Incidence and case-fatality rates resulting from the 1998 enterovirus 71 outbreak in Taiwan

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.

The secular trend of enterovirus A71 after the implementation of preventive measures in Taiwan

BACKGROUND

Enterovirus A71 (EV A71) is one of the most important enteroviruses related to morbidity and mortality in children worldwide. This study aimed to analyse the secular trend of EV A71 in Taiwan from 1998 to 2020 and to evaluate the effectiveness of infection control measures.

METHODS

We collected the epidemiological data of EV A71 from disease surveillance systems in Taiwan. We analysed the association between the secular trend of EV A71 and preventive measures such as hand washing, case isolation, and suspension of classes.

RESULTS

The incidence of enterovirus infections with severe complications (EVSC) decreased from 16.25 per 100,000 children under six in 1998 to less than 9.73 per 100,000 children under six after 2012 (P = 0.0022). The mortality rate also decreased significantly, from 3.52 per 100,000 children under six in 1998 to 0 per 100,000 children under six in 2020 (P < 0.0001). The numbers of EVSC and fatalities were significantly higher in the years when EV A71 accounted for more than 10% of the annual predominant serotypes (p < 0.05). After the implementation of many non-pharmaceutical interventions in 2012, the incidence of EVSC and mortality rate decreased significantly (p < 0.001).

CONCLUSIONS

After implementing active enterovirus surveillance and preventive measures, we found that the incidence of EVSC and fatalities due to EV A71 in Taiwan decreased significantly from 1998 to 2020. Continuous surveillance and strengthened infection control policies are still needed in the future.

Can judgments according to case fatality rate be correct all the time during epidemics? Estimated cases based on CFR in different scenarios and some lessons from early case fatality rate of coronavirus disease 2019 in Iran

Background: The new Coronavirus disease (COVID-19) was first identified in China in 2019. Case fatality rate (CFR) indicator of the disease is one of the most important indices noticed by experts, policymakers, and managers, based on which daily evaluations and many judgments are made. CFR can change during epidemics. This study aimed to estimate the actual number of COVID-19 cases in Iran and to calculate the early CFR for the disease based on official statistics. Methods: This was a descriptive study whose data were obtained from the website of the Ministry of Health and Medical Education of Iran from February 20, 2020 until March 26, 2020. CFR has been obtained by dividing the total number of deaths by the total number of confirmed cases at one point in time. In this study, the actual number of COVID-19 cases in Iran was estimated based on the mortality model in 4 scenarios. Excel 2013 software was used to analyze the data. Results: According to the findings of this study, In Iran, until March 26, 2020, a total of 27 017 people have been infected by COVID-19 and 2077 died of it. However, CFR indicator had a descending trend in Iran: 100%, 18.6%, 8.8%, 3.3%, 6.9%, and 7.7% on days 1, 5, 10, 20, 30, and 35, respectively. The actual number of COVID-19 cases in Iran was estimated to be 4 789 454, 2 873 673, 1 436 836, and 718418 as of March 26, 2020 according to the 4 scenarios, respectively. Conclusion: In emerging epidemics, CFR indicator must not be used as a basis to judge the performance of a health system unless that epidemic condition has been clarified. Moreover, it is suggested that in the outbreak of an epidemic, specifically emerging diseases, CFR must not be the base of judgment. Making judgments, specifically in the outbreak of emerging epidemics, based on fatality rate can lead to information bias. It is also possible to estimate the total number of patients based on the CFR in circumstances where little information is available on the disease.

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.

Immunogenicity and safety of an inactivated enterovirus A71 vaccine in children 3-6 years and 2-35 months of age- an open-label, randomized phase IIb clinical trial

BACKGROUND

Enterovirus A71 (EV-A71) infection can cause severe debilitating complications and even death in young children. The immunogenicity and safety of an inactivated whole EV-A71 virus vaccine were assessed in children 2 months to 6 years of age.

METHODS

This was an open-label, multi-center and randomized phase IIb study, which divided into part A and B. In part A, children 36 months to 6 years of age were enrolled and randomized into 3 groups, receiving 0.5 μg total viral protein (TP) with adjuvant Al(OH)3, 1.0 μg TP with Al(OH)3 or 1.0 μg TP only. Two doses of vaccines were administered at a 28-day interval and blood was taken before immunization, at week 4, 8, 28 and 52 (optional) for virus neutralization assay. Safety profiles were also monitored. After safety profiles had shown no concerns, children 2 months to 35 months of age (part B) were subsequently enrolled following the same protocol.

RESULTS

A total of 135 children completed two doses of immunization, including 58 in part A and 77 in part B. Both adjuvanted 0.5 μg and 1.0 μg TP elicited significant raise of neutralizing antibody titers and seroconversion rate was up to 93.75-100.0% after 2 doses of immunization. Adjuvanted 1.0 μg TP induced higher titers of neutralizing antibodies than adjuvanted 0.5 μg TP. By contrast, non-adjuvanted 1.0 μg TP was not immunogenic. No major adverse events were reported.

CONCLUSIONS

This EV-A71 vaccine containing adjuvant is immunogenic and safe in children 2 months to 6 years of age.

CLINICAL TRIALS REGISTRATION

NCT03268083.

Enterovirus and parechovirus infections in children: differences in clinical presentation, mechanisms for meningitis without pleocytosis and mechanisms involved in the neurological outcome

Enterovirus (EV) and Parechovirus (HPeV) are a frequent cause of infection in children. This review gives an overview of possible causes for differences in clinical presentation. EV and HPeV can cause a meningitis with or without pleocytosis. Different possible mechanisms for meningitis without pleocytosis are given. Little is known about the prognosis and long-term effects of EV and HPeV meningitis in children. Only some studies with a small number of children with EV or HPeV meningitis are reported. The different possible mechanisms involved in the neurological outcome after EV or HPeV meningitis will be discussed.

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.

Severity and burden of hand, foot and mouth disease in Asia: a modelling study

Background

Hand, foot and mouth disease (HFMD) affects millions of children across Asia annually, leading to an increase in implemented control policies such as surveillance, isolation and social distancing in affected jurisdictions. However, limited knowledge of disease burden and severity causes difficulty in policy optimisation as the associated economic cost cannot be easily estimated. We use a data synthesis approach to provide a comprehensive picture of HFMD disease burden, estimating infection risk, symptomatic rates, the risk of complications and death, and overall disability-adjusted life-year (DALY) losses, along with associated uncertainties.

Methods

Complementary data from a variety of sources were synthesised with mathematical models to obtain estimates of severity of HFMD. This includes serological and other data extracted through a systematic review of HFMD epidemiology previously published by the authors, and laboratory investigations and sentinel reports from Singapore's surveillance system.

Results

HFMD is estimated to cause 96 900 (95% CI 40 600 to 259 000) age-weighted DALYs per annum in eight high-burden countries in East and Southeast Asia, with the majority of DALYs attributed to years of life lost. The symptomatic case hospitalisation rate of HFMD is 6% (2.8%-14.9%), of which 18.7% (6.7%-31.5%) are expected to develop complications. 5% (2.9%-7.4%) of such cases are fatal, bringing the overall case fatality ratio to be 52.3 (24.4-92.7) per 100 000 symptomatic infections. In contrast, the EV-A71 case fatality ratio is estimated to be at least 229.7 (75.4-672.1) per 100 000 symptomatic cases. Asymptomatic rate for EV-A71 is 71.4% (68.3%-74.3%) for ages 1-4, the years of greatest incidence.

Conclusion

Despite the high incidence rate of HFMD, total DALY due to HFMD is limited in comparison to other endemic diseases in the region, such as dengue and upper respiratory tract infection. With the majority of DALY caused by years of life lost, it is possible to mitigate most with increased EV-A71 vaccine coverage.

Identifying novel antiviral targets against enterovirus 71: where are we?

Human enterovirus 71 (HEV71) has been considered as an essential human pathogen, which causes hand, foot and mouth disease in young children. Several HEV71 outbreaks have been observed in many Asia-Pacific countries for the past two decades with significant fatalities. However, there are no competent vaccines or antivirals against HEV71 infection to date. Thus, it is of critical priority to delve into the search for anti-HEV71 agents. Prior to this, there is a need to gain knowledge about the distinct targets of HEV71 that are available and that have been exploited for antiviral therapy. This review aims to provide a better understanding of HEV71 virology and feature potential antivirals for progressive clinical development with respect to their elucidated mechanistic actions.

The Epidemiology of Hand, Foot and Mouth Disease in Asia: A Systematic Review and Analysis

CONTEXT

Hand, foot and mouth disease (HFMD) is a widespread pediatric disease caused primarily by human enterovirus 71 (EV-A71) and Coxsackievirus A16 (CV-A16).

OBJECTIVE

This study reports a systematic review of the epidemiology of HFMD in Asia.

DATA SOURCES

PubMed, Web of Science and Google Scholar were searched up to December 2014.

STUDY SELECTION

Two reviewers independently assessed studies for epidemiologic and serologic information about prevalence and incidence of HFMD against predetermined inclusion/exclusion criteria.

DATA EXTRACTION

Two reviewers extracted answers for 8 specific research questions on HFMD epidemiology. The results are checked by 3 others.

RESULTS

HFMD is found to be seasonal in temperate Asia with a summer peak and in subtropical Asia with spring and fall peaks, but not in tropical Asia; evidence of a climatic role was identified for temperate Japan. Risk factors for HFMD include hygiene, age, gender and social contacts, but most studies were underpowered to adjust rigorously for confounding variables. Both community-level and school-level transmission have been implicated, but their relative importance for HFMD is inconclusive. Epidemiologic indices are poorly understood: No supporting quantitative evidence was found for the incubation period of EV-A71; the symptomatic rate of EV-A71/Coxsackievirus A16 infection was from 10% to 71% in 4 studies; while the basic reproduction number was between 1.1 and 5.5 in 3 studies. The uncertainty in these estimates inhibits their use for further analysis.

LIMITATIONS

Diversity of study designs complicates attempts to identify features of HFMD epidemiology.

CONCLUSIONS

Knowledge on HFMD remains insufficient to guide interventions such as the incorporation of an EV-A71 vaccine in pediatric vaccination schedules. Research is urgently needed to fill these gaps.

Cyclical Patterns of Hand, Foot and Mouth Disease Caused by Enterovirus A71 in Malaysia

Enterovirus A71 (EV-A71) is an important emerging pathogen causing large epidemics of hand, foot and mouth disease (HFMD) in children. In Malaysia, since the first EV-A71 epidemic in 1997, recurrent cyclical epidemics have occurred every 2–3 years for reasons that remain unclear. We hypothesize that this cyclical pattern is due to changes in population immunity in children (measured as seroprevalence). Neutralizing antibody titers against EV-A71 were measured in 2,141 residual serum samples collected from children ≤12 years old between 1995 and 2012 to determine the seroprevalence of EV-A71. Reported national HFMD incidence was highest in children <2 years, and decreased with age; in support of this, EV-A71 seroprevalence was significantly associated with age, indicating greater susceptibility in younger children. EV-A71 epidemics are also characterized by peaks of increased genetic diversity, often with genotype changes. Cross-sectional time series analysis was used to model the association between EV-A71 epidemic periods and EV-A71 seroprevalence adjusting for age and climatic variables (temperature, rainfall, rain days and ultraviolet radiance). A 10% increase in absolute monthly EV-A71 seroprevalence was associated with a 45% higher odds of an epidemic (adjusted odds ratio, aOR1.45; 95% CI 1.24–1.69; P<0.001). Every 10% decrease in seroprevalence between preceding and current months was associated with a 16% higher odds of an epidemic (aOR = 1.16; CI 1.01–1.34 P<0.034). In summary, the 2–3 year cyclical pattern of EV-A71 epidemics in Malaysia is mainly due to the fall of population immunity accompanying the accumulation of susceptible children between epidemics. This study will impact the future planning, timing and target populations for vaccine programs.

Enterovirus A71 (EV-A71) is a major cause of hand, foot, and mouth disease (HFMD) in children. Since the first outbreak in Malaysia in 1997, EV-A71 epidemics have occurred every 2–3 years, in 2000, 2003, 2006, 2008/2009, and 2012. As the reasons for this cyclical pattern are not known, we hypothesize that it is due to changes in population immunity in children. In this study, we measured the EV-A71 neutralizing antibody prevalence in serum collected from children ≤12 years old between 1995 and 2012, covering 18 years and 6 epidemics. HFMD incidence was highest in children <2 years, and seroprevalence increased with age, and was higher during epidemics compared to non-epidemic periods. Peaks in EV-A71 genetic diversity coincided with reported EV-A71 epidemics. Decreases in EV-A71 seroprevalence over time were significantly associated with subsequent epidemic periods. This suggests that epidemics lead to high levels of population seroprevalence; but during the 2–3 years between epidemics, the population of young children with no immunity is replenished and increases, making it more likely that a new epidemic will occur. This is the first study to show that the cyclical pattern of EV-A71 epidemics is associated with changes in EV-A71 seroprevalence.

Enteroviruses in the early 21st century: new manifestations and challenges

PURPOSE OF REVIEW

Enteroviruses cause a wide variety of diseases with neurologic, respiratory, skin, and gastrointestinal findings. The purpose of this review is to clarify changes in the classification of enteroviruses, provide information about recent disease outbreaks, and to summarize progress toward the treatment and prevention of these infections.

RECENT FINDINGS

Enteroviruses are now classified into four distinct species. New variants of coxsackievirus B1, enterovirus-A71, and enterovirus-D68 (EV-D68) have emerged as causes of recent outbreaks in the United States and other countries, including more severe disease manifestations than previously described. EV-D68 now commonly circulates in the United States, and has been linked to severe respiratory disease and associated with acute flaccid myelitis (AFM). Overcoming enormous political and logistical challenges, fewer than 100 cases of polio have been reported in 2015, and the initiation of 'endgame' strategies appears imminent. Unfortunately, treatment for enterovirus infections remains supportive, although the recently completed pleconaril trial in newborns suggests that antiviral therapy may reduce mortality in neonatal disease.

SUMMARY

Clinicians should be aware of the respiratory and neurological manifestations associated with EV-D68 and the potential for severe disease seen with other recently described enterovirus variants. Healthcare professionals should recognize the utility of rapid diagnostic methods and progress toward prevention and treatment of enterovirus infections.

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.

Clinical utility of serum samples for human parechovirus type 3 infection in neonates and young infants: The 2014 epidemic in Japan

During the 2014 human parechovirus type 3 (HPeV3) epidemic in Niigata, Japan, this prospective observational study identified HPeV3 from 43/85 (51%) febrile young infants <4 months using PCR analysis of serum (n = 42) and/or cerebrospinal fluid (CSF) (n = 32) and genetic sequencing of the VP1 region of HPeV3. HPeV3-infected patients (median age, 32 days; range, 4-113 days) were diagnosed as having sepsis (79%), sepsis-like syndrome (19%), or encephalitis with septic shock (2%). Other than fever, mottled skin (67%) was significantly more frequent in HPeV3-infected patients than other virus-infected patients (P = 0.005). The rate of HPeV3 RNA detection in CSF without pleocytosis was high (88%; 28/32). Among the 32 patients whose serum and CSF samples were available, all patients were positive for serum PCR; however, 4 (12%) patients were negative for CSF PCR. Serum HPeV3 RNA level on admission was associated with younger age (P = 0.002), bad temper (P = 0.041), and grunting (P = 0.008). Among 6 patients with sequential data on serum HPeV3 RNA level, levels decreased rapidly without specific therapy. In conclusion, serum samples at disease onset are the most useful compared to CSF in detection of HPeV RNA and serum HPeV3 RNA level on admission was associated with important clinical manifestations in HPeV3-infected patients.

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.

Epidemiology of enterovirus 71 infections in Taiwan

Enterovirus 71 (EV71) was first described in USA in 1969 but retrospective studies in The Netherlands further detected EV71 in the clinical specimens collected in 1963. EV71 has one single serotype measured by using hyperimmune animal antisera but can be phylogenetically classified into three genogroups (A, B, and C) including 11 genotypes (A, B1-B5, C1-C5). In Taiwan, EV71 caused a large-scale nationwide epidemic in 1998. Retrospective studies further detected EV71 in clinical specimens collected from hand-foot-mouth disease patients in 1980 and 1986. Therefore, EV71 may have circulated in Taiwan prior to 1980. Since 1998, EV71 has cyclically caused nationwide epidemics with different predominant genotypes in 1998 (genotype C2), 2000-2001 (B4), 2005 (C4), 2008 (B5), and 2012 (B5). Phylogenetic analysis revealed that C4 viruses isolated in 2005 were probably from China, B5 viruses isolated in 2008 were probably from South Eastern Asia, and B5 viruses isolated in 2012 were probably from Xiamen, China. Several studies have collected postinfection sera from children to measure cross-reactive neutralizing antibody titers against different EV71 genotypes and found that antigenic differences between genogroup B and C viruses did not have a clear pattern but that genotype A virus was antigenically different from genogroup B and C viruses. In conclusion, EV71 cyclically caused nationwide epidemics through international importations. EV71 surveillance in Taiwan should combine genetic and serological methods.

Seroepidemiology and molecular epidemiology of enterovirus 71 in Russia

Enterovirus 71 (EV71) is an emerging human pathogen causing massive epidemics of hand, foot and mouth disease with severe neurological complications in Asia. EV71 also circulates in Europe, however it does not cause large outbreaks. The reason for distinct epidemiological patterns of EV71 infection in Europe and Asia and the risk of EV71 epidemic in Europe and Russia remain unknown. Seroepidemiology of EV71 and molecular epidemiology of occasional EV71 isolates were studied to explore circulation of EV71 in Russia. In six regions of Russian Federation, seroprevalence of EV71 in sera collected in 2008 ranged from 5% to 20% in children aged 1-2 years and from 19% to 83% in children aged 3-5 years. The seroprevalence among elder children was significantly higher (41-83% vs. 19-27%) in Asian regions of Russia. EV71 strains identified in Russia in 2001-2011 belonged to subtypes C1 and C2, while genotype C4 that was causing epidemics in Asia since 1998 emerged in 2009 and became dominant in 2013.

Elucidating the host-pathogen interaction between human colorectal cells and invading Enterovirus 71 using transcriptomics profiling

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Enterovirus 71 (EV71) is one of the main etiological agents for Hand, Foot and Mouth Disease (HFMD).

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Types I, II and III interferon may be a key antiviral response against EV71.

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We examine the transcriptomic changes in human colorectal cells during EV71 infection.

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The intestinal epithelial immune system plays a key role in the progression of HFMD.

Enterovirus 71 (EV71) is one of the main etiological agents for Hand, Foot and Mouth Disease (HFMD) and has been shown to be associated with severe clinical manifestation. Currently, there is no antiviral therapeutic for the treatment of HFMD patients owing to a lack of understanding of EV71 pathogenesis. This study seeks to elucidate the transcriptomic changes that result from EV71 infection. Human whole genome microarray was employed to monitor changes in genomic profiles between infected and uninfected cells. The results reveal altered expression of human genes involved in critical pathways including the immune response and the stress response. Together, data from this study provide valuable insights into the host–pathogen interaction between human colorectal cells and EV71.

Epidemiology and seroepidemiology of human enterovirus 71 among Thai populations

Background

Human enterovirus 71 (EV71) is an important pathogen caused large outbreaks in Asian-Pacific region with severe neurological complications and may lead to death in young children. Understanding of the etiological spectrum and epidemic changes of enterovirus and population’s immunity against EV71 are crucial for the implementation of future therapeutic and prophylactic intervention.

Results

A total of 1,182 patients who presented with the symptoms of hand foot and mouth disease (67.3%) or herpangina (HA) (16.7%) and admitted to the hospitals during 2008-2013 were tested for enterovirus using pan-enterovirus PCR targeting 5′-untranslated region and specific PCR for viral capsid protein 1 gene. Overall, 59.7% were pan-enterovirus positive comprising 9.1% EV71 and 31.2% coxsackievirus species A (CV-A) including 70.5% CV-A6, 27.6% CV-A16, 1.1% CV-A10, and 0.8% CV-A5. HFMD and HA occurred endemically during 2008-2011. The number of cases increased dramatically in June 2012 with the percentage of the recently emerged CV-A6 significantly rose to 28.4%. Co-circulation between different EV71 genotypes was observed during the outbreak. Total of 161 sera obtained from healthy individuals were tested for neutralizing antibodies (NAb) against EV71 subgenotype B5 (EV71-B5) using microneutralization assay. The seropositive rate of EV71-B5 was 65.8%. The age-adjusted seroprevalence for individuals was found to be lowest in children aged >6 months to 2 years (42.5%). The seropositive rate remained relatively low in preschool children aged > 2 years to 6 years (48.3%) and thereafter increased sharply to more than 80% in individuals aged > 6 years.

Conclusions

This study describes longitudinal data reflecting changing patterns of enterovirus prevalence over 6 years and demonstrates high seroprevalences of EV71-B5 NAb among Thai individuals. The rate of EV71 seropositive increased with age but without gender-specific significant difference. We identified that relative lower EV71 seropositive rate in early 2012 may demonstrate widely presented of EV71-B5 in the population before account for a large outbreak scale epidemic occurred in 2012 with due to a relatively high susceptibility of the younger population.

Bedside immunochromatographic test for enterovirus 71 infection in children

BACKGROUND

Enterovirus 71 (EV71) causes frequent outbreaks worldwide, particularly in the Asia-Pacific area. Its quick spread is a critical challenge for public health and timely preventive measures and clinical management therefore rely on early detection. There is a need for a rapid, easy-to-use, and reliable method for detecting EV71 infections.

OBJECTIVE

The study aimed to evaluate a bedside immunochromatography (ICT) kit for diagnosing acute EV71 infection in children.

STUDY DESIGN

Pediatric patients with herpangina or hand-foot-mouth disease were randomly and prospectively enrolled from hospitals across Taiwan. Throat or rectal swabs were collected for viral culture and reverse-transcriptase polymerase chain reaction (RTPCR). For the ICT kit, whole blood was obtained by ear piercing, finger-sticking, or venipuncture. The results of ICT, virus isolation and RTPCR in clinical samples were compared.

RESULTS

Of the 156 patients enrolled, 91 (58%), 64 (41%) and 72 (46%) had positive results of the ICT kit, viral culture and RTPCR, respectively. Laboratory-confirmed infection with either positive EV71 culture or RTPCR was used as the diagnostic standard. The sensitivity and specificity of the ICT kit was 84% and 77%, respectively. The viral culture and RTPCR had relatively lower sensitivity but higher specificity. The patient's age did not affect the performance of the ICT, viral culture and RTPCR. However, a low sensitivity of ICT kit was noted before the second day of disease onset.

CONCLUSIONS

The ICT kit may serve as a simple, quick and reliable method for the bedside diagnosis of acute EV71 infection in children.

Proactive approach to containment of enterovirus infection in the nursery

Administration of prophylactic intravenous immunoglobulins to contacts of infants actively shedding enterovirus during a hospital nursery outbreak may attenuate severity of disease in those contacts and aid in containment of the outbreak. Four cases of neonatal enteroviral disease were treated in our hospital nursery in July and August 2011; 3 were presumed or proven vertical transmission cases and 1 was a presumed horizontal transmission. We aimed to prevent development of severe illness in contacts of affected neonates following a ministry of health advisory during the summer of 2011 warning of increased neonatal enteroviral morbidity and mortality in Israel. Strict infection control measures were implemented, including meticulous decontamination of the nursery environment and administration of intravenous immunoglobulin prophylaxis to contacts. No further horizontal transmission occurred after infection control interventions. Immunoglobulin prophylaxis to control enteroviral infection in the nursery should be considered as an auxiliary infection control intervention during a nursery outbreak.

Characterisation of enterovirus 71 replication kinetics in human colorectal cell line, HT29

Hand, Foot and Mouth Disease (HFMD), a contagious viral disease that commonly affects infants and children with blisters and flu like symptoms, is caused by a group of enteroviruses such as Enterovirus 71 (EV71) and coxsackievirus A16 (CA16). However some HFMD caused by EV71 may further develop into severe neurological complications such as encephalitis and meningitis. The route of transmission was postulated that the virus transmit from one person to another through direct contact of vesicular fluid or droplet from the infected or via faecal-oral route. To this end, this study utilised a human colorectal adenocarcinoma cell line (HT29) with epithelioid morphology as an in vitro model for the investigation of EV71 replication kinetics. Using qPCR, viral RNA was first detected in HT29 cells as early as 12 h post infection (hpi) while viral protein was first detected at 48 hpi. A significant change in HT29 cells’ morphology was also observed after 48 hpi. Furthermore HT29 cell viability also significantly decreased at 72 hpi. Together, data from this study demonstrated that co-culture of HT29 with EV71 is a useful in vitro model to study the pathogenesis of EV71.

Implications of Age-Dependent Immune Responses to Enterovirus 71 Infection for Disease Pathogenesis and Vaccine Design

Epidemics of enterovirus serotype 71 (EV71) infection in Asia appear to be increasing in size and severity, and there is increasing concern for pandemic spread. Efforts are underway to develop an effective EV71 vaccine. However, the immunologic correlates of protection against EV71 infection are not fully understood, and studies suggest that severe complications may result from a combination of pathological immune responses and direct viral effects. Severe disease and death typically occur only in young children, which is likely due in part to a lack of EV71-specific adaptive immunity but possibly also due to age-dependent hyperactive innate immune responses. Infants are the primary targets of EV71 vaccination strategies. Therefore, studies are needed to understand the interplay between age, immunopathology, and severity of EV71 infection to distinguish protective from harmful immune responses and to guide the development of effective EV71 vaccines. This review summarizes our current understanding and outlines the next steps forward.

Strategies to develop antivirals against enterovirus 71

Enterovirus 71 (EV71) is an important human pathogen which may cause severe neurological complications and death in children. The virus caused several outbreaks in the Asia-Pacific region during the past two decades and has been considered a significant public health problem in the post-poliovirus eradication era. Unlike poliovirus, there is no effective vaccine or approved antivirals against EV71. To explore anti-EV71 agents therefore is of vital importance. Several strategies have been employed to develop antivirals based on the molecular characteristics of the virus. Among these, some small molecules that were developed against human rhinoviruses and poliovirus are under evaluation. In this review, we discuss the recent development of such small molecules against EV71, known drug resistance and possible solutions to it, and animal models for evaluating the efficacy of these antivirals. Although further investigation is required for clinical applications of the existing candidates, the molecular mechanisms revealed for the inhibition of EV71 replication can be used for designing new molecules against this virus in the future.

Seroepidemiology of human enterovirus71 and coxsackievirusA16 in Jiangsu province, China

Background

The major etiology of hand, foot and mouth disease (HFMD) is infection with human enterovirus A (HEV-A). Among subtypes of HEV-A, coxsackievirusA16 (CoxA16) and enterovirus 71 (EV71) are major causes for recurrent HFMD among infants and children in Jiangsu Province, mainland China. Here, we analyzed maternal antibodies between prenatal women and their neonates, to determine age-specific seroprevalence of human EV71 and CoxA16 infections in infants and children aged 0 to 15 years. The results may facilitate the development of immunization against HFMD.

Methods

This study used cross-section of 40 pairs of pregnant women and neonates and 800 subjects aged 1 month to 15 years old. Micro-dose cytopathogenic effects measured neutralizing antibodies against EV71 and CoxA16. Chi-square test compared seroprevalence rates between age groups and McNemar test, paired-Samples t-test and independent-samples t-test analyzed differences of geometric mean titers.

Results

A strong correlation between titers of neutralizing antibody against EV71 and CoxA16 in prenatal women and neonates was observed (r_EV71 = 0.67, r_CoxA16 = 0.56, respectively, p < 0.05). Seroprevalence rates of anti-EV71 antibody gradually decreased with age between 0 to 6 months old, remained low between 7 to 11 months (5.0–10.0%), and increased between 1 and 4 years (22.5–87.5%). Age-specific seroprevalence rates of anti-EV71 antibody stabilized in >80% of children between 5 to 15 years of age. However, seroprevalence rates of anti-CoxA16 antibody were very low (0.0–13.0%) between 0 to 6 months of age, gradually increased between 7 months to 4 years (15.0–70.0%), and stabilized at 54.0% (108/200) between 5 to 15 years. Seroprevalence rates against EV71 and CoxA16 were low under 1 year (0.0–10.0%), and showed an age dependent increase with high seroprevalence (52.5–62.5%) between 4 and10 years of age.

Conclusions

Concomitant infection of EV71 and CoxA16 was common in Jiangsu Province. Therefore, development of bivalent vaccine against both EV71 and CoxA16 is critical. The optimal schedule for vaccination may be 4 to11 months of age.

Adoptive transfer of macrophages from adult mice reduces mortality in mice infected with human enterovirus 71

Human enterovirus 71 (EV71) causes hand, foot and mouth disease in children under 6 years of age, and the neurological complications of this virus can lead to death. Until now, no vaccines or drugs have been available for the clinical control of this epidemic. Macrophages can engulf pathogens and mediate a series of host immune responses that play a role in the defence against infectious diseases. Using immunohistochemistry, we observed the localizations of virus in muscle tissues of EV71-infected mice. The macrophages isolated from the adult mice could kill the virus gradually in vitro, as shown using quantitative real-time PCR (qRT-PCR) and virus titration. Co-localisation of lysosomes and virus within macrophages suggested that the lysosomes were possibly responsible for the phagocytosis of EV71. Activation of the macrophages in the peritoneal cavity of mice four days pre-infection reduced the mortality of mice upon lethal EV71 infection. The adoptive transfer of macrophages from adult mice inhibited virus replication in the muscle tissues of infected mice, and this was followed by a relief of symptoms and a significant reduction of mortality, which suggested that the adoptive transfer of macrophages from adult humans represents a potential strategy to treat EV71-infected patients.

Challenges to licensure of enterovirus 71 vaccines

Human enteroviruses usually cause self-limited infections except polioviruses and enterovirus 71 (EV71), which frequently involve neurological complications. EV71 vaccines are being evaluated in humans. However, several challenges to licensure of EV71 vaccines need to be addressed. Firstly, EV71 and coxsackievirus A (CA) are frequently found to co-circulate and cause hand-foot-mouth disease (HFMD). A polyvalent vaccine that can provide protection against EV71 and prevalent CA are desirable. Secondly, infants are the target population of HFMD vaccines and it would need multi-national efficacy trials to prove clinical protection and speed up the licensure and usage of HFMD vaccines in children. An international network for enterovirus surveillance and clinical trials is urgently needed. Thirdly, EV71 is found to evolve quickly in the past 15 years. Prospective cohort studies are warranted to clarify clinical and epidemiological significances of the antigenic and genetic variations between different EV71 genogroups, which is critical for vaccine design.

Retrospective study of the incidence of HFMD and seroepidemiology of antibodies against EV71 and CoxA16 in prenatal women and their infants

Background

Hand, foot, and mouth disease (HFMD) has been emerging as an important public problem over the past few decades, especially in Asian and Pacific regions. A national program on EV71 vaccine development against HFMD was initiated in China, in 2008, which called for a need for seroepidemiological study for the target population.

Methodology/Principal Findings

This was a retrospective study conducted in Jiangsu Province, in October, 2010. We measured the neutralizing antibodies against EV71 and CoxA16 in a cohort of infants aged of 2, 7, 12, and 27–38 months and their mothers just before delivery. Series sera samples from 975 infants and 555 mothers were collected and analyzed. Questionnaires on the history of HFMD were completed in the survey. A total of 143 HFMD cases were collected, but only 11.2% were reported to the National Infectious Disease Information Management System. The level of maternal antibody titers decreased dramatically during the first 7 month and remained at a relatively low level thereafter. But it increased significantly from month 12 to months 27–38. The accumulate incidence density of HFMD demonstrated a significant increase after 14 months of age, resulting in a accumulate incidence density of 50.8/1000 person-years in survey period. Seropositivity of EV71 antibody in infants at the age of 2 months seems to demonstrate a protective effect against HFMD.

Conclusions and Significance

High seropositive rate of EV71 and CoxA16 antibody was found in prenatal women in mainland China, and there is a need to enhance the HFMD case management and the current surveillance system. We suggest that infants aged between 6 to 14 months should have the first priority to receive EV71 vaccine.

Phylodynamic inference of infectious diseases caused by HIV, enterovirus 71 and the 2009 swine-origin human influenza virus

The rapidly evolving nature of viruses, particularly RNA viruses, exhibit complex phylodynamic behaviors, accumulating mutations across the genome on a timescale observable by humans. Phylodynamic investigations provide unique and quantitative evolutionary data on the origin, progression in terms of time and space, and epidemic and transmission history of pathogens. This review describes recent phylodynamic conjectures on three distinct categories of human viruses, including HIV, enterovirus 71 and the swine-origin pandemic influenza virus H1N1, which are of enormous importance to public health.

Incidence rates of enterovirus 71 infections in young children during a nationwide epidemic in Taiwan, 2008-09

Objective

Enterovirus 71 (EV71) is causing life-threatening outbreaks in tropical Asia. In Taiwan and other tropical Asian countries, although nationwide EV71 epidemics occur cyclically, age-specific incidence rates of EV71 infections that are critical to estimate disease burden and design vaccine trials are not clear. A nationwide EV71 epidemic occurred in 2008–09 in Taiwan, which provided a unique opportunity to estimate age-specific incidence rates of EV71 infections.

Study Design

We prospectively recruited 749 healthy neonates and conducted follow-ups from June 2006 to December 2009. Sera were obtained from participants at 0, 6, 12, 24, and 36 months of age for measuring EV71 neutralizing antibody titers. If the participants developed suspected enterovirus illnesses, throat swabs were collected for virus isolation.

Results

We detected 28 EV71 infections including 20 symptomatic and 8 asymptomatic infections. Age-specific incidence rates of EV71 infection increased from 1.71 per 100 person-years at 0–6 months of age to 4.09, 5.74, and 4.97 per 100 person-years at 7–12, 13–24, and 25–36 months of age, respectively. Cumulative incidence rate was 15.15 per 100 persons by 36 months of age, respectively.

Conclusions

Risk of EV71 infections in Taiwan increased after 6 months of age during EV71 epidemics. The cumulative incidence rate was 15% by 36 months of age, and 29% of EV71 infections were asymptomatic in young children.

Enterovirus 71 (EV71) was first isolated in California, USA, in 1969. Since then, EV71 has been identified globally. Recently, EV71 caused several life-threatening outbreaks in young children in tropical Asia. Development of EV71 vaccines becomes national priority in several Asia countries including Taiwan. To design clinical trials of EV71 vaccines, age-specific incidence rates of EV71 infections are required to identify target populations, estimate disease burdens, select endpoints of clinical efficacy, and estimate sample size. In Taiwan, nationwide EV71 epidemics occurred every 3–4 years but age-specific incidences of EV71 infection are not available. In 2006, we initiated a prospective cohort study in northern Taiwan to recruit neonates and follow up them. In 2008–09, a nationwide EV71 epidemic occurred and we found that age-specific incidence rates of EV71 infection increased from 1.71 per 100 person-years at 0–6 months of age to 4.09, 5.74, and 4.97 per 100 person-years at 7–12, 13–24, and 25–36 months of age, respectively. The cumulative incidence rate was 15% by 36 months of age, and 29% of EV71 infections were asymptomatic in young children. These findings would be helpful to development of EV71 vaccines in Taiwan and other Asian tropical countries.

Seroepidemiology of Enterovirus 71 infection prior to the 2011 season in children in Shanghai

BACKGROUND

In 2010, China experienced the largest outbreak on record of Enterovirus 71 (EV71)-associated Hand Foot and Mouth Disease (HFMD) with more than 1.7 million cases, 27,000 patients with severe neurological complications and 905 deaths. Understanding of the seroprevalence of neutralizing antibodies (NAb) against EV71 and their protective role against HFMD in children is crucial for the implementation of future therapeutic and prophylactic intervention.

OBJECTIVES

To correlate the prevalence of NAb against EV71 genotype C4a in children prior to the 2011 epidemic season with severe EV71-associated HFMD disease during the subsequent 2011 epidemic season.

STUDY DESIGN

614 sera samples were collected from children without HFMD. EV71 NAb were tested by a quantitative PCR assay. Samples with NAb ≥1:8 were scored as positive.

RESULTS

122 (19.9%) of 614 sera were EV71-seropositive. The NAb seroprevalence was highest in infants 0-5 months of age (28.6%) and lowest in children 1-1.9 years of age (13.4%). 64.1% of severe EV71-associated HFMD occurred in children 1-2.9 years.

CONCLUSIONS

Despite the large 2010 outbreak, the overall seroprevalence of EV71 in children is relatively low. The seropositive rate of EV71 NAb prior to the 2011 season was inversely correlated with the number of EV71-infected severe cases in 2011. Loss of maternal antibodies in infants and lack of acquired anti-EV71 immunity are responsible for increased proportion of severe HFMD in the 1-2 years age group. Our data suggest that future vaccination campaigns should be initiated as early as 6 months.

The characteristics of blood glucose and WBC counts in peripheral blood of cases of hand foot and mouth disease in China: a systematic review

BACKGROUND

Outbreaks of Hand Foot and Mouth Disease (HFMD) have occurred in many parts of the world especially in China. We aimed to summarize the characteristics of the levels of blood glucose and white blood cell (WBC) counts in cases of HFMD in Mainland China and Taiwan, using meta-analysis based on systematic review of published articles.

METHODS

We systematically reviewed published studies, from the MEDLINE and WANFANG Data, about the levels of blood glucose and WBC counts in cases of HFMD until 15(th) June 2011, and quantitatively summarized the characteristics of them using meta-analysis.

RESULTS

In total, 37 studies were included in this review. In Mainland China and Taiwan, generally, the average level of blood glucose, the prevalence of hyperglycemia, WBC counts and the prevalence of leukocytosis increased with the severity of the illness. There was no significant difference in the prevalence of leukocytosis between ANS (autonomic nervous system dysregulation)/PE (pulmonary edema) group and CNS (central nervous system) group, and in the average level of blood glucose between healthy controls and mild cases of HFMD. WBC counts in cases infected by EV71 were less than those in cases infected by CA16.

CONCLUSIONS

our analyses indicated that blood glucose and WBC counts increased with the severity of HFMD disease, which would help doctors to manage patients efficiently.

MRI and associated clinical characteristics of EV71-induced brainstem encephalitis in children with hand-foot-mouth disease

INTRODUCTION

This study was conducted to investigate MRI and associated clinical characteristics of brainstem encephalitis induced by enterovirus 71 (EV71) in children with hand-foot-mouth disease (HFMD).

METHODS

We analyzed clinical and imaging data from 42 HFMD cases with EV71-induced brainstem encephalitis. All patients underwent plain and enhanced MRI cranial scans and were placed into one of two groups according to MRI enhancement results, an enhanced group or a nonenhanced group.

RESULTS

Thirty-two cases were positive on MRI exam. The primary location of the lesion for brainstem encephalitis was the dorsal pons and medulla oblongata (32 cases), followed by the cerebellar dentate nucleus (8 cases), midbrain (5 cases), and thalamus (2 cases). Plain T1-weighted images showed isointense or hypointense signals, and T2-weighted images showed isointense and hyperintense signals. Enhanced MRI scans showed that 12 cases had slight to moderate enhancement; 4 of these were normal on plain scan. The time from MRI examination to disease onset was statistically different between the enhanced (n = 12) and nonenhanced (n = 21) groups with a mean of 7.67 days (SD = 1.07) vs 11.95 days (SD = 5.33), respectively. The most common neurological symptoms for brainstem encephalitis were myoclonus and tremor. The greater the area of affected brain, the more severe the clinical symptoms were.

CONCLUSION

The locations of EV71-induced HFMD-associated brainstem encephalitis lesions are relatively specific. Enhanced MRI scans could also identify the lesions missed by early plain scans. MRI scans can provide important information for clinical evaluation and treatment.

Comparing Enterovirus 71 with Coxsackievirus A16 by analyzing nucleotide sequences and antigenicity of recombinant proteins of VP1s and VP4s

BACKGROUND

Enterovirus 71 (EV71) and Coxsackievirus A16 (CA16) are two major etiological agents of Hand, Foot and Mouth Disease (HFMD). EV71 is associated with severe cases but not CA16. The mechanisms contributed to the different pathogenesis of these two viruses are unknown. VP1 and VP4 are two major structural proteins of these viruses, and should be paid close attention to.

RESULTS

The sequences of vp1s from 14 EV71 and 14 CA16, and vp4s from 10 EV71 and 1 CA16 isolated in this study during 2007 to 2009 HFMD seasons were analyzed together with the corresponding sequences available in GenBank using DNAStar and MEGA 4.0. Phylogenetic analysis of complete vp1s or vp4s showed that EV71 isolated in Beijing belonged to C4 and CA16 belonged to lineage B2 (lineage C). VP1s and VP4s from 4 strains of viruses expressed in E. coli BL21 cells were used to detect IgM and IgG in human sera by Western Blot. The detection of IgM against VP1s of EV71 and CA16 showed consistent results with current infection, while none of the sera were positive against VP4s of EV71 and CA16. There was significant difference in the positive rates between EV71 VP1 and CA16 VP1 (χ(2) = 5.02, P < 0.05) as well as EV71 VP4 and CA16 VP4 (χ(2) = 15.30, P < 0.01) in the detection of IgG against recombinant proteins with same batch of serum samples. The sera-positive rate of IgG against VP1 was higher than that against VP4 for both EV71 (χ(2) = 26.47, P < 0.01) and CA16 (χ(2) = 16.78, P < 0.01), which might be because of different positions of VP1 and VP4 in the capsid of the viruses.

CONCLUSIONS

EV71 and CA16 were highly diverse in the nucleotide sequences of vp1s and vp4s. The sera positive rates of VP1 and VP4 of EV71 were lower than those of CA16 respectively, which suggested a less exposure rate to EV71 than CA16 in Beijing population. Human serum antibodies detected by Western blot using VP1s and VP4s as antigen indicated that the immunological reaction to VP1 and VP4 of both EV71 and CA16 was different.

Reemerging of enterovirus 71 in Taiwan: the age impact on disease severity

Enterovirus 71 (EV71) infection commonly strike children under the age of 3 years, with an occasionally unfavorable outcome in children. This study was designed to explore the relationship between age and the severity of complications, which may associate with antibody-dependent enhancement (ADE) in EV71. All EV71-infected patients during the outbreak of 2008 were recruited. In total, 134 patients were enrolled and categorized into two age groups, 0-12 months (n = 18) and >12 months (n = 116). Pulmonary edema/hemorrhage more commonly occur in patients younger than 12 months. No difference in the occurrence of herpangina/hand-foot-and-mouth disease (HFMD), uncomplicated brainstem encephalitis (BE), or autonomic nervous system (ANS) dysregulation was noted between the two age groups. Patients with pulmonary edema/hemorrhage (11.9 ± 14.7 months) were younger than patients with herpangina/HFMD (35.8 ± 26.4 months) or ANS dysregulation (33.9 ± 20.9 months). Our findings are in agreement with the data regarding the outbreak in Taiwan, in which a decrease in age corresponded to an increase in disease severity with regard to central nervous system complications. A reduction of maternal antibodies to the subneutralizing level within 1 year of age may be associated with the ADE of the infection. This study could provide possible clinical significance with regard to ADE phenomena in young infants infected by EV71.

Antibody dependent enhancement infection of enterovirus 71 in vitro and in vivo

BACKGROUND

Human enterovirus 71 (EV71) has emerged as a significant cause of acute encephalitis and deaths in young children. The clinical manifestations caused by EV71 varied from mild hand, foot and mouth disease to severe neurological complications and deaths, but its pathogenesis remains elusive. Antibody dependent enhancement (ADE) infection has been reported in various viruses and has been shown to contribute to disease severity.

RESULTS

In this study, the presence of sub-neutralizing antibody was demonstrated to enhance EV71 infection in THP-1 cells and increase the mortality of EV71 infection in a suckling mouse model. Further, a secondary infection model was established to characterize the correlation between ADE and disease severity, and primary asymptomatic EV71 infection was shown to increase the mortality of the secondary EV71 infection in suckling mice.

CONCLUSIONS

Together, these in vitro and in vivo experiments strongly supported the hypothesis of ADE infection of EV71. The present findings indicate ADE might contribute to the pathogenesis of severe EV71 infection, and raise practical issues of vaccine development and antibody-based therapy.

Biochemical characterization of enterovirus 71 3D RNA polymerase

An unusual enterovirus 71 (EV71) epidemic has begun in China since 2008. EV71 RNA polymerases (3D(pol)) showed polymerase activity with an Mn(2+). Little activity was detected with Co(2+), and no activity was detected with Mg(2+), Ca(2+), Cu(2+), Ni(2+), Cd(2+), or Zn(2+). It is a primer-dependent polymerase, and the enzyme functioned with both di- and 10-nucleotide RNA primers. DNA primer, dT15, increased primer activity, similar to other enterovirus 3D(pol). However, EV71 3D(pol) initiated de novo transcription with a poly(C) template and genome RNA. Its RNA binding activity was weak. Terminal nucleotidyl transferase and reverse transcriptase activity were not detected. The Km and Vmax for EV71 3D(pol) were calculated from classic Lineweaver-Burk plots. The Km values were 2.35±0.05 (ATP), 5.40±0.93 (CTP), 1.12±0.10 (GTP) and 2.81±0.31 (UTP), and the Vmax values were 0.00078±0.00005/min (ATP), 0.011±0.0017/min (CTP), 0.050±0.0043/min (GTP) and 0.0027±0.0005/min (UTP). The Km of EV71 3D(pol) was similar to that of foot and mouth disease virus and rhinovirus. Polymerase activity of BrCr-TR strain and a strain from a clinical isolate in Beijing, 2008 were similar, indicating the potential for 3D(pol) as an antiviral drug target.

Virology, epidemiology, pathogenesis, and control of enterovirus 71

First isolated in California, USA, in 1969, enterovirus 71 (EV71) is a major public health issue across the Asia-Pacific region and beyond. The virus, which is closely related to polioviruses, mostly affects children and causes hand, foot, and mouth disease with neurological and systemic complications. Specific receptors for this virus are found on white blood cells, cells in the respiratory and gastrointestinal tract, and dendritic cells. Being an RNA virus, EV71 lacks a proofreading mechanism and is evolving rapidly, with new outbreaks occurring across Asia in regular cycles, and virus gene subgroups seem to differ in clinical epidemiological properties. The pathogenesis of the severe cardiopulmonary manifestations and the relative contributions of neurogenic pulmonary oedema, cardiac dysfunction, increased vascular permeability, and cytokine storm are controversial. Public health interventions to control outbreaks involve social distancing measures, but their effectiveness has not been fully assessed. Vaccines being developed include inactivated whole-virus, live attenuated, subviral particle, and DNA vaccines.

Clinical and etiological characteristics of enterovirus 71-related diseases during a recent 2-year period in Korea

Human enterovirus 71 (EV 71) has caused large-scale outbreaks of hand-foot-and-mouth disease (HFMD), particularly in the Asian-Pacific region. In this study, we report a major outbreak of EV 71 infection in Korea and describe the clinical differences between EV 71 and non-EV 71 enterovirus infections. We prospectively enrolled patients with suspected viral infections during a recent 2-year period through a nationwide surveillance system. We identified 719 patients with suspected HFMD or herpangina using real-time PCR and genotyping based on VP1 sequence analysis. The major pathogen causing HFMD changed substantially from 2008 to 2009, with EV 71 becoming the most common cause of HFMD in Korea in 2009. We successfully identified the enteroviral genotypes for 218 of the 719 patients. Patients with EV 71 infections tended to be younger than those with non-EV 71 enteroviral infections and presented with HFMD and meningoencephalitis. In addition, the occurrence of fever, headache, and neck stiffness was significantly higher in patients with EV 71 infections. Multivariable analysis showed that for patients presenting with HFMD, fever, or a sore throat, each covariate was independently associated with EV 71 infection; the adjusted odds ratios (with 95% confidence intervals in parentheses) for these variables were 31.86 (10.04 to 101.09), 4.76 (1.71 to 13.25), and 0.18 (0.04 to 0.77), respectively. Our results indicate that EV 71 was a major cause of HFMD in Korea during the study period. In addition, we found that clinical symptoms may be helpful in the early identification of patients with EV 71 infections.

Development of enterovirus 71 vaccines

Enterovirus 71 (EV71) was first isolated in 1969 in California, USA. Several epidemic outbreaks with high mortality rates have occurred in European and Asian Countries (Bulgaria in 1975, Hungary in 1978, Malaysia in 1997, Taiwan in 1998 and China in 2008). EV71 CNS involvement may be associated with neurological sequelae, delayed neurodevelopment and reduced cognitive functioning. Since poliovirus was nearly eradicated by vaccination, EV71 is now considered as one of the top candidates for new vaccine development against human enteroviruses. Recently, several EV71 vaccine candidates, including live-attenuated virus, inactivated whole virus, recombinant viral protein, virus-like particle and DNA vaccines, have been evaluated in animals but no clinical trial has yet been conducted. Based on historical experiences with poliovirus vaccines and animal studies, the inactivated whole-virus vaccines are feasible and could be licensed readily, so these are targeted for preparing clinical trials in several organizations in Asia.

Evolutionary genetics of human enterovirus 71: origin, population dynamics, natural selection, and seasonal periodicity of the VP1 gene

Human enterovirus 71 (EV-71) is one of the major etiologic causes of hand, foot, and mouth disease (HFMD) among young children worldwide, with fatal instances of neurological complications becoming increasingly common. Global VP1 capsid sequences (n = 628) sampled over 4 decades were collected and subjected to comprehensive evolutionary analysis using a suite of phylogenetic and population genetic methods. We estimated that the common ancestor of human EV-71 likely emerged around 1941 (95% confidence interval [CI], 1929 to 1952), subsequently diverging into three genogroups: B, C, and the now extinct genogroup A. Genealogical analysis revealed that diverse lineages of genogroup B and C (subgenogroups B1 to B5 and C1 to C5) have each circulated cryptically in the human population for up to 5 years before causing large HFMD outbreaks, indicating the quiescent persistence of EV-71 in human populations. Estimated phylogenies showed a complex pattern of spatial structure within well-sampled subgenogroups, suggesting endemicity with occasional lineage migration among locations, such that past HFMD epidemics are unlikely to be linked to continuous transmission of a single strain of virus. In addition, rises in genetic diversity are correlated with the onset of epidemics, driven in part by the emergence of novel EV-71 subgenogroups. Using subgenogroup C1 as a model, we observe temporal strain replacement through time, and we investigate the evidence for positive selection at VP1 immunogenic sites. We discuss the consequences of the evolutionary dynamics of EV-71 for vaccine design and compare its phylodynamic behavior with that of influenza virus.

Enterovirus 71: epidemiology, pathogenesis and management

Enterovirus 71 (EV71) has emerged as a major cause of neurological threat in the world following the eradication of poliovirus. Most EV71 infections commonly result in hand-foot-mouth disease or herpangina, and some cases are associated with brainstem encephalitis and acute flaccid paralysis. Mortality was high in EV71 brainstem encephalitis complicated with pulmonary edema, particularly in children below 5 years of age. Destruction of vasomotor in the brainstem by EV71 produces autonomic nervous system dysregulation prior to the pulmonary edema. The pulmonary edema is the result of increased pulmonary vascular permeability caused by the direct brainstem lesions and/or a systemic inflammatory response syndrome produced by the release of cytokines and chemokines. There is currently no specific antiviral agent to treat or vaccine to prevent EV71 diseases. Treating severe EV71 brainstem encephalitis patients with intravenous IgG and milrinone is associated with significantly decreased mortality by attenuated sympathetic activity and cytokine production.