Norovirus infection in immunocompromised hosts

Structural insight of cell surface sugars in viral infection and human milk glycans as natural antiviral substance

Viral infections are caused by the adhesion of viruses to host cell receptors, including sialylated glycans, glycosaminoglycans, and human blood group antigens (HBGAs). Atomic-level structural information on the interactions between viral particles or proteins with glycans can be determined to provide precise targets for designing antiviral drugs. Milk glycans, existing as free oligosaccharides or glycoconjugates, have attracted increasing attention; milk glycans protect infants against infectious diseases, particularly poorly manageable viral infections. Furthermore, several glycans containing structurally distinct sialic acid/fucose/sulfate modifications in human milk acting as a "receptor decoy" and serving as the natural antiviral library, could interrupt virus-receptor interaction in the first line of defense for viral infection. This review highlights the basis of virus-glycan interactions, presents specific glycan receptor binding by gastroenterovirus viruses, including norovirus, enteroviruses, and the breakthroughs in the studies on the antiviral properties of human milk glycans, and also elucidates the role of glycans in respiratory viruses infection. In addition, recent advances in methods for performing virus/viral protein-glycan interactions were reported. Finally, we discuss the prospects and challenges of the studies on the clinical application of human milk glycan for viral interventions.

Household economic costs of norovirus gastroenteritis in two community cohorts in Peru, 2012-2019

While costs of norovirus acute gastroenteritis (AGE) to healthcare systems have been estimated, out-of-pocket and indirect costs incurred by households are not well documented in community settings, particularly in developing countries. We conducted active surveillance for AGE in two communities in Peru: Puerto Maldonado (October 2012-August 2015) and San Jeronimo (April 2015-April 2019). Norovirus AGE events with PCR-positive stool specimens were included. Data collected in follow-up interviews included event-related medical resource utilization, associated out-of-pocket costs, and indirect costs. There were 330 norovirus-associated AGE events among 3,438 participants from 685 households. Approximately 49% of norovirus events occurred among children <5 years of age and total cost to the household per episode was highest in this age group. Norovirus events cost a median of US $2.95 (IQR $1.04-7.85) in out-of-pocket costs and $12.58 (IQR $6.39-25.16) in indirect costs. Medication expenses accounted for 53% of out-of-pocket costs, and productivity losses accounted for 59% of the total financial burden on households. The frequency and associated costs of norovirus events to households in Peruvian communities support the need for prevention strategies including vaccines. Norovirus interventions targeting children <5 years of age and their households may have the greatest economic benefit.

Quantification and Potential Viability of Human Noroviruses in Final Effluent from Wastewater Treatment Works in Pretoria, South Africa

Growing global concerns over water scarcity, worsened by climate change, drive wastewater reclamation efforts. Inadequately treated wastewater presents significant public health risks. Previous studies in South Africa (SA) have reported high norovirus levels in final effluent and sewage-polluted surface water, indicating pathogen removal inefficiency. However, the viability of these virions was not explored. This study assessed human norovirus viability in final effluent from wastewater treatment works (WWTWs) in Pretoria, SA. Between June 2018 and August 2020, 200 samples were collected from two WWTWs, including raw sewage and final effluent. Norovirus concentrations were determined using in-house RNA standards. Viability of noroviruses in final effluent was assessed using viability RT-qPCR (vPCR) with PMAxx™-Triton X-100. There was no significant difference in GI concentrations between raw sewage (p = 0.5663) and final effluent (p = 0.4035) samples at WWTW1 and WWTW2. WWTW1 had significantly higher GII concentrations in raw sewage (p < 0.001) compared to WWTW2. No clear seasonal pattern was observed in norovirus concentrations. At WWTW1, 50% (7/14) of GI- and 64.9% (24/37) of GII-positive final effluent samples had no quantifiable RNA after vPCR. At WWTW2, the majority (92.6%, 25/27) of GII-positive final effluent samples showed a 100% RNA reduction post vPCR. PMAxx™-Triton X-100 vPCR provides a more accurate reflection of discharge of potentially viable noroviruses in the environment than standard RT-qPCR. Despite significant reductions in potentially viable noroviruses after wastewater treatment, the levels of potentially viable viruses in final effluent are still of concern due to the high initial load and low infectious dose of noroviruses.

Advancements in Human Norovirus Cultivation in Human Intestinal Enteroids

Human noroviruses (HuNoVs) are a significant cause of both epidemic and sporadic acute gastroenteritis worldwide. The lack of a reproducible culture system for HuNoVs was a major obstacle in studying virus replication and pathogenesis for almost a half-century. This barrier was overcome with our successful cultivation of multiple HuNoV strains in human intestinal enteroids (HIEs), which has significantly advanced HuNoV research. We previously optimized culture media conditions and generated genetically-modified HIE cultures to enhance HuNoV replication in HIEs. Building upon these achievements, we now present additional advancements to this culture system, which involve testing different media, unique HIE lines, and additional virus strains. HuNoV infectivity was evaluated and compared in new HIE models, including HIEs generated from different intestinal segments of individual adult organ donors, HIEs made from human embryonic stem cell-derived human intestinal organoids that were transplanted into mice (H9tHIEs), genetically-engineered (J4 FUT2 knock-in [ KI ], J2 STAT1 knock-out [ KO ]) HIEs, as well as HIEs derived from a patient with common variable immunodeficiency (CVID) and from infants. Our findings reveal that small intestinal HIEs, but not colonoids, from adults, H9tHIEs, HIEs from a CVID patient, and HIEs from infants support HuNoV replication with segment and strain-specific differences in viral infection. J4 FUT2-KI HIEs exhibit the highest susceptibility to HuNoV infection, allowing the cultivation of a broader range of GI and GII HuNoV strains than previously reported. Overall, these results contribute to a deeper understanding of HuNoVs and highlight the transformative potential of HIE cultures in HuNoV research.

Importance

Human noroviruses (HuNoVs) are very contagious and cause significant acute gastroenteritis globally, but studying them has been hindered by the lack of a reproducible culture system for nearly 50 years. This barrier was overcome by successfully cultivating multiple HuNoV strains in human intestinal enteroids (HIEs), advancing HuNoV research. We previously optimized culture conditions and developed genetically modified HIEs to enhance HuNoV replication. In this study, we tested different media, unique HIE lines, and additional virus strains, evaluating HuNoV infectivity in new HIE models. These models include HIEs from various intestinal segments of adult donors, human embryonic stem cell-derived HIEs transplanted into mice (H9tHIEs), genetically-engineered HIEs (J4 FUT2 knock-in [ KI ], J2 STAT1 knock-out [ KO ]), HIEs from a common variable immunodeficiency (CVID) patient, and from infants. Our findings show that adult small intestinal HIEs, H9tHIEs, CVID patient HIEs, and infant HIEs support HuNoV replication with segment and strain-specific differences. J4 FUT2-KI HIEs exhibited the highest susceptibility, allowing cultivation of a broader range of HuNoV strains. These results enhance the understanding of HuNoVs and highlight the transformative potential of HIE cultures in HuNoV research.

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.

Case report: Rapidly progressive neurocognitive disorder with a fatal outcome in a patient with PU.1 mutated agammaglobulinemia

Introduction

PU.1-mutated agammaglobulinemia (PU.MA) represents a recently described autosomal-dominant form of agammaglobulinemia caused by mutation of the SPI1 gene. This gene codes for PU.1 pioneer transcription factor important for the maturation of monocytes, B lymphocytes, and conventional dendritic cells. Only six cases with PU.MA, presenting with chronic sinopulmonary and systemic enteroviral infections, have been previously described. Accumulating literature evidence suggests a possible relationship between SPI1 mutation, microglial phagocytic dysfunction, and the development of Alzheimer's disease (AD).

Case description

We present a Caucasian female patient born from a non-consanguineous marriage, who was diagnosed with agammaglobulinemia at the age of 15 years when the immunoglobulin replacement therapy was started. During the following seventeen years, she was treated for recurrent respiratory and intestinal infections. At the age of 33 years, the diagnosis of celiac-like disease was established. Five years later progressive cognitive deterioration, unstable gait, speech disturbances, and behavioral changes developed. Comprehensive microbiological investigations were negative, excluding possible infective etiology. Brain MRI, 18FDG-PET-CT, and neuropsychological testing were suggestive for a diagnosis of a frontal variant of AD. Clinical exome sequencing revealed the presence of a novel frameshift heterozygous variant c.441dup in exon 4 of the SPI1 gene. Despite intensive therapy, the patient passed away a few months after the onset of the first neurological symptoms.

Conclusion

We describe the first case of PU.MA patient presenting with a rapidly progressive neurocognitive deterioration. The possible role of microglial dysfunction in patients with SPI1 mutation could explain their susceptibility to neurodegenerative diseases thus highlighting the importance of genetic testing in patients with inborn errors of immunity. Since PU.MA represents a newly described form of agammaglobulinemia, our case expands the spectrum of manifestations associated with SPI1 mutation.

The role of rapid syndromic diagnostic testing of gastrointestinal pathogens as a clinical decision support tool in a pediatric emergency department

PURPOSE

This study aimed to investigate the role of rapid syndromic diagnostic testing of gastrointestinal pathogens as a clinical decision support tool in a pediatric emergency department (ED) by comparing clinical decision and patient outcome parameters pre- and post-implementation.

METHODS

This was a big data analytical study of children < 18 years old without any underlying diseases, that visited the ED with acute moderate to severe diarrhea during a 34-month period from 2018 to 2022 using Seoul St. Mary's hospital's healthcare corporate data warehouse to retrieve demographic, clinical, and laboratory parameters. Outcome measures pre- and post-implementation of a rapid syndromic multiplex gastrointestinal panel (GI panel) were compared.

RESULTS

A total of 4,184 patients' data were included in the analyses. Broad spectrum antibiotics were prescribed at a significantly lower rate to patients presenting with acute infectious diarrhea at discharge from the ED (9.9% vs 15.8%, P < 0.001) as well as upon admission (52.2% vs 66.0%, P < 0.001) during the post-implementation period compared to the pre-implementation period. Although the duration of ED stay was found to be significantly longer (6.5 vs 5.5 h, P < 0.0001), the rate of ED revisit due to persistent or aggravated symptoms was significantly lower (Δ in intercept, β = -0.027; SE = 0.013; P = 0.041), and the admission rate at follow up after being discharged from the ED shown to be significantly lower during the post-implementation period compared to the pre-implementation period (0.8% vs. 2.1%, P = 0.001, respectively). No significant difference in disease progression was observed (P = 1.000).

CONCLUSION

Using the GI panel in the ED was shown to decrease broad spectrum antibiotic prescribing practices and reduce revisits or admission at follow up by aiding clinical decisions and improving patient outcome.

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

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.

Standardization of an antiviral pipeline for human norovirus in human intestinal enteroids demonstrates nitazoxanide has no to weak antiviral activity

Human noroviruses (HuNoVs) are the leading cause of acute gastroenteritis. In immunocompetent hosts, symptoms usually resolve within 3 days; however, in immunocompromised persons, HuNoV infection can become persistent, debilitating, and sometimes life-threatening. There are no licensed therapeutics for HuNoV due to a near half-century delay in its cultivation. Treatment for chronic HuNoV infection in immunosuppressed patients anecdotally includes nitazoxanide, a broad-spectrum antimicrobial licensed for treatment of parasite-induced gastroenteritis. Despite its off-label use for chronic HuNoV infection, nitazoxanide has not been clearly demonstrated to be an effective treatment. In this study, we standardized a pipeline for antiviral testing using multiple human small intestinal enteroid lines representing different intestinal segments and evaluated whether nitazoxanide inhibits replication of five HuNoV strains in vitro. Nitazoxanide did not exhibit high selective antiviral activity against any HuNoV strain tested, indicating it is not an effective antiviral for HuNoV infection. Human intestinal enteroids are further demonstrated as a model to serve as a preclinical platform to test antivirals against HuNoVs to treat gastrointestinal disease. Abstr.

Norovirus infection among HIV-infected patients in Abuja, Nigeria: impact of combination antiretroviral therapy status

BACKGROUND

Norovirus is now recognized to be major cause of gastroenteritis worldwide, with significantly higher disease burden among immunocompromised patients. This study aimed to determine the prevalence of Norovirus among HIV-infected patients and to evaluate the impact of combination antiretroviral therapy (cART) status on Norovirus prevalence in a sub-urban area of Abuja, Nigeria.

METHODS

This study included a total of Two hundred and fifteen subjects (85 cART-naïve and 130 cART-exposed) HIV-infected patients. Age range of study participants was 18 to 60 years. Faecal specimens where collected in screw capped containers and analyzed for Norovirus using Accupower Norovirus real-time PCR Test kit. CD4 + cell count was determined using flow cytometry.

RESULTS

The prevalence of Norovirus among cART-naïve HIV-infected patients was 10.6%. Age and gender was not associated with norovirus infection. cART -naïve HIV-infected patients with CD4 + cell count < 200 was significantly more infected with Norovirus as compared to those with CD4 + count ≥ 200 (OR: 28.000, 95% CI 3.2237, 243.2007, P = 0.0025). Norovirus was also found to be significantly higher in cART-naïve HIV-infected patients than amongst cART-exposed counterparts (OR: 6.882, 95% CI: 1.4514, 32.6343, P = 0.015).

CONCLUSIONS

The prevalence of Norovirus among cART-naïve HIV-infected patients was high; and was significantly higher in subjects with low CD4 + counts. Screening for Norovirus among cART-naïve HIV-infected patients is however emphasized to allow for effective Norovirus disease management.

A Standardized Antiviral Pipeline for Human Norovirus in Human Intestinal Enteroids Demonstrates No Antiviral Activity of Nitazoxanide

Human noroviruses (HuNoVs) are the leading cause of acute gastroenteritis. In immunocompetent hosts, symptoms usually resolve within three days; however, in immunocompromised persons, HuNoV infection can become persistent, debilitating, and sometimes life-threatening. There are no licensed therapeutics for HuNoV due to a near half-century delay in its cultivation. Treatment for chronic HuNoV infection in immunosuppressed patients anecdotally includes nitazoxanide, a broad-spectrum antimicrobial licensed for treatment of parasite-induced gastroenteritis. Despite its off-label use for chronic HuNoV infection, nitazoxanide has not been clearly demonstrated to be an effective treatment. In this study, we established a standardized pipeline for antiviral testing using multiple human small intestinal enteroid (HIE) lines representing different intestinal segments and evaluated whether nitazoxanide inhibits replication of 5 HuNoV strains in vitro . Nitazoxanide did not exhibit high selective antiviral activity against any HuNoV strains tested, indicating it is not an effective antiviral for norovirus infection. HIEs are further demonstrated as a model to serve as a pre-clinical platform to test antivirals against human noroviruses to treat gastrointestinal disease.

Recent insights into reverse genetics of norovirus

Norovirus is the leading cause of viral gastroenteritis globally, and poses substantial threats to public health. Despite substantial progress made in preventing norovirus diseases, the lack of a robust virus culture system has hampered biological research and effective strategies to combat this pathogen. Reverse genetic system is the technique to generate infectious viruses from cloned genetic constructs, which is a powerful tool for the investigation of viral pathogenesis and for the development of novel drugs and vaccines. The strategies of reverse genetics include bacterial artificial chromosomes, vaccinia virus vectors, and entirely plasmid-based systems. Since each strategy has its pros and cons, choosing appropriate approaches will greatly improve the efficiency of virus rescue. Reverse genetic systems that have been employed for norovirus greatly extend its life cycle and facilitate the development of medical countermeasures. In this review, we summarize the current knowledge on the structure, transmission, genetic evolution and clinical manifestations of norovirus, and describe recent advances in the studies of norovirus reverse genetics as well as its future prospects for therapeutics and vaccine development.

Feasibility of Polyclonal Avian Immunoglobulins (IgY) as Prophylaxis against Human Norovirus Infection

BACKGROUND

Human norovirus (HuNoV) is the leading viral cause of diarrhea, with GII.4 as the predominant genotype of HuNoV outbreaks globally. However, new genogroup variants emerge periodically, complicating the development of anti-HuNoV vaccines; other prophylactic or therapeutic medications specifically for HuNoV disease are lacking. Passive immunization using oral anti-HuNoV antibodies may be a rational alternative. Here, we explore the feasibility of using avian immunoglobulins (IgY) for preventing HuNoV infection in vitro in a human intestinal enteroid (HIE) model.

METHODS

Hens were immunized with virus-like particles (VLP) of a GII.4 HuNoV strain (GII.4/CHDC2094/1974/US) by intramuscular injection. The resulting IgY was evaluated for inhibition of binding to histo-blood group antigens (HBGA) and viral neutralization against representative GII.4 and GII.6 clinical isolates, using an HIE model.

RESULTS

IgY titers were detected by three weeks following initial immunization, persisting at levels of 1:2²¹ (1:2,097,152) from 9 weeks to 23 weeks. Anti-HuNoV IgY significantly (p < 0.05) blocked VLP adhesion to HBGA up to 1:12,048 dilution (0.005 mg/mL), and significantly (p < 0.05) inhibited replication of HuNoV GII.4[P16] Sydney 2012 in HIEs up to 1:128 dilution (0.08 mg/mL). Neutralization was not detected against genotype GII.6.

CONCLUSIONS

We demonstrate the feasibility of IgY for preventing infection of HIE by HuNoV GII.4. Clinical preparations should cover multiple circulating HuNoV genotypes for comprehensive effects. Plans for animal studies are underway.

Cross-reactive neutralizing human monoclonal antibodies mapping to variable antigenic sites on the norovirus major capsid protein

Human noroviruses are the major viral cause of acute gastroenteritis around the world. Although norovirus symptoms are in most cases mild and self-limited, severe and prolonged symptoms can occur in the elderly and in immunocompromised individuals. Thus, there is a great need for the development of specific therapeutics that can help mitigate infection. In this study, we sought to characterize a panel of human monoclonal antibodies (mAbs; NORO-123, -115, -273A, -263, -315B, and -250B) that showed carbohydrate blocking activity against the current pandemic variant, GII.4 Sydney 2012. All antibodies tested showed potent neutralization against GII.4 Sydney virus in human intestinal enteroid culture. While all mAbs recognized only GII.4 viruses, they exhibited differential binding patterns against a panel of virus-like particles (VLPs) representing major and minor GII.4 variants spanning twenty-five years. Using mutant VLPs, we mapped five of the mAbs to variable antigenic sites A (NORO-123, -263, -315B, and -250B) or C (NORO-115) on the major capsid protein. Those mapping to the antigenic site A showed blocking activity against multiple variants dating back to 1987, with one mAb (NORO-123) showing reactivity to all variants tested. NORO-115, which maps to antigenic site C, showed reactivity against multiple variants due to the low susceptibility for mutations presented by naturally-occurring variants at the proposed binding site. Notably, we show that cross-blocking and neutralizing antibodies can be elicited against variable antigenic sites. These data provide new insights into norovirus immunity and suggest potential for the development of cross-protective vaccines and therapeutics.

Ribavirin-resistant chronic norovirus infection-associated enteropathy in common variable immunodeficiency. Case report and review of the literature

Chronic Norovirus infection is particularly challenging in patients with common variable immunodeficiency (CVID) because of their inability to achieve viral clearance and the risk of developing enteropathy leading to intestinal villous atrophy and malabsorption. To date, therapeutic options to eliminate the virus are limited and only ribavirin has been shown to induce viral clearance in norovirus enteropathy associated with CVID. We report a case of a 48-year-old female patient diagnosed with CVID enteropathy possibly related to norovirus infection who failed a ribavirin-based therapy despite dosage optimization through drug plasma level monitoring.

Developing an Integrated "Regression-QMRA method" to Predict Public Health Risks of Low Impact Developments (LIDs) for Improved Planning

Worldwide Low Impact Developments (LIDs) are used for sustainable stormwater management; however, both the stormwater and LIDs carry microbial pathogens. The widespread development of LIDs is likely to increase human exposure to pathogens and risk of infection, leading to unexpected disease outbreaks in urban communities. The risk of infection from exposure to LIDs has been assessed via Quantitative Microbial Risk Assessment (QMRA) during the operation of these infrastructures; no effort is made to evaluate these risks during the planning phase of LID treatment train in urban communities. We developed a new integrated "Regression-QMRA method" by examining the relationship between pathogens' concentration and environmental variables. Applying of this methodology to a planned LID train shows that the predicted disease burden of diarrhea from Campylobacter is highest (i.e. 16.902 DALYs/1000 persons/yr) during landscape irrigation and playing on the LID train, followed by Giardia, Cryptosporidium, and Norovirus. These results illustrate that the risk of microbial infection can be predicted during the planning phase of LID treatment train. These predictions are of great value to municipalities and decision-makers to make informed decisions and ensure risk-based planning of stormwater systems before their development.

Glucose Reduces Norovirus Binding to Enterobacter cloacae and Alters Gene Expression of Bacterial Surface Structures in a Growth Phase Dependent Manner

Norovirus is the leading cause of acute viral gastroenteritis. Both human and murine noroviruses attach to commensal bacteria belonging to the mammalian gut flora, and binding levels are influenced by nutrients present in bacterial media. However, it is not known which nutrients are responsible for altering viral binding or why binding is altered. Gene expression of commensal bacteria can be changed by the external environment as well as by interaction with pathogens. For example, growth phase and incubation conditions impact expression levels of specific bacterial genes in Escherichia coli. We have previously shown that binding by both human and murine noroviruses to the commensal bacterium Enterobacter cloacae induces genome-wide changes in gene expression with a large number of differentially expressed genes associated with the surface structure of the bacterial cell. The current study evaluated norovirus binding under nutrient-limited conditions and assessed the expression of a select panel of these genes that are significantly altered by norovirus binding under these conditions. The goal of this work was to determine how norovirus attachment to Enterobacter cloacae affected the expression of these genes under varying nutrient and growth phase conditions. We found that the presence of glucose in minimal media reduced murine norovirus binding to E. cloacae and viral binding in the presence of glucose reduced gene expression for surface structures previously associated with norovirus attachment. Changes in viral binding and gene expression occurred in a growth phase-dependent manner. Collectively, these data demonstrate that both the growth phase and nutrient availability alter viral interactions with commensal bacteria and the subsequent changes in gene expression. Ultimately, this work advances our understanding of norovirus-bacterium interactions and provides a foundation for elucidating the conditions and surface structures that regulate norovirus attachment to bacteria.

CRISPR-Cas9-Based Technology for Studying Enteric Virus Infection

Enteric viruses, including numerous viruses that initiate infection in enteric canal, are recognized as important agents that cause wide spectrum of illnesses in humans, depending on the virus type. They are mainly transmitted by fecal-oral route with several vector such as contaminated water or food. Infections by enteric viruses, such as noroviruses and rotaviruses, frequently cause widespread acute gastroenteritis, leading to significant health and economic burdens and therefore remain a public health concern. Like other viruses, enteric viruses ''hijack'' certain host factors (so called pro-viral factors) for replication in infected cells, while escaping the host defense system by antagonizing host anti-viral factors. Identification(s) of these factors is needed to better understand the molecular mechanisms underlying viral replication and pathogenicity, which will aid the development of efficient antiviral strategies. Recently, the advancement of genome-editing technology, especially the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 system, has precipitated numerous breakthroughs across the field of virology, including enteric virus research. For instance, unbiased genome-wide screening employing the CRISPR-Cas9 system has successfully identified a number of previously unrecognized host factors associated with infection by clinically relevant enteric viruses. In this review, we briefly introduce the common techniques of the CRISPR-Cas9 system applied to virological studies and discuss the major findings using this system for studying enteric virus infection.

Infection prevention requirements for the medical care of immunosuppressed patients: recommendations of the Commission for Hospital Hygiene and Infection Prevention (KRINKO) at the Robert Koch Institute

In Germany, guidelines for hygiene in hospitals are given in form of recommendations by the Commission for Hospital Hygiene and Infection Prevention (Kommission für Krankenhaushygiene und Infektionsprävention, "KRINKO"). The KRINKO and its voluntary work are legitimized by the mandate according to § 23 of the Infection Protection Act (Infektionsschutzgesetz, "IfSG"). The original German version of this document was published in February 2021 and has now been made available to the international professional public in English. The guideline provides recommendations on infection prevention and control for immunocompromised individuals in health care facilities. This recommendation addresses not only measures related to direct medical care of immunocompromised patients, but also management aspects such as surveillance, screening, antibiotic stewardship, and technical/structural aspects such as patient rooms, air quality, and special measures during renovations.

Illuminating Human Norovirus: A Perspective on Disinfection of Water and Surfaces Using UVC, Norovirus Model Organisms, and Radiation Safety Considerations

Human noroviruses (HuNoVs) are a major cause of gastroenteritis and are associated with high morbidity because of their ability to survive in the environment and small inoculum size required for infection. Norovirus is transmitted through water, food, high touch-surfaces, and human-to-human contact. Ultraviolet Subtype C (UVC) light-emitting diodes (LEDs) can disrupt the norovirus transmission chain for water, food, and surfaces. Here, we illuminate considerations to be adhered to when picking norovirus surrogates for disinfection studies and shine light on effective use of UVC for norovirus infection control in water and air and validation for such systems and explore the blind spot of radiation safety considerations when using UVC disinfection strategies. This perspective also discusses the promise of UVC for norovirus mitigation to save and ease life.

Association of fucosyltransferase 2 gene with norovirus infection: A systematic review and meta-analysis

BACKGROUND

Norovirus is a leading cause of viral gastroenteritis outbreaks worldwide. Histo-blood group antigens (HBGAs) are important host attachment factors in susceptibility to norovirus. In this study, the association of FUT2 gene, which participates in the biosynthesis of HBGAs, with norovirus infection has been investigated.

METHODS

All relevant studies on the associations of FUT2 gene with norovirus were retrieved from PubMed, Web of Science, Embase, and Cochrane Library databases. Odds ratios (ORs) and 95% confidence interval (CI) were used to analyze the extracted data. I2 statistic, sensitivity analysis and publication bias analysis were used to confirm the findings. Subgroup analyses were performed for races, genotypes, development degree of the countries, publication years, age and setting when heterogeneity was recorded.

RESULTS

Twenty studies including 4066 participants were included for the meta-analysis. This analysis showed that there is a significant association between FUT2 gene and norovirus infection (OR = 3.02, 95%CI = 2.00-4.55, P < 0.001). Additionally, the ORs of norovirus infection among Chinese (OR = 4.49, 95%CI = 2.37-8.50, P < 0.001) were higher than those among Caucasian (OR = 3.23, 95%CI = 2.20-4.74, P < 0.001).

CONCLUSIONS

The meta-analysis suggested that FUT2 gene is associated with susceptibility to norovirus infection.

Prevalence of GII.4 Sydney Norovirus Strains and Associated Factors of Acute Gastroenteritis in Children: 2019/2020 Season in Guangzhou, China

Norovirus, the leading cause of non-bacterial acute gastroenteritis (AGE) worldwide, is constantly mutating. Continuous monitoring of the evolution of epidemic genotypes and emergence of novel genotypes is, therefore, necessary. This study determined the prevalence and clinical characteristics of norovirus strains in AGE in Guangzhou, China in 2019/2020 season. This study included children aged 2-60 months diagnosed with AGE in Guangzhou Women and Children Hospital, from August 2019 to January 2020. Norovirus was detected by real-time polymerase chain reaction and clinical data were obtained. Genotyping and phylogenetic analyses were performed with partial gene sequence fragments located within the open reading frames 1 and 2. During the study period, 168 children (61.3% males) were confirmed as norovirus infectious AGE. The main symptoms were diarrhoea and vomiting and 38 patients (22.6%) had seizures. Norovirus was mainly prevalent in October and November, and GII.4 Sydney[P31] was the major genotype circulating in Guangzhou. The phylogenetic tree showed that the Guangzhou strains had high homology with the strains circulating in 2017-2019 worldwide. GII.4 Sydney was the main prevalent norovirus genotype in Guangzhou from August 2019 to January 2020, which had more severe diarrhoea than those of other genotypes. These findings provide a valuable reference for the prevention, control, and treatment of norovirus in the future.

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.

Current and Future Antiviral Strategies to Tackle Gastrointestinal Viral Infections

Acute gastroenteritis caused by virus has a major impact on public health worldwide in terms of morbidity, mortality, and economic burden. The main culprits are rotaviruses, noroviruses, sapoviruses, astroviruses, and enteric adenoviruses. Currently, there are no antiviral drugs available for the prevention or treatment of viral gastroenteritis. Here, we describe the antivirals that were identified as having in vitro and/or in vivo activity against these viruses, originating from in silico design or library screening, natural sources or being repurposed drugs. We also highlight recent advances in model systems available for this (hard to cultivate) group of viruses, such as organoid technologies, and that will facilitate antiviral studies as well as fill some of current knowledge gaps that hamper the development of highly efficient therapies against gastroenteric viruses.

The dark side of the gut: Virome-host interactions in intestinal homeostasis and disease

The diverse enteric viral communities that infect microbes and the animal host collectively constitute the gut virome. Although recent advances in sequencing and analysis of metaviromes have revealed the complexity of the virome and facilitated discovery of new viruses, our understanding of the enteric virome is still incomplete. Recent studies have uncovered how virome-host interactions can contribute to beneficial or detrimental outcomes for the host. Understanding the complex interactions between enteric viruses and the intestinal immune system is a prerequisite for elucidating their role in intestinal diseases. In this review, we provide an overview of the enteric virome composition and summarize recent findings about how enteric viruses are sensed by and, in turn, modulate host immune responses during homeostasis and disease.

Norovirus Infections in Kidney Transplant Recipients

BACKGROUND

Norovirus (NoV) infection frequently progresses to chronic disease after kidney transplant (KTx). This study aims to assess potential risk factors helping to determine patients at risk of chronic NoV infection and to analyse the effect of NoV on allograft outcome. Additionally, we assessed the effectiveness of intravenous immunoglobulin (IVIg) therapy for chronic NoV infection.

METHODS

The study enrolled 60 KTx patients requiring hospitalization because of NoV infection. Clinical parameters, severity of NoV infection and potential risk factors were evaluated. Outcome parameters were clinical symptoms, rehospitalizations, persistent shedding of virus and effects on allograft function.

RESULTS

Patients were divided into 2 groups: 29 had acute NoV infection only, 31 progressed to chronic NoV infection. Chronic NoV infection was defined as a recurrence of clinical symptoms plus redetection of NoV in stool. Lymphocyte-depleting induction therapy and diabetes mellitus were independent risk factors for chronic infection. For patients with chronic NoV infection, length of stay in hospital was significantly prolonged (p= 0.024). Allograft function remained impaired in the chronic NoV group 6 and 12 months after initial admission.IVIg was administered to 18 patients with chronic NoV infection. No further clinical symptoms of NoV infection occurred in 13 (72%) of these patients. However, NoV was still detectable in stool specimens from 10 (77%) of these patients.

CONCLUSIONS

Chronic NoV infection is associated with reduced allograft function. Administration of IVIg to patients with chronic NoV infection seems beneficial in achieving freedom from clinical symptoms, despite limited effects on shedding of virus.

Molecular detection and characterization of norovirus in asymptomatic food handlers in Chiang Mai, Thailand

Norovirus (NoV) is the leading cause of nonbacterial foodborne outbreaks of gastroenteritis. Individuals who are asymptomatically infected may act as reservoirs to facilitate transmission of NoV. This retrospective study was conducted to identify the viral agent and investigate potential transmission of NoV infection in a foreigner patient who had severe acute gastroenteritis after having a meal in a restaurant in Chiang Mai province, Thailand. The fecal specimens collected from the patient and 26 restaurant staffs were tested for the presence of gastroenteritis viruses by PCR and RT-PCR. The NoV positive cases were confirmed by real-time PCR and IC kits. The sensitivity of detection of IC kit B, as compared to those of real-time PCR, could detect the viral load down to at least 2.1 × 10⁴ copies/g of stool. The diarrheic patient was infected solely with GII.3 NoV without co-infection with any other gastroenteritis viruses while 4 staffs (15.4%) were positive for different NoV strains (3 with GII.4 and 1 with GII.17) and all were asymptomatic. Interestingly, the GII.3 NoV strain detected in fecal sample of the patient was closely related to GII.3 NoV strains detected previously in fecal samples of children hospitalized with acute diarrhea in Chiang Mai, in the same year and the same geographical area where the patient was infected, suggesting the circulation and transmission of GII.3 NoV in this area. In conclusion, our data indicated that the patient was infected with GII.3 NoV and the virus was not directly transmitted to the patient by asymptomatic food handlers instead it might be transmitted by consumption of NoV-contaminated food provided by the restaurant. In addition, the existence of NoV in asymptomatic food handlers could be a potential source of NoV transmission. Therefore, strict adherence to hand hygiene practices should be reinforced to prevent foodborne outbreaks.

Assessment of the anti-norovirus activity in cell culture using the mouse norovirus: Identification of active compounds

Human norovirus is the main cause of viral gastroenteritis, resulting annually in ∼ 700 million infections and 200,000 deaths, of whom most are children <5 years. Mouse norovirus-infected macrophages are the most widely used in vitro system to screen and characterize the antiviral effect of norovirus-targeting small molecules. We have previously established antiviral assays using this system, identified novel inhibitors and performed additional studies in order to have a first insight into their mechanism of action. As potent and safe anti-norovirus small molecules are urgently needed, we here describe the detailed protocol for a set of assays that will allow the identification of novel norovirus inhibitors.

Human norovirus exhibits strain-specific sensitivity to host interferon pathways in human intestinal enteroids

Human noroviruses (HuNoVs) are the leading cause of viral gastroenteritis worldwide; yet currently, no vaccines or FDA-approved antiviral drugs are available to counter these pathogens. To understand HuNoV biology and the epithelial response to infection, we performed transcriptomic analyses, RT-qPCR, CRISPR-Cas9 modification of human intestinal enteroid (HIE) cultures, and functional studies with two virus strains (a pandemic GII.4 and a bile acid-dependent GII.3 strain). We identified a predominant type III interferon (IFN)-mediated innate response to HuNoV infection. Replication of both strains is sensitive to exogenous addition of IFNs, suggesting the potential of IFNs as therapeutics. To obtain insight into IFN pathway genes that play a role in the antiviral response to HuNoVs, we developed knockout (KO) HIE lines for IFN alpha and lambda receptors and the signaling molecules, MAVS, STAT1, and STAT2 An unexpected differential response of enhanced replication and virus spread was observed for GII.3, but not the globally dominant GII.4 HuNoV in STAT1-knockout HIEs compared to parental HIEs. These results indicate cellular IFN responses restrict GII.3 but not GII.4 replication. The strain-specific sensitivities of innate responses against HuNoV replication provide one explanation for why GII.4 infections are more widespread and highlight strain specificity as an important factor in HuNoV biology. Genetically modified HIEs for innate immune genes are useful tools for studying immune responses to viral or microbial pathogens.

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.

Altered Microbiota, Impaired Quality of Life, Malabsorption, Infection, and Inflammation in CVID Patients With Diarrhoea

Background: Diarrhoea is the commonest gastrointestinal symptom in patients with common variable immunodeficiency (CVID). Objective: The aim of this study was to describe the prevalence and clinical presentation of chronic and recurrent diarrhoea in the Royal-Free-Hospital (RFH) London CVID cohort, including symptoms, infections, level of inflammation, and microbial diversity. Methods: A cross-sectional study of adult CVID patients (139 out of 172 diagnosed with CVID completed the screening questionnaire). Those with diarrhoea ≥6 days/month had stool and blood samples analysed and completed the short Inflammatory Bowel Disease Questionnaire (sIBDQ). BMI, spleen-size, lymphocytes and gut-microbial diversity were compared. Due to logistical and clinical restraints, not all patients could be analysed on all measures. Results: 46/139 (33.1%) patients had current significant diarrhoea. In patients with past or present diarrhoea, BMI was lower (median 23.7 vs. 26, p = 0.005), malabsorption more common (57.97 vs. 35.71%, p = 0.011). CD4+ lymphocytes were higher in patients with diarrhoea (p = 0.028; n = 138), but CD4+ naïve lymphocytes were significantly higher in non-diarrhoea patients (p = 0.009, N = 28). Nine patients had confirmed or probable current gastrointestinal infections. Calprotectin was >60 μg/g in 13/29 with significant diarrhoea including 9 without infection. SIBDQ revealed a low median score of 4.74. Microbial alpha diversity was significantly lower in CVID patients compared to healthy household controls. There was no significant difference in alpha diversity in relation to antibiotic intake during the 6 weeks prior to providing samples. Conclusion: Patients with CVID and significant diarrhoea had infections, raised calprotectin, malabsorption, a lower BMI, an impaired quality of life (comparable to active IBD), and they differed from non-diarrhoea patients in their lymphocyte phenotyping. Furthermore, microbial diversity was altered. These findings strongly imply that there may be an inflammatory nature and a systemic predisposition to diarrhoea in CVID, which necessitates further investigation.

Norovirus in health care and implications for the immunocompromised host

PURPOSE OF REVIEW

The majority of norovirus outbreaks in the United States occur in healthcare facilities. With the growing population of immunocompromised hosts who are in frequent contact with healthcare facilities, norovirus is not only a threat to hospitals and nursing homes but also to these individuals. This review summarizes the impact of norovirus infection on healthcare facilities and immunocompromised hosts.

RECENT FINDINGS

The natural history of norovirus infection in immunocompromised individuals remains poorly understood. Although host immune responses play a critical role in reducing duration of viral shedding and viral load in norovirus-infected individuals, why some immunocompromised patients spontaneously recover while others develop a chronic and protracted course of illness remains unclear. Norovirus outbreaks occur in healthcare facilities because the virus is highly contagious, resistant to disinfection and efficiently transmitted. The use of real-time metagenomic next-generation sequencing and phylogenetic analyses has provided valuable information on transmission patterns in complex hospital-associated norovirus outbreaks. The development of human intestinal enteroid cultures enables the determination of effectiveness of disinfectants against human noroviruses, circumventing the validity questions with surrogate virus models due to differences in susceptibility to inactivation and disinfectants.

SUMMARY

Metagenomics next-generation sequencing can enhance our understanding of norovirus transmission and lead to more timely mitigation strategies to curb norovirus outbreaks in healthcare facilities. With new in-vitro cultivation methods for human noroviruses, candidate vaccines and effective antivirals could be available in the near future.

Infectious Norovirus Is Chronically Shed by Immunocompromised Pediatric Hosts

Noroviruses are a leading cause of gastroenteritis worldwide. Although infections in healthy individuals are self-resolving, immunocompromised individuals are at risk for chronic disease and severe complications. Chronic norovirus infections in immunocompromised hosts are often characterized by long-term virus shedding, but it is unclear whether this shed virus remains infectious. We investigated the prevalence, genetic heterogeneity, and temporal aspects of norovirus infections in 1140 patients treated during a 6-year period at a pediatric research hospital. Additionally, we identified 20 patients with chronic infections lasting 37 to >418 days. Using a new human norovirus in vitro assay, we confirmed the continuous shedding of infectious virus for the first time. Shedding lasted longer in male patients and those with diarrheal symptoms. Prolonged shedding of infectious norovirus in immunocompromised hosts can potentially increase the likelihood of transmission, highlighting the importance of isolation precautions to prevent nosocomial infections.

Identification of a norovirus outbreak on a hematopoietic stem cell transplant unit and development and implementation of a novel infection prevention algorithm for controlling transmission

Controlling norovirus transmission in units with immunocompromised patients is challenging. We present a cluster of norovirus cases that occurred on a stem-cell transplant unit and the prevention efforts that were implemented to limit the outbreak. Protocols developed to control this cluster may provide a model for other facilities.

Generation of Norovirus-Specific T Cells From Human Donors With Extensive Cross-Reactivity to Variant Sequences: Implications for Immunotherapy

BACKGROUND

Chronic norovirus infection in immunocompromised patients can be severe, and presently there is no effective treatment. Adoptive transfer of virus-specific T cells has proven to be safe and effective for the treatment of many viral infections, and this could represent a novel treatment approach for chronic norovirus infection. Hence, we sought to generate human norovirus-specific T cells (NSTs) that can recognize different viral sequences.

METHODS

Norovirus-specific T cells were generated from peripheral blood of healthy donors by stimulation with overlapping peptide libraries spanning the entire coding sequence of the norovirus genome.

RESULTS

We successfully generated T cells targeting multiple norovirus antigens with a mean 4.2 ± 0.5-fold expansion after 10 days. Norovirus-specific T cells comprised both CD4+ and CD8+ T cells that expressed markers for central memory and effector memory phenotype with minimal expression of coinhibitory molecules, and they were polyfunctional based on cytokine production. We identified novel CD4- and CD8-restricted immunodominant epitopes within NS6 and VP1 antigens. Furthermore, NSTs showed a high degree of cross-reactivity to multiple variant epitopes from clinical isolates.

CONCLUSIONS

Our findings identify immunodominant human norovirus T-cell epitopes and demonstrate that it is feasible to generate potent NSTs from third-party donors for use in antiviral immunotherapy.

Molecular epidemiology of norovirus outbreaks in Argentina, 2013-2018

Noroviruses are a leading cause of endemic and epidemic acute gastroenteritis in all age groups. However, in Latin America, there are limited and updated data regarding circulating genotypes. The aim of this study was to assess the prevalence and genetic diversity of norovirus outbreaks in Argentina from 2013 to 2018. Stool samples from 29 acute gastroenteritis (AGE) outbreaks were available for viral testing. Norovirus was detected in samples from 18 (62.1%) outbreaks (2 GI and 16 GII). Both GI outbreaks were typed as GI.6[P11] whereas 10 different GII genotypes were detected, in which GII.4 viruses were the most frequently detected (29.4%, associated with GII.P31 and GII.P16) followed by GII.1[P33] and GII.6[P7] (17.6% each). Like GII.4 viruses, GII.2 viruses were also detected in association with different polymerases (GII.P2 and GII.P16). Our findings underscore the importance of dual RNA-dependent RNA polymerase-VP1 typing since recombinant strains with new polymerase sequences emerge frequently suggesting a possible role in improved fitness of these viruses. This study represents the most recent multi-year assessment of the molecular epidemiology of norovirus strains associated with AGE outbreaks in Argentina. Molecular surveillance of norovirus has to be considered to monitor possible changes in dominant genotypes which may assist to inform the formulation of future vaccines.

Norovirus Transmission Dynamics in a Pediatric Hospital Using Full Genome Sequences

Background

Norovirus is a leading cause of worldwide and nosocomial gastroenteritis. The study aim was to assess the utility of molecular epidemiology using full genome sequences compared to routine infection prevention and control (IPC) investigations.

Methods

Norovirus genomes were generated from new episodes of norovirus at a pediatric tertiary referral hospital over a 19-month period (n = 182). Phylogeny identified clusters of related sequences that were verified using epidemiological and clinical data.

Results

Twenty-four clusters of related norovirus sequences (“sequence clusters”) were observed, including 8 previously identified by IPC investigations (“IPC outbreaks”). Seventeen sequence clusters (involving 77/182 patients) were corroborated by epidemiological data (“epidemiologically supported clusters”), suggesting transmission between patients. Linked infections were identified among 44 patients who were missed by IPC investigations. Thirty-three percent of norovirus sequences were linked, suggesting nosocomial transmission; 24% of patients had nosocomial infections from an unknown source; and 43% were norovirus positive on admission.

Conclusions

We show there are frequent introductions of multiple norovirus strains with extensive onward nosocomial transmission of norovirus in a pediatric hospital with a high proportion of immunosuppressed patients nursed in isolation. Phylogenetic analysis using full genome sequences is more sensitive than classic IPC investigations for identifying linked cases and should be considered when investigating norovirus nosocomial transmission. Sampling of staff, visitors, and the environment may be required for complete understanding of infection sources and transmission routes in patients with nosocomial infections not linked to other patients and among patients with phylogenetically linked cases but no evidence of direct contact.

[On Statistical Underreporting of Norovirus-Infections: Insights from Register Data of Two Local Public Health Authorities]

BACKGROUND

Only laboratory-confirmed norovirus (NoV) cases have to be notified to the Robert Koch Institute (RKI) since 2011, but not other, e. g. clinical-epidemiological cases. It can be assumed that the extent of underreporting of NoV cases in Germany has significantly increased since then.

OBJECTIVES

To discuss the extent of underreporting, we wanted to find out how many laboratory tests were carried out during gastroenteritis outbreaks. Furthermore, the significance of NoV outbreaks in occupational health is discussed.

MATERIALS AND METHODS

Of all pseudonymized gastroenteritis outbreak data reported to 2 local health authorities between 2011 and 2015, the proportion of NoV outbreaks and reported cases of infection among employees in hospitals and community facilities (nursing homes for the elderly, day-care centers, schools) confirmed by laboratory tests was calculated retrospectively.

RESULTS

Only a few gastroenteritis outbreaks in day-care centers were etiologically diagnosed, so that only 6% and less could be classified as NoV outbreaks. In nursing homes for the elderly, about half of the outbreaks were classified as NoV, in hospitals almost all of them. Employees accounted for up to 23% of those affected in NoV outbreaks.

CONCLUSIONS

The low level of laboratory diagnostics carried out during gastroenteritis outbreaks in day-care centers suggests a considerable number of hidden NoV cases. The significant proportion of staff relative to the total number of infected persons during the outbreaks highlights the importance of the burden of NoV outbreaks as a topic in occupational health. Further, large-scale prospective studies are needed to empirically substantiate these initial findings.

Emergence of norovirus strains: A tale of two genes

Noroviruses are a very diverse group of viruses that infect different mammalian species. In humans, norovirus is a major cause of acute gastroenteritis. Multiple norovirus infections can occur in a lifetime as the result of limited duration of acquired immunity and cross-protection among different strains. A combination of advances in sequencing methods and improvements on surveillance has provided new insights into norovirus diversification and emergence. The generation of diverse norovirus strains has been associated with (1) point mutations on two different genes: ORF1, encoding the non-structural proteins, and ORF2, encoding the major capsid protein (VP1); and (2) recombination events that create chimeric viruses. While both mechanisms are exploited by all norovirus strains, individual genotypes utilize each mechanism differently to emerge and persist in the human population. GII.4 noroviruses (the most prevalent genotype in humans) present an accumulation of amino acid mutations on VP1 resulting in the chronological emergence of new variants. In contrast, non-GII.4 noroviruses present co-circulation of different variants over long periods with limited changes on their VP1. Notably, genetic diversity of non-GII.4 noroviruses is mostly related to the high number of recombinant strains detected in humans. While it is difficult to determine the precise mechanism of emergence of epidemic noroviruses, observations point to multiple factors that include host-virus interactions and changes on two regions of the genome (ORF1 and ORF2). Larger datasets of viral genomes are needed to facilitate comparison of epidemic strains and those circulating at low levels in the population. This will provide a better understanding of the mechanism of norovirus emergence and persistence.

Norovirus encounters in the gut: multifaceted interactions and disease outcomes

Noroviruses are major causes of gastroenteritis, with epidemic outbreaks occurring frequently. They are an important global health concern, especially for pediatric and immunocompromised populations, and are challenging pathogens to target immunologically due to their rapid rates of genetic and antigenic evolution and failure to stimulate durable protective immunity. In this Review, we summarize our current understanding of norovirus pathogenesis, noting the prominent role of murine norovirus as a small animal model for norovirus research. We highlight intriguing data supporting the possible involvement of norovirus in sequelae including irritable bowel syndrome and inflammatory bowel diseases, and describe the innate and adaptive immune mechanisms involved in control of both human and murine norovirus infection. Furthermore, we discuss the potential implications of recent discoveries regarding norovirus interactions with the gut microbiota, and briefly detail current understanding of noroviral evolution and its influence on viral pathogenesis. Our mechanistic understanding of norovirus pathogenesis continues to improve with increasing availability of powerful model systems, which will ultimately facilitate development of effective preventive and therapeutic approaches for this pathogen.

A pLOT of Viral Persistence

In this issue of Cell Host & Microbe, Bouziat et al. (2018) and Van Winkle et al. (2018) find that the capsid gene of murine norovirus (MNV) functions as a trigger of host inflammation. These studies specifically describe how MNV-induced inflammation promotes loss of oral tolerance and persistent viral infection, respectively.

Norovirus Infections and Disease in Lower-MiddleandLow-Income Countries, 1997⁻2018

Noroviruses are a major cause of viral gastroenteritis. The burden of the norovirus in low-resource settings is not well-established due to limited data. This study reviews the norovirus prevalence, epidemiology, and genotype diversity in lower-middle-income countries (LMIC) and in low-income countries (LIC). PubMed was searched up to 14 January 2019 for norovirus studies from all LIC and LMIC (World Bank Classification). Studies that tested gastroenteritis cases and/or asymptomatic controls for norovirus by reverse transcription-polymerase chain reaction (RT-PCR) were included. Sixty-four studies, the majority on children <5 years of age, were identified, and 14% (95% confidence interval; CI 14–15, 5158/36,288) of the gastroenteritis patients and 8% (95% CI 7–9, 423/5310) of healthy controls tested positive for norovirus. In LMIC, norovirus was detected in 15% (95% CI 15–16) of cases and 8% (95% CI 8–10) of healthy controls. In LIC, 11% (95% CI 10–12) of symptomatic cases and 9% (95% CI 8–10) of asymptomatic controls were norovirus positive. Norovirus genogroup II predominated overall. GII.4 was the predominant genotype in all settings, followed by GII.3 and GII.6. The most prevalent GI strain was GI.3. Norovirus causes a significant amount of gastroenteritis in low-resource countries, albeit with high levels of asymptomatic infection in LIC and a high prevalence of coinfections.

Update on infection control practices in cancer hospitals

Therapies in oncology have evolved rapidly over the last years. At the same pace, supportive care for patients receiving cancer therapy has also evolved, allowing patients to safely receive the newest advances in treatment in both an inpatient and outpatient basis. The recognition of the role of infection control and prevention (ICP) in the outcomes of patients living with cancer has been such that it is now a requirement for hospitals and involves multidisciplinary groups. Some unique aspects of ICP for patients with cancer that have gained momentum over the past few decades include catheter-related infections, multidrug-resistant organisms, community-acquired viral infections, and the impact of the health care environment on the horizontal transmission of organisms. Furthermore, as the potential for infections to cross international borders has increased, alertness for outbreaks or new infections that occur outside the area have become constant. As the future approaches, ICP in immunocompromised hosts will continue to integrate emerging disciplines, such as antibiotic stewardship and the microbiome, and new techniques for environmental cleaning and for controlling the spread of infections, such as whole-genome sequencing. CA Cancer J Clin 2018;000:000-000. © 2018 American Cancer Society.

Chronic norovirus infection in primary immune deficiency disorders: an international case series

OBJECTIVE

Predictive factors associated with clinical outcomes of chronic norovirus infection (CNI) in primary immunodeficiency diseases (PIDD) are lacking.

METHOD

We sought to characterize CNI using a multi-institutional cohort of patients with PIDD and CNI using the Clinical Immunology Society's CIS-PIDD Listserv e-mail group.

RESULTS

Thirty-four subjects (21 males and 13 females) were reported from centers across North America, Europe, and Asia. All subjects were receiving high doses (median IgG dose: 1200 mg/kg/month) of supplemental immunoglobulin therapy. Fifty-three percent had a complete absence of B cells (median B-cell count 0; range 0-139 cells/μL). Common Variable Immune Deficiency (CVID) subjects manifested a unique phenotype with B-cell lymphopenia, non O+ blood type, and villous atrophy (logistic regression model, P = 0.01). Five subjects died, all of whom had no evidence of villous atrophy.

CONCLUSION

While Norovirus (NoV) is thought to replicate in B cells, in this PIDD cohort of CNI, B-cell lymphopenia was common, indicating that the presence of B lymphocytes is not essential for CNI.

Assessing the Efficacy of Small Molecule Inhibitors in aMouse Model of Persistent Norovirus Infection

Human norovirus is the most common cause of acute gastroenteritis worldwide, resulting in estimated mortality of ~210,000 each year, of whom most are children under the age of five. However, norovirus can infect people of all age groups. There is a risk of prolonged infection in children, the elderly and patients who are immunocompromised. To study the inhibition of persistent norovirus replication by small molecule antivirals in vivo, we used a murine norovirus CR6 strain (MNV.CR6). We demonstrated earlier that efficient small molecules can reduce viral shedding in the stool of infected mice. Here we present how to generate the MNV.CR6 virus stock, infect type I and II interferon receptor knockout AG129 mice via oral gavage, administer antivirals to mice, and quantify viral genome copies in the stool of these mice.

Intrahost Norovirus Evolution in Chronic Infection Over 5 Years of Shedding in a Kidney Transplant Recipient

Noroviruses are the leading cause of acute gastroenteritis, and they can affect humans of all age groups. In immunocompromised patients, norovirus infections can develop into chronic diarrhea or show prolonged asymptomatic virus shedding. Chronic norovirus infections are frequently reported for solid organ transplant recipients, with rapid intrahost norovirus evolution seen. In this report, we describe a case of chronic norovirus infection in an immunocompromised patient who was followed up for over 5 years. The purpose of the study was to specify the norovirus evolution in a chronically infected immunocompromised host and identify possible selection sites in norovirus capsid protein. During the follow-up period, 25 sequential stool samples were collected and nine of them were selected to generate amplicons covering viral RNA-dependent RNA polymerase (RdRp) and viral capsid protein (VP1) genes. Amplicons were sequenced using next-generation sequencing. Single nucleotide polymorphisms were defined, which demonstrated a nearly 3-fold greater mutation rate in the VP1 genome region compared to the RdRp genome region (7.9 vs. 2.8 variable sites/100 nucleotides, respectively). This indicates that mutations in the virus genome were not accumulated randomly, but are rather the result of mutant selection during the infection cycle. Using ShoRAH software we were able to reconstruct haplotypes occurring in each of the nine selected samples. The deduced amino-acid haplotype sequences were aligned and the positions were analyzed for selective pressure using the Datamonkey program. Only 12 out of 25 positive selection sites were within the commonly described epitopes A, B, C, and D of the VP1 protein. New positive selection sites were determined that have not been described before and might reflect adaptation of the norovirus toward optimal histo-blood-group antigen binding, or modification of the norovirus antigenic properties. These data provide new insights into norovirus evolutionary dynamics and indicate new putative epitope “hot-spots” of modified and optimized norovirus–host interactions.