Noroviruses on surfaces: detection, persistence, disinfection and role in environmental transmission

The attachment factors and attachment receptors of human noroviruses

Human noroviruses (HuNoVs) are the leading etiological agent causing the worldwide outbreaks of acute epidemic non-bacterial gastroenteritis. Histo-blood group antigens (HBGAs) are commonly acknowledged as cellular receptors or co-receptors for HuNoVs. However, certain genotypes of HuNoVs cannot bind with any HBGAs, suggesting potential additional co-factors and attachment receptors have not been identified yet. In addition, food items, such as oysters and lettuce, play an important role in the transmission of HuNoVs. In the past decade, a couple of attachment factors other than HBGAs have been identified and analyzed from foods and microbiomes. Attachment factors exhibit potential as inhibitors of viral binding to receptors on host cells. Therefore, it is imperative to further characterize the attachment factors for HuNoVs present in foods to effectively control the spread of HuNoVs within the food chain. This review summarizes the potential attachment factors/receptors of HuNoVs in humans, foods, and microbiome.

A coupled hand and surface hygiene criterion on heterogeneous surface touch networks

Contaminated hands of people and contaminated surfaces of inanimate objects (fomites) can spread microbes that cause enteric and respiratory infections. Thus, hand hygiene and surface hygiene are probably the most widely adopted public health interventions for controlling such infections. However, conclusions of studies on the effectiveness of these interventions are often inconsistent, likely because such studies have examined these interventions separately and thus not detected their interactions, leading to differing conclusions about their individual impact. In this study, it is proposed that hand and environmental surface hygiene (including disinfection) should be coupled to control contamination spread between surfaces, especially within heterogeneous surface touch networks. In these networks, surfaces and individuals have varying contact frequencies and patterns, reflecting the diverse and non-uniform interactions that typically occur in real-world environments. Accordingly, we propose a new theoretical framework to delineate the relationships between hand hygiene and surface hygiene. In addition, the performance of a model based on this framework that used real-world behavioural data from a graduate student office is reported. Moreover, a coupled hygiene criterion for heterogeneous networks is derived. This criterion stipulates that the product of the pathogen-removal rates for hands and surfaces must exceed a cleaning threshold to ensure the exponential decay of contamination. Failure to meet this threshold results in a non-zero steady prevalence of contamination. Furthermore, the cleaning threshold increases as the numbers of surfaces and hands increase, highlighting the significant impact of network structures on hygiene practices. Thus, extensive cleaning may be necessary in crowded indoor environments with many surfaces and occupants, such as cruise ships, to prevent super-large outbreaks of, for example, noroviral infections. Overall, the findings of this study reveal how improved and integrated hygiene control can prevent fomite transmission.

Soluble extracellular polymeric substance (SEPS) of histo-blood group antigen (HBGA) expressing bacterium Sphingobacterium sp. SC015 influences the survival and persistence of norovirus on lettuce

Foodborne norovirus (NoV) outbreaks linked to leafy greens are common due to a lack of efficient strategies to prevent NoV spread from contaminated surfaces. We previously found that Sphingobacterium sp. SC015 in lettuce phyllosphere expresses histo-blood group antigen (HBGA)-like substances in soluble extracellular polymeric substances (SEPS) that contribute to NoV adherence on lettuce. Here, we extracted SEPS from bacterium SC015 (SEPS-SC015), analyzed their chemical composition, and examined their roles in the survival and protection of NoV and surrogates [murine norovirus (MNV-1) and Tulane virus (TuV)] on lettuce. Presence of SEPS-SC015 significantly increased survival and persistence of human NoV (HuNoV), MNV-1, and TuV at days 7 and 14, compared with virus alone. HuNoV, TuV, and MNV-1 seeded with SEPS-SC015 were more resistant to heat (70 °C, 2 min) than these viruses alone. SEPS-SC015 also increased viral resistance to sodium hypochlorite inactivation by treatment with 30 and 300 ppm bleach at 26 °C for 10 min. However, SEPS-SC015 was not effective at protecting these viruses under UV inactivation. Binding of TuV to SC015 bacteria and SEPS-SC015, visualized using transmission electron microscopy, suggests that protection might be related to direct interaction between SEPS-SC015 and viral particles. This study provides important insights that will help inform strategies to improve food safety.

Efficacy and Mechanisms of Copper Ion-Catalyzed Inactivation of Human Norovirus

The antinoroviral effect of copper ions is well known, yet most of this work has previously been conducted in copper and copper alloy surfaces, not copper ions in solution. In this work, we characterized the effects that Cu ions have on human norovirus capsids' and surrogates' integrity to explain empirical data, indicating virus inactivation by copper alloy surfaces, and as means of developing novel metal ion-based virucides. Comparatively high concentrations of Cu(II) ions (>10 mM) had little effect on the infectivity of human norovirus surrogates, so we used sodium ascorbate as a reducing agent to generate unstable Cu(I) ions from solutions of copper bromide. We found that significantly lower concentrations of monovalent copper ions (∼0.1 mM) compared to divalent copper ions cause capsid protein damage that prevents human norovirus capsids from binding to cell receptors in vitro and induce a greater than 4-log reduction in infectivity of Tulane virus, a human norovirus surrogate. Further, these Cu(I) solutions caused reduction of GII.4 norovirus from stool in suspension, producing about a 2-log reduction of virus as measured by a reverse transcriptase-quantitative polymerase chain reaction. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) data indicate substantial major capsid protein cleavage of both GI.7 and GII.4 norovirus capsids, and TEM images show the complete loss of capsid integrity of GI.7 norovirus. GII.4 virus-like particles (VLPs) were less susceptible to inactivation by copper ion treatments than GI.7 VLPs based upon receptor binding and SDS-PAGE analysis of viral capsids. The combined data demonstrate that stabilized Cu(I) ion solutions show promise as highly effective noroviral disinfectants in solution that can potentially be utilized at low concentrations for inactivation of human noroviruses.

A Survey of Analytical Techniques for Noroviruses

As the leading cause of acute gastroenteritis worldwide, human noroviruses (HuNoVs) have caused around 685 million cases of infection and nearly $60 billion in losses every year. Despite their highly contagious nature, an effective vaccine for HuNoVs has yet to become commercially available. Therefore, rapid detection and subtyping of noroviruses is crucial for preventing viral spread. Over the past half century, there has been monumental progress in the development of techniques for the detection and analysis of noroviruses. However, currently no rapid, portable assays are available to detect and subtype infectious HuNoVs. The purpose of this review is to survey and present different analytical techniques for the detection and characterization of noroviruses.

Sampling methods for recovery of human enteric viruses from environmental surfaces

•

Environmental surfaces (ES) are a significant route of enteric virus transmission.

•

A variety of surface sampling methods are applied for virus recovery from ES.

•

There is a need for standardization of ES sampling for recovery of enteric viruses.

Acute gastroenteritis causes the second highest infectious disease burden worldwide. Human enteric viruses have been identified as leading causative agents of acute gastroenteritis as well as foodborne illnesses in the U.S. and are generally transmitted by fecal-oral contamination. There is growing evidence of transmission occurring via contaminated fomite including food contact surfaces. Additionally, human enteric viruses have been shown to remain infectious on fomites over prolonged periods of time. To better understand viral persistence, there is a need for more studies to investigate this phenomenon. Therefore, optimization of surface sampling methods is essential to aid in understanding environmental contamination to ensure proper preventative measures are being applied. In general, surface sampling studies are limited and highly variable among recovery efficiencies and research parameters used (e.g., virus type/density, surface type, elution buffers, tools). This review aims to discuss the various factors impacting surface sampling of viruses from fomites and to explore how researchers could move towards a more sensitive and standard sampling method.