Emergence of a novel GII.17 norovirus – End of the GII.4 era?

Nucleic Acid Aptamers for Human Norovirus GII.4 and GII.17 Virus-Like Particles (VLPs) Exhibit Specific Binding and Inhibit VLPs from Entering Cells

Purpose

Human noroviruses (HuNoVs) are the main cause of non-bacterial acute gastroenteritis. Due to antigenic diversity, the discovery of ligands that can sensitively and specifically detect HuNoVs remains challenging. Limited by laboratory culture, no vaccines or drugs have been developed against HuNoVs. Here, we screened nucleic acid aptamers against the widespread HuNoV GII.4 and emerging HuNoV GII.17.

Methods

After ten rounds of sieving for HuNoV GII.4 and GII.17 virus-like particles (VLPs), eight ssDNA aptamers were generated and characterized for each genotype.

Results

Four of the eight aptamers generated for GII.4 VLP had dissociation constants (Kd) less than 100 nM, and all aptamers for GII.17 VLP had Kd less than 10 nM. All aptamers bound to their targets in VLP concentration-dependent manner. Two aptamers (AP4-2 and AP17-4) were selected for enzyme-linked aptamer sorbent assay (ELASA) and further analysis. Binding affinity was enhanced as the concentration of both aptamer and VLPs increased. The specificity of the aptamers was verified by ELASA and dot blotting. AP4-2 and AP17-4 were able to differentiate HuNoV from other diarrhea-causing pathogens or unrelated proteins (P < 0.0001). VLP/porcine gastric mucin (PGM) binding blockade assays revealed that AP4-2 and AP17-4 blocked the binding of HuNoV VLPs to PGM. VLP internalization inhibition assays showed that at a concentration of 0.5 µM, both AP4-2 and AP17-4 effectively inhibited attachment and internalization of HuNoV VLPs into 293T cell (P < 0.05). Cell viability assays confirmed that aptamers did not induce cellular toxicity.

Conclusion

AP4-2 and AP17-4 showed strong affinity and specificity for their target VLPs and represent promising candidates for HuNoV capture and detection. This is the first study to demonstrate that aptamers can effectively inhibit HuNoV VLPs from binding to or entering cells, thus providing a new concept for the treatment of HuNoVs.

Increased circulation of GII.17 noroviruses, six European countries and the United States, 2023 to 2024

We report an increase in GII.17 norovirus outbreaks and sporadic infections of acute gastroenteritis in Austria, Germany, France, Ireland, the Netherlands, England and the United States during the 2023/24 season. A decrease in GII.4 coincided with GII.17 prevalence increasing to between 17% and 64% of all GII detections. Overall, 84% of the GII.17 strains clustered closely with strains first reported in Romania in 2021 and two new sub-lineages were identified. Norovirus surveillance and molecular characterisation should be prioritised this winter.

Bile acid-sensitive human norovirus strains are susceptible to sphingosine-1-phosphate receptor 2 inhibition

Human noroviruses (HuNoVs) are a diverse group of RNA viruses that cause endemic and pandemic acute viral gastroenteritis. Previously, we reported that many HuNoV strains require bile or bile acid (BA) to infect human jejunal intestinal enteroid cultures. BA was not essential for the replication of a pandemic-causing GII.4 HuNoV strain. We found the hydrophobic BA glycochenodeoxycholic acid (GCDCA) promotes the replication of the BA-dependent strain GII.3 in jejunal enteroids. Furthermore, we found that inhibition of the G-protein-coupled BA receptor, sphingosine-1-phosphate receptor 2 (S1PR2), by JTE-013, reduced GII.3 infection dose-dependently and inhibited GII.3 cellular uptake in enteroids. Herein, we sought to determine whether S1PR2 is required for other BA-dependent HuNoV strains, the BA-independent GII.4, and whether S1PR2 is required for BA-dependent HuNoV infection in HIEs from other small intestinal segments. We found a second S1PR2 inhibitor, GLPG2938, reduces GII.3 infection dose-dependently, and an S1PR2 agonist (CYM-5520) enhances GII.3 replication in the absence of GCDCA. GII.3 replication also is abrogated in the presence of JTE-013 and CYM-5520. JTE-013 inhibition of S1PR2 in jejunal HIEs reduces GI.1, GII.3, and GII.17 (BA-dependent) but not GII.4 Sydney (BA-independent) infection, providing additional evidence of strain-specific differences in HuNoV infection. Finally, GII.3 infection of duodenal, jejunal, and ileal lines derived from the same individual is reduced with S1PR2 inhibition, indicating a common mechanism of BA-dependent infection among multiple segments of the small intestine. Our results support a model where BA-dependent HuNoVs exploit BA effects on S1PR2 to infect the entire small intestine.IMPORTANCEHuman noroviruses (HuNoVs) are important viral human pathogens that cause both outbreaks and sporadic gastroenteritis. These viruses are diverse, and many strains are capable of infecting humans. Our previous studies have identified strain-specific requirements for hydrophobic bile acids (BAs) to infect intestinal epithelial cells. Moreover, we identified a BA receptor, sphingosine-1-phosphate receptor 2 (S1PR2), required for infection by a BA-dependent strain. To better understand how various HuNoV strains enter and infect the small intestine and the role of S1PR2 in HuNoV infection, we evaluated infection by additional HuNoV strains using an expanded repertoire of intestinal enteroid cell lines. We found that multiple BA-dependent strains, but not a BA-independent strain, all require S1PR2 for infection. In addition, BA-dependent infection requires S1PR2 in multiple segments of the small intestine. Together, these results indicate that S1PR2 has value as a potential therapeutic target for BA-dependent HuNoV infection.

Global prevalence of norovirus gastroenteritis after emergence of the GII.4 Sydney 2012 variant: a systematic review and meta-analysis

Introduction

Norovirus is widely recognized as a leading cause of both sporadic cases and outbreaks of acute gastroenteritis (AGE) across all age groups. The GII.4 Sydney 2012 variant has consistently prevailed since 2012, distinguishing itself from other variants that typically circulate for a period of 2-4 years.

Objective

This review aims to systematically summarize the prevalence of norovirus gastroenteritis following emergence of the GII.4 Sydney 2012 variant.

Methods

Data were collected from PubMed, Embase, Web of Science, and Cochrane databases spanning the period between January 2012 and August 2022. A meta-analysis was conducted to investigate the global prevalence and distribution patterns of norovirus gastroenteritis from 2012 to 2022.

Results

The global pooled prevalence of norovirus gastroenteritis was determined to be 19.04% (16.66-21.42%) based on a comprehensive analysis of 70 studies, which included a total of 85,798 sporadic cases with acute gastroenteritis and identified 15,089 positive cases for norovirus. The prevalence rate is higher in winter than other seasons, and there are great differences among countries and age groups. The pooled attack rate of norovirus infection is estimated to be 36.89% (95% CI, 36.24-37.55%), based on a sample of 6,992 individuals who tested positive for norovirus out of a total population of 17,958 individuals exposed during outbreak events.

Conclusion

The global prevalence of norovirus gastroenteritis is always high, necessitating an increased emphasis on prevention and control strategies with vaccine development for this infectious disease, particularly among the children under 5 years old and the geriatric population (individuals over 60 years old).

Assessment of Gastroenteric Viruses in Marketed Bivalve Mollusks in the Tourist Cities of Rio de Janeiro, Brazil, 2022

This study investigated the prevalence and genetic diversity of gastroenteric viruses in mussels and oysters in Rio de Janeiro, Brazil. One hundred and thirty-four marketed bivalve samples were obtained between January and December 2022. The viral analysis was performed according to ISO/TS 15216, and the screening revealed the detection of norovirus GII/GI (40.3%), sapovirus (SaV; 12.7%), human mastadenovirus (7.5%), and rotavirus A (RVA; 5.9%). In total, 44.8% (60) of shellfish samples tested positive for one or more viruses, 46.7% (28/60) of the positive samples tested positive for a single viral agent, 26.7% (16) tested positive for two viral agents, 8.3% (5) for three viral agents, and 13.3% (8) for four viral agents. Additionally, three mussel samples were contaminated with the five investigated viruses (5%, 3/60). Norovirus GII showed the highest mean viral load (3.4 × 105 GC/g), followed by SaV (1.4 × 104 GC/g), RVA (1.1 × 104 GC/g), human mastadenovirus (3.9 × 103 GC/g), and norovirus GI (6.7 × 102 GC/g). Molecular characterization revealed that the recovered norovirus strains belonged to genotypes GII.2, GII.6, GII.9, GII.17, and GII.27; SaV belonged to genotypes GI.1 and GIV.1; RVA to genotypes G6, G8, P[8]-III, and human mastadenovirus to types F40 and F41. The GII.27 norovirus characterized in this study is the only strain of this genotype reported in Brazil. This study highlights the dissemination and diversity of gastroenteric viruses present in commercialized bivalves in a touristic area, indicating the potential risk to human health and the contribution of bivalves in the propagation of emerging pathogens.

Establishment and application of a rapid assay for GII.4/GII.17 NoV detection based on the combination of CRISPR/Cas13a and isothermal amplification

Introduction

Norovirus (NoV) is one of the most important agents responsible for viral acute gastroenteritis, among which GII.4 NoV is the predominant strain worldwide, and GII.17 NoV surpassed GII.4 in some epidemic seasons. Rapid and accurate gene recognition is essential for a timely response to NoV outbreaks.

Methods

In the present study, the highly conserved regions of GII.4 and GII.17 NoVs were identified in the junction of open reading frame (ORF) 1 and ORF2 and then amplified by isothermal recombinase-aided amplification (RAA), followed by the cleavage of CRISPR-Cas13a with screened CRISPR RNAs (crRNAs) and RAA primers. The entire detection procedure could be completed within 40 min using a thermostat, and the results could be read out by the naked eye under a portable blue light transilluminator.

Discussion

The assay showed a high sensitivity of 97.96% and a high specificity of 100.0%. It offered a low limit of detection (LOD) of 2.5×100 copies/reaction and a coincidence rate of 96.75% in 71 clinical fecal samples. Overall, rapid and inexpensive detection of GII.4/GII.17 NoVs was established, which makes it possible to be used in areas with limited resources, particularly in low-income countries. Furthermore, it will contribute to assessing transmission risks and implementing control measures for GII.4/GII.17 NoVs, making healthcare more accessible worldwide.

Bile acid-sensitive human norovirus strains are susceptible to sphingosine-1-phosphate receptor 2 inhibition

Human noroviruses (HuNoVs) are a diverse group of RNA viruses that cause both endemic and pandemic acute viral gastroenteritis. Previously we reported that many strains of HuNoV require bile or bile acid (BA) to infect human jejunal intestinal enteroid cultures. Of note, BA was not essential for replication of a pandemic-causing GII.4 HuNoV strain. Using the BA-requiring strain GII.3, we found that the hydrophobic BA GCDCA induces multiple cellular responses that promote replication in jejunal enteroids. Further, we found that chemical inhibition of the G-protein coupled receptor, sphingosine-1- phosphate receptor 2 (S1PR2), by JTE-013 reduced both GII.3 infection in a dose- dependent manner and cellular uptake in enteroids. Herein, we sought to determine if S1PR2 is required by other BA-dependent HuNoV strains and BA-independent GII.4, and if S1PR2 is required for BA-dependent HuNoV infection in other segments of the small intestine. We found JTE-013 inhibition of S1PR2 in jejunal HIEs reduces GI.1, GII.3, and GII.17 (BA-dependent) but not the GII.4 Sydney variant (BA-independent) infection, providing additional evidence of strain-specific differences in HuNoV infection. GII.3 infection of duodenal, jejunal and ileal lines derived from the same individual was also reduced with S1PR2 inhibition, indicating a common mechanism of BA-dependent infection among multiple segments of the small intestine. Our results support a model where BA-dependent HuNoV exploit the activation of S1PR2 by BA to infect the entire small intestine.

Importance

Human noroviruses (HuNoVs) are important viral human pathogens that cause both outbreaks and sporadic gastroenteritis. These viruses are diverse, and many strains are capable of infecting humans. Our previous studies have identified strain-specific requirements for hydrophobic bile acids (BAs) to infect intestinal epithelial cells. Moreover, we identified a BA receptor, sphingosine-1-phosphate receptor 2 (S1PR2), required for infection by a BA-dependent strain. To better understand how various HuNoV strains enter and infect the small intestine and the role of S1PR2 in HuNoV infection, we evaluated infection by additional HuNoV strains using an expanded repertoire of intestinal enteroid cell lines. We found that multiple BA-dependent strains, but not a BA- independent strain, all required S1PR2 for infection. Additionally, BA-dependent infection required S1PR2 in multiple segments of the small intestine. Together these results indicate S1PR2 has value as a potential therapeutic target for BA-dependent HuNoV infection.

Molecular epidemiology and genetic diversity of norovirus among hospitalized patients with acute gastroenteritis in Shandong, China, 2016-2018

Norovirus (NoV) infection is a leading cause of acute gastroenteritis (AGE) for people of all ages. Here, we reported the molecular epidemiology and genetic diversity of NoVs among hospitalized patients with AGE between 2016 and 2018 in Shandong Province, China. Two thousand sixty-nine AGE patients from sentinel hospitals were enrolled. The stool samples were collected and tested for NoVs by real-time RT-PCR. The RNA-dependent RNA polymerase (RdRp) and capsid gene of 163 strains were amplified and sequenced for genotyping. Phylogenetic analyses and genomic characterization were conducted with the VP1 and RdRp region of the full genome sequences. Four hundred seventy two (21.76%) samples were NoV-positive. The positive rate in 2016 was higher than those of 2017 and 2018. We observed diverse NoV genotypes. GII.2[P16] emerged in January 2017 and became the dominant genotype between May and June 2017. Phylogenetic analyses showed that our GII.2[P16] genomes clustered in the SC1 in VP1 region, while they belonged to the Emerging GⅡ.P16 (2015-2017) clade in RdRp region. Our GⅡ.4 strains displayed two amino acid mutations, positions R297H and D372N, in epitope A of the VP1 region. Our study highlighted that NoV is an important pathogen of viral AGE in Shandong and, therefore, it is necessary to strengthen its surveillance.

Acute gastroenteritis outbreak associated with multiple and rare norovirus genotypes after storm events in Santa Catarina, Brazil

Norovirus is a major cause of acute diarrheal disease (ADD) outbreaks worldwide. In the present study, we investigated an ADD outbreak caused by norovirus in several municipalities of Santa Catarina state during the summer season, southern Brazil in 2023. As of the 10th epidemiological week of 2023, approximately 87 000 ADD cases were reported, with the capital, Florianópolis, recording the highest number of cases throughout the weeks. By using RT-qPCR and sequencing, we detected 10 different genotypes, from both genogroups (G) I and II. Some rare genotypes were also identified. Additionally, rotavirus and human adenovirus were sporadically detected among the ADD cases. Several features of the outbreak suggest that sewage-contaminated water could played a role in the surge of ADD cases. Storm events in Santa Catarina state that preceded the outbreak likely increased the discharge of contaminated wastewater and stormwater into water bodies, such as rivers and beaches during a high touristic season in the state. Climate change-induced extreme weather events, including intensified rainfall and frequent floods, can disturb healthcare and sanitation systems. Implementing public policies for effective sanitation, particularly during peak times, is crucial to maintain environmental equilibrium and counter marine pollution.

Infant antibody and B-cell responses following confirmed pediatric GII.17 norovirus infections functionally distinguish GII.17 genetic clusters

Genogroup II (GII) noroviruses are a major cause of diarrheal disease burden in children in both high- and low-income countries. GII.17 noroviruses are composed of distinct genetic clusters (I, II, IIIa, and IIIb) and have shown potential for replacing historically more prevalent GII.4 strains, but the serological basis for GII.17 antigenic diversity has not been studied in children. Utilizing samples from a birth cohort, we investigated antibody and B-cell responses to GII.17 cluster variants in confirmed GII.17 infections in young children as well as demonstrated that the distinct genetic clusters co-circulate. Polyclonal serum antibodies bound multiple clusters but showed cluster-specific blockade activity in a surrogate virus neutralization assay. Antibodies secreted by immortalized memory B cells (MBCs) from an infant GII.17 case were highly specific to GII.17 and exhibited blockade activity against this genotype. We isolated an MBC-derived GII.17-specific Immunoglobulin A (IgA) monoclonal antibody called NVA.1 that potently and selectively blocked GII.17 cluster IIIb and recognized an epitope targeted in serum from cluster IIIb-infected children. These data indicate that multiple antigenically distinct GII.17 variants co-circulate in young children, suggesting retention of cluster diversity alongside potential for immune escape given the existence of antibody-defined cluster-specific epitopes elicited during infection.

Epidemiology and genetic diversity of norovirus GII genogroups among children in Hubei, China, 2017-2019

Norovirus (NoV) is an important cause of viral acute gastroenteritis (AGE). To gain insights into the epidemiological characteristics and genetic diversity of NoV among children in Hubei, 1216 stool samples from children (≤ 5 years) obtained under AGE surveillance from January 2017 to December 2019 were analyzed. The results showed that NoV was responsible for 14.64% of AGE cases, with the highest detection rate in children aged 7-12 months (19.76%). Statistically significant differences were found between male and female infection rates (χ2 ​= ​8.108, P ​= ​0.004). Genetic analysis of RdRp and VP1 sequences showed that NoV GII genotypes were GII.4 Sydney [P31] (34.35%), GII.3 [P12] (25.95%), GII.2 [P16] (22.90%), GII.4 Sydney [P16] (12.98%), GII.17 [P17] (2.29%), GII.6 [P7] and GII.3 [P16] (each at 0.76%). GII.17 [P17] variants were divided into the Kawasaki323-like lineage and the Kawasaki308-like lineage. A unique recombination event was detected between strains of GII.4 Sydney 2012 and GII.4 Sydney 2016. Significantly, all GII.P16 sequences associated with GII.4/GII.2 obtained in Hubei were correlated with novel GII.2 [P16] variants that re-emerged in Germany in 2016. Antigenic site analysis of complete VP1 sequences from all GII.4 variants from Hubei identified notable variable residues of antibody epitopes. Genotyping under continuous AGE surveillance and observation of the antigenic sites of VP1 are important monitoring strategies for emerging NoV strains.

Genome characterisation of norovirus GII.P17-GII.17 detected during a large gastroenteritis outbreak in Romania in 2021

Norovirus (NoV) is one of the leading causes of acute gastroenteritis worldwide. Genotype GII.P17-G.II.17 emerged in Asia between 2013 and 2015 and transiently replaced the GII.4 Sydney 2012 variant circulating at that time. We present the genome characterisation of a GII.P17-GII.17 strain causing a large outbreak in Romania in 2021. Our study shows that the 2021 strain belongs to a novel cluster of genotype GII.17, different from the two previously recognised P.17 clusters. Distinctive substitutions in predicted conformational epitopes of VP1 were identified for this new cluster. Also, our phylogenetic analysis showed the existence of another P.17 cluster grouping strains from France and Canada.

First report of coinfection and whole-genome sequencing of norovirus and sapovirus in an acute gastroenteritis patient from Pakistan

Acute gastroenteritis is one of the most common diseases in infants and children in developing countries including Pakistan. In Pakistan, rotavirus (RVA) is known to contribute significantly to pediatric diarrheal illness, but the contribution of other viruses is still unclear. In the current study we have identified a case of mixed infection of norovirus (NoV) and sapovirus (SaV) in a 2-year-old child with acute gastroenteritis. The sample was initially processed for the detection of group A RVA through ELISA followed by NoV using RT-PCR assay. The sample tested positive for NoV RNA and was later subjected to whole-genome sequencing using meta-genome approach on Miseq (Illumina) platform. Sequencing results revealed GII.15 genotype of NoV that clustered with viruses from China and USA from 2017 to 2021. We also retrieved the complete genome of SaV (GI.1 genotype) from the same sample and phylogenetic analysis showed clustering with strains reported from Japan, South Korea, US, and Taiwan during 2012-2016. This is the first report from Pakistan that confirms coinfection of NoV and SaV and elucidates their whole genomes. We recommend initiation of NoV and SaV surveillance program to ascertain disease burden and explore genetic diversity, especially as RVA vaccines have been included in national immunization program.

Rapid screening for antigenic characterization of GII.17 norovirus strains with variations in capsid gene

The emergence of the novel GII.17 Kawasaki 2014 norovirus variant raising the interest of the public, has replaced GII.4 as the predominant cause of noroviruses outbreaks in East Asia during 2014–2015. Antigenic variation of the capsid protein is considered as one of the key mechanisms of norovirus evolution. In this study, we screened a panel of GII.17 mutants. First, we produced norovirus P proteins using cell-free protein synthesis (CFPS) system, comparing the results to pure proteins expressed in a cell-based system. Next, we determined the binding capability of specific monoclonal antibody (mAb) 2D11 using a unique set of wild-type GII.17 strains. Results of the EIA involving a panel of mutant cell-free proteins indicated that Q298 was the key residue within loop 1. These data highlighted the essential residues in the linear antibody binding characteristics of novel GII.17. Furthermore, it supported the CFPS as a promising tool for rapidly screening mutants via the scalable expression of norovirus P proteins.

Investigation of genotype diversity of 7,804 norovirus sequences in humans and animals of China

Norovirus is a prominent enteric virus responsible for severe acute gastroenteritis disease burden worldwide. In our current study, we analyzed 7,804 norovirus sequences of human and animals in China which were detected from 1980 to 2020 from GenBank. The GenBank database was searched up to May 2021 with the following search terms: "norovirus" or "norwalk virus" and "China." The 7,804 norovirus sequences were collected and evaluated by phylogenetic analysis using MEGA X software package. The online typing tool (https://www.rivm.nl/mpf/typingtool/norovirus/) was used to confirm the genotypes. There were 36 norovirus genotypes prevailing in China. GII.4 was the most prevalent genotype, and GII.2, GII.3 and GII.17 also emerged during different time periods. Most sequences were detected in East China (41.72%, 3,256/7,804), but different norovirus genotypes were distributed widely across the country. A variety of norovirus genotypes, including GI, GII, GIII, GIV, GV, GVI, GVII and GX, were reported in different animals. Furthermore, a GI.3 sequence detected from animal had high identity with norovirus detected in human from the same region, indicating the potential norovirus zoonotic transmission in China. In conclusion, these results indicated that norovirus sequences with considerable genetic diversity distributed widely in China, with potential reverse zoonotic transmission from human to animals.

Molecular epidemiology, genetic diversity, and vaccine availability of viral acute gastroenteritis in the middle East and North Africa (MENA) region

Acute gastroenteritis is the cause of considerable mortality and morbidity worldwide, particularly among children under five years in underdeveloped countries. Most acute gastroenteritis (AGE) cases are attributed to viral etiologies, including rotavirus, norovirus, adenovirus, astrovirus, and sapovirus. This paper aimed to determine the prevalence rate of different viral etiologies of AGE in the Middle East and North Africa (MENA) region. Moreover, this paper explored rotavirus phylogenetic relatedness, compared VP7 and VP4 antigenic regions of rotavirus with vaccine strains, and explored the availability of vaccines in the MENA region. The literature search identified 160 studies from 18 countries from 1980 to 2019. The overall prevalence of rotavirus, norovirus, adenovirus, astrovirus, and sapovirus were 29.8 %, 13.9 %, 6.3 %, 3.5 %, and 3.2 % of tested samples, respectively. The most common rotavirus genotype combinations in the MENA region were G1P[8], G9P[9], and G2P[4], whereas GII.4 was the predominant norovirus genotype all of which were reported in almost all the studies with genotyping data. The comparison of VP7 and VP4 between circulating rotavirus in the MENA region and vaccine strains has revealed discrete divergent regions, including the neutralizing epitopes. Rotavirus vaccine was introduced to most of the countries of the MENA region; however, only a few studies have assessed the effectiveness of vaccine introduction. This paper provides a comprehensive update on the prevalence of the different viral agents of AGE in the MENA region.

Bayesian estimation of seasonal and between year variability of norovirus infection risks for workers in agricultural water reuse using epidemiological data

Norovirus infections are among the major causes of acute gastroenteritis worldwide. In Germany, norovirus infections are the most frequently reported cause of gastroenteritis, although only laboratory confirmed cases are officially counted. The high infectivity and environmental persistence of norovirus, makes the virus a relevant pathogen for water related infections. In the 2017 guidelines for potable water reuse, the World Health Organization proposes Norovirus as a reference pathogen for viral pathogens for quantitative microbial risk assessment (QMRA). A challenge for QMRA is, that norovirus data are rarely available over long monitoring periods to assess inter-annual variability of the associated health risk, raising the question about the relevance of this source of variability regarding potential risk management alternatives. Moreover, norovirus infections show high prevalence during winter and early spring and lower incidence during summer. Therefore, our objective is to derive risk scenarios for assessing the potential relevance of the within and between year variability of norovirus concentrations in municipal wastewater for the assessment of health risks of fieldworkers, if treated wastewater is used for irrigation in agriculture. To this end, we use the correlation between norovirus influent concentration and reported epidemiological incidence (R²=0.93), found at a large city in Germany. Risk scenarios are subsequently derived from long-term reported epidemiological data, by applying a Bayesian regression approach. For assessing the practical relevance for wastewater reuse we apply the risk scenarios to different irrigation patterns under various treatment options, namely "status-quo" and "irrigation on demand". While status-quo refers to an almost all-year irrigation, the latter assumes that irrigation only takes place during the vegetation period from May - September. Our results indicate that the log-difference of infection risks between scenarios may vary between 0.8 and 1.7 log given the same level of pre-treatment. They also indicate that under the same exposure scenario the between-year variability of norovirus infection risk may be > 1log, which makes it a relevant factor to consider in future QMRA studies and studies which aim at evaluating safe water reuse applications. The predictive power and wider use of epidemiological data as a suitable predictor variable should be further validated with paired multi-year data.

Ultrasensitive and visual detection of human norovirus genotype GII.4 or GII.17 using CRISPR-Cas12a assay

Background

Integrating CRISPR-Cas12a sensors with isothermal signal amplification can be exploited to develop low-cost, disposable, and ultrasensitive assays for the diagnostics of human pathogens.

Methods

RT-RAA-Cas12a-mediated real-time or end-point fluorescent and lateral flow strip (LFS) assays for direct detection of norovirus (NOV) genotype GII.4 or GII.17 were explored.

Results

The results showed that our RT-RAA-Cas12a-mediated fluorescent and LFS assay could detect NOV GII.4 or GII.17 by targeting the viral protein 1 gene. Our RT-RAA-Cas12a-mediated fluorescent and LFS assay can specifically detect NOV GII.4 or GII.17 with no cross-reactivity for other related viruses. The low limit of detection could reach 0.1 copies/μL within approximately 30–40 min, and the results were visualized using an ultraviolet light illuminator or on a LFS without complex equipment. In addition, our RT-RAA-Cas12a-mediated fluorescent and LFS assay provided a visual and faster alternative to real-time RT-PCR assay, with 95.7% and 94.3% positive predictive agreement and 100% negative predictive agreement.

Conclusions

Together, our RT-RAA-Cas12a-mediated approach would have a great potential for point-of-care diagnostics of NOV GII.4 and/or GII.17 in resource-limited settings.

Norovirus Infection in Young Nicaraguan Children Induces Durable and Genotype-Specific Antibody Immunity

There are significant challenges to the development of a pediatric norovirus vaccine, mainly due to the antigenic diversity among strains infecting young children. Characterizing human norovirus serotypes and understanding norovirus immunity in naïve children would provide key information for designing rational vaccine platforms. In this study, 26 Nicaraguan children experiencing their first norovirus acute gastroenteritis (AGE) episode during the first 18 months of life were investigated. We used a surrogate neutralization assay that measured antibodies blocking the binding of 13 different norovirus virus-like particles (VLPs) to histo-blood group antigens (HBGAs) in pre- and post-infection sera. To assess for asymptomatic norovirus infections, stools from asymptomatic children were collected monthly, screened for norovirus by RT-qPCR and genotyped by sequencing. Seroconversion of an HBGA-blocking antibody matched the infecting genotype in 25 (96%) of the 26 children. A subset of 13 (50%) and 4 (15%) of the 26 children experienced monotypic GII and GI seroconversion, respectively, strongly suggesting a type-specific response in naïve children, and 9 (35%) showed multitypic seroconversion. The most frequent pairing in multitypic seroconversion (8/12) were GII.4 Sydney and GII.12 noroviruses, both co-circulating at the time. Blocking antibody titers to these two genotypes did not correlate with each other, suggesting multiple exposure rather than cross-reactivity between genotypes. In addition, GII titers remained consistent for at least 19 months post-infection, demonstrating durable immunity. In conclusion, the first natural norovirus gastroenteritis episodes in these young children were dominated by a limited number of genotypes and induced responses of antibodies blocking binding of norovirus VLPs in a genotype-specific manner, suggesting that an effective pediatric norovirus vaccine likely needs to be multivalent and include globally dominant genotypes. The duration of protection from natural infections provides optimism for pediatric norovirus vaccines administered early in life.

The Intrapopulation Genetic Diversity of RNA Virus May Influence the Sensitivity of Chlorine Disinfection

RNA virus populations are not clonal; rather, they comprise a mutant swarm in which sequences are slightly different from the master sequence. Genetic diversity within a population (intrapopulation genetic diversity) is critical for RNA viruses to survive under environmental stresses. Disinfection has become an important practice in the control of pathogenic viruses; however, the impact of intrapopulation genetic diversity on the sensitivity of disinfection, defined as -log10 (postdisinfected infectious titer/predisinfected titer), has not been elucidated. In this study, we serially passaged populations of rhesus rotavirus. We demonstrated that populations with reduced chlorine sensitivity emerged at random and independently of chlorine exposure. Sequencing analysis revealed that compared with sensitive populations, less-sensitive ones had higher non-synonymous genetic diversity of the outer capsid protein gene, suggesting that changes in the amino acid sequences of the outer capsid protein were the main factors influencing chlorine sensitivity. No common mutations were found among less-sensitive populations, indicating that rather than specific mutations, the diversity of the outer capsid protein itself was associated with the disinfection sensitivity and that the disinfection sensitivity changed stochastically. Simulation results suggest that the disinfection sensitivity of a genetically diverse population is destabilized if cooperative viral clusters including multiple sequences are formed. These results advocate that any prevention measures leading to low intrapopulation genetic diversity are important to prevent the spread and evolution of pathogenic RNA viruses in society.

Epidemiological Impact of GII.17 Human Noroviruses Associated With Attachment to Enterocytes

For the last 30 years, molecular surveys have shown that human norovirus (HuNoV), predominantly the GII.4 genotype, is one of the main causative agents of gastroenteritis. However, epidemiological surveys have revealed the worldwide emergence of GII.17 HuNoVs. Genetic analysis confirmed that GII.17 strains are distributed into three variants (i.e., Kawasaki 308, Kawasaki 323, and CS-E1). Here, virus-like particles (VLPs) were baculovirus-expressed from these variants to study putative interactions with HBGA. Qualitative analysis of the HBGA binding profile of each variant showed that the most recent and predominant GII.17 variant, Kawasaki 308, possesses a larger binding spectrum. The retrospective study of GII.17 strains documented before the emergence of the dominant Kawasaki 308 variant showed that the emergence of a new GII.17 variant could be related to an increased binding capacity toward HBGA. The use of duodenal histological sections confirmed that recognition of enterocytes involved HBGA for the three GII.17 variants. Finally, we observed that the relative affinity of recent GII.17 VLPs for HBGA remains lower than that of the GII.4-2012 variant. These observations suggest a model whereby a combination of virological factors, such as polymerase fidelity and increased affinity for HBGA, and immunological factors was responsible for the incomplete and non-persistent replacement of GII.4 by new GII.17 variants.

Human Norovirus Induces Aquaporin 1 Production by Activating NF-κB Signaling Pathway

Human norovirus (HuNoV) is one of the major pathogens of acute nonbacterial gastroenteritis. Due to the lack of a robust and reproducible in vitro culture system and an appropriate animal model, the mechanism underlying HuNoV-caused diarrhea remains unknown. In the current study, we found that HuNoV transfection induced the expression of aquaporin 1 (AQP1), which was further confirmed in the context of virus infection, whereas the enterovirus EV71 (enterovirus 71) did not have such an effect. We further revealed that VP1, the major capsid protein of HuNoV, was crucial in promoting AQP1 expression. Mechanistically, HuNoV induces AQP1 production through the NF-κB signaling pathway via inducing the expression, phosphorylation and nuclear translocation of p65. By using a model of human intestinal epithelial barrier (IEB), we demonstrated that HuNoV and VP1-mediated enhancement of small molecule permeability is associated with the AQP1 channel. Collectively, we revealed that HuNoV induced the production of AQP1 by activating the NF-κB signaling pathway. The findings in this study provide a basis for further understanding the significance of HuNoV-induced AQP1 expression and the potential mechanism underlying HuNoV-caused diarrhea.

Genetic diversity of norovirus associated with outbreaks in school children with acute gastroenteritis in Changzhou, China, 2018-2019

OBJECTIVE

Norovirus is one of the major causes of outbreaks and sporadic cases of acute gastroenteritis in school children. Obtaining local genotype diversity information regarding norovirus is important for developing and evaluating prevention strategies of the transmission of this virus in school children.

METHODS

Clinical specimens, obtained from the routine acute gastroenteritis surveillance network from 2018 to 2019, were primarily tested using commercial real-time PCR Kit. Samples with Ct value less than 25 were selected and used for complete genome sequencing and those with Ct value between 25 and 30 were selected and used for he partial VP1 and RdRp regions sequencing. Phylogenetic trees of the viral genome were constructed by using the neighbor-joining method with bootstrap analysis of 1,000 replicates in MEGA 6.0 RESULTS: Epidemiological surveillance of acute intestinal infections (n=384) showed high-level detection (73.18%) of human norovirus in school endemic acute gastroenteritis events in Changzhou, with obvious epidemic characteristics in autumn and winter. Through genotyping, it was found that 93.12% of norovirus were GII, including GII.2, GII.3, GII.4, GII.6, GII.7 and GII.17. By October 2019, two norovirus genotypes, GII.4[P31] and GII.17[P17], became the preponderant epidemic strains. Phylogenetic analysis of the new GII.17[P17] complete genomes showed close relationship with Miyagi strain identified in Japan in 2015, and GII.4[P31] showed close relationship with Jinan strain indentified in China in 2017.

CONCLUSION

The study highlights the emerging role of GII.4[P31] and GII.17[P17] in causing endemic acute gastroenteritis outbreaks at school children, in Changzhou, China in 2019. This article is protected by copyright. All rights reserved.

Multiplex PCR method for the detection of human norovirus, Salmonella spp., Shigella spp., and shiga toxin producing Escherichia coli in blackberry, coriander, lettuce and strawberry

A multiplex PCR method was developed for the simultaneous detection of murine norovirus (MNV-1) as a surrogate for human norovirus (HuNoV) GI and GII, Salmonella spp., Shigella spp., and Shiga toxin producing Escherichia coli (STEC) in fresh produce. The toxicity of the glycine buffer on bacterial pathogens viability was evaluated. The growth of each of the three pathogens (previously stressed) was evaluated at 35 and 41.5 °C in modified buffered peptone water (mBPW) and trypticase soy broth (TSB), supplemented with vancomycin, novobiocin and brilliant green at two concentration levels. The selected conditions for simultaneous enrichment were: 41.5 °C/mBPW/supplemented with 8 ppm vancomycin, 0.6 ppm novobiocin and 0.2 ppm brilliant green. The pathogens and aerobic plate count (APC) growth was evaluated in the enrichment of lettuce, coriander, strawberry and blackberry under the best enrichment conditions. Starting from 1 to 10 CFU/mL, Salmonella reached from 7.63 to 8.91, Shigella 6.81 to 7.76 and STEC 7.43 to 9.27 log CFU/mL. The population reached for the APC was 5.11-6.56 log CFU/mL. Simultaneous detection by PCR was done using designed primers targeting invA, ipaH, stx1 and stx2 genes, and MNV-1. The detection sensitivity was 10-100 PFU for the MNV-1 and 1-10 CFU for each pathogenic bacteria. This protocol takes 6 h for MNV-1 and 24 h for Salmonella spp., Shigella spp., and STEC detection from the same food portion. In total, 200 samples were analyzed from retail markets from Queretaro, Mexico. Two strawberry samples were positive for HuNoV GI and one lettuce sample was positive for STEC. In conclusion, the method developed in this study is capable of detecting HuNoV GI and GII, Salmonella spp., Shigella spp and STEC from the same fresh produce sample.

Norovirus detection in wastewater and its correlation with human gastroenteritis: a systematic review and meta-analysis

Norovirus (NoV) is a major cause of sporadic cases and outbreaks of acute gastroenteritis (AGE), thereby imposing threat to health globally. It is unclear how quantitation of wastewater NoV reflects the incidence of human AGE infections; therefore, we conducted this systematic review and meta-analysis of published NoV wastewater surveillance studies. A literature search was performed, and all studies on NoV wastewater surveillance were identified. Quantitative results were evaluated. The results showed that the overall detection rate of NoV in wastewater was 82.10% (95% confidence interval [CI]: 74.22-89.92%); NoV concentration was statistically significant in terms of season (P < 0.001), with higher concentration in spring and winter. There were positive correlations between NoV GII concentration in wastewater and GII AGE cases (rs = 0.51, 95% CI: 0.18-0.74, I2 = 0%), total AGE cases (rs = 0.40, 95% CI: 0.15-0.61, I2 = 23%) and NoV outbreaks (rs = 0.47, 95% CI: 0.30-0.62, I2 = 0%). Results of cross-correlation analysis of partial data indicated that variations in GII concentration were consistent with or ahead of those in the number of AGE cases. The diversity of NoV genotypes in wastewater was elucidated, and the dominant strains in wastewater showed a consistent temporal distribution with those responsible for human AGE. Our study demonstrated the potential association of NoV detected in wastewater with AGE infections, and further studies are needed to confirm this conclusion.

Detection of Norovirus Recombinant GII.2[P16] Strains in Oysters in Thailand

Human norovirus causes sporadic and epidemic acute gastroenteritis worldwide, and the predominant strains are genotype GII.4 variants. Recently, a novel GII.17[P17] and a recombinant GII.2[P16] strain have been reported as the causes of gastroenteritis outbreaks. Outbreaks of norovirus are frequently associated with foodborne illness. In this study, each of 75 oyster samples processed by a proteinase K extraction method and an adsorption-elution method were examined for noroviruses using RT-nested PCR with capsid primers. Thirteen (17.3%) samples processed by either method tested positive for norovirus genogroup II (GII). PCR amplicons were characterized by DNA sequencing and phylogenetic analysis as GII.2 (n = 6), GII.4 (n = 1), GII.17 (n = 3), and GII.unclassified (n = 3). Norovirus-positive samples were further amplified by semi-nested RT-PCR targeting the polymerase-capsid genes. One nucleotide sequence revealed GII.17[P17] Kawasaki strain. Five nucleotide sequences were identified as belonging to the recombinant GII.2[P16] strains by recombination analysis. The collected oyster samples were quantified for norovirus GII genome copy number by RT-quantitative PCR. Using the proteinase K method, GII was found in 13/75 (17.3%) of samples with a range of 8.83-1.85 × 10⁴ genome copies/g of oyster. One sample (1/75, 1.3%) processed by the adsorption-elution method was positive for GII at 5.00 × 10¹ genome copies/g. These findings indicate the circulation of a new variant GII.17 Kawasaki strain and the recombinant GII.2[P16] in oyster samples corresponding to the circulating strains reported at a global scale during the same period of time. The detection of the recombinant strains in oysters emphasizes the need for continuing systematic surveillance for control and prevention of norovirus gastroenteritis.

Epidemiological and Genetic Characterization of Norovirus Outbreaks That Occurred in Catalonia, Spain, 2017–2019

Molecular characterization of human norovirus (HuNoV) genotypes enhances the understanding of viral features and illustrates distinctive evolutionary patterns. The aim of our study was to describe the prevalence of the genetic diversity and the epidemiology of the genotypes involved in HuNoV outbreaks in Catalonia (Spain) between 2017 and 2019. A total of 100 HuNoV outbreaks were notified with the predominance of GII (70%), followed by GI (27%) and mixed GI/GII (3%). Seasonality was observed for GII outbreaks only. The most prevalent genotypes identified were GII.4[P31] Sydney 2012, GII.4[P16] Sydney 2012 and GII.2[P16]. As compared to person-to-person (P/P) transmitted outbreaks, foodborne outbreaks showed significantly higher attack rates and lower duration. The average attack rate was higher in youth hostel/campgrounds compared to nursing homes. Only genotypes GI.4[P4], GII.2[P16], GII.4[P16], GII.4[P31] and GII.17[P17] were consistently detected every year, and only abundance of GII.2[P16] showed a negative trend over time. GII.4 Sydney 2012 outbreaks were significantly associated to nursing homes, while GII.2[P16] and GI.3[P3] were most frequently identified in youth hostel/campgrounds. The average attack rate was significantly higher when comparing GII.2[P16] vs. GI.4[P4], GII.2[P16] vs. GII.4[P31] Sydney 2012, and GII.6[P7] vs. GII.4[P31] Sydney 2012. No correlations were found between genotype and outbreak duration or age of affected individuals.

A Bibliometric Analysis of the Literature on Norovirus Disease from 1991-2021

Norovirus (NoV) is one of the oldest recognized diseases and the leading causal pathogen for acute gastroenteritis (AGE) worldwide. Though numerous studies have been reported on NoV disease, limited research has explored the publication trends in this area. As a result, the objective of this work was to fill the void by conducting a bibliometric study in publication trends on NoV studies as well as discovering the hotspots. The Web of Science central assemblage database was hunted for publications from 1991 to 2021 with “norovirus” in the heading. Microsoft Excel 2016, VOSviewer, R Bibliometrix, and Biblioshiny packages were deployed for the statistical analysis of published research articles. A total of 6021 published documents were identified in the Web of Science database for this thirty-year study period (1991–2021). The analyses disclosed that the Journal of Medical Virology was the leading journal in publications on norovirus studies with a total of 215 published articles, the Journal of Virology was the most cited document with 11,185 total citations. The United States of America (USA) has the most significant productivity in norovirus publications and is the leading country with the highest international collaboration. Analysis of top germane authors discovered that X. Jiang (135) and J. Vinje (119) were the two top relevant authors of norovirus publications. The commonly recognized funders were US and EU-based, with the US emerging as a top funder. This study reveals trends in scientific findings and academic collaborations and serves as a leading-edge model to reveal trends in global research in the field of norovirus research. This study points out the progress status and trends on NoV research. It can help researchers in the medical profession obtain a comprehensive understanding of the state of the art of NoV. It also has reference values for the research and application of the NoV visualization methods. Further, the research map on AGE obtained by our analysis is expected to help researchers efficiently and effectively explore the NoV field.

Norovirus Foodborne Outbreak Associated With the Consumption of Ice Pop, Southern Brazil, 2020

Norovirus is a major cause of foodborne-associated acute gastroenteritis (AGE) outbreaks worldwide. Usually, food products are contaminated either during harvesting or preparation, and the most common products associated to norovirus outbreaks are raw or undercooked bivalve shellfish, fruits (frozen berries) and ready-to-eat produce. In the present study, we investigated an AGE outbreak caused by norovirus associated with the consumption of ice pops in southern Brazil. Clinical stool samples from patients and ice pops samples were collected and analyzed for viruses' detection. By using RT-qPCR and sequencing, we detected the uncommon genotype GII.12[P16] in clinical samples and GII.12 in samples of ice pop. Strains shared identity of 100% at nucleotide level strongly suggesting the consumption of ice pops as the source of the outbreak.

Investigation and analysis on an outbreak of norovirus infection in a health school in Guangdong Province, China

Our objective was to describe the epidemiological features of an outbreak of norovirus infection in a health school in Guangdong province, China, to identify the cause of such a large scale outbreak of norovirus among older students, to simulate the transmission dynamics, and to evaluate the effect of intervention measures of GII.17 [P17] genotype norovirus infection. We identified all cases during the outbreak. Descriptive epidemiological, analytical epidemiological and hygiene survey methods were used to described the outbreak epidemic course and identify the cause of the outbreak of norovirus infection. We also used dynamical model to simulate the transmission dynamics of norovirus infection and evaluate the effect of intervention measures. Norovirus genotyping was assigned to the newly obtained strains, with a maximum likelihood phylogenetic analysis conducted. There were 360 cases of 42 classes in five grades with a 12.99% attack rate. Proportionally, more students were in contact with sick students and vomit in the suspected case group than the control group (χ² = 5.535, P = 0.019 and χ² = 5.549, P = 0.019, respectively). The basic reproduction number was 8.32 before and 0.49 after the intervention. Dynamical modeling showed that if the isolation rate was higher or case isolation began earlier, the total attack rate would decrease. Molecular characterization identified the GII.17 [P17] genotype in all stains obtained from the health school, which were clustered with high support in the phylogenetic tree. This was an outbreak of norovirus infection caused by contact transmission. The main reasons for the spread of the epidemic were the later control time, irregular treatment of vomit and no case isolation. The transmission dynamics of contact transmission was high, more efficient control measures should be employed.

Dynamics of norovirus genotype change and early characterization of variants in children with diarrhea in central Tunisia, 2001-2012

Human noroviruses (HuNoVs), especially GII.4 strains, are a major cause of gastroenteritis epidemics in both children and adults. Stool samples were collected from 113 Tunisian children with acute gastroenteritis in 2001 and 2002 and were retrospectively tested for HuNoVs. Fifteen (13.2%) of the 113 samples were positive for HuNoVs, all of which were genogroup II strains, and the GII.4-2004/Hunter variant was predominant (67%). We reconstituted the temporal circulation of HuNoV strains in central Tunisia between 2003 and 2012 using HuNoV isolates reported in our previous studies. A comparative analysis showed a dynamic change in the molecular profile of the HuNoV strains over a 12-year period. We found that GII.4-2004/Hunter strains were circulating as early as June 2002 and that GIX.1[GII.P15] HuNoVs were already circulating four years before this genotype was first reported in Japan in 2006. Our data suggest that epidemic strains of HuNoV circulate for several years in the pediatric population before becoming predominant. This study suggests that children from low-income countries with poor sanitation may play a significant role in the molecular evolution of noroviruses and the global emergence of new epidemic strains.

Global prevalence of norovirus in cases of acute gastroenteritis from 1997 to 2021: An updated systematic review and meta-analysis

BACKGROUND

The worldwide response towards the acute gastroenteritis epidemic was well known, but the absence of an updated systematic review of global norovirus epidemiology in cases of gastroenteritis existed. We aimed to conduct and update a systematic review and meta-analysis of studies assessing norovirus prevalence among gastroenteritis patients worldwide.

METHODS

Four databases (PubMed, EMBASE, Cochrane Library, and Web of Science) were searched for epidemiological papers from 2014 to 2021 which applied the PCR method to access the prevalence of norovirus in acute gastroenteritis patients more than a full year. Statistical analysis was conducted using R-4.0.0 software.

RESULTS

A total of 405 records with 842, 926 cases were included. The pooled prevalence of norovirus was 16% (95%CI 15, 17). Children under 5 years old were at a higher risk with norovirus. A higher prevalence was seen in South America (22%, 95% CI 18, 27), while other continents showed a similar result with the overall prevalence of norovirus. No association was found between national income level and norovirus prevalence. A gradient of decreasing prevalence was noticed from community (20%, 95% CI 16, 24) to outpatients (18%, 95% CI 16, 20) to hospital setting (included both in- and outpatients, 17%, 95% CI 16, 19) to inpatients (15%, 95% CI 13, 17).

CONCLUSION

Norovirus were associated with 16% acute gastroenteritis globally. To fully understand the prevalence of norovirus worldwide, the continual surveillance of norovirus epidemics was required.

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.

Molecular epidemiology of norovirus infections in children with acute gastroenteritis in 2017-2019 in Tianjin, China

Norovirus (NoV) is the leading cause of acute gastroenteritis (AGE) worldwide. Globally, the GII.4 Sydney 2012 strain has predominated since 2012, although GII.4 variant strains have caused AGE outbreaks in China. Recent patterns of NoV genotype distributions in 6011 children with AGE in Tianjin, China were investigated. NoV was detected using real-time reverse-transcriptase polymerase chain reaction and sequencing of partial sequences of the viral capsid gene. NoV genotypes were determined, and phylogenetic analysis was conducted. Epidemiological and clinical data were compared between children infected with different NoV genotypes. NoV was detected in 27.6% of the specimens tested. GII.4 strains comprised 49.4% infections, followed by GII.3 at 39.9%. Genotypes GII.2, GII.13, GII.17, GII.1, GII.6, and GII.14 were also detected. NoV was detected during most of the year, with a peak season of cases in the winter. Diarrhea, vomiting, fever, abdominal pain, and dehydration were present in patients with NoV infection. The main genotypes were GII.4 and GII.3, with a slight increase in GII.2, beginning in March 2017. Among the GII.4 strains, GII.4 Sydney 2012 was the only epidemic strain in Tianjin. Patients with GII.4 genotypes were more likely to present with diarrhea and vomiting than those with GII.3. Children with GII. Others were prone to suffered from dehydration and abdominal pain than those with GII.3. NoV GII has become the main cause of viral AGE in Tianjin, China. The predominant genotypes of NoV were GII.4 and GII.3. Identification of emerging genotypes is crucial for the prevention and control of NoV-caused AGE.

Virological and Epidemiological Features of Norovirus Infections in Brazil, 2017-2018

Noroviruses are considered an important cause of acute gastroenteritis (AGE) across all age groups. Here, we investigated the incidence of norovirus, genotypes circulation, and norovirus shedding in AGE stool samples from outpatients in Brazil. During a two-year period, 1546 AGE stool samples from ten Brazilian states were analyzed by RT-qPCR to detect and quantify GI and GII noroviruses. Positive samples were genotyped by dual sequencing using the ORF1/2 junction region. Overall, we detected norovirus in 32.1% of samples, with a massive predominance of GII viruses (89.1%). We also observed a significant difference between the median viral load of norovirus GI (3.4×10⁵ GC/g of stool) and GII (1.9×10⁷ GC/g). The most affected age group was children aged between 6 and 24 m old, and norovirus infection was detected throughout the year without marked seasonality. Phylogenetic analysis of partial RdRp and VP1 regions identified six and 11 genotype combinations of GI and GII, respectively. GII.4 Sydney[P16] was by far the predominant genotype (47.6%), followed by GII.2[P16], GII.4 Sydney[P31], and GII.6[P7]. We detected, for the first time in Brazil, the intergenogroup recombinant genotype GIX.1[GII.P15]. Our study contributes to the knowledge of norovirus genotypes circulation at the national level, reinforcing the importance of molecular surveillance programs for future vaccine designs.

Prevalence and Evolution of Noroviruses between 1966 and 2019, Implications for Vaccine Design

Noroviruses (NoVs), a group of single-stranded RNA viruses causing epidemic acute gastroenteritis in humans, are highly diverse, consisting of multiple genogroups with >30 genotypes. Their continual evolutions make NoV vaccine design and development difficult. Here, we report a study of NoV sequences obtained from a population-based diarrhea surveillance in Zhengding County of Hebei Province spanning from 2001 to 2019 and those available in the GenBank database from 1966 to 2019. NoV genotypes and/or variants that may evade immunity were screened and identified based on primary and conformational structures for vaccine design. We selected 366, 301, 139, 74 and 495 complete VP1-coding nucleotide sequences representing the predominant genotypes of GII.4, GII.2, GII.3, GII.6 and GII.17, respectively. A total of 16 distinct GII.4 variants were identified, showing a typical linear evolutionary pattern of variant replacement, while only 1–4 variants of the other genotypes were found to co-circulate over the 40–50-year period without typical variant replacement. The vaccine strain GII.4c is close to variant Sydney_2012 (0.053) in their primary structure, but they are distinct at epitopes A and E in conformations. Our data suggested GII.4 variant Sydney_2012, GII.2 variant A, a GII.3 strain, GII.6 variants B and C and GII.17 variant D are primary candidate strains for NoV vaccine development.

NGS Techniques Reveal a High Diversity of RNA Viral Pathogens and Papillomaviruses in Fresh Produce and Irrigation Water

Fresh fruits and vegetables are susceptible to microbial contamination at every stage of the food production chain, and as a potential source of pathogens, irrigation water quality is a critical factor. Next-generation sequencing (NGS) techniques have been flourishing and expanding to a wide variety of fields. However, their application in food safety remains insufficiently explored, and their sensitivity requires improvement. In this study, quantitative polymerase chain reaction (qPCR) assays showed low but frequent contamination of common circulating viral pathogens, which were found in 46.9% of samples of fresh produce: 6/12 lettuce samples, 4/12 strawberries samples, and 5/8 parsley samples. Furthermore, the application of two different NGS approaches, target enrichment sequencing (TES) for detecting viruses that infect vertebrates and amplicon deep sequencing (ADS), revealed a high diversity of viral pathogens, especially Norovirus (NoV) and Human Papillomavirus (HPV), in fresh produce and irrigation water. All NoV and HPV types found in fresh fruit and vegetable samples were also detected in irrigation water sources, indicating that these viruses are common circulating pathogens in the population and that irrigation water may be the most probable source of viral pathogens in food samples.

Noroviruses-The State of the Art, Nearly Fifty Years after Their Initial Discovery

Human noroviruses are recognised as the major global cause of viral gastroenteritis. Here, we provide an overview of notable advances in norovirus research and provide a short recap of the novel model systems to which much of the recent progress is owed. Significant advances include an updated classification system, the description of alternative virus-like protein morphologies and capsid dynamics, and the further elucidation of the functions and roles of various viral proteins. Important milestones include new insights into cell tropism, host and microbial attachment factors and receptors, interactions with the cellular translational apparatus, and viral egress from cells. Noroviruses have been detected in previously unrecognised hosts and detection itself is facilitated by improved analytical techniques. New potential transmission routes and/or viral reservoirs have been proposed. Recent in vivo and in vitro findings have added to the understanding of host immunity in response to norovirus infection, and vaccine development has progressed to preclinical and even clinical trial testing. Ongoing development of therapeutics includes promising direct-acting small molecules and host-factor drugs.

Advances in Human Norovirus Vaccine Research

Human norovirus (HuNoV) is the leading cause of acute gastroenteritis (AGE) worldwide, which is highly stable and contagious, with a few virus particles being sufficient to establish infection. Although the World Health Organization in 2016 stated that it should be an absolute priority to develop a HuNoV vaccine, unfortunately, there is currently no licensed HuNoV vaccine available. The major barrier to the development of an effective HuNoV vaccine is the lack of a robust and reproducible in vitro cultivation system. To develop a HuNoV vaccine, HuNoV immunogen alone or in combination with other viral immunogens have been designed to assess whether they can simultaneously induce protective immune responses against different viruses. Additionally, monovalent and multivalent vaccines from different HuNoV genotypes, including GI and GII HuNoV virus-like particles (VLPs), have been assessed in order to induce broad protection. Although there are several HuNoV vaccine candidates based on VLPs that are being tested in clinical trials, the challenges to develop effective HuNoV vaccines remain largely unresolved. In this review, we summarize the advances of the HuNoV cultivation system and HuNoV vaccine research and discuss current challenges and future perspectives in HuNoV vaccine development.

Pediatric Norovirus Gastroenteritis in Ireland: Seasonal Trends, Correlation with Disease Severity, Nosocomial Acquisition and Viral Co-Infection

OBJECTIVES

To determine norovirus frequency, seasonal trends, disease severity and nosocomial acquisition in a region of Ireland.

METHODS

From November 18th 2016 to November 18th 2017, all children up to 3 y of age who presented to Mayo University Hospital with vomiting and diarrhea, had their stool tested for norovirus and other viruses. Each week of the year was studied in relation to the total number of stool samples requested for norovirus testing, the number of positive stool samples, the calculated median of positive stool samples in two consecutive weeks and their calculated median percentage of positive stool samples in each two consecutive week period.

RESULTS

During the study period, norovirus was the third leading cause of gastroenteritis (12%), norovirus G2 was the predominant strain; 61% were male; 56% older than 1 y, 78% of cases were severe. No nosocomial disease was detected. The fifth week of January was the week peak. Viral Co- infection was confirmed in four cases of which astrovirus was confirmed in two cases. Three seasons of norovirus gastroenteritis and four short episodes of norovirus infection were noted during 2016/2017.

CONCLUSIONS

Norovirus is a predominant cause of gastroenteritis. Co- infection with other viruses, mainly astrovirus may occur. Norovirus infections occur throughout the year with a peak in winter.

Identification of a blockade epitope of human norovirus GII.17

Human noroviruses are the dominant causative agent of acute viral gastroenteritis worldwide. During the winter of 2014-2015, genotype GII.17 cluster IIIb strains emerged as the leading cause of norovirus infection in Asia and later spread to other parts of the world. It is speculated that mutation at blockade epitopes may have resulted in virus escape from herd immunity, leading to the emergence of GII.17 cluster IIIb variants. Here, we identify a GII.17 cluster IIIb-specific blockade epitope by monoclonal antibody (mAb)-based epitope mapping. Four mAbs (designated as M1 to M4) were generated from mice immunized with virus-like particle (VLP) of a GII.17 cluster IIIb strain. Among them, M1 and M3 reacted specifically with the cluster IIIb VLP but not with the VLPs from clusters II or IIIa. Moreover, M1 and M3 dose-dependently blocked cluster IIIb VLP binding with its ligand, histo-blood group antigens (HBGAs). Epitope mapping revealed that M1 and M3 recognized the same highly exposed epitope consisting of residues 293-296 and 299 in the capsid protein VP1. Sequence alignment showed that the M1/M3 epitope sequence is highly variable among different GII.17 clusters whereas it is identical for cluster IIIIb strains. These data define a dominant blockade epitope of GII.17 norovirus and provide evidence that blockade epitope evolution contributes to the emergence of GII.17 cluster IIIb strains.

Glycan-Induced Protein Dynamics in Human Norovirus P Dimers Depend on Virus Strain and Deamidation Status

Noroviruses are the major cause of viral gastroenteritis and re-emerge worldwide every year, with GII.4 currently being the most frequent human genotype. The norovirus capsid protein VP1 is essential for host immune response. The P domain mediates cell attachment via histo blood-group antigens (HBGAs) in a strain-dependent manner but how these glycan-interactions actually relate to cell entry remains unclear. Here, hydrogen/deuterium exchange mass spectrometry (HDX-MS) is used to investigate glycan-induced protein dynamics in P dimers of different strains, which exhibit high structural similarity but different prevalence in humans. While the almost identical strains GII.4 Saga and GII.4 MI001 share glycan-induced dynamics, the dynamics differ in the emerging GII.17 Kawasaki 308 and rare GII.10 Vietnam 026 strain. The structural aspects of glycan binding to fully deamidated GII.4 P dimers have been investigated before. However, considering the high specificity and half-life of N373D under physiological conditions, large fractions of partially deamidated virions with potentially altered dynamics in their P domains are likely to occur. Therefore, we also examined glycan binding to partially deamidated GII.4 Saga and GII.4 MI001 P dimers. Such mixed species exhibit increased exposure to solvent in the P dimer upon glycan binding as opposed to pure wildtype. Furthermore, deamidated P dimers display increased flexibility and a monomeric subpopulation. Our results indicate that glycan binding induces strain-dependent structural dynamics, which are further altered by N373 deamidation, and hence hint at a complex role of deamidation in modulating glycan-mediated cell attachment in GII.4 strains.

Evolutionary Mechanism of Immunological Cross-Reactivity Between Different GII.17 Variants

Human norovirus is regarded as the leading cause of epidemic acute gastroenteritis with GII.4 being the predominant genotype during the past decades. In the winter of 2014/2015, the GII.17 Kawasaki 2014 emerged as the predominant genotype, surpassing GII.4 in several East Asian countries. Hence, the influence of host immunity response on the continuous evolution of different GII.17 variants needs to be studied in depth. Here, we relate the inferences of evolutionary mechanisms of different GII.17 variants with the investigation of cross-reactivity and cross-protection of their respective antisera using the expression of norovirus P particles in Escherichia coli. The cross-reactivity assay showed that the antisera of previous strains (GII.17 A and GII.17 B) reacted with recent variants (GII.17 C and GII.17 D) at high OD values from 0.8 to 1.16, while recent variant antisera cross-reacting with previous strains were weak with OD values between 0.26 and 0.56. The cross-protection assay indicated that the antisera of previous strains had no inhibitory effect on recent variants. Finally, mutations at amino acids 353–363, 373–384, 394–404, and 444–454 had the greatest impact on cross-reactivity. These data indicate that the recent pandemic variants GII.17 C and GII.17 D avoided the herd immunity effect of previous GII.17 A and GII.17 B strains through antigenic variation.

Trends in acute viral gastroenteritis among children aged ≤5 years through the national surveillance system in South Korea, 2013-2019

Acute gastroenteritis is a global public health concern. This study aimed to analyze the trend and characteristics of acute viral gastroenteritis through a national surveillance network. Enteric viruses were detected in 9510 of 31,750 (30.1%) cases assessed from 2013 to 2019 by EnterNet. The most prevalent pathogens were norovirus (15.2%) and group A rotavirus (9.7%); most infections were reported in 2017 (34.0%). Norovirus and rotavirus coinfections were the most common. Norovirus infections were prevalent among 1‐year‐old children (1835 out of 9510 cases) during winter, and group A rotavirus infections were common during spring. Seasonality was not observed among enteric adenovirus, astrovirus, and sapovirus. The prevalent viral genotypes detected included norovirus GII.4, enteric adenovirus F41, astrovirus genotype 1, and sapovirus GI.1. However, changes in enteric virus trends were noted during the study period. Norovirus prevalence extended into spring, and new genotypes of enteric adenovirus, astrovirus, and sapovirus were identified. These surveillance data elucidate enteric virus epidemiological characteristics.

Pairing of Parental Noroviruses with Unequal Competitiveness Provides a Clear Advantage for Emergence of Progeny Recombinants

Genetic recombination plays a pivotal role in the appearance of human norovirus recombinants that cause global epidemics. However, the factors responsible for the appearance of these recombinants remains largely unknown. In this study, we revealed a selective pressure that restricts parental combinations leading to the emergence of norovirus recombinants. To investigate traces of emerging novel recombinants and their parents in the human population, we isolated mass nucleotide sequence clones of human norovirus genogroups I and II in sewage-affected waters over a 4-year sampling period. Fourteen different phylogenetic combinations of recombinants and their parents were defined from the dozens of phylogenetic lineages circulating in the human population. To evaluate the probability of these combinations, parental lineages of each recombinant were categorized into two groups as HP (relatively higher-competitiveness parents) and LP (relatively lower-competitiveness parents), according to their relative detection frequency. Strong categorization of HP and LP was confirmed by tests with modified data and additional variables. An algorithm that was developed in this study to visualize the chance of mixed infection between parents revealed that HP lineages have a higher chance of mixed infection than LP lineages in the human population. Three parental pairing types in recombinants were defined: HP-HP, HP-LP, and LP-LP. Among these, most recombinants were identified as HP-LP, despite the prediction of dominant emergence of HP-HP-type recombinants. These results suggest that nature favors recombinants of human norovirus that originate from parental pairing of heterogeneous competitiveness.IMPORTANCE Novel recombinants, generated from inter- and intraspecies recombination of norovirus lineages, often emerge and pose a threat to public health. However, the factors determining emergence of these particular recombinants from all possible combinations of parental lineages remain largely unknown. Therefore, current investigations on these recombinants are inevitably limited to postepidemic analyses, which merely identify genetic or phenotypic changes in the newly emerged recombinants compared to their parents. Here, we provide a new theoretical concept that emergence of novel recombinants could be explained by a combination of parental noroviruses thriving in the human population and those circulating at lower levels. This study could provide an additional and important rationale for the proactive environmental monitoring of potential future epidemics due to viral recombinants.

Influence of fucosidase-producing bifidobacteria on the HBGA antigenicity of oyster digestive tissue and the associated norovirus binding

Bivalve molluscan shellfish such as oysters are filter feeders and are able to accumulate human noroviruses (NoVs) largely due to the presence of human histo-blood group antigens (HBGAs)-like carbohydrates in their intestine. Since the fucose contents play a key role in the binding of NoVs to HBGAs, this study intended to investigate the influence of fucosidase-producing bifidobacteria on the HBGA antigenicity of oyster digestive tissue and the associated NoV binding. On the contrary to the expected, after a treatment of the oyster digestive tissue extracts with Bifidobacterium bifidum strain JCM 1254, the binding of human NoV GII.4 virus like particles (VLPs) to the oyster digestive tissue extracts enhanced significantly (OD₄₅₀ from 1.15 ± 0.05 to 1.51 ± 0.02, P < 0.001) in an in vitro direct binding assay. The accumulation of human NoV GII·P16-GII.4 also enhanced significantly in the intestine of B. bifidum JCM 1254 treated oysters from 4.27 ± 0.25 log genomic copies/g oyster digestive tissue to 5.25 ± 0.29 log genomic copies/g oyster digestive tissue (P < 0.005) as observed in an in vivo test. Correspondingly, the type A antigenicity of the oyster digestive tissue extracts enhanced (OD₄₅₀ from 0.77 ± 0.04 to 1.06 ± 0.05, P < 0.01) after the treatment with B. bifidum JCM 1254. These results could be explained by the substrate specificity of the B. bifidum JCM 1254 associated fucosidases. This study identified an indirect interaction possibly happening between the bacterial microbiota with human NoVs during their transmission in the food systems. We also supplied a potential strategy to mitigate the NoV contamination from shellfish, suppose bacterial strains with specified fucosidase production could be obtained in the future.

N-terminal VP1 Truncations Favor T = 1 Norovirus-Like Particles

Noroviruses cause immense sporadic gastroenteritis outbreaks worldwide. Emerging genotypes, which are divided based on the sequence of the major capsid protein VP1, further enhance this public threat. Self-assembling properties of the human norovirus major capsid protein VP1 are crucial for using virus-like particles (VLPs) for vaccine development. However, there is no vaccine available yet. Here, VLPs from different variants produced in insect cells were characterized in detail using a set of biophysical and structural tools. We used native mass spectrometry, gas-phase electrophoretic mobility molecular analysis, and proteomics to get clear insights into particle size, structure, and composition, as well as stability. Generally, noroviruses have been known to form mainly T = 3 particles. Importantly, we identified a major truncation in the capsid proteins as a likely cause for the formation of T = 1 particles. For vaccine development, particle production needs to be a reproducible, reliable process. Understanding the underlying processes in capsid size variation will help to produce particles of a defined capsid size presenting antigens consistent with intact virions. Next to vaccine production itself, this would be immensely beneficial for bio-/nano-technological approaches using viral particles as carriers or triggers for immunological reactions.

Detection of Norovirus in Saliva Samples from Acute Gastroenteritis Cases and Asymptomatic Subjects: Association with Age and Higher Shedding in Stool

Norovirus infections are a leading cause of acute gastroenteritis outbreaks worldwide and across all age groups, with two main genogroups (GI and GII) infecting humans. The aim of our study was to investigate the occurrence of norovirus in saliva samples from individuals involved in outbreaks of acute gastroenteritis in closed and semiclosed institutions, and its relationship with the virus strain, virus shedding in stool, the occurrence of symptoms, age, and the secretor status of the individual. Epidemiological and clinical information was gathered from norovirus outbreaks occurring in Catalonia, Spain during 2017–2018, and stool and saliva samples were collected from affected and exposed resident individuals and workers. A total of 347 saliva specimens from 25 outbreaks were analyzed. Further, 84% of individuals also provided a paired stool sample. For GII infections, norovirus was detected in 17.9% of saliva samples from symptomatic cases and 5.2% of asymptomatic individuals. Positivity in saliva occurred in both secretors and nonsecretors. None of the individuals infected by norovirus GI was positive for the virus in saliva. Saliva positivity did not correlate with any of the studied symptoms but did correlate with age ≥ 65 years old. Individuals who were positive in saliva showed higher levels of virus shedding in stool. Mean viral load in positive saliva was 3.16 ± 1.08 log₁₀ genome copies/mL, and the predominance of encapsidated genomes was confirmed by propidium monoazide (PMA)xx-viability RTqPCR assay. The detection of norovirus in saliva raises the possibility of oral-to-oral norovirus transmission during the symptomatic phase and, although to a lesser extent, even in cases of asymptomatic infections.