A murine oral enterovirus 71 infection model with central nervous system involvement

Caboxamycin Inhibits Heart Inflammation in a Coxsackievirus B3-Induced Myocarditis Mouse Model

Coxsackievirus B3 (CVB3) is a positive single-strand RNA genome virus which belongs to the enterovirus genus in the picornavirus family, like poliovirus. It is one of the most prevalent pathogens that cause myocarditis and pancreatitis in humans. However, a suitable therapeutic medication and vaccination have yet to be discovered. Caboxamycin, a benzoxazole antibiotic isolated from the culture broth of the marine strain Streptomyces sp., SC0774, showed an antiviral effect in CVB3-infected HeLa cells and a CVB3-induced myocarditis mouse model. Caboxamycin substantially decreased CVB3 VP1 production and cleavage of translation factor eIF4G1 from CVB3 infection. Virus-positive and -negative strand RNA was dramatically reduced by caboxamycin treatment. In addition, the cleavage of the pro-apoptotic molecules BAD, BAX, and caspase3 was significantly inhibited by caboxamycin treatment. In animal experiments, the survival rate of mice was improved following caboxamycin treatment. Moreover, caboxamycin treatment significantly decreased myocardial damage and inflammatory cell infiltration. Our study showed that caboxamycin dramatically suppressed cardiac inflammation and mouse death. This result suggests that caboxamycin may be suitable as a potential antiviral drug for CVB3.

Experimental animal models for development of human enterovirus vaccine

Enterovirus infections induce infectious diseases in young children, such as hand, foot, and mouth disease which is characterized by highly contagious rashes or blisters around the hands, feet, buttocks, and mouth. This predominantly arises from enterovirus A71 or coxsackievirus A16 infections and in severe cases, they can lead to encephalitis, paralysis, pulmonary edema, or even fatality, representing a global health threat. Due to the absence of effective therapeutic strategies for these infections, various experimental animal models are being investigated for the development of vaccines. During the early stages of research on enterovirus infections, non-human primate infections exhibited symptoms like those in humans, leading to their utilization as model animals. However, due to economic and ethical considerations, their current usage is limited. While enterovirus infections do not readily occur in mice, an infection model with mouse-adapted strain in neonatal mice has been employed. Cellular receptors have been identified in human cells, and genetically modified mice expressing these receptors have been used. Most recently, the utilization of Mongolian gerbil model is actively being considered and should be pursued for further animal model development. So, herein, we provide a summarized overview of the current portfolio of available enterovirus infection models, emphasizing their respective advantages and limitations.

Research progress on pathogenic and therapeutic mechanisms of Enterovirus A71

In recent years, enterovirus A71 (EV-A71) infection has become a major global public health problem, especially for infants and young children. The results of epidemiological research show that EV-A71 infection can cause acute hand, foot, and mouth disease (HFMD) and complications of the nervous system in severe cases, including aseptic pediatric meningoencephalitis, acute flaccid paralysis, and even death. Many studies have demonstrated that EV-A71 infection may trigger a variety of intercellular and intracellular signaling pathways, which are interconnected to form a network that leads to the innate immune response, immune escape, inflammation, and apoptosis in the host. This article aims to provide an overview of the possible mechanisms underlying infection, signaling pathway activation, the immune response, immune evasion, apoptosis, and the inflammatory response caused by EV-A71 infection and an overview of potential therapeutic strategies against EV-A71 infection to better understand the pathogenesis of EV-A71 and to aid in the development of antiviral drugs and vaccines.

ML390 inhibits enterovirus 71 replication by targeting de novo pyrimidine biosynthesis pathway

Enterovirus 71 (EV71), a small, single-stranded, positive-sense RNA virus belonging to the enterovirus genus in the family Picornaviridae, causes hand, foot, and mouth disease. Although EV71 seriously threatens to public health, no effective antiviral drugs are available for treating this disease. In this study, we found that ML390, a dihydroorotate dehydrogenase inhibitor, has potential anti-EV71 activity. ML390 dose-dependently inhibited EV71 replication with IC₅₀ and selectivity index values of 0.06601 μM and 156.5, respectively. Supplementation with the downstream product orotate significantly suppressed the ability of ML390 to inhibit EV71 replication. Moreover, an adequate supply of exogenous uridine and cytosine suppressed the anti-EV71 activity of ML390. Thus, the antiviral activity of ML390 is mediated by the inhibition of the pyrimidine synthesis pathway. In an EV71-infected mouse model, ML390 reduced the load of EV71 in the brain, liver, heart, spleen, front legs, and hind legs, and significantly increased the survival rate of the mice infected by EV71. ML390 shows potential for the treatment of hand, foot, and mouth disease caused by EV71 infection.

Gasdermin E is required for induction of pyroptosis and severe disease during enterovirus 71 infection

Pyroptosis is an inflammatory form of programmed cell death that is executed by the gasdermin (GSDM)-N domain of GSDM family proteins, which form pores in the plasma membrane. Although pyroptosis acts as a host defense against invasive pathogen infection, its role in the pathogenesis of enterovirus 71 (EV71) infection is unclear. In the current study, we found that EV71 infection induces cleavage of GSDM E (GSDME) by using western blotting analysis, an essential step in the switch from caspase-3-mediated apoptosis to pyroptosis. We show that this cleavage is independent of the 3C and 2A proteases of EV71. However, caspase-3 activation is essential for this cleavage, as GSDME could not be cleaved in caspase-3-KO cells upon EV71 infection. Further analyses showed that EV71 infection induced pyroptosis in WT cells but not in caspase-3/GSDME double-KO cells. Importantly, GSDME is required to induce severe disease during EV71 infection, as GSDME deficiency in mice was shown to alleviate pathological symptoms. In conclusion, our results reveal that GSDME is important for the pathogenesis of EV71 via mediating initiation of pyroptosis.

A broad and potent IgM antibody against tetra-EV-As induced by EVA71 and CVA16 co-immunization

OBJECTIVE

To determine the potent and broad neutralizing monoclonal antibody (mAb) against enterovirus A (EV-A) in vitro and in vivo induced by enterovirus A71(EVA71) and coxsackievirus 16 (CVA16) co-immunization.

METHODS

The mAb was Generated by co-immunization with EVA71 and CVA16 through hybridomas technology. The characteristics and neutralizing ability of mAb were analysed in vitro and in mice.

RESULTS

We screened three mAb, the IgM antibody M20 and IgG antibody B1 and C31. All three antibodies showed cross-reactivity against tetra-EV-As. However, M20 showed potent and broad neutralizing ability against tetra-EV-As than B1 and C31. Meanwhile, M20 provided cross-antiviral efficacy in tetra-EV-As orally infected mice. Moreover, M20 binds to a conserved neutralizing epitope within the GH loop of tetra-EV-As VP1.

CONCLUSIONS

M20 and its property exhibited potent and broad antiviral activity against tetra-EV-As, and that is expected to be a potential preventive and therapeutic candidate against EV-As.

Muscle Tissue Damage and Recovery After EV71 Infection Correspond to Dynamic Macrophage Phenotypes

Enterovirus 71 (EV71) is a positive single-stranded RNA virus from the enterovirus genus of the Picornaviridae family. Most young children infected with EV71 develop mild symptoms of hand, foot and mouth disease, but some develop severe symptoms with neurological involvement. Limb paralysis from EV71 infection is presumed to arise mainly from dysfunction of motor neurons in the spinal cord. However, EV71 also targets and damages skeletal muscle, which may also contribute to the debilitating symptoms. In this study, we have delineated the impacts of EV71 infection on skeletal muscle using a mouse model. Mouse pups infected with EV71 developed limb paralysis, starting at day 3 post-infection and peaking at day 5-7 post-infection. At later times, mice recovered gradually but not completely. Notably, severe disease was associated with high levels of myositis accompanied by muscle calcification and persistent motor end plate abnormalities. Interestingly, macrophages exhibited a dynamic change in phenotype, with inflammatory macrophages (CD45⁺CD11b⁺Ly6C^hi) appearing in the early stage of infection and anti-inflammatory/restorative macrophages (CD45⁺CD11b⁺Ly6C^low/-) appearing in the late stage. The presence of inflammatory macrophages was associated with severe inflammation, while the restorative macrophages were associated with recovery. Altogether, we have demonstrated that EV71 infection causes myositis, muscle calcification and structural defects in motor end plates. Subsequent muscle regeneration is associated with a dynamic change in macrophage phenotype.

TLR7 Is Critical for Anti-Viral Humoral Immunity to EV71 Infection in the Spinal Cord

Enterovirus 71 (EV71) is a positive single-stranded RNA (ssRNA) virus from the enterovirus genus of Picornaviridae family and causes diseases ranged from the mild disease of hand, foot and mouth disease (HFMD) to the severe disease of neurological involvement in young children. TLR7 is an intracellular pattern recognition receptor (PRR) recognizing viral ssRNA. In this study, we investigated the role of TLR7 in EV71 infection in mouse pups (10-12 days old) and found that wild-type (WT) and TLR7 knock-out (TLR7KO) mice infected with EV71 showed similar limb paralysis at the onset and peak of the disease, comparable loss of motor neurons, and similar levels of antiviral molecules in the spinal cord. These results suggest that TLR7 is not the absolute PRR for EV71 in the spinal cord. Interestingly, TLR7KO mice infected with EV71 exhibited significantly delayed recovery from limb paralysis compared with WT mice. TLR7KO mice infected with EV71 showed significantly decreased levels of IgM and IgG2, important antibodies for antiviral humoral immunity. Furthermore, TLR7KO mice infected with EV71 showed a decrease of germinal center B cells in the spleen compared with WT mice. Altogether, our study suggests that TLR7 plays a critical role in anti-viral humoral immunity rather than in being a PRR in the spinal cord during EV71 infection in young mice.

Enterovirus 71 induces autophagy in mice via mTOR inhibition and ERK pathway activation

AIMS

Enterovirus 71 (EV71) is one of the main viruses that cause hand-foot-mouth disease; however, its pathogenic mechanism remains unclear. This study characterized the relationship between EV71 infection and autophagy in vivo and explored the molecular mechanism underlying EV71-induced autophagy.

MATERIALS AND METHODS

A mouse model of EV71 infection was prepared by intraperitoneally injecting one-day-old BALB/c suckling mice with 30 μL/g of EV71 virus stock solution for 3 days. The behavior, fur condition, weight, and mice mortality were monitored, and disease scores were calculated. The pathological damage to the brain, lung, and muscle tissues after the viral infection was assessed by hematoxylin and eosin staining. Western blot and immunofluorescence analyses were used to detect the expression levels of viral protein 1, Beclin-1, microtubule-associated protein light chain 3B, mammalian target of rapamycin (mTOR), phosphorylated (p)-mTOR, extracellular signal-regulated protein kinase (ERK) 1/2, and p-ERK.

KEY FINDINGS

EV71 infection can trigger autophagy in the brains, lungs, and muscles of infected mice. The autophagy response triggered by EV71 is achieved by the simultaneous mTOR inhibition and the ERK pathway activation. Blocking the mTOR pathway may aggravate autophagy, whereas ERK inhibition alleviates autophagy but cannot completely prevent it.

SIGNIFICANCE

EV71 infection can induce autophagy in mice, involving mTOR and ERK signaling pathways. These two signaling pathways are independent and do not interfere with each other.

Inhibition of Enterovirus A71 by a Novel 2-Phenyl-Benzimidazole Derivative

Enterovirus A71 (EV-A71) infection has emerged as a significant public health concern at the global level. Epidemic events of EV-A71 have been reported worldwide, and this succession of outbreaks has heightened concern that EV-A71 may become a public health threat. In recent years, widespread A71 enterovirus also occurred in European countries. EV-A71 infection causes hand-foot-mouth disease (HFMD), herpangina, and fever. However, it can sometimes induce a variety of neurological complications, including encephalitis, aseptic meningitis, pulmonary edema, and acute flaccid paralysis. We identified new benzimidazole derivatives and described theirin vitrocytotoxicity and broad-spectrum anti-enterovirus activity. Among them, derivative 2b resulted in interesting activity against EV-A71, and therefore it was selected for further investigations. Compound 2b proved to be able to protect cell monolayers from EV-A71-induced cytopathogenicity, with an EC₅₀ of 3 µM. Moreover, Vero-76 cells resulted in being significantly protected from necrosis and apoptosis when treated with 2b at 20 and 80 µM. Compound 2b reduced viral adsorption to Vero-76 cells, and when evaluated in a time-of-addition assay, the derivative had the highest effect when added during the infection period. Moreover, derivative 2b reduced viral penetration into host cells. Besides, 2b did not affect intestinal monolayers permeability, showing no toxic effects. A detailed insight into the efficacy of compound 2b against EV-A71 showed a dose-dependent reduction in the viral titer, also at low concentrations. Mechanism of action investigations suggested that our derivative can inhibit viral endocytosis by reducing viral attachment to and penetration into host cells. Pharmacokinetic and toxicity predictions validated compound 2b as a good candidate for furtherin vivoassays.

Amino acid substitutions in VP2, VP1, and 2C attenuate a Coxsackievirus A16 in mice

Coxsackievirus A16 (CVA16) is one of the major etiological agents of hand, foot and mouth disease (HFMD), a common acute infectious disease affecting infants and young children. Severe symptoms of the central nervous system may develop and even lead to death. Here, a plaque-purified CVA16 strain, L731-P1 (P1), was serially passaged in Vero cells for six times and passage 6 (P6) stock became highly attenuated in newborn mice. Genomic sequencing of the P1 and P6 revealed seven nucleotide substitutions at positions 1434 (C to U), 2744 (A to G), 2747 (A to G), 3161 (G to A), 3182 (A to G), 4968 (C to U), and 6064 (C to U). Six of these substitutions resulted in amino acid changes at VP2-T161 M, VP1-N102D, VP1-T103A, VP1-E241K, VP1-T248A, and 2C-S297F, respectively. P1-based infectious cDNA was generated to further investigate these virulent determinants. Independent reverse transcription-polymerase chain reaction (RT-PCR) amplifications for mutant constructions and plaque-purification of the P6 for isolation of variants were performed to determine dominant mutations and strains more related to attenuation. The virulent P1, attenuated P6, as well as a plaque purified strain (PP) and other four recombinant mutants, were inoculated into one-day-old BALB/c mice and the 50% lethal dose of each strain was determined. Comparison of virulence among these strains indicated that amino acid changes of VP1-N102D, VP1-E241K and 2C-S297F might be associated more closely with a high level attenuation of CVA16-L731-P6 than other mutations. Identification of novel residues associated with virulence may contribute to understanding of molecular basis of virulence of CVA16 and other enteroviruses.

A novel orally infected hamster model for Coxsackievirus A16 hand-foot-and-mouth disease and encephalomyelitis

Coxsackievirus A16 (CV-A16) is one of the major causes of mild and self-limiting hand-foot-and-mouth disease (HFMD) in young children, which may occasionally leads to serious neurological complications. In this study, we had developed a novel, consistent, orally infected CV-A16 HFMD hamster model with encephalomyelitis. Four groups of 7-day-old hamsters in a kinetic study were orally infected with mouse-adapted CV-A16 strains and sacrificed at 1-4 days post infection (dpi), respectively. Tissues were studied by light microscopy, immunohistochemistry to detect viral antigens, in situ hybridization to detect viral RNA, and by viral titration. In a separate transmission experiment, orally infected index hamsters were housed together with contact hamsters to investigate oral and fecal viral shedding by virus culture and reverse transcription polymerase chain reaction (RT-PCR). At severe infection/death endpoints, index and contact hamster infection were also histopathologically analyzed. In the kinetic study, infected hamsters developed signs of infection at 4 dpi. Viral antigens/RNA were localized to brainstem (medulla/pons; reticular formation and motor trigeminal nucleus) and spinal cord anterior horn neurons, oral squamous epithelia and epidermis from 3 to 4 dpi. Salivary and lacrimal glands, myocardium, brown adipose tissue, intestinal smooth muscle, and skeletal muscle infection was also demonstrated. Viremia at 1 dpi and increasing viral titers in various tissues were observed from 2 dpi. In the transmission study, all contact hamsters developed disease 3-5 days later than index hamsters, but demonstrated similar histopathological findings at endpoint. Viral culture and RT-PCR positive oral washes and feces confirmed viral shedding. Our hamster model, orally infected by the natural route for human infection, confirmed CV-A16 neurotropism and demonstrated squamous epitheliotropism reminiscent of HFMD, attributes not found in other animal models. It should be useful to investigate neuropathogenesis, model person-to-person transmission, and for testing antiviral drugs and vaccines.

A Mouse Model for Infection with Enterovirus A71 in Small Extracellular Vesicles

EV-A71 was supposed to infect the CNS through the neural pathway and the circulation of the blood in previous studies. Reverse axon transport had been confirmed as an important pathway for EV-A71 to infect the CNS; however, it is still unknown how EV-A71 infects the CNS through the circulation of the blood. Combined with the infectivity of sEVs secreted from EV-A71-infected cells and the characteristic that sEVs could cross the blood-brain barrier, we considered that sEVs may play a vital role in EV-A71 pathogenesis of the CNS.

Enterovirus A71 (EV-A71) is the major pathogen of hand, foot, and mouth disease (HFMD); in some severe cases, it could develop into central nervous system (CNS) disease such as aseptic meningitis, encephalitis, and neurogenic pulmonary edema in children under 5 years. The EV-A71 pathogenesis which is involved with the CNS is unclear due to the lack of a simple and reliable mouse model thus far. Most clinical EV-A71 isolates could not effectively infect the neonatal mouse, which used to be an EV-A71 infection model. The small extracellular vesicles (sEVs) released from clinical EV-A71 isolate-infected cells were infectious in cell lines and could cause a high viral replication in mice. Neonatal ICR mice were injected intraperitoneally with these infectious sEVs and showed more weight loss and higher mortality than those mice injected with the clinical EV-A71 isolate. By using these sEVs, we provided a simple and effective method by which we can generate a stable and valuable animal model for the studies of EV-A71 pathogenesis and therapy.

IMPORTANCE EV-A71 was supposed to infect the CNS through the neural pathway and the circulation of the blood in previous studies. Reverse axon transport had been confirmed as an important pathway for EV-A71 to infect the CNS; however, it is still unknown how EV-A71 infects the CNS through the circulation of the blood. Combined with the infectivity of sEVs secreted from EV-A71-infected cells and the characteristic that sEVs could cross the blood-brain barrier, we considered that sEVs may play a vital role in EV-A71 pathogenesis of the CNS.

Muscle destruction caused by coxsackievirus A10 in gerbils: Construction of a novel animal model for antiviral evaluation

The morbidity and mortality of coxsackievirus A10 (CVA10)-associated hand, foot, and mouth disease (HFMD) have been increasing in recent years, while few studies on the vaccine and animal model of CVA10 have been reported. Here, we first established a CVA10-infected gerbil model and employed it to evaluate the immunoprotective effect of an inactivated CVA10 vaccine. The results showed that gerbils up to the age of 14 days were fully susceptible to CVA10, and all died within five days post-infection by intraperitoneal inoculation. Lethargy, wasting, hind-limb paralysis, and even death could be observed in the CVA10-infected gerbils. Pathological examination suggested that CVA10 has a strong tropism toward muscle tissue, and muscle bundle fracture and muscular fibers necrosis were observed in the limb muscles. Additionally, active immunization results showed that gerbils immunized with the inactivated CVA10 vaccine were 100 % protected from lethal CVA10 challenge. The antisera from vaccinated gerbils also showed high neutralizing titers against CVA10. Based on these results, the CVA10-infected gerbil model was a suitable tool for analyzing the pathogenesis of CVA10 and assessing the protective efficacy of CVA10 candidate vaccines.

Coxsackievirus A16 in a 1-Day-Old Mouse Model of Central Nervous System Infection Shows Lower Neurovirulence than Enterovirus A71

Coxsackievirus A16 (CV-A16) and enterovirus A71 (EV-A71) are the major causes of hand, foot and mouth disease in young children. Although less so with CV-A16, both viruses are associated with serious neurological syndromes, but the differences between their central nervous system infections remain unclear. We conducted a comparative infection study using clinically-isolated CV-A16 and EV-A71 strains in a 1-day-old mouse model to better understand the neuropathology and neurovirulence of the viruses. New serotype-specific probes for in situ hybridization were developed and validated to detect CV-A16 and EV-A71 RNA in infected tissues. Demonstration of CV-A16 virus antigens/RNA, mainly in the brainstem and spinal cord neurons, confirmed neurovirulence, but showed lower densities than in EV-A71 infected animals. A higher lethal dose₅₀ for CV-A16 suggested that CV-A16 is less neurovirulent. Focal virus antigens/RNA in the anterior horn white matter and adjacent efferent motor nerves suggested that neuroinvasion is possibly via retrograde axonal transport in peripheral motor nerves.

Acarbose, as a potential drug, effectively blocked the dynamic metastasis of EV71 from the intestine to the whole body

Enterovirus 71 (EV71) is one of the main pathogens causing hand-foot-and-mouth disease (HFMD). The nose and mouth are usually the main infection entries of EV71 virus. However, its dynamic transport pathway from mouth to the whole body remains unknown. The reveal of this physiological mechanism in vivo will help to understand its transport direction, find its key proliferation nodes, and develop new preventive strategies. We trained a new strain of GFP-EV71 virus to be susceptible to mice brain by intracranial injection of mice. The adapted virus was oral-administrated to suckling mice. Then, the dynamic distributions of the virus in vivo were detected by living image system and fluorescence quantitation polymerase chain reaction (qPCR). We figured out the dynamic pathway of EV71 transport in vivo from intestine to peripheral tissue, then to the other organs. Small intestine was identified as a gateway for EV71 infection in vivo. Ileum was proved to be the main part of proliferation and transport of EV71 in small intestine of mice. EV71 was verified to enter small intestinal villus of mice through the infection of small intestinal epithelial cell. Acarbose displayed a good preventive effect on EV71 infection both in vivo and in vitro. Acarbose possibly decreased the intestinal infection of EV71 by blocking the receptor-binding sites on the surface of EV71 virion or by inhibiting various glycolic receptors on the cell surface. Thus, acarbose and its analogue may be the potential medicines to prevent EV71 infection.

Electrostatic interactions at the five-fold axis alter heparin-binding phenotype and drive enterovirus A71 virulence in mice

Enterovirus A71 (EV-A71) causes hand, foot and mouth disease epidemics with neurological complications and fatalities. However, the neuropathogenesis of EV-A71 remains poorly understood. In mice, adaptation and virulence determinants have been mapped to mutations at VP2-149, VP1-145 and VP1-244. We investigate how these amino acids alter heparin-binding phenotype and shapes EV-A71 virulence in one-day old mice. We constructed six viruses with varying residues at VP1-98, VP1-145 (which are both heparin-binding determinants) and VP2-149 (based on the wild type 149K/98E/145Q, termed KEQ) to generate KKQ, KKE, KEE, IEE and IEQ variants. We demonstrated that the weak heparin-binder IEE was highly lethal in mice. The initially strong heparin-binding IEQ variant acquired an additional mutation VP1-K244E, which confers weak heparin-binding phenotype resulting in elevated viremia and increased virus antigens in mice brain, with subsequent high virulence. IEE and IEQ-244E variants inoculated into mice disseminated efficiently and displayed high viremia. Increasing polymerase fidelity and impairing recombination of IEQ attenuated the virulence, suggesting the importance of population diversity in EV-A71 pathogenesis in vivo. Combining in silico docking and deep sequencing approaches, we inferred that virus population diversity is shaped by electrostatic interactions at the five-fold axis of the virus surface. Electrostatic surface charges facilitate virus adaptation by generating poor heparin-binding variants for better in vivo dissemination in mice, likely due to reduced adsorption to heparin-rich peripheral tissues, which ultimately results in increased neurovirulence. The dynamic switching between heparin-binding and weak heparin-binding phenotype in vivo explained the neurovirulence of EV-A71.

Enterovirus A71 (EV-A71) is the primary cause of hand, foot and mouth disease, and it can also infect the central nervous system and cause fatal outbreaks in young children. EV-A71 pathogenesis remains elusive. In this study, we demonstrated that EV-A71 variants with strong affinity to heparan sulfate (heparin) have a growth advantage in cell culture, but are disadvantaged in vivo. When inoculated into one-day old mice, strong heparin-binding virus variants are more likely to be adsorbed to peripheral tissues, resulting in impaired ability to disseminate, and are cleared from the bloodstream rapidly. The lower viremia level resulted in no neuroinvasion. In contrast, weak heparin-binding variants show greater levels of viremia, dissemination and subsequent neurovirulence in mice. We also provide evidence that the EV-A71 heparin-binding pattern is mediated by electrostatic surface charges on the virus capsid surface. In mice, EV-A71 undergoes adaptive mutation to acquire greater negative surface charges, thus generating new virulent variants with weak heparin-binding ability which allows greater viral spread. Our study underlines the importance of electrostatic surface charges in shaping EV-A71 virulence.

Construction and characterization of an infectious cDNA clone of coxsackievirus A 10

Background

Coxsackievirus A10 (CA10) constitutes one of the four major pathogens causing hand, foot and mouth disease in infants. Infectious clones are of great importance for studying viral gene functions and pathogenic mechanism. However, there is no report on the construction of CA10 infectious clones.

Methods

The whole genome of CA10 derived from a clinical isolate was amplified into two fragments and ligated into a linearized plasmid vector in one step by In-Fusion Cloning. The obtained CA10 cDNA clones and plasmids encoding T7 RNA polymerase were co-transfected into 293 T cells to rescue CA10 virus. The rescued virus was identified by SDS-PAGE, Western blotting and transmission electron microscopic. One-day-old ICR mice were intracerebrally inoculated with the CA10 virus and clinical symptoms were observed. Multiple tissues of moribund mice were harvested for analysis of pathogenic changes and viral distribution by using H&E staining, real-time PCR and immunohistochemical staining.

Results

CA10 viruses were rescued from the constructed cDNA clone and reached a maximum titer of 10^8.125TCID₅₀/mL after one generation in RD cells. The virus exhibited similar physical and chemical properties to those of the parental virus. It also showed high virulence and the ability to induce death of neonatal ICR mice. Severe necrotizing myositis, intestinal villus interstitial edema and severe alveolar shrinkage were observed in infected mice. The viral antigen and the maximum amount of viral RNA were detected in limb skeletal muscles, which suggested that the limb skeletal muscles were the most likely site of viral replication.

Conclusion

Infectious clones of CA10 were successfully constructed for the first time, which will facilitate the establishment of standardized neonatal mouse models infected with CA10 for the evaluation of vaccines and antiviral drugs, as well as preservation and sharing of model strains.

Enterovirus 71 targets the cardiopulmonary system in a robust oral infection mouse model

Severe infection with the re-emerging enterovirus 71 (EV71 or EV-A71) can cause cardiopulmonary failure. However, in patients' heart and lung, viral protein has not been detected. In mouse models, heart disease has not been reported. EV71-infected brainstem is generally believed to be responsible for the cardiopulmonary collapse. One major limitation in EV71 research is the lack of an efficient oral infection system using non-mouse-adapted clinical isolates. In a robust oral infection NOD/SCID mouse model, we detected EV71 protein at multiple organs, including heart and lung, in 100% of moribund mice with limb paralysis. Infiltrating leukocytes were always detected in heart and muscle, and VP1-positive M2 macrophages were abundant in the lung. Functional dissection on the pathogenesis mechanism revealed severe apoptosis, inflammatory cytokines, and abnormal electrocardiogram (EKG) in orally infected hearts. Therefore, cardiopulmonary disease could be one plausible cause of death in this mouse model. Inoculation of EV71 through an oral route resulted in viral infection in the intestine, viremia, and EV71 appeared to spread to peripheral tissues via blood circulation. Infectious virus was no longer detected in the blood on day 5 post-infection by the plaque formation assay. We demonstrated that both EV71 clinical isolate and cloned virus can target the cardiopulmonary system via a natural infection-like oral route.

An adult gerbil model for evaluating potential coxsackievirus A16 vaccine candidates

A suitable animal model of CVA16 infection is crucial in order to understand its pathogenesis and to help develop antiviral vaccines or screen therapeutic drugs. The neonatal mouse model has a short sensitivity period to CA16 infection, which is a major limitation. In this study, we demonstrate that adult (60-day-old) gerbils are susceptible to CVA16 infection at high doses (10^8.0 TCID₅₀). A clinical isolate strain of CVA16 was inoculated intraperitoneally into adult gerbils, which subsequently developed significant clinical symptoms, including hind limb weakness, paralysis of one or both hind limbs, tremors, and eventual death from neurological disorders. Real-time RT-PCR revealed that viral loads in the spinal cord and brainstem were higher than those in other organs/tissues. Histopathological changes, such as neuronal degeneration, neuronal loss, and neuronophagia, were observed in the spinal cord, brainstem, and heart muscle, along with necrotizing myositis. Gerbils receiving both prime and boost immunizations of alum adjuvant inactivated vaccine exhibited no clinical signs of disease or mortality following challenge by CVA16, whereas 80% of control animals showed obvious clinical signs, including slowness, paralysis of one or both hind limbs, and eventual death, suggesting that the CVA16 vaccine can fully protect gerbils against CVA16 challenge. These results demonstrate that an adult gerbil model provides us with a useful tool for studying the pathogenesis and evaluating antiviral reagents of CVA16 infection. The development of this animal model would also be conducive to screening promising CVA16 vaccine candidates as well as further vaccination evaluation.

Enteroviruses: A Gut-Wrenching Game of Entry, Detection, and Evasion

Enteroviruses are a major source of human disease, particularly in neonates and young children where infections can range from acute, self-limited febrile illness to meningitis, endocarditis, hepatitis, and acute flaccid myelitis. The enterovirus genus includes poliovirus, coxsackieviruses, echoviruses, enterovirus 71, and enterovirus D68. Enteroviruses primarily infect by the fecal–oral route and target the gastrointestinal epithelium early during their life cycles. In addition, spread via the respiratory tract is possible and some enteroviruses such as enterovirus D68 are preferentially spread via this route. Once internalized, enteroviruses are detected by intracellular proteins that recognize common viral features and trigger antiviral innate immune signaling. However, co-evolution of enteroviruses with humans has allowed them to develop strategies to evade detection or disrupt signaling. In this review, we will discuss how enteroviruses infect the gastrointestinal tract, the mechanisms by which cells detect enterovirus infections, and the strategies enteroviruses use to escape this detection.

An update on enterovirus 71 infection and interferon type I response

Enteroviruses are members of Pichornaviridae family consisting of human enterovirus group A, B, C, and D as well as nonhuman enteroviruses. Hand, foot, and mouth disease (HFMD) is a serious disease which is usually seen in the Asia-Pacific region in children. Enterovirus 71 and coxsackievirus A16 are two important viruses responsible for HFMD which are members of group A enterovirus. IFN α and β are two cytokines, which have a major activity in the innate immune system against viral infections. Most of the viruses have some weapons against these cytokines. EV71 has two main proteases called 2A and 3C, which are important for polyprotein processing and virus maturation. Several studies have indicated that they have a significant effect on different cellular pathways such as interferon production and signaling pathway. The aim of this study was to investigate the latest findings about the interaction of 2A and 3C protease of EV71 and IFN production/signaling pathway and their inhibitory effects on this pathway.

Toll-Like Receptor 3 Is Involved in Detection of Enterovirus A71 Infection and Targeted by Viral 2A Protease

Enterovirus A71 (EV-A71) has emerged as a major pathogen causing hand, foot, and mouth disease, as well as neurological disorders. The host immune response affects the outcomes of EV-A71 infection, leading to either resolution or disease progression. However, the mechanisms of how the mammalian innate immune system detects EV-A71 infection to elicit antiviral immunity remain elusive. Here, we report that the Toll-like receptor 3 (TLR3) is a key viral RNA sensor for sensing EV-A71 infection to trigger antiviral immunity. Expression of TLR3 in HEK293 cells enabled the cells to sense EV-A71 infection, leading to type I, IFN-mediated antiviral immunity. Viral double-stranded RNA derived from EV-A71 infection was a key ligand for TLR3 detection. Silencing of TLR3 in mouse and human primary immune cells impaired the activation of IFN-β upon EV-A71 infection, thus reinforcing the importance of the TLR3 pathway in defending against EV-A71 infection. Our results further demonstrated that TLR3 was a target of EV-A71 infection. EV-A71 protease 2A was implicated in the downregulation of TLR3. Together, our results not only demonstrate the importance of the TLR3 pathway in response to EV-A71 infection, but also reveal the involvement of EV-A71 protease 2A in subverting TLR3-mediated antiviral defenses.

Immunocompetent and Immunodeficient Mouse Models for Enterovirus 71 Pathogenesis and Therapy

Enterovirus 71 (EV71) is a global health threat. Children infected with EV71 could develop hand-foot-and-mouth disease (HFMD), encephalitis, paralysis, pulmonary edema, and death. At present, no effective treatment for EV71 is available. We reviewed here various mouse models for EV71 pathogenesis and therapy. Earlier studies relied on the use of mouse-adapted EV71 strains. To avoid artificial mutations arising de novo during the serial passages, recent studies used EV71 clinical isolates without adaptation. Several human receptors for EV71 were shown to facilitate viral entry in cell culture. However, in vivo infection with human SCARB2 receptor transgenic mice appeared to be more limited to certain strains and genotypes of EV71. Efficacy of oral infection in these transgenic models is extremely low. Intriguingly, despite the lack of human receptors, immunodeficient neonatal mouse models can still be infected with EV71 clinical isolates via oral or intraperitoneal routes. Crossbreeding between SCARB2 transgenic and stat1 knockout mice generated a more sensitive and user-friendly hybrid mouse model. Infected hybrid mice developed a higher incidence and earlier onset of CNS disease and death. Different pathogenesis profiles were observed in models deficient in various arms of innate or humoral immunity. These models are being actively used for antiviral research.

A neonatal mouse model of central nervous system infections caused by Coxsackievirus B5

As one of the key members of the coxsackievirus B group, coxsackievirus B5 (CV-B5) can cause many central nervous system diseases, such as viral encephalitis, aseptic meningitis, and acute flaccid paralysis. Notably, epidemiological data indicate that outbreaks of CV-B5-associated central nervous system (CNS) diseases have been reported worldwide throughout history. In this study, which was conducted to promote CV-B5 vaccine and anti-virus drug research, a 3-day-old BALB/c mouse model was established using a CV-B5 clinical isolate (CV-B5/JS417) as the challenge strain. Mice challenged with CV-B5/JS417 exhibited a series of neural clinical symptoms and death with necrosis of neuronal cells in the cerebral cortex and the entire spinal cord, hindlimb muscles, and cardiomyocytes. The viral load of each tissue at various post-challenge time points suggested that CV-B5 replicated in the small intestine and was subsequently transmitted to various organs via viremia; the virus potentially entered the brain through the spinal axons, causing neuronal cell necrosis. In addition, this mouse model was used to evaluate the protective effect of a CV-B5 vaccine. The results indicated that both the inactivated CV-B5 vaccine and anti-CVB5 serum significantly protected mice from a lethal infection of CV-B5/JS417 by producing neutralizing antibodies. In summary, the first CV-B5 neonatal mouse model has been established and can sustain CNS infections in a manner similar to that observed in humans. This model will be a useful tool for studies on pathogenesis, vaccines, and anti-viral drug evaluations.

Chinese guidelines for the diagnosis and treatment of hand, foot and mouth disease (2018 edition)

BACKGROUND

Hand, foot, and mouth disease (HFMD) is a common infectious disease in childhood caused by an enterovirus (EV), and which is principally seen in children under 5 years of age. To promote diagnostic awareness and effective treatments, to further standardize and strengthen the clinical management and to reduce the mortality of HFMD, the guidelines for diagnosis and treatment have been developed.

METHODS

National Health Commission of China assembled an expert committee for a revision of the guidelines. The committee included 33 members who are specialized in diagnosis and treatment of HFMD.

RESULTS

Early recognition of severe cases is utmost important in diagnosis and treatment of patients with HFMD. The key to diagnosis and treatment of severe cases lies in the timely and accurate recognition of stages 2 and 3 of HFMD, in order to stop progression to stage 4. Clinicians should particularly pay attention to those EV-A71 cases in children aged less than 3 years, and those with disease duration less than 3 days. The following indicators should alert the clinician of possible deterioration and impending critical disease: (1) persistent hyperthermia; (2) involvement of nervous system; (3) worsening respiratory rate and rhythm; (4) circulatory dysfunction; (5) elevated peripheral WBC count; (6) elevated blood glucose and (7) elevated blood lactic acid. For treatment, most mild cases can be treated as outpatients. Patients should be isolated to avoid cross-infection. Intense treatment modalities should be given for those severe cases.

CONCLUSION

The guidelines can provide systematic guidance on the diagnosis and management of HFMD.

Establishment and characterization of an oral gerbil model for a non-mouse-adapted enterovirus 71 strain

Enterovirus 71 (EV71) is one of the major pathogens causing hand, foot, and mouth disease (HFMD) with neurological and systemic complications worldwide, and it is mostly discovered in infants and young children. It is of great significance to establish suitable animal models of EV71 infection on research of distribution and pathogenesis of the virus. In this study, we established a successful infection of a non-mouse-adapted isolate of EV71 via oral route in 7-day-old Mongolian gerbil (Meriones unguiculatus), all of which were paralyzed and died within 10 days post infection. Analysis of virus loads in twelve tissues showed that virus was first detected in intestine, blood, heart, lung, and muscle one day post-infection, and then in the rest of the tissues/organs within the next few days, among which thymus, spleen, spinal cord and muscles had the highest virus titer at 5 days post infection. Pathological examination showed that severe necrosis was observed in skeletal muscle and spinal cord, and edema was observed in both heart and lung. Comparisons of host gene expression of various tissues from infected and non-infected gerbils revealed a general up-regulation of genes related to anti-viral response and a viral receptor gene (sialic acid-linked glycans), as well as a tissue(gut)-specific up-regulation of genes related to neuronal communication. Collectively, our results showed that EV71 could induce severe neurological complications as well as massive tissue damage all over the body, which indicates that oral infection of 7-day gerbils can be a suitable animal model to study the infection of EV71 in human.

Pyroptosis induced by enterovirus A71 infection in cultured human neuroblastoma cells

Enterovirus A71 (EV-A71) infection can cause hand, foot and mouth disease (HFMD), and even fatal meningoencephalitis. Unfortunately, there is currently no effective treatment for EV-A71 infection due to the lack of understanding of the mechanism of neurological diseases. In this study, we employed SH-SY5Y human neuroblastoma cells to explore the roles of caspase-1 in neuropathogenesis. The expression and activity of caspase-1 were analyzed. The potential immuneconsequences mediated by caspase-1 including cell death, lysis, DNA degradation, and secretion of pro-inflammatory were also examined. We found the gene expression levels of caspase-1, IL-1β, IL-18 and active caspase-1 were markedly increased in the SH-SY5Y cells at 48 h post EV-A71 infection. The cell death, lysis, and DNA degradation were also increased during infection, which could be significantly alleviated by caspase-1 inhibition. These observations provided additional experimental evidence supporting caspase-1-mediated pyroptosis as a novel pathway of inflammatory programmed cell death.

Factors associated with fatal outcome of children with enterovirus A71 infection: a case series

Enterovirus A-71 (EV-A71) may be fatal, but the natural history, symptoms, and signs are poorly understood. This study aimed to examine the natural history of fatal EV-A71 infection and to identify the symptoms and signs of early warning of deterioration. This was a clinical observational study of fatal cases of EV-A71 infection treated at five Chinese hospitals between 1 January 2010 and 31 December 2012. We recorded and analysed 91 manifestations of EV-A71 infection in order to identify early prognosis indicators. There were 54 fatal cases. Median age was 21.5 months (Q1−Q3: 12–36). The median duration from onset to death was 78.5 h (range, 6 to 432). The multilayer perceptron analysis showed that ataxia respiratory, ultrahyperpyrexia, excessive tachycardia, refractory shock, absent pharyngeal reflex, irregular respiratory rhythm, hyperventilation, deep coma, pulmonary oedema and/or haemorrhage, excessive hypertension, tachycardia, somnolence, CRT extension, fatigue or sleepiness and age were associated with death. Autopsy findings (n = 2) showed neuronal necrosis, softening, perivascular cuffing, colloid and neuronophagia phenomenon in the brainstem. The fatal cases of enterovirus A71 had neurologic involvement, even at the early stage. Direct virus invasion through the neural pathway and subsequent brainstem damage might explain the rapid progression to death.

Enterovirus A71 Proteins: Structure and Function

Enterovirus A71 (EV-A71) infection has grown to become a serious threat to global public health. It is one of the major causes of hand, foot, and mouth disease (HFMD) in infants and young children. EV-A71 can also infect the central nervous system (CNS) and induce diverse neurological complications, such as brainstem encephalitis, aseptic meningitis, and acute flaccid paralysis, or even death. Viral proteins play a crucial role in EV-A71 infection. Many recent studies have discussed the structure and function of EV-A71 proteins, and the findings reported will definitely aid the development of vaccines and therapeutic approaches. This article reviews the progress in the research on the structure and function of EV-A71 proteins. Available literature can provide a basis for studying the pathogenesis of EV-A71 infection in detail.

Neuro-Magnetic Resonance Imaging in Hand, Foot, and Mouth Disease: Finding in 412 Patients and Prognostic Features

Purpose

The aims of this study were to describe the neuroimaging findings in hand, foot, and mouth disease and determine those who may provide prognosis.

Material and Methods

Magnetic resonance imaging scans in 412 severe hand, foot, and mouth disease between 2009 and 2014 were retrospectively evaluated. The patients who had the neurological signs were followed for 6 months to 1 year. According to the good or poor prognosis, 2 groups were categorized. The incidence of lesions in different sites between the 2 groups was compared, and multivariate analysis was used to look for risk factors.

Results

The major sites of involvement for all patients with percentages were the medulla oblongata (16.1%), spinal anterior nerve roots (12.4%), thoracic segments (11.1%), brain or spinal meninges (8.3%), and so on. There were 347 patients (84.2%) with good prognosis and 65 (15.8%) with poor prognosis in the follow-up. There was a significantly higher rate of lesions involving the cerebral white substance, thalamus, medulla oblongata, pons, midbrain, and spinal cord in the group with poor prognosis. Multivariate analysis showed 2 independent risk factors associated with poor prognosis: lesions located in the medulla oblongata (P < 0.015) and spinal cord (P < 0.001) on magnetic resonance imaging; the latter was the most significant prognostic factor (odds ratio, 29.11; P < 0.001).

Conclusions

We found that the distribution patterns for all patients mainly involved the medulla oblongata, spinal anterior nerve roots, thoracic segments, and brain or spinal meninges. Our findings suggested that patients with lesions located in the medulla oblongata and spinal cord may be closely monitored for early intervention and meticulous management. For children with the symptom of nervous system, they are strongly recommended for magnetic resonance examination.

Immunopathogenesis and Virus-Host Interactions of Enterovirus 71 in Patients with Hand, Foot and Mouth Disease

Enterovirus 71 (EV71) is a global infectious disease that affects millions of people. The virus is the main etiological agent for hand, foot, and mouth disease with outbreaks and epidemics being reported globally. Infection can cause severe neurological, cardiac, and respiratory problems in children under the age of 5. Despite on-going efforts, little is known about the pathogenesis of EV71, how the host immune system responds to the virus and the molecular mechanisms behind these responses. Moreover, current animal models remain limited, because they do not recapitulate similar disease patterns and symptoms observed in humans. In this review the role of the host-viral interactions of EV71 are discussed together with the various models available to examine: how EV71 utilizes its proteins to cleave host factors and proteins, aiding virus replication; how EV71 uses its own viral proteins to disrupt host immune responses and aid in its immune evasion. These discoveries along with others, such as the EV71 crystal structure, have provided possible targets for treatment and drug interventions.

A comparative study of multiple clinical enterovirus 71 isolates and evaluation of cross protection of inactivated vaccine strain FY-23 K-B in vitro

Background

Enterovirus 71 (EV71) is one of the causative agents of hand, foot and mouth disease, which mostly affects infants and children and leads to severe neurological diseases. Vaccination offers the best option for disease control. We have screened the virus strain FY-23 K-B, which is used as an inactivated vaccine strain. An important issue in the development of vaccines is whether they provide cross protection against all other strains.

Methods

We collected and identified 19 clinical EV71 isolates from mainland China, which all belong to the C4 genotype. We established growth curves of the strains in Vero cells, performed genetic analysis, and evaluated the cross protection efficacy through neutralizing assays using antisera from a rabbit, monkey and adult human immunized with the FY-23 K-B vaccine strain.

Results

The antisera showed broad cross protection among the C4 subgroup strains and homotype strain. Neutralizing indexes (NIs) among the isolates and homotype strain of antisera varied between 56.2–1995.3 for rabbit, 17.8–42,169.7 for monkey and 31.6–17,782.8 for human, whereas NIs against Coxsackievirus A16 or other enteroviruses were below 10.

Conclusions

These results suggested that FY-23 K-B used as an antigen could elicit broad spectrum neutralizing antibodies with cross protective efficacy among C4 genotype strains.

Machine Learning Algorithms for Risk Prediction of Severe Hand-Foot-Mouth Disease in Children

The identification of indicators for severe HFMD is critical for early prevention and control of the disease. With this goal in mind, 185 severe and 345 mild HFMD cases were assessed. Patient demographics, clinical features, MRI findings, and laboratory test results were collected. Gradient boosting tree (GBT) was then used to determine the relative importance (RI) and interaction effects of the variables. Results indicated that elevated white blood cell (WBC) count > 15 × 10⁹/L (RI: 4⁹.47, p < 0.001) was the top predictor of severe HFMD, followed by spinal cord involvement (RI: 26.62, p < 0.001), spinal nerve roots involvement (RI: 10.34, p < 0.001), hyperglycemia (RI: 3.40, p < 0.001), and brain or spinal meninges involvement (RI: 2.45, p = 0.003). Interactions between elevated WBC count and hyperglycemia (H statistic: 0.231, 95% CI: 0-0.262, p = 0.031), between spinal cord involvement and duration of fever ≥3 days (H statistic: 0.291, 95% CI: 0.035-0.326, p = 0.035), and between brainstem involvement and body temperature (H statistic: 0.313, 95% CI: 0-0.273, p = 0.017) were observed. Therefore, GBT is capable to identify the predictors for severe HFMD and their interaction effects, outperforming conventional regression methods.

Modelling person-to-person transmission in an Enterovirus A71 orally infected hamster model of hand-foot-and-mouth disease and encephalomyelitis

Enterovirus A71 (EV-A71) causes hand-foot-and-mouth disease (HFMD), which may be complicated by fatal encephalomyelitis. Although fecal–oral or oral–oral routes are important in person-to-person transmission, how viral shedding and exposure may predispose individuals to infection remains unknown. We investigated person-to-person transmission by using a model of HFMD and encephalomyelitis based on EV-A71 oral infection of 2-week-old hamsters. Animals (index animals) infected with 10⁴ 50% cell culture infective doses of virus uniformly developed severe disease four days post-infection (dpi), whereas littermate contacts developed severe disease after six to seven days of exposure to index animals. Virus was detected in oral washes and feces at 3–4 dpi in index animals and at three to eight days after exposure to index animals in littermate contact animals. In a second experiment, non-littermate contact animals exposed for 8 or 12 h to index animals developed the disease six and four days post-exposure, respectively. Tissues from killed index and contact animals, studied by light microscopy, immunohistochemistry and in situ hybridization, exhibited mild inflammatory lesions and/or viral antigens/RNA in the squamous epithelia of the oral cavity, tongue, paws, skin, esophagus, gastric epithelium, salivary glands, lacrimal glands, central nervous system neurons, muscles (skeletal, cardiac and smooth muscles) and liver. Orally shed viruses were probably derived from infected oral mucosa and salivary glands, whereas fecal viruses may have derived from these sites as well as from esophageal and gastric epithelia. Asymptomatic seroconversion in exposed mother hamsters was demonstrated. Our hamster model should be useful in studying person-to-person EV-A71 transmission and how drugs and vaccines may interrupt transmission.

A neonatal mouse model of coxsackievirus A10 infection for anti-viral evaluation

Epidemiological data indicate that coxsackievirus A10 (CVA10) has become one of the main causative agents of hand, foot and mouth disease (HFMD) and in recent years has often been found to co-circulate with other enteroviruses, which poses a challenge for the prevention and control of HFMD. Although most CVA10-associated HFMD cases present mild symptoms, severe manifestations and even death can also occur. However, the study of the pathogenesis and the development of drugs and vaccines for CVA10 infection are still far from complete. In this study, we established a neonatal mouse model for anti-viral evaluation and characterized the pathology of CVA10 infection. To develop the mouse model, both inbred and outbred mouse strains were used to compare their sensitivity to CVA10 infection; then, one-day-old BALB/c mice were selected and inoculated intraperitoneally with a CVA10 clinical strain, CVA10-FJ-01. Clinical symptoms, such as wasting, hind-limb paralysis and even death were observed in the CVA10-infected mice. Moreover, pathological examination and immunohistochemistry staining showed that severe myonecrosis with inflammatory infiltration was observed in CVA10-infected mice, indicating that CVA10 exhibited strong tropism to muscle tissue. Using real-time PCR, we also found that the viral load in the blood and muscle was higher than that in other organs/tissues at different time points post-infection, suggesting that CVA10 had a strong tropism to mice muscle and that viremic spread may also contribute to the death of the CVA10-infected mice. Additionally, to evaluate the neonatal mouse model of CVA10 infection, female mice were immunized with formalin-inactivated CVA10 and then allowed to mate after the third immunization. The results showed that maternal antibodies could protect mice against CVA10 infection. In summary, the results demonstrated that the neonatal mice model was a useful tool for evaluating the protective effects of CVA10 vaccines and anti-viral reagents.

Enterovirus 71-induced has-miR-21 contributes to evasion of host immune system by targeting MyD88 and IRAK1

Enterovirus71(EV71), the etiological agent of hand-foot-and-mouth disease, has increasingly become a public health challenge around the world. Type I interferons (IFNs) are an important family of cytokines that regulate innate and adaptive immune responses to pathogens.These pathways are tightly regulated by the host to prevent an inappropriate cellular response, but viruses can modulate these pathways to proliferate and spread. In this study, we demonstrated that EV71 evades the immune surveillance system to proliferate by activating microRNA-21. We demonstrated that EV71 infection upregulates miR-21, which in turn suppresses EV71-triggered type I IFN production, thus promoting EV71 replication. Furthermore, we demonstrated that miR-21 targets the myeloid differentiation factor 88(MyD88) and interleukin-1 receptor-associated kinase 1(IRAK1), which are involved in EV71-induced type I IFN production.

The Preferential Infection of Astrocytes by Enterovirus 71 Plays a Key Role in the Viral Neurogenic Pathogenesis

The pathological manifestations of fatal cases of human hand, foot, and mouth disease (HFMD) caused by enterovirus 71 (EV71) are characterized by inflammatory damage to the central nervous system (CNS). Here, the dynamic distribution of EV71 in the CNS and the subsequent pathological characteristics within different regions of neonatal rhesus macaque brain tissue were studied using a chimeric EV71 expressing green fluorescence protein. The results were compared with brain tissue obtained from the autopsies of deceased EV71-infected HFMD patients. These observations suggested that the virus was prevalent in areas around the blood vessels and nerve nuclei in the brain stem and showed a preference for astrocytes in the CNS. Interestingly, infected astrocytes within the in vivo and in vitro human and macaque systems exhibited increased expression of excitatory neurotransmitters and cytokines that also stimulated the neuronal secretion of the excitatory neurotransmitters noradrenalin and adrenalin, and this process most likely plays a role in the pathophysiological events that occur during EV71 infection.

Enterovirus 71 infection of motor neuron-like NSC-34 cells undergoes a non-lytic exit pathway

Enterovirus 71 (EV71) causing Hand, Foot and Mouth Disease, is regarded as the most important neurotropic virus worldwide. EV71 is believed to replicate in muscles and infect motor neurons to reach the central nervous system (CNS). To further investigate the mechanisms involved, we have employed the motor neuron cell line NSC-34. NSC-34 cells were permissive to EV71 and virus production yields were strain-dependent with differential efficacy at the entry, replication and egress steps. Furthermore, unlike all the other cell lines previously reported, EV71-infected NSC-34 cells neither displayed cytopathic effect nor underwent apoptosis. Instead, autophagy was markedly up-regulated and virus-containing autophagic vacuoles were isolated from the culture supernatant, providing the first experimental evidence that EV71 can adopt a non-lytic exit pathway. Finally, the ability of EV71 to infect productively NSC-34 cells correlated with its ability to invade the CNS in vivo, supporting the relevance of NSC-34 cells to study the intrinsic neurovirulence of EV71 strains.

Enterovirus 71 infection and neurological complications

Since the outbreak of the enterovirus 71 (EV71) infection in Malaysia in 1997, large epidemics of EV71 have occurred in the Asia-Pacific region. Many children and infants have died from serious neurological complications during these epidemics, and EV71 infection has become a serious public health problem in these areas. EV71 infection causes hand, foot and mouth disease (HFMD) in children, and usually resolves spontaneously. However, EV71 occasionally involves the central nervous system (CNS), and induces diverse neurological complications such as brainstem encephalitis, aseptic meningitis, and acute flaccid paralysis. Among those complications, brainstem encephalitis is the most critical neurological manifestation because it can cause neurogenic pulmonary hemorrhage/edema leading to death. The characteristic clinical symptoms such as myoclonus and ataxia, cerebrospinal fluid (CSF) pleocytosis, and brainstem lesions on magnetic resonance imaging, in conjunction with the skin rash of HFMD and the isolation of EV71 from a stool, throat-swab, or CSF sample are typical findings indicating CNS involvement of EV71 infection. Treatment with intravenous immunoglobulin and milrinone are recommended in cases with severe neurological complications from EV71 infection, such as brainstem encephalitis. Despite the recent discovery of receptors for EV71 in human cells, such as the scavenger receptor B2 and P-selection glycoprotein ligand 1, it is not known why EV71 infection predominantly involves the brainstem. Recently, 3 companies in China have completed phase III clinical trials of EV71 vaccines. However, the promotion and approval of these vaccines in various countries are problems yet to be resolved.

A clinically authentic mouse model of enterovirus 71 (EV-A71)-induced neurogenic pulmonary oedema

Enterovirus 71 (EV-A71) is a neurotropic virus that sporadically causes fatal neurologic illness among infected children. Animal models of EV-A71 infection exist, but they do not recapitulate in animals the spectrum of disease and pathology observed in fatal human cases. Specifically, neurogenic pulmonary oedema (NPE)—the main cause of EV-A71 infection-related mortality—is not observed in any of these models. This limits their utility in understanding viral pathogenesis of neurologic infections. We report the development of a mouse model of EV-A71 infection displaying NPE in severely affected animals. We inoculated one-week-old BALB/c mice with an adapted EV-A71 strain and identified clinical signs consistent with observations in human cases and other animal models. We also observed respiratory distress in some mice. At necropsy, we found their lungs to be heavier and incompletely collapsed compared to other mice. Serum levels of catecholamines and histopathology of lung and brain tissues of these mice strongly indicated onset of NPE. The localization of virally-induced brain lesions also suggested a potential pathogenic mechanism for EV-A71-induced NPE. This novel mouse model of virally-induced NPE represents a valuable resource for studying viral mechanisms of neuro-pathogenesis and pre-clinical testing of potential therapeutics and prophylactics against EV-A71-related neurologic complications.

Susceptibilities of enterovirus D68, enterovirus 71, and rhinovirus 87 strains to various antiviral compounds

Compounds were evaluated for antiviral activity in rhabdomyosarcoma (RD) cells against a recent 2014 clinical isolate of enterovirus D68 (EV-D68), a 1962 strain of EV-68D, rhinovirus 87 (RV-87, serologically the same as EV-D68), and enterovirus 71 (EV-71). Test substances included known-active antipicornavirus agents (enviroxime, guanidine HCl, pirodavir, pleconaril, and rupintrivir), nucleobase/nucleoside analogs (3-deazaguanine and ribavirin), and three novel epidithiodiketopiperazines (KCN-2,2'-epi-19, KCN-19, and KCN-21). Of these, rupintrivir was the most potent, with 50% inhibition of viral cytopathic effect (EC50) and 90% inhibition (EC90) of virus yield at 0.0022-0.0053 μM against EV-D68. Enviroxime, pleconaril and the KCN compounds showed efficacy at 0.01-0.3 μM; 3-deazaguanine and pirodavir inhibited EV-D68 at 7-13 μM, and guanidine HCl and ribavirin were inhibitory at 80-135 μM. Pirodavir was active against EV-71 (EC50 of 0.78 μM) but not against RV-87 or EV-D68, and all other compounds were less effective against EV-71 than against RV-87 and EV-D68. The most promising compound inhibiting both virus infections at low concentrations was rupintrivir. Antiviral activity was confirmed for the ten compounds in virus yield reduction (VYR) assays in RD cells, and for enviroxime, guanidine HCl, and pirodavir by cytopathic effect (CPE) assays in A549, HeLa-Ohio-1, and RD cells. These studies may serve as a basis for further pre-clinical discovery of anti-enterovirus inhibitors. Furthermore, the antiviral profiles and growth characteristics observed herein support the assertion that EV-D68 should be classified together with RV-87.

Neuropathogenicity of Two Saffold Virus Type 3 Isolates in Mouse Models

Objective

Saffold virus (SAFV), a picornavirus, is occasionally detected in children with acute flaccid paralysis, meningitis, and cerebellitis; however, the neuropathogenicity of SAFV remains undetermined.

Methods

The virulence of two clinical isolates of SAFV type 3 (SAFV-3) obtained from a patient with aseptic meningitis (AM strain) and acute upper respiratory inflammation (UR strain) was analyzed in neonatal and young mice utilizing virological, pathological, and immunological methods.

Results

The polyproteins of the strains differed in eight amino acids. Both clinical isolates were infective, exhibited neurotropism, and were mildly neurovirulent in neonatal ddY mice. Both strains pathologically infected neural progenitor cells and glial cells, but not large neurons, with the UR strain also infecting epithelial cells. UR infection resulted in longer inflammation in the brain and spinal cord because of demyelination, while the AM strain showed more infectivity in the cerebellum in neonatal ddY mice. Additionally, young BALB/c mice seroconverted following mucosal inoculation with the UR, but not the AM, strain.

Conclusions

Both SAFV-3 isolates had neurotropism and mild neurovirulence but showed different cell tropisms in both neonatal and young mouse models. This animal model has the potential to recapitulate the potential neuropathogenicity of SAFV-3.

A Consistent Orally-Infected Hamster Model for Enterovirus A71 Encephalomyelitis Demonstrates Squamous Lesions in the Paws, Skin and Oral Cavity Reminiscent of Hand-Foot-and-Mouth Disease

Enterovirus A71 (EV-A71) causes self-limiting, hand-foot-and-mouth disease (HFMD) that may rarely be complicated by encephalomyelitis. Person-to-person transmission is usually by fecal-oral or oral-oral routes. To study viral replication sites in the oral cavity and other tissues, and to gain further insights into virus shedding and neuropathogenesis, we developed a consistent, orally-infected, 2-week-old hamster model of HFMD and EV-A71 encephalomyelitis. Tissues from orally-infected, 2-week-old hamsters were studied by light microscopy, immunohistochemistry and in situ hybridization to detect viral antigens and RNA, respectively, and by virus titration. Hamsters developed the disease and died after 4–8 days post infection; LD₅₀ was 25 CCID₅₀. Macroscopic cutaneous lesions around the oral cavity and paws were observed. Squamous epithelium in the lip, oral cavity, paw, skin, and esophagus, showed multiple small inflammatory foci around squamous cells that demonstrated viral antigens/RNA. Neurons (brainstem, spinal cord, sensory ganglia), acinar cells (salivary gland, lacrimal gland), lymphoid cells (lymph node, spleen), and muscle fibres (skeletal, cardiac and smooth muscles), liver and gastric epithelium also showed varying amounts of viral antigens/RNA. Intestinal epithelium, Peyer’s patches, thymus, pancreas, lung and kidney were negative. Virus was isolated from oral washes, feces, brain, spinal cord, skeletal muscle, serum, and other tissues. Our animal model should be useful to study squamous epitheliotropism, neuropathogenesis, oral/fecal shedding in EV-A71 infection, person-to-person transmission, and to test anti-viral drugs and vaccines.

Efficacy of a Trivalent Hand, Foot, and Mouth Disease Vaccine against Enterovirus 71 and Coxsackieviruses A16 and A6 in Mice

Hand, foot, and mouth disease (HFMD) has recently emerged as a major public health concern across the Asian-Pacific region. Enterovirus 71 (EV71) and Coxsackievirus A16 (CVA16) are the primary causative agents of HFMD, but other members of the Enterovirus A species, including Coxsackievirus A6 (CVA6), can cause disease. The lack of small animal models for these viruses have hampered the development of a licensed HFMD vaccine or antivirals. We have previously reported on the development of a mouse model for EV71 and demonstrated the protective efficacy of an inactivated EV71 vaccine candidate. Here, mouse-adapted strains of CVA16 and CVA6 were produced by sequential passage of the viruses through mice deficient in interferon (IFN) α/β (A129) and α/β and γ (AG129) receptors. Adapted viruses were capable of infecting 3 week-old A129 (CVA6) and 12 week-old AG129 (CVA16) mice. Accordingly, these models were used in active and passive immunization studies to test the efficacy of a trivalent vaccine candidate containing inactivated EV71, CVA16, and CVA6. Full protection from lethal challenge against EV71 and CVA16 was observed in trivalent vaccinated groups. In contrast, monovalent vaccinated groups with non-homologous challenges failed to cross protect. Protection from CVA6 challenge was accomplished through a passive transfer study involving serum raised against the trivalent vaccine. These animal models will be useful for future studies on HFMD related pathogenesis and the efficacy of vaccine candidates.

Enterovirus 71 induces autophagy by regulating has-miR-30a expression to promote viral replication

Enterovirus 71 (EV71), the etiological agent of hand-foot-and-mouth disease, has increasingly become a public health challenge around the world. Previous studies reported that EV71 infection can induce autophagic machinery to enhance viral replication in vitro and in vivo, but did not address the underlying mechanisms. Increasing evidence suggests that autophagy, in a virus-specific manner, may function to degrade viruses or facilitate viral replication. In this study, we reported that EV71 infection of human epidermoid carcinoma (Hep2) and African green monkey kidney cells (Vero) induced autophagy, which is beneficial for viral replication. Our investigation of the mechanisms revealed that EV71 infection resulted in the reduction of cellular miR-30a, which led to the inhibition of Beclin-1, a key autophagy-promoting gene that plays important roles at the early phase of autophagosome formation. We provided further evidence that by modulating cellular miR-30a level through either overexpression or inhibition, one can inhibit or promote EV71 replication, respectively, through regulating autophagic activity.

Enterovirus 71 infection caused neuronal cell death and cytokine expression in cultured rat neural cells

Fatal enterovirus type-71 (EV71) cases are associated with central nervous system infection characterized by inflammatory cell infiltration and activation, cytokine overproduction, and neuronal cell death. Although EV71 antigen has been detected in neurons and glia, the molecular mechanisms underlying EV71-associated neuroinflammation and neuronal cell death are not fully understood. Using cultured rodent neural cell models, we found that EV71 infection preferentially caused cell death in neurons but not brain-resident immune cells astrocytes and microglia. Neurons, astrocytes, and microglia responded to EV71 infection by releasing distinct profiles of cytokines, including nitric oxide (NO), tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, regulated on activation normal T cell expressed and secreted (RANTES), and glutamate. EV71 infection-induced neuronal cell death correlated well with the elevated production of NO, TNF-α, IL-1β, and glutamate as well as activation of microglia. Exogenous addition studies further demonstrated the neurotoxic potential of NO, TNF-α, IL-1β, and glutamate. EV71 infection-induced cytokine expression was accompanied by activation of protein tyrosine phosphorylation, mitogen-activated protein kinases (MAPKs), and NF-κB. Intriguingly, EV71 susceptibility was accompanied by infection-elevated neuronal human scavenger receptor class B member 2 expression in cultured neural cells with age-dependent manner. Biochemical and pharmacological studies revealed that after EV71 infection, microglia and accompanied cytokines play an active role in triggering bystander damage to neurons involving the tyrosine kinase/MAPKs/NF-κB signaling cascade. These data suggest that bystander damage caused by activated glia particularly the microglia could be an alternative mechanism of EV71-associated neuronal cell death. However, its clinical importance and implication require further investigation.

Clinical Analysis of 134 Children with Nervous System Damage Caused by Enterovirus 71 Infection

OBJECTIVE

The purpose of this study was to evaluate the clinical characteristics of nervous system damage caused by enterovirus 71 (EV71) infection in pediatric patients.

STUDY DESIGN

Clinical data and outcomes were retrospectively analyzed for 134 cases of laboratory confirmed pediatric EV71 infection admitted to the Children's Hospital of Chongqing Medical University from January to December 2013.

RESULTS

EV71 infection was significantly more common in patients 1-4 years of age, in males and during the months of April-July. Fifty-six cases complicated by hand, foot and mouth disease were diagnosed. Fever was the most common symptom (128 of 134 patients) and lasted on average 5.3 ± 2.1 days. The most common neurologic complication was aseptic meningitis (n = 74), followed by brain stem encephalitis (n = 24), acute flaccid paralysis (AFP; n = 20), acute parencephalitis (n = 12) and encephalomyelitis (n = 4). Each was characterized by a unique profile of clinical symptoms. Damage to the pons and medulla oblongata was apparent in 28 brain magnetic resonance images. Lesions associated with AFP were concentrated in the cervical spinal cord and thoracic 8. The anterior root of the spinal anterior horn was a specific lesion. Fourteen of the AFP patients had unilateral or bilateral femoral nerve involvement. None of the patients died, and in 132 of 134 patients, follow-up visits showed that their physical and neuropsychologic abilities had returned to normal.

CONCLUSIONS

Most children infected with EV71 have a good prognosis if they are diagnosed early and receive proper supportive treatment.