E. coli as fecal pollution indicators in water but were found to be very useful in shellfish. Their concentrations in shellfish were higher than those found in the surrounding water, confirming bioaccumulation. This study also underlines a relationship between the presence of human norovirus genomes (HuNoVs) and those of FRNAPH subgroup II (FRNAPH-II). Considering that the two virus types have similar behaviors and since FRNAPH infectivity can be investigated, the specific detection of infectious FRNAPH-II could be regarded as an indication of the presence of infectious HuNoVs. The contribution of infectious human FRNAPH targeting for assessing the viral risk associated with HuNoVs in shellfish should thus be investigated.