Seroepidemiology and molecular epidemiology of enterovirus 71 in Russia

Seroprevalence of Enterovirus 71 Among Children in Western India

Hand-foot-and-mouth disease (HFMD) caused by Enterovirus 71 (EV71) is highly infectious and can lead to serious neurological complications. This study proposed to evaluate the seroprevalence of EV71 in children of two states of western India by estimating neutralizing antibodies (nAbs) to EV71 genotypes D, G, and C isolated in India, using micro-neutralization assay. Among the serum samples of 612 children tested, 213 (34.80%, 95% CI: 31.00-38.73) and 312 (51.00%, 95% CI: 47.00-55.00) were positive for nAbs to EV71 BrCr and indigenous genotype D, respectively, with a significant rise with age for genotype D. However, compared to other age groups, only 23.2% of children aged 1-5 years showed nAbs to EV71 genotype D with a considerably lower Geometric Mean Titer, indicating the susceptibility of this age group to EV71 infection. Our study confirms the circulation of EV71 in India with relatively high susceptibility of children up to 5 years to EV71 infections.

Seroprevalence of coxsackievirus A6 and enterovirus A71 infection in humans: a systematic review and meta-analysis

Hand, foot, and mouth disease (HFMD) is a common infectious disease in children. Enterovirus A71 (EV-A71) is one of the main pathogens, and coxsackievirus A6 (CVA6) has gradually become the dominant pathogen of HFMD in recent years. This study was conducted mainly to assess the serological prevalence of EV-A71 and CVA6 antibodies in people of different ages, sexes, and regions through a systematic review and meta-analysis. A comprehensive study was performed based on the EV-A71 and CVA6 serological literature published before May 2022. Heterogeneity analysis (Cochrane's Q test and the I2 statistic) and random effect models were adopted. Subgroup and meta-regression analyses were used to identify potential sources of heterogeneity in the data, and all analysis was performed using STATA version 16.0. This study included 71 studies involving 55,176 people from 13 countries that met the inclusion criteria. The serological prevalence of EV-A71 antibody in different studies was 4.31-88.8%, and that of CVA6 antibody was 40.8-80.9%. Meta-analysis results showed that the serum positive rate for EV-A71 antibody was 45.9% (95% CI: 37.6-54.1%). The rate in the Chinese population was 47.8% (95% CI: 42.4-53.2%), and in the other countries, it was 38% (95% CI: 23-55%). The serum positive rate for CVA6 antibody was 58.3% (95% CI: 46.5-70.2%). The rate in the Chinese population was 49.1% (95% CI: 38.3-59.9%), and in the other countries, it was 68% (95% CI: 51-83%). Subgroup analysis was also conducted. The seroprevalence of EV-A71 and CVA6 antibodies is related to age rather than gender or region. The rates of EV-A71 and CVA6 seropositivity are considerably lower in children younger than five years of age. However, the rates gradually increase with age. The findings of this study suggest that children under five years of age may be susceptible to EV-A71 and CVA6. Thus, safety education and vaccination should be strengthened accordingly. This study provides a basis for understanding the risk factors for EV-A71 and CVA6 infection in China and for deciding how to formulate standard preventive measures to prevent the spread of the virus.

Drug Repositioning for Hand, Foot, and Mouth Disease

Hand, foot, and mouth disease (HFMD) is a highly contagious disease in children caused by a group of enteroviruses. HFMD currently presents a major threat to infants and young children because of a lack of antiviral drugs in clinical practice. Drug repositioning is an attractive drug discovery strategy aimed at identifying and developing new drugs for diseases. Notably, repositioning of well-characterized therapeutics, including either approved or investigational drugs, is becoming a potential strategy to identify new treatments for virus infections. Various types of drugs, including antibacterial, cardiovascular, and anticancer agents, have been studied in relation to their therapeutic potential to treat HFMD. In this review, we summarize the major outbreaks of HFMD and the progress in drug repositioning to treat this disease. We also discuss the structural features and mode of action of these repositioned drugs and highlight the opportunities and challenges of drug repositioning for HFMD.

Neutralizing antibody against Enterovirus-A71 in Thai children: A longitudinal study from birth to age 4 years

Thailand is one of the countries in the Asia-pacific region that has been most affected by the Enterovirus-A71 (EV-A71) epidemic. An individual who is susceptible to EV-A71 may also be infected asymptomatically, thus, a serological assay is a useful tool to estimate the cumulative incidence of infection in the community and to provide guidance for vaccination scheduling. There have been several candidate EV-A71 vaccines, of which three have been approved and licensed in China. The population target for EV-A71 vaccine is children younger than three years of age. In Thailand, there are limited data available on the seroprevalence of EV-A71 neutralizing (NT) antibodies and the timing of seroconversion in children. This study aims to investigate the seroprevalence and seroconversion rate of EV-A71 NT antibody in a cohort of Thai children. Sera were collected at the King Chulalongkorn Memorial Hospital in Bangkok, Thailand from 100 children between 2015 and 2020. Maternal sera were collected on the day of delivery. Serum samples from children were collected at birth (month 0) and at 2, 7, 18, 24, 36, and 48 months of age to test for EV-A71 NT antibody titers using an enzyme-linked immunosorbent assay (ELISA)-based microneutralization test. The seroprotection rate (NT antibody ≥1:16) in children at months 0, 2, 7, 18, 24, 36, and 48 was 81.0%, 60.0%, 9.0%, 10.0%, 13.0%, 17.0%, and 37.1%, respectively. The seroprotection rate was lowest at month 7 due to waning of the maternal antibody and the immunity of children increased with increasing age. At 48 months of age, less than 40% of children were seroprotected. Children at the age of 6 months should be considered a primary target for vaccination.

Intra-host emergence of an enterovirus A71 variant with enhanced PSGL1 usage and neurovirulence

Enterovirus A71 (EV-A71) is one of the main causative agents of hand-foot-and-mouth disease and is occasionally associated with severe neurological complications. EV-A71 pathophysiology is poorly understood due to the lack of small animal models that robustly support viral replication in relevant organs/tissues. Here, we show that adult severe combined immune-deficient (SCID) mice can serve as an EV-A71 infection model to study neurotropic determinants and viral tropism. Mice inoculated intraperitoneally with an EV-A71 clinical isolate had an initial infection of the lung compartment, followed by neuroinvasion and infection of (motor)neurons, resulting in slowly progressing paralysis of the limbs. We identified a substitution (V135I) in the capsid protein VP2 as a key requirement for neurotropism. This substitution was also present in a mouse-adapted variant, obtained by passaging the clinical isolate in the brain of one-day-old mice, and induced exclusive neuropathology and rapid paralysis, confirming its role in neurotropism. Finally, we showed that this residue enhances the capacity of EV-A71 to use mouse PSGL1 for viral entry. Our data reveal that EV-A71 initially disseminates to the lung and identify viral and host determinants that define the neurotropic character of EV-A71, pointing to a hitherto understudied role of PSGL1 in EV-A71 tropism and neuropathology.

Hypoxia and therapeutic treatment of EV-A71 with an immune modulator TLR7 agonist in a new immunocompetent mouse model

Background

Enterovirus 71 (EV71 or EV-A71) was first identified in California about half a century ago. In recent years, outbreaks of EV-A71 were prevalent worldwide, including Taiwan, Malaysia, Singapore, Japan, and China. Between 2008 and 2011, China alone reported 1894 deaths associated with EV-A71 infection. In mild cases, EV-A71 can cause herpangina and hand-foot-and-mouth disease (HFMD). However, in severe cases, it could cause neurological disorders, including meningitis and encephalitis. Cardiopulmonary failure is common among hospitalized children with EV-A71 infection. No effective FDA-approved therapeutics against EV-A71 are clinically available.

Methods

We report the establishment of an immunocompetent wild type strain 129 (wt-129) mouse model, which can be cross-species infected with human EV-A71 clinical isolates via an intraperitoneal route.

Results

One intriguing disease phenotype of this new model is the development of characteristic “White-Jade” patches in the muscle, which lost sporadically the normal pink color of uninfected muscle. Viral VP1 protein and massive leukocyte infiltration were detected in muscles with or without white-jades. We demonstrated further that hypoxia is a general phenomenon associated with white-jades in both immunocompetent and immunodeficient mouse models. Therefore, hypoxia appears to be a feature intrinsic to EV-A71 infection, irrespective of its host’s immunogenetic background. To date, no effective treatment for EV-A71 is available. Here, using this new wt-129 mouse model, we showed that timely treatment with compound R837 (a TLR7 immune modulator) via oral or intraperitoneal routes, rescued the hypoxia, limb paralysis, and death at a high therapeutic efficacy.

Conclusions

In this new immunocompetent mouse 129 model, we observed an unexpected white-jade phenotype and its associated hypoxia. The successful treatment with TLR7 immune modulators via an oral route, provide us a new research direction for EV-A71 basic science and translational research. It remains an open issue whether R837 or its related compounds, will be a promising drug candidate in clinical trials in EV-A71 endemic or epidemic areas in the future.

Enterovirus 71 seroepidemiology in Taiwan in 2017 and comparison of those rates in 1997, 1999 and 2007

Background

During recent 20 years, enterovirus 71 (EV71) has emerged as a major concern among children, particularly in the Asia-Pacific region. To understand current EV71 serostatus, to find risk factors associated with EV71 infection and to establish future EV71 vaccine policy, we performed a seroepidemiology study in Taiwan in 2017.

Methods

After informed consent was obtained, we enrolled preschool children, 6–15-year-old students, 16–50-year-old people. They received a questionnaire and a blood sample was collected to measure the EV71 neutralization antibody.

Results

Altogether, 920 subjects were enrolled with a male-to-female ratio of 1.03. The EV71 seropositive rate was 10% (8/82) in infants, 4% (6/153) in 1-year-old children, 8% (7/83) in 2-year-old children, 8% (13/156) in 3–5-year-old children, 31% (38/122) in 6–11-year-old primary school students, 45% (54/121) in 12–15-year-old high school students and 75% (152/203) in 16-50-year-old people. Risk factors associated with EV71 seropositivity in preschool children were female gender, having siblings, more siblings, and contact with herpangina or hand-foot-and-mouth disease. The risk factor with EV71 seropositivity in 16–50-year-old people was having children in their families in addition to older age (p<0.001). Compared with the rates in 1997, 1999 and 2007, the rates in children were significantly lower in 2017.

Conclusion

EV71 seropositive rates were very low, at 4% to 10%, in preschool children and not high, at 31%, in primary school students. Preschool children are highly susceptible and need EV71 vaccine most.

Molecular epidemiology of enteroviruses in Cyprus 2008-2017

Enteroviruses (EVs) are associated with a broad spectrum of disease manifestations, including aseptic meningitis, encephalitis, hand, foot and mouth disease, acute flaccid paralysis and acute flaccid myelitis with outbreaks being reported frequently world-wide. The aim of this study was the molecular characterization of all enteroviruses detected in Cyprus in the ten-year period from January 2008 and December 2017 as well as a description of the circulation patterns associated with the most frequently encountered genotypes. For this purpose, serum, cerebrospinal fluid, nasal swab, skin swab and/or stool samples from 2666 patients with a suspected EV infection were analysed between January 2008 and December 2017. Enteroviruses were detected in 295 (11.1%) patients, which were then investigated further for epidemiological analysis by VP1 genotyping. Overall, 24 different enterovirus types belonging to three different species were identified. The predominant species was EV-B (209/295, 71%), followed by species EV-A (77/295, 26.1%). Only one virus belonged to species EV-D, whereas EV-C enteroviruses were not identified at all. The most frequent genotypes identified were echovirus 30 (26.1%), echovirus 6 (14.2%) and coxsackievirus A6 (10.9%). While Echovirus 30 and echovirus 6 frequency was significantly higher in patients older than 3 years of age, the opposite was observed for CV-A16 and EV-A71, which dominated in young children less than 3 years. Importantly, for the current study period a significant increase of previously only sporadically observed EV-A types, such as EV-A71 and CV-A16 was noted. A phylogenetic analysis of EV-A71 showed that the majority of the EV-A71 strains from Cyprus belonged to sub-genogroup C1 and C2, with the exception of one C4 strain that was observed in 2011. The data presented provide a comprehensive picture of enteroviruses circulating in Cyprus over the last decade and will be helpful to clinicians and researchers involved in the treatment, prevention and control of enteroviral infections by helping interpret trends in enteroviral diseases by associating them with circulating serotypes, for studying the association of enteroviruses with clinical manifestations and develop strategies for designing future EV vaccines.

Immunocompetent and Immunodeficient Mouse Models for Enterovirus 71 Pathogenesis and Therapy

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

Seroprevalence of antibodies to enterovirus 71 and coxsackievirus A16 among people of various age groups in a northeast province of Thailand

BACKGROUND

Hand, foot and mouth disease (HFMD) is endemic among population of young children in Thailand. The disease is mostly caused by enterovirus 71 (EV71) and coxsackievirus A16 (CA16).

METHODS

This study conducted serosurveillance for neutralizing (NT) antibodies to EV71 subgenotypes B5 and C4a, and to CA16 subgenotypes B1a and B1b, in 579 subjects of various ages using a microneutralization assay in human rhabdomyosarcoma (RD) cells. These test viruses were the major circulating subgenotypes associated with HFMD in Thailand during the study period.

RESULTS

We found that the levels of seropositivity against all 4 study viruses were lowest in the age group of 6-11 months, i.e., 5.5% had antibody to both EV71 subgenotypes, while 14.5% and 16.4% had antibody to CA16 subgenotypes B1a and B1b, respectively. The percentages of subjects with antibodies to these 4 viruses gradually increased with age, but were still less than 50% in children younger than 3 years. These laboratory data were consistent with the epidemiological data collected by the Ministry of Public Health which showed repeatedly that the highest number of HFMD cases was in children aged 1 year. Analyses of amino acid sequences of the test viruses showed 97% identity between the two subgenotypes of EV71, and 99% between the two subgenotypes of CA16. Nevertheless, the levels of seropositivity and antibody titer against the two subgenotypes of EV71 and of CA16 were not significantly different.

CONCLUSIONS

This study clearly demonstrated NT antibody activity across EV71-B5 and EV71-C4a subgenotypes, and also across CA16-B1a and CA16-B1b subgenotypes. Moreover, there were no significant differences by gender in the seropositive rates and antibody levels to any of the 4 virus subgenotypes.

Molecular epidemiology and phylogenetics of human enteroviruses: Is there a forest behind the trees?

Enteroviruses are among the best studied small non-enveloped enteric RNA viruses. Most enteroviruses are easy to isolate in cell culture, and many non-polio enterovirus strains were archived worldwide as a byproduct of the WHO poliovirus surveillance system. Common outbreaks and epidemics, most prominently the epidemic of hand-foot-and-mouth disease with severe neurological complications in East and South-East Asia, justify practical interest of non-polio enteroviruses. As a result, there are over 50 000 enterovirus nucleotide sequences available in GenBank. Technical possibilities have been also improving, as Bayesian phylogenetic methods with an integrated molecular clock were introduced a decade ago and provided unprecedented opportunities for phylogenetic analysis. As a result, hundreds of papers were published on the molecular epidemiology of enteroviruses. This review covers the modern methodology, structure, and biases of the sequence dataset available in GenBank. The relevance of the subtype classification, findings of co-circulation of multiple genetic variants, previously unappreciated complexity of viral populations, and global evolutionary patterns are addressed. The most relevant conclusions and prospects for further studies on outbreak emergence mechanisms are discussed.

Inhibition of enterovirus 71 replication and viral 3C protease by quercetin

BACKGROUND

Enterovirus 71 (EV71) is one of the major causative agents of hand, foot, and mouth disease (HFMD), which is sometimes associated with severe central nervous system disease in children. There is currently no specific medication for EV71 infection. Quercetin, one of the most widely distributed flavonoids in plants, has been demonstrated to inhibit various viral infections. However, investigation of the anti-EV71 mechanism has not been reported to date.

METHODS

The anti-EV71 activity of quercetin was evaluated by phenotype screening, determining the cytopathic effect (CPE) and EV71-induced cells apoptosis. The effects on EV71 replication were evaluated further by determining virus yield, viral RNA synthesis and protein expression, respectively. The mechanism of action against EV71 was determined from the effective stage and time-of-addition assays. The possible inhibitory functions of quercetin via viral 2Apro, 3Cpro or 3Dpol were tested. The interaction between EV71 3Cpro and quercetin was predicted and calculated by molecular docking.

RESULTS

Quercetin inhibited EV71-mediated cytopathogenic effects, reduced EV71 progeny yields, and prevented EV71-induced apoptosis with low cytotoxicity. Investigation of the underlying mechanism of action revealed that quercetin exhibited a preventive effect against EV71 infection and inhibited viral adsorption. Moreover, quercetin mediated its powerful therapeutic effects primarily by blocking the early post-attachment stage of viral infection. Further experiments demonstrated that quercetin potently inhibited the activity of the EV71 protease, 3Cpro, blocking viral replication, but not the activity of the protease, 2Apro, or the RNA polymerase, 3Dpol. Modeling of the molecular binding of the 3Cpro-quercetin complex revealed that quercetin was predicted to insert into the substrate-binding pocket of EV71 3Cpro, blocking substrate recognition and thereby inhibiting EV71 3Cpro activity.

CONCLUSIONS

Quercetin can effectively prevent EV71-induced cell injury with low toxicity to host cells. Quercetin may act in more than one way to deter viral infection, exhibiting some preventive and a powerful therapeutic effect against EV71. Further, quercetin potently inhibits EV71 3Cpro activity, thereby blocking EV71 replication.

Prediction of Protection against Asian Enterovirus 71 Outbreak Strains by Cross-neutralizing Capacity of Serum from Dutch Donors, The Netherlands

Herd immunity induced by locally circulating strains could provide protection against introduction of new strains.

Outbreaks of human enterovirus 71 (EV-71) in Asia are related to high illness and death rates among children. To gain insight into the potential threat for the population of Europe, we determined the neutralizing activity in intravenous immunoglobulin (IVIg) batches and individual serum samples from donors in the Netherlands against EV-71 strains isolated in Europe and in Asia. All IVIg batches and 41%, 79%, and 65% of serum samples from children ≤5 years of age, women of childbearing age, and HIV-positive men, respectively, showed high neutralizing activity against a Dutch C1 strain, confirming widespread circulation of EV-71 in the Netherlands. Asian B3–4 and C4 strains were efficiently cross-neutralized, predicting possible protection against extensive circulation and associated outbreaks of those types in Europe. However, C2 and C5 strains that had few mutations in the capsid region consistently escaped neutralization, emphasizing the importance of monitoring antigenic diversity among circulating EV-71 strains.

Enterovirus 71 3C Promotes Apoptosis through Cleavage of PinX1, a Telomere Binding Protein

Enterovirus 71 (EV71) is an emerging pathogen causing hand, foot, and mouth disease (HFMD) and fatal neurological diseases in infants and young children due to their underdeveloped immunocompetence. EV71 infection can induce cellular apoptosis through a variety of pathways, which promotes EV71 release. The viral protease 3C plays an important role in EV71-induced apoptosis. However, the molecular mechanism responsible for 3C-triggered apoptosis remains elusive. Here, we found that EV71 3C directly interacted with PinX1, a telomere binding protein. Furthermore, 3C cleaved PinX1 at the site of Q50-G51 pair through its protease activity. Overexpression of PinX1 reduced the level of EV71-induced apoptosis and EV71 release, whereas depletion of PinX1 by small interfering RNA promoted apoptosis induced by etoposide and increased EV71 release. Taken together, our study uncovered a mechanism that EV71 utilizes to promote host cell apoptosis through cleavage of cellular protein PinX1 by 3C.

IMPORTANCE

EV71 3C plays an important role in processing viral proteins and interacting with host cells. In this study, we showed that 3C promoted apoptosis through cleaving PinX1, a telomere binding protein, and that this cleavage facilitated EV71 release. Our study demonstrated that PinX1 plays an important role in EV71 release and revealed a novel mechanism that EV71 utilizes to induce apoptosis. This finding is important in understanding EV71-host cell interactions and has potential impact on understanding other enterovirus-host cell interactions.

Seroprevalence of Enterovirus A71 and Coxsackievirus A16 in Healthy People in Shandong Province, China

Background

Hand, foot, and mouth disease has become very common in mainland of China in recent years, and enterovirus A71 and coxsackievirus A16 are its major etiologic factors. Here we investigated the seroprevalence of enterovirus A71 and coxsackievirus A16 based on a large group of healthy individuals in Shandong province, China.

Methods

A total of 1378 healthy individuals were tested for serum neutralizing antibodies against enterovirus A71 and coxsackievirus A16 using a micro neutralization test.

Results

The overall seroprevalence of enterovirus A71 neutralizing antibodies was 74.75%. It increased significantly from 48.84% in children aged 0–1 years old to 88.64% in those aged 20–29 years (p < 0.01) and decreased to 85.71% in adults > 40 years old with a significant gender-specific difference (p < 0.01). The overall coxsackievirus A16 antibody prevalence was 71.77%. It increased significantly from 39.53% in children aged 0–1 years to 80.68% in those aged 10–19 years (p < 0.01) and decreased to 75.63% in adults >40 years without a gender-specific difference. Nearly 50% of the children <1 year were susceptible to enterovirus A71 infection versus 40% to coxsackievirus A16 infection. Sample collection time and place also played a role in the enterovirus A71 and coxsackievirus A16 positive rates. The overall rates in January were significantly lower than those in April and August (p < 0.01); enterovirus A71 positive rates in Jinan city (capital city of Shandong province) were lower than those in Jining city and Zibo city (p < 0.05); and oxsackievirus A16 positive rates in Jining city were significantly higher than those in Jinan city and Zibo city (p < 0.01).

Conclusion

There were significant differences among age groups, locations, and time points in the seroprevalence rates of enterovirus A71 and coxsackievirus A16 neutralizing antibodies in healthy people in Shandong province.

Disease burden of enterovirus 71 in rural central China: A community-based survey

In recent years, the epidemics of hand, foot, and mouth disease (HFMD) centered in the Asian-Pacific region have been characterized by high morbidity and mortality. Enterovirus 71 (EV71) infections were responsible for the majority of the infections leading to severe cases of HFMD and death. This is a community-based survey aimed to estimate the disease burden of EV71 in rural central China, especially for HFMD. From 2011 to 2013, demographic and socio-economic data were gathered from 343 ill children and their parents using a structured questionnaire. We quantified the health burden of disease resulting from EV71 infection in disability-adjusted life years (DALYs). Among 343 cases, 303 had confirmed HFMD, 6 presented with herpangina, 25 presented with respiratory symptoms, and 9 presented with non-specific symptoms. The number of severe cases was 47 (including 1 death) and all of these presented with HFMD. The total cost per patient for severe HFMD, mild HFMD, herpangina, respiratory disease, and non-specific disease was $2149.47, $513.22, $53.28, $31.95, and $39.25, respectively. The overall cost of EV71-related diseases as a proportion of local farmers' per capita net income ranged from 0.18% for those with non-specific disease to 187.12% for those with severe HFMD. The loss of DALYs for the 5 forms of disease were 3.47, 1.76, 1.07, 1.44, 1.22 person-years per 1000 persons, respectively. This study provides data on cost of treatment and health burden for diseases caused by EV71, which can be used in the evaluation of EV71 vaccine cost-effectiveness.

Enterovirus A71 Meningoencephalitis Outbreak, Rostov-on-Don, Russia, 2013

Seventy-eight cases of enterovirus infection, including 25 neuroinfections, occurred in Rostov-on-Don, Russia, during May–June 2013. The outbreak was caused by an enterovirus A type 71 (EV-A71) subgenotype C4 lineage that spread to neighboring countries from China ≈3 years earlier. Enterovirus associated neuroinfection may emerge in areas with a preceding background circulation of EV-A71 with apparently asymptomatic infection.

Seroprevalence of Enterovirus 71 Antibody Among Children in China: A Systematic Review and Meta-analysis

BACKGROUND

Hand, foot and mouth disease mostly affects children and carries a substantial disease burden in the Western Pacific region. Enterovirus 71 (EV71) is the most virulent causative agent, and a monovalent vaccine against EV71 will soon become commercially available in China. An improved understanding of EV71 epidemiology would aid policy decisions regarding childhood immunization in China. We aimed to assess and summarize information to date from individual seroepidemiologic studies of EV71 in mainland China to determine patterns of the age-specific risk of infection.

METHODS

A systematic review and meta-analysis of studies of children aged 0-15 years, published in English or Chinese, was conducted. Estimates of seroprevalence were summarized by age group. A mixed-effects regression model was used to explore factors covarying with EV71 seroprevalence.

RESULTS

We identified 42 published studies, 15 in English. We found that an average of 78% of neonates was seropositive to EV71 infection, but such maternally conferred immunity almost completely waned by 5 months. The seroprevalence of EV71 antibody increased directly with age among preschool children, from 26% (95% confidence interval: 18%-33%) at 1 year to 70% (95% confidence interval: 62%-78%) at 5 years. Age of subjects, sample size, sampling year, sampling method, geographic latitude and publication language were associated with variations of individual seroprevalence estimates.

CONCLUSIONS

Seroprevalence of EV71 antibody gradually declined during the first 5 months in infants. Infection of EV71 was most likely to occur between 2 and 4 years. Our findings may be useful in informing population-based EV71 vaccination strategies.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Epidemiological Characteristics and Spatial-Temporal Clusters of Hand, Foot, and Mouth Disease in Zhejiang Province, China, 2008-2012

Hand, foot and mouth disease (HFMD) is one of the major public health concerns in China. Being the province with high incidence rates of HFMD, the epidemiological features and the spatial-temporal patterns of Zhejiang Province were still unknown. The objective of this study was to investigate the epidemiological characteristics and the high-incidence clusters, as well as explore some potential risk factors. The surveillance data of HFMD during 2008-2012 were collected from the communicable disease surveillance network system of Zhejiang Provincial Center for Disease Control and Prevention. The distributions of age, gender, occupation, season, region, pathogen's serotype and disease severity were analyzed to describe the epidemiological features of HFMD in Zhejiang Province. Seroprevalence survey for human enterovirus 71 (EV71) in 549 healthy children of Zhejiang Province was also performed, as well as 27 seroprevalence publications between 1997 and 2015 were summarized. The spatial-temporal methods were performed to explore the clusters at county level. Furthermore, pathogens' serotypes such as EV71 and coxsackievirus A16 (Cox A16) and meteorological factors were analyzed to explore the potential factors associated with the clusters. A total of 454,339 HFMD cases were reported in Zhejiang Province during 2008-2012, including 1688 (0.37%) severe cases. The annual average incidence rate was 172.98 per 100,000 (ranged from 72.61 to 270.04). The male-to-female ratio for mild cases was around 1.64:1, and up to 1.87:1 for severe cases. Of the total cases, children aged under three years old and under five years old accounted for almost 60% and 90%, respectively. Among all enteroviruses, the predominant serotype was EV71 (49.70%), followed by Cox A16 (26.05%) and other enteroviruses (24.24%) for mild cases. In severe cases, EV71 (82.85%) was the major causative agent. EV71 seroprevalence survey in healthy children confirmed that occult infection was common in children. Furthermore, literature summary for 26 seroprevalence studies during 1997-2015 confirmed that 0-5 years group showed lowest level of EV71 seroprevalence (29.1% on average) compared to the elder children (6-10 years group: 54.6%; 11-20 years group: 61.8%). Global positive spatial autocorrelation patterns (Moran's Is>0.25, P<0.05) were discovered not only for mild cases but also for severe cases, and local positive spatial autocorrelation patterns were revealed for counties from the eastern coastal and southern regions. The retrospective space-time cluster analysis also confirmed these patterns. Risk factors analyses implied that more EV71 and less sunshine were associated with the clusters of HFMD in Zhejiang Province. Our study confirmed that Zhejiang Province was one of the highly epidemic provinces in China and that the epidemiological characteristics of HFMD were similar to other provinces. Occult infection in elder children and adults was one of the important reasons why most HFMD cases were children aged under-five. Combining the results of spatial autocorrelation analysis and the space-time cluster analysis, the major spatial-temporal clusters were from the eastern coastal and southern regions. The distribution of pathogens' serotypes and the level of sunshine could be risk factors for, and serve as an early warning of, the outbreak of HFMD in Zhejiang Province.

New introductions of enterovirus 71 subgenogroup C4 strains, France, 2012

In France during 2012, human enterovirus 71 (EV-A71) subgenogroup C4 strains were detected in 4 children hospitalized for neonatal fever or meningitis. Phylogenetic analysis showed novel and independent EV-A71 introductions, presumably from China, and suggested circulation of C4 strains throughout France. This observation emphasizes the need for monitoring EV-A71 infections in Europe.