Internationally Distributed Frozen Oyster Meat Causing Multiple Outbreaks of Norovirus Infection in Australia

c Noroviruses (NoVs) are a leading cause of epidemic and sporadic cases of acute gastroenteritis worldwide. Oysters are well recognized as the main vectors of environmentally transmitted NoVs, and disease outbreaks linked to oyster consumption have been commonly observed. Here, to quantify the genetic diversity, temporal distribution, and circulation of oyster-related NoVs on a global scale, 1,077 oyster-related NoV sequences deposited from 1983 to 2014 were downloaded from both NCBI GenBank and the NoroNet outbreak database and were then screened for quality control. A total of 665 sequences with reliable information were obtained and were subsequently subjected to genotyping and phylogenetic analyses. The results indicated that the majority of oyster-related NoV sequences were obtained from coastal countries and regions and that the numbers of sequences in these regions were unevenly distributed. Moreover, >80% of human NoV genotypes were detected in oyster samples or oysterrelated outbreaks. A higher proportion of genogroup I (GI) (34%) was observed for oyster-related sequences than for nonoyster-related outbreaks, where GII strains dominated with an overwhelming majority of >90%, indicating that the prevalences of GI and GII are different in humans and oysters. In addition, a related convergence of the circulation trend was found between oyster-related NoV sequences and human pandemic outbreaks. This suggests that oysters not only act as a vector of NoV through environmental transmission but also serve as an important reservoir of human NoVs. These results highlight the importance of oysters in the persistence and transmission of human NoVs in the environment and have important implications for the surveillance of human NoVs in oyster samples. N orovirus (NoV) is known as the leading cause of nonbacterial acute gastroenteritis in humans and can infect people of all ages across the world (1). As a member of the family Caliciviridae, NoV is a nonenveloped, positive-sense, single-stranded RNA virus with a linear genome that contains three open reading frames (ORFs) (2). The genus Norovirus currently contains at least 6 distinct genogroups (genogroup I [GI], GII, GIII, GIV, GV, and GVI), each of which has been subdivided into multiple genotypes (3, 4). GI, GII, and GIV strains have been detected in humans and are further subdivided into 9, 22, and 2 genotypes, respectively (3, 4). One important genotype, genogroup II genotype 4 (GII.4), has been recognized recently as the predominant cause of major viral gastroenteritis epidemics worldwide (5-7) and contains a number of genetic variants (4,8).Over the past 20 years, new epidemic variants of GII.4 have emerged every 2 to 3 years (9) and usually have become the dominant strains in every season (7, 10, 11). For example, the Yerseke 2006a variant emerged in 2006, disappeared in 2008, and was replaced by the Den Haag 2006b variant (see Fig. S1 in the supplemental material). The New Orleans 2009 variant was the major player in the worldwide NoV outbreaks from 2010 to ...

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confidence: 99%

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confidence: 99%

Molecular Epidemiology of Oyster-Related Human Noroviruses and Their Global Genetic Diversity and Temporal-Geographical Distribution from 1983 to 2014

Cai

et al. 2015

“…The literature contains abundant case and outbreak reports of NoV infection associated with the consumption of bivalve shellfish (20,21,22,23,24). Such outbreaks continue to occur on a regular basis worldwide (23,24,25) with potentially very significant associated economic costs.…”

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confidence: 99%

Environmental Transmission of Human Noroviruses in Shellfish Waters

Campos

Lees

2014

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.

“…Noroviruses are highly infectious and transmitted primarily via the fecal-oral route. Food-borne outbreaks of acute gastroenteritis associated with noroviruses have been frequently reported worldwide, including Singapore (17,24,29,45,46). There have been a number of documented waterborne outbreaks of noroviruses originating from contaminated drinking water (10,19,26,30,33) and recreational waters (7,13).…”

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confidence: 99%

Prevalence and Genotypes of Human Noroviruses in Tropical Urban Surface Waters and Clinical Samples in Singapore

Gin

Oon

et al. 2009

The prevalence and genotypes of norovirus genogroup I (GI) and GII in tropical urban catchment waters and an estuarine bay were studied. A comparative analysis was performed with environmental isolates of noroviruses and concurrently identified clinical isolates in Singapore during gastroenteritis outbreaks between August 2006 to January 2007. Noroviruses in environmental water samples were concentrated by using ultrafiltration techniques and then analyzed by reverse transcription-seminested PCR assay targeting the partial capsid region of noroviruses and DNA sequencing. Among the 60 water samples collected, noroviruses were detected in 43 (71.7%) of these samples. Of these 43 norovirus-positive samples, the coexistence of both GI and GII strains was identified in 23 (53.5%) water samples. The phylogenetic analysis revealed multiple genotypes of noroviruses GI and GII in environmental water samples. GI and GII strains were clustered into seven and nine (including two unclassified) genotypes, respectively. The major norovirus genotypes in environmental water samples were GI/2 and GI/4 and GII/4. Genotyping of the 21 norovirus-positive clinical samples showed that all of the strains belonged to the GII/4 cluster. The environmental and clinical norovirus GII/4 isolates showed high levels of nucleotide sequence identity to each other and to the novel GII/4 variant associated with global epidemics of gastroenteritis during 2006. This study suggests the emergence and circulation of multiple novel norovirus GI and GII genotypes in water environments. Further comprehensive surveillance of water environments for noroviruses and routine clinical reporting is warranted.