Molecular epidemiology of enterovirus 71 infection in the central region of Taiwan from 2002 to 2012

Targeting 7-dehydrocholesterol reductase against EV-A71 replication by upregulating interferon response

Recent studies have shown a close link between viral infections and cholesterol metabolism. Here, we reported that 7-dehydrocholesterol reductase (DHCR7), a terminal enzyme for catalyzing cholesterol synthesis in the Kandutsch-Russell pathway, is harnessed by enterovirus A71 (EV-A71) benefitting for its replication. Overexpression of DHCR7 resulted in upregulating of EV-A71 replication, while the S14A mutation, which reduces DHCR7 enzyme activity, has no effect on EV-A71 replication. Knockdown of DHCR7 expression with small interfering RNA (siRNA) or enzyme activity inhibition with pharmacological inhibitor AY9944 could significantly inhibit EV-A71 replication. Adding cholesterol to DHCR7 knockdown cells or AY9944-treated cells could rescue EV-A71 replication. More importantly, prophylactic administration of AY9944 effectively protected mice from lethal EV-A71 infection. In addition, the natural cholesterol precursor 7-dehydrocholesterol (7-DHC), which is converted to cholesterol by DHCR7, has a similar effect against EV-A71 infection. Mechanistically, AY9944 or 7-DHC treatment can specifically promote IRF3 phosphorylation to activate interferon response. Moreover, AY9944 effectively cleared coxsackievirus B3 (CVB3) and coxsackievirus A16 (CVA16) infections in vitro. In conclusion, pharmacological modulation of DHCR7 might provide a chance for treatment of enterovirus infection, including EV-A71.

Evolutionary and Genetic Recombination Analyses of Coxsackievirus A6 Variants Associated with Hand, Foot, and Mouth Disease Outbreaks in Thailand between 2019 and 2022

Coxsackievirus (CV)-A6 infections cause hand, foot, and mouth disease (HFMD) in children and adults. Despite the serious public health threat presented by CV-A6 infections, our understanding of the mechanisms by which new CV-A6 strains emerge remains limited. This study investigated the molecular epidemiological trends, evolutionary dynamics, and recombination characteristics of CV-A6-associated HFMD in Thailand between 2019 and 2022. In the HFMD patient samples collected during the 4-year study period, we identified enterovirus (EV) RNA in 368 samples (48.7%), of which CV-A6 (23.7%) was the predominant genotype, followed by CV-A4 (6%), EV-A71 (3.7%), and CV-A16 (3.4%). According to the partial viral protein (VP) 1 sequences, all these CV-A6 strains belonged to the D3 clade. Based on the viral-RNA-dependent RNA polymerase (RdRp) gene, four recombinant forms (RFs), RF-A (147, 84.5%), RF-N (11, 6.3%), RF-H (1, 0.6%), and newly RF-Y (15, 8.6%), were identified throughout the study period. Results from the similarity plot and bootscan analyses revealed that the 3D polymerase (3Dpol) region of the D3/RF-Y subclade consists of sequences highly similar to CV-A10. We envisage that the epidemiological and evolutionarily insights presented in this manuscript will contribute to the development of vaccines to prevent the spread of CV-A6 infection.

Genomic Epidemiology and Phylodynamic Analysis of Enterovirus A71 Reveal Its Transmission Dynamics in Asia

Enterovirus A71 (EV-A71) is one of the main pathogens causing hand, foot, and mouth disease (HFMD) outbreaks in Asian children under 5 years of age. In severe cases, it can cause neurological complications and be life-threatening. In this study, 200 newly sequenced EV-A71 whole-genome sequences were combined with 772 EV-A71 sequences from GenBank for large-scale analysis to investigate global EV-A71 epidemiology, phylogeny, and Bayesian phylodynamic characteristics. Based on the phylogenetic analysis of the EV-A71 3D^pol region, six new evolutionary lineages (lineages B, J, K, O, P, and Q) were found in this study, and the number of evolutionary lineages was expanded from 11 to 17. Temporal dynamics and recombination breakpoint analyses based on genotype C revealed that recombination of nonstructural protein-coding regions, including 3D^pol, is an important reason for the emergence of new lineages. The EV-A71 epidemic in the Asia-Pacific region is complex, and phylogeographic analysis found that Vietnam played a key role in the spread of subgenotypes B5 and C4. The origin of EV-A71 subgenotype C4 in China is East China, which is closely related to the prevalence of subgenotype C4 in the south and throughout China. Selection pressure analysis revealed that, in addition to VP1 amino acid residues VP1-98 and VP1-145, which are associated with EV-A71 pathogenicity, amino acid residues VP1-184 and VP1-249 were also positively selected, and their functions still need to be determined by biology and immunology. This study aimed to provide a solid theoretical basis for EV-A71-related disease surveillance and prevention, antiviral research, and vaccine development through a comprehensive analysis. IMPORTANCE EV-A71 is one of the most important pathogens causing HFMD outbreaks; however, large-scale studies of EV-A71 genomic epidemiology are currently lacking. In this study, 200 new EV-A71 whole-genome sequences were determined. Combining these with 772 EV-A71 whole-genome sequences in the GenBank database, the evolutionary and transmission characteristics of global and Asian EV-A71 were analyzed. Six new evolutionary lineages were identified in this study. We also found that recombination in nonstructural protein-coding regions, including 3D^pol, is an important cause for the emergence of new lineages. The results provided a solid theoretical basis for EV-A71-related disease surveillance and prevention, antiviral research, and vaccine development.

Neurocognitive Deficits and Sequelae Following Severe hand, foot, and mouth disease from 2009 to 2017, in JiangSu Province, China: A Long-Term Follow-Up Study

BACKGROUND

To evaluate the long-term sequela and cognitive profile resulting from severe hand, foot and mouth disease (HFMD) with central nervous system (CNS) involvement.

METHODS

Two-hundred-and-ninety-four HFMD cases were included in a retrospective follow-up study. Physical examination were conducted. The Chinese Wechsler Preschool and Primary Scale of Intelligence, Fourth Edition (WPPSI-IV) was used to assess intelligence.

RESULTS

Fifty-eight mild HFMD cases and 99 severe HFMD cases with mild CNS involvement did not present any neurological sequelae. While the sequelae incidence of severe HFMD with more severe CNS complications were 50.0%. The proportion of full scale intelligence quotient (FSIQ) impairment was 45.0%. In the 2:6-3:11 age group, severe HFMD with more severe CNS complications and lower maternal education level were risk factors for verbal comprehension disorder. Urban-rural residence and lower paternal education level were risk factors for FSIQ disorder. Furthermore, in the 4:0-6:11 age group, severe HFMD with more severe CNS complication was a risk factor for visual spatial disorder and fluid reasoning disorder. Lower paternal education level was a risk factor for FSIQ disorder.

CONCLUSION

Early assessment and intervention among severe HFMD patients with more severe CNS involvement at a very young age will prove beneficial for their future performance.

Changing trends in dialysis modalities utilization and mortality in children, adolescents and young adults with acute kidney injury, 2010-2017

The aim of the study was to assess trends in the relative use of dialysis modalities in the hospital-based pediatric cohort and to determine risk factors associated with in-hospital morality among pediatric patients receiving dialysis for acute kidney injury (AKI). Patients aged < 20 years who received dialysis between 2010 and 2017 were identified from electronic health records databases of a Taiwan's healthcare delivery system. The annual uses of intermittent hemodialysis (HD), continuous and automated peritoneal dialysis (PD) and continuous kidney replacement therapy (CKRT) were assessed using Cochran-Armitage Tests for trend. Among patients who received their first dialysis as inpatients for AKI, a multivariate logistic regression model was employed to assess mortality risks associated with dialysis modalities, patient demographics, complexity of baseline chronic disease, and healthcare service use during their hospital stays. Kidney dialysis was performed 37.9 per patient per year over the study period. Intermittent hemodialysis (HD) (73.3%) was the most frequently used dialysis modality. In the inpatient setting, the relative annual use of CKRT increased over the study period, while HD use concomitantly declined (P < 0.0001). The overall in-hospital mortality rate after dialysis for AKI was 33.6%, which remained steady over time (P = 0.2411). Patients aged < 2 years [adjusted odds ratio: (aOR) 3.36; 95% confidence interval (CI) 1.34-8.93] and greater vasoactive regimen use (aOR: 17.1; 95% CI: 5.3-55.21) were significantly associated with dialysis-related mortality. Overall treatment modality used for dialysis in pediatric patients increased slowly in the study period, and HD and CRKT modality uses largely evolved in the inpatient setting. Younger ages and use of more vasoactive medication regimens were independently associated with increased early mortality in patients on AKI-dialysis.

Sporadic hand, foot, and mouth disease cases associated with non-C4 enterovirus 71 strains in Xiamen, China, from 2009 to 2018

Enterovirus 71 (EV71) has caused large hand, foot, and mouth disease (HFMD) epidemics among young children, and EV71 infection is the leading cause of severe HFMD cases and deaths. In mainland China, the prevalence and risk factors of non-C4 EV71 strains are still unclear. In this study, we monitored non-C4 strains over a 10-year HFMD epidemiological surveillance period in Xiamen. The 5’UTR and VP1 coding region of EV71 strains were amplified by RT-nested PCR and sequenced. Thirty-two non-C4 EV71 strains were identified during 2009-2018. This study provides important information about the prevalence of EV71 in China that will be applicable for development of vaccines and diagnostic reagents as well as establishment of policies for HFMD prevention and control.

Novel Naturally Occurring Mutations of Enterovirus 71 Associated With Disease Severity

Infection with the re-emerging enterovirus 71 (EV-A71) is associated with a wide range of disease severity, including herpangina, encephalitis, and cardiopulmonary failure. At present, there is no FDA-approved therapeutics for EV-A71. Early diagnosis for the high-risk children is the key to successful patient care. We examined viral genome sequences at the 5′ untranslated region (UTR) and the capsid protein VP1 from 36 mild and 27 severe cases. We identified five EV-A71 mutations associated with severe diseases, including (1) the 5′ UTR mutations C580U, A707G, C709U; (2) a VP1 alanine-to-threonine mutation at position 280 (280T), and (3) a VP1 glutamic acid-to-(non-glutamic acid) at position 145 [145(non-E)]. SCARB2 is a known entry receptor for EV-A71. Based on a recent cryoEM structure of the EV-A71-SCARB2 binding complex, VP1-280T is near the binding interface between the VP1-VP2 complex and its entry receptor SCARB2. A de novo created hydrogen bonding between the mutant VP1-280T and the VP2-139T, could help strengthen a web-like interaction structure of the VP1-VP2 complex. A stabilized loop turn of VP2, once in contact with SCARB2, can enhance interaction with the host SCARB2 receptor for viral entry. Our findings here could facilitate early detection of severe cases infected with EV-A71 in clinical medicine. In addition, it opens up the opportunity of functional studies via infectious cDNA cloning, site-directed mutagenesis, and animal models in the future.

Clinical, etiological and epidemiological investigations of hand, foot and mouth disease in southern Vietnam during 2015 - 2018

Hand, foot and mouth disease (HFMD) continues to challenge Asia with pandemic potential. In Vietnam, there have been two major outbreaks occurring during 2011-2012 (>200,000 hospitalizations and >200 deaths) and more recently in 2018 (>130,000 hospitalizations and 17 deaths). Given the high burden and the complex epidemic dynamics of HFMD, synthesizing its clinical and epidemiological data remains essential to inform the development of appropriate interventions and design public health measures. We report the results of a hospital-based study conducted during 2015-2018, covering the severe HFMD outbreak recently documented in Vietnam in 2018. The study was conducted at three major hospitals responsible for receiving HFMD patients from southern Vietnam with a population of over 40 million. A total of 19 enterovirus serotypes were detected in 1196 HFMD patients enrolled in the clinical study during 2015-2018, with enterovirus A71 (EV-A71), coxsackievirus A6 (CV-A6), CV-A10 and CV-A16 being the major causes. Despite the emergence of coxsackieviruses, EV-A71 remains the leading cause of severe HFMD in Vietnam. EV-A71 was consistently detected at a higher frequency during the second half of the years. The emergence of EV-A71 subgenogroup C4 in late 2018 was preceded by its low activity during 2017-early 2018. Compared with EV-A71 subgenogroup B5, C4 was more likely to be associated with severe HFMD, representing the first report demonstrating the difference in clinical severity between subgenogroup C4 and B5, the two predominant EV-A71 subgenogroups causing HFMD worldwide. Our data have provided significant insights into important aspects of HFMD over four years (2015-2018) in Vietnam, and emphasize active surveillance for pathogen circulation remains essential to inform the local public health authorities in the development of appropriate intervention strategies to reduce the burden of this emerging infections. Multivalent vaccines are urgently needed to control HFMD.

The History of Enterovirus A71 Outbreaks and Molecular Epidemiology in the Asia-Pacific Region

Enterovirus A71 (EV-A71) is one of the common causative pathogens for hand foot and mouth disease (HFMD) affecting young children. HFMD outbreak can result in a substantial pediatric hospitalization and burden the healthcare services, especially in less-developed countries. Since the initial epidemic of predominantly EV-A71 in California in 1969, the high prevalence of HFMD in the Asia-pacific region and elsewhere around the world represents a significant morbidity in this age group. With the advent of rapid and accurate diagnostic tools, there has been a dramatic increase in the number of laboratory-confirmed EV-A71 infection over the past two decades. The population, cultural, and socioeconomic diversity among countries in the Asia-Pacific region all influence the transmission and morbidity associated with HFMD. This review summarizes the current state of epidemiology of EV-A71 in Asia-Pacific countries based on the most recent epidemiological data and available information on the prevalence and disease burden. This knowledge is important in guiding the prevention, control and future research on vaccine development of this highly contagious disease of significant socioeconomic implications in public health.

Molecular characterization of enterovirus-A71 in children with acute flaccid paralysis in the Philippines

Background

Several inactivated enterovirus-A71 (EV-A71) vaccines are currently licensed in China; however, the development of additional EV-A71 vaccines is ongoing, necessitating extensive analysis of the molecular epidemiology of the virus worldwide. Until 2012, laboratory confirmation of EV-A71 for hand, foot, and mouth disease (HFMD) and other associated diseases had not occurred in the Philippines. Because EV-A71 has been linked with cases of acute flaccid paralysis (AFP), AFP surveillance is one strategy for documenting its possible circulation in the country. To expand current knowledge on EV-A71, molecular epidemiologic analysis and genetic characterization of EV-A71 isolates were performed in this study.

Methods

A retrospective study was performed to identify and characterize nonpolio enteroviruses (NPEVs) associated with AFP in the Philippines, and nine samples were found to be EV-A71–positive. Following characterization of these EV-A71 isolates, the complete viral protein 1 (VP1) gene was targeted for phylogenetic analysis.

Results

Nine EV-A71 isolates detected in 2000 (n = 2), 2002 (n = 4), 2005 (n = 2), and 2010 (n = 1) were characterized using molecular methods. Genomic regions spanning the complete VP1 region were amplified and sequenced using specific primers. Phylogenetic analysis of the full-length VP1 region identified all nine EV-A71 Philippine isolates as belonging to the genogroup C lineage, specifically the C2 cluster. The result indicated a genetic linkage with several strains isolated in Japan and Taiwan, suggesting that strains in the C2 cluster identified in the Asia-Pacific region were circulating in the Philippines.

Conclusion

The study presents the genetic analysis of EV-A71 in the Philippines. Despite some limitations, the study provides additional genetic data on the circulating EV-A71 strains in the Asia-Pacific region, in which information on EV-A71 molecular epidemiology is incomplete. Considering that EV-A71 has a significant public health impact in the region, knowledge of its circulation in each country is important, especially for formulating vaccines covering a wide variety of strains.

APOBEC3G is a restriction factor of EV71 and mediator of IMB-Z antiviral activity

Enterovirus 71 (EV71), a single-stranded positive-sense RNA virus, is the causative agent of hand, foot, and mouth disease (HFMD), for which no effective antiviral therapy is currently available. Apolipoprotein B messenger RNA-editing enzyme catalytic polypeptide-like 3G (APOBEC3G or A3G) is a cytidine deaminase that inhibits the replication of several viruses, such as human immunodeficiency virus-1, hepatitis B virus and hepatitis C virus. In our efforts toward understanding the antiviral spectrum and mechanism of A3G, we found that ectopic expression of A3G inhibited EV71 replication, whereas knockdown of endogenous A3G expression promoted EV71 replication. Moreover, inhibition of EV71 replication by IMB-Z, a N-phenylbenzamide derivative, is associated with increased levels of intracellular A3G, but reducing the level of A3G by RNA interference diminished the antiviral activity of IMB-Z. Mechanistically, we obtained evidence suggesting that the cytidine deaminase activity is not required for A3G inhibition of EV71 replication. Instead, we demonstrated that A3G can interact with viral 3D RNA-dependent RNA polymerase (RdRp) and viral RNA and be packaged into progeny virions to reduce its infectivity. Taken together, our results indicate that A3G is a cellular restriction factor of EV71 and mediator of the antiviral activity of IMB-Z. Pharmacological induction and/or stabilization of A3G is a potential therapeutic approach to treat diseases caused by EV71 infection, such as HFMD.

Surveillance for severe hand, foot, and mouth disease from 2009 to 2015 in Jiangsu province: epidemiology, etiology, and disease burden

Background

Severe hand, foot, and mouth disease (HFMD) is a common childhood illness caused by various enteroviruses. The disease has imposed increased burden on children younger than 5 years old. We aimed to determine the epidemiology, CNS complication, and etiology among severe HFMD patients, in Jiangsu, China.

Methods

Epidemiological, clinical, and laboratory data of severe HFMD cases were extracted from 2009 to 2015. The CNS complication, annually severe illness rates, mortality rates, severity-PICU admission rates, severity-hospitalization rates, and so on were analyzed to assess the disease burden of severe HFMD. All analyses were stratified by time, region, population, CNS involvement and serotypes. The VP1 gene from EV-A71, CV-A16, CV-A6, CV-A10 and other enteroviruses isolates was amplified. Phylogenetic analysis was performed using MEGA5.0.

Results

Seven thousand nine hundred ninety-four severe HFMD cases were reported, of them, 7224 cases were inpatients, 611 were PICU inpatients, and 68 were fatal. The average severe illness rate, mortality rate, severity−fatality rate, severity-PICU admission rate, and severity-hospitalization rate were 14.54, 0.12,8506, 76,430, and 903,700 per 1 million, respectively. The severe illness rate was the highest in the 12–23 months age group, and the greatest mortality rate was in the 6–11 months age group. Geographical difference in severe illness rate and mortality were found. Patients infected with EV-A71 were at a higher proportion in different CNS involvement even death. EV-A71, CV-A16 and other enteroviruses accounted for 79.14, 6.49, and 14.47%, respectively. A total of 14 non-EV-A71/ CV-A16 genotypes including CV-A2, CV-A4, CV-A 6, CV-A9, CV-A10, CV-B1, CV-B2, CV-B3, CV-B4, CV-B5, E-6, E-7, E-18, and EV-C96 were identified. Phylogentic analyses demonstrated that EV-A71 strains belonged to subgenotype C4a, while CV-A16 strains belonged to sub-genotype B1a and sub-genotype B1b of genotype B1. CV-A6 strains were assigned to genogroup F, and CV-A10 strains belonged to genogroup D.

Conclusions

Future mitigation policies should take into account the age, region heterogeneities, CNS conditions and serotype of disease. Additional a more rigorous study between the mild and severe HFMD should be warranted to elucidate the difference epidemiology, pathogen spectrum and immunity patterns and to optimize interventions in the following study.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3659-7) contains supplementary material, which is available to authorized users.

Longitudinal study on enterovirus A71 and coxsackievirus A16 genotype/subgenotype replacements in hand, foot and mouth disease patients in Thailand, 2000-2017

BACKGROUND

Enterovirus A71 (EV-A71) and coxsackievirus A16 (CV-A16) are the major causative agents of hand, foot and mouth disease (HFMD) worldwide, particularly in the Asia-Pacific region. Several strains have emerged, circulated, and faded out over time in recent decades. This study investigated the EV-A71 and CV-A16 circulating strains and replacement of genotypes/subgenotypes in Thailand during the years 2000-2017.

METHODS

The complete VP1 regions of 92 enteroviruses obtained from 90 HFMD patients, one asymptomatic adult contact case, and one encephalitic case were sequenced and investigated for serotypes, genotypes, and subgenotypes using a phylogenetic analysis.

RESULTS

The 92 enterovirus isolates were identified as 67 (72.8%) EV-A71 strains comprising subgenotypes B4, B5, C1, C2, C4a, C4b and C5, and 25 (27.2%) CV-A16 strains comprising subgenotypes B1a and B1b. Genotypic/subgenotypic replacements were evidenced during the study period. EV-A71 B5 and C4a have been the major circulating strains in Thailand for more than a decade, and CV-A16 B1a has been circulating for almost two decades.

CONCLUSIONS

This study provides chronological data on the molecular epidemiology of EV-A71 and CV-A16 subgenotypes in Thailand. Subgenotypic replacement frequently occurred with EV-A71, but not CV-A16. Monitoring for viral genetic and subgenotypic changes is important for molecular diagnosis, vaccine selection, and vaccine development.

Enterovirus A71 Proteins: Structure and Function

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

Epidemics and aetiology of hand, foot and mouth disease in Xiamen, China, from 2008 to 2015

Over the past 8 years, human enteroviruses (HEVs) have caused 27 227 cases of hand, foot and mouth disease (HFMD) in Xiamen, including 99 severe cases and six deaths. We aimed to explore the molecular epidemiology of HFMD in Xiamen to inform the development of diagnostic assays, vaccines and other interventions. From January 2009 to September 2015, 5866 samples from sentinel hospitals were tested using nested reverse transcription PCR that targeted the HEV 5' untranslated region and viral protein 1 region. Of these samples, 4290 were tested positive for HEV and the amplicons were sequenced and genotyped. Twenty-two genotypes were identified. Enterovirus 71 (EV71) and coxsackieviruses A16, A6 and A10 (CA16, CA6 and CA10) were the most common genotypes, and there were no changes in the predominant lineages of these genotypes. EV71 became the most predominant genotype every 2 years. From 2013, CA6 replaced CA16 as one of the two most common genotypes. The results demonstrate the vast diversity of HFMD pathogens, and that minor genotypes are able to replace major genotypes. We recommend carrying-out long-term monitoring of the full spectrum of HFMD pathogens, which could facilitate epidemic prediction and the development of diagnostic assays and vaccines.

Motor coordination and balance measurements reveal differential pathogenicity of currently spreading enterovirus 71 strains in human SCARB2 transgenic mice

Enterovirus 71 (EV71) has caused large-scale epidemics with neurological complications in the Asia-Pacific region. The C4a and B5 strains are the two major genotypes circulating in many countries recently. This study used a new protocol, a motor coordination task, to assess the differential pathogenicity of C4a and B5 strains in human SCARB2 transgenic mice. We found that the pathogenicity of C4a viruses was more severe than that of B5 viruses. Moreover, we discovered that an increased level of monocyte chemoattractant protein-1 was positively correlated with severely deficient motor function. This study provides a new method for evaluating EV71 infection in mice and distinguishing the severity of the symptoms caused by different clinical strains, which would contribute to studies of pathogenesis and development of vaccines and antivirals in EV71 infections.

Molecular epidemiology of human enterovirus 71 at the origin of an epidemic of fatal hand, foot and mouth disease cases in Cambodia

Human enterovirus 71 (EV-A71) causes hand, foot and mouth disease (HFMD). EV-A71 circulates in many countries and has caused large epidemics, especially in the Asia-Pacific region, since 1997. In April 2012, an undiagnosed fatal disease with neurological involvement and respiratory distress occurred in young children admitted to the Kantha Bopha Children's Hospital in Phnom Penh, Cambodia. Most died within a day of hospital admission, causing public panic and international concern. In this study, we describe the enterovirus (EV) genotypes that were isolated during the outbreak in 2012 and the following year. From June 2012 to November 2013, 312 specimens were collected from hospitalized and ambulatory patients and tested by generic EV and specific EV-A71 reverse transcription PCR. EV-A71 was detected in 208 clinical specimens while other EVs were found in 32 patients. The VP1 gene and/or the complete genome were generated. Our phylogenetic sequencing analysis demonstrated that 80 EV-A71 strains belonged to the C4a subgenotype and 3 EV-A71 strains belonged to the B5 genotype. Furthermore, some lineages of EV-A71 were found to have appeared in Cambodia following separate introductions from neighboring countries. Nineteen EV A (CV-A6 and CV-A16), 9 EV B (EV-B83, CV-B3, CV-B2, CV-A9, E-31, E-2 and EV-B80) and 4 EV C (EV-C116, EV-C96, CV-A20 and Vaccine-related PV-3) strains were also detected. We found no molecular markers of disease severity. We report here that EV-A71 genotype C4 was the main etiological agent of a large outbreak of HFMD and particularly of severe forms associated with central nervous system infections. The role played by other EVs in the epidemic could not be clearly established.

Study of the epidemiology and etiological characteristics of hand, foot, and mouth disease in Suzhou City, East China, 2011-2014

Hand, foot, and mouth disease (HFMD) is a common childhood illness that is caused by enteroviruses, and the prevalence of HFMD in China and around the world has resulted in a huge disease burden. Since 2010, the HFMD incidence has been the highest among infectious diseases in Suzhou, China. To investigate the epidemical, features, etiological characteristics, and clinical characteristics of HFMD in Suzhou City, East China, from 2011 to 2014. We retrospectively analyzed HFMD epidemiological data in Suzhou from 2011 to 2014. A total of 80,723 outpatients in the city of Suzhou were diagnosed with HFMD, including 1,846 severe cases. There were 2,387 (3.0 %) laboratory-confirmed cases, 807 of which exhibited severe symptoms. All analyses were stratified by age, disease severity, laboratory confirmation status, and enterovirus subtype. From 2011 to 2014, HFMD mainly affected children aged 1-3, and boys were more affected than girls. The highest peak incidences of HFMD occurred in May or June from 2011 to 2014, and lower peak incidences were observed from November to December and in districts with higher humidity. Enterovirus 71 and coxsackievirus A16 were the predominant viral genotypes in Suzhou in 2011 to 2012 and 2014, and the severe cases mainly correlated with EV71 subtypes. In 2013, other EVs were dominant. The proportion of patients with severe disease decreased significantly, and the VP1 capsid proteins of EV71 and CA16 from severe and mild cases were nearly identical. This study shows that it is time to start monitoring EVs in China and that we should accelerate vaccine research and develop public-health interventions for the control and prevention of HFMD, all of which will play an important role in the prevention of HFMD.

Human IgG Fc promotes expression, secretion and immunogenicity of enterovirus 71 VP1 protein

Enterovirus (EV71) can cause severe neurological diseases, but the underlying pathogenesis remains unclear. The capsid protein, viral protein 1 (VP1), plays a critical role in the pathogenicity of EV71. High level expression and secretion of VP1 protein are necessary for structure, function and immunogenicity in its natural conformation. In our previous studies, 5 codon-optimized VP1 DNA vaccines, including wt-VP1, tPA-VP1, VP1-d, VP1-hFc and VP1-mFc, were constructed and analyzed. They expressed VP1 protein, but the levels of secretion and immunogenicity of these VP1 constructs were significantly different (P<0.05). In this study, we further investigated the protein levels of these constructs and determined that all of these constructs expressed VP1 protein. The secretion level was increased by including a tPA leader sequence, which was further increased by fusing human IgG Fc (hFc) to VP1. VP1-hFc demonstrated the most potent immunogenicity in mice. Furthermore, hFc domain could be used to purify VP1-hFc protein for additional studies.

Determinants of EV71 immunogenicity and protection against lethal challenge in a mouse model

Circulating enterovirus 71 (EV71)-associated hand, foot, and mouth disease (HFMD) is a major public health problem in the Asian-Pacific region. An EV71 vaccine for HFMD prevention is currently being developed. However, viral determinants that could influence the vaccine's efficacy have not been well characterized. In this study, we isolated and characterized several EV71 strains that are currently circulating in northern and southern China. We determined that VP1 variation is a major determinant of EV71 immunogenicity. A single amino acid variation in VP1 can lead to significant differences in the breadth and potency of immune responses against primary EV71 isolates as well as the sensitivity of EV71 to heterologous neutralizing antibody responses. We also identified EV71 strains that could induce potent immunogenic and cross-neutralizing antibody responses against diverse EV71 strains. Furthermore, these neutralizing antibodies could protect neonatal mice from lethal dose challenge with various circulating EV71 viruses. Our study provides useful information for EV71 vaccine development and evaluation.

MicroRNA and Pathogenesis of Enterovirus Infection

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

The polio eradication endgame: Why immunization and continued surveillance is critical

The poliovirus is very close to being eradicated from the world. To this end, the four main objectives of the World Health Organization's Polio Eradication & Endgame Strategic Plan 2013-2018 are to: detect and interrupt all poliovirus transmission; strengthen immunization systems and withdraw oral polio vaccine; contain poliovirus and certify interruption of transmission; and plan polio's legacy. There is a need to maintain vigilance for circulating vaccine-derived polioviruses as well as maintaining both epidemiological and laboratory surveillance for polio at this critical point in history. Despite the elimination of indigenous wild poliovirus transmission in Canada, the risk of wild poliovirus importation from endemic countries, and the risk of importation of circulating vaccine strains remains. Due to this ongoing risk, active surveillance of acute flaccid paralysis (AFP) in children less than 15 years of age remains important. At least one stool specimen from all suspect AFP cases should be sent to the National Microbiology Laboratory at the Public Health Agency of Canada for polio isolation and testing to support and verify Canada's polio-free status. An added benefit of this is that it may also help identify other non-polio enteroviruses, such as enterovirus D68.

Immunogenicity and performance of an enterovirus 71 virus-like-particle vaccine in nonhuman primates

A vaccine against human enterovirus 71 (EV-A71) is urgently needed to combat outbreaks of EV-A71 and in particular, the serious neurological complications that manifest during these outbreaks. In this study, an EV-A71 virus-like-particle (VLP) based on a B5 subgenogroup (EV-A71-B5 VLP) was generated using an insect cell/baculovirus platform. Biochemical analysis demonstrated that the purified VLP had a highly native procapsid structure and initial studies in vivo demonstrated that the VLPs were immunogenic in mice. The impact of VLP immunization on infection was examined in non-human primates using a VLP prime-boost strategy prior to EV-A71 challenge. Rhesus macaques were immunized on day 0 and day 21 with VLPs (100 μg/dose) containing adjuvant or with adjuvant alone (controls), and were challenged with EV-A71 on day 42. Complete blood counts, serum chemistry, magnetic resonance imaging (MRI) scans, and histopathology results were mostly normal in vaccinated and control animals after virus challenge demonstrating that the fatal EV-A71-B3 clinical isolate used in this study was not highly virulent in rhesus macaques. Viral genome and/or infectious virus were detected in blood, spleen or brain of two of three control animals, but not in any specimens from the vaccinated animals, indicating that VLP immunization prevented systemic spread of EV-A71 in rhesus macaques. High levels of IgM and IgG were detected in VLP-vaccinated animals and these responses were highly specific for EV-A71 particles and capsid proteins. Serum from vaccinated animals also exhibited similar neutralizing activity against different subgenogroups of EV-A71 demonstrating that the VLPs induced cross-neutralizing antibodies. In conclusion, our EV-A71-B5 VLP is safe, highly immunogenic, and prevents systemic EV-A71-B3 infection in nonhuman primates making it a viable attractive vaccine candidate for EV-A71.

Broad protection with an inactivated vaccine against primary-isolated lethal enterovirus 71 infection in newborn mice

Background

Circulating enterovirus 71 (EV-A71)-associated hand, foot, and mouth disease is on the rise in the Asian-Pacific region. Although animal models have been developed using mouse-adapted EV-A71 strains, mouse models using primary EV-A71 isolates are scarce. Lethal animal models with circulating EV-A71 infection would contribute to studies of pathogenesis as well as vaccine development and evaluation.

Results

In this study, we established a lethal mouse model using primary EV-A71 isolates from patients infected with serotypes that are currently circulating in humans. We also characterized the dose-dependent virulence and pathologic changes of circulating EV-A71 in this mouse model. Most importantly, we have established this mouse model as a suitable system for EV-A71 vaccine evaluation. An inactivated EV-A71 vaccine candidate offered complete protection from death induced by various circulating EV-A71 viruses to neonatal mice that were born to immunized female mice. The sera of the immunized dams and their pups showed higher neutralization titers against multiple circulating EV-A71 viruses.

Conclusions

Thus, our newly established animal model using primary EV-A71 isolates is helpful for future studies on viral pathogenesis and vaccine and drug development.

Etiology, pathogenesis, antivirals and vaccines of hand, foot, and mouth disease

Hand, foot, and mouth disease (HFMD), caused by enteroviruses, is a syndrome characterized by fever with vesicular eruptions mainly on the skin of the hands, feet, and oral cavity. HFMD primarily affects infants and young children. Although infection is usually self-limited, severe neurological complications in the central nervous system can present in some cases, which can lead to death. Widespread infection of HFMD across the Asia-Pacific region over the past two decades has made HFMD a major public health challenge, ranking first among the category C notifiable communicable diseases in China every year since 2008. This review summarizes our understanding of HFMD, focusing on the etiology and pathogenesis of the disease, as well as on progress toward antivirals and vaccines. The review also discusses the implications of these studies as they relate to the control and prevention of the disease.

Reemergence of enterovirus 71 epidemic in northern Taiwan, 2012

BACKGROUND

Enterovirus 71 (EV71) belongs to picornavirus family and could be classified phylogenetically into three major genogroups (A, B and C) including 11 genotypes (A, B1-B5 and C1-C5). Since 1997, EV71 has caused large-scale of epidemics with neurological complications in Asian children. In Taiwan, nationwide EV71 epidemics with different predominant genotypes have occurred cyclically since 1998. A nationwide EV71 epidemic occurred again in 2012. We conducted genetic and antigenic characterizations of the 2012 epidemic.

METHODS

Chang Gung Memorial Hospital (CGMH) is a medical center in northern Taiwan. In CGMH, specimens were collected from pediatric inpatients with suspected enterovirus infections for virus isolation. Enterovirus isolates were serotyped and genotyped and sera from EV71 inpatients were collected for measuring neutralizing antibody titers.

RESULTS

There were 10, 16 and 99 EV71 inpatients identified in 2010, 2011 and 2012, respectively. There were 82 EV71 isolates genotyped, which identified 17 genotype C4a viruses and 65 genotype B5 viruses. The genotype B5 viruses were not detected until November 2011 and caused epidemics in 2012. Interestingly, the B5-2011 viruses were genetically distinguishable from the B5 viruses causing the 2008 epidemic and are likely introduced from China or Southeastern Asia. Based on antigenic analysis, minor antigenic variations were detected among the B5-2008, B5-2011, C4a-2008 and C4a-2012 viruses but these viruses antigenically differed from genotype A.

CONCLUSIONS

Genotype B5 and C4a viruses antigenically differ from genotype A viruses which have disappeared globally for 30 years but have been detected in China since 2008. Enterovirus surveillance should monitor genetic and antigenic variations of EV71.

National surveillance for non-polio enteroviruses in Canada: Why is it important?

A widespread outbreak of enterovirus D68 (EV-D68) was detected in association with respiratory illness in children across Canada and the United States during the autumn of 2014. The majority of cases were mild, but some were associated with more severe illness requiring hospitalization; some of the cases also had neurological symptoms including paralysis, and three deaths were reported in British Columbia. EV-D68 is one of many enteroviruses that include Coxsackieviruses, echovirusesand polio virus. Other than polio virus, there are no vaccines available for the prevention of enterovirus infections, nor are there any antiviral medications that have been approved for their treatment. More than 46 different serotypes have been identified to be circulating in Canada over the last 25 years. Until 2014, EV-D68 was rare. Routine genotyping surveillance done by Canada's National Microbiology Laboratory (NML) identified only 85 isolates of EV-D68 between 1991 and 2013, while 282 were detected between July and October 2014. The complexity of the epidemiology of these enteroviruses demonstrates the need for genotype surveillance, to detect outbreaks spatially and temporally, to determine their relative incidence and impact on the population, and to investigate evolutionary trends, such as recombination events, that are thought to play an important part in strain variation and emergence of epidemic strains. In particular, it is important to carry out virological testing on unusual cases of paralysis in children, and to genotype and sequence any viruses identified. Submission of specimens (virus cultures, stool, cerebrospinal fluid or respiratory specimens) from any such cases to the National Centre for Enteroviruses at NML is encouraged.

Considerations for developing an immunization strategy with enterovirus 71 vaccine

Enterovirus 71 (EV71) is a common pathogen for hand, foot, and mouth disease (HFMD), which has significant morbidity and mortality, and for which children aged 6-59 months age are at highest risk. Due to lack of effective treatment options, control of EV71 epidemics has mainly focused on development of EV71 vaccines. Clinical trials have been completed on 3 EV71 vaccines, with trial results demonstrating good vaccine efficacy and safety. When EV71 vaccine is approved by China's national regulatory authority, an evidence-based strategy should be developed to optimize impact and safety. An immunization strategy for EV71 vaccine should consider several factors, including the target population age group, the number of doses for primary immunization, the need for a booster dose, concomitant administration of other vaccines, economic value, program capacity and logistics, and public acceptance. Once EV71 vaccines are in use, vaccine effectiveness and safety must be monitored in large populations, and the epidemiology of HFMD must be evaluated to assure a match between vaccination strategy and epidemiology. Evaluation in China is especially important because there are no other EV71 vaccines globally.

Enterovirus-71 virus-like particles induce the activation and maturation of human monocyte-derived dendritic cells through TLR4 signaling

Enterovirus 71 (EV71) causes seasonal epidemics of hand-foot-and-mouth disease and has a high mortality rate among young children. We recently demonstrated potent induction of the humoral and cell-mediated immune response in monkeys immunized with EV71 virus-like particles (VLPs), with a morphology resembling that of infectious EV71 virions but not containing a viral genome, which could potentially be safe as a vaccine for EV71. To elucidate the mechanisms through which EV71 VLPs induce cell-mediated immunity, we studied the immunomodulatory effects of EV71 VLPs on human monocyte-derived dendritic cells (DCs), which bind to and incorporate EV71 VLPs. DC treatment with EV71 VLPs enhanced the expression of CD80, CD86, CD83, CD40, CD54, and HLA-DR on the cell surface; increased the production of interleukin (IL)-12 p40, IL-12 p70, and IL-10 by DCs; and suppressed the capacity of DCs for endocytosis. Treatment with EV71 VLPs also enhanced the ability of DCs to stimulate naïve T cells and induced secretion of interferon (IFN)-γ by T cells and Th1 cell responses. Neutralization with antibodies against Toll-like receptor (TLR) 4 suppressed the capacity of EV71 VLPs to induce the production of IL-12 p40, IL-12 p70, and IL-10 by DCs and inhibited EV71 VLPs binding to DCs. Our study findings clarified the important role for TLR4 signaling in DCs in response to EV71 VLPs and showed that EV71 VLPs induced inhibitor of kappaB alpha (IκBα) degradation and nuclear factor of kappaB (NF-κB) activation.

Update on the development of enterovirus 71 vaccines

INTRODUCTION

Enterovirus 71 (EV71) is an etiological agent that causes severe neurological complications in children. EV71 outbreaks have occurred throughout the Asia-Pacific region, posing a severe global public health threat; however, no specific therapeutic strategy exists for treating EV71-infected children.

AREAS COVERED

Five manufacturers have produced inactivated EV71 whole virus vaccines in mainland China, Taiwan, and Singapore, which have completed Phase III (mainland China) and Phase I (Taiwan and Singapore) clinical trials. Various EV71 vaccine candidates are being researched in animal models, including live-attenuated virus vaccine, recombinant VP1 vaccine, VP1-based DNA vaccine, synthetic peptide vaccine and virus-like particle vaccine. In this review, the present situation is summarized, and feasible improvements to the EV71 vaccine are explored.

EXPERT OPINION

Although inactivated EV71 vaccines are safe, efficient and elicit strong immune responses to protect adults, children and infants against infection, the quality control of production is critical.

Update of enterovirus 71 infection: epidemiology, pathogenesis and vaccine

Enterovirus 71 (EV71) is a neurotropic human pathogen that is the causative agent of hand foot and mouth disease (HFMD), herpangina and brain stem encephalitis. Recurrent EV71 epidemics of various scales have occurred in the Asia-Pacific region. Several specific cell surface molecules serve as the receptors for EV71. Identification of the receptors is an important step to understand EV71 disease. Cytokines, lymphocytes and monocytes contribute significantly to EV71 pathogenesis. The interaction of EV71 and receptors may be associated with the cytokines immunopathogenesis. Some animal models have been established and aim to explore the pathogenesis of EV71 infections. EV71 antibodies can neutralize or enhance infection at subneutralizing levels. These results are important for EV71 vaccine and therapeutics design. Several clinical trials of human inactivated EV71 vaccine have recently been completed. The purpose of this review is to summarize recent discoveries about the epidemiology and pathogenesis of EV71 and provide insights into human vaccine development.