The globally re-emerging norovirus GII.2 manifests higher heat resistance than norovirus GII.4 and Tulane virus

Sensitivity-enhanced hydrogel digital RT-LAMP with in situ enrichment and interfacial reaction for norovirus quantification in food and water

Low levels of human norovirus (HuNoV) in food and environment present challenges for nucleic acid detection. This study reported an evaporation-enhanced hydrogel digital reverse transcription loop-mediated isothermal amplification (HD RT-LAMP) with interfacial enzymatic reaction for sensitive HuNoV quantification in food and water. By drying samples on a chamber array chip, HuNoV particles were enriched in situ. The interfacial amplification of nucleic acid at the hydrogel-chip interface was triggered after coating HD RT-LAMP system. Nanoconfined spaces in hydrogels provided a simple and rapid "digital format" to quantify single virus within 15 min. Through in situ evaporation for enrichment, the sensitivity level was increased by 20 times. The universality of the sensitivity-enhanced assay was also verified using other bacteria and virus. Furthermore, a deep learning model and smartphone app were developed for automatic amplicon analysis. Multiple actual samples, including 3 lake waters, strawberry, tap water and drinking water, were in situ enriched and detected for norovirus quantification using the chamber arrays. Therefore, the sensitivity-enhanced HD RT-LAMP is an efficient assay for testing biological hazards in food safety monitoring and environmental surveillance.

Norovirus replication, host interactions and vaccine advances

Human noroviruses (HuNoVs) are the leading cause of acute gastroenteritis worldwide in all age groups and cause significant disease and economic burden globally. To date, no approved vaccines or antiviral therapies are available to treat or prevent HuNoV illness. Several candidate vaccines are in clinical trials, although potential barriers to successful development must be overcome. Recently, significant advances have been made in understanding HuNoV biology owing to breakthroughs in virus cultivation using human intestinal tissue-derived organoid (or enteroid) cultures, advances in structural biology technology combined with epitope mapping and increased metagenomic sequencing. New and unexpected strain-specific differences in pandemic versus non-pandemic virus structures, replication properties and virus-host interactions, including host factors required for susceptibility to infection and pathogenesis, are discussed.

Human norovirus cultivation models, immune response and vaccine landscape

Norovirus infections are a leading cause of gastroenteritis worldwide. Despite the substantial global health burden and economic impact, there are currently no approved antiviral therapeutics or vaccines. Additionally, much of our knowledge of norovirus comes from experiments using surrogate viruses, such as murine norovirus and feline calicivirus. The challenge surrounding human norovirus research arises from a lack of robust cell culture systems and efficient animal models. In this review, we explore recent advances in the in vitro cultivation of human norovirus and reverse genetics systems and discuss commonly used in vivo models. We summarize the current understanding of both innate and adaptive immune responses to norovirus infection and provide an overview of vaccine strategies and the current clinical trial landscape, with a focus on the only vaccine candidate that has reached phase III clinical development stage.

Biological and immunological characterization of major capsid protein VP1 from distinct GII.2 norovirus clusters

Human noroviruses (HuNoVs) are a leading cause of acute viral gastroenteritis worldwide. Infectious outbreaks due to recombinant NoV genotype called GII.P16-GII.2 have been frequently reported since 2016. In this study, we expressed the major capsid protein VP1 from three GII.2 NoV strains using the recombinant baculovirus expression system. The assembly, histo-blood group antigen (HBGA)-binding patterns, and cross-blocking abilities of VP1 proteins were investigated. All the three NoV VP1 proteins successfully assembled into virus-like particles (VLPs). The HBGA-binding assay demonstrated a temporal binding pattern. The latest isolate bound to saliva samples of all blood types. Sequence alignment suggested that the observed gain in HBGA-binding ability was attributed to a limited number of amino acid mutations. Using chimeric VP1 proteins, we demonstrated that synergistic effects resulted in enhanced binding ability. Bile salts increased GII.2 VLP avidity for HBGAs except GII.2-2011/M1. In vitro blockade assay of salivary HBGA-VLP binding demonstrated the presence of cross-blocking effects among different strains. This study provides insight into the evolutionary binding characteristics and cross-blocking effects of GII.2 NoVs to facilitate the development of measures to control this type of viruses.

Out-of-sync evolutionary patterns and mutual interplay of major and minor capsid proteins in norovirus GII.2

Human noroviruses are the most common cause of viral gastroenteritis, resulting annually in 219 000 deaths and a societal cost of $60 billion, and no antivirals or vaccines are available. The minor capsid protein may play a significant role in the evolution of norovirus. GII.4 is the predominant genotype of norovirus, and its VP2 undergoes epochal co-evolution with the major capsid protein VP1. Since the sudden emergence of norovirus GII.2[P16] in 2016, it has consistently remained a significant epidemic strain in recent years. In the construction of phylogenetic trees, the phylogenetic trees of VP2 closely parallel those of VP1 due to the shared tree topology of both proteins. To investigate the interaction patterns between the major and minor capsid proteins of norovirus GII.2, we chose five representative strains of GII.2 norovirus and investigated their evolutionary patterns using a yeast two-hybrid experiment. Our study shows VP1-VP2 interaction in GII.2, with critical interaction sites at 167-178 and 184-186 in the highly variable region. In the intra-within GII.2, we observed no temporal co-evolution between VP1 and VP2 of GII.2. Notable distinctions were observed in the interaction intensity of VP2 among inter-genotype (P<0.05), highlighting the divergent evolutionary patterns of VP2 within different norovirus genotypes. In summary, the interactions between VP2 and VP1 of GII.2 norovirus exhibit out-of-sync evolutionary patterns. This study offered valuable insights for further understanding and completing the evolutionary mechanism of norovirus.

Heat stability of foodborne viruses - Findings, methodological challenges and current developments

Heat treatment of food represents an important measure to prevent pathogen transmission. Thus far, evaluation of heat treatment processes is mainly based on data from bacteria. However, foodborne viruses have gained increasing attention during the last decades. Here, the published literature on heat stability and inactivation of human norovirus (NoV), hepatitis A virus (HAV) and hepatitis E virus (HEV) was reviewed. Data for surrogate viruses were not included. As stability assessment for foodborne viruses is often hampered by missing infectivity assays, an overview of applied methods is also presented. For NoV, molecular capsid integrity assays were mainly applied, but data from initial studies utilizing novel intestinal enteroid or zebrafish larvae assays are available now. However, these methods are still limited in applicability and sensitivity. For HAV, sufficient cell culture-based inactivation data are available, but almost exclusively for one single strain, thus limiting interpretation of the data for the wide range of field strains. For HEV, data are now available from studies using pig inoculation or cell culture. The results of the reviewed studies generally indicate that NoV, HAV and HEV possess a high heat stability. Heating at 70-72 °C for 2 min significantly reduces infectious titers, but often does not result in a >4 log10 decrease. However, heat stability greatly varied dependent on virus strain, matrix and heating regime. In addition, the applied method largely influenced the result, e.g. capsid integrity assays tend to result in higher measured stabilities than cell culture approaches. It can be concluded that the investigated foodborne viruses show a high heat stability, but can be inactivated by application of appropriate heating protocols. For HAV, suggestions for safe time/temperature combinations for specific foods can be derived from the published studies, with the limitation that they are mostly based on one strain only. Although significant improvement of infectivity assays for NoV and HEV have been made during the last years, further method development regarding sensitivity, robustness and broader applicability is important to generate more reliable heat inactivation data for these foodborne viruses in future.

High prevalence of norovirus GII.4 Sydney among children with acute gastroenteritis in Bangladesh, 2018-2021

BACKGROUND

Active molecular surveillance and rapid diagnosis method to track an outbreak of norovirus in Bangladesh is lacking. This study aims to determine the genotypic diversity, molecular epidemiology and evaluate a rapid diagnosis method.

METHODS

A total of 404 fecal specimens were collected from children aged below 60 months from January 2018 to December 2021. All samples were analyzed by reverse transcriptase polymerase chain reaction molecular sequencing of partial VP1 nucleotide. Immunochromatography kit (IC, IP Rota/Noro) was evaluated against reference test method.

RESULTS

We found norovirus in 6.7 % (27 of 404) fecal specimens. A wide diversity of norovirus genotype including GII.3, GII.4, GII.5, GII.6, GII.7, and GII.9 were detected. Norovirus strain GII.4 Sydney-2012 was the most predominant (74 %, 20 of 27) followed by GII.7 (7.4 %), GII.9 (7.4 %), GII.3 (3.7 %), GII.5 (3.7 %) and GII.6 (3.7 %), respectively. Co-infection of rotavirus and norovirus (19 [4.7 %] of 404) was the most prevalent. We found higher odds of prolonged health impact [OR 1.93 (95 % CI 0.87-3.12) (p = .001)] among patients with co-infection. The incidence of norovirus was significant among the children below 24 months (p = 0.001). Significant relation of temperature with the cases of norovirus was detected (p = 0.001). The IC kit provided high specificity (99.3 %) and sensitivity (100 %) for the detection of norovirus.

CONCLUSIONS

This study will provide an integrated insight on the genotypic diversity and rapid identification method of norovirus in Bangladesh.

Use of Zebrafish Embryos To Reproduce Human Norovirus and To Evaluate Human Norovirus Infectivity Decay after UV Treatment

This study reports an essential improvement of the method for replication of human norovirus (HNoV) with the use of zebrafish (Danio rerio) embryos. With three HNoV genotypes and P-types GII.2[P16], GII.4[P16], and GII.17[P31], we demonstrated that this tool had higher efficiency and robustness than the zebrafish larvae as reported previously. When zebrafish larvae were injected with virus (1.6 ± 0.3 log genome copies/10 larvae), a significant increase of virus genome copies was detected at 2 days postinfection (dpi; 4.4 ± 0.8 log genome copies/10 larvae, P < 0.05) and the viral loads started to decrease gradually from 3 dpi. In comparison, when the viruses were injected into the zebrafish embryos, significant virus replication was noticed from 1 dpi and lasted to 6 dpi (P < 0.05). The virus levels detected at 3 dpi had the highest mean value and the smallest variation (7.7 ± 0.2 log genome copies/10 larvae). The high levels of virus replication enabled continuous passaging for all three strains up to four passages. The zebrafish embryo-generated HNoVs showed clear patterns of binding to human histo-blood group antigens (HBGAs) in human saliva by a simple saliva-binding reverse transcription-quantitative PCR (RT-qPCR). Last, in a disinfection study, it was shown that a dose of 6 mJ/cm2 UV254 was able induce a >2-log reduction in HNoV infectivity for all three HNoV strains tested, suggesting that HNoVs were more UV susceptible than multiple enteric viruses and commonly used HNoV surrogates as tested before. IMPORTANCE HNoVs are a leading cause of gastroenteritis outbreaks worldwide. The zebrafish embryo tool as developed in this study serves as an efficient way to generate viruses with high titers and clean background and a straightforward platform to evaluate HNoV inactivation efficacies. It is expected that this tool will not only benefit epidemiological research on HNoV but also be used to generate HNoV inactivation parameters which are highly needed by the water treatment and food industries.