A screening study on the detection strain of Coxsackievirus A6: the key to evaluating neutralizing antibodies in vaccines

The increasing incidence of diseases caused by Coxsackievirus A6 (CV-A6) and the presence of various mutants in the population present significant public health challenges. Given the concurrent development of multiple vaccines in China, it is challenging to objectively and accurately evaluate the level of neutralizing antibody response to different vaccines. The choice of the detection strain is a crucial factor that influences the detection of neutralizing antibodies. In this study, the National Institutes for Food and Drug Control collected a prototype strain (Gdula), one subgenotype D1, as well as 13 CV-A6 candidate vaccine strains and candidate detection strains (subgenotype D3) from various institutions and manufacturers involved in research and development. We evaluated cross-neutralization activity using plasma from naturally infected adults (n = 30) and serum from rats immunized with the aforementioned CV-A6 strains. Although there were differences between the geometric mean titer (GMT) ranges of human plasma and murine sera, the overall trends were similar. A significant effect of each strain on the neutralizing antibody test (MAX/MIN 48.0 ∼16410.3) was observed. Among all strains, neutralization of the S112 strain by 15 different sera resulted in higher neutralizing antibody titers (GMTS112 = 132.0) and more consistent responses across different genotypic immune sera (MAX/MIN = 48.0). Therefore, S112 may serve as a detection strain for NtAb testing in various vaccines, minimizing bias and making it suitable for evaluating the immunogenicity of the CV-A6 vaccine.

Effects of glycine 64 substitutions in RNA-dependent RNA polymerase on ribavirin sensitivity and pathogenicity of coxsackievirus A6

Hand, foot, and mouth disease (HFMD) caused by a group of enteroviruses is a global public health problem. In recent years, coxsackievirus A6 (CVA6) has emerged as an important HFMD agent. Previous studies have shown that mutations of glycine 64 in RNA-dependent RNA polymerase (3D polymerase), which is central to viral replication, cause phenotypic changes such as ribavirin resistance, increased replication fidelity, and virulence attenuation in poliovirus and enterovirus A71. In this study, we constructed CVA6 mutants with G64R, G64S, and G64T substitutions by site-directed mutagenesis in full-length cDNA of an infectious CVA6 strain cloned in pcDNA3.1. Viral RNA was obtained by in vitro transcription, and the rescued virus strains were propagated in RD cells. Sequencing after six passages revealed that G64S and G64T mutations were stably inherited, whereas G64R was genetically unstable and reversed to the wild type. Comparison of the biological characteristics of the wild-type and mutant CVA6 strains in an in vivo model (one-day-old ICR mice) revealed that the pathogenicity of CVA6-G64S and CVA6-G64T was significantly reduced compared to wild-type CVA6. In vitro experiments indicated the mutant CVA6-G64S and CVA6-G64T strains had increased resistance to 0.8 mM ribavirin and a decreased replication rate in the presence of 0.8 mM guanidine hydrochloride. Our results show that mutation of residue 64 reduces CVA6 susceptibility to ribavirin and increases CVA6 susceptibility to guanidine hydrochloride, together with increased replication fidelity and attenuated viral pathogenicity, thus laying a foundation for the development of safe and effective live attenuated CVA6 vaccine.

Establishment of the 1st Chinese national standard for CA6 neutralizing antibody

Coxsackievirus A6 (CA6) is one of the major causative agents of herpangina and hand-foot-mouth disease (HFMD). Since 2008, CA6 has circulated widely around the world. Especially in Asia-Pacific region CA6 had even replaced enterovirus A71 (EV71) and coxsackievirus A16 (CA16) as the main prevalent strain of HFMD. In the recent 10 years, monovalent and multivalent vaccines against CA6 have been researched and developed by manufacturers from China, Korea, and the USA. The neutralizing antibody titer is a key indicator for accurately evaluating immunogenicity of vaccine. However, so far, the World Health Organization international standard for CA6 neutralizing antibody has not been available. In order to meet the needs of evaluating the immunogenicity of vaccines against CA6, the first Chinese national standard for CA6 neutralizing antibody was established, which was conducted to ensure that methods used to measure the neutralizing antibody titers against CA6 are accurate, reliable, and comparable. Three lyophilized candidate standards (29#, 39# and 44#) were produced with 0.40 ml/vial from plasma samples donated by healthy individuals. The collaborative study showed that the 29# candidate standard could effectively minimize the variability in neutralization titers between labs and across challenging viruses of different genotypes (A, D1, and D3). Therefore, the 29# candidate sample was established as the first Chinese national standard for CA6 neutralizing antibody test. This standard has good long-term stability and was assigned a potency of 150 units per milliliter (U/ml) of CA6 neutralizing antibody. It will contribute to ensure uniformity of potency or activity of vaccines and potentially therapeutic antibody preparations.

Epidemiological and molecular characterization of Coxsackievirus A6 causing hand, foot, and mouth disease in the Philippines, 2012-2017

Coxsackievirus A6 (CVA6) is emerging as the dominant serotype among enteroviruses (EVs) responsible for hand, foot, and mouth disease (HFMD) outbreaks in multiple countries. However, details regarding this serotype in the Philippines are limited. In this study, we investigated the epidemiological and molecular characteristics of laboratory-confirmed CVA6 HFMD cases in the Philippines between 2012 and 2017. Data collected from case report forms submitted to the National Reference Laboratory for Poliovirus and other Enteroviruses were used to determine the distribution and clinical findings of laboratory-confirmed CVA6 HFMD. Phylogenetic analyses of the complete viral protein 1 (VP1) and partial 3D polymerase (3Dpol) gene sequences were performed to determine the genotype and recombinant (RF) form of the selected samples. An increase in the detection rate of CVA6 among enterovirus-positive HFMD cases was observed from 61.9% (140/226) in 2012 to 88.1% (482/587) in 2017, with most cases coming from the Luzon island group. Among the detected cases, the majority were children, with a median age of 2 years old (interquartile range: 1.17-3.40). Respiratory-related morbidities were the commonly reported complications (7.9%; 72/907). Based on the VP1 and 3Dpol gene sequence analysis, the CVA6 strains in this study were classified as genotype D3b and RF-A group, respectively. This study elucidated that CVA6 was the most prevalent enterovirus serotype causing HFMD in the Philippines in 2012-2017, with genotype D3b/RF-A circulating within this period. This study highlights the importance of viral surveillance and molecular epidemiological analysis to broaden our understanding of HFMD in the Philippines.

Vertical Transmission of Coxsackievirus A6 with Severe Congenital Pneumonia/Sepsis

We report a case of vertical transmission of Coxsackievirus (CV)-A6 with severe congenital pneumonia/sepsis. A male infant presented with severe respiratory symptoms at birth and was treated with full cardiopulmonary support, including inhaled nitric oxide. Three days before delivery, his older brother was diagnosed with hand, foot, and mouth disease (HFMD). His mother developed transient fever 1 day before delivery and presented a blister on her thumb 2 days after delivery. A multiplex polymerase chain reaction test on day 2 was positive for human rhinovirus/enterovirus. CV-A6 was later detected in the serum, tracheal aspirate, and stool of the patient sampled on day 6, and in the maternal serum sampled on the day of delivery. He was diagnosed with congenital CV-A6 pneumonia/sepsis caused by vertical transmission, based on VP1 consensus sequences used for typing of the virus that demonstrated a 100% match between the mother and infant. Further, the strain was closely related to the lethal CV-A6-Changchun strains in the phylogenetic analysis of the P2 region, which contributes to the pathogenicity. In conclusion, congenital CV-A6 infection should be considered if a woman exhibits HFMD symptoms during the perinatal period. Detailed virologic examination is useful for understanding its pathogenesis.

Genetic characteristics of Coxsackievirus A6 from children with hand, foot and mouth disease in Beijing, China, 2017-2019

OBJECT

To investigate the evolution and genetic characteristics of Coxsackievirus A6 (CVA6) which acted as the predominant pathogen of hand, foot and mouth disease (HFMD) in children in Beijing, China, 2017-2019.

METHODS

Throat swab specimens were collected for general Enterovirus (EV), enterovirus A71 (EV-A71) and CVA16 detection by Real-time PCR. These general EV-positive samples were identified by semi-nested RT-PCR method and sequencing. The CVA6 VP1 gene and genome sequences were amplified and sequenced. The phylogenetic, variation and recombination analyses were performed.

RESULTS

A total of 1721 HFMD patients were enrolled in this study, with the male to female ratio of 1.62:1. The majority of cases were less than five years, which accounted for 73.50%. The overall detection rate of EV was 88.32% (1520/1721). A total of 8 EV types were identified, including CVA6 (55.86%), CVA16 (26.32%), EV-A71 (2.24%), CVA10 (2.04%), CVA4 (1.05%), CVA5 (0.59%), CVA2 (0.33%), and CVA8 (0.07%), while 175 (11.51%) EV were untyped. The main pathogen of HFMD was CVA6 from 2017 to 2018, while CVA6 and CVA16 were the main causative pathogens in 2019. The nucleotide and amino acid sequence identities of the 120 CVA6 complete VP1 gene sequences in this study were 91.2%-100.0% and 97.7%-100.0%, respectively. Compared with the prototype strain (Gdula) of CVA6, the nucleotide and amino acid sequence identities were 81.7%-84% and 94.7%-96.3%, respectively. The phylogenetic tree indicated that all 120 CVA6 sequences belonged to sub-genotype D3, while 119 CVA6 sequences belonged to evolutionary branch D3a, except one from 2017 belonged to D3b. Recombination analysis based on the complete genome sequences showed that potential multiple recombination may have occurred in 2B and 3D protein coding regions with EV-A114.

CONCLUSIONS

The main pathogens of HFMD were CVA6 and CVA16 in Beijing, China, 2017-2019; while these CVA6, as recombination strains, belonged to the D3a evolutionary branch.

Coxsackievirus A6 was the most common enterovirus serotype causing hand, foot, and mouth disease in Shiyan City, central China

BACKGROUND

Hand, foot, and mouth disease (HFMD) has become one of the most common infectious diseases in China. Before 2016, the primary causal serotypes were enterovirus A71 (EV-A71) and coxsackievirus A16 (CV-A16). Following the introduction of EV-A71 vaccines in China since 2016, the situation could change. CV-A6 has recently replaced EV-A71 and CV-A16 in some areas of China. However, the epidemiological characteristics of central China remain unknown.

AIM

To investigate the clinical symptoms and pathogen spectrum of HFMD in Shiyan City, central China, in recent years.

METHODS

The epidemiological, clinical, and laboratory data from HFMD cases reported to the Shiyan Center for Disease Control and Prevention between January 2016 and December 2020 were analyzed. 196 throat swab specimens were collected from hospitalized HFMD patients between January 2018 and December 2020. To detect and genotype enteroviruses, real-time reverse transcription-polymerase chain reaction and sequencing of the 5'-untranslated region were used. In Shiyan, 168 laboratory-confirmed HFMD cases were studied using a logistic regression model to determine the effect of predominant enterovirus serotypes. Based on the logistic regression model, the least absolute shrinkage and selection operator model was used to analyze the correlation between CV-A6 infection and various clinical characteristics in HFMD patients in Shiyan.

RESULTS

From 2016 to 2020, 35840 HFMD cases were reported in Shiyan. The number of cases decreased by 48.4% from 2016 to 2017. Approximately 1.58-fold increases were found in 2018 and 2019 when compared to the previous year, respectively. In 2020, a decrease of about 85.5% was reported when compared to 2019. The most common serotypes shifted from EV-A71 and CV-A16 (about 60%-80% in 2016 and 2018) to others (more than 80.0% in 2017, 2019, and 2020). EV-A71 lost its dominance in 2017 in Shiyan. Among 196 confirmed HFMD cases, 85.7% tested positive for enterovirus, with CV-A6 being the most common serotype (121/168, 72.0%). The positive rates for CV-A16 and CV-A10 were 4.8% and 3.0%, respectively. There was no EV-A71 discovered. Infection with CV-A6 was linked to fever, myocardial damage, increased creatine kinase MB isoenzyme, and lactate dehydrogenase levels.

CONCLUSION

CV-A6 was the most common enterovirus serotype in Shiyan City, replacing EV-A71 and CV-A16 as the HFMD pathogen. Developing vaccines against CV-A6 or multiple pathogens, as well as rising CV-A6 surveillance, will help prevent HFMD in central China.

Epidemiological and etiological characteristics of mild hand, foot and mouth disease in children under 7 years old, Nanjing, China, 2010-2019

Background

Mild hand, foot and mouth disease (HFMD) cases make up a relatively high proportion of HFMD while have often been overlooked. This study aimed to investigate the epidemiological and etiological characteristics of mild HFMD in Nanjing.

Methods

Data on mild HFMD cases, during 2010–2019 in Nanjing, were collected from the China Information System for Disease Control and Prevention. This study mainly focused on mild cases aged < 7 years. Descriptive analysis was used to summarize epidemiological and etiological characteristics of mild cases. Flexible spatial scan statistic was used to detect spatial clusters of mild cases.

Results

A total of 175,339 mild cases aged < 7 years were reported, accounting for 94.4% of all mild cases. There was a higher average annual incidence of mild HFMD in children aged < 7 years (4,428 cases/100,000) compared with children aged ≥ 7 years (14 cases/100,000, P < 0.001), and especially children aged 1-year-old (7,908 cases/100,000). Mild cases showed semi-annual peaks of activity, including a major peak (April to July) and a minor peak (September to November). The average annual incidence was higher in males (5,040 cases/100,000) than females (3,755 cases/100,000). Based on the cumulative reported cases, the most likely cluster was detected, including Yuhuatai District, Jiangning District, Jiangbei new Area, and Pukou District. The annual distribution of enterovirus serotypes showed a significant difference. During 2010–2016, Enterovirus 71 (EV71), Coxsackievirus A16 (Cox A16), and other non-EV71/Cox A16 EVs, accounted for 29.1%, 34.6%, 36.3% of all the enterovirus test positive cases, respectively. Moreover, during 2017–2019, Cox A6, Cox A16, EV71, and other non-EV71/Cox A16/Cox A6 EVs, accounted for 47.3%, 32.5%, 10.7%, 9.5%, respectively.

Conclusions

Children under 7 years old are at higher risk of mild HFMD. Regions with high risk are mainly concentrated in the areas surrounding central urban areas. Cox A16 and Cox A6 became the dominant serotypes and they alternated or were co-epidemic. Our findings could provide valuable information for improving the regional surveillance, prevention and control strategies of HFMD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13690-022-00974-4.

Surveillance, Epidemiology and Impact of EV-A71 Vaccination on Hand, Foot, and Mouth Disease in Nanchang, China, 2010-2019

After the first national-scale outbreak of Hand, foot, and mouth disease (HFMD) in China, a national surveillance network was established. Here we described the epidemiology and pathogenic profile of HFMD and the impact of EV-A71 vaccination on pathogen spectrum of enteroviruses in the southeastern Chinese city of Nanchang during 2010–2019. A total of 7,951 HFMD cases from sentinel hospitals were included, of which 4,800 EV-positive cases (60.4%) were identified by real-time RT-PCR. During 2010–2012, enterovirus 71 (EV-A71) was the main causative agent of HFMD, causing 63.1% of cases, followed by 19.3% cases associated with coxsackievirus A16 (CV-A16). Since 2013, the proportion of other enteroviruses has increased dramatically, with the sub genotype D3 strain of Coxsackievirus A6 (CV-A6) replacing the dominance of EV-A71. These genetically diverse native strains of CV-A6 have co-transmitted and co-evolved in Nanchang. Unlike EV-A71 and CV-A16, most CV-A6 infections were concentrated in autumn and winter. The incidence of EV-A71 infection negatively correlated with EV-A71 vaccination (r = −0.990, p = 0.01). And severe cases sharply declined as the promotion of EV-A71 vaccines. After 2-year implementation of EV-A71 vaccination, EV-A71 is no longer detected from the reported HFMD cases in Nanchang. In conclusion, EV-A71 vaccination changed the pattern of HFMD epidemic, and CV-A6 replaced the dominance of EV-A71 over time.

Characterization of Coxsackievirus A6 Strains Isolated From Children With Hand, Foot, and Mouth Disease

Coxsackievirus A6 (CVA6) is a key pathogen causing hand, foot and mouth disease (HFMD). However, there are currently no specific antiviral drugs or vaccines for treating infections caused by CVA6. In this study, human rhabdomyosarcoma (RD), African green monkey kidney (Vero), and human embryonic lung diploid fibroblast (KMB17) cells were used to isolate CVA6 from 327 anal swab and fecal samples obtained during HFMD monitoring between 2009 and 2017. The VP1 genes of the isolates were sequenced and genotyped, and the biological characteristics of the representative CVA6 strains were analyzed. A total of 37 CVA6 strains of the D3 gene subtypes were isolated from RD cells, all of which belonged to the epidemic strains in mainland China. Using the adaptive culture method, 10 KMB17 cell-adapted strains were obtained; however, no Vero cell-adapted strains were acquired. Among the KMB17 cell-adapted strains, only KYN-A1205 caused disease or partial death in suckling mice, and its virulence was stronger than its RD cell-adapted strain. The pathogenic KYN-A1205 strain caused strong tropism to the muscle tissue and led to pathological changes, including muscle necrosis and nuclear fragmentation in the forelimb and hindlimb. Sequence analysis demonstrated that the KYN-A1205 strain exhibited multiple amino acid mutations after KMB17 cell adaptation. Moreover, it showed strong pathogenicity, good immunogenicity and genetic stability, and could be used as an experimental CVA6 vaccine candidate.

One-Step Reverse-Transcription Recombinase Polymerase Amplification Using Lateral Flow Strips for the Detection of Coxsackievirus A6

Hand, foot, and mouth disease (HFMD) is a common infectious disease affecting mainly children under 5 years of age. Coxsackievirus A6 (CVA-6), a major causative pathogen of HFMD, has caused outbreaks in recent years. Currently, no effective vaccine or antiviral treatments are available. In this study, one-step reverse-transcription recombinase polymerase amplification (RT-RPA), combined with a disposable lateral flow strip (LFS) assay, was developed to detect CVA-6. This assay can be performed in less than 35 min at 37°C without expensive instruments, and the result can be observed directly with the naked eye. The sensitivity of the RT-RPA-LFS was 10 copies per reaction, which was comparable to that of the conventional real-time quantitative polymerase chain reaction (qPCR) assays. Moreover, the assay specificity was 100%. The clinical performance of the RT-RPA-LFS assay was evaluated using 142 clinical samples, and the coincidence rate between RT-RPA-LFS and qPCR was 100%. Therefore, our RT-RPA-LFS assay provides a simple and rapid approach for point-of-care CVA-6 diagnosis.

[Atypical hand-foot-mouth disease virus genotyping in a pediatric hospital in Buenos Aires city, Argentina]

Typical hand-foot-mouth disease (HFMD) is an exanthematous viral disease with a classic symptomatology of fever, papulovesicular rash on the hands and feet with or without herpangina. It is usually caused by enterovirus 71 and Coxsackievirus A16, members of the genus Enterovirus. Recently, worldwide outbreaks of HFMD with atypical manifestations caused by Coxsackievirus A6 have been described. Atypical HFMD is considered an emerging disease due to its peculiar clinical and epidemiological characteristics: it affects adults, has a wide spectrum of clinical manifestations in the extension and distribution of the lesions and occurs in winter. The morphological characteristics of the lesions are very variable and can be misdiagnosed as chickenpox, impetigo or vasculitis. Here we describe the symptoms, clinical evolution, diagnostic methodology and treatment employed on a 4-yearold male patient with atypical HFMD.

Risk factors of hand, foot, and mouth disease caused by Coxsackievirus A6 in children under 6 years of age in Tianjin, China: a case-control study

Hand, foot, and mouth disease (HFMD) infected with Coxsackievirus A6 (CV-A6) have demonstrated an increasing trend in China. Our study aimed to explore the risk factors of HFMD cases infected with CV-A6 in children under 6 years of age in Tianjin, China. A non-matching case-control study was conducted in Tianjin, China. Cases were HFMD patients infected with CV-A6 while controls were HFMD patients infected with other enteroviruses. Multivariate logistic regression analysis was used to explore the risk factors of HFMD cases infected with CV-A6. A total of 1,264 eligible cases were included in our study, including 589 cases and 675 controls. Our study indicates that the CV-A6 caused HFMD patients were more likely to present with fever and rash on limbs, and home-care children and children having a history of contacting HFMD patient had a high risk of infection with CV-A6, while toy sterilization regularly at home and parents' hand-washing habits after toilet use were the protecting factors for children against CV-A6 infection.

Coxsackieviruses A6 and A16 associated with hand, foot, and mouth disease in Vietnam, 2008-2017: Essential information for rational vaccine design

Development of multivalent hand, foot, and mouth disease (HFMD) vaccines against enterovirus A71 (EV-A71) and several non-EV-A71 enteroviruses is needed for this life-threatening disease with a huge economic burden in Asia-Pacific countries. Comprehensive studies on the molecular epidemiology and genetic and antigenic characterization of major causative enteroviruses will provide information for rational vaccine design. Compared with molecular studies on EV-A71, that for non-EV-A71 enteroviruses remain few and limited in Vietnam. Therefore, we conducted a 10-year study on the circulation and genetic characterization of coxsackievirus A16 (CV-A16) and CV-A6 isolated from patients with HFMD in Northern Vietnam between 2008 and 2017. Enteroviruses were detected in 2228 of 3212 enrolled patients. Of the 42 serotypes assigned, 28.4% and 22.4% accounted for CV-A6 and CV-A16, being the second and the third dominant serotypes after EV-A71 (31.7%), respectively. The circulation of CV-A16 and CV-A6 showed a wide geographic distribution and distinct periodicity. Phylogenetic analyses revealed that the majority of Vietnamese CV-A6 and CV-A16 strains were located within the largest sub-genotypes or sub-genogroups. These comprised strains isolated from patients with HFMD worldwide during the past decade and the Vietnamese strains have been evolving in a manner similar to the strains circulating worldwide. Amino acid sequences of the putative functional loops on VP1 and other VPs among Vietnamese CV-A6 and CV-A16 isolates were highly conserved. Moreover, the functional loop patterns of VP1 were similar to the dominant patterns found worldwide, except for the T164K substitution on the EF loop in Vietnamese CV-A16. The findings suggest that the development of a universal HFMD vaccine, at least in Vietnam, must target CV-A6 and CV-A16 as two of the three major HFMD-causing serotypes. Vietnamese isolates or their genome sequences can be considered for rational vaccine design.

Neonatal hand, foot, and mouth disease due to coxsackievirus A6 in Shanghai

BACKGROUND

Evidence of hand, foot, and mouth disease (HFMD) in neonates is limited. The aim of this study was to evaluate the clinical symptoms, pathogens, possible transmission routes, and prognosis of neonatal HFMD in Shanghai.

METHODS

This was a case-control study based on the HFMD registry surveillance system. All neonates and infected family members were enrolled between 2016 and 2017 in Shanghai. Neonates with HFMD were followed for at least half a year. Detailed questionnaires, medical history, and physical examination were recorded. Routine blood examination, liver and renal function, immunophenotypes of peripheral blood lymphocytes (CD3, CD4, and CD8 T-cells; NK cells), immunoglobulin (Ig) M, IgG, and IgA, and cytokine interleukin (IL-1β, IL-2R, IL-6, IL-8, IL-10, and TNF-α) levels were measured. All rectal swab specimens were collected and genotyped for enterovirus, and phylogenetic analysis based on the VP1 sequences of coxsackievirus A6 (CV-A6) was performed to investigate molecular and evolutionary characteristics. T-test or nonparametric test was used to evaluate the differences. Logistic analysis was applied to calculate the risk of clinical manifestations in the group of HFMD neonates and their paired siblings.

RESULTS

There were 16 neonates among the 12,608 diagnosed patients with HFMD, accounting for 0.13%. All neonatal infections were transmitted by other members of the family, mainly the elder siblings, and were caused by CV-A6. CV-A6 was the emerging and predominant causative agent of HFMD in Shanghai. None of the neonates with HFMD experienced fever, onychomadesis, or severe complications. However, two elder sibling patients showed lethargy, and one developed hypoperfusion. In the elder siblings with HFMD, the proportion of white blood cells was generally higher than in neonates with HFMD. The immunologic function of the neonates with HFMD was basically normal. The levels of inflammatory markers were higher in both neonates and elder siblings with HFMD compared to age-matched controls. The clinical symptoms receded about 1 week after onset. None of the neonates had sequelae.

CONCLUSIONS

In our study, CV-A6 infection in neonates was benign, but had the character of family clustering. Due to the two-child policy in China, elder siblings may be the main route of HFMD transmission.

Coxsackievirus A6-induced Hand-Foot-and-Mouth Disease Mimicking Stevens-Johnson Syndrome in an Immunocompetent Adult

Hand-foot-and-mouth disease, a highly contagious viral infection, occurs more common in children than in adults. However, there was a recent outbreak of Coxsackievirus A6-induced infection with an atypical presentation among the adult population. Stevens–Johnson syndrome is a severe mucocutaneous disease characterized by extensive necrosis and detachment of the epidermis, and this condition is commonly caused by medications. Herein, we describe a 30-year-old male patient taking allopurinol for the management of gout. The patient presented with numerous erythematous papules, vesicles, and patches with mucosal eruptions on the whole body, oral mucositis, and fever, and he was finally diagnosed with hand-foot-and-mouth disease.

Sub-genotype change and recombination of coxsackievirus A6s may be the cause of it being the predominant pathogen for HFMD in children in Beijing, as revealed by analysis of complete genome sequences

OBJECTIVES

To investigate why coxsackievirus A6 (CVA6) has replaced enterovirus A71 (EV71) and coxsackievirus A16 (CVA16), which used to be the most predominant etiological agents, for hand, foot and mouth disease (HFMD) in children in Beijing, China.

METHODS

Sixty-four CVA6-positive samples were identified from 2010 to 2016 and selected for whole genome sequence amplification and analysis.

RESULTS

It was demonstrated that the whole genome sequences of CVA6s in this study were 7432-7435 nucleotides in length, and the different lengths were only in the 5'UTR region. The phylogenetic tree analysis of the full-length VP1 region of CVA6s indicated that the prevalent CVA6s in Beijing changed from the previous D2 sub-genotype to the D3 sub-genotype in 2013. In this study, two recombinant forms (RFs)- RF-C and RF-D - of CVA6 mainly appeared in 2010 and 2011. Since 2013, three recombinant CVA6 variants - RF-A, J and L - have been prevalent in children with HFMD in Beijing. The recombination region of RF-J was located at the 2C region, while RF-L had a new recombination point in the 3D region. The recombination of prevalent CVA6s in Beijing from 2013 to 2016 occurred within non-capsid regions of the genome, especially the P2 and P3 regions.

CONCLUSIONS

The sub-genotype change and recombination of CVA6s indicated from this study may explain why CVA6 has become the predominant pathogen causing HFMD since 2013.

Genetic recombination in fast-spreading coxsackievirus A6 variants: a potential role in evolution and pathogenicity

Hand, foot, and mouth disease (HFMD) is a common global epidemic. From 2008 onwards, many HFMD outbreaks caused by coxsackievirus A6 (CV-A6) have been reported worldwide. Since 2013, with a dramatically increasing number of CV-A6-related HFMD cases, CV-A6 has become the predominant HFMD pathogen in mainland China. Phylogenetic analysis based on the VP1 capsid gene revealed that subtype D3 dominated the CV-A6 outbreaks. Here, we performed a large-scale (near) full-length genetic analysis of global and Chinese CV-A6 variants, including 158 newly sequenced samples collected extensively in mainland China between 2010 and 2018. During the global transmission of subtype D3 of CV-A6, the noncapsid gene continued recombining, giving rise to a series of viable recombinant hybrids designated evolutionary lineages, and each lineage displayed internal consistency in both genetic and epidemiological features. The emergence of lineage –A since 2005 has triggered CV-A6 outbreaks worldwide, with a rate of evolution estimated at 4.17 × 10⁻³ substitutions site^-1 year⁻¹ based on a large number of monophyletic open reading frame sequences, and created a series of lineages chronologically through varied noncapsid recombination events. In mainland China, lineage –A has generated another two novel widespread lineages (–J and –L) through recombination within the enterovirus A gene pool, with robust estimates of occurrence time. Lineage –A, –J, and –L infections presented dissimilar clinical manifestations, indicating that the conservation of the CV-A6 capsid gene resulted in high transmissibility, but the lineage-specific noncapsid gene might influence pathogenicity. Potentially important amino acid substitutions were further predicted among CV-A6 variants. The evolutionary phenomenon of noncapsid polymorphism within the same subtype observed in CV-A6 was uncommon in other leading HFMD pathogens; such frequent recombination happened in fast-spreading CV-A6, indicating that the recovery of deleterious genomes may still be ongoing within CV-A6 quasispecies. CV-A6-related HFMD outbreaks have caused a significant public health burden and pose a great threat to children’s health; therefore, further surveillance is greatly needed to understand the full genetic diversity of CV-A6 in mainland China.

The Mechanism of Onychomadesis (Nail Shedding) and Beau's Lines Following Hand-Foot-Mouth Disease

Background: Nail changes, including onychomadesis (nail shedding) and Beau’s line, following hand-foot-mouth disease (HFMD) are a common emergence at the stage of late complications of HFMD. However, the exact mechanism is still unknown. Therefore, we conducted this study to elucidate the mechanism of nail changes following HFMD. Methods: We collected 11 patients suffering from onychomadesis following HFMD. Nail samples from all of them were collected. Real time reverse transcription polymerase chain reaction (RT-PCR) and sequencing for human enteroviruses (HEV) were performed. Throat swabs for RT-PCR and sequencing for HEV were performed for three cases. Results: RT-PCR demonstrated the presence of Coxackievirus A6 (CVA6) in nail samples from three patients and one with Echovirus. Conclusion: In conclusion, we believe that the major cause of onychomadesis following HFMD is that certain novel viruses, mostly CVA6, are virulent and may damage nail matrix. Direct injury caused by cutaneous lesions of HFMD around nail matrix is a minor cause. There are still other virulent HEV which may result in onychomadesis. In addition, the novel strain of CVA6 also causes atypical clinical presentations, such as adult involvement and delayed-onset palmar and plantar desquamation. Physicians should be familiar with atypical presentations caused by novel viruses to avoid misdiagnosis and even inform patients of the possibility of onychomadesis that may take place weeks later to reassure patients.

Phylogenetic and antigenic analyses of coxsackievirus A6 isolates in Yamagata, Japan between 2001 and 2017

Although coxsackievirus A6 (CV-A6) is generally recognized as a causative agent of herpangina in children, CV-A6 infections globally emerged as a new and major cause of epidemic hand-foot-and-mouth-diseases (HFMDs) around 2008. To clarify the longitudinal epidemiology of CV-A6, we carried out sequence and phylogenetic analyses for the VP1 and partially for the VP4-3D regions as well as antigenic analysis using 115 CV-A6 isolates and 105 human sera in Yamagata, Japan between 2001 and 2017. Phylogenetic analysis revealed that CV-A6 isolates were clearly divided into two clusters; strains in circulation between 2001 and 2008 and those between 2010 and 2017. Neutralizing antibody titers of two rabbit antisera, which were immunized with Yamagata isolates in 2001 and 2015, respectively, against 28 Yamagata representative strains as well as the prototype Gdula strain were 1:2560-1:5120 and 1:160-1:640, respectively. The neutralizing antibody titers among residents in Yamagata against the above two strains were similar. Our analyses revealed that there were cross-antigenicities among all analyzed CV-A6 strains, although the newly emerged strains were introduced into Yamagata around 2010 and replaced the previous ones. With regard to control measures, these findings suggest that we can prevent CV-A6 infections through the development of a vaccine that effectively induces neutralizing antibodies against CV-A6, irrespective of genetic cluster.

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

Background

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

Methods

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

Results

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

Conclusions

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

Electronic supplementary material

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

Characterization of an inactivated whole-virus bivalent vaccine that induces balanced protective immunity against coxsackievirus A6 and A10 in mice

Coxsackievirus A6 (CVA6) and CVA10 are two of the major pathogens associated with hand, foot and mouth disease (HFMD) in children. The majority of CVA6 and CVA10 infections result in mild, self-limiting episodes (fever and herpangina) in pediatric populations; however, in some cases, can proceed to severe neurological disease and death. Efforts to mitigate viral transmission to decrease the morbidity and mortality associated with infection would be greatly strengthened by the availability of an efficacious CVA6 and CVA10 bivalent vaccine. Here we report the immunogenicity and protective efficacy of a bivalent combination vaccine comprised of formaldehyde-inactivated, whole-virus CVA6 and CVA10. We demonstrate that subcutaneous delivery of the bivalent vaccine can induce antigen-specific systemic immune responses, particularly the induction of polyfunctional T cells, which elicit active immunization to achieve a protection rate of >80% in the infected neonatal mice. Furthermore, passive transfer of the antisera from vaccinated mice potently protected recipient mice against CVA6 and CVA10 challenge. Importantly, the bivalent vaccine could induce high levels of IgG and neutralizing antibodies in adult female mice and the maternal antibody transmitted to the recipient mice played an important role in controlling homotypic and heterotypic CVA6 and CVA10 infections and viral replication in vivo. Collectively, these findings indicate that there is no immunological interference between the two antigens with respect to their ability to induce virus-specific immune responses, and thus provides proof-of-concept for further development of multivalent vaccines for broad protection against HFMD.

Atypical hand, foot, and mouth disease caused by Coxsackievirus A6 in Argentina in 2015

We present two groups of cases of atypical hand, foot, and mouth disease (HFMD) caused by Coxsackievirus A6 (CV-A6) detected in Argentina in 2015. The first group involved 14 patients from Chubut province and the second group affected 12 patients from San Luis province. Molecular analysis of the complete VP1 protein gene revealed the circulation of E2 sublineage, the most predominant worldwide. To our knowledge, this is the first report of CV-A6 infections associated with atypical HFMD in Argentina and South America.

Molecular epidemiology of coxsackievirus A6 circulating in Hong Kong reveals common neurological manifestations and emergence of novel recombinant groups

BACKGROUND

Coxsackievirus A6 (CV-A6) represents the predominant enterovirus serotype in Hong Kong, but its epidemiology in our population was unknown.

OBJECTIVES

To examine the clinical and molecular epidemiology of CV-A6 and detect emerging recombinant strains in Hong Kong.

STUDY DESIGN

Nasopharyngeal aspirates (NPAs) from patients with febrile or respiratory illness were subject to RT-PCR for CV-A6 and sequencing of 5'-NCR and VP1. CV-A6-positive samples were further subject to 2C and 3D gene sequencing. Complete genome sequencing was performed on potential recombinant strains.

RESULTS

Thirty-six (0.35%) NPAs were positive for CV-A6 by 5'-NCR RT-PCR and sequencing, 28 of which confirmed by partial VP1 gene sequencing. Among the 28 patients (mainly young children) with CV-A6 infection, hand-foot-and-mouth disease (HFMD) (43%), herpangina (18%) and tonsillitis (11%) were the most common diagnoses. Seven (25%) patients had neurological manifestations, including febrile seizures, encephalitis and meningitis. VP1 gene analysis showed that 24 CV-A6 strains circulating in Hong Kong belonged to genotype D5, while 4 strains belonged to D4. Further 2C and 3D gene analysis revealed eight potential recombinant strains. Genome sequencing of five selected strains confirmed four recombinant strains: HK459455/2013 belonging to recombination group RJ arisen from CV-A6/CV-A4, HK458288/2015 and HK446377/2015 representing novel group RL arisen from CV-A6/CV-A4, and HK462069/2015 representing novel group RM arisen from CV-A6/EV-A71. Recombination breakpoints located at 3D were identified in the latter three recombinant strains, with HK462069/2015 (from a child with encephalitis) having acquired 3D region from EV-A71.

CONCLUSIONS

We identified novel recombinant CV-A6 strains in Hong Kong, with 3D being a common recombination site.

An outbreak of Coxsackievirus A6-associated hand, foot, and mouth disease in a kindergarten in Beijing in 2015

Background

Coxsackievirus A6 (CVA6) is one of the major agents to cause hand, foot and mouth disease (HFMD) outbreaks globally. The objective of this study is to investigate the epidemiologic and clinical manifestations of CVA6 outbreak, and thus guide the diagnosis and treatment of the disease, as well as disease prevention.

Methods

An HFMD outbreak in a kindergarten was reported to Shijingshan District Center for Disease Control and Prevention (SCDC) on November 2, 2015 in Beijing, China. Epidemiological investigation was conducted. We performed a nine-week follow-up study to collect and analyze the clinical manifestations of HFMD cases.

Results

The outbreak yield 56 (15.7%) clinical diagnosed HFMD cases out of 357 registered children in the kindergarten with the mean age of 3.5 years old. This outbreak lasted for three days and ceased after initiating infectious disease controlling procedures, including periodical suspension of the kindergarten activities, environmental disinfection, and family health education. Fifty-one cases were followed for nine weeks. The positive rate of clinical manifestations of rash, fever, desquamation, pigmentation and onychomadesis were 100.0%, 84.3%, 68.6%, 17.6% and 43.1%, respectively. Children developed desquamation within the first 4 weeks after disease onset and developed onychomadesis between the 3th and 8th week after disease onset. Children with desquamation had 9.3 (95%CI: 1.836–47.437) times higher odds of developing onychomadesis compared to those without this manifestation. Ten out of 14 collected samples were CVA6 positive, and five positive samples shared a high degree of similarity in the VP1 nucleotide and amino acid sequences (99.9–100.0% and 100%).

Conclusion

This HFMD outbreak was caused by CVA6, featured with delayed symptoms. Emerging CVA6-associated HFMD and its delayed symptoms should be paid more attention to reduce outbreaks and provide more information to doctors and parents.

Electronic supplementary material

The online version of this article (10.1186/s12887-018-1253-1) contains supplementary material, which is available to authorized users.

A surrogate assay for measuring Coxsackievirus A6 neutralizing antibodies

Coxsackievirus A6 (CV-A6) is one of pathogens causing hand, foot and mouth disease (HFMD) and becomes a new challenge to HFMD control. In this study, we first built a single-round pseudovirus infection system for CV-A6, and then developed a pseudovirus luciferase assay (PVLA) for anti-CV-A6 neutralizing antibody (NtAb) quantification. Since cytopahtic effect (CPE) is considered as the gold standard test for anti-enterovirus NtAb detection, a comparison study has been performed using 318 clinical serum samples, as measured both by PVLA and CPE. The sensitivity and specificity of PVLA was 94.9% (95% CI between 90.8-97.5%) and 92.7% (95% CI between 86.6-96.6%), respectively. Statistical analysis revealed that PVLA and CPE were highly correlated (spearman r = 0.931, P < 0.0001) and in good agreement (94.0%, 95% CI between 90.8-96.4%), showing that PVLA could be used as a surrogate assay for anti-CV-A6 NtAb detection and served as a valuable tool for CV-A6 vaccine evaluation and CV-A6 epidemiological surveillance.

Synonymous codon usage analysis of hand, foot and mouth disease viruses: A comparative study on coxsackievirus A6, A10, A16, and enterovirus 71 from 2008 to 2015

Enterovirus 71 (EV71) and coxsackievirus A16 (CVA16) have been considered major pathogens of hand, foot and mouth disease (HFMD) throughout the world for decades. In recent years, coxsackievirus A6 (CVA6) and coxsackievirus A10 (CVA10) have raised attention as two other serious pathogens of HFMD. The present study focused on the synonymous codon usage of four viruses isolated from 2008 to 2015, with particular attention on P1 (encoding capsid proteins) and P2-P3 regions (both encoding non-structural proteins) in the genomic RNA. Relative synonymous codon usage, effective number of codons, neutrality and correspondence were analyzed. The results indicated that these viruses prefer A/T at the third position in codons rather than G/C. The most frequent codons of 4 essential and 2 semi-essential amino acids, as well as a key amino acid of metabolic junctions (Glu) used in the four viruses are also the most frequently used in humans. Effective number of codons (ENC) values indicated weak codon usage bias in all the viruses. Relatively, the force of mutation pressure in the P1 region was found to be stronger than that in the P2-P3 region, and this force in the P1 region of CVA6 and EV71 was stronger than that of CVA10 and A16. The neutrality analysis results implied that mutation pressure plays a minor role in shaping codon bias of these viruses. Correspondence analysis indicated that the codon usage of EV71 strains varied much more than that of other viruses. In conclusion, the present study provides novel and comparative insight into the evolution of HFMD pathogens at the codon level.

Development and evaluation of a rapid recombinase polymerase amplification assay for detection of coxsackievirus A6

Coxsackievirus A6 (CV-A6) is an important pathogen causing hand, foot and mouth disease (HFMD). The aim of this study was to develop and evaluate a rapid real-time reverse transcription recombinase polymerase amplification (RT-RPA) assay for detection of CV-A6. The sensitivity of this assay was 202 copies/reaction, with 100 % specificity. Furthermore, this assay yielded consistent results comparable with a commercial qRT-PCR diagnostic kit. This assay is therefore potentially useful for surveillance of CV-A6 infections and outbreak control.

Outbreak of hand, foot, and mouth disease caused by coxsackievirus A6 in a Juku in Fengtai District, Beijing, China, 2015

An outbreak of hand, foot, and mouth disease (HFMD) that occurred in a Juku in Fengtai District, Beijing, China, in 2015 was monitored by the China Information System for Disease Control and Prevention. Epidemiological investigation showed that 11 cases occurred from two classes in the preschool art training department in the Juku. Coxsackievirus A6 (CV-A6) was identified as the causative pathogen of the outbreak via sequences analysis of products of real-time reverse-transcription polymerase chain reaction (RT-PCR) and nested RT-PCR. Phylogenetic analysis showed that CV-A6 strains isolated in this study clustered with epidemic strains isolated in China since 2013. The outbreak ended quickly with effective measures. This event indicates that continuous surveillance of HFMD etiological agents other than enterovirus 71 and coxsackievirus A16 is necessary.

A neonatal mouse model for the evaluation of antibodies and vaccines against coxsackievirus A6

Coxsackievirus A6 (CA6) can induce atypical hand, foot, and mouth disease, which is characterized by severe rash, onychomadesis and a higher rate of infection in adults. Increasing epidemiological data indicated that outbreaks of CA6-associated hand, foot, and mouth disease have markedly increased worldwide in recent years. However, the current body of knowledge on the infection, pathogenic mechanism, and immunogenicity of CA6 is still very limited. In this study, we established the first neonatal mouse model for the evaluation of antibodies and vaccines against CA6. The CA6 strain CA6/141 could infect a one-day-old BALB/c mouse through intraperitoneal and intracerebral routes. The infected mice developed clinical symptoms, such as inactivity, wasting, hind-limb paralysis and even death. Pathological examination indicated that CA6 showed special tropism to skeletal muscles and skin, but not to nervous system or cardiac muscles. Infections with CA6 could induce vesicles in the dermis without a rash in mice, and the CA6 antigen was mainly localized in hair follicles. The strong tropism of CA6 to the skin may be related to its severe clinical features in infants. This mouse model was further applied to evaluate the efficacy of a therapeutic antibody and an experimental vaccine against CA6. A potential mAb 1D5 could fully protect mice from a lethal CA6 infection and also showed good therapeutic effects in the CA6-infected mice. In addition, an inactivated CA6 vaccine was evaluated through maternal immunization and showed 100% protection of neonatal mice from lethal CA6 challenge. Collectively, these results indicate that this infection model will be a useful tool in future studies on vaccines and antiviral reagents against CA6.

Yeast-produced recombinant virus-like particles of coxsackievirus A6 elicited protective antibodies in mice

Coxsackievirus A6 (CA6) has recently emerged as the predominant pathogen of hand, foot and mouth disease (HFMD), causing significant morbidity in children and adults. The increasing prevalence of CA6 infection and its associated disease burden underscore the need for effective CA6 vaccines. However, CA6 grows poorly in cultured cells, making it difficult to develop inactivated whole-virus or live attenuated vaccines. Here we report the development of a recombinant virus-like particle (VLP) based CA6 vaccine. CA6 VLPs were produced in Pichia pastoris yeast transformed with a vector encoding both P1 and 3CD proteins of CA6. Immunization with CA6 VLPs elicited CA6-specific serum antibodies in mice. Passive transfer of anti-VLP antisera protected recipient mice against lethal CA6 challenge. Collectively, these results demonstrate that CA6 VLPs represent a viable CA6 vaccine candidate which warrants further preclinical and clinical development.

Characterization of Coxsackievirus A6- and Enterovirus 71-Associated Hand Foot and Mouth Disease in Beijing, China, from 2013 to 2015

BACKGROUND

Etiology surveillance of Hand Foot and Mouth disease (HFMD) in Beijing showed that Coxsackievirus A6 (CVA6) became the major pathogen of HFMD in 2013 and 2015. In order to understand the epidemiological characteristics and clinical manifestations of CVA6-associated HFMD, a comparison study among CVA6-, EV71- (Enterovirus 71), and CVA16- (Coxsackievirus A16) associated HFMD was performed.

METHODS

Epidemiological characteristics and clinical manifestations among CVA6-, EV71- and CVA16-associated mild or severe cases were compared from 2013 to 2015. VP1 gene of CVA6 and EV71 from mild cases, severe cases were sequenced, aligned, and compared with strains from 2009 to 2015 in Beijing and strains available in GenBank. Phylogenetic tree was constructed by neighbor-joining method.

RESULTS

CVA6 became the predominant causative agent of HFMD and accounted for 35.4 and 36.9% of total positive cases in 2013 and 2015, respectively. From 2013 to 2015, a total of 305 severe cases and 7 fatal cases were reported. CVA6 and EV71 were responsible for 57.5% of the severe cases. Five out six samples from fatal cases were identified as EV71. High fever, onychomadesis, and decrustation were the typical symptoms of CVA6-associated mild HFMD. CVA6-associated severe cases were characterized by high fever with shorter duration and twitch compared with EV71-associated severe cases which were characterized by poor mental condition, abnormal pupil, and vomiting. Poor mental condition, lung wet rales, abnormal pupil, and tachycardia were the most common clinical features of fatal cases. The percentage of lymphocyte in CVA6-associated cases was significantly lower than that of EV71. High percentage of lymphocyte and low percentage of neutrophils were the typical characteristics of fatal cases. VP1 sequences between CVA6- or EV71-associated mild and severe cases were highly homologous.

CONCLUSION

CVA6 became one of the major pathogens of HFMD in 2013 and 2015 in Beijing. Epidemiological characteristics, clinical manifestations of CVA6-, EV71- and CVA16-associated cases in this study enriched the definition of HFMD caused by different pathogens and shed light to accurate diagnosis, appropriate treatment and effective prevention of HFMD.

Meteorological factors affect the hand, foot, and mouth disease epidemic in Qingdao, China, 2007-2014

Hand, foot, and mouth disease (HFMD) has caused public health concerns worldwide. We aimed to investigate the effect of meteorological factors on the HFMD epidemic in Qingdao, a port city in China. A total of 78641 cases were reported in Qingdao between January 2007 and December 2014. Of those, 71084 (90·39%) occurred in children aged 0-5 years, with an incidence of 1691·2/100000. The incidence increased from early spring, peaked between spring and summer, and decreased in late summer. Aetiological agents in all severe cases and selected mild cases were characterized by examining throat swabs. Except for enterovirus 71 (EV71) and coxsackievirus A16 (CA16), other EVs caused >50% of the HFMD cases between 2011 and 2014. EV71 was more frequent in the off-peak months than in the peak months and prone to causing more severe cases compared to CA16 (χ 2 = 46·3, P < 0·001). CA10 caused more severe HFMD than did CA6 (χ 2 = 20·49, P < 0·001) and all non-CA10 EVs (χ 2 = 41·01, P < 0·001). Community-derived HFMD cases accounted for 65·11%. Spearman rank correlation analysis showed that HFMD incidence in children aged 0-5 years was positively correlated with atmospheric temperature (r s = 0·77, P < 0·001), relative humidity (r s = 0·507, P < 0·001), and precipitation (r s = 0·328, P < 0·001). Climate changes and CA10 surveillance in communities should be integrated into the current prophylactic programme.

Efficacy of a Trivalent Hand, Foot, and Mouth Disease Vaccine against Enterovirus 71 and Coxsackieviruses A16 and A6 in Mice

Hand, foot, and mouth disease (HFMD) has recently emerged as a major public health concern across the Asian-Pacific region. Enterovirus 71 (EV71) and Coxsackievirus A16 (CVA16) are the primary causative agents of HFMD, but other members of the Enterovirus A species, including Coxsackievirus A6 (CVA6), can cause disease. The lack of small animal models for these viruses have hampered the development of a licensed HFMD vaccine or antivirals. We have previously reported on the development of a mouse model for EV71 and demonstrated the protective efficacy of an inactivated EV71 vaccine candidate. Here, mouse-adapted strains of CVA16 and CVA6 were produced by sequential passage of the viruses through mice deficient in interferon (IFN) α/β (A129) and α/β and γ (AG129) receptors. Adapted viruses were capable of infecting 3 week-old A129 (CVA6) and 12 week-old AG129 (CVA16) mice. Accordingly, these models were used in active and passive immunization studies to test the efficacy of a trivalent vaccine candidate containing inactivated EV71, CVA16, and CVA6. Full protection from lethal challenge against EV71 and CVA16 was observed in trivalent vaccinated groups. In contrast, monovalent vaccinated groups with non-homologous challenges failed to cross protect. Protection from CVA6 challenge was accomplished through a passive transfer study involving serum raised against the trivalent vaccine. These animal models will be useful for future studies on HFMD related pathogenesis and the efficacy of vaccine candidates.

Construction and characterization of an infectious clone of coxsackievirus A6 that showed high virulence in neonatal mice

Atypical hand, foot, and mouth disease (aHFMD) outbreaks have been frequently reported worldwide in recent years. It is believed that coxsackievirus A6 (CA6) is the major pathogen for aHFMD. Studies regarding CA6 infection are limited and the genetic mechanism for the high pathogenicity of some new CA6 variants is still unclear. Infectious clones are powerful tools for studying the genetic mechanisms of RNA viruses. In this study, we describe the construction of a full-length cDNA clone of CA6 strain TW-2007-00141. The whole genome of CA6 was amplified in a single step and ligated into a plasmid vector through an efficient cloning method, Gibson assembly. The whole genome sequence of CA6 strain TW-2007-00141 was determined and phylogenetic analysis indicated that it shared a high degree of similarity (≥94%) with the CA6 strains found in Taiwan in 2009. The infectious clone of CA6 viruses were recovered by transfection into 293FT cells and showed similar biological properties to the parental virus. Viral particles were purified by CsCl isopycnic centrifugation, and two types of viral particles were observed under transmission electron microscopy. The rescued virus showed high virulence in one-day-old suckling mice. This clone may be useful for establishing animal models for the evaluation of CA6 vaccine efficiency in future.

Unusual skin manifestation of hand, foot and mouth disease associated with coxsackievirus A6: cases report

Background

Hand, food, and mouth disease (HFMD) is a highly contagious disease caused by enteroviruses infection. It is a health problem in young children under 5 years of age worldwide. The common causative agents are coxsackievirus A 16 (CA16) and enterovirus 71 (EV71). In recent years, coxsackievirus A6 (CA6) has emerged to be one of the major etiologic agents of HFMD worldwide including in Thailand.

Case description

We reported cases with unusual skin manifestations of CA6-associated HFMD such as widespread severe cutaneous eruption, large vesicles (varicelliform), purpuric-like lesions or Gianotti–Crosti like eruptions.

Discussion and evaluation

Molecular characterization of the CA6 strains from those patients found that all were clustered in the same group of CA6 that are currently circulating in Thailand.

Conclusions

Clinicians need to be aware of the expanded range of cutaneous findings in CA6-associated HFMD in order to properly consider the diagnosis, management and prevention.

Fourteen types of co-circulating recombinant enterovirus were associated with hand, foot, and mouth disease in children from Wenzhou, China

BACKGROUND

Although hand, foot, and mouth disease (HFMD) is a major public concern in China, the prevalence and clinical symptoms associated with the different agents of HFMD in this country remain poorly understood.

OBJECTIVES

We investigated the clinical and molecular characteristics of enteroviruses in patients with HFMD from Wenzhou, China.

STUDY DESIGN

Patients with laboratory-confirmed HFMD admitted to the Yuying Children's Hospital in Wenzhou, China during 2013 were included in this study. Viral RNA sequences were amplified using RT-PCR, determined by sequencing, and compared by phylogenetic analysis.

RESULTS

A total of 955 clinically diagnosed HFMD cases were determined using PCR, with whole viral genomes obtained for each enterovirus type. 14 types of enterovirus belonging to two viral species were identified. Notably, Coxsackievirus A6 (CV-A6) was the most common species detected (77.8%), followed by EV-A71 (8.2%) and CV-A10 (8.1%). Phylogenetic analysis revealed multiple independent introductions of these viruses into Wenzhou. In addition, the enterovirus observed in Wenzhou had a recombinant history, with two or three recombination breakpoints. Although the illness associated with CV-A6 was milder than that of EV-A71, CV-A6 infection caused more widespread rash, larger blisters, and subsequent skin peeling and/or nail shedding.

CONCLUSION

Our study revealed the co-circulation of 14 types of enteroviruses in a single location - Wenzhou, China - with CV-A6 virus the predominant agent of HFMD. This work highlights the need to perform larger-scale surveillance to fully understand the epidemiology of enteroviruses in China and the wider Asia-Pacific region.

An atypical course of coxsackievirus A6 associated hand, foot and mouth disease in extremely low birth weight preterm twins

The incidence of coxsackievirus A6 (CV-A6) associated hand, foot and mouth disease (HFMD) has reportedly increased since 2008 with sometimes severe complications. We here describe an atypical course of CV-A6-associated HFMD in extremely low birth weight twins. The CV-A6-strains are genetically closely related to international strains isolated from HFMD outbreaks.

Hand, foot and mouth disease in Guangdong, China, in 2013: new trends in the continuing epidemic

Millions of incidents of hand, foot and mouth disease occur annually in China, with EVA71 and CVA16 as two major causative pathogens. A provincial surveillance system has been implemented in Guangdong for almost 5 years to analyze the aetiological spectrum and epidemic changes. An unusual enterovirus type, CVA6, was identified as the predominant serotype associated with an HFMD epidemic from late 2012 to 2013. In contrast to virus strains isolated before, all CVA6/CHN/2012-2013 strains segregated into one major genetic cluster. This study suggested that one cluster of circulating CVA6 strain had emerged as a new and major cause during a continuing HFMD epidemic in Guangdong, China.

Coxsackievirus A6-related hand foot and mouth disease: skin manifestations in a cluster of adult patients

BACKGROUND

Hand foot and mouth disease (HFMD) is a common childhood manifestation of enterovirus (EV) infection. It predominantly affects young children, and has been mainly associated with coxsackievirus (CV) A16 and EV 71.

OBJECTIVES

We report an unusual cluster of adult patients with HFMD.

STUDY DESIGN

Throat swabs and vesicular fluid samples obtained from patients admitted to the emergency room (ER) with HFMD were tested for EV by reverse transcription (RT)-real time PCR, and further subjected to sequencing and phylogenetic analysis.

RESULTS

CVA6 was identified as the causative agent of HFMD in five epidemiologically-unrelated adult patients (28-37 years old) admitted to the ER between December 2012 and February 2013. Phylogenetic analysis mapped the CVA6 strains into one cluster. All patients manifested with fever and a severe vasculitis-like rash, followed by spontaneous recovery.

CONCLUSIONS

This cluster identifies CVA6 as an emerging cause of HFMD of unusual age distribution, seasonality, and clinical severity, underscoring the need for continued alertness and clinical-genotypic surveillance of EV HFMD.

Coxsackievirus A6 and Hand, Foot and Mouth Disease: Three Case Reports of Familial Child-to-Immunocompetent Adult Transmission and a Literature Review

Hand, foot and mouth disease (HFMD) is a highly contagious viral infection characterized by typical maculopapular or vesicular eruptions on the hands and feet and in the oral cavity. It affects predominantly children and/or immunocompromised adults. It usually follows a benign and self-limiting course. However, HFMD cases with severe or lethal complications such as encephalitis, meningitis, pulmonary edema and myocarditis have also been reported, mostly in children, but also in adults. High infectivity of HFMD has contributed to several large outbreaks of this disease in recent decades in East and Southeast Asia, the United States and Finland. The most common pathogens were Coxsackievirus A16, Enterovirus 71 and, recently, also Coxsackieviruses A6 and A10. Differences in the course of HFMD have been observed, depending on the virus type. Recently, many cases of atypical HFMD have been described in the literature with unusual morphology and/or localization of skin lesions. Atypical HFMD manifestations including vesiculobullous exanthema, often on the trunk or extremities, and perioral zone involvement were often caused by Coxsackievirus A6 infections. We present 3 cases of familial transmission of HFMD caused by Coxsackievirus A6 with some atypical features, benign course and complete recovery among immunocompetent adults.