Detection of a novel intergenogroup recombinant Norovirus from Kolkata, India

Comprehensive full genome analysis of norovirus strains from eastern India, 2017-2021

BACKGROUND

Worldwide, noroviruses are the leading cause of acute gastroenteritis (AGE) in people of all age groups. In India, norovirus rates between 1.4 to 44.4% have been reported. Only a very few complete norovirus genome sequences from India have been reported.

OBJECTIVE

To perform full genome sequencing of noroviruses circulating in India during 2017-2021, identify circulating genotypes, assess evolution including detection of recombination events.

METHODOLOGY

Forty-five archived norovirus-positive samples collected between October 2017 to July 2021 from patients with AGE from two hospitals in Kolkata, India were processed for full genome sequencing. Phylogenetic analysis, recombination breakpoint analysis and comprehensive mutation analysis were also performed.

RESULTS

Full genome analysis of norovirus sequences revealed that strains belonging to genogroup (G)I were genotyped as GI.3[P13]. Among the different norovirus capsid-polymerase combinations, GII.3[P16], GII.4 Sydney[P16], GII.4 Sydney[P31], GII.13[P16], GII.16[P16] and GII.17 were identified. Phylogenetic analysis confirmed phylogenetic relatedness with previously reported norovirus strains and all viruses were analyzed by Simplot. GII[P16] viruses with multiple residue mutations within the non-structural region were detected among circulating GII.4 and GII.3 strains. Comprehensive mutation analysis and selection pressure analysis of GII[P16] viruses showed positive as well as negative selection sites. A GII.17 strain (NICED-BCH-11889) had an untypeable polymerase type, closely related to GII[P38].

CONCLUSION

This study highlights the circulation of diverse norovirus strains in eastern India. These findings are important for understanding norovirus epidemiology in India and may have implications for future vaccine development.

Influence of herd immunity on norovirus: a long-term field study of repeated viral gastroenteritis outbreaks at the same facilities

BACKGROUND

Viral acute gastroenteritis (AG) is detected worldwide annually. Outbreaks caused by viruses associated with gastroenteritis have been reported repeatedly at the same facilities in Yokohama, Japan over several years. We investigated the statuses of these repeated outbreaks to consider herd immunity at the facility level.

METHODS

Between September 2007 and August 2017, 1459 AG outbreaks were reported at 1099 facilities. Stool samples were collected for virological testing, and the norovirus gene was amplified and sequenced to determine the genotype using the N-terminal region of the capsid.

RESULTS

The outbreaks were caused by norovirus, sapovirus, rotavirus A, and rotavirus C. Norovirus was consistently predominant over the 10-year period. Of 1099 facilities, 227 reported multiple outbreaks, of which norovirus-only combinations accounted for 76.2%. More outbreaks were due to different genotype combinations than the same genotype combinations. For facilities that experienced two norovirus outbreaks, the average interval between outbreaks was longer for groups with the same combinations than for groups with different genogroup or genotype combinations, although no statistically significant differences were observed. At 44 facilities, outbreaks occurred repeatedly during the same AG season, and most exhibited combinations of different norovirus genotypes or viruses. Among 49 combinations with the same norovirus genotype at the same facilities over 10 years, the most prevalent genotypes were combinations of genogroup II genotype 4 (GII.4), followed by GII.2, GII.6, GII.3, GII.14, and GI.3. The mean interval between outbreaks was 31.2 ± 26.8 months for all combinations, and the mean intervals were longer for non-GII.4 genotype cases than for GII.4 cases, and statistically significant differences were observed (t-test, P < 0.05). Additionally, these average intervals were longer for kindergarten/nursery schools and primary schools than for nursing homes for older adults (t-test, P < 0.05).

CONCLUSIONS

Repeated AG outbreaks at the same facilities in Yokohama during the 10-year study period included mainly norovirus combinations. Herd immunity at the facility level was maintained for at least the same AG season. Norovirus genotype-specific herd immunity was maintained for an average of 31.2 months during the study period, and these intervals differed depending on genotype.

Patterns and Temporal Dynamics of Natural Recombination in Noroviruses

Noroviruses infect a wide range of mammals and are the major cause of gastroenteritis in humans. Recombination at the junction of ORF1 encoding nonstructural proteins and ORF2 encoding major capsid protein VP1 is a well-known feature of noroviruses. Using all available complete norovirus sequences, we systematically analyzed patterns of natural recombination in the genus Norovirus both throughout the genome and across the genogroups. Recombination events between nonstructural (ORF1) and structural genomic regions (ORF2 and ORF3) were found in all analyzed genogroups of noroviruses, although recombination was most prominent between members of GII, the most common genogroup that infects humans. The half-life times of recombinant forms (clades without evidence of recombination) of human GI and GII noroviruses were 10.4 and 8.4-11.3 years, respectively. There was evidence of many recent recombination events, and most noroviruses that differed by more than 18% of nucleotide sequence were recombinant relative to each other. However, there were no distinct recombination events between viruses that differed by over 42% in ORF2/3, consistent with the absence of systematic recombination between different genogroups. The few inter-genogroup recombination events most likely occurred between ancient viruses before they diverged into contemporary genogroups. The recombination events within ORF1 or between ORF2/3 were generally rare. Thus, noroviruses routinely exchange full structural and nonstructural blocks of the genome, providing a modular evolution.

Overview of Foodborne viruses: Important viruses, outbreaks, health concerns, food Handling and fresh produce

Foodborne viruses can transmit through food in lots of ways including consuming items of animal origin containing zoonotic viruses, consuming contaminated food handled by infected food workers, and consuming contaminated food produced by humans. Viral foodborne illnesses are now a major contributor to all foodborne illness reports in recent years and are seen as a rising issue to the public health of humans and animals. Noroviruses and hepatitis A viruses were shown to be predominantly linked to the food-handler transmission and sewage-contaminated foods, according to microbiological research. In order to facilitate source attribution and identify risk preventive measures, routine, standard surveillance of viral outbreaks, and surveillance of virus occurrence in food products, combined with systematic strain typing, food and clinical microbiologists, would be advocated.

Global and regional circulation trends of norovirus genotypes and recombinants, 1995-2019: A comprehensive review of sequences from public databases

Human noroviruses are the leading global cause of viral gastroenteritis. Attempts at developing effective vaccines and treatments against norovirus disease have been stymied by the extreme genetic diversity and rapid geographic distribution of these viruses. The emergence and replacement of predominantly circulating norovirus genotypes has primarily been attributed to mutations on the VP1 capsid protein leading to genetic drift, and more recently to recombination events between the ORF1/ORF2 junction. However, large‐scale research into the historical and geographic distribution of recombinant norovirus strains has been limited in the literature. We performed a comprehensive historical analysis on 30,810 human norovirus sequences submitted to public databases between the years 1995 and 2019. During this time, 37 capsid genotypes and 56 polymerase types were detected across 90 different countries, and 97 unique recombinant genomes were also identified. GII.4, both capsid and polymerase, was the predominately circulating type worldwide for the majority of this time span, save for a brief swell of GII.17 and GII.2 capsid genotypes and a near‐total eclipse by GII.P16, GII.P21 and GII.P31 beginning in 2013. Interestingly, an analysis of 4067 recombinants found that 50.2% (N = 2039) of all recorded sequences belonged to three recently emerged recombinant strains: GII.2[P16], GII.4[P31], and GII.4[P16]. This analysis should provide an important historical foundation for future studies that evaluate the emergence and distribution of noroviruses, as well as the design of cross‐protective vaccines.

Genetic characterization and evolutionary analysis of norovirus genotypes circulating among children in eastern India during 2018-2019

Noroviruses are significant etiological agents of acute gastroenteritis (AGE) across all age groups, especially in children under 5 years of age. Although the prevalence of norovirus infection is known to have increased in various countries, in India there are few reports pertaining to the norovirus disease burden. We investigated the epidemiology and molecular characteristics of noroviruses in children seeking health care at two hospitals in Kolkata, Eastern India. Faecal specimens were collected between January 2018 and December 2019 from 2812 children under 5 years of age with acute gastroenteritis. Noroviruses were detected in 6.04% (170/2812) of the samples, and 12.9% (22/170) of these were cases of coinfection with rotavirus. Among children (≤5 years), a higher infection rate (8.2%, n = 94/1152) was observed in the 6 to 12 month age group. GII.4 Sydney 2012 was the dominant norovirus capsid genotype (n = 75/90, 83.3%), followed by GII.3 (n = 10/90, 11.1%). Other capsid types GII.13 (n = 4/90, 4.4%) and GII.17 (n = 1/90; 1.1%) were also detected at low frequency. Phylogenetic analysis showed that the GII.P16 polymerase of strains in this region clustered with those of the phylogenetically distinct monophyletic clade of GII.P16 strains, whose members have been circulating worldwide since 2014. Inter-genotypic norovirus recombinants such as GII.P16-GII.3 (n = 10) and GII.P16-GII.13 (n = 4) were also observed among the circulating strains. In comparison to previous studies from eastern India, the present study shows a higher detection rate of norovirus infection in the paediatric population suffering from acute gastroenteritis. Continuous surveillance is required for predicting the emergence of novel genotypes and recombinant strains and for future vaccine development.

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.

Animals as Reservoir for Human Norovirus

Norovirus is the most common cause of non-bacterial gastroenteritis and is a burden worldwide. The increasing norovirus diversity is currently categorized into at least 10 genogroups which are further classified into more than 40 genotypes. In addition to humans, norovirus can infect a broad range of hosts including livestock, pets, and wild animals, e.g., marine mammals and bats. Little is known about norovirus infections in most non-human hosts, but the close genetic relatedness between some animal and human noroviruses coupled with lack of understanding where newly appearing human norovirus genotypes and variants are emerging from has led to the hypothesis that norovirus may not be host restricted and might be able to jump the species barrier. We have systematically reviewed the literature to describe the diversity, prevalence, and geographic distribution of noroviruses found in animals, and the pathology associated with infection. We further discuss the evidence that exists for or against interspecies transmission including surveillance data and data from in vitro and in vivo experiments.

First detection of bovine noroviruses and detection of bovine coronavirus in Australian dairy cattle

Background and objective

Noroviruses have been recognised as a significant cause of neonatal enteritis in calves in many countries, but there has been no investigation of their occurrence in Australian cattle. This study aimed to establish whether bovine noroviruses could be detected in faecal samples from Australian dairy cattle. It also sought to determine whether bovine coronaviruses, also associated with neonatal enteritis in calves, could be detected in the same faecal samples.

Methods

A selection of faecal samples that were negative for rotaviruses from dairy farms located in three geographically distinct regions of Victoria were pooled and tested by reverse transcription‐PCR for the presence of noroviruses (genogroup III), neboviruses and bovine coronaviruses.

Results and conclusion

Genetically distinct genogroup III noroviruses were detected in two sample pools from different geographic regions and bovine coronavirus was detected in a third pool of samples. This is the first report of bovine norovirus infection in Australian cattle and suggests that future work is required to determine the significance of these agents as a cause of bovine enteric disease in Australia.

Norovirus recombinants: recurrent in the field, recalcitrant in the lab - a scoping review of recombination and recombinant types of noroviruses

Noroviruses are recognized as the major global cause of sporadic and epidemic non-bacterial gastroenteritis in humans. Molecular mechanisms driving norovirus evolution are the accumulation of point mutations and recombination. Intragenotypic recombination has long been postulated to be a driving force of GII.4 noroviruses, the predominant genotype circulating in humans for over two decades. Increasingly, emergence and re-emergence of different intragenotype recombinants have been reported. The number and types of norovirus recombinants remained undefined until the 2007 Journal of General Virology research article 'Norovirus recombination' reported an assembly of 20 hitherto unclassified intergenotypic norovirus recombinant types. In the intervening decade, a host of novel recombinants has been analysed. New recombination breakpoints have been described, in vitro and in vivo studies supplement in silico analyses, and advances have been made in analysing factors driving norovirus recombination. This work presents a timely overview of these data and focuses on important aspects of norovirus recombination and its role in norovirus molecular evolution. An overview of intergenogroup, intergenotype, intragenotype and 'obligatory' norovirus recombinants as detected via in silico methods in the field is provided, enlarging the scope of intergenotypic recombinant types to 80 in total, and notably including three intergenogroup recombinants. A recap of advances made studying norovirus recombination in the laboratory is given. Putative drivers and constraints of norovirus recombination are discussed and the potential link between recombination and norovirus zoonosis risk is examined.

Molecular Diagnostic Methods for Detection and Characterization of Human Noroviruses

Human noroviruses are a group of viral agents that afflict people of all age groups. The viruses are now recognized as the most common causative agent of nonbacterial acute gastroenteritis and foodborne viral illness worldwide. However, they have been considered to play insignificant roles in the disease burden of acute gastroenteritis for the past decades until the recent advent of new and more sensitive molecular diagnostic methods. The availability and application of the molecular diagnostic methods have led to enhanced detection of noroviruses in clinical, food and environmental samples, significantly increasing the recognition of noroviruses as an etiologic agent of epidemic and sporadic acute gastroenteritis. This article aims to summarize recent efforts made for the development of molecular methods for the detection and characterization of human noroviruses.

A Cell-based Fluorescence Resonance Energy Transfer (FRET) Sensor Reveals Inter- and Intragenogroup Variations in Norovirus Protease Activity and Polyprotein Cleavage

The viral protease represents a key drug target for the development of antiviral therapeutics. Because many protease inhibitors mimic protease substrates, differences in substrate recognition between proteases may affect their sensitivity to a given inhibitor. Here we use a cell-based FRET sensor to investigate the activity of different norovirus proteases upon cleavage of various norovirus cleavage sites inserted into a linker region separating cyan fluorescent protein and yellow fluorescent protein. Using this system, we demonstrate that differences in substrate processing exist between proteases from human noroviruses (genogroups I (GI) and II) and the commonly used murine norovirus (MNV, genogroup V) model. These altered the cleavage efficiency of specific cleavage sites both within and between genogroups. The differences observed between these proteases may affect sensitivity to protease inhibitors and the suitability of MNV as a model system for testing such molecules against the human norovirus protease. Finally, we demonstrate that replacement of MNV polyprotein cleavage sites with the GI or GII equivalents, with the exception of the NS6–7 junction, leads to the production of infectious virus when the MNV NS6 protease, but not the GI or GII proteases, are present.

Deciphering the Diversities of Astroviruses and Noroviruses in Wastewater Treatment Plant Effluents by a High-Throughput Sequencing Method

Although clinical epidemiology lists human enteric viruses to be among the primary causes of acute gastroenteritis in the human population, their circulation in the environment remains poorly investigated. These viruses are excreted by the human population into sewers and may be released into rivers through the effluents of wastewater treatment plants (WWTPs). In order to evaluate the viral diversity and loads in WWTP effluents of the Paris, France, urban area, which includes about 9 million inhabitants (approximately 15% of the French population), the seasonal occurrence of astroviruses and noroviruses in 100 WWTP effluent samples was investigated over 1 year. The coupling of these measurements with a high-throughput sequencing approach allowed the specific estimation of the diversity of human astroviruses (human astrovirus genotype 1 [HAstV-1], HAstV-2, HAstV-5, and HAstV-6), 7 genotypes of noroviruses (NoVs) of genogroup I (NoV GI.1 to NoV GI.6 and NoV GI.8), and 16 genotypes of NoVs of genogroup II (NoV GII.1 to NoV GII.7, NoV GII.9, NoV GII.12 to NoV GII.17, NoV GII.20, and NoV GII.21) in effluent samples. Comparison of the viral diversity in WWTP effluents to the viral diversity found by analysis of clinical data obtained throughout France underlined the consistency between the identified genotypes. However, some genotypes were locally present in effluents and were not found in the analysis of the clinical data. These findings could highlight an underestimation of the diversity of enteric viruses circulating in the human population. Consequently, analysis of WWTP effluents could allow the exploration of viral diversity not only in environmental waters but also in a human population linked to a sewerage network in order to better comprehend viral epidemiology and to forecast seasonal outbreaks.

Emergence of a new GII.17 norovirus variant in patients with acute gastroenteritis in Jiangsu, China, September 2014 to March 2015

From September 2014 to March 2015, 23 outbreaks of norovirus (NoV) acute gastroenteritis occurred in Jiangsu, China. Partial sequencing of the NoV capsid gene suggested that 16 of the 23 outbreaks were related to a new GII.17 variant. This variant was first detected in sporadic specimens in October 2014, and became predominant in February 2015. Analysis of the RNA-dependent RNA polymerase (RdRp), and complete capsid including the protruding domain P2 sequences confirmed this GII.17 variant as distinct from previously identified GII variants.

Genetic heterogeneity of bovine noroviruses in Italy

By screening 104 faecal samples from asymptomatic calves in Italy, bovine norovirus RNA was detected with a prevalence rate of 10.5 % (11/104). A continuous sequence spanning the RdRp region and the 5' end of the capsid gene was generated for 7 of the 11 strains. Upon phylogenetic analysis, five strains were grouped with GIII.2 Newbury2-like viruses, and one strain was grouped with GIII.1 Jena-like noroviruses. Interestingly, one strain (80TE/IT) was genetically related to the GIII.1/Jena/80/De in the RdRp but resembled the GIII.2/Newbury2/76/UK in the capsid gene, suggesting a recombination event occurring in the ORF1/ORF2 junction region.

Characterization of novel intergenogroup and intergenotype recombinant noroviruses from central Greece

Noroviruses (NoVs) are a major causative agent of acute gastroenteritis in humans. They are members of the Caliciviridae family and based on the genetic analysis of the RdRp and capsid regions, human NoVs are divided into three genogroups (Gs), GI, GII, and GIV. The three genogroups further segregate into distinct lineages called genotypes. The NoV genus is genetically diverse and recombination of viral RNA is known to depend upon various immunological and intracellular constraints that may allow the emergence of viable recombinants. In this study, three Noroviral strains detected in clinical samples revealed two hitherto unobserved recombination events between GII.9/GII.4 and GII.9/GI.7 genogroups. To our knowledge, these intergenotype and intergenogroup recombination events of GII.9/GII.4 and GII.9/GI.7, in ORF1 and ORF2 genes respectively are reported for the first time and highlight the ongoing evolution of noroviruses.

Different norovirus genotypes in patients with gastroenteritis in Kuwait

Norovirus is a leading cause of acute gastroenteritis worldwide. The importance of this virus infection in Kuwait is not known. Eight out of 100 stool samples (8.0%) from children up to 5 years of age with gastroenteritis studied during 2006-2007 from one hospital, and 6 out of 70 stool samples (8.5%) from similar children studied from another hospital during 2010-2011 were positive for norovirus by RT-PCR. Out of these 170 samples studied from both hospitals, 10 samples were positive for norovirus when tested by ELISA. Phylogenetic tree analysis of norovirus strains showed that 50% of the norovirus strains belonged to genotype GII.4, and the predominant strain was GII.4 2006b. Other detected genotypes were GII.12, GII.b, GII.3, GII.8, and GII.7. This study highlights the importance of screening for norovirus infection in acute gastroenteritis and having a reporting system to understand better the epidemiology of norovirus infection in Kuwait.

Molecular and epidemiological features of gastroenteritis outbreaks involving genogroup I norovirus in Victoria, Australia, 2002-2010

GI noroviruses are relatively rare and systematic studies of the molecular epidemiology of GI norovirus outbreaks are lacking. The current study examined the molecular virology of GI norovirus outbreaks in Victoria, Australia (2002-2010). Of 1,617 norovirus outbreaks identified, 69 (4.3%) were associated with GI norovirus alone, 1,540 (95.2%) with GII norovirus alone and 8 (0.5%) with GI + GII. Some differences between GI and GII outbreak epidemiology were found. GI outbreaks peaked in the 2-month period November/December whereas GII outbreaks peaked in the 2-month period September/October and GI norovirus outbreaks were significantly more common in non-healthcare settings (37.7%) than GII outbreaks (9.5%). ORF 1/ORF 2 genotypes found in the 69 outbreaks involving GI norovirus alone were: GI.2/GI.2, 7 outbreaks; GI.2/GI.6, 18 outbreaks; GI.3b/GI.3, 14 outbreaks; GI.4/GI.4, 21 outbreaks; GI.8/GI.8, one outbreak; GI.d/GI.3, four outbreaks; and GI.e/GI.13, one outbreak. The current study appears to be the first to have identified the recombinant form, GI.2/GI.6. Whereas GI.2/GI.6 and GI.3b/GI.3 outbreaks occurred with equal frequency in both healthcare and non-healthcare settings, GI.4/GI.4 occurred predominantly in healthcare settings. GI ORF 1/ORF 2 genotypes found in the eight outbreaks involving GI + GII norovirus were GI.2/GI.6, GI.3b/GI.3, and GI.4/GI.4, indicating GI genotypes in GI + GII outbreaks were similar to those found in outbreaks involving GI alone. Apparent differences in the evolution of different GI genotypes were noted. GI.2/GI.2, GI.2/GI.6, and GI.4/GI.4 strains tended to undergo periodic shifts in nucleotide sequence whereas various GI.3b/GI.3 strains tended to circulate simultaneously.

Emergence of a new norovirus GII.6 variant in Japan, 2008-2009

Norovirus (NoV) is recognized as one of the most common causative agents of diarrhea disease in young children. A total of 187 fecal specimens collected from non-hospitalized children with acute gastroenteritis in Shizuoka, Japan during July 2008 to June 2009 were investigated for the presence of diarrhea viruses by a multiplex RT-PCR. Diarrhea viruses were overall detected in 158 of 187 (84.5%). Of the viruses detected, NoV was the most prevalent (55.6%). Most of the NoV sequences belonged to GII.4 (53.8%). NoV GII.6 emerged as the second most common strain (40.4%). The full-length capsid sequences of five representative Shizuoka GII.6 strains were compared with all 12 GII.6 strains available in GenBank database between 1990 and 2009. At least three distinct GII.6 subclusters (a-c) appeared in different parts of the world. Shizuoka GII.6 strains formed their own subcluster c, distinct from other complete GII.6 reference sequences. The Shizuoka strains had significant amino acid divergence, particularly in the P2 domain up to 10.9-17.5% and contained eight unique mutations in the P domains, compared with subcluster a and b viruses. The homology model showed that the eight mutations were predicted to be located at the surface-exposed P1 and P2 domains. The data suggest the emergence of a new NoV GII.6 variant in Shizuoka, with a high level of genetic variation.

First outbreak of norovirus in Albania

AIMS

Noroviruses (NoVs) represent the most important enteric viruses responsible for acute gastroenteritis world-wide. This study objective is to characterize the first outbreak of NoV that occurred in Ballsh, a small city in Albania.

METHODS AND RESULTS

Stool specimens were collected from people attending to the hospital. Samples were also collected from the aqueduct for bacteriological and virological tests. Overall 33 stools and five drinking water samples were collected, respectively, from the hospital in Ballsh and from the municipal aqueduct. No water samples were scored positive whereas ten stool samples (30.3%) were scored GGII NoV positive. All the GGII isolates were identified as GGII·4 genotype, and no GGI was identified. The alignment and protein analysis were performed using, respectively, ClustalV and the mega 4 software.

CONCLUSIONS

This is the first report of NoV GGII·4 in Albania causing an outbreak. The genetic analysis showed several point mutations and amino acid substitutions with respect to the international strains.

SIGNIFICANCE AND IMPACT OF STUDY

Over the last decades, Albania has suffered from different outbreaks as cholera, poliomyelitis, hepatitis A and now, for the first time, it has been documented an outbreak of NoV.

Molecular epidemiology of norovirus gastroenteritis in children in Jiangmen, China, 2005-2007

Human noroviruses (NoVs) are an important cause of epidemic acute gastroenteritis. Their role in sporadic cases, however, is less clear. In this study, we performed a two-year surveillance (September 2005 to August 2007) of NoV gastroenteritis in outpatient clinics in a southern city of China, Jiangmen City. NoVs were detected in 115 patients (115/881, 13.1%) with 30 (26.1%) co-infections with rotaviruses. Sequence analysis showed that all 115 NoVs belonged to genogroup II, with GII.4 being the most predominant (87.8%). NoV-associated infection can be seen year-around, with autumn and winter peaks. This study provides basic information on sporadic cases of major NoV gastroenteritis in children in different seasons, which is valuable for future disease control and prevention.

Emergence of norovirus GII-4/2008 variant and recombinant strains in Seoul, Korea

Recently, the emergence of a new NoV GII-4 variant strain every 2 or 3 years has been reported. One hundred seventeen NoV GII strains were detected by RT-PCR in children with AGE between August 2008 and February 2010. In phylogenetic analyses, GII-4 and GII-3 were the most frequently detected strains. The detection rate of the 2008 variant was similar to that of the 2006b variant in the winter seasons of 2009 and 2010. This study shows a changing pattern of a predominant GII-4/2006b variant to the 2008 variant, as well as a novel NoV recombinant strain, GII-6/GII-14, in Korea.

[Survival strategies of human norovirus]

Human norovirus is a mutatable non-enveloped RNA virus capable of causing acute gastroenteritis in humans. Thus far, no experimental systems can propagate this virus in large amounts. Recent progresses in viral genomics and bioinformatics have led to a better understanding of molecular evolution of this virus in human populations. In addition, progresses in studies of the related noroviruses, those are replicable in laboratory systems, have led to a rapid accumulation of information on structural biology of norovirus. Furthermore, progresses in public health and water environment researches have led to a better understanding of viral ecology. In this review, I will first summarize fundamental characteristics of norovirus and its molecules. Then, I will summarize structure and molecular evolution of norovirus GII/4 subtype, which is now responsible for majorities of norovirus outbreaks in the world. Finally I will discuss survival strategies of human norovirus in nature by integrating the information.

Complete genome sequence and phylogenetic analysis of a recombinant Korean norovirus, CBNU1, recovered from a 2006 outbreak

We have determined the complete nucleotide and deduced amino acid sequences of the RNA genome of CBNU1, a human norovirus (NoV) recovered from a 2006 outbreak in South Korea. The genome of 7547 nucleotides, excluding a 3'-poly(A) tail of 11-105 nucleotides, encodes three overlapping open reading frames (ORFs): ORF1 (nucleotides 5-5104), ORF2 (nucleotides 5085-6731), and ORF3 (nucleotides 6731-7495). In a comparison to 108 other currently available completely sequenced NoVs representing all five genogroups (GI-GV) except GIV, the CBNU1 strain was highly similar to GII.3 NoVs. Multiple sequence alignments of the completely sequenced NoV genomes revealed five hypervariable regions throughout their genomes: two in ORF1, one in ORF2, and two in ORF3. At both the nucleotide and amino acid levels, genome-based phylogenetic analyses invariably showed that the CBNU1 strain was most closely related to three GII.3 NoVs: the American Texas/TCH04-577 and the two Japanese Saitama U18 and Saitama U201 strains; furthermore, these genome-based phylogenetic topologies corresponded most closely to those based on the ORF2 genes, as compared to those based on the ORF1 and ORF3 genes. Subsequent ORF2-based phylogenetic analyses of a selection of 126 other NoVs representing all 19 GII genotypes, in combination with genome-based Simplot analyses, showed that the CBNU1 strain was a recombinant GII.3 NoV with a breakpoint at the ORF1/ORF2 junction between two putative parent-like strains, Guangzhou/NVgz01 and Texas/TCH04-577. Overall, the CBNU1 strain represents the first Korean human NoV whose genome has been completely sequenced and for which its relationship with a large panel of genetically diverse NoVs has been extensively characterized.

Divergent evolution of norovirus GII/4 by genome recombination from May 2006 to February 2009 in Japan

Norovirus GII/4 is a leading cause of acute viral gastroenteritis in humans. We examined here how the GII/4 virus evolves to generate and sustain new epidemics in humans, using 199 near-full-length GII/4 genome sequences and 11 genome segment clones from human stool specimens collected at 19 sites in Japan between May 2006 and February 2009. Phylogenetic studies demonstrated outbreaks of 7 monophyletic GII/4 subtypes, among which a single subtype, termed 2006b, had continually predominated. Phylogenetic-tree, bootscanning-plot, and informative-site analyses revealed that 4 of the 7 GII/4 subtypes were mosaics of recently prevalent GII/4 subtypes and 1 was made up of the GII/4 and GII/12 genotypes. Notably, single putative recombination breakpoints with the highest statistical significance were constantly located around the border of open reading frame 1 (ORF1) and ORF2 (P <or= 0.000001), suggesting outgrowth of specific recombinant viruses in the outbreaks. The GII/4 subtypes had many unique amino acids at the time of their outbreaks, especially in the N-term, 3A-like, and capsid proteins. Unique amino acids in the capsids were preferentially positioned on the outer surface loops of the protruding P2 domain and more abundant in the dominant subtypes. These findings suggest that intersubtype genome recombination at the ORF1/2 boundary region is a common mechanism that realizes independent and concurrent changes on the virion surface and in viral replication proteins for the persistence of norovirus GII/4 in human populations.

Visualization of feline calicivirus replication in real-time with recombinant viruses engineered to express fluorescent reporter proteins

Caliciviruses are non-enveloped, icosahedral viruses with a single-stranded, positive sense RNA genome. Transposon-mediated insertional mutagenesis was used to insert a transprimer sequence into random sites of an infectious full-length cDNA clone of the feline calicivirus (FCV) genome. A site in the LC gene (encoding the capsid leader protein) of the FCV genome was identified that could tolerate foreign insertions, and two viable recombinant FCV variants expressing LC fused either to AcGFP, or DsRedFP were recovered. The effects of the insertions on LC processing, RNA replication, and stability of the viral genome were analyzed, and the progression of a calicivirus single infection and co-infection were captured by real-time imaging fluorescent microscopy. The ability to engineer viable recombinant caliciviruses expressing foreign markers enables new approaches to investigate virus and host cell interactions, as well as studies of viral recombination, one of the driving forces of calicivirus evolution.

Characterization of novel porcine sapoviruses

Sapoviruses are common caliciviruses known to cause enteric diseases in humans and animals. SaVs are genetically highly heterogeneous and are presently classified in five genogroups that are further subdivided in a number of genotypes. In recent years, a number of novel animal SaV strains, mostly of swine origin, have been partially characterized and proposed to represent novel genogroups or genotypes. We previously reported the detection and partial characterization of a wide range of variable and novel SaV strains of uncertain taxonomic status in Canadian swine. We now report on further genomic characterization of two novel strains to clarify their taxonomic relationship to other swine and human SaVs. Detailed analysis of different regions of their genomes, including determination of their complete capsid sequence, did not permit clear taxonomic assignment according to current criteria. This situation appears reminiscent of that of a number of SaV strains of swine origin and calls for a classification update for this calicivirus genus. We also report the detection of swine GIII SaVs for the first time in Canada.

Frequent detection of noroviruses and sapoviruses in swine and high genetic diversity of porcine sapovirus in Japan during Fiscal Year 2008

A molecular biological survey on porcine norovirus (NoV) and sapovirus (SaV) was conducted in Toyama Prefecture, Japan, during fiscal year 2008. Both NoV and SaV were detected from swine fecal samples throughout the surveillance period, indicating that these viruses were circulating in this region. NoV strains detected in this study belonged to three genotypes that are known as typical swine NoVs. Although human NoVs were occasionally detected, it was unclear whether they replicated in pigs. As for SaV, genogroup VII (GVII) and other divergent genogroups were identified in addition to the dominant genogroup, GIII, which is the prototypic porcine SaV. In addition, 3 strains genetically related to human SaV were detected. Two of these 3 strains were closely related to human SaV GV. Our study showed that genetic diversification of porcine SaV is currently progressing in the swine population.

[Diagnosis and molecular epidemiology of viral gastroenteritis in the past, present and future]

Outline, history of research, diagnosis and molecular epidemiology of viral gastroenteritis were described. Rotavirus, adenovirus, norovirus, sapovirus, astrovirus, human parechovirus, Aichivirus, and human bocavirus are the major target viruses which cause acute gastroenteritis. The viruses were differentiated into genogroup, genotypes and subgenotypes/clusters/lineages. The changing of their genetic backgrounds was well recognized in different areas and years. Some reassortments or recombinations were observed not only between humans and humans but also between humans and animals. Viral gastroenteritis diseases were transmitted by food-borne and humans to humans contact. The environmental factors were also impacted on the infections. Recently, situation of the diseases in the natural ecosystem is becoming clearly. Diagnoses by immunological methods and gene technology are available for the known viruses. Further development of diagnosis and discovery of new viruses will be expected. Therefore, the research on molecular epidemiology is needed to be conducted continuously and then new findings will appear. We need to precede the research by using new techniques and we need to cope with the demand of society especially during acute gastroenteritis outbreak seasons.

Assessment of norovirus contamination in environmental samples from Florianópolis City, Southern Brazil

AIMS

To assess norovirus (NoV) contamination in aquatic ecosystems in the city of Florianópolis, in Southern Brazil, to provide epidemiological data that can support actions for environmental contamination control.

METHODS AND RESULTS

An adsorption-elution method, followed by ultrafiltration, was performed to concentrate the viruses. NoV were detected using semi-nested PCR and quantified by real-time PCR. From June 2007 to May 2008, NoV were detected in 23% (22/94) of the samples analysed, including seawater, drinking water, superficial water (creek and brackish lagoon) and treated sewage. The mean viral loads for genogroups (G)I and GII in treated sewage samples were 297 and 440 genomic copies (gc) l(-1) , respectively, whereas creek water samples contained 2603 and 1361 gc l(-1) , respectively. Six samples were sequenced: two samples were GII.4, two were GII.2 and two were GI.3.

CONCLUSIONS

NoV were detected in all water types analysed, demonstrating the widespread contamination of this geographical area with several cocirculating strains belonging to GI and GII.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the environmental spread of NoV in environmental waters and highlights the potential hazard for human health following the consumption of or contact with these waters, which could result in waterborne or foodborne acute gastroenteritis.

Molecular characterization of three novel intergenotype norovirus GII recombinant strains from western India

The phenomenon of recombination has been widely described among noroviruses (NoVs) in the past few years. In a NoV surveillance study conducted in western India, 3 novel and 3 known combinations of RNA-dependent RNA polymerase (RdRp) and capsid genes were identified in genogroup (G) II NoV strains. The present study pertains to the characterization of three novel intergenotype NoV GII recombinant strains. RT-PCRs were carried out for the amplification of nearly complete RdRp and complete capsid genes spanning ORF1/2 overlap of three strains followed by sequencing of the amplicons. The recombination event was confirmed by phylogenetic analysis using Bayesian MCMC approach, SimPlot analysis and Maximum chi(2) method. Three novel intergenotype (GII) recombinations of GII.b/GII.18, GII.1/GII.12 and GII.3/GII.13 specificities were identified respectively in the strains PC03, PC24 and PC25 for the first time. The breakpoint in the novel recombinants was placed in the vicinity of the 20 bp ORF1/2 overlap, a common hotspot known to exist in NoV recombinants. The capsid genes of all of the 3 recombinants were closely related to their counter parts in reference strains however, a high degree of variation emerged in the polymerase genes especially of PC24 and PC25 in comparison to the reference strains.

Molecular and epidemiological features of GIIb norovirus outbreaks in Victoria, Australia, 2002-2005

The epidemiology of GIIb norovirus outbreaks and the characteristics of GIIb open reading frame (ORF) 2 recombinant forms are poorly understood and this study examined these questions using norovirus-associated gastroenteritis outbreaks in Victoria, Australia, during 2002-2005. Twenty-one GIIb outbreaks were detected and were the second most common ORF 1 norovirus outbreak genotype (5%) after GII.4 (90%). Both GIIb and GII.4 outbreaks peaked in warmer months of the year but their periodicity was different. ORF 2 sequencing analysis was carried out in the two regions previously designated C and D. RT-PCR region D primers were less sensitive than region C primers. No evidence of recombination between regions C and D was found. ORF 2 genotypes for the 21 GIIb outbreaks were: GII.1 (10 outbreaks), GII.3 (10 outbreaks) and, apparently for the first time, GII.13 (1 outbreak). GIIb outbreaks could occur in a broad range of settings and there was no correlation between ORF 2 genotype and setting except that all 5 outbreaks involving mainly young children were associated with GIIb/GII.3.

Genetic heterogeneity and recombination in canine noroviruses

Alphatronlike (genogroup IV [GIV]) noroviruses (NoVs) have been recently identified in carnivores. By screening a collection of 183 fecal samples collected during 2007 from dogs with enteric signs, the overall NoV prevalence was found to be 2.2% (4/183). A unique strain, Bari/91/07/ITA, resembled GIV.2 NoVs in its ORF1 (polymerase complex), while it was genetically unrelated in its full-length ORF2 (capsid gene) to GIV animal and human NoVs (54.0 to 54.4% amino acid identity) and to any other NoV genogroup (<54.7% amino acid identity). It displayed the highest identity (58.1% amino acid identity) to unclassified human strain Chiba/040502/04/Jp. Interestingly, the very 5' end of ORF2 of the canine virus matched short noroviral sequences (88.9% nucleotide identity and 98.9% amino acid identity) identified from oysters in Japan, indicating that similar viruses may be common environmental contaminants.

Sequence characteristics of potato virus Y recombinants

Potato virus Y (PVY) is one of the most economically important plant pathogens. The PVY genome has a high degree of genetic variability and is also subject to recombination. New recombinants have been reported in many countries since the 1980s, but the origin of these recombinant strains and the physical and evolutionary mechanisms driving their emergence are not clear at the moment. The replicase-mediated template-switching model is considered the most likely mechanism for forming new RNA virus recombinants. Two factors, RNA secondary structure (especially stem-loop structures) and AU-rich regions, have been reported to affect recombination in this model. In this study, we investigated the influence of these two factors on PVY recombination from two perspectives: their distribution along the whole genome and differences between regions flanking the recombination junctions (RJs). Based on their distributions, only a few identified RJs in PVY genomes were located in lower negative FORS-D, i.e. having greater secondary-structure potential and higher AU-content regions, but most RJs had more negative FORS-D values upstream and/or higher AU content downstream. Our whole-genome analyses showed that RNA secondary structures and/or AU-rich regions at some sites may have affected PVY recombination, but in general they were not the main forces driving PVY recombination.

The alphaGal epitope of the histo-blood group antigen family is a ligand for bovine norovirus Newbury2 expected to prevent cross-species transmission

Among Caliciviridae, the norovirus genus encompasses enteric viruses that infect humans as well as several animal species, causing gastroenteritis. Porcine strains are classified together with human strains within genogroup II, whilst bovine norovirus strains represent genogroup III. Various GI and GII human strains bind to carbohydrates of the histo-blood group family which may be shared among mammalian species. Genetic relatedness of human and animal strains as well as the presence of potentially shared ligands raises the possibility of norovirus cross-species transmission. In the present study, we identified a carbohydrate ligand for the prototype bovine norovirus strain Bo/Newbury2/76/UK (NB2). Attachment of virus-like particles (VLPs) of the NB2 strain to bovine gut tissue sections showed a complete match with the staining by reagents recognizing the Galalpha1,3 motif. Alpha-galactosidase treatment confirmed involvement of a terminal alpha-linked galactose. Specific binding of VLPs to the alphaGal epitope (Galalpha3Galbeta4GlcNAcbeta-R) was observed. The binding of Galalpha3GalalphaOMe to rNB2 VLPs was characterized at atomic resolution employing saturation transfer difference (STD) NMR experiments. Transfection of human cells with an alpha1,3galactosyltransferase cDNA allowed binding of NB2 VLPs, whilst inversely, attachment to porcine vascular endothelial cells was lost when the cells originated from an alpha1,3galactosyltransferase KO animal. The alphaGal epitope is expressed in all mammalian species with the exception of the Hominidaea family due to the inactivation of the alpha1,3galactosyltransferase gene (GGTA1). Accordingly, the NB2 carbohydrate ligand is absent from human tissues. Although expressed on porcine vascular endothelial cells, we observed that unlike in cows, it is not present on gut epithelial cells, suggesting that neither man nor pig could be infected by the NB2 bovine strain.

Prevalence and genotypes of human noroviruses in tropical urban surface waters and clinical samples in Singapore

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.