Complete sequence analyses of enterovirus 71 strains from fatal and non-fatal cases of the hand, foot and mouth disease outbreak in Singapore (2000)

Enterovirus-A71 preferentially infects and replicates in human motor neurons, inducing neurodegeneration by ferroptosis

Enterovirus A71 (EV-A71) causes Hand, Foot, and Mouth Disease and has been clinically associated with neurological complications. However, there is a lack of relevant models to elucidate the neuropathology of EV-A71 and its mechanism, as the current models mainly utilize animal models or immortalized cell lines. In this study, we established a human motor neuron model for EV-A71 infection. Single cell transcriptomics of a mixed neuronal population reveal higher viral RNA load in motor neurons, suggesting higher infectivity and replication of EV-A71 in motor neurons. The elevated RNA load in motor neurons correlates with the downregulation of ferritin-encoding genes. Subsequent analysis confirms that neurons infected with EV-A71 undergo ferroptosis, as evidenced by increased levels of labile Fe2+ and peroxidated lipids. Notably, the Fe2+ chelator Deferoxamine improves mitochondrial function and promotes survival of motor neurons by 40% after EV-A71 infection. These findings deepen understanding of the molecular pathogenesis of EV-A71 infection, providing insights which suggest that improving mitochondrial respiration and inhibition of ferroptosis can mitigate the impact of EV-A71 infection in the central nervous system.

The Association of Helicobacter pylori Biofilm with Enterovirus 71 Prolongs Viral Viability and Survival

The transition time during which a virus leaves its host and infects the next susceptible host is critical for virus survival. Enterovirus 71 (EV71) is stable in aqueous environments, but its molecular interactions with bacteria and their biofilms are not well-established. Helicobacter pylori is a highly successful gut bacterial pathogen, with its capacity to form biofilms being linked to its transmission. Given that both are gut-associated microbes, we hypothesized that biofilms formed by H. pylori may play a significant role in the survival of EV71 in the external environment. In this study, we examine the interactions of EV71 with the preformed biofilm of H. pylori to mimic its natural state in the environment. Immunofluorescence confocal microscopy and scanning electron microscopy revealed that EV71 particles persisted for up to 10 days when incubated with the H. pylori biofilm. Furthermore, the presence of the H. pylori biofilm significantly augmented viral viability, as verified through virus plaque assays. Interestingly, the viability of EV71 was dependent on the quantity of H. pylori biofilm formation. Thus, two H. pylori strains able to generate large amounts of biofilm could facilitate EV71 viability for up to 17 days, whereas two other H. pylori strains that produced moderate or low quantities of biofilm could not prolong virus viability. It is interesting that biofilm contains N-acetyl-glucosamine and glycosaminoglycan, and that EV71 has binding affinity to cell-surface heparan sulfate glycosaminoglycan, which acts as an EV71 attachment receptor. The synergistic ability of H. pylori biofilm to promote EV71 viability for extended periods implies that H. pylori biofilm may serve as an additional pathway of EV71 transmission.

Insights into In Vitro Adaptation of EV71 and Analysis of Reduced Virulence by In Silico Predictions

EV-A71 is a common viral pathogen that causes hand, foot and mouth disease. It is a single-stranded RNA virus that has a low fidelity RNA polymerase and, as a result, spontaneous mutations frequently occur in the EV-A71 genome. The mutations within the genome give rise to quasispecies within the viral population that could be further defined by haplotypes. In vitro virulence of EV-A71 was shown by plaque size in Rhabdomyosarcoma (RD) cells, which was substantiated by in vitro characterizations of growth, RNA replication, binding, attachment and host cell internalization. Viruses could exhibit different host cell adaptations in different cell lines during viral passaging. The EV-A71/WT (derived from EV-A71 subgenotype B4) was shown to comprise six haplotypes through next-generation sequencing, where only EV-A71/Hap2 was found to be cultivable in RD cells, while EV-A71/Hap4 was the only cultivable haplotype in Vero cells. The EV-A71/WT produced plaques of four different sizes (small, medium, big, huge) in RD cells, while only two plaque variants (small, medium) were present in Vero cells. The small plaque variant isolated from RD cells displayed lower RNA replication rates, slower in vitro growth kinetics, higher TCID50 and lower attachment, binding and entry ability when compared against EV-A71/WT due to the mutation at 3D-S228P that disrupted the active site of the RNA polymerase, resulting in low replication and growth of the variant.

Recent advances in anti-coxsackievirus A16 viral drug research

Hand, foot and mouth disease, a childhood disorder caused by enteroviruses, is intermittently endemic in the Asia-Pacific region and endangers the lives of many infants and young children. Coxsackievirus A16 (CV-A16) is one of the major pathogens causing hand, foot, and mouth disease on occasion, resulting in catastrophic neurological sequelae and patient death. Currently, no clinical interventions are available that completely block the CV-A16 infection. Therefore, research on anti-CV-A16 treatment continues to be a significant focus of interest. This report provides a detailed background on and an introduction to CV-A16; a description of the viral gene and protein structures and a summary of the current advances in pharmaceutical targets, drug research and other related areas.

A Single Amino Acid Substitution in Structural Protein VP2 Abrogates the Neurotropism of Enterovirus A-71 in Mice

Enterovirus 71 (EV-A71) causes hand, foot, and mouth disease (HFMD) in children and has been associated with neurological complications. With no specific treatment and a monovalent vaccine limited to the Chinese market, HFMD remains a serious public health concern and an economic burden to affected societies. The molecular mechanisms underpinning EV-A71 neurovirulence have yet to be fully elucidated. In this work, we provide experimental evidence that a single amino acid substitution (I to K) at position 149 in structural protein VP2 of a non-mouse-adapted EV-A71 strain completely and specifically abrogated its infectivity in murine motor neuron-like NSC-34 cells. We showed that VP2 I149K mutant was impaired in murine SCARB2-mediated entry step but retained the ability to attach at the cell surface. In vivo, VP2 I149K mutant was fully attenuated in a symptomatic mouse model of progressive limb paralysis. While viral titers in limb muscles were comparable to mice infected with parental wild-type strain, significantly lower viral titers were measured in the spinal cord and brain, with minimal tissue damage, therefore indicating that VP2 I149K mutant is specifically impaired in its ability to invade the central nervous system (CNS). This study highlights the key role of amino acid at position 149 in VP2 in EV-A71 neurovirulence, and lends further support that the EF loop of VP2 represents a potential therapeutic target.

Coxsackievirus A16 in Southern Vietnam

Background: Hand, Foot and Mouth Disease (HFMD) is a major public health concern in the Asia-Pacific region. Most recent HFMD outbreaks have been caused by enterovirus A71 (EV-A71), coxsackievirus A16 (CVA16), CVA10, and CVA6. There has been no report regarding the epidemiology and genetic diversity of CVA16 in Vietnam. Such knowledge is critical to inform the development of intervention strategies.

Materials and Methods: From 2011 to 2017, clinical samples were collected from in- and outpatients enrolled in a HFMD research program conducted at three referral hospitals in Ho Chi Minh City (HCMC), Vietnam. Throat or rectal swabs positive for CVA16 with sufficient viral load were selected for whole genome sequencing and evolutionary analysis.

Results: Throughout the study period, 320 CVA16 positive samples were collected from 2808 HFMD patients (11.4%). 59.4% of patients were male. The median age was 20.8 months (IQR, 14.96–31.41). Patients resided in HCMC (55.3%), Mekong Delta (22.2%), and South East Vietnam (22.5%). 10% of CVA16 infected patients had moderately severe or severe HFMD. CVA16 positive samples from 153 patients were selected for whole genome sequencing, and 66 complete genomes were obtained. Phylogenetic analysis demonstrated that Vietnamese CVA16 strains belong to a single genogroup B1a that clusters together with isolates from China, Japan, Thailand, Malaysia, France and Australia. The CVA16 strains of the present study were circulating in Vietnam some 4 years prior to its detection in HFMD cases.

Conclusion: We report for the first time on the molecular epidemiology of CVA16 in Vietnam. Unlike EV-A71, which showed frequent replacement between subgenogroups B5 and C4 every 2–3 years in Vietnam, CVA16 displays a less pronounced genetic alternation with only subgenogroup B1a circulating in Vietnam since 2011. Our collective findings emphasize the importance of active surveillance for viral circulation in HFMD endemic countries, critical to informing outbreak response and vaccine development.

Honeysuckle Aqueous Extracts Induced let-7a Suppress EV71 Replication and Pathogenesis In Vitro and In Vivo and Is Predicted to Inhibit SARS-CoV-2

Honeysuckle (Lonicera japonica Thunb) is a traditional Chinese medicine (TCM) with an antipathogenic activity. MicroRNAs (miRNAs) are small non-coding RNA molecules that are ubiquitously expressed in cells. Endogenous miRNA may function as an innate response to block pathogen invasion. The miRNA expression profiles of both mice and humans after the ingestion of honeysuckle were obtained. Fifteen overexpressed miRNAs overlapped and were predicted to be capable of targeting three viruses: dengue virus (DENV), enterovirus 71 (EV71) and SARS-CoV-2. Among them, let-7a was examined to be capable of targeting the EV71 RNA genome by reporter assay and Western blotting. Moreover, honeysuckle-induced let-7a suppression of EV71 RNA and protein expression as well as viral replication were investigated both in vitro and in vivo. We demonstrated that let-7a targeted EV71 at the predicted sequences using luciferase reporter plasmids as well as two infectious replicons (pMP4-y-5 and pTOPO-4643). The suppression of EV71 replication and viral load was demonstrated in two cell lines by luciferase activity, RT-PCR, real-time PCR, Western blotting and plaque assay. Furthermore, EV71-infected suckling mice fed honeysuckle extract or inoculated with let-7a showed decreased clinical scores and a prolonged survival time accompanied with decreased viral RNA, protein expression and virus titer. The ingestion of honeysuckle attenuates EV71 replication and related pathogenesis partially through the upregulation of let-7a expression both in vitro and in vivo. Our previous report and the current findings imply that both honeysuckle and upregulated let-7a can execute a suppressive function against the replication of DENV and EV71. Taken together, this evidence indicates that honeysuckle can induce the expression of let-7a and that this miRNA as well as 11 other miRNAs have great potential to prevent and suppress EV71 replication.

Characterization of Plaque Variants and the Involvement of Quasi-Species in a Population of EV-A71

Viral plaque morphologies in human cell lines are markers for growth capability and they have been used to assess the viral fitness and selection of attenuated mutants for live-attenuated vaccine development. In this study, we investigate whether the naturally occurring plaque size variation reflects the virulence of the variants of EV-A71. Variants of two different plaque sizes (big and small) from EV-A71 sub-genotype B4 strain 41 were characterized. The plaque variants displayed different in vitro growth kinetics compared to the parental wild type. The plaque variants showed specific mutations being present in each variant strain. The big plaque variants showed four mutations I97L, N104S, S246P and N282D in the VP1 while the small plaque variants showed I97T, N237T and T292A in the VP1. No other mutations were detected in the whole genome of the two variants. The variants showed stable homogenous small plaques and big plaques, respectively, when re-infected in rhabdomyosarcoma (RD) and Vero cells. The parental strain showed faster growth kinetics and had higher viral RNA copy number than both the big and small plaque variants. Homology modelling shows that both plaque variants have differences in the structure of the VP1 protein due to the presence of unique spontaneous mutations found in each plaque variant This study suggests that the EV-A71 sub-genotype B4 strain 41 has at least two variants with different plaque morphologies. These differences were likely due to the presence of spontaneous mutations that are unique to each of the plaque variants. The ability to maintain the respective plaque morphology upon passaging indicates the presence of quasi-species in the parental population.

Pathogenesis of hand-foot-mouth disease caused by enterovirus 71

Hand-foot-mouth disease (HFMD) is a global infectious disease. The infected population is mainly infants and young children. Enterovirus 71 (EV71) is the main pathogen. In addition to HFMD, EV71 infection can also affect the nervous system and other organs, resulting in aseptic meningitis, brainstem encephalitis, and poliomyelitis-like paralysis, causing serious harm to children's health. At present, the pathogenesis of HFMD caused by EV71 is still unclear, and there is no effective treatment. In this paper, we discuss the factors influencing EV71 infection from the aspects of virus gene recombination and spontaneous mutation, host genes, and receptor sites, review the pathogenesis of HFMD caused by EV71 based on the study findings from animal infection models, and explore the main problems in the study of pathogenesis of this condition, in order to provide reference for the prevention and treatment of HFMD and for the development of new drugs or effective vaccines for EV71 infection.

Polypyrimidine Tract-Binding Protein Regulates Enterovirus 71 Translation Through Interaction with the Internal Ribosomal Entry Site

Enterovirus 71 (EV71), a major causative agent of hand, foot, and mouth disease, has caused periodic infection outbreaks in children in the Asia–Pacific region. In order to describe the largely unknown life cycle of EV71, the molecular basis of its virus-host interactions must first be determined. The 5′ untranslated region of EV71 contains a cloverleaf-like structure and internal ribosomal entry site (IRES), which play an important role in transcription and translation of viral protein. We found that polypyrimidine tract-binding protein 1 (PTB) bound to the IRES of EV71. RNA recognition motifs 1 and 2 of PTB were responsible for its binding to the EV71 IRES. Moreover, PTB protein was shuttled from nucleus to cytoplasm after EV71 infection. Additionally, IRES activity and viral protein production were inhibited by PTB knockdown. These results suggest that PTB interacts with the EV71 IRES, and positively regulates viral protein translation.

Enterovirus A71 Infection Activates Human Immune Responses and Induces Pathological Changes in Humanized Mice

Since the discovery of enterovirus A71 (EV-A71) half a century ago, it has been recognized as the cause of large-scale outbreaks of hand-foot-and-mouth disease worldwide, particularly in the Asia-Pacific region, causing great concern for public health and economic burdens. Detailed mechanisms on the modulation of immune responses after EV-A71 infection have not been fully known, and the lack of appropriate models hinders the development of promising vaccines and drugs. In the present study, NOD-scid IL2Rγ^-/- (NSG) mice with a human immune system (humanized mice) at the age of 4 weeks were found to be susceptible to a human isolate of EV-A71 infection. After infection, humanized mice displayed limb weakness, which is similar to the clinical features found in some of the EV-A71-infected patients. Histopathological examination indicated the presence of vacuolation, gliosis, or meningomyelitis in brain stem and spinal cord, which were accompanied by high viral loads detected in these organs. The numbers of activated human CD4⁺ and CD8⁺ T cells were upregulated after EV-A71 infection, and EV-A71-specific human T cell responses were found. Furthermore, the secretion of several proinflammatory cytokines, such as human gamma interferon (IFN-γ), interleukin-8 (IL-8), and IL-17A, was elevated in the EV-A71-infected humanized mice. Taken together, our results suggested that the humanized mouse model permits insights into the human immune responses and the pathogenesis of EV-A71 infection, which may provide a platform for the evaluation of anti-EV-A71 drug candidates in the future.IMPORTANCE Despite causing self-limited hand-food-and-mouth disease in younger children, EV-A71 is consistently associated with severe forms of neurological complications and pulmonary edema. Nevertheless, only limited vaccines and drugs have been developed over the years, which is possibly due to a lack of models that can more accurately recapitulate human specificity, since human is the only natural host for wild-type EV-A71 infection. Our humanized mouse model not only mimics histological symptoms in patients but also allows us to investigate the function of the human immune system during infection. It was found that human T cell responses were activated, accompanied by an increase in the production of proinflammatory cytokines in EV-A71-infected humanized mice, which might contribute to the exacerbation of disease pathogenesis. Collectively, this model allows us to delineate the modulation of human immune responses during EV-A71 infection and may provide a platform to evaluate anti-EV-A71 drug candidates in the future.

Acute Flaccid Paralysis and Enteroviral Infections

PURPOSE OF REVIEW

The focus of this review is on enterovirus (EV)-associated acute flaccid paralysis (AFP) due to spinal cord anterior horn cell disease. Emphasis is placed on the epidemiology, pathogenesis, diagnosis, treatment, and outcome of AFP caused by polioviruses, vaccine-derived polioviruses, EV-D68, and EV-A71.

RECENT FINDINGS

Since the launch of The Global Polio Eradication Initiative in 1988, the worldwide incidence of polio has been reduced by 99.9%, with small numbers of poliomyelitis cases being reported only in Afghanistan, Pakistan, and Nigeria. With the planned phaseout of oral polio vaccine, vaccine-associated poliomyelitis is also expected to be eliminated. In their place, other EVs, chiefly EV-D68 and EV-A71, have emerged as the principal causes of AFP. There is evidence that the emergence of EV-D68 as a cause of severe respiratory disease and AFP was due to recent genetic virus evolution. Antiviral medications targeting EV-D68, EV-A71, and other EVs will likely be available in the near future. An effective EV-A71 vaccine has been developed, and preliminary investigations suggest an EV-D68 vaccine could be on the horizon. The eradication of poliomyelitis and vaccine-associated poliomyelitis is near, after which other EVs, presently EV-D68 and EV-A71, will be the principle viral causes of AFP. Moving forward, it is essential that EV outbreaks, in particular those associated with neurologic complications, be investigated carefully and the causal strains identified, so that treatment and prevention efforts can be rapidly developed and implemented.

Changes in the EV-A71 Genome through Recombination and Spontaneous Mutations: Impact on Virulence

Enterovirus 71 (EV-A71) is a major etiological agent of hand, foot and mouth disease (HFMD) that mainly affects young children less than five years old. The onset of severe HFMD is due to neurological complications bringing about acute flaccid paralysis and pulmonary oedema. In this review, we address how genetic events such as recombination and spontaneous mutations could change the genomic organization of EV-A71, leading to an impact on viral virulence. An understanding of the recombination mechanism of the poliovirus and non-polio enteroviruses will provide further evidence of the emergence of novel strains responsible for fatal HFMD outbreaks. We aim to see if the virulence of EV-A71 is contributed solely by the presence of fatal strains or is due to the co-operation of quasispecies within a viral population. The phenomenon of quasispecies within the poliovirus is discussed to reflect viral fitness, virulence and its implications for EV-A71. Ultimately, this review gives an insight into the evolution patterns of EV-A71 by looking into its recombination history and how spontaneous mutations would affect its virulence.

Prohibitin plays a critical role in Enterovirus 71 neuropathogenesis

A close relative of poliovirus, enterovirus 71 (EV71) is regarded as an important neurotropic virus of serious public health concern. EV71 causes Hand, Foot and Mouth Disease and has been associated with neurological complications in young children. Our limited understanding of the mechanisms involved in its neuropathogenesis has hampered the development of effective therapeutic options. Here, using a two-dimensional proteomics approach combined with mass spectrometry, we have identified a unique panel of host proteins that were differentially and dynamically modulated during EV71 infection of motor-neuron NSC-34 cells, which are found at the neuromuscular junctions where EV71 is believed to enter the central nervous system. Meta-analysis with previously published proteomics studies in neuroblastoma or muscle cell lines revealed minimal overlapping which suggests unique host-pathogen interactions in NSC-34 cells. Among the candidate proteins, we focused our attention on prohibitin (PHB), a protein that is involved in multiple cellular functions and the target of anti-cancer drug Rocaglamide (Roc-A). We demonstrated that cell surface-expressed PHB is involved in EV71 entry into neuronal cells specifically, while membrane-bound mitochondrial PHB associates with the virus replication complex and facilitates viral replication. Furthermore, Roc-A treatment of EV71-infected neuronal cells reduced significantly virus yields. However, the inhibitory effect of Roc-A on PHB in NSC-34 cells was not through blocking the CRAF/MEK/ERK pathway as previously reported. Instead, Roc-A treated NSC-34 cells had lower mitochondria-associated PHB and lower ATP levels that correlated with impaired mitochondria integrity. In vivo, EV71-infected mice treated with Roc-A survived longer than the vehicle-treated animals and had significantly lower virus loads in their spinal cord and brain, whereas virus titers in their limb muscles were comparable to controls. Together, this study uncovers PHB as the first host factor that is specifically involved in EV71 neuropathogenesis and a potential drug target to limit neurological complications.

Impact of genetic changes, pathogenicity and antigenicity on Enterovirus- A71 vaccine development

Enterovirus-A71 (EV-A71) is an etiological agent of the hand, foot and mouth disease (HFMD). EV-A71 infection produces high fever and ulcers in children. Some EV-A71 strains produce severe infections leading to pulmonary edema and death. Although the protective efficacy of the inactivated vaccine (IV) was ≥90% against mild HFMD, there was approximately 80% protection against severe HFMD. The monovalent EV-A71 IV elicits humoral immunity but lacks long-term immunogenicity. Spontaneous mutations of the EV-A71 genome could lead to antigenicity changes and the virus may not be neutralized by antibodies elicited by the IV. A better alternative would be the live attenuated vaccine (LAV) that elicits cellular and humoral immunity. The LAV induces excellent antigenicity and chances of reversion is reduced by presence of multiple mutations which could reduce pathogenicity. Besides CV-A16, outbreaks have been caused by CV-A6 and CV-A10, hence the development of bivalent and trivalent vaccines is required.

Identification of molecular determinants of cell culture growth characteristics of Enterovirus 71

BACKGROUND

Hand, foot and mouth disease is caused by Enterovirus 71 (EV-A71) and Coxsackieviruses. EV-A71 infection is associated with high fever, rashes and ulcers but more severe symptoms such as cardiopulmonary failure and death have been reported. The lack of vaccines highlighted the urgency of developing preventive agents against EV-A71. The molecular determinants of virulent phenotypes of EV-A71 is unclear. It remains to be investigated if specific molecular determinants would affect the cell culture growth characteristics of the EV-A71 fatal strain in Rhabdomyosarcoma (RD) cells.

RESULTS

In this study, several genetically modified sub-genotype B4 EV-A71 mutants were constructed by site-directed mutations at positions 158, 475, 486, 487 and 5262 or through partial deletion of the 5'-NTR region (∆ 11 bp from nt 475 to 486) to generate a deletion mutant (PD). EV-A71 mutants 475 and PD caused minimal cytopathic effects, produced lowest viral RNA copy number, viral particles as well as minimal amount of viral protein (VP1) in RD cells when compared to mutants 158, 486, 487 and 5262.

CONCLUSIONS

The molecular determinants of virulent phenotypes of EV-A71 sub-genotype B4 strain 41 (5865/Sin/000009) were found to differ from the C158 molecular determinant reported for the fatal EV-A71 sub-genotype B1 strain (clinical isolate 237). The site-directed mutations (SDM) introduced at various sites of the cDNA affected growth of the various mutants when compared to the wild type. Lowest viral RNA copy number, minimal number of plaques formed, higher infectious doses required for 50% lethality of RD cells and much reduced VP1 of the EV-A71 sub-genotype B4 strain 41 genome was attained in mutants carrying SDM at position 475 and through partial deletion of 11 bp at the 5'-NTR region.

VP1 residues around the five-fold axis of enterovirus A71 mediate heparan sulfate interaction

Enterovirus A71 (EV-A71) is a neurotropic enterovirus that uses heparan sulfate as an attachment receptor. The molecular determinants of EV-A71-heparan sulfate interaction are unknown. With In silico heparin docking and mutagenesis of all possible lysine residues in VP1, we identified that K162, K242 and K244 are responsible for heparin interaction and inhibition. EV-A71 mutants with K242A and K244A rapidly acquired compensatory mutations, T100K or E98A, and Q145R-T237N respectively, which restored the heparin-binding phenotype. Both VP1-98 and VP1-145 modulates heparin binding. Heparin-binding phenotype was completely abolished with VP1-E98-E145, but was restored by an E98K or E145Q substitution. During cell culture adaptation, EV-A71 rapidly acquired K98 or Q/G145 to restore the heparin-binding phenotype. Together with next-generation sequencing analysis, our results implied that EV-A71 has high genetic plasticity by modulating positively-charged residues at the five-fold axis during in vitro heparin adaptation. Our finding has impact on EV-A71 vaccine production, evolutionary studies and pathogenesis.

Gene sequencing and variable site analyzing of coding region of two enterovirus A71 isolates with different clinical phenotypes

Currently, it is still controversial that if the pathogenicity of EV-A71 causing severe or mild hand, foot, and mouth disease (HFMD) is associated with viral nucleotide or amino acid sequence(s). In this study, 19 clinical strains were detected in samples from diagnosed patients of EV-A71-caused HFMD with mild or severe symptoms. Then, VP1-2A fragment sequences of 19 EV-A71 isolates were determined, the phylogenetic analysis, based on VP1 sequences of 19 EV-A71 stains in this study and which of 62 EV-A71 strains with different clinical phenotypes reported before, were carried out. Our results showed that no difference in the genotype and evolution distribution was observed among the EV-A71 strains mentioned above. Furthermore, two EV-A71 isolates, which with much close evolutionary relationship but different clinical manifestations, were purified by plaque assay, the complete genome sequencing was done, and deduced amino acid sequence analysis of 11 proteins coded by EV-A71 was carried out. Eight variable amino acid sites were found and further verified with those of 62 strains reported before. Our study provides further evidence that the potential pathogenicity of EV-A71 causing severe or mild HFMD seems not to be associated with viral genotype and even the amino acid substitution.

Antiviral activity of Lactobacillus reuteri Protectis against Coxsackievirus A and Enterovirus 71 infection in human skeletal muscle and colon cell lines

Background

Recurrence of hand, foot and mouth disease (HFMD) pandemics continues to threaten public health. Despite increasing awareness and efforts, effective vaccine and drug treatment have yet to be available. Probiotics have gained recognition in the field of healthcare worldwide, and have been extensively prescribed to babies and young children to relieve gastrointestinal (GI) disturbances and diseases, associated or not with microbial infections. Since the faecal-oral axis represents the major route of HFMD transmission, transient persistence of probiotic bacteria in the GI tract may confer some protection against HFMD and limit transmission among children.

Methods

In this work, the antiviral activity of two commercially available probiotics, namely Lactobacillus reuteri Protectis (L. reuteri Protectis) and Lactobacillus casei Shirota (L. casei Shirota), was assayed against Coxsackieviruses and Enterovirus 71 (EV71), the main agents responsible for HFMD. In vitro infection set-ups using human skeletal muscle and colon cell lines were designed to assess the antiviral effect of the probiotic bacteria during entry and post-entry steps of the infection cycle.

Results

Our findings indicate that L. reuteri Protectis displays a significant dose-dependent antiviral activity against Coxsackievirus type A (CA) strain 6 (CA6), CA16 and EV71, but not against Coxsackievirus type B strain 2. Our data support that the antiviral effect is likely achieved through direct physical interaction between bacteria and virus particles, which impairs virus entry into its mammalian host cell. In contrast, no significant antiviral effect was observed with L. casei Shirota.

Conclusions

Should the antiviral activity of L. reuteri Protectis observed in vitro be translated in vivo, such probiotics-based therapeutic approach may have the potential to address the urgent need for a safe and effective means to protect against HFMD and limit its transmission among children.

Clinical and Associated Immunological Manifestations of HFMD Caused by Different Viral Infections in Children

Hand, foot, and mouth disease (HFMD), with vesiculae on the hands, feet and mouth, is an infectious disease caused by many viral pathogens. However, the differences of immune response induced by these pathogens are unclear. We compared the clinical manifestations and the levels of immunologic indicators from 60 HFMD patients caused by different viral pathogens to analyze the differences in the immune response. It was shown that Th2 cytokines (IL-4 and IL-10) increased significantly in EV71-infected children; Th1 cytokines (IL-2 and IFN-γ) rose in CA16-infected children; both Th1 and Th2 cytokines elevated in non-EVG-infected children; only individual cytokines (such as IL-10) went up in EVG-infected children. Meanwhile, the antibodies induced by viral infection could not cross-interfere between the different pathogens. These differences might be due to variations in the immune response induced by the individual pathogens or to the pathogenesis of the infections by the individual pathogens.

Human Sentinel Surveillance of Influenza and Other Respiratory Viral Pathogens in Border Areas of Western Cambodia

Little is known about circulation of influenza and other respiratory viruses in remote populations along the Thai-Cambodia border in western Cambodia. We screened 586 outpatients (median age 5, range 1–77) presenting with influenza-like-illness (ILI) at 4 sentinel sites in western Cambodia between May 2010 and December 2012. Real-time reverse transcriptase (rRT) PCR for influenza was performed on combined nasal and throat specimens followed by viral culture, antigenic analysis, antiviral susceptibility testing and full genome sequencing for phylogenetic analysis. ILI-specimens negative for influenza were cultured, followed by rRT-PCR for enterovirus and rhinovirus (EV/RV) and EV71. Influenza was found in 168 cases (29%) and occurred almost exclusively in the rainy season from June to November. Isolated influenza strains had close antigenic and phylogenetic relationships, matching vaccine and circulating strains found elsewhere in Cambodia. Influenza vaccination coverage was low (<20%). Western Cambodian H1N1(2009) isolate genomes were more closely related to 10 earlier Cambodia isolates (94.4% genome conservation) than to 13 Thai isolates (75.9% genome conservation), despite sharing the majority of the amino acid changes with the Thai references. Most genes showed signatures of purifying selection. Viral culture detected only adenovirus (5.7%) and parainfluenza virus (3.8%), while non-polio enteroviruses (10.3%) were detected among 164 culture-negative samples including coxsackievirus A4, A6, A8, A9, A12, B3, B4 and echovirus E6 and E9 using nested RT-PCR methods. A single specimen of EV71 was found. Despite proximity to Thailand, influenza epidemiology of these western Cambodian isolates followed patterns observed elsewhere in Cambodia, continuing to support current vaccine and treatment recommendations from the Cambodian National Influenza Center. Amino acid mutations at non-epitope sites, particularly hemagglutinin genes, require further investigation in light of an increasingly important role of permissive mutations in influenza virus evolution. Further research about the burden of adenovirus and non-polio enteroviruses as etiologic agents in acute respiratory infections in Cambodia is also needed.

Pluripotent Human embryonic stem cell derived neural lineages for in vitro modelling of enterovirus 71 infection and therapy

BACKGROUND

The incidence of neurological complications and fatalities associated with Hand, Foot & Mouth disease has increased over recent years, due to emergence of newly-evolved strains of Enterovirus 71 (EV71). In the search for new antiviral therapeutics against EV71, accurate and sensitive in vitro cellular models for preliminary studies of EV71 pathogenesis is an essential prerequisite, before progressing to expensive and time-consuming live animal studies and clinical trials.

METHODS

This study thus investigated whether neural lineages derived from pluripotent human embryonic stem cells (hESC) can fulfil this purpose. EV71 infection of hESC-derived neural stem cells (NSC) and mature neurons (MN) was carried out in vitro, in comparison with RD and SH-SY5Y cell lines.

RESULTS

Upon assessment of post-infection survivability and EV71 production by the various types, it was observed that NSC were significantly more susceptible to EV71 infection compared to MN, RD (rhabdomyosarcoma) and SH-SY5Y cells, which was consistent with previous studies on mice. The SP81 peptide had significantly greater inhibitory effect on EV71 production by NSC and MN compared to the cancer-derived RD and SH-SY5Y cell lines.

CONCLUSIONS

Hence, this study demonstrates that hESC-derived neural lineages can be utilized as in vitro models for studying EV71 pathogenesis and for screening of antiviral therapeutics.

MicroRNA and Pathogenesis of Enterovirus Infection

There are no currently available specific antiviral therapies for non-polio Enterovirus infections. Although several vaccines have entered clinical trials, the efficacy requires further evaluation, particularly for cross-strain protective activity. Curing patients with viral infections is a public health problem due to antigen alterations and drug resistance caused by the high genomic mutation rate. To conquer these limits in the development of anti-Enterovirus treatments, a comprehensive understanding of the interactions between Enterovirus and host cells is urgently needed. MicroRNA (miRNA) constitutes the biggest family of gene regulators in mammalian cells and regulates almost a half of all human genes. The roles of miRNAs in Enterovirus pathogenesis have recently begun to be noted. In this review, we shed light on recent advances in the understanding of Enterovirus infection-modulated miRNAs. The impacts of altered host miRNAs on cellular processes, including immune escape, apoptosis, signal transduction, shutdown of host protein synthesis and viral replication, are discussed. Finally, miRNA-based medication provides a promising strategy for the development of antiviral therapy.

Enterovirus 71 infection in children with hand, foot, and mouth disease in Shanghai, China: epidemiology, clinical feature and diagnosis

BACKGROUND

In 2012 a large outbreak of hand, foot, and mouth disease (HFMD) widely spread over China, causing more than 2 million cases and 567 deaths. Our purpose was to characterize the major pathogens responsible for the 2012 HFMD outbreak and analyze the genetic characterization of the enterovirus 71 (EV71) strains in Shanghai; also, to analyze the dynamic patterns of neutralizing antibody (NAb) against EV71 and evaluate the diagnostic value of several methods for clinical detection of EV71.

METHODS

Clinical samples including stool, serum and CSF were collected from 396 enrolled HFMD inpatients during the peak seasons in 2012. We analyzed the molecular epidemiology, clinical feature, and diagnostic tests of EV71 infection.

RESULTS

EV71 was responsible for 60.35 % of HFMD inpatients and 88.46 % of severe cases. The circulating EV71 strains belonged to subgenogroup C4a. The nucleotide sequences of VP1 between severe cases and uncomplicated cases shared 99.2 ~ 100 % of homology. Among 218 cases with EV71 infection, 211 (96.79 %) serum samples showed NAb positive against EV71 and NAb titer reached higher level 3 days after disease onset. Of 92 cases with EV71-associated meningitis or encephalitis, 5 (5.43 %) of 92 had EV71 RNA detected in CSF samples. The blood anti-EV71 IgM assay showed a sensitivity of 93.30 % and a specificity of 50 %.

CONCLUSIONS

EV71 C4a remained the predominant subgenotype circulating in Shanghai. The severity of the EV71 infection is not associated with the virulence determinants in VP1. RT-PCR together with IgM detection can enhance the early diagnosis of severe EV71-associated HFMD.

Seroepidemiology of Coxsackievirus A6, Coxsackievirus A16, and Enterovirus 71 Infections among Children and Adolescents in Singapore, 2008-2010

Coxsackieviruses A6 (CV-A6) and A16 (CV-A16) and Enterovirus 71 (EV-A71) have caused periodic epidemics of hand, foot and mouth disease (HFMD) among children in Singapore. We conducted a cross-sectional study to estimate the seroprevalence of these enteroviruses among Singapore children and adolescents. The study was conducted between August 2008 and July 2010. It involved 700 Singapore residents aged 1-17 years whose residual sera were obtained following the completion of routine biochemical investigations in two public acute-care hospitals. The levels of neutralizing antibodies (NtAb) against CV-A6, CV-A16 and EV-A71 were analyzed by the microneutralization test. The age-specific geometric mean titer (GMT) of antibodies against each of the three enteroviruses and the 95% confidence intervals (CI) were calculated. The seroprevalence of CV-A6 and CV-A16 was high at 62.7% (95% CI: 59.1-66.2%) and 60.6% (95% CI: 56.9-64.1%), respectively. However, the seroprevalence of EV-A71 was significantly lower at 29.3% (95% CI: 26.0-32.8%). About 89.7% of the children and adolescents had been infected by at least one of the three enteroviruses by 13-17 years of age. About half (52.3%) were seropositive for two or all three enteroviruses, while only 16.1% had no NtAb against any of the three enteroviruses. High NtAb levels were observed in the younger age groups. CV-A6 and CV-A16 infections are very common among Singapore children and adolescents, while EV-A71 infections are less common. Infection is continually acquired from early childhood to adolescent age.

Proteomic analysis of human brain microvascular endothelial cells reveals differential protein expression in response to enterovirus 71 infection

2D DIGE technology was employed on proteins prepared from human brain microvascular endothelial cells (HBMEC), to study the differentially expressed proteins in cells at 0 h, 1 h, 16 h, and 24 h after infection. Proteins found to be differentially expressed were identified with matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDITOF/TOF MS) analysis. We identified 43 spots showing changes of at least 2.5 fold up- or downregulated expressions in EV71-infected cells at different time when comparing to control, and 28 proteins could be successfully identified by MALDI TOF/TOF mass spectrometry analysis. 4 proteins were significantly upregulated, and 6 proteins were downregulated, another 18 proteins were different expression at different incubation time. We identified changes in the expression of 12 cellular metabolism-related proteins, 5 molecules involved in cytoskeleton, 3 molecules involved in energy metabolism, 2 molecules involved in signal transduction, 1 molecule involved in the ubiquitin-proteasome pathway, 1 molecule involved in cell cycle, 1 molecule involved in apoptosis-related protein, 1 molecular chaperone, and 2 unknown proteins. These findings build up a comprehensive profile of the HBMEC proteome and provide a useful basis for further analysis of the pathogenic mechanism that underlies EV71 infections to induce severe neural complications.

The role of Misshapen NCK-related kinase (MINK), a novel Ste20 family kinase, in the IRES-mediated protein translation of human enterovirus 71

Human Enterovirus 71 (EV71) commonly causes Hand, Foot and Mouth Disease in young children, and occasional occurrences of neurological complications can be fatal. In this study, a high-throughput cell-based screening on the serine/threonine kinase siRNA library was performed to identify potential antiviral agents against EV71 replication. Among the hits, Misshapen/NIKs-related kinase (MINK) was selected for detailed analysis due to its strong inhibitory profile and novelty. In the investigation of the stage at which MINK is involved in EV71 replication, virus RNA transfection in MINK siRNA-treated cells continued to cause virus inhibition despite bypassing the normal entry pathway, suggesting its involvement at the post-entry stage. We have also shown that viral RNA and protein expression level was significantly reduced upon MINK silencing, suggesting its involvement in viral protein synthesis which feeds into viral RNA replication process. Through proteomic analysis and infection inhibition assay, we found that the activation of MINK was triggered by early replication events, instead of the binding and entry of the virus. Proteomic analysis on the activation profile of p38 Mitogen-activated Protein Kinase (MAPK) indicated that the phosphorylation of p38 MAPK was stimulated by EV71 infection upon MINK activation. Luciferase reporter assay further revealed that the translation efficiency of the EV71 internal ribosomal entry site (IRES) was reduced after blocking the MINK/p38 MAPK pathway. Further investigation on the effect of MINK silencing on heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) localisation demonstrated that cytoplasmic relocalisation of hnRNP A1 upon EV71 infection may be facilitated via the MINK/p38 MAPK pathway which then positively regulates the translation of viral RNA transcripts. These novel findings hence suggest that MINK plays a functional role in the IRES-mediated translation of EV71 viral RNA and may provide a potential target for the development of specific antiviral strategies against EV71 infection.

Comparative epidemiology and virology of fatal and nonfatal cases of hand, foot and mouth disease in mainland China from 2008 to 2014

This study aimed to analyze the epidemiology and virology of fatal and nonfatal hand, foot, and mouth disease (HFMD) cases in Mainland China. A total of 10,714,237 survivors and 3046 deaths were reported from 2008 to 2014 June, with a case fatality rate of 0.03%. The morbidity of the survivors increased from 37.6/100,000 in 2008 to 139.6/100,000 in 2013 and peaked in 2012 at 166.8/100,000. However, the mortality varied around 0.03-0.04/100,000 across the time. Most of the survivors were distributed in the southern and eastern China, predominantly in the Guangxi and Hainan Province, whereas deaths were dominant in southern (Guangxi) and southwestern (Guizhou) China. The two groups showed similar seasonal fluctuations from 2008 to 2014, peaking in spring and early summer. Of the total cases, 93.97% were children less than 5 years of age, with those ≤ 2 years old accounting for 60.08% versus 84.02% in the survivor and death groups, respectively. Boys were at higher risk of infection than girls in both groups. Five years of virological surveillance showed that 43.73%, 22.04%, and 34.22% of HFMD cases were due to EV71, CoxA16 and other enteroviruses, respectively. EV71 was encountered in most deaths, with no substantial effect of age, gender, month, and year on incidence. Subgenotype C4a was the prevalent EV71 strain in Mainland China, with no significant difference in the VP1 gene related to virulence between the two groups. In conclusion, based on the largest population study, fatal and nonfatal HFMD cases, mainly caused by C4a of EV71, are circulating in Mainland China with a low-cause fatality rate.

Inhibition of enterovirus 71 by adenosine analog NITD008

Enterovirus 71 (EV71) is a major viral pathogen in China and Southeast Asia. There is no clinically approved vaccine or antiviral therapy for EV71 infection. NITD008, an adenosine analog, is an inhibitor of flavivirus that blocks viral RNA synthesis. Here we report that NITD008 has potent antiviral activity against EV71. In cell culture, the compound inhibits EV71 at a 50% effective concentration of 0.67 μM and a 50% cytotoxic concentration of 119.97 μM. When administered at 5 mg/kg in an EV71 mouse model, the compound reduced viral loads in various organs and completely prevented clinical symptoms and death. To study the antiviral mechanism and drug resistance, we selected escape mutant viruses by culturing EV71 with increasing concentrations of NITD008. Resistance mutations were reproducibly mapped to the viral 3A and 3D polymerase regions. Resistance analysis with recombinant viruses demonstrated that either a 3A or a 3D mutation alone could lead to resistance to NITD008. A combination of both 3A and 3D mutations conferred higher resistance, suggesting a collaborative interplay between the 3A and 3D proteins during viral replication. The resistance results underline the importance of combination therapy required for EV71 treatment. Importance: Human enterovirus 71 (EV71) has emerged as a major cause of viral encephalitis in children worldwide, especially in the Asia-Pacific region. Vaccines and antivirals are urgently needed to prevent and treat EV71 infections. In this study, we report the in vitro and in vivo efficacy of NITD008 (an adenosine analog) as an inhibitor of EV71. The efficacy results validated the potential of nucleoside analogs as antiviral drugs for EV71 infections. Mechanistically, we showed that mutations in the viral 3A and 3D polymerases alone or in combination could confer resistance to NITD008. The resistance results suggest an intrinsic interaction between viral proteins 3A and 3D during replication, as well as the importance of combination therapy for the treatment of EV71 infections.

Molecular epidemiology of enterovirus 71 strains isolated from children in Yamagata, Japan, between 1990 and 2013

Enterovirus 71 infections have become a major public issue in the Asia-Pacific region due to the large number of fatal cases. To clarify the longitudinal molecular epidemiology of enterovirus 71 (EV71) in a community, we isolated 240 strains from children, mainly with hand-foot-and-mouth diseases, between 1990 and 2013 in Yamagata, Japan. We carried out a sequence analysis of the VP1 region (891 bp) using 223 isolates and identified six subgenogroups (B2, B4, B5, C1, C2 and C4) during the study period. Subgenogroups C1 and B2 were found only between 1990 and 1993 and have not reappeared since. In contrast, strains in subgenogroups C2, C4 and B5 appeared repeatedly with genomic variations. Recent reports from several local communities in Japan have suggested that identical predominant subgenogroup strains, which have also been found in the Asia-Pacific region, have been circulating in a wide area in Japan. However, it is likely that there is a discrepancy between the major subgenogroups circulating in the Asia-Pacific region and those in Europe. It is necessary to continue the analysis of the longitudinal epidemiology of EV71 in local communities, as well as on regional and global levels, to develop strategies against severe EV71 infections.

A novel universal neutralizing monoclonal antibody against enterovirus 71 that targets the highly conserved "knob" region of VP3 protein

Hand, foot and mouth disease caused by enterovirus 71(EV71) leads to the majority of neurological complications and death in young children. While putative inactivated vaccines are only now undergoing clinical trials, no specific treatment options exist yet. Ideally, EV71 specific intravenous immunoglobulins could be developed for targeted treatment of severe cases. To date, only a single universally neutralizing monoclonal antibody against a conserved linear epitope of VP1 has been identified. Other enteroviruses have been shown to possess major conformational neutralizing epitopes on both the VP2 and VP3 capsid proteins. Hence, we attempted to isolate such neutralizing antibodies against conformational epitopes for their potential in the treatment of infection as well as differential diagnosis and vaccine optimization. Here we describe a universal neutralizing monoclonal antibody that recognizes a conserved conformational epitope of EV71 which was mapped using escape mutants. Eight escape mutants from different subgenogroups (A, B2, B4, C2, C4) were rescued; they harbored three essential mutations either at amino acid positions 59, 62 or 67 of the VP3 protein which are all situated in the “knob” region. The escape mutant phenotype could be mimicked by incorporating these mutations into reverse genetically engineered viruses showing that P59L, A62D, A62P and E67D abolish both monoclonal antibody binding and neutralization activity. This is the first conformational neutralization epitope mapped on VP3 for EV71.

Over the last decade, EV71 has emerged as a major cause of severe hand, foot and mouth disease in the Asia-Pacific region, occasionally leading to fatal brain stem encephalitis in young children. The rapid progression and high mortality of severe EV71 infection makes it vital to identify neutralization epitopes and putative therapeutic monoclonal antibodies. In this study we mapped the first conformational neutralization epitope on the VP3 protein of EV71. This epitope was confirmed by introducing the mutations into reverse genetically engineered viruses which abolished neutralization with monoclonal antibody (mAb)10D3. The importance of this novel neutralization epitope lies in the optimization of putative EV71 vaccines because the VP3 knob could be incorporated together with VP1 into a bivalent subunit vaccine. Further, the universal recognition of a conserved site on EV71 VP3 and not CVA16 makes mAb 10D3 a valuable tool for differential diagnosis of hand, foot and mouth disease. An additional hope is that mAb 10D3 could be used as a therapeutic intravenous immunoglobulin (IVIG).

An atypical winter outbreak of hand, foot, and mouth disease associated with human enterovirus 71, 2010

BACKGROUND

To analyze the epidemiological characteristics and pathogenic molecular characteristics of an hand, foot, and mouth disease (HFMD) outbreak caused by enterovirus 71 in Linyi City, Shandong Province, China during November 30 to December 28, 2010.

METHODS

One hundred and seventy three stool specimens and 40 throat samples were collected from 173 hospitalized cases. Epidemiologic and clinical investigations, laboratory testing, and genetic analyses were performed to identify the causal pathogen of the outbreak.

RESULTS

Among the 173 cases reported in December 2010, the male-female ratio was 1.88: 1; 23 cases (13.3%) were severe. The majority of patients were children aged < 5 years (95.4%). Some patients developed respiratory symptoms including runny nose (38.2%), cough (20.2%), and sore throat (14.5%). One hundred and thirty eight EV71 positive cases were identified based on real time reverse-transcription PCR detection and 107 isolates were sequenced with the VP1 region. Phylogenetic analysis of full-length VP1 sequences of 107 Linyi EV71 isolates showed that they belonged to the C4a cluster of the C4 subgenotype and were divided into 3 lineages (Lineage I, II and III). The two amino acid substitutions (Gly and Gln for Glu) at position 145 within the VP1 region are more likely to appear in EV71 isolates from severe cases (52.2%) than those recovered from mild cases (8.3%).

CONCLUSION

This outbreak of HMFD was caused by EV71 in an atypical winter. EV71 strains associated with this outbreak represented three separate chains of transmission. Substitution at amino acid position 145 of the VP1 region of EV71 might be an important virulence marker for severe cases. These findings suggest that continued surveillance for EV71 variants has the potential to greatly impact HFMD prevention and control.

Phenotypic and genomic characterization of human coxsackievirus A16 strains with distinct virulence in mice

Human coxsackievirus A16 (CA16) infection results in hand, foot, and mouth disease (HFMD) along with other severe neurological diseases in children and poses an important public health threat in Asian countries. During an HFMD epidemic in 2009 in Guangdong, China, two CA16 strains (GD09/119 and GD09/24) were isolated and characterized. Although both strains were similar in plaque morphology and growth properties in vitro, the two isolates exhibited distinct pathogenicity in neonatal mice upon intraperitoneal or intracranial injection. Complete genome sequences of both CA16 strains were determined, and the possible virulence determinants were analyzed and predicted. Phylogenetic analysis revealed that these CA16 isolates from Guangdong belonged to the B1b genotype and were closely related to other recent CA16 strains isolated in mainland China. Similarity and bootscanning analyses of these CA16 strains detected homologous recombination with the EV71 prototype strain BrCr in the non-structural gene regions and the 3'-untranslated regions. Together, the phenotypic and genomic characterizations of the two clinical CA16 isolates circulating in China were compared in detail, and the potential amino acid residues responsible for CA16 virulence in mice were predicted. These findings will help explain the evolutionary relationship of the CA16 strains circulating in China, warranting future studies investigating enterovirus virulence.

Picornavirus and enterovirus diversity with associated human diseases

Members of the Picornaviridae family are non-enveloped, positive-stranded RNA viruses with a 30nm icosahedral capsid. This virus family exhibits a considerable amount of genetic variability driven both by mutation and recombination. Recently, three previously unknown human picornaviruses, namely the human Saffold cardiovirus, cosavirus and salivirus, have been identified in stools or respiratory samples from subjects presenting symptoms ranging from gastroenteritis to acute flaccid paralysis. However, these viruses were also frequently detected in asymptomatic subjects and their clinical relevance remains to be elucidated. The Enterovirus genus is a prototype example of the Picornaviridae heterogeneity at both genetic and phenotypic levels. This genus is divided into 10 species, seven of which contain human viruses, including three Rhinovirus species. Both human rhino- and enteroviruses are also characterized by high levels of genetic variability, as exemplified by the existence of over 250 different serotypes and the recent discovery of new enterovirus genotypes and the Rhinovirus C species. Despite their common genomic features, rhinoviruses are restricted to the respiratory tract, whereas the vast majority of enteroviruses infect the gastrointestinal tract and can spread to other organs, such as the heart or the central nervous system. Understanding the genetic determinants of such phenotypic diversity is an important challenge and a field for future investigation. Better characterization of these ubiquitous human pathogens may help to develop vaccines or antiviral treatments and to monitor the emergence of new strains.

Virological investigation of hand, foot, and mouth disease in a tertiary care center in South India

Context:

Hand, foot, and mouth disease (HFMD) remains a common problem in India, yet its etiology is largely unknown as diagnosis is based on clinical characteristics. There are very few laboratory-based molecular studies on HFMD outbreaks.

Aim:

The aim of this study was to characterize HFMD-related isolates by molecular techniques.

Settings and Design:

Between 2005 and 2008, during two documented HFMD outbreaks, 30 suspected HFMD cases presented at the Outpatient Unit of the Department of Dermatology, Christian Medical College (CMC), Vellore. Seventy-eight clinical specimens (swabs from throat, mouth, rectum, anus, buttocks, tongue, forearm, sole, and foot) were received from these patients at the Department of Clinical Virology, CMC, for routine diagnosis of hand, foot, and mouth disease.

Materials and Methods:

Samples from these patients were cultured in Vero and rhabdomyosarcoma (RD) cell lines. Isolates producing enterovirus-like cytopathogenic effect (CPE) in cell culture were identified by a nested reverse transcription–based polymerase chain reaction (RT-PCR) and sequenced. The nucleotide sequences were analyzed using the BioEdit sequence program. Homology searches were performed using the Basic Local Alignment Search Tool (BLAST) algorithm.

Statistical Analysis used:

The statistical analysis was performed using Epi Info version 6.04b and Microsoft Excel 2002 (Microsoft Office XP).

Results:

Of the 30 suspected HFMD cases, only 17 (57%) were laboratory confirmed and Coxsackievirus A16 (CVA16) was identified as the etiological agent in all these cases.

Conclusions:

Coxsackievirus A16 (CVA16) was identified as the virus that caused the HFMD outbreaks in Vellore between 2005 and 2008. Early confirmation of HFMD helps to initiate control measures to interrupt virus transmission. In the laboratory, classical diagnostic methods, culture and serological tests are being replaced by molecular techniques. Routine surveillance systems will help understand the epidemiology of HFMD in India.

Identification of site-specific adaptations conferring increased neural cell tropism during human enterovirus 71 infection

Enterovirus 71 (EV71) is one of the most virulent enteroviruses, but the specific molecular features that enhance its ability to disseminate in humans remain unknown. We analyzed the genomic features of EV71 in an immunocompromised host with disseminated disease according to the different sites of infection. Comparison of five full-length genomes sequenced directly from respiratory, gastrointestinal, nervous system, and blood specimens revealed three nucleotide changes that occurred within a five-day period: a non-conservative amino acid change in VP1 located within the BC loop (L97R), a region considered as an immunogenic site and possibly important in poliovirus host adaptation; a conservative amino acid substitution in protein 2B (A38V); and a silent mutation in protein 3D (L175). Infectious clones were constructed using both BrCr (lineage A) and the clinical strain (lineage C) backgrounds containing either one or both non-synonymous mutations. In vitro cell tropism and competition assays revealed that the VP1₉₇ Leu to Arg substitution within the BC loop conferred a replicative advantage in SH-SY5Y cells of neuroblastoma origin. Interestingly, this mutation was frequently associated in vitro with a second non-conservative mutation (E167G or E167A) in the VP1 EF loop in neuroblastoma cells. Comparative models of these EV71 VP1 variants were built to determine how the substitutions might affect VP1 structure and/or interactions with host cells and suggest that, while no significant structural changes were observed, the substitutions may alter interactions with host cell receptors. Taken together, our results show that the VP1 BC loop region of EV71 plays a critical role in cell tropism independent of EV71 lineage and, thus, may have contributed to dissemination and neurotropism in the immunocompromised patient.

Fisetin and rutin as 3C protease inhibitors of enterovirus A71

Enterovirus A71 (EV-A71) causes severe complications: encephalitis, pulmonary edema, and death. No effective drug has been approved for clinical use. This study investigated the antiviral effects of flavonoids against EV-A71. An in vitro inhibitor screening assay using recombinant EV-A71 3C protease (3Cpro) demonstrated fisetin and rutin inhibiting 3Cpro enzymatic activity in a dose-dependent manner. Cell-based fluorescence resonance energy transfer (FRET) assay with an EV-A71 3Cpro cleavage motif probe also confirmed that fisetin and rutin inhibited the replication of EV-A71 in cells. A virus replication assay indicated that fisetin and rutin reduced significantly the EV-A71-induced cytopathic effect and viral plaque titers in RD cells culture. The IC(50) values of plaque reduction against EV-A71 were 85 μM for fisetin and 110 μM for rutin. Therapeutic indices (CC50/IC50 of plaque reduction assays) of fisetin and rutin exceeded 10. The study suggests that fisetin and rutin inhibit the replication of EV-A71.

The association of recombination events in the founding and emergence of subgenogroup evolutionary lineages of human enterovirus 71

Enterovirus 71 (EV71) is responsible for frequent large-scale outbreaks of hand, foot, and mouth disease worldwide and represent a major etiological agent of severe, sometimes fatal neurological disease. EV71 variants have been classified into three genogroups (GgA, GgB, and GgC), and the latter two are further subdivided into subgenogroups B1 to B5 and C1 to C5. To investigate the dual roles of recombination and evolution in the epidemiology and transmission of EV71 worldwide, we performed a large-scale genetic analysis of isolates (n = 308) collected from 19 countries worldwide over a 40-year period. A series of recombination events occurred over this period, which have been identified through incongruities in sequence grouping between the VP1 and 3Dpol regions. Eleven 3Dpol clades were identified, each specific to EV71 and associated with specific subgenogroups but interspersed phylogenetically with clades of coxsackievirus A16 and other EV species A serotypes. The likelihood of recombination increased with VP1 sequence divergence; mean half-lives for EV71 recombinant forms (RFs) of 6 and 9 years for GgB and GgC overlapped with those observed for the EV-B serotypes, echovirus 9 (E9), E30, and E11, respectively (1.3 to 9.8 years). Furthermore, within genogroups, sporadic recombination events occurred, such as the linkage of two B4 variants to RF-W instead of RF-A and of two C4 variants to RF-H. Intriguingly, recombination events occurred as a founding event of most subgenogroups immediately preceding their lineage expansion and global emergence. The possibility that recombination contributed to their subsequent spread through improved fitness requires further biological and immunological characterization.

A non-mouse-adapted enterovirus 71 (EV71) strain exhibits neurotropism, causing neurological manifestations in a novel mouse model of EV71 infection

Enterovirus 71 (EV71) is a neurotropic pathogen that has been consistently associated with the severe neurological forms of hand, foot, and mouth disease. The lack of a relevant animal model has hampered our understanding of EV71 pathogenesis, in particular the route and mode of viral dissemination. It has also hindered the development of effective prophylactic and therapeutic approaches, making EV71 one of the most pressing public health concerns in Southeast Asia. Here we report a novel mouse model of EV71 infection. We demonstrate that 2-week-old and younger immunodeficient AG129 mice, which lack type I and II interferon receptors, are susceptible to infection with a non-mouse-adapted EV71 strain via both the intraperitoneal (i.p.) and oral routes of inoculation. The infected mice displayed progressive limb paralysis prior to death. The dissemination of the virus was dependent on the route of inoculation but eventually resulted in virus accumulation in the central nervous systems of both animal groups, indicating a clear neurotropism of the virus. Histopathological examination revealed massive damage in the limb muscles, brainstem, and anterior horn areas. However, the minute amount of infectious viral particles in the limbs from orally infected animals argues against a direct viral cytopathic effect in this tissue and suggests that limb paralysis is a consequence of EV71 neuroinvasion. Together, our observations support that young AG129 mice display polio-like neuropathogenesis upon infection with a non-mouse-adapted EV71 strain, making this mouse model relevant for EV71 pathogenesis studies and an attractive platform for EV71 vaccine and drug testing.

Molecular analysis of virulent determinants of enterovirus 71

Enterovirus 71 (EV71) is the most important causative agent of hand, foot and mouth disease (HFMD) in children. In most cases, it is a self-limiting illness. However some EV71 infectious cases can develop severe clinical outcomes, such as encephalitis, meningitis, poliomyelitis like paralysis, and even death. To identify the determinants of virulence, the deduced amino acid sequence of polyprotein and nucleotide sequence of 5′-NTR and 3′-NTR in 25 SC-EV71 strains (strains from severe cases) and 31 MC-EV71 strains (strains from mild cases) were analyzed. Results showed four amino acids on two positions (Gly^P710/Gln^P710/Arg^P710 and Glu^P729) on the DE and EF loop of VP1, one (Lys^P930) on the surface of protease 2A and four nucleotides on three positions (G^P272, U^P488 and A^P700/U^P700) in the 5'-NTR region are associated with EV71 virulent phenotype. Predicted secondary structure of RNA using the consensus sequence of 5'-NTR by RNAStructure showed the mutation of nucleotide at position 488 in strain BJ08-Z004-3 (position 491 in prototype strain BrCr) can result in the discrepancy of an additional pair of nucleotides and thus change the stability of the second structure of IRES. Fragment base content analysis showed that in the region 696 to 714 bp at the 5'-NTR, where the A^P700/U^P700 was located, the nucleotide constitution ratios differed significantly between SC-EV71 and MC-EV71 strains. In conclusion, comparative genomic analysis showed that virulence of EV71 strains are mainly determined by the amino acids on two positions of VP1, one position of protease 2A and the nucleotides on three positions in 5'-NTR.

The changing seroepidemiology of enterovirus 71 infection among children and adolescents in Singapore

BACKGROUND

Enterovirus 71 (EV71) has caused recurrent epidemics of hand, foot and mouth disease among children in Singapore. Between August 2008 and July 2010, we conducted a survey to estimate the seroprevalence of EV71 infection among children and adolescents aged 1-17 years. We compared our EV71 seroepidemiologic findings with a previous study conducted in 1996-1997.

METHODS

The survey involved the prospective collection of 1,200 residual sera from Singapore residents aged 1-17 years in two hospitals. Neutralizing antibodies to EV71 were detected by the microneutralization test. The geometric mean titer (GMT) of EV71 antibodies and 95% confidence intervals (CI) were calculated and compared by age groups. Statistical significance was taken as P < 0.05.

RESULTS

The overall EV71 antibody prevalence was 26.9% (95% CI: 24.5-29.5%). It increased significantly from 14.3% in children aged 1-6 years to 27.8% in those aged 7-12 years, and reached 38.8% in adolescents aged 13-17 years. The seroconversion rate differed by about 12% between the consecutive age groups. The GMT of EV71 antibodies was higher among primary school children aged 7-12 years in our study than that among the 6-12 year age group in the 1996-1997 study.

CONCLUSIONS

Higher antibody titers were observed in children aged 1-6 years than those in the other two age groups, indicating that most of the infections had been acquired during early childhood. EV71 infection is common among children and adolescents in Singapore, with 39% infected by the time they are in secondary school (13-17 years of age).

Genus-specific substitution rate variability among picornaviruses

Picornaviruses have some of the highest nucleotide substitution rates among viruses, but there have been no comparisons of evolutionary rates within this broad family. We combined our own Bayesian coalescent analyses of VP1 regions from four picornaviruses with 22 published VP1 rates to produce the first within-family meta-analysis of viral evolutionary rates. Similarly, we compared our rate estimates for the RNA polymerase 3D(pol) gene from five viruses to four published 3D(pol) rates. Both a structural and a nonstructural gene show that enteroviruses are evolving, on average, a half order of magnitude faster than members of other genera within the Picornaviridae family.

A mouse muscle-adapted enterovirus 71 strain with increased virulence in mice

Enterovirus 71 (EV71) infections can usually cause epidemic hand, foot, and mouth disease (HFMD), and occasionally lead to aseptic meningitis, encephalitis, and polio-like illness. Skeletal muscles have been thought to be crucial for the pathogenesis of EV71-related diseases. However, little is known about the virulence of mouse muscle-adapted EV71. The EV71 0805 were subjected to four passages in the mouse muscle to generate a mouse-adapted EV71 strain of 0805a. In comparison with the parental EV71 0805, the mouse muscle-adapted EV71 0805a displayed stronger cytotoxicity against Rhabdomyosarcoma (RD) cells and more efficient replication in RD cells. Furthermore, infection with the EV71 0805a significantly inhibited the gain of body weight, accompanied by increased muscle virus load and multiple tissue distribution in the infected mouse. Histological examinations indicated that infection with the EV71 0805 did not cause obvious pathogenic lesions in mice, while infection with the muscle-adapted 0805a resulted in severe necrotizing myositis in the skeletal and cardio muscles, and intestinitis in mice on day 5 post infection. Further analysis revealed many mutations in different regions of the genome of mouse muscle-adapted virus. Collectively, these data demonstrated the mouse muscle-adapted EV71 0805a with increased virulence in mice.

Sustained high levels of interleukin-6 contribute to the pathogenesis of enterovirus 71 in a neonate mouse model

Enterovirus 71 (EV71) is the major causative agent of hand, foot, and mouth disease (HFMD) in young children and has been consistently associated with the most severe complications of the disease, including central nervous system inflammation and pulmonary edema. Increasing frequency and amplitude of EV71 outbreaks have raised awareness and concerns worldwide. Previous reports proposed that overwhelming virus replication combined with the induction of massive proinflammatory cytokines is responsible for the pathogenicity of EV71. Specifically, elevated interleukin-6 (IL-6) levels were observed consistently in patients and strongly correlated with disease severity. In this study, we show in the neonate mouse model that sustained high levels of IL-6 produced upon EV71 infection lead to severe tissue damage and eventually death of the animals. Administration of anti-IL-6 neutralizing antibodies after the onset of the clinical symptoms successfully improved the survival rates and clinical scores of the infected hosts. Compared to untreated infected controls, anti-IL-6-treated mice displayed reduced tissue damage, absence of splenic atrophy, and increased immune cell activation. In addition, markedly elevated systemic levels of IL-10 were measured in the protected animals. Furthermore, there was no significant difference in virus titers between anti-IL-6-treated mice and untreated mice, indicating that the anti-IL-6 antibody-mediated protection is independent of the virus load. Our findings thus demonstrate that IL-6 plays a major role in EV71-induced immunopathogenesis. As there is still neither vaccine nor treatment available against EV71, anti-IL-6 antibody treatment represents a potential therapeutic approach to providing protection from the most severe complications of the disease.

Virology, epidemiology, pathogenesis, and control of enterovirus 71

First isolated in California, USA, in 1969, enterovirus 71 (EV71) is a major public health issue across the Asia-Pacific region and beyond. The virus, which is closely related to polioviruses, mostly affects children and causes hand, foot, and mouth disease with neurological and systemic complications. Specific receptors for this virus are found on white blood cells, cells in the respiratory and gastrointestinal tract, and dendritic cells. Being an RNA virus, EV71 lacks a proofreading mechanism and is evolving rapidly, with new outbreaks occurring across Asia in regular cycles, and virus gene subgroups seem to differ in clinical epidemiological properties. The pathogenesis of the severe cardiopulmonary manifestations and the relative contributions of neurogenic pulmonary oedema, cardiac dysfunction, increased vascular permeability, and cytokine storm are controversial. Public health interventions to control outbreaks involve social distancing measures, but their effectiveness has not been fully assessed. Vaccines being developed include inactivated whole-virus, live attenuated, subviral particle, and DNA vaccines.

The largest outbreak of hand; foot and mouth disease in Singapore in 2008: the role of enterovirus 71 and coxsackievirus A strains

BACKGROUND

During 2008, Singapore experienced its largest ever outbreak of hand, foot and mouth disease (HFMD), resulting in 29686 cases, including four cases of encephalitis and one fatality.

METHODS

A total of 51 clinical specimens from 43 patients with suspected HFMD at the National University Hospital, Singapore were collected for virus isolation and identification by reverse transcription polymerase chain reaction (RT-PCR) and sequencing.

RESULTS

Enteroviruses were identified in 34 samples (66.7%), with 11 samples (21.6%) being positive for enterovirus 71 (EV71). Other non-EV71 enteroviruses (including coxsackievirus A4, A6, A10, and A16) were identified in 23 samples (45.1%). The most prevalent virus serotypes were CA6, CA10, and EV71. CA6 and CA10 accounted for 35.3% of all HFMD cases, which may explain the high transmissibility and low fatality that characterized this unprecedented epidemic associated with relatively mild disease. Phylogenetic analyses of 10 circulating EV71 strains indicated that they belonged to two subgenogroups, i.e., B5 (80%) and C2 (20%). The VP1 sequences of the 2008 EV71 strains also exhibited continuous mutations during the outbreak, reflecting the relatively high mutation rate of the EV71 capsid protein, which may have implications for future vaccine development.

CONCLUSIONS

A safe and effective vaccine against EV71 is certainly warranted in view of its potential neurovirulence and its role in HFMD epidemics of recurring frequency with resultant fatalities in Asia, as well as other parts of the world.

Recent advances in research on human enterovirus 71

Over the past decade, Human enterovirus (HEV)71 has emerged as a highly significant cause of viral encephalitis in the south-east Asian region. A pattern of increased epidemic activity has been observable since 1997, the cause of which is unclear. Ongoing investigations into the molecular basis of HEV71 infection and virulence, in particular viral translation and replication, have confirmed similarities between HEV71 and other enteroviruses, including the prototype species Poliovirus, but more work is required in this field. Although several putative receptors for HEV71 have been identified, it remains likely that other, as yet unidentified, receptors exist. Work in several established animal models for HEV71 infection has confirmed the protective efficacy of several inactivated vaccines. As more information emerges regarding the molecular processes involved in HEV71 infection, further advances may lead to the development of more effective antiviral treatments and, ultimately, a vaccine protection strategy.