Contemporary Circulating Enterovirus D68 Strains Have Acquired the Capacity for Viral Entry and Replication in Human Neuronal Cells

Pharmacological activation of TLR7 exerts inhibition on the replication of EV-D68 in respiratory cells

The globally reemerging respiratory pathogen enterovirus D68 (EV-D68) is implicated in outbreaks of severe respiratory illness and associated with acute flaccid myelitis. However, there remains a lack of effective treatments for EV-D68 infection. In this work, we found that the host Toll-like receptor 7 (TLR7) proteins, which function as powerful innate immune sensors, were selectively elevated in expression in response to EV-D68 infection. Subsequently, we investigated the impact of Vesatolimod (GS-9620), a Toll-like receptor 7 agonist, on EV-D68 replication. Our findings revealed that EV-D68 infection resulted in increased mRNA levels of TLR7. Treatment with Vesatolimod significantly inhibited EV-D68 replication [half maximal effective concentration (EC50) = 0.1427 µM] without inducing significant cytotoxicity at virucidal concentrations. Although Vesatolimod exhibited limited impact on EV-D68 attachment, it suppressed RNA replication and viral protein synthesis after virus entry. Vesatolimod broadly inhibited the replication of circulating isolated strains of EV-D68. Furthermore, our findings demonstrated that treatment with Vesatolimod conferred resistance to both respiratory and neural cells against EV-D68 infection. Overall, these results present a promising strategy for drug development by pharmacologically activating TLR7 to initiate an antiviral state in EV-D68-infected cells selectively.IMPORTANCEConventional strategies for antiviral drug development primarily focus on directly targeting viral proteases or key components, as well as host proteins involved in viral replication. In this study, based on our intriguing discovery that enterovirus D68 (EV-D68) infection specifically upregulates the expression of immune sensor Toll-like receptor 7 (TLR7) protein, which is either absent or expressed at low levels in respiratory cells, we propose a potential antiviral approach utilizing TLR7 agonists to activate EV-D68-infected cells into an anti-viral defense state. Notably, our findings demonstrate that pharmacological activation of TLR7 effectively suppresses EV-D68 replication in respiratory tract cells through a TLR7/MyD88-dependent mechanism. This study not only presents a promising drug candidate and target against EV-D68 dissemination but also highlights the potential to exploit unique alterations in cellular innate immune responses induced by viral infections, selectively inducing a defensive state in infected cells while safeguarding uninfected normal cells from potential adverse effects associated with therapeutic interventions.

In vitro and in vivo models for the study of EV-D68 infection

Enterovirus D68 (EV-D68) is one of hundreds of non-polio enteroviruses that typically cause cold-like respiratory illness. The first EV-D68 outbreak in the United States in 2014 aroused widespread concern among the public and health authorities. The infection was found to be associated with increased surveillance of acute flaccid myelitis, a neurological condition that causes limb paralysis in conjunction with spinal cord inflammation. In vitro studies utilising two-dimensional (2D) and three-dimensional (3D) culture systems have been employed to elucidate the pathogenic mechanism of EV-D68. Various animal models have also been developed to investigate viral tropism and distribution, pathogenesis, and immune responses during EV-D68 infection. EV-D68 infections have primarily been investigated in respiratory, intestinal and neural cell lines/tissues, as well as in small-size immunocompetent rodent models that were limited to a young age. Some studies have implemented strategies to overcome the barriers by using immunodeficient mice or virus adaptation. Although the existing models may not fully recapitulate both respiratory and neurological disease observed in human EV-D68 infection, they have been valuable for studying pathogenesis and evaluating potential vaccine or therapeutic candidates. In this review, we summarise the methodologies and findings from each experimental model and discuss their applications and limitations.

Structure-Based Lead Optimization of Enterovirus D68 2A Protease Inhibitors

Enterovirus D68 (EV-D68) virus is a nonpolio enterovirus that typically causes respiratory illness and, in severe cases, can lead to paralysis and death in children. There is currently no vaccine or antiviral for EV-D68. We previously discovered the viral 2A protease (2Apro) as a viable antiviral drug target and identified telaprevir as a 2Apro inhibitor. 2Apro is a viral cysteine protease that cleaves the viral VP1-2A polyprotein junction. In this study, we report the X-ray crystal structures of EV-D68 2Apro, wild-type, and the C107A mutant and the structure-based lead optimization of telaprevir. Guided by the X-ray crystal structure, we predicted the binding pose of telaprevir in 2Apro using molecular dynamics simulations. We then utilized this model to inform structure-based optimization of the telaprevir's reactive warhead and P1-P4 substitutions. These efforts led to the discovery of 2Apro inhibitors with improved antiviral activity than telaprevir. These compounds represent promising lead compounds for further development as EV-D68 antivirals.

Contemporary enterovirus-D68 isolates infect human spinal cord organoids

Enterovirus D68 (EV-D68) is a nonpolio enterovirus associated with severe respiratory illness and acute flaccid myelitis (AFM), a polio-like illness causing paralysis in children. AFM outbreaks have been associated with increased circulation and genetic diversity of EV-D68 since 2014, although the virus was discovered in the 1960s. The mechanisms by which EV-D68 targets the central nervous system are unknown. Since enteroviruses are human pathogens that do not routinely infect other animal species, establishment of a human model of the central nervous system is essential for understanding pathogenesis. Here, we describe two human spinal cord organoid (hSCO)-based models for EV-D68 infection derived from induced, pluripotent stem cell (iPSC) lines. One hSCO model consists primarily of spinal motor neurons, while the another model comprises multiple neuronal cell lineages, including motor neurons, interneurons, and glial cells. These hSCOs can be productively infected with contemporary strains, but not a historic strain, of EV-D68 and produce extracellular virus for at least 2 weeks without appreciable cytopathic effect. By comparison, infection with hSCO with another enterovirus, echovirus 11, causes significant structural destruction and apoptosis. Together, these findings suggest that EV-D68 infection is not the sole mediator of neuronal cell death in the spinal cord in those with AFM and that secondary injury from the immune response likely contributes to pathogenesis. IMPORTANCE AFM is a rare condition that causes significant morbidity in affected children, often contributing to life-long sequelae. It is unknown how EV-D68 causes paralysis in children, and effective therapeutic and preventative strategies are not available. Mice are not native hosts for EV-D68, and thus, existing mouse models use immunosuppressed or neonatal mice, mouse-adapted viruses, or intracranial inoculations. To complement existing models, we report two hSCO models for EV-D68 infection. These three-dimensional, multicellular models comprised human cells and include multiple neural lineages, including motor neurons, interneurons, and glial cells. These new hSCO models for EV-D68 infection will contribute to understanding how EV-D68 damages the human spinal cord, which could lead to new therapeutic and prophylactic strategies for this virus.

Clinical and molecular epidemiologic features of enterovirus D68 infection in children with acute lower respiratory tract infection in China

Acute flaccid paralysis (AFP) associated with enterovirus D68 (EV-D68) infection has attracted much attention since an outbreak in the USA in 2014. Notably, EV-D68 was detected in a child with AFP for the first time in China in 2018. In a multicentre study from May 2017 to December 2019, we monitored EV-D68 infections in hospitalized children with acute lower respiratory tract infection (ALRTI) in China. Out of 3,071 samples collected from patients with ALRTI, ten were positive for EV-D68. All patients presented with mild diseases with no neurological symptoms or signs. Phylogenetic analysis based on the VP1 gene showed that all EV-D68 sequences obtained in this study belonged to subclade B3 and were close to sequences of EV-D68 strains obtained from patients with AFP in the USA. Four EV-D68 strains were isolated, and their complete genome sequences were determined. These sequences did not show any evidence of recombination events. To assess their neurotropism, the isolates were used to infect the "neuronal-like" cell line SH-SY5Y, and resulted in a cytopathic effect. We further analysed the structure and sites that may be associated with neurovirulence, including the stem-loop structure in the untranslated region (3'UTR) and identified amino acid substitutions (M291T, V341A, T860N, D927N, S1108G, and R2005K) in the coding region and specific nucleotides (127T, 262C, and 339T) in the 5' UTR. In conclusion, EV-D68 infection was detected in a small number of children with ALRTI in China from 2017 to 2019. Disease symptoms in these children were relatively mild with no neurological complications, and all EV-D68 sequences belonged to subclade B3.

Enterovirus D-68 Infection of Primary Rat Cortical Neurons: Entry, Replication, and Functional Consequences

Enterovirus D68 (EV-D68) is an emerging pathogen associated with mild to severe respiratory disease. Since 2014, EV-D68 is also linked to acute flaccid myelitis (AFM), causing paralysis and muscle weakness in children. However, it remains unclear whether this is due to an increased pathogenicity of contemporary EV-D68 clades or increased awareness and detection of this virus. Here, we describe an infection model of primary rat cortical neurons to study the entry, replication, and functional consequences of different EV-D68 strains, including historical and contemporary strains. We demonstrate that sialic acids are important (co)receptors for infection of both neurons and respiratory epithelial cells. Using a collection of glycoengineered isogenic HEK293 cell lines, we show that sialic acids on either N-glycans or glycosphingolipids can be used for infection. Additionally, we show that both excitatory glutamatergic and inhibitory GABA-ergic neurons are susceptible and permissive to historical and contemporary EV-D68 strains. EV-D68 infection of neurons leads to the reorganization of the Golgi-endomembranes forming replication organelles, first in the soma and later in the processes. Finally, we demonstrate that the spontaneous neuronal activity of EV-D68-infected neuronal network cultured on microelectrode arrays (MEA) is decreased, independent of the virus strain. Collectively, our findings provide novel insights into neurotropism and -pathology of different EV-D68 strains, and argue that it is unlikely that increased neurotropism is a recently acquired phenotype of a specific genetic lineage. IMPORTANCE Acute flaccid myelitis (AFM) is a serious neurological illness characterized by muscle weakness and paralysis in children. Since 2014, outbreaks of AFM have emerged worldwide, and they appear to be caused by nonpolio enteroviruses, particularly enterovirus-D68 (EV-D68), an unusual enterovirus that is known to mainly cause respiratory disease. It is unknown whether these outbreaks reflect a change of EV-D68 pathogenicity or are due to increased detection and awareness of this virus in recent years. To gain more insight herein, it is crucial to define how historical and circulating EV-D68 strains infect and replicate in neurons and how they affect their physiology. This study compares the entry and replication in neurons and the functional consequences on the neural network upon infection with an old "historical" strain and contemporary "circulating" strains of EV-D68.

Enterovirus characterized from cerebrospinal fluid in a cohort from the Eastern United States

BACKGROUND

Enteroviruses (EVs) are predominant causes of a spectrum of neurological diseases. To better understand the origins of the outbreaks of disease associated with EV, it is essential to develop an efficient surveillance system that identifies the circulating EVs and correlate their genomic evolution with the disease presentations.

METHODS

The clinical presentations of patients with positive EV from cerebrospinal fluid (CSF) between 2014 and 2022, diagnosed at the Johns Hopkins Medical Microbiology Laboratory, were compared from year to year. EV typing and whole genome sequencing were performed and correlated to the spectrum of disease.

RESULTS

A total of 95 CSF specimens were positive for EV between 2014 and 2022. The percentage positivity ranged from the lowest of 1.1% in 2020 to the highest of 3.2% in 2015. The median ages declined from 22 years in 2014 to less than one year starting in 2016 to 34 in 2022. Typing using VP1 sequencing revealed that E30 and E6 were associated with meningitis in adults but coxsackieviruses (CVs-B3 and B5) were detected from pediatric patients with fever. Whole genome sequencing revealed multiple recombination events. In 2020, a recombinant CV-A9 was detected in a CSF sample associated with unusual presentation of sepsis, profound acute bilateral sensory neural hearing loss, and myofasciitis.

CONCLUSIONS

EV genomic surveillance is needed for a better understanding of the genetic determinants of neurovirulence. Whole genome sequencing can reveal recombination events missed by traditional molecular surveillance methods.

Acute flaccid myelitis in Switzerland - association with enterovirus D68

Poliomyelitis-like acute flaccid myelitis associated with enterovirus D68 (EV-D68) has emerged globally during the past decade. Here we describe the first documented case reported from Switzerland, and a second, suspected case occurring in temporal association. AFM occurs primarily in children, is usually heralded by a febrile, respiratory prodrome followed by acute-onset, usually asymmetrical, limb weakness with some predilection for the upper extremities, and respiratory muscle compromise in one third of reported cases. There is no specific therapy and the majority of cases result in permanent neurological sequelae. A comprehensive diagnostic workup and timely reporting to the health authorities are essential. Surveillance of respiratory and stool samples for EV-D68 and other neurotropic enteroviruses is in place in several European countries and warrants consideration in Switzerland. This could entail the extension of the poliomyelitis surveillance program of the Federal Office of Public Health by monitoring and enteroviral typing of respiratory samples from patients with acute flaccid paralysis.

RNA Structure in the 5' Untranslated Region of Enterovirus D68 Strains with Differing Neurovirulence Phenotypes

Enterovirus-D68 (EV-D68) is a positive-sense single-stranded RNA virus within the family Picornaviridae. EV-D68 was initially considered a respiratory virus that primarily affected children. However, in 2014, EV-D68 outbreaks occurred causing the expected increase in respiratory illness cases, but also an increase in acute flaccid myelitis cases (AFM). Sequencing of 2014 outbreak isolates revealed variations in the 5' UTR of the genome compared to the historical Fermon strain. The structure of the 5' UTR RNA contributes to enterovirus virulence, including neurovirulence in poliovirus, and could contribute to neurovirulence in contemporary EV-D68 strains. In this study, the secondary and tertiary structures of 5' UTR RNA from the Fermon strain and 2014 isolate KT347251.1 are analyzed and compared. Secondary structures were determined using SHAPE-MaP and TurboFold II and tertiary structures were predicted using 3dRNAv2.0. Comparison of RNA structures between the EV-D68 strains shows significant remodeling at the secondary and tertiary levels. Notable secondary structure changes occurred in domains II, IV and V. Shifts in the secondary structure changed the tertiary structure of the individual domains and the orientation of the domains. Our comparative structural models for EV-D68 5' UTR RNA highlight regions of the molecule that could be targeted for treatment of neurotropic enteroviruses.

Starvation after infection restricts enterovirus D68 replication

Enterovirus D68 (EV-D68) is a respiratory pathogen associated with acute flaccid myelitis, a childhood paralysis disease. No approved vaccine or antiviral treatment exists against EV-D68. Infection with this virus induces the formation of autophagosomes to enhance its replication but blocks the downstream autophagosome- lysosome fusion steps. Here, we examined the impact of autophagy induction through starvation, either before (starvation before infection, SBI) or after (starvation after infection, SAI) EV-D68 infection. We showed that SAI, but not SBI, attenuated EV-D68 replication in multiple cell lines and abrogated the viral-mediated cleavage of host autophagic flux-related proteins. Furthermore, SAI induced autophagic flux during EV-D68 replication and prevented production of virus-induced membranes, which are required for picornavirus replication. Pharmacological inhibition of autophagic flux during SAI did not rescue EV-D68 titers. SAI had the same effect in multiple cell types, and restricted the replication of several medically relevant picornaviruses. Our results highlight the significance of autophagosomes for picornavirus replication and identify SAI as an attractive broad-spectrum anti-picornavirus strategy.Abbreviations: BAF: bafilomycin A₁; CCCP: carbonyl cyanide m-chlorophenylhydrazone; CQ: chloroquine; CVB3: coxsackievirus B3; EV-D68: enterovirus D68; hpi: hour post-infection; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; NSP2B: nonstructural protein 2B; PV: poliovirus; RES: resveratrol; RV14: rhinovirus 14; SAI: starvation after infection; SBI: starvation before infection; SNAP29: synaptosome associated protein 29; SQSTM1/p62: sequestosome 1; TFEB: transcription factor EB.

Acute Flaccid Myelitis: Review of Clinical Features, Diagnosis, and Management with Nerve Transfers

BACKGROUND

Acute flaccid myelitis (AFM) is a devastating neurologic condition in children, manifesting as acute limb weakness and/or paralysis. Despite increased awareness of AFM following initiation of U.S. surveillance in 2014, no treatment consensus exists. The purpose of this systematic review was to summarize the most current knowledge regarding AFM epidemiology, cause, clinical features, diagnosis, and supportive and operative management, including nerve transfer.

METHODS

The authors systematically reviewed the literature based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using multiple databases to search the keywords ("acute flaccid myelitis"), ('acute flaccid myelitis'/exp OR 'acute flaccid myelitis'), and (Acute AND flaccid AND myelitis). Included articles reported on (1) AFM diagnosis and (2) patient-specific data regarding epidemiology, cause, clinical features, diagnostic features, or management of AFM.

RESULTS

Ninety-nine articles were included in this review. The precise cause and pathophysiologic mechanism of AFM remain undetermined, but AFM is strongly associated with nonpolio enterovirus infections. Clinical presentation typically comprises preceding viral prodrome, pleocytosis, spinal cord lesions on T2-weighted magnetic resonance imaging, and acute onset of flaccid weakness/paralysis with hyporeflexia in at least one extremity. Supportive care includes medical therapy and rehabilitation. Early studies of nerve transfer for AFM have shown favorable outcomes for patients with persistent weakness.

CONCLUSIONS

Supportive care and physical therapy are the foundation of a multidisciplinary approach to managing AFM. For patients with persistent limb weakness, nerve transfer has shown promise for improving function in distal muscle groups. Surgeons must consider potential spontaneous recovery, patient selection, donor nerve availability, recipient nerve appropriateness, and procedure timing.

Enterovirus D68 Infection in Human Primary Airway and Brain Organoids: No Additional Role for Heparan Sulfate Binding for Neurotropism

Enterovirus D68 (EV-D68) is an RNA virus that can cause outbreaks of acute flaccid paralysis (AFP), a polio-like disease. Before 2010, EV-D68 was a rare pathogen associated with mild respiratory symptoms, but the recent EV-D68 related increase in severe respiratory illness and outbreaks of AFP is not yet understood. An explanation for the rise in severe disease is that it may be due to changes in the viral genome resulting in neurotropism. In this regard, in addition to sialic acid, binding to heparan sulfate proteoglycans (HSPGs) has been identified as a feature for viral entry of some EV-D68 strains in cell lines. Studies in human primary organotypic cultures that recapitulate human physiology will address the relevance of these HSPG-binding mutations for EV-D68 infection in vivo. Therefore, in this work, we studied the replication and neurotropism of previously determined sialic acid-dependent and HSPG-dependent strains using primary human airway epithelial (HAE) cultures and induced human pluripotent stem cell (iPSC)-derived brain organoids. All three strains (B2/2042, B2/947, and A1/1348) used in this study infected HAE cultures and human brain organoids (shown for the first time). Receptor-blocking experiments in both cultures confirm that B2/2042 infection is solely dependent on sialic acid, while B2/947 and A1/1348 (HSPG to a lesser extent) binds to sialic acid and HSPG for cell entry. Our data suggest that HSPG-binding can be used by EV-D68 for entry in human physiological models but offers no advantage for EV-D68 infection of brain cells. IMPORTANCE Recent outbreaks of enterovirus D68, a nonpolio enterovirus, is associated with a serious neurological condition in young children, acute flaccid myelitis (AFM). As there is no antiviral treatment or vaccine available for EV-D68 it is important to better understand how EV-D68 causes AFM and why only recent outbreaks are associated with AFM. We investigated if a change in receptor usage of EV-D68 increases the virulence of EV-D68 in the airway or the central nervous system and thus could explain the increase in AFM cases. We studied this using physiologically relevant human airway epithelium and cerebral organoid cultures that are physiologically relevant human models. Our data suggest that heparan sulfate proteoglycans can be used by EV-D68 as an additional entry receptor in human physiological models but offers no advantage for EV-D68 infection of brain cells, and our data show the potential of these 46 innovative models for virology.

Host neuronal PRSS3 interacts with enterovirus A71 3A protein and its role in viral replication

Enterovirus A71 (EV-A71) causes hand, foot, and mouth disease associated with neurological complications in young children. Currently, there is no specific treatment for EV-A71 infection due to the inadequate information on viral biology and neuropathogenesis. Among enteroviruses, nonstructural 3A protein mediates the formation of replication organelles which plays a major role in viral RNA synthesis and assembly. Although enteroviral 3A proteins have been intensively studied, the data on EV-A71 3A, especially in neuronal cells, are still limited. In this study, PRSS3 (mesotrypsinogen, also known as brain trypsinogen) was identified as EV-A71 3A-interacting counterpart from the transfected human neuroblastoma SH-SY5Y cells by pull-down assay and liquid chromatography tandem mass spectrometry. It was confirmed that PRSS3 variant 3 derived from human SH-SY5Y cells had the physical interaction with EV-A71 3A. Importantly, the role of PRSS3 in EV-A71 replication was verified by overexpression and siRNA-mediated gene silencing approaches. The detailed mechanism of the PRSS3 involved in EV-A71 replication and neuropathogenesis warrants further experimental elucidation. In conclusion, this study has discovered a novel EV-A71 3A interacting protein that offers the opportunity to study the neuropathogenesis of the infection which paves the way for developing a specific and effective treatment for the disease.

Animal Models of Enterovirus D68 Infection and Disease

Human enterovirus D68 (EV-D68) is a globally reemerging respiratory pathogen that is associated with the development of acute flaccid myelitis (AFM) in children. Currently, there are no approved vaccines or treatments for EV-D68 infection, and there is a paucity of data related to the virus and host-specific factors that predict disease severity and progression to the neurologic syndrome. EV-D68 infection of various animal models has served as an important platform for characterization and comparison of disease pathogenesis between historic and contemporary isolates. Still, there are significant gaps in our knowledge of EV-D68 pathogenesis that constrain the development and evaluation of targeted vaccines and antiviral therapies. Continued refinement and characterization of animal models that faithfully reproduce key elements of EV-D68 infection and disease is essential for ensuring public health preparedness for future EV-D68 outbreaks.

Enterovirus D68 epidemic, UK, 2018, was caused by subclades B3 and D1, predominantly in children and adults, respectively, with both subclades exhibiting extensive genetic diversity

Enterovirus D68 (EV-D68) has recently been identified in biennial epidemics coinciding with diagnoses of non-polio acute flaccid paralysis/myelitis (AFP/AFM). We investigated the prevalence, genetic relatedness and associated clinical features of EV-D68 in 193 EV-positive samples from 193 patients in late 2018, UK. EV-D68 was detected in 83 (58 %) of 143 confirmed EV-positive samples. Sequencing and phylogenetic analysis revealed extensive genetic diversity, split between subclades B3 (n=50) and D1 (n=33), suggesting epidemiologically unrelated infections. B3 predominated in children and younger adults, and D1 in older adults and the elderly (P=0.0009). Clinical presentation indicated causation or exacerbation of respiratory distress in 91.4 % of EV-D68-positive individuals, principally cough (75.3 %), shortness of breath (56.8 %), coryza (48.1 %), wheeze (46.9 %), supplemental oxygen required (46.9 %) and fever (38.9 %). Two cases of AFM were observed, one with EV-D68 detectable in the cerebrospinal fluid, but otherwise neurological symptoms were rarely reported (n=4). Both AFM cases and all additional instances of intensive care unit (ICU) admission (n=5) were seen in patients infected with EV-D68 subclade B3. However, due to the infrequency of severe infection in our cohort, statistical significance could not be assessed.

Pathological Characteristics of Echovirus 30 Infection in a Mouse Model

Echovirus 30 (E30), a member of species B enterovirus, is associated with outbreaks of aseptic meningitis and has become a global health emergency. However, the pathogenesis of E30 remains poorly understood due to the lack of appropriate animal models. In this study, we established a mouse infection model to explore the pathogenicity of E30. The 2-day-old IFNAR^-/- mice infected with E30 strain WZ16 showed lethargy and paralysis, and some died. Obvious pathological changes were observed in the skeletal muscle, brain tissue, and other tissues, with the highest viral load in the skeletal muscles. Transcriptome analysis of brain and skeletal muscle tissues from infected mice showed that significant differentially expressed genes were enriched in complement response and neuropathy-related pathways. Using immunofluorescence assay, we found that the viral double-stranded RNA (dsRNA) was detected in the mouse brain region and could infect human glioma (U251) cells. These results indicated that E30 affects the nervous system, and they provide a theoretical basis for understanding its pathogenesis. IMPORTANCE Echovirus 30 (E30) infection causes a wide spectrum of diseases with mild symptoms, such as hand, foot, and mouth disease (HFMD), acute flaccid paralysis, and aseptic meningitis and other diseases, especially one of the most common pathogens causing aseptic meningitis outbreaks. We established a novel mouse model of E30 infection by inoculating neonatal mice with clinical isolates of E30 and observed the pathological changes induced by E30. Using the E30 infection model, we found complement responses and neuropathy-related genes in the mice tissues at the transcriptome level. Moreover, we found that the viral dsRNA localized in the mouse brain and could replicate in human glioma cell line U251 rather than in the neuroblastoma cell line, SK-N-SH.

Global prevalence and case fatality rate of Enterovirus D68 infections, a systematic review and meta-analysis

A substantial amount of epidemiological data has been reported on Enterovirus D68 (EV-D68) infections after the 2014 outbreak. Our goal was to map the case fatality rate (CFR) and prevalence of current and past EV-D68 infections. We conducted a systematic review (PROSPERO, CRD42021229255) with published articles on EV-68 infections in PubMed, Embase, Web of Science and Global Index Medicus up to January 2021. We determined prevalences using a model random effect. Of the 4,329 articles retrieved from the databases, 89 studies that met the inclusion criteria were from 39 different countries with apparently healthy individuals and patients with acute respiratory infections, acute flaccid myelitis and asthma-related diseases. The CFR estimate revealed occasional deaths (7/1353) related to EV-D68 infections in patients with severe acute respiratory infections. Analyses showed that the combined prevalence of current and past EV-D68 infections was 4% (95% CI = 3.1-5.0) and 66.3% (95% CI = 40.0-88.2), respectively. The highest prevalences were in hospital outbreaks, developed countries, children under 5, after 2014, and in patients with acute flaccid myelitis and asthma-related diseases. The present study shows sporadic deaths linked to severe respiratory EV-D68 infections. The study also highlights a low prevalence of current EV-D68 infections as opposed to the existence of EV-D68 antibodies in almost all participants of the included studies. These findings therefore highlight the need to implement and/or strengthen continuous surveillance of EV-D68 infections in hospitals and in the community for the anticipation of the response to future epidemics.

Analysis of the long noncoding RNA profiles of RD and SH-SY5Y cells infected with coxsackievirus B5, using RNA sequencing

Hand, foot, and mouth disease caused by coxsackievirus B5 (CV-B5) is a considerable threat to infant health, especially with regard to neurological damage. Long noncoding RNAs (lncRNAs) are known to play pivotal roles in virus-host interactions. However, the roles of lncRNAs in CV-B5-host interactions have not yet been elucidated. In the current study, we used RNA sequencing to determine the expression profiles of lncRNAs in CV-B5-infected human rhabdomyosarcoma (RD) and SH-SY5Y cells. Our results showed that, of the differentially expressed lncRNAs, 508 were upregulated and 760 were downregulated in RD cells. Of these, 46.2% were long noncoding intergenic RNAs (lincRNAs), 28.6% were antisense lncRNAs, 24.1% were sense overlapping lncRNAs, and 1.0% were sense intronic lncRNAs. Moreover, 792 lncRNAs were upregulated and 811 lncRNAs were downregulated in SH-SY5Y cells, 48.6% of which were lincRNAs, 34.7% were antisense lncRNAs, 16.0% were sense overlapping lncRNAs, and 0.8% were sense intronic lncRNAs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that lncRNAs that were differentially expressed in CV-B5-infected RD cells were associated with disease, and those differentially expressed in SH-SY5Y cells were involved in signaling pathways. RT-qPCR analysis of seven lncRNAs supported these results. Moreover, our study revealed that lncRNA-IL12A inhibits viral replication. We conclude that lncRNAs constitute potential novel molecular targets for the prevention and treatment of CV-B5 infection and also may serve to distinguish neurogenic diseases caused by CV-B5 infection.

Infection-Related Myelopathies

Recent years have seen growing attention to inflammatory and infectious disorders of the spinal cord, not only due to the discovery of autoantibody-mediated disorders of the spinal cord [e.g., aquaporin-4 immunoglobulin G (IgG) antibodies and myelin oligodendrocyte glycoprotein IgG antibodies], but also due to the emergence of clusters of infection-related myelopathy, now known as acute flaccid myelitis. We review the spectrum of infection-related myelopathies and outline a nosological classification system based on association with infection. We describe the epidemiology and definitions of myelopathies, with a discussion of clinical presentation and neuroimaging features, and then turn to specific discussion of myelopathies due to direct pathogen invasion and those considered to be post- or parainfectious. Expected final online publication date for the Annual Review of Pathology: Mechanisms of Disease, Volume 17 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The pathogenesis and virulence of enterovirus-D68 infection

In 2014, enterovirus D68 (EV-D68) emerged causing outbreaks of severe respiratory disease in children worldwide. In a subset of patients, EV-D68 infection was associated with the development of central nervous system (CNS) complications, including acute flaccid myelitis (AFM). Since then, the number of reported outbreaks has risen biennially, which emphasizes the need to unravel the systemic pathogenesis in humans. We present here a comprehensive review on the different stages of the pathogenesis of EV-D68 infection – infection in the respiratory tract, systemic dissemination and infection of the CNS – based on observations in humans as well as experimental in vitro and in vivo studies. This review highlights the knowledge gaps on the mechanisms of systemic dissemination, routes of entry into the CNS and mechanisms to induce AFM or other CNS complications, as well as the role of virus and host factors in the pathogenesis of EV-D68.

Respiratory and intestinal epithelial cells exhibit differential susceptibility and innate immune responses to contemporary EV-D68 isolates

Enterovirus D68 (EV-D68) has been implicated in outbreaks of severe respiratory illness and is associated with acute flaccid myelitis (AFM). EV-D68 is often detected in patient respiratory samples but has also been detected in stool and wastewater, suggesting the potential for both respiratory and enteric routes of transmission. Here, we used a panel of EV-D68 isolates, including a historical pre-2014 isolate and multiple contemporary isolates from AFM outbreak years, to define the dynamics of viral replication and the host response to infection in primary human airway cells and stem cell-derived enteroids. We show that some recent EV-D68 isolates have decreased sensitivity to acid and temperature compared with earlier isolates and that the respiratory, but not intestinal, epithelium induces a robust type III interferon response that restricts infection. Our findings define the differential responses of the respiratory and intestinal epithelium to contemporary EV-D68 isolates and suggest that a subset of isolates have the potential to target both the human airway and gastrointestinal tracts.

Viruses Like Sugars: How to Assess Glycan Involvement in Viral Attachment

The first step of viral infection requires interaction with the host cell. Before finding the specific receptor that triggers entry, the majority of viruses interact with the glycocalyx. Identifying the carbohydrates that are specifically recognized by different viruses is important both for assessing the cellular tropism and for identifying new antiviral targets. Advances in the tools available for studying glycan-protein interactions have made it possible to identify them more rapidly; however, it is important to recognize the limitations of these methods in order to draw relevant conclusions. Here, we review different techniques: genetic screening, glycan arrays, enzymatic and pharmacological approaches, and surface plasmon resonance. We then detail the glycan interactions of enterovirus D68 and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), highlighting the aspects that need further clarification.

Discovery of Potent and Broad-Spectrum Pyrazolopyridine-Containing Antivirals against Enteroviruses D68, A71, and Coxsackievirus B3 by Targeting the Viral 2C Protein

The enterovirus genus of the picornavirus family contains many important human pathogens. EV-D68 primarily infects children, and the disease manifestations range from respiratory illnesses to neurological complications such as acute flaccid myelitis (AFM). EV-A71 is a major pathogen for the hand, foot, and mouth disease (HFMD) in children and can also lead to AFM and death in severe cases. CVB3 infection can cause cardiac arrhythmias, acute heart failure, as well as type 1 diabetes. There is currently no FDA-approved antiviral for any of these enteroviruses. In this study, we report our discovery and development of pyrazolopyridine-containing small molecules with potent and broad-spectrum antiviral activity against multiple strains of EV-D68, EV-A71, and CVB3. Serial viral passage experiments, coupled with reverse genetics and thermal shift binding assays, suggested that these molecules target the viral protein 2C. Overall, the pyrazolopyridine inhibitors represent a promising class of candidates for the urgently needed nonpolio enterovirus antivirals.

Enterovirus D68 in hospitalized children with respiratory symptoms in Guangdong from 2014 to 2018: Molecular epidemiology and clinical characteristics

BACKGROUND

Enterovirus D68 (EV-D68) is an emerging pathogen in humans. EV-D68 causes a wide range of respiratory symptoms in children and has the propensity to cause severe complications. EV-D68 outbreaks are rarely investigated in mainland China. Therefore, in this study, we aimed to investigate the prevalence of EV-D68 in children and to describe the clinical manifestations as well as the phylogeny of EV-D68 in Guangdong Province from 2014 to 2018.

METHODS

Nasopharyngeal swabs were collected from hospitalized children with respiratory symptoms and screened for respiratory pathogens by fluorescence quantitative PCR and culture. The EV-positive samples were subsequently typed by sequencing the 5'-untranslated region and EV-D68-specific VP1 capsid gene. A phylogenetic tree was constructed by the maximum-likelihood method based on the VP1 gene using ClustalW.

RESULTS

A total of 1,498 (59.8%) out of 2,503 children were screened positive for ≥1 virus species. Among the 158 (6.31%) EV-positive samples, 17 (0.68%) were identified as EV-D68. Most EV-D68 cases (n = 14) were diagnosed with pneumonia and bronchial pneumonia. No deaths were found in EV-D68 cases. Wheezing occurred in EV-D68 cases more frequently (70.59% vs. 43.26%, P = 0.040) than that of other EVs. All the EV-D68 were of clade B3, which were highly similar to the strains circulating in China.

CONCLUSION

EV-D68 was the predominant enterovirus type in hospitalized children with respiratory symptoms in Guangdong Province. All the EV-D68 strains belong to clade B3. The development of diagnostic tools is warranted in order to monitor EV-D68 infections in China.

Epidemiological dynamics of enterovirus D68 in the United States and implications for acute flaccid myelitis

Acute flaccid myelitis (AFM) recently emerged in the United States as a rare but serious neurological condition since 2012. Enterovirus D68 (EV-D68) is thought to be a main causative agent, but limited surveillance of EV-D68 in the United States has hampered the ability to assess their causal relationship. Using surveillance data from the BioFire Syndromic Trends epidemiology network in the United States from January 2014 to September 2019, we characterized the epidemiological dynamics of EV-D68 and found latitudinal gradient in the mean timing of EV-D68 cases, which are likely climate driven. We also demonstrated a strong spatiotemporal association of EV-D68 with AFM. Mathematical modeling suggested that the recent dominant biennial cycles of EV-D68 dynamics may not be stable. Nonetheless, we predicted that a major EV-D68 outbreak, and hence an AFM outbreak, would have still been possible in 2020 under normal epidemiological conditions. Nonpharmaceutical intervention efforts due to the ongoing COVID-19 pandemic are likely to have reduced the sizes of EV-D68 and AFM outbreaks in 2020, illustrating the broader epidemiological impact of the pandemic.

A food-responsive switch modulates TFEB and autophagy, and determines susceptibility to coxsackievirus infection and pancreatitis

Almost a billion people worldwide are chronically undernourished. Herein, using a mouse model of coxsackievirus B3 (CVB3) infection, we report that a single day of food restriction (FR) markedly increases susceptibility to attenuated enterovirus infection, replication, and disease. These "pro-viral" effects, which are rapidly-reversed by the restoration of food, are mediated by several genes whose expression is altered by FR, and which support CVB3 replication. Central to this is TFEB, a protein whose expression and activation status are rapidly increased by FR. TFEB, which regulates the transcription of >100 genes involved in macroautophagy/autophagy and lysosomal biogenesis, responds similarly to both FR and CVB3 infection and plays a pivotal role in determining host susceptibility to CVB3. We propose that, by upregulating TFEB, FR generates an intracellular environment that is more hospitable to the incoming virus, facilitating its replication. This interplay between nutritional status and enterovirus replication has implications for human health and, perhaps, for the evolution of these viruses.Abbreviations: Atg/ATG: autophagy-related; CAR: Coxsackievirus and adenovirus receptor; Cas9: CRISPR associated protein 9; Cre: recombinase that causes recombination; CRISPR: clustered regularly interspaced short palindromic repeats; Ctsb/CTSB: cathepsin B; CVB3: coxsackievirus B3; DsRedCVB3: a recombinant CVB3 that encodes the Discosoma red fluorescent protein; EL: elastase; FR: food restriction; GFP: green fluorescent protein; gRNA: guide RNA; HBSS: Hanks Buffered Salt Solution; LYNUS: lysosomal nutrient sensing machinery; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MFI: mean fluorescence intensity; MOI: multiplicity of infection; MTOR: mechanistic target of rapamycin kinase; Nluc: nanoluciferase; NlucCVB3: a recombinant CVB3 encoding nanoluciferase; pfu: plaque-forming unit(s); p.i.: post infection; rCVB: recombinant coxsackievirus B3; RPS6KB/p70S6K: ribosomal protein S6 kinase; RT: room temperature; siRNA: small interfering RNA; TFEB: transcription factor EB; tg: transgenic; TUBB: β-tubulin; UNINF: uninfected; wrt: with respect to; WT: wild type.

Epidemiological dynamics of enterovirus D68 in the US: implications for acute flaccid myelitis

The lack of active surveillance for enterovirus D68 (EV-D68) in the US has hampered the ability to assess the relationship with predominantly biennial epidemics of acute flaccid myelitis (AFM), a rare but serious neurological condition. Using novel surveillance data from the BioFire® Syndromic Trends (Trend) epidemiology network, we characterize the epidemiological dynamics of EV-D68 and demonstrate strong spatiotemporal association with AFM. Although the recent dominant biennial cycles of EV-D68 dynamics may not be stable, we show that a major EV-D68 epidemic, and hence an AFM outbreak, would still be possible in 2020 under normal epidemiological conditions. Significant social distancing due to the ongoing COVID-19 pandemic could reduce the size of an EV-D68 epidemic in 2020, illustrating the potential broader epidemiological impact of the pandemic.

Acute flaccid myelitis: cause, diagnosis, and management

Acute flaccid myelitis (AFM) is a disabling, polio-like illness mainly affecting children. Outbreaks of AFM have occurred across multiple global regions since 2012, and the disease appears to be caused by non-polio enterovirus infection, posing a major public health challenge. The clinical presentation of flaccid and often profound muscle weakness (which can invoke respiratory failure and other critical complications) can mimic several other acute neurological illnesses. There is no single sensitive and specific test for AFM, and the diagnosis relies on identification of several important clinical, neuroimaging, and cerebrospinal fluid characteristics. Following the acute phase of AFM, patients typically have substantial residual disability and unique long-term rehabilitation needs. In this Review we describe the epidemiology, clinical features, course, and outcomes of AFM to help to guide diagnosis, management, and rehabilitation. Future research directions include further studies evaluating host and pathogen factors, including investigations into genetic, viral, and immunological features of affected patients, host-virus interactions, and investigations of targeted therapeutic approaches to improve the long-term outcomes in this population.

Return of the Neurotropic Enteroviruses: Co-Opting Cellular Pathways for Infection

Enteroviruses are among the most common human infectious agents. While infections are often mild, the severe neuropathogenesis associated with recent outbreaks of emerging non-polio enteroviruses, such as EV-A71 and EV-D68, highlights their continuing threat to public health. In recent years, our understanding of how non-polio enteroviruses co-opt cellular pathways has greatly increased, revealing intricate host-virus relationships. In this review, we focus on newly identified mechanisms by which enteroviruses hijack the cellular machinery to promote their replication and spread, and address their potential for the development of host-directed therapeutics. Specifically, we discuss newly identified cellular receptors and their contribution to neurotropism and spread, host factors required for viral entry and replication, and recent insights into lipid acquisition and replication organelle biogenesis. The comprehensive knowledge of common cellular pathways required by enteroviruses could expose vulnerabilities amenable for host-directed therapeutics against a broad spectrum of enteroviruses. Since this will likely include newly arising strains, it will better prepare us for future epidemics. Moreover, identifying host proteins specific to neurovirulent strains may allow us to better understand factors contributing to the neurotropism of these viruses.

Viral meningitis: an overview

Meningitis is a serious condition that affects the central nervous system. It is an inflammation of the meninges, which is the membrane that surrounds both the brain and the spinal cord. Meningitis can be caused by bacterial, viral, or fungal infections. Many viruses, such as enteroviruses, herpesviruses, and influenza viruses, can cause this neurological disorder. However, enteroviruses have been found to be the underlying cause of most viral meningitis cases worldwide. With few exceptions, the clinical manifestations and symptoms associated with viral meningitis are similar for the different causative agents, which makes it difficult to diagnose the disease at early stages. The pathogenesis of viral meningitis is not clearly defined, and more studies are needed to improve the health care of patients in terms of early diagnosis and management. This review article discusses the most common causative agents, epidemiology, clinical features, diagnosis, and pathogenesis of viral meningitis.

Database and Analytical Resources for Viral Research Community

Many public databases and analytical resources are available to facilitate virology research. The Virus Pathogen Database and Analysis Resource (ViPR, see “Relevant Websites section”) and Influenza Research Database (IRD, see “Relevant Websites section”) are comprehensive and highly curated repositories of genome and protein sequence records and annotations, protein structures, immune epitopes, and epidemiological and surveillance data about human and related viral pathogens. These data are acquired from public repositories, direct submissions and in-house bioinformatics analyses. The resources offer seamless integration of data, analytics and visualization, and are freely available without cost or restriction to facilitate diagnostics and therapeutics development for priority pathogens.

Enterovirus D68 molecular and cellular biology and pathogenesis

In recent years, enterovirus D68 (EV-D68) has advanced from a rarely detected respiratory virus to a widespread pathogen responsible for increasing rates of severe respiratory illness and acute flaccid myelitis (AFM) in children worldwide. In this review, we discuss the accumulating data on the molecular features of EV-D68 and place these into the context of enterovirus biology in general. We highlight similarities and differences with other enteroviruses and genetic divergence from own historical prototype strains of EV-D68. These include changes in capsid antigens, host cell receptor usage, and viral RNA metabolism collectively leading to increased virulence. Furthermore, we discuss the impact of EV-D68 infection on the biology of its host cells, and how these changes are hypothesized to contribute to motor neuron toxicity in AFM. We highlight areas in need of further research, including the identification of its primary receptor and an understanding of the pathogenic cascade leading to motor neuron injury in AFM. Finally, we discuss the epidemiology of the EV-D68 and potential therapeutic approaches.

Epidemiology and Sequence-Based Evolutionary Analysis of Circulating Non-Polio Enteroviruses

Enteroviruses (EVs) are positive-sense RNA viruses, with over 50,000 nucleotide sequences publicly available. While most human infections are typically associated with mild respiratory symptoms, several different EV types have also been associated with severe human disease, especially acute flaccid paralysis (AFP), particularly with endemic members of the EV-B species and two pandemic types—EV-A71 and EV-D68—that appear to be responsible for recent widespread outbreaks. Here we review the recent literature on the prevalence, characteristics, and circulation dynamics of different enterovirus types and combine this with an analysis of the sequence coverage of different EV types in public databases (e.g., the Virus Pathogen Resource). This evaluation reveals temporal and geographic differences in EV circulation and sequence distribution, highlighting recent EV outbreaks and revealing gaps in sequence coverage. Phylogenetic analysis of the EV genus shows the relatedness of different EV types. Recombination analysis of the EV-A species provides evidence for recombination as a mechanism of genomic diversification. The absence of broadly protective vaccines and effective antivirals makes human enteroviruses important pathogens of public health concern.

Association of outcomes in acute flaccid myelitis with identification of enterovirus at presentation: a Canadian, nationwide, longitudinal study

BACKGROUND

Acute flaccid myelitis (AFM) is characterised by rapid onset of limb weakness with spinal cord grey-matter abnormalities on MRI scan. We aimed to assess whether detection of enterovirus in respiratory or other specimens can help predict prognosis in children with AFM.

METHODS

In this nationwide, longitudinal study, we evaluated the significance of detection of enterovirus in any sample in predicting outcomes in a cohort of Canadian children younger than 18 years presenting with AFM to tertiary paediatric hospitals in Canada in 2014 and 2018. All patients fulfilled the 2015 US Centers for Disease Control and Prevention case definition for definite AFM or probable AFM. Clinical data, laboratory findings, treatment, and neuroimaging results were collected (follow up period up to 5 years). We assessed neurological function and motor outcomes using Kurtzke's Expanded Disability Status Scale (EDSS) and a Weakest Limb Score.

FINDINGS

58 children with AFM (median age 5·1 years, IQR 3·8-8·3) were identified across five of Canada's ten provinces and three territories. 25 (43%) children had enterovirus detected in at least one specimen: 16 (64%) with EV-D68, two (8%) with EV-A71, two (8%) with coxsackievirus, 10 (40%) with untyped enterovirus. Children who were enterovirus positive were more likely than those that were negative to have had quadriparesis (12 [48%] of 25 vs four [13%] of 30; p=0·028), bulbar weakness (11 [44%] of 25 vs two [7%] of 30; p=0·028), bowel or bladder dysfunction (14 [56%] of 25 vs seven [23%] of 30; p=0·040), cardiovascular instability (nine [36%] of 25 vs one [3%] of 30; p=0·028), and were more likely to require intensive care unit admission (13 [52%] of 25 vs 5 [17%] of 30; p=0·028). On MRI, most children who were enterovirus positive showed brainstem pontine lesions (14 [61%] of 23), while other MRI parameters did not correlate with enterovirus status. Median EDSS of enterovirus positive (EV+) and enterovirus negative (EV-) groups was significantly different at all timepoints: baseline (EDSS 8·5, IQR 4·1-9·5 vs EDSS 4·0, IQR 3·0-6·0; p=0·0067), 3 months (EDSS 4·0, IQR 3·0-7·4 vs EDSS 3·0, IQR 1·5-4·3; p=0·0067), 6 months (EDSS 3·5, IQR 3·0-7·0 vs EDSS 3·0, IQR 1·0-4·0; p=0·029), and 12 months (EDSS 3·0, IQR 3·0-6·9 vs EDSS 2·5 IQR 0·3-3·0; p=0·0067). Kaplan-Meier survival analysis of a subgroup of patients showed significantly poorer motor recovery among children who tested positive for enterovirus than for those who tested negative (p=0·037).

INTERPRETATION

Detection of enterovirus in specimens from non-sterile sites at presentation correlated with more severe acute motor weakness, worse overall outcomes and poorer trajectory for motor recovery. These results have implications for rehabilitation planning as well as counselling of families of children with these disorders. The findings of this study support the need for early testing for enterovirus in non-CNS sites in all cases of AFM.

FUNDING

None.

Comprehensive analysis of differential expression profiles via transcriptome sequencing in SH-SY5Y cells infected with CV-A16

Coxsackievirus A16 (CV-A16) is one of the viruses that is most frequently associated with hand-foot-and-mouth disease (HFMD). Previous studies have shown that CV-A16 infections are mostly self-limiting, but in recent years, it has been gradually found that CV-A16 infections can also induce neurological complications and eventually cause death in children with HFMD. Moreover, no curative drugs or preventative vaccines have been developed for CV-A16 infection. Therefore, it is particularly important to investigate the mechanism of CV-A16 infection-induced neuropathy. In the current study, transcriptome sequencing technology was used to identify changes in the transcriptome of SH-SY5Y cells infected with CV-A16, which might hide the mechanism of CV-A16-induced neuropathology. The transcriptome profiling showed that 82,406,974, 108,652,260 and 97,753,565 clean reads were obtained in the Control, CV-A16-12 h and CV-A16-24 h groups, respectively. And it was further detected that a total of 136 and 161 differentially expressed genes in CV-A16-12 h and CV-A16-24 h groups, respectively, when compared with Control group. Then, to explore the mechanism of CV-A16 infection, we focused on the common differentially expressed genes at different time points of CV-A16 infection and found that there were 34 differentially expressed genes based on which clustering analysis and functional category enrichment analysis were performed. The results indicated that changes in oxidation levels were particularly evident in the GO term analysis, while only the “Gonadotropin-releasing hormone receptor pathway” was enriched in the KEGG pathway analysis, which might be closely related to the neurotoxicity caused by CV-A16 infection. Meanwhile, the ID2 closely related to nervous system has been demonstrated to be increased during CV-A16 infection. Additionally, the data on differentially expressed non-protein-coding genes of different types within the transcriptome sequencing results were analyzed, and it was speculated that these dysregulated non-protein-coding genes played a pivotal role in CV-A16 infection. Ultimately, qRT-PCR was utilized to validate the transcriptome sequencing findings, and the results of qRT-PCR were in agreement with the transcriptome sequencing data. In conclusion, transcriptome profiling was carried out to analyze response of SH-SY5Y cells to CV-A16 infection. And our findings provide important information to elucidate the possible molecular mechanisms which were linked to the neuropathogenesis of CV-A16 infection.

Enhanced Enterovirus D68 Replication in Neuroblastoma Cells Is Associated with a Cell Culture-Adaptive Amino Acid Substitution in VP1

Enterovirus D68 (EV-D68) causes mild to severe respiratory disease and is associated with acute flaccid myelitis since 2014. Currently, the understanding of the ability of EV-D68 to replicate in the central nervous system (CNS), and whether it is associated with a specific clade of EV-D68 viruses or specific viral factors, is lacking. Comparing different EV-D68 clades did not reveal clade-specific phenotypic characteristics. However, we did show that viruses which acquired a cell culture-adapted amino acid substitution in VP1 (E271K) recognized heparan sulfate as an additional receptor. Recognition of heparan sulfate resulted in an increase in attachment, infection, and replication in neuroblastoma cells compared with viruses without this specific amino acid substitution. The ability of EV-D68 viruses to acquire cell culture-adaptive substitutions which have a large effect in experimental settings emphasizes the need to sequence virus stocks.

Since its emergence in the United States in 2014, enterovirus D68 (EV-D68) has been and is associated with severe respiratory diseases and acute flaccid myelitis. Even though EV-D68 has been shown to replicate in different neuronal cells in vitro, it is currently poorly understood which viral factors contribute to the ability to replicate efficiently in cells of the central nervous system and whether this feature is a clade-specific feature. Here, we determined the replication kinetics of clinical EV-D68 isolates from (sub)clades A, B1, B2, B3, and D1 in human neuroblastoma cells (SK-N-SH). Subsequently, we compared sequences to identify viral factors associated with increased viral replication. All clinical isolates replicated in SK-N-SH cells, although there was a large difference in efficiency. Efficient replication of clinical isolates was associated with an amino acid substitution at position 271 of VP1 (E271K), which was acquired during virus propagation in vitro. Recognition of heparan sulfate in addition to sialic acids was associated with increased attachment, infection, and replication. Removal of heparan sulfate resulted in a decrease in attachment, internalization, and replication of viruses with E271K. Taken together, our study suggests that the replication kinetics of EV-D68 isolates in SK-N-SH cells is not a clade-specific feature. However, recognition of heparan sulfate as an additional receptor had a large effect on phenotypic characteristics in vitro. These observations emphasize the need to compare sequences from virus stocks with clinical isolates in order to retrieve phenotypic characteristics from original virus isolates.

IMPORTANCE Enterovirus D68 (EV-D68) causes mild to severe respiratory disease and is associated with acute flaccid myelitis since 2014. Currently, the understanding of the ability of EV-D68 to replicate in the central nervous system (CNS), and whether it is associated with a specific clade of EV-D68 viruses or specific viral factors, is lacking. Comparing different EV-D68 clades did not reveal clade-specific phenotypic characteristics. However, we did show that viruses which acquired a cell culture-adapted amino acid substitution in VP1 (E271K) recognized heparan sulfate as an additional receptor. Recognition of heparan sulfate resulted in an increase in attachment, infection, and replication in neuroblastoma cells compared with viruses without this specific amino acid substitution. The ability of EV-D68 viruses to acquire cell culture-adaptive substitutions which have a large effect in experimental settings emphasizes the need to sequence virus stocks.

Advances in the development of entry inhibitors for sialic-acid-targeting viruses

Over the past decades, several antiviral drugs have been developed to treat a range of infections. Yet the number of treatable viral infections is still limited, and resistance to current drug regimens is an ever-growing problem. Therefore, additional strategies are needed to provide a rapid cure for infected individuals. An interesting target for antiviral drugs is the process of viral attachment and entry into the cell. Although most viruses use distinct host receptors for attachment to the target cell, some viruses share receptors, of which sialic acids are a common example. This review aims to give an update on entry inhibitors for a range of sialic-acid-targeting viruses and provides insight into the prospects for those with broad-spectrum potential.

Enterovirus D68-Associated Acute Flaccid Myelitis, United States, 2020

Acute flaccid myelitis (AFM) is a serious neurologic condition that causes limb weakness or paralysis in previously healthy children. Since clusters of cases were first reported in 2014, nationwide surveillance has demonstrated sharp increases in AFM cases in the United States every 2 years, most occurring during late summer and early fall. Given this current biennial pattern, another peak AFM season is expected during fall 2020 in the United States. Scientific understanding of the etiology and the factors driving the biennial increases in AFM has advanced rapidly in the past few years, although areas of uncertainty remain. The Centers for Disease Control and Prevention and AFM partners are focused on answering key questions about AFM epidemiology and mechanisms of disease. This article summarizes the current understanding of AFM etiology and outlines priorities for surveillance and research as we prepare for a likely surge in cases in 2020.

Enterovirus infection and acute flaccid myelitis

Recent outbreaks of limb paralysis similar to poliomyelitis, termed acute flaccid myelitis (AFM), have prompted intense investigation into potential etiology. Peaks of AFM were seen in the United States in 2012, 2014, 2016 and 2018, coincident with peaks in enterovirus transmission, particularly EV-D68. Similar peaks of AFM and EV-D68 circulation were reported in other parts of the world. The causal relationship between EV-D68 is still not widely accepted as it is for poliovirus and EV-A71, the latter of which is endemic in the US. Recent in vitro and mouse model data as well as enhanced-sensitivity diagnostic assays have provided further evidence linking the causal relationship between EV-D68 and AFM. In addition, an outbreak of EV-A71-associated AFM was recently described, highlighting the possibility of an additional emerging non-polio enterovirus of public health concern. As AFM is a devastating disease with poor prognosis in many children, particularly those with EV-D68, recent studies call for increased surveillance, pursuit of novel therapeutics and strategies to prevent transmission before the next outbreak.

Enterovirus D68 Antivirals: Past, Present, and Future

Enterovirus D68 (EV-D68) is an RNA virus that causes respiratory illnesses mainly in children. In severe cases, it can lead to neurological complications such as acute flaccid myelitis (AFM). EV-D68 belongs to the enterovirus genera of the Picornaviridae family, which also includes many other significant human pathogens such as poliovirus, enterovirus A71, and rhinovirus. There are currently no vaccines or antivirals against EV-D68. In this review, we present the current understanding of the link between EV-D68 and AFM, the mechanism of viral replication, and recent progress in developing EV-D68 antivirals by targeting various viral proteins and host factors that are essential for viral replication. The future directions of EV-D68 antiviral drug discovery and the criteria for drugs to reach clinical trials are also discussed.

Emergence of enterovirus D68 clade D1, France, August to November 2018

We report a seasonal increase of enterovirus D68 (EV-D68) cases in France, with 54 cases detected between 19 August and 14 November 2018. Molecular typing revealed that 20 of 32 of the isolates belonged to clade D1, only sporadically detected before in France. Median age of D1-cases was 42 years, 10 developed severe respiratory signs and one had neurological complications. The 2018-D1 viruses showed a genetic divergence of 3.34 % with D1 viruses identified previously.

Development of broad-spectrum enterovirus antivirals based on quinoline scaffold

Non-polio enteroviruses such as enterovirus A71 (EV-A71), EV-D68, and coxsackievirus B3 (CVB3) are significant human pathogens with disease manifestations ranging from mild flu-like symptoms to more severe encephalitis, myocarditis, acute flaccid paralysis/myelitis, and even death. There is currently no effective antivirals to prevent or treat non-polio enterovirus infection. In this study, we report our progress in developing potent and broad-spectrum antivirals against these non-polio enteroviruses. Starting from our previously developed lead compounds that had potent antiviral activity against EV-D68, we synthesized 43 analogs and profiled their broad-spectrum antiviral activity against additional EV-D68, EV-A71, and CVB3 viruses. Promising candidates were also selected for mouse microsomal stability test to prioritize lead compounds for future in vivo mouse model studies. Collectively, this multi-parameter optimization process revealed a promising lead compound 6aw that showed single-digit to submicromolar EC₅₀ values against two EV-D68 strains (US/KY and US/MO), two EV-A71 strains (Tainan and US/AK), and one CVB3 strain, with a high selectivity index. Encouragingly, 6aw was stable in mouse microsomes with a half-life of 114.7 min. Overall, 6aw represents one of the most potent broad-spectrum antiviral against non-polio enteroviruses, rendering it a promising lead candidate for non-polio enteroviruses with translational potential.

Asian Zika Virus Isolate Significantly Changes the Transcriptional Profile and Alternative RNA Splicing Events in a Neuroblastoma Cell Line

The alternative splicing of pre-mRNAs expands a single genetic blueprint to encode multiple, functionally diverse protein isoforms. Viruses have previously been shown to interact with, depend on, and alter host splicing machinery. The consequences, however, incited by viral infection on the global alternative slicing (AS) landscape are under-appreciated. Here, we investigated the transcriptional and alternative splicing profile of neuronal cells infected with a contemporary Puerto Rican Zika virus (ZIKV^PR) isolate, an isolate of the prototypical Ugandan ZIKV (ZIKV^MR), and dengue virus 2 (DENV2). Our analyses revealed that ZIKV^PR induced significantly more differential changes in expressed genes compared to ZIKV^MR or DENV2, despite all three viruses showing equivalent infectivity and viral RNA levels. Consistent with the transcriptional profile, ZIKV^PR induced a higher number of alternative splicing events compared to ZIKV^MR or DENV2, and gene ontology analyses highlighted alternative splicing changes in genes associated with mRNA splicing. In summary, we show that ZIKV affects cellular RNA homeostasis not only at the transcriptional levels but also through the alternative splicing of cellular transcripts. These findings could provide new molecular insights into the neuropathologies associated with this virus.

Molecular Pathogenicity of Enteroviruses Causing Neurological Disease

Enteroviruses are single-stranded positive-sense RNA viruses that primarily cause self-limiting gastrointestinal or respiratory illness. In some cases, these viruses can invade the central nervous system, causing life-threatening neurological diseases including encephalitis, meningitis and acute flaccid paralysis (AFP). As we near the global eradication of poliovirus, formerly the major cause of AFP, the number of AFP cases have not diminished implying a non-poliovirus etiology. As the number of enteroviruses linked with neurological disease is expanding, of which many had previously little clinical significance, these viruses are becoming increasingly important to public health. Our current understanding of these non-polio enteroviruses is limited, especially with regards to their neurovirulence. Elucidating the molecular pathogenesis of these viruses is paramount for the development of effective therapeutic strategies. This review summarizes the clinical diseases associated with neurotropic enteroviruses and discusses recent advances in the understanding of viral invasion of the central nervous system, cell tropism and molecular pathogenesis as it correlates with host responses.

Enterovirus D68-associated respiratory and neurological illness in Spain, 2014-2018

During 2014, enterovirus D68 (EV-D68) outbreaks were described globally, causing severe respiratory diseases in children and, in some cases, subsequent paralysis. In this study, the type characterization of enterovirus (EV) detected in respiratory illnesses and the epidemiology and clinical association of EV-D68 infections in Spain over a five-year period were described. A total of 546 EV-positive samples from hospitalized patients with respiratory infections were included. EV-D68 was the most frequently detected type (46.6%, 191/410 typed EV). Other EV from species A (25.1%), B (27.8%) and C (0.5%) were also identified. EV-D68 infections were more associated with bronchitis while EV-A/B types were more frequent in upper respiratory illness (p < 0.01). EV-D68 was also detected in patients with neurological symptoms (nine meningitis/meningoencephalitis and eight acute flaccid paralysis cases). Phylogenetic analysis of 3′-VP1 region showed most Spanish EV-D68 sequences from 2014 to 2016 belonged to subclades B2/B3, as other American and European strains circulating during the same period. However, those detected in 2017 and 2018 clustered to the emerged subclade D1. In summary, different EV can cause respiratory infections but EV-D68 was the most prevalent, with several strains circulating in Spain at least since 2014. Association between EV-D68 infection and neurological disease was also described.

Acute Flaccid Myelitis: Lessons From Polio

With the eradication of poliomyelitis in the United States, the appearance of acute flaccid myelitis outbreaks has raised questions regarding their causation. Review of the epidemiology, clinical aspects, and laboratory findings of bygone cases of poliomyelitis have revealed shows important similarities with those of newer cases of acute flaccid myelitis. Many occurrences are preceded by an apparent viral illness, and a number of viruses, particularly enteroviruses A71 and D68, can be isolated from respiratory or stool specimens. Our inability to detect these viruses in cerebrospinal fluid samples from these patients does not eliminate them as etiologic agents, because poliovirus is often not detected in cerebrospinal fluid samples of patients with paralysis caused by poliomyelitis.

2019 meeting of the global virus network

The Global Virus Network (GVN) was established in 2011 to strengthen research and responses to emerging viral causes of human disease and to prepare against new viral pandemics. There are now 52 GVN Centers of Excellence and 9 Affiliate laboratories in 32 countries. The 11th International GVN meeting was held from June 9-11, 2019 in Barcelona, Spain and was jointly organized with the Spanish Society of Virology. A common theme throughout the meeting was globalization and climate change. This report highlights the recent accomplishments of GVN researchers in several important areas of medical virology, including severe virus epidemics, anticipation and preparedness for changing disease dynamics, host-pathogen interactions, zoonotic virus infections, ethical preparedness for epidemics and pandemics, one health and antivirals.

Molecular and Clinical Comparison of Enterovirus D68 Outbreaks among Hospitalized Children, Ohio, USA, 2014 and 2018

Enterovirus D68 (EV-D68) causes respiratory tract infections and neurologic manifestations. We compared the clinical manifestations from 2 EV-D68 outbreaks in 2014 and 2018 and a low-activity period in 2016 among hospitalized children in central Ohio, USA, and used PCR and sequencing to enable phylogenetic comparisons. During both outbreak periods, infected children had respiratory manifestations that led to an increase in hospital admissions for asthma. The 2018 EV-D68 outbreak appeared to be milder in terms of respiratory illness, as shown by lower rates of pediatric intensive care unit admission. However, the frequency of severe neurologic manifestations was higher in 2018 than in 2014. During the same period in 2016, we noted neither an increase in EV-D68 nor a significant increase in asthma-related admissions. Phylogenetic analyses showed that EV-D68 isolates from 2018 clustered differently within clade B than did isolates from 2014 and are perhaps associated with a different EV-D68 subclade.