Norovirus encounters in the gut: multifaceted interactions and disease outcomes

Establishment of a Nucleic Acid Detection Method for Norovirus GII.2 Genotype Based on RT-RPA and CRISPR/Cas12a-LFS

To establish a rapid detection method for norovirus GII.2 genotype, this study employed reverse transcription recombinase polymerase amplification (RT-RPA) combined with CRISPR/Cas12a and lateral flow strip (RT-RPA-Cas12a-LFS). Here, the genome of norovirus GII.2 genotype was compared to identify highly conserved sequences, facilitating the design of RT-RPA primers and crRNA specific to the conserved regions of norovirus GII.2. Subsequently, the reaction parameters of RT-RPA were optimized and evaluated using agar-gel electrophoresis and LFS. The results indicate that the conserved sequences of norovirus GII.2 were successfully amplified through RT-RPA at 37°C for 25 minutes. Additionally, CRISPR/Cas12a-mediated cleavage detection was achieved through LFS at 37°C within 10 minutes using the amplification products as templates. Including the isothermal amplification reaction time, the total time is 35 minutes. The established RT-RPA-Cas12a-LFS method demonstrated specific detection of norovirus GII.2, yielding negative results for other viral genomes, and exhibited an excellent detection limit of 10 copies/μl. The RT-RPA-Cas12a-LFS method was further compared with qRT-PCR by analyzing 60 food-contaminated samples. The positive conformity rate was 100%, the negative conformity rate was 95.45%, and the overall conformity rate reached 98.33%. This detection method for norovirus GII.2 genotype is cost-effective, highly sensitive, specific, and easy to operate, offering a promising technical solution for field-based detection of the norovirus GII.2 genotype.

A narrative review of norovirus epidemiology, biology, and challenges to vaccine development

Norovirus is a leading cause of acute gastroenteritis (AGE) globally. AGE resulting from norovirus causes significant morbidity and mortality in countries of all income levels, particularly among young children and older adults. Prevention of norovirus AGE represents a unique challenge as the virus is genetically diverse with multiple genogroups and genotypes cocirculating globally and causing disease in humans. Variants of the GII.4 genotype are typically the most common genotype, and other genotypes cause varying amounts of disease year-to-year, with GII.2, GII.3, and GII.6 most prevalent in recent years. Noroviruses are primarily transmitted via the fecal-oral route and only a very small number of virions are required for infection, which makes outbreaks of norovirus extremely difficult to control when they occur. Settings like long-term care facilities, daycares, and hospitals are at high risk of outbreaks and can have very high attack rates resulting in substantial costs and disease burden. Severe cases of norovirus AGE are most common in vulnerable patient populations, such as infants, the elderly, and immunocompromised individuals, with available treatments limited to rehydration therapies and supportive care. To date, there are no FDA-approved norovirus vaccines; however, several candidates are currently in development. Given the substantial human and economic burden associated with norovirus AGE, a vaccine to prevent morbidity and mortality and protect vulnerable populations could have a significant impact on global public health.

Current trends and new approaches for human norovirus replication in cell culture: a literature review

Human norovirus (HuNoV) is one of the world's leading causes of acute gastroenteritis. At present, effective reproduction of the virus in cell cultures remains a challenge for virologists, as there is a lack of a permissive cell line that allows the entire viral life cycle to be reproduced. This is a barrier to the study of the HuNoV life cycle, its tropism, and virus-host interactions. It is also a major hurdle for the development of viral detection platforms, and ultimately for the development of therapeutics. The lack of an inexpensive, technically simple, and easily implemented cultivation method also negatively affects our ability to evaluate the efficacy of a variety of control measures (disinfectants, food processes) for human norovirus. In the process of monitoring this pathogen, it is necessary to detect infectious viral particles in water, food, and other environmental samples. Therefore, improvement of in vitro replication of HuNoV is still needed. In this review, we discuss current trends and new approaches to HuNoV replication in cell culture. We highlight ways in which previous research on HuNoV and other noroviruses has guided and influenced the development of new HuNoV culture systems and discuss the improvement of in vitro replication of HuNoV.

Norovirus evolves as one or more distinct clonal populations in immunocompromised hosts

Noroviruses are a major cause of acute gastroenteritis worldwide and can establish chronic infection in immunocompromised individuals. To investigate the mechanisms of norovirus evolution during chronic infection, we selected seven representative patients from a National Institutes of Health study cohort who sustained norovirus infection for periods ranging from 73 to 1,492 days. Six patients shed viruses belonging to a single genotype (GII.2[PNA], GII.4 New Orleans[P4], GII.4 Den Haag[P4], GII.3[P21], GII.6[P7], or GII.14[P7]) over the period examined, while one patient sequentially shed two genotypes (GII.6[P7] followed by GII.4 Sydney[P31]). Norovirus genomes from consecutive stool samples were sequenced at high resolution (>3,300 reads/nucleotide position) using the Illumina platform and subjected to bioinformatics analysis. Norovirus sequences could be resolved into one or more discrete clonal RNA genomes that persisted within these patients over time. Phylogenetic analyses inferred that clonal populations originated from a single founder virus and not by reinfection with community strains. Estimated evolutionary rates of clonal populations during persistent infection were similar to those of noroviruses from acute infection in the global database, suggesting that inherently higher RNA-dependent polymerase error rates were not associated with the ability to persist. The high-resolution analysis of norovirus diversity and evolution at the population level described here should allow a better understanding of adaptive mutations sustained during chronic infection. IMPORTANCE Noroviruses are an important cause of chronic diarrhea in patients with compromised immune systems. Presently, there are no effective therapies to clear the virus, which can persist for years in the intestinal tract. The goal of our study was to develop a better understanding of the norovirus strains that are associated with these long-term infections. With the remarkable diversity of norovirus strains detected in the immunocompromised patient cohort we studied, it appears that most, if not all, noroviruses circulating in nature may have the capacity to establish a chronic infection when a person is unable to mount an effective immune response. Our work is the most comprehensive genetic data set generated to date in which near full-length genomes from noroviruses associated with chronic infection were analyzed by high-resolution next-generation sequencing. Analysis of this data set led to our discovery that certain patients in our cohort were shedding noroviruses that could be subdivided into distinct haplotypes or populations of viruses that were co-evolving independently. The ability to track haplotypes of noroviruses during chronic infection will allow us to fine-tune our understanding of how the virus adapts and maintains itself in the human host, and how selective pressures such as antiviral drugs can affect these distinct populations.

Norovirus Infection in Children with Acute Lymphoblastic Leukemia

Norovirus infection in children on treatment for acute lymphoblastic leukemia can lead to severe morbidity due to chronic viral shedding, malabsorption, failure to thrive, and interruption of chemotherapy. We had four children with norovirus diarrhoea in eight years period in our pediatric oncology unit. Three children under two years of age had chronic noroviral shedding and persistent diarrhoea, probably due to poor adaptive immune responses. Two of those children didn't respond to nitazoxanide and succumbed to the illness. The third patient who received nitazoxanide and favipiravir, is currently well on chemotherapy.

Emerging role of the gut microbiome in post-infectious irritable bowel syndrome: A literature review

Post-infectious irritable bowel syndrome (PI-IBS) is a particular type of IBS, with symptom onset after an acute episode of infectious gastroenteritis. Despite infectious disease resolution and clearance of the inciting pathogen agent, 10% of patients will develop PI-IBS. In susceptible individuals, the exposure to pathogenic organisms leads to a marked shift in the gut microbiota with prolonged changes in host-microbiota interactions. These changes can affect the gut-brain axis and the visceral sensitivity, disrupting the intestinal barrier, altering neuromuscular function, triggering persistent low inflammation, and sustaining the onset of IBS symptoms. There is no specific treatment strategy for PI-IBS. Different drug classes can be used to treat PI-IBS similar to patients with IBS in general, guided by their clinical symptoms. This review summarizes the current evidence for microbial dysbiosis in PI-IBS and analyzes the available data regarding the role of the microbiome in mediating the central and peripheral dysfunctions that lead to IBS symptoms. It also discusses the current state of evidence on therapies targeting the microbiome in the management of PI-IBS. The results of microbial modulation strategies used in relieving IBS symptomatology are encouraging. Several studies on PI-IBS animal models reported promising results. However, published data that describe the efficacy and safety of microbial targeted therapy in PI-IBS patients are scarce. Future research is required.

Cloning, Expression, and Functional Characterization of FUT1, a Key Gene for Histo-Blood Group Antigens Synthesis in Crassostrea gigas

Histo-blood group antigens (HBGAs) comprise a family of cell-surface carbohydrates that are considered norovirus-specific binding receptors or ligands. HBGA-like molecules have also been detected in oysters as common norovirus carriers, although the pathway involved in the synthesis of these molecules in oysters has yet to be elucidated. We isolated and identified a key gene involved in the synthesis of HBGA-like molecules, FUT1, from Crassostrea gigas, named CgFUT1. Real-time quantitative polymerase chain reaction analysis showed that CgFUT1 mRNA was expressed in the mantle, gill, muscle, labellum, and hepatopancreatic tissues of C. gigas, with the hepatopancreas exhibiting the highest expression level. A recombinant CgFUT1 protein with a molecular mass of 38.0 kDa was expressed in Escherichia coli using a prokaryotic expression vector. A eukaryotic expression plasmid was constructed and transfected into Chinese hamster ovary (CHO) cells. The expression of CgFUT1 and membrane localization of type H-2 HBGA-like molecules in CHO cells were detected using Western blotting and cellular immunofluorescence, respectively. This study indicated that CgFUT1, expressed in C. gigas tissues, can synthesize type H-2 HBGA-like molecules. This finding provides a new perspective for analyzing the source and synthetic pathway of HBGA-like molecules in oysters.

Elucidating the Implications of Norovirus N- and O-Glycosylation, O-GlcNAcylation, and Phosphorylation

Norovirus is the most common cause of foodborne gastroenteritis, affecting millions of people worldwide annually. Among the ten genotypes (GI-GX) of norovirus, only GI, GII, GIV, GVIII, and GIX infect humans. Some genotypes reportedly exhibit post-translational modifications (PTMs), including N- and O-glycosylation, O-GlcNAcylation, and phosphorylation, in their viral antigens. PTMs have been linked to increased viral genome replication, viral particle release, and virulence. Owing to breakthroughs in mass spectrometry (MS) technologies, more PTMs have been discovered in recent years and have contributed significantly to preventing and treating infectious diseases. However, the mechanisms by which PTMs act on noroviruses remain poorly understood. In this section, we outline the current knowledge of the three common types of PTM and investigate their impact on norovirus pathogenesis. Moreover, we summarize the strategies and techniques for the identification of PTMs.

Interferon-Driven Immune Dysregulation in Common Variable Immunodeficiency-Associated Villous Atrophy and Norovirus Infection

PURPOSE

About 15% of patients with common variable immunodeficiency (CVID) develop a small intestinal enteropathy, which resembles celiac disease with regard to histopathology but evolves from a distinct, poorly defined pathogenesis that has been linked in some cases to chronic norovirus (NV) infection. Interferon-driven inflammation is a prominent feature of CVID enteropathy, but it remains unknown how NV infection may contribute.

METHODS

Duodenal biopsies of CVID patients, stratified according to the presence of villous atrophy (VA), IgA plasma cells (PCs), and chronic NV infection, were investigated by flow cytometry, multi-epitope-ligand cartography, bulk RNA-sequencing, and RT-qPCR of genes of interest.

RESULTS

VA development was connected to the lack of intestinal (IgA+) PC, a T helper 1/T helper 17 cell imbalance, and increased recruitment of granzyme+CD8+ T cells and pro-inflammatory macrophages to the affected site. A mixed interferon type I/III and II signature occurred already in the absence of histopathological changes and increased with the severity of the disease and in the absence of (IgA+) PCs. Chronic NV infection exacerbated this signature when compared to stage-matched NV-negative samples.

CONCLUSIONS

Our study suggests that increased IFN signaling and T-cell cytotoxicity are present already in mild and are aggravated in severe stages (VA) of CVID enteropathy. NV infection preempts local high IFN-driven inflammation, usually only seen in VA, at milder disease stages. Thus, revealing the impact of different drivers of the pathological mixed IFN type I/III and II signature may allow for more targeted treatment strategies in CVID enteropathy and supports the goal of viral elimination.

Current assumptions for quantitative microbial risk assessment (QMRA) of Norovirus contamination of drinking water catchments due to recreational activities: an update

Contamination of drinking water from Norovirus (NoV) and other waterborne viruses is a major public health concern globally. Increasingly, quantitative microbial risk assessment (QMRA) is being used to assess the various risks from waterborne pathogens and evaluate control strategies. As urban populations grow and expand, there is increasing demand for recreational activities in drinking water catchments. QMRA relies on context-specific data to map out the pathways by which viruses can enter water and be transferred to drinking water consumers and identify risk factors and appropriate controls. This review examines the current evidence base and assumptions for QMRA analysis of NoV and other waterborne viral pathogens and recommends numerical values based on the most recent evidence to better understand the health risks associated with recreators in Australian drinking water sources; these are broadly applicable to all drinking water sources where recreational access is allowed. Key issues include the lack of an agreed upon data and dose-response models for human infectious NoV genotypes, faecal shedding by bathers, the extent of NoV infectivity and aggregation, resistance (secretor status) to NoV and the extent of secondary transmission.

Mechanisms involved in controlling RNA virus-induced intestinal inflammation

Gastroenteritis is inflammation of the lining of stomach and intestines and causes significant morbidity and mortality worldwide. Many viruses, especially RNA viruses are the most common cause of enteritis. Innate immunity is the first line of host defense against enteric RNA viruses and virus-induced intestinal inflammation. The first layer of defense against enteric RNA viruses in the intestinal tract is intestinal epithelial cells (IECs), dendritic cells and macrophages under the intestinal epithelium. These innate immune cells express pathogen-recognition receptors (PRRs) for recognizing enteric RNA viruses through sensing viral pathogen-associated molecular patterns (PAMPs). As a result of this recognition type I interferon (IFN), type III IFN and inflammasome activation occurs, which function cooperatively to clear infection and reduce viral-induced intestinal inflammation. In this review, we summarize recent findings about mechanisms involved in enteric RNA virus-induced intestinal inflammation. We will provide an overview of the enteric RNA viruses, their RNA sensing mechanisms by host PRRs, and signaling pathways triggered by host PRRs, which shape the intestinal immune response to maintain intestinal homeostasis.

Epidemiology, Clinical Features, and Unusual Complications of Norovirus Infection in Taiwan: What We Know after Rotavirus Vaccines

Noroviruses (NoVs) are one of the emerging and rapidly spreading groups of pathogens threatening human health. A reduction in sporadic NoV infections was noted following the start of the COVID-19 pandemic, but the return of NoV gastroenteritis during the COVID-19 pandemic has been noted recently. Research in recent years has shown that different virus strains are associated with different clinical characteristics; moreover, there is a paucity of research into extraintestinal or unusual complications that may be associated with NoV. The genomic diversity of circulating NoVs is also complex and may vary significantly. Therefore, this short narrative review focuses on sharing the Taiwan experience of NoV infection including epidemiology, clinical features, and complications following suboptimal rotavirus immunization in Taiwan (after October 2006). We also highlight the unusual complications associated with NoV infections and the impacts of NoV infection during the COVID-19 pandemic in the literature for possible future research directions. To conclude, further research is needed to quantify the burden of NoV across the spectrum of disease severity in Taiwan. The evidence of the connection between NoV and the unusual complications is still lacking.

Microbiome-mediated incapacitation of interferon lambda production in the oral mucosa

Here, we show that Porphyromonas gingivalis (Pg), an endogenous oral pathogen, dampens all aspects of interferon (IFN) signaling in a manner that is strikingly similar to IFN suppression employed by multiple viral pathogens. Pg suppressed IFN production by down-regulating several IFN regulatory factors (IRFs 1, 3, 7, and 9), proteolytically degrading STAT1 and suppressing the nuclear translocation of the ISGF3 complex, resulting in profound and systemic repression of multiple interferon-stimulated genes. Pg-induced IFN paralysis was not limited to murine models but was also observed in the oral tissues of human periodontal disease patients, where overabundance of Pg correlated with suppressed IFN generation. Mechanistically, multiple virulence factors and secreted proteases produced by Pg transcriptionally suppressed IFN promoters and also cleaved IFN receptors, making cells refractory to exogenous IFN and inducing a state of broad IFN paralysis. Thus, our data show a bacterial pathogen with equivalence to viruses in the down-regulation of host IFN signaling.

Norovirus: Facts and Reflections from Past, Present, and Future

Human Norovirus is currently the main viral cause of acute gastroenteritis (AGEs) in most countries worldwide. Nearly 50 years after the discovery of the "Norwalk virus" by Kapikian and colleagues, the scientific and medical community continue to generate new knowledge on the full biological and disease spectrum of Norovirus infection. Nevertheless, several areas remain incompletely understood due to the serious constraints to effectively replicate and propagate the virus. Here, we present a narrated historic perspective and summarize our current knowledge, including insights and reflections on current points of interest for a broad medical community, including clinical and molecular epidemiology, viral-host-microbiota interactions, antivirals, and vaccine prototypes. We also include a reflection on the present and future impacts of the COVID-19 pandemic on Norovirus infection and disease.

Akt plays differential roles during the life cycles of acute and persistent murine norovirus strains in macrophages

Akt (Protein kinase B) is a key signaling protein in eukaryotic cells that controls many cellular processes such as glucose metabolism and cell proliferation for survival. As obligate intracellular pathogens, viruses modulate host cellular processes, including Akt signaling, for optimal replication. The mechanisms by which viruses modulate Akt and the resulting effects on the infectious cycle differ widely depending on the virus. In this study, we explored the effect of Akt serine 473 phosphorylation (p-Akt) during murine norovirus (MNV) infection. p-Akt increased during infection of murine macrophages with acute MNV-1 and persistent CR3 and CR6 strains. Inhibition of Akt with MK2206, an inhibitor of all three isoforms of Akt (Akt1/2/3), reduced infectious virus progeny of all three virus strains. This reduction was due to decreased viral genome replication (CR3), defective virus assembly (MNV-1), or diminished cellular egress (CR3 and CR6) in a virus strain-dependent manner. Collectively, our data demonstrate that Akt activation increases in macrophages during the later stages of the MNV infectious cycle, which may enhance viral infection in unique ways for different virus strains. The data, for the first time, indicate a role for Akt signaling in viral assembly and highlight additional phenotypic differences between closely related MNV strains. Importance Human noroviruses (HNoV) are a leading cause of viral gastroenteritis, resulting in high annual economic burden and morbidity; yet there are no small animal models supporting productive HNoV infection, or robust culture systems producing cell culture-derived virus stocks. As a result, research on drug discovery and vaccine development against norovirus infection has been challenging, and no targeted antivirals or vaccines against HNoV are approved. On the other hand, murine norovirus (MNV) replicates to high titers in cell culture and is a convenient and widespread model in norovirus research. Our data demonstrate the importance of Akt signaling during the late stage of the MNV life cycle. Notably, the effect of Akt signaling on genome replication, virus assembly and cellular egress is virus strain specific, highlighting the diversity of biological phenotypes despite small genetic variability among norovirus strains. This study is the first to demonstrate a role for Akt in viral assembly.

The evaluation of novel oral vaccines based on self-amplifying RNA lipid nanparticles (saRNA LNPs), saRNA transfected Lactobacillus plantarum LNPs, and saRNA transfected Lactobacillus plantarum to neutralize SARS-CoV-2 variants alpha and delta

The aim of this study was to present and evaluate novel oral vaccines, based on self-amplifying RNA lipid nanparticles (saRNA LNPs), saRNA transfected Lactobacillus plantarum LNPs, and saRNA transfected Lactobacillus plantarum, to neutralize severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) variants alpha and delta. After invitro evaluation of the oral vaccines on HEK293T/17 cells, we found that saRNA LNPs, saRNA transfected Lactobacillus plantarum LNPs, and saRNA transfected Lactobacillus plantarum could express S-protein at both mRNA and protein levels. In the next step, BALB/c mice were orally vaccinated with saRNA LNPs, saRNA transfected Lactobacillus plantarum LNPs, and saRNA transfected Lactobacillus plantarum at weeks 1 and 3. Importantly, a high titer of IgG and IgA was observed by all of them, sharply in week 6 (P < 0.05). In all study groups, their ratio of IgG2a/IgG1 was upper 1, indicating Th1-biased responses. Wild-type viral neutralization assay showed that the secreted antibodies in vaccinated mice and recovered COVID-19 patients could neutralize SARS-COV-2 variants alpha and delta. After oral administration of oral vaccines, biodistribution assay was done. It was found that all of them had the same biodistribution pattern. The highest concentration of S-protein was seen in the small intestine, followed by the large intestine and liver.

Protective effect of pogostone on murine norovirus infected-RAW264.7 macrophages through inhibition of NF-κB/NLRP3-dependent pyroptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Pogostemon cablin, the dry overground parts of Pogostemon cablin (Blanco) Benth, has been widely used in the treatment of gastrointestinal dysfunction, such as nausea, diarrhea, headaches and fever. Pogostone (PO) is a major component of Pogostemon cablin which has a variety of pharmacological properties, including antiinflammatory, and immunosuppressive activities, and antioxidant. However, the effect of PO on norovirus gastroenteritis and the underlying molecular mechanism remain unclear.

AIM OF THE STUDY

The purpose of our study is to investigate the effects of PO against MNV infection using RAW264.7 cells and to elucidate its active mechanisms.

MATERIALS AND METHODS

The cell viability was assessed using Cell Counting Kit-8 (CCK-8) assay and Fluorescein diacetate (FDA) staining. The activation of nuclear factor kappa B (NF-κB) signaling and NOD-like receptor 3 (NLRP3) inflammasome was evaluated by assessing the level of phospho-NF-κB p65, interleukin (IL)-6, TNF-α, NLRP3, cleaved caspase-1, IL-18, IL-1β using Western blot and quantitative real-time PCR (qPCR), respectively. The number of infected cells were determined by immunofluorescence microscopic assay.

RESULTS

PO did not possess a cytotoxic effect toward RAW264.7 cells. The cytotoxic damage caused by MNV infection in RAW264.7 cells decreased significantly in the presence of PO. Cell viability assays showed that pyroptosis is the major mechanism of death in MNV-infected RAW264.7 cells. PO could decreased the expression levels of p-p65, IL-6, TNF-α, NLRP3, cleaved caspase-1, IL-1β, and IL-18.

CONCLUSIONS

These results demonstrate that PO decreases MNV-induced RAW264.7 macrophages death and MNV replication through repressing NF-κB/NLRP3-dependent pyroptosis. Therefore PO may be considered as a potential therapeutic agent for preventing and treating norovirus gastroenteritis.

Effect of Direct Viral-Bacterial Interactions on the Removal of Norovirus From Lettuce

Norovirus (NoV) is the main non-bacterial pathogen causing outbreaks of gastroenteritis and is considered to be the leading cause of foodborne illness. This study aims to determine whether lettuce-encapsulated bacteria can express histo-blood group antigen (HBGA)–like substances to bind to NoV and, if so, to explore its role in protecting NoV from disinfection practices. Fifteen bacterial strains (HBGA-SEBs) were isolated from the lettuce microbiome and studied as they were proved to have the ability to express HBGA-like substances through indirect ELISA detection. By using attachment assay, HBGA-SEBs showed great abilities in carrying NoVs regarding the evaluation of binding capacity, especially for the top four strains from genera Wautersiella, Sphingobacterium, and Brachybacterium, which could absorb more than 60% of free-flowing NoVs. Meanwhile, the direct viral–bacterial binding between HBGA-like substance-expressing bacteria (HBGA-SEB) and NoVs was observed by TEM. Subsequently, results of simulated environmental experiments showed that the binding of NoVs with HBGA-SEBs did have detrimental effects on NoV reduction, which were evident in short-time high-temperature treatment (90°C) and UV exposure. Finally, by considering the relative abundance of homologous microorganisms of HBGA-SEBs in the lettuce microbiome (ca. 36.49%) and the reduction of NoVs in the simulated environments, we suggested putting extra attention on the daily disinfection of foodborne-pathogen carriers to overcome the detrimental effects of direct viral–bacterial interactions on the reduction of NoVs.

An Increased Risk of School-Aged Children with Viral Infection among Diarrhea Clusters in Taiwan during 2011-2019

Acute diarrhea is mainly caused by norovirus and rotavirus. Numerous factors modify the risk of diarrhea cluster infections and outbreaks. The purpose of this study was to explore the epidemiological characteristics, differences, and trends in the distribution of viral and bacterial pathogens that cause diarrhea cluster events as well as the public places where diarrhea cluster events took place in Taiwan from 2011 to 2019. We examined publicly available, annual summary data on 2865 diarrhea clusters confirmed by the Taiwan Centers for Disease Control (CDC) from 2011 to 2019. There were statistically significant differences (p < 0.001) in event numbers of diarrhea clusters among viral and bacterial pathogens, and statistically significant differences (p < 0.001) in event numbers of diarrhea clusters among bacterial pathogens. There were also statistically significant differences (p < 0.001) in the event numbers of diarrhea clusters among public places. Norovirus infections were the first most numerous (77.1%, 1810/2347) diarrhea clusters among viral and bacterial infections. Among bacterial infections, Staphylococcus aureus infections accounted for the greatest number of diarrhea clusters (35.5%, 104/293). Schools were the places with the greatest number of diarrhea clusters (49.1%, 1406/2865) among various institutions. Norovirus single infection (odds ratio, OR = 4.423), Staphylococcus aureus single infection (OR = 2.238), and school (OR = 1.983) were identified as risk factors. This is the first report of confirmed events of diarrhea clusters taken from surveillance data compiled by Taiwan's CDC (2011-2019). This study highlights the importance of long-term and geographically extended studies, particularly for highly fluctuating pathogens, to understand the implications of the transmission of diarrhea clusters in Taiwan's populations. Importantly, big data have been identified that can inform future surveillance and research efforts in Taiwan.

Emerging Roles of Gut Virome in Pediatric Diseases

In the last decade, the widespread application of shotgun metagenomics provided extensive characterization of the bacterial "dark matter" of the gut microbiome, propelling the development of dedicated, standardized bioinformatic pipelines and the systematic collection of metagenomic data into comprehensive databases. The advent of next-generation sequencing also unravels a previously underestimated viral population (virome) present in the human gut. Despite extensive efforts to characterize the human gut virome, to date, little is known about the childhood gut virome. However, alterations of the gut virome in children have been linked to pathological conditions such as inflammatory bowel disease, type 1 diabetes, malnutrition, diarrhea and celiac disease.

Potential intestinal infection and faecal-oral transmission of SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread to more than 200 countries and regions globally. SARS-CoV-2 is thought to spread mainly through respiratory droplets and close contact. However, reports have shown that a notable proportion of patients with coronavirus disease 2019 (COVID-19) develop gastrointestinal symptoms and nearly half of patients confirmed to have COVID-19 have shown detectable SARS-CoV-2 RNA in their faecal samples. Moreover, SARS-CoV-2 infection reportedly alters intestinal microbiota, which correlated with the expression of inflammatory factors. Furthermore, multiple in vitro and in vivo animal studies have provided direct evidence of intestinal infection by SARS-CoV-2. These lines of evidence highlight the nature of SARS-CoV-2 gastrointestinal infection and its potential faecal-oral transmission. Here, we summarize the current findings on the gastrointestinal manifestations of COVID-19 and its possible mechanisms. We also discuss how SARS-CoV-2 gastrointestinal infection might occur and the current evidence and future studies needed to establish the occurrence of faecal-oral transmission.

Norovirus evolution in immunodeficient mice reveals potentiated pathogenicity via a single nucleotide change in the viral capsid

Interferons (IFNs) are key controllers of viral replication, with intact IFN responses suppressing virus growth and spread. Using the murine norovirus (MNoV) system, we show that IFNs exert selective pressure to limit the pathogenic evolutionary potential of this enteric virus. In animals lacking type I IFN signaling, the nonlethal MNoV strain CR6 rapidly acquired enhanced virulence via conversion of a single nucleotide. This nucleotide change resulted in amino acid substitution F514I in the viral capsid, which led to >10,000-fold higher replication in systemic organs including the brain. Pathogenicity was mediated by enhanced recruitment and infection of intestinal myeloid cells and increased extraintestinal dissemination of virus. Interestingly, the trade-off for this mutation was reduced fitness in an IFN-competent host, in which CR6 bearing F514I exhibited decreased intestinal replication and shedding. In an immunodeficient context, a spontaneous amino acid change can thus convert a relatively avirulent viral strain into a lethal pathogen.

Enteric Viral Co-Infections: Pathogenesis and Perspective

Enteric viral co-infections, infections involving more than one virus, have been reported for a diverse group of etiological agents, including rotavirus, norovirus, astrovirus, adenovirus, and enteroviruses. These pathogens are causative agents for acute gastroenteritis and diarrheal disease in immunocompetent and immunocompromised individuals of all ages globally. Despite virus–virus co-infection events in the intestine being increasingly detected, little is known about their impact on disease outcomes or human health. Here, we review what is currently known about the clinical prevalence of virus–virus co-infections and how co-infections may influence vaccine responses. While experimental investigations into enteric virus co-infections have been limited, we highlight in vivo and in vitro models with exciting potential to investigate viral co-infections. Many features of virus–virus co-infection mechanisms in the intestine remain unclear, and further research will be critical.

Acute Infectious Diarrhea and Gastroenteritis in Children

PURPOSE OF REVIEW

We aimed to summarize the most current evidence on the main aspects of the diarrheal diseases in children. The following key elements were addressed: definitions, etiology, pathogenesis, diagnosis, dietary management, pharmacological treatments, and prevention. We covered the following questions: What are the most important clinical and laboratory features of the disease? What are the best approaches for the dietary management? What is the best way to classify the hydration status, and to prevent and treat the dehydration? What are the most effective and safe interventions for reducing the diarrhea and vomiting?

RECENT FINDINGS

Diarrheal diseases are one of the most common diseases in childhood. The most common cause is rotavirus. A key element in the approach of a child with diarrhea is determining their hydration status, which determines the fluid management. Laboratory tests are nor routinely required, as most of the cases, they do not affect the management and it should be indicated only in selected cases. Several treatments have been studied to reduce the duration of the diarrhea. Only symbiotics and zinc have shown to be effective and safe with high certainty on the evidence. Rest of the interventions although seem to be effective have low to very low quality of the evidence. The only effective and safe antiemetic for controlling vomiting is ondansetron. A list of antimicrobials indications according to the identified microorganisms is provided. We summarized the most current evidence on diagnosis, management, and prevention of diarrhea in children. More research is needed in some areas such as dehydration scales, rehydration management, antidiarrheals, and antibiotic treatments.