Seroepidemiology of enterovirus D68 infection in China

Insights Into Enterovirus D68 Immunology: Unraveling the Mysteries of Host-Pathogen Interactions

BACKGROUND

Enterovirus D68 (EV-D68) has emerged as a significant respiratory and neurological pathogen, particularly affecting children with severe respiratory illnesses and acute flaccid myelitis. Understanding the interaction between EV-D68 and the host immune system is crucial for developing effective prevention and treatment strategies.

OBJECTIVES

This review aims to examine the immune response to EV-D68, its mechanisms of immune evasion, and the current progress in vaccine and antiviral development while identifying gaps in knowledge and future research directions.

METHODS

A comprehensive review of the literature was conducted, focusing on the innate and adaptive immune responses to EV-D68, its strategies for immune evasion, and advancements in therapeutic interventions.

RESULTS

Pattern recognition receptors detect EV-D68 and trigger antiviral defenses, including interferon production and activation of natural killer cells. B cells generate antibodies, while T cells coordinate a targeted response to the virus. EV-D68 employs mechanisms such as antigenic variation and disruption of host antiviral pathways to evade immune detection. Progress in vaccine and antiviral research shows promise but remains in the early stages.

CONCLUSIONS

EV-D68 represents a complex and evolving public health challenge. Although the immune system mounts a robust response, the virus's ability to evade these defenses complicates efforts to control it. Continued research is essential to develop effective vaccines and antivirals and to address gaps in understanding its pathogenesis and immune interactions.

IMPLICATIONS

A multidisciplinary approach is critical to improving diagnostic, preventive, and therapeutic strategies for EV-D68, ensuring better preparedness for future outbreaks.

Global age-stratified seroprevalence of enterovirus D68: a systematic literature review

Enterovirus D68 (EV-D68), first isolated in 1962, emerged in 2014, causing outbreaks of severe respiratory infections and acute flaccid myelitis. In this systematic review, we have compiled all available literature on age-stratified seroprevalence estimates of EV-D68. Ten studies from six countries were retained, all conducted using microneutralisation assays, despite wide variations in protocols and challenge viruses. The age profiles of seroprevalence were similar across time and regions; seroprevalence increased quickly with age, reaching roughly 100% by the age of 20 years and with no sign of decline throughout adulthood. This suggests continuous or frequent exposure of the populations to the virus, or possible cross-reactivity with other viruses. Studies with two or more cross-sectional surveys reported consistently higher seroprevalence at later timepoints, suggesting a global increase in transmission over time. This systematic review concludes that standardising serological protocols, understanding the contribution of cross-reactivity with other pathogens to the high reported seroprevalence, and quantifying individual exposure to EV-D68 over time are the main research priorities for the future.

Seroprevalence of enterovirus D68 in Yamagata, Japan, between 1976 and 2019

To clarify the epidemiology of enterovirus D68 (EV-D68), an enterovirus rarely identified in the 20th century, we performed seroepidemiological analysis against EV-D68 using sera collected in 1976, 1985, 1990, 1999, 2009, and 2019, as well as Yamagata isolate (EVD68/Yamagata.JPN/2023-89), in Yamagata, Japan. The neutralizing antibody (Ab)-positive rates for those under 20 years old were 61.0%, 82.5%, 84.3%, 46.7%, 50.5%, and 67.9%, in each year, whereas the rates for those above 20 years old were between 93.4% and 99.1%. Generally, geometric mean titers (GMTs）increased with age among children and the total GMT in each year was 25.4, 49.2, 37.2, 30.8, 29.5, and 33.9, from 1976 to 2019, respectively. The findings in this Yamagata-based study showed that the seroprevalence of EV-D68 over the last four decades has increased with age among children, as a susceptible group, and then reaches a plateau of over approximately 80% among adults. This study clearly revealed that EV-D68 was stably transmitted among children in the 20th century, when EV-D68 detection was quite rare.

Clinical and molecular epidemiology of enterovirus D68 from 2013 to 2020 in Shanghai

Enterovirus D68 (EV-D68) is an emerging pathogen that has caused outbreaks of severe respiratory disease worldwide, especially in children. We aim to investigate the prevalence and genetic characteristics of EV-D68 in children from Shanghai. Nasopharyngeal swab or bronchoalveolar lavage fluid samples collected from children hospitalized with community-acquired pneumonia were screened for EV-D68. Nine of 3997 samples were EV-D68-positive. Seven of nine positive samples were sequenced and submitted to GenBank. Based on partial polyprotein gene (3D) or complete sequence analysis, we found the seven strains belong to different clades and subclades, including three D1 (detected in 2013 and 2014), one D2 (2013), one D3 (2019), and two B3 (2014 and 2018). Overall, we show different clades and subclades of EV-D68 spread with low positive rates (0.2%) among children in Shanghai between 2013 and 2020. Amino acid mutations were found in the epitopes of the VP1 BC and DE loops and C-terminus; similarity analysis provided evidence for recombination as an important mechanism of genomic diversification. Both single nucleotide mutations and recombination play a role in evolution of EV-D68. Genetic instability within these clinical strains may indicate large outbreaks could occur following cumulative mutations.

Molecular epidemiology and recombination of enterovirus D68 in China

Enterovirus D68 (EV-D68), a member of Enterovirus genus of the Picornaviridae family, mainly causes respiratory system-related diseases as well as neurological complications in some patients. At present, there is no effective vaccine or treatment for the virus. The aim of this research was to systematically analyse the molecular epidemiology, recombination and changes in the epitope of EV-D68 in China from 2008 to 2022. Through phylogenetic analysis based on VP1 sequences, it was found that there was limited information about EV-D68 infection before 2011 and that EV-D68 infection was dominated by the A2 gene subtype from 2011 to 2013 and the B3 genotype from 2014 to 2018, during which A2 and B3 were coprevalent and alternately prevalent. We also constructed a phylogenetic tree using the EV-D68 full-length genome sequences, and the genotype of each sequence was consistent with that of the VP1 sequence evolutionary tree. Recombination analysis showed that MH341715 underwent intertypic recombination with the A2 genotype MH341729 at the 5' untranslated region (5'UTR) and that P1-P3 underwent recombination with the B3 genotype MH341712. The capsid protein VP1 is one of the most important structural proteins. In VP1, the BC-loop (89-105 amino acids) and DE-loop (140-152 amino acids) are the most variable domains on the surface of the virus and are associated with epitopes. In this study, it was found that the dominant amino acid composition of the BC-loop and DE-loop continued to change with the epidemic of the virus; the amino acid composition also differed in different regions of the same genotypes. The ongoing genomic and molecular epidemiology of EV-D68 remains important for predicting emergence of new viruses and preventing major outbreaks of respiratory diseases.

Seroprevalence of Enterovirus D68 Infection among Humans: A Systematic Review and Meta-Analysis

INTRODUCTION

Human enterovirus D68 (EV-D68), which belongs to enteroviruses of the small RNA family, is a type of enterovirus that can cause acute respiratory tract infection and central nervous system diseases. This study systematically analysed and summarized EV-D68 antibody studies in databases and identified the seropositivity rates of different regions, ages, and sexes.

METHODS

Meta-analysis was performed using STATA 16.0 software. I2 and Q tests were used to analyse the heterogeneity of the included studies. Meta-regression analysis was performed for different groups, and Egger's linear regression analysis was used to evaluate publication bias.

RESULTS

The results of multiple studies indicated that the serological prevalence range of EV-D68 antibody was 17.78-96.69%. The results of the meta-analysis showed that the seropositivity rate of EV-D68 antibody was 76% (95% confidence interval [CI]: 67-84%), among which that of the Chinese population was 74% (95% CI: 61-86%) and that of other countries was 79% (95% CI: 65-91%). At the same time, a subgroup analysis was conducted. The seroprevalence of EV-D68 antibody was related to age but not sex or region.

CONCLUSION

The seropositivity rate was lower in the below 5-year age group; however, it gradually increased with age. The results of this study showed that EV-D68 infection was widespread in the population, and the current clinical infection situation could not reflect the actual epidemic situation of the virus, among which children under 5 years old were vulnerable to infection, which should be given greater attention for epidemic prevention and control.

Serostatus of echovirus 11, coxsackievirus B3 and enterovirus D68 in cord blood: The implication of severe newborn enterovirus infection

BACKGROUND

Maternal transplacental antibody is an important origins of passive immunity against neonatal enterovirus infection. Echovirus 11 (E11) and coxsackievirus B3 (CVB3) are important types causing neonatal infections. There were few investigations of enterovirus D68 (EVD68) infection in neonates. We aimed to investigate the serostatus of cord blood for these three enteroviruses and evaluate the factors associated with seropositivity.

METHODS

We enrolled 222 parturient (gestational age 34-42 weeks) women aged 20-46 years old between January and October 2021. All participants underwent questionnaire investigation and we collected the cord blood to measure the neutralization antibodies against E11, CVB3 and EVD68.

RESULTS

The cord blood seropositive rates were 18% (41/222), 60% (134/232) and 95% (211/222) for E11, CVB3 and EVD68, respectively (p < 0.001). Geometric mean titers were 3.3 (95% CI 2.9-3.8) for E11, 15.9 (95% CI 12.5-20.3) for CVB3 and 109.9 (95% CI 92.4-131.6) for EVD68. Younger parturient age (33.8 ± 3.6 versus 35.2 ± 4.4, p = 0.04) was related to E11 seropositivity. Neonatal sex, gestational age and birth body weight were not significantly different between the seropositive group and the seronegative group.

CONCLUSION

Cord blood seropositive rate and geometric mean titer of E11 were very low, so a large proportion of newborns are susceptible to E11. The circulation of E11 was low after 2019 in Taiwan. A large cohort of immune naïve newborns existed currently due to lack of protective maternal antibodies. It is imminent to monitor the epidemiology of neonates with enterovirus infections and strengthen the relevant preventive policies.

Neutralizing activity of intravenous immune globulin products against enterovirus D68 strains isolated in Japan

BACKGROUND

Enterovirus D68 (EV-D68), belonging to Enterovirus D, is a unique human enterovirus mainly associated with common respiratory diseases. However, EV-D68 can cause severe respiratory diseases, and EV-D68 endemic is epidemiologically linked to current global epidemic of acute flaccid myelitis.

METHODS

In this study, we measured neutralizing antibody titers against six clinical EV-D68 isolates in nine intravenous immune globulin (IVIG) products commercially available in Japan to assess their potential as therapeutic options for severe EV-D68 infection.

RESULTS

Seven IVIG products manufactured from Japanese donors contained high neutralizing antibody titers (IC₅₀ = 0.22-85.01 µg/mL) against all six EV-D68 strains. Apparent differences in neutralizing titers among the six EV-D68 strains were observed for all IVIG products derived from Japanese and non-Japanese blood donors.

CONCLUSIONS

High levels of EV-D68-neutralizing antibodies in IVIG products manufactured from Japanese donors suggest that anti-EV-D68 antibodies are maintained in the Japanese donor population similarly as found in foreign blood donors. Apparent differences in neutralizing antibody titers against the six EV-D68 strains suggest distinct antigenicity among the strains used in this study regardless of the genetic similarity of EV-D68.

Changes in transmission of Enterovirus D68 (EV-D68) in England inferred from seroprevalence data

The factors leading to the global emergence of Enterovirus D68 (EV-D68) in 2014 as a cause of acute flaccid myelitis (AFM) in children are unknown. To investigate potential changes in virus transmissibility or population susceptibility, we measured the seroprevalence of EV-D68-specific neutralising antibodies in serum samples collected in England in 2006, 2011, and 2017. Using catalytic mathematical models, we estimate an approximately 50% increase in the annual probability of infection over the 10-year study period, coinciding with the emergence of clade B around 2009. Despite such increase in transmission, seroprevalence data suggest that the virus was already widely circulating before the AFM outbreaks and the increase of infections by age cannot explain the observed number of AFM cases. Therefore, the acquisition of or an increase in neuropathogenicity would be additionally required to explain the emergence of outbreaks of AFM. Our results provide evidence that changes in enterovirus phenotypes cause major changes in disease epidemiology.

Virome-wide detection of natural infection events and the associated antibody dynamics using longitudinal highly-multiplexed serology

Current methods for detecting infections either require a sample collected from an actively infected site, are limited in the number of agents they can query, and/or yield no information on the immune response. Here we present an approach that uses temporally coordinated changes in highly-multiplexed antibody measurements from longitudinal blood samples to monitor infection events at sub-species resolution across the human virome. In a longitudinally-sampled cohort of South African adolescents representing >100 person-years, we identify >650 events across 48 virus species and observe strong epidemic effects, including high-incidence waves of Aichivirus A and the D68 subtype of Enterovirus D earlier than their widespread circulation was appreciated. In separate cohorts of adults who were sampled at higher frequency using self-collected dried blood spots, we show that such events temporally correlate with symptoms and transient inflammatory biomarker elevations, and observe the responding antibodies to persist for periods ranging from ≤1 week to >5 years. Our approach generates a rich view of viral/host dynamics, supporting novel studies in immunology and epidemiology.

Chemokine PF4 Inhibits EV71 and CA16 Infections at the Entry Stage

Platelet factor 4 (PF4) or the CXC chemokine CXCL4 is the most abundant protein within the α-granules of platelets. Previous studies found that PF4 regulates infections of several viruses, including HIV-1, H1N1, hepatitis C virus (HCV), and dengue virus. Here, we show that PF4 is an inhibitor of enterovirus A71 (EV71) and coxsackievirus A16 (CA16) infections. The secreted form of PF4 from transfected cells or soluble purified PF4 from Escherichia coli, even lacking signal peptide affected secretion, obviously inhibited the propagation of EV71 and CA16. Mechanistically, we demonstrated that PF4 blocked the entry of the virus into the host cells by interactions with VP3 proteins of EV71/CA16 and the interaction with SCARB2 receptor-mediated EV71 and CA16 endocytosis. As expected, the incubation of anti-PF4 antibody with PF4 blocked PF4 inhibition on EV71 and CA16 infections further supported the above conclusion. Importantly, pretreatment of EV71 viruses with PF4 significantly protected the neonatal mice from EV71 lethal challenge and promoted the survival rate of infected mice. PF4 derived from natural platelets by EV71/CA16 activation also presented strong inhibition on EV71 and CA16. In summary, our study identified a new host factor against EV71 and CA16 infections, providing a novel strategy for EV71 and CA16 treatment. IMPORTANCE The virus's life cycle starts with binding to cell surface receptors, resulting in receptor-mediated endocytosis. Targeting the entry of the virus into target cells is an effective strategy to develop a novel drug. EV71 and CA16 are the major pathogens that cause hand, foot, and mouth disease (HFMD) outbreaks worldwide since 2008. However, the treatment of EV71 and CA16 infections is mainly symptomatic because there is no approved drug. Therefore, the underlying pathogenesis of EV71/CA16 and the interaction between host-EV71/CA16 need to be further investigated to develop an inhibitor. Here, we identified PF4 as a potent entry inhibitor of EV71 and CA16 via binding to VP3 proteins of EV71 and CA16 or binding to receptor SCARB2. In the EV71 infection model, PF4 protected mice from EV71 lethal challenge and promoted the survival rate of EV71-infected mice. Our study suggests that PF4 represents a potential candidate host factor for anti-EV71 and CA16 infections.

Inhibitory effect of tanshinone IIA, resveratrol and silibinin on enterovirus 68 production through inhibiting ATM and DNA-PK pathway

BACKGROUND

Human enterovirus 68 (EV68) is a primary etiological agent for respiratory illnesses, while no effective drug has yet used in clinics largely because the pathogenesis of EV68 is not clear. DNA damage response (DDR) responds to cellular DNA breaks and is also involved in viral replication. Three DDR pathways includes ataxia telangiectasia mutated (ATM), ATM and Rad3-related (ATR), and DNA-dependent protein kinase (DNA-PK). Natural products proved to be an excellent source for the discovery and isolation of novel antivirals. Among them, tanshinone IIA, resveratrol, silibinin, rutin and quercetin are reported to target DDR, therefore their roles in anti-EV68 are investigated in this study.

PURPOSE

This study investigated the anti-EV68 ability of various natural compounds related to DDR.

STUDY DESIGN AND METHODS

The methods include cell counting, flow cytometry, western blot, Immunofluorescence staining, comet assays, quantitative real-time RT PCR and short interfering RNAs (siRNAs) for analysis of cell number, cell cycle, protein expression, protein location, DNA damage, mRNA level and knock down target gene, respectively.

RESULTS

EV68 infection induced DDR. Down-regulation or inhibition of ATM or DNA-PK lowered DDR in EV68-infected cells and mitigated viral protein expression, however, down-regulation or inhibition of ATR unexpectedly up-regulated DDR, and promoted viral protein expression. Meanwhile tanshinone IIA, resveratrol, and silibinin inhibited ATM and/or DNA-PK activation and decreased viral proliferation, while rutin and quercetin inhibited ATR activation and promoted viral production. The role of them in ATM, DNA-PK and ATR activation was consistent with previous reports.

CONCLUSION

Tanshinone IIA, resveratrol and silibinin inhibited EV68 proliferation through inhibiting ATM and/or DNA-PK activation, and they were effective anti-EV68 candidates.

Neutralizing Enterovirus D68 Antibodies in Children after 2014 Outbreak, Kansas City, Missouri, USA

Antibodies to B1, B2, and D clade viruses were detected.

Enterovirus D68 (EV-D68) causes severe respiratory illness outbreaks among children, particularly those with asthma. We previously detected neutralizing antibodies against the predominant EV-D68 B1 clade in the 2014 outbreak in serum collected before the outbreak (2012–2013) from persons 24 months to 85 years of age. We recently detected neutralizing antibodies to the 2014 B1, B2, and D clade viruses in serum collected after the 2014 outbreak (April–May 2017) from 300 children 6 months to 18 years of age. B1 virus neutralizing antibodies were found in 100% of patients, even children born after 2014; B2 in 84.6%, and D in 99.6%. In 2017, titers increased with patient age and were higher than titers in 2012–2013 from comparably aged children. Rate of seronegativity was highest (15.3%) for B2 virus. Multivariate analysis revealed an association between asthma and higher titers against B2 and D viruses. EV-D68 seems to have circulated during 2014–2017.

Total infectome characterization of respiratory infections in pre-COVID-19 Wuhan, China

At the end of 2019 Wuhan witnessed an outbreak of "atypical pneumonia" that later developed into a global pandemic. Metagenomic sequencing rapidly revealed the causative agent of this outbreak to be a novel coronavirus denoted SARS-CoV-2. To provide a snapshot of the pathogens in pneumonia-associated respiratory samples from Wuhan prior to the emergence of SARS-CoV-2, we collected bronchoalveolar lavage fluid samples from 408 patients presenting with pneumonia and acute respiratory infections at the Central Hospital of Wuhan between 2016 and 2017. Unbiased total RNA sequencing was performed to reveal their "total infectome", including viruses, bacteria and fungi. We identified 35 pathogen species, comprising 13 RNA viruses, 3 DNA viruses, 16 bacteria and 3 fungi, often at high abundance and including multiple co-infections (13.5%). SARS-CoV-2 was not present. These data depict a stable core infectome comprising common respiratory pathogens such as rhinoviruses and influenza viruses, an atypical respiratory virus (EV-D68), and a single case of a sporadic zoonotic pathogen-Chlamydia psittaci. Samples from patients experiencing respiratory disease on average had higher pathogen abundance than healthy controls. Phylogenetic analyses of individual pathogens revealed multiple origins and global transmission histories, highlighting the connectedness of the Wuhan population. This study provides a comprehensive overview of the pathogens associated with acute respiratory infections and pneumonia, which were more diverse and complex than obtained using targeted PCR or qPCR approaches. These data also suggest that SARS-CoV-2 or closely related viruses were absent from Wuhan in 2016-2017.

Host restriction factor A3G inhibits the replication of Enterovirus D68 through competitively binding 5' UTR with PCBP1

The host restriction factor APOBEC3G (A3G) presents extensively inhibition on a variety of viruses, including retroviruses, DNA and RNA viruses. Our recent study showed that A3G inhibits enterovirus 71 (EV71) and coxsackievirus A16 (CA16) via competitively binding 5'UTR with the host protein poly(C)-binding protein 1 (PCBP1) that is required for multiple EVs replication. However, in addition to EV71 and CA16, whether A3G inhibits other EVs has not been investigated. Here, we demonstrate that A3G could inhibit EVD68 replication, which needs PCBP1 for its replication, but not CA6 that PCBP1 is dispensable for CA6 replication. Further investigation revealed that nucleic acid binding activity of A3G is required for EVD68 restriction, which is similar to the mechanism presented in EV71 restriction. Mechanistically, A3G competitively binds to the cloverleaf (1-123) and the stem-loop IV (234-446) domains of EVD68 5'UTR with PCBP1, thereby inhibiting the 5'UTR activity of EVD68, whereas A3G doesn't interact with CA6 5'UTR results in no effect on CA6 replication. Moreover, non-structural protein 2C encoded by EVD68 overcomes A3G suppression through inducing A3G degradation via the autophagy-lysosome pathway. Our finding revealed that A3G might have broad spectrum antiviral activity against multiple EVs through the general mechanism, which might provide important information for the development of anti-EVs strategy. Importance As the two major pathogens causing hand, food, and mouth disease (HFMD), EV71 and CA16 attract more attention for the discovery of pathogenesis, the involvement of cellular proteins and so on. However, other EVs such as CA6 or EVD68 constantly occurred sporadic or might spread widely in recent years worldwide. Therefore, more information related to these EVs needs to be further investigated so as to develop broad-spectrum anti-EVs inhibitor. In this study, we first reveal that PCBP1 involved in PV and EV71 virus replication, also is required for the replication of EVD68 but not CA6. Then we found that the host restriction factor A3G specifically inhibits the replication of EVD68 but not CA6 via competitively binding to the 5'UTR of EVD68 with PCBP1. Our findings broaden the knowledge related to EVs replication and the interplay between EVs and host factors.

Seroepidemiology of enterovirus D68 infection in Kuala Lumpur, Malaysia between 2013 and 2015

Enterovirus D68 (EV-D68) is an emerging respiratory pathogen since the 2014 outbreak in the United States. A low level of virus circulation has been reported in Kuala Lumpur, Malaysia, in the past. However, the extent of the infection in Malaysia is not known. In the present study, we determine the seroepidemiology of EV-D68 in Kuala Lumpur, Malaysia, before and after the United States outbreak in August 2014. A luciferase-based seroneutralization test was developed using a clone-derived prototype Fermon strain carrying a nanoluciferase marker. We screened the neutralization capacity of 450 serum samples from children and adults (1-89 years old) collected between 2013 and 2015. EV-D68 seropositivity increased with age, with children aged 1-3 showing significantly lower seroprevalence compared to adults. Multivariate analysis showed that older age groups 13-49 years (odds ratio [OR] = 4.78; 95% confidence interval [CI] = 2.69-8.49; p < 0.0001) and ≥50 years (OR = 3.83; 95% CI = 2.19-6.68; p < 0.0001) were more likely to be EV-D68 seropositive than children <13 years. Sampling post-September 2014 compared to pre-Sept 2014 also predicted seropositivity (OR = 1.66; 95% CI = 1.04-2.65). The presence of neutralizing antibodies against EV-D68 in the study population suggests that EV-D68 was circulating before 2014. A higher seropositivity post-September 2014 suggests that Malaysia also experienced an upsurge in EV-D68 infections after the United States outbreaks in August 2014. A low seropositivity rate observed in children, especially those aged 1-3 years old, suggests that they are at risk and should be prioritized for future vaccination.

SAMHD1 Inhibits Multiple Enteroviruses by Interfering with the Interaction between VP1 and VP2 Proteins

Sterile alpha motif and histidine-aspartic acid domain-containing protein 1 (SAMHD1) possesses multiple biological activities such as virus restriction, innate immunity regulation, and autoimmunity. Our previous study demonstrated that SAMHD1 potently inhibits the replication of enterovirus 71 (EV71). In this study, we observed that SAMHD1 also restricts multiple enteroviruses (EVs), including coxsackievirus A16 (CA16) and enterovirus D68 (EVD68), but not coxsackievirus A6 (CA6). Mechanistically, SAMHD1 competitively interacted with the same domain in VP1 that binds to VP2 of EV71 and EVD68, thereby interfering with the interaction between VP1 and VP2 , and therefore viral assembly. Moreover, we showed that the SAMHD1 T592A mutant maintained the EV71 inhibitory effect by attenuating the interaction between VP1 and VP2, whereas the T592D mutant failed to. We also demonstrated that SAMHD1 could not inhibit CA6 because a different binding site is required for the SAMHD1 and VP1 interaction. Our findings reveal the mechanism of SAMHD1 inhibition of multiple EVs, and this could potentially be important for developing drugs against a broad range of EVs. IMPORTANCE Enterovirus causes a wide variety of diseases, such as hand, foot, and mouth disease (HFMD), which is a severe public problem threatening children under 5 years. Therefore, identifying essential genes which restrict EV infection and exploring the underlying mechanisms are necessary to develop an effective strategy to inhibit EV infection. In this study, we report that host restrictive factor SAMHD1 has broad-spectrum antiviral activity against EV71, CA16, and EVD68 independent of its well-known deoxynucleoside triphosphate triphosphohydrolase (dNTPase) or RNase activity. Mechanistically, SAMHD1 restricts EVs by competitively interacting with the same domain in VP1 that binds to VP2 of EVs, thereby interfering with the interaction between VP1 and VP2, and therefore viral assembly. In contrast, we also demonstrated that SAMHD1 could not inhibit CA6 because a different binding site is required for the SAMHD1 and CA6 VP1 interaction. Our study reveals a novel mechanism for the SAMHD1 anti-EV replication activity.

Seroepidemiology of enterovirus D68 in a healthy population in Beijing, China, between 2012 and 2017: A retrospective study

To investigate the seroepidemiological features of enterovirus D68 (EV-D68) in the healthy population from 2012 to 2017 in Beijing, China. A retrospective cross-sectional investigation was conducted using serum specimens collected from healthy individuals in Beijing from 2012 to 2017. These samples were tested for neutralization antibodies (NtAbs) against EV-D68. The sera from six EV-D68 infected patients in the acute or convalescent phase were used to determine the protection level of NtAbs against EV-D68. The geometric means of the titers (GMT) of EV-D68 NtAbs in 2012 and 2017 were 92.82 and 242.91, respectively; the seroprevalences of EV-D68 were 89.43% and 98.43%, respectively. The GMT reached its peak in the 11 to 15 age group in 2012, while in 16 to 20 age group in 2017. We also observed that EV-D68 NtAbs titers of six sera from the acute phase were all less than equal to  1:64 and that of three sera from the convalescent phase were all more than 1:64. Anti-EV-D68 NtAbs in the population remained low from 2012 to 2016 but increased significantly in 2017. Although most of the EV-D68 infections remain undetected in Beijing, the risk of a large outbreak of EV-D68 exists and should be taken seriously.

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.

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 D68 serosurvey: evidence for endemic circulation in the Netherlands, 2006 to 2016

BackgroundEnterovirus D68 (EV-D68) has caused major outbreaks of severe respiratory illness worldwide since 2010.AimOur aim was to evaluate EV-D68 circulation in the Netherlands by conducting a serosurvey of EV-D68 neutralising antibodies (nAb) among the Dutch general population.MethodsWe screened 280 sera from children and adults in the Netherlands and used two independent sets of samples collected in the years 2006 and 2007 and in the years 2015 and 2016, time points before and after the first EV-D68 upsurge in 2010. Neutralisation capacity of the sera was tested against the prototype Fermon EV-D68 strain isolated in 1962 and against a recent EV-D68 strain (genotype B3) isolated in France in 2016.ResultsRegardless of the time of serum collection, we found remarkably high overall seropositivity (94.3-98.3%) for nAb against both EV-D68 strains. Geometric mean titres increased in an age-dependent manner.ConclusionsOur data suggest that EV-D68 has been circulating in the Netherlands for decades and that the enterovirus surveillance does not accurately capture the prevalence of this clinically relevant pathogen.

Enterovirus D68-associated respiratory infection in southern Brazil, 2018 - A population-based laboratory surveillance

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Patients with SARI or ILI notified during epidemiological surveillance are investigated to detect respiratory virus.

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Enteroviruses were detected in 69/6535 (1%), being 39/69 (56.5 %) of SARI, and 30/69 (43.5 %) of ILI cases.

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EV-D68 was detected in the 36 samples previously identified as EV/RV co-detection.

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This finding settles the sustained circulation of EV-D68 in southern Brazil.

Enterovirus D68 (EV-D68) strain was confirmed in 36/69−52.2% of enterovirus-positive samples collected through surveillance networks for severe acute respiratory infections (SARI) and influenza-like illness (ILI) in southern Brazil in 2018. This finding settles the sustained circulation of EV-D68 in southern Brazil.

Enterovirus D68 seroepidemiology in Taiwan, a cross sectional study from 2017

BACKGROUND

Enterovirus D68 (EV-D68) was discovered in 1962 and has unique characteristics compared to the characteristics of other enteroviruses. There were few documented cases before the epidemic in the United States in 2014. The Taiwan Centers for Diseases Control also confirmed that EV-D68 has been endemic, and some cases of acute flaccid myelitis were reported in Taiwan. To understand the current EV-D68 serostatus, we performed an EV-D68 seroepidemiology study in Taiwan in 2017.

METHODS

After informed consent was obtained, we enrolled preschool children, 6- to 15-year-old students and 16- to 49-year-old people. The participants underwent a questionnaire investigation and blood sampling to measure the EV-D68 neutralization antibody.

RESULTS

In total, 920 subjects were enrolled from the northern, central, southern and eastern parts of Taiwan with a male-to-female ratio of 1.03. The EV-D68 seropositive rate was 32% (26/82) in infants, 18% (27/153) in 1-year-old children, 43% (36/83) in 2-year-old children, 60% (94/156) in 3- to 5-year-old children, 89% (108/122) in 6- to 11-year-old primary school students, 98% (118/121) in 12- to 15-year-old high school students, 100% (122/122) in 16- to 49-year-old women and 100% (81/81) in 16- to 49-year-old males in 2017. Among preschool children, EV-D68 seropositivity was related to age (p for trend <0.0001), size of household ≧4 members (p = 0.037) and kindergarten attendance (p = 0.027). The seropositive rate varied among different geographic regions.

CONCLUSION

EV-D68 infection was prevalent, and its seropositive rates increased with age, larger household size and kindergarten attendance among preschool children.

Current status of enterovirus D68 worldwide and in Taiwan

Enterovirus D68 was first identified in 1962 and caused a worldwide outbreak starting from the North America in 2014. Enterovirus D68 has been in continuous circulation among many countries recently, including Taiwan. Reports also reveal high seroprevalence, which indicates that the disease burden of enterovirus D68 may be underestimated via viral culture or polymerase chain reaction results. Although most infected cases have mild respiratory illness, severe complications including acute flaccid myelitis and acute respiratory distress syndrome have also been reported. In the position of an emerging pathogen, enterovirus D68 poses a threat to public health and may cause devastating diseases. Diverse severity of neurological sequelae remains inevitable among acute flaccid myelitis patients, but no curable treatment is available currently. According to the management suggestions of the American Centers of Disease Control, uses of corticosteroids and plasmapheresis are either preferred or avoided and intravenous immunoglobulin also has no clear indication in the treatment for acute flaccid myelitis. In this review article, we provide information about the epidemiology, clinical recognition and treatment strategy of enterovirus D68. Better understanding of this disease is the foothold for advanced investigation and monitoring in the future.

Fluctuations in Antibody Titers against Enterovirus D68 in Pediatric Sera Collected in a Community before, during, and after a Possible Outbreak

We previously reported a hospital-based epidemiological study on enterovirus (EV)-D68 infection among children during the autumn of 2015, which indirectly inferred an outbreak in Sendai, Japan. In this study, stocked sera of children (aged 0-6 years; without symptoms of infectious diseases) in the Sendai community collected during 4 periods (1 year before, 6 months before, immediately after, and 1 year after the possible outbreak period) were analyzed using the neutralization antibody titer assay to determine community children's immunity levels against EV-D68 infection. The immunity levels were confirmed to have increased during the possible outbreak period and to have gradually waned over 1 year without another outbreak. These results provide background information supporting the results of our previous hospital-based surveillance study.

Current Understanding of Human Enterovirus D68

Human enterovirus D68 (EV-D68), a member of the species Enterovirus D of the Picornaviridae family, was first isolated in 1962 in the United States. EV-D68 infection was only infrequently reported until an outbreak occurred in 2014 in the US; since then, it has continued to increase worldwide. EV-D68 infection leads to severe respiratory illness and has recently been reported to be linked to the development of the neurogenic disease known as acute flaccid myelitis (AFM), mostly in children, seriously endangering public health. Hitherto, treatment options for EV-D68 infections were limited to supportive care, and as yet there are no approved, specific antiviral drugs or vaccines. Research on EV-D68 has mainly focused on its epidemiology, and its virologic characteristics and pathogenesis still need to be further explored. Here, we provide an overview of current research on EV-D68, including the genotypes and genetic characteristics of recent epidemics, the mechanism of infection and virus-host interactions, and its relationship to acute flaccid myelitis (AFM), in order to broaden our understanding of the biological features of EV-D68 and provide a basis for the development of effective antiviral agents.

A case report of the enterovirus-D68 associated severe acute respiratory illness in a pediatric case from India

Since, early 2000s, there have been several clusters of enterovirus-D68 (EV D68) associated respiratory illness reported from various countries. Recent largest and most wide-spread outbreak of EV-D68 associated severe acute respiratory illness (SARI) occurred in North America. Present report describes a case of EV-D68 associated severe acute respiratory illness from India with a whole genome sequence. The case was identified through retrospective analysis of Influenza SARI surveillance sample collected during September 2017 using Next Generation sequencing. EV D68 positive child aged two years and presented with asthma like symptoms for which he was admitted to ICU. The child tested negative for Influenza, RSV, Rhinovirus, PIV, hMPV and adenovirus, on real time RT-PCR. And on NGS full EV D68 genome was retrieved belonging to sub-clade B3. In ICU, child received anti-bacterial and anti-viral therapy. The child recovered with-out any sequelae and was discharged one week later. Present report highlights the importance of studying this emergent virus EV-D68 through prospective studies to understand the burden and epidemiological pattern in the country and its implications.

Neutralizing Antibody against Enterovirus D68 in Children and Adults before 2014 Outbreak, Kansas City, Missouri, USA1

We evaluated enterovirus D68 seroprevalence in Kansas City, Missouri, USA, from samples obtained during 2012-2013. Neutralizing antibodies against Fermon and the dominant 2014 Missouri isolate were universally detected. Titers increased with age. Widespread circulation of enterovirus D68 occurred before the 2014 outbreak. Research is needed to determine a surrogate of protection.

Current Understanding of Humoral Immunity to Enterovirus D68

Enterovirus D68 (EV-D68) is a pathogen that causes outbreaks of respiratory illness across the world, mostly in children, and can be especially severe in those with asthma. Clusters of acute flaccid myelitis, a poliomyelitis-like neuromuscular weakness syndrome, often occur concurrent with EV-D68 respiratory outbreaks. Seroepidemiologic studies have found that the serum of nearly everyone older than 2 to 5 years contains anti-EV-D68 neutralizing antibodies, which suggests that EV-D68 is a ubiquitous pathogen of childhood. However, knowledge of the viral epitopes against which the humoral immune response is directed is only inferred from previous studies of related viruses. Although neutralizing antibodies protect newborn mice from lethal EV-D68 inoculation via nonphysiologic routes, cotton rats have a mixed phenotype of both benefit and possible exacerbation when inoculated intranasally. The human antibody response to EV-D68 needs to be studied further to clarify the role of antibodies in protection versus pathogenesis, which might differ among respiratory and neurologic disease phenotypes.

A Novel Neutralizing Antibody Specific to the DE Loop of VP1 Can Inhibit EV-D68 Infection in Mice

Enterovirus D68 (EV-D68) belongs to the picornavirus family and was first isolated in CA, USA, in 1962. EV-D68 can cause severe cranial nerve system damage such as flaccid paralysis and acute respiratory diseases such as pneumonia. There are currently no efficient therapeutic methods or effective prophylactics. In this study, we isolated the mAb A6-1 from an EV-D68-infected rhesus macaque (Macaca mulatta) and found that the Ab provided effective protection in EV-D68 intranasally infected suckling mice. We observed that A6-1 bound to the DE loop of EV-D68 VP1 and interfered with the interaction between the EV-D68 virus and α2,6-linked sialic acids of the host cell. The production of A6-1 and its Ab properties present a bridging study for EV-D68 vaccine design and provide a tool for analyzing the process by which Abs can inhibit EV-D68 infection.

A cross-sectional seroepidemiology study of EV-D68 in China

Enterovirus 68 (EV-D68) is associated with respiratory diseases, such as acute upper respiratory tract infections (URTIs), lower respiratory tract infections (LRTIs), pneumonia, neurological diseases, and acute flaccid myelitis (AFM). In recent years, there have been global outbreaks of EV-D68 epidemics. However, there is no effective vaccine against EV-D68, and the understanding of the seroprevalence characteristics of EV-D68 is limited. To evaluate the epidemiological features of this emerging infection in mainland China, serum samples from 20 pairs of pregnant women and their neonates, 405 infants and children (ages 1 month-15 years), and 50 adults were collected to measure EV-D68 neutralizing antibodies (NtAbs). The results showed that the geometric mean titers (GMTs) of pregnant women and their neonates were 168 (95%CI: 93.6-301.7) and 162.3 (95%CI: 89.9-293.1), respectively. The seroprevalence rate of EV-D68 antibodies was negatively correlated with age in 1-month-old to 12-month-old infants (84% for 1-month-old infants vs 10% for 1-year-old infants), whereas it was positively correlated with age for 1-year-old to 15-year-old children (10% for 1-year-old children vs 92% for 15-year-old children). This study evaluated maternal antibodies against EV-D68 in neonates. Our results showed that if mothers had high levels of anti-EV-D68 NtAbs, the NtAbs titers in their neonates were also high. The GMTs and seroprevalence rates of each age group indicated that EV-D68 infection was very common in China. Periodical EV-D68 seroprevalence surveys and vaccination campaigns should be the top priority for preventing EV-D68 infection.

A Mouse Model of Enterovirus D68 Infection for Assessment of the Efficacy of Inactivated Vaccine

In recent years, enterovirus D68 (EVD68) has been reported increasingly to be associated with severe respiratory tract infections and acute flaccid myelitis (AFM) in children all over the world. Yet, no effective vaccines or antiviral drugs are currently available for EVD68. Although several experimental animal models have been developed, immunogenicity and protective efficacy of inactivated EVD68 vaccines has not been fully evaluated. To promote the development of vaccines, we established an Institute of Cancer Research (ICR) suckling mouse model of EVD68 infection in this study. The results showed that ICR neonatal mice up to about nine days of age were susceptible to infection with EVD68 clinical strain US/MO/14-18947 by intraperitoneal injection. The infected mice exhibited progressive limb paralysis prior to death and the mortality of mice was age- and virus dose-dependent. Tissue viral load analysis showed that limb muscle and spinal cord were the major sites of viral replication. Moreover, histopathologic examination revealed the severe necrosis of the limb and juxtaspinal muscles, suggesting that US/MO/14-18947 has a strong tropism toward muscle tissues. Additionally, β-propiolactone-inactivated EVD68 vaccine showed high purity and quality and induced robust EVD68-specific neutralizing antibody responses in adult mice. Importantly, results from both antisera transfer and maternal immunization experiments clearly showed that inactivated EVD68 vaccine was able to protect against lethal viral infection in the mouse model. In short, these results demonstrate the successful establishment of the mouse model of EVD68 infection for evaluating candidate vaccines against EVD68 and also provide important information for the development of inactivated virus-based EVD68 vaccines.