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

Transition of D3c branch and novel recombination events contribute to the diversity of Coxsackievirus A6 in Beijing, China, from 2019 to 2023

Coxsackievirus A6 (CVA6) is a major pathogen responsible for numerous outbreaks of hand, foot, and mouth disease (HFMD) worldwide. This study investigates the molecular evolution and recombination of CVA6 in Beijing, China. Full-length sequences of 54 CVA6 from Beijing (2019-2023) were obtained through metagenomic next-generation sequencing and Sanger sequencing. These sequences were compared with representative sequences from GenBank to analyse their phylogenetic characteristics, recombination diversity, and evolutionary dynamics. The 54 CVA6 strains co-circulated with those from multiple provinces in China, as well as from South Korea and Japan. Phylogenetic analysis revealed a novel D3c branch, with the VP1 T283A amino acid mutation identified as a key change in its formation. One sequence belonged to the D3a branch, while 53 sequences belonged to the D3c branch. Recombination analysis identified RF-A (46, 85.1%) and three novel recombinant forms (RFs): RF-Z (1, 1.9%), RF-AA (1, 1.9%), and RF-AB (6, 11.1%). Bayesian phylogenetic analysis estimated that the most recent common ancestor of D3c emerged in August 2013 (95% highest probability density (HPD): May 2012 to September 2014), with recombination events occurring in RF-Z (2017-2019), RF-AA (2019-2023), and RF-AB (2021-2023). In conclusion, we revealed a globally circulating CVA6 D3c branch and identified three novel RFs, providing valuable insights for the intervention and control of HFMD.

Concurrent Circulation of Viral Agents in Pediatric Patients Presenting with Respiratory Illness and Diarrheal Symptoms in Metropolitan Region of São Paulo, Brazil, 2021

Pneumonia and diarrhea are the leading causes of death in children under 5 globally, worsened by viral infections. This study investigates viral agents in children ≤ 3 years with respiratory illness and diarrhea in Metropolitan Region of São Paulo, Brazil, during spring 2021. Twenty paired samples (oropharyngeal swab and feces) were tested using in-house qPCR for HBoV and HAdV, RT-qPCR for RVA, EV, PeV-A, and NoV, and a commercial RT-qPCR kit for SARS-CoV-2, Flu A/B, and RSV. HAstV was detected with conventional nested (RT)-PCR. Positive samples were sequenced for molecular characterization and phylogenetic analysis. Seven viruses were identified: HBoV, NoV, HAdV, PeV-A, EV, RSV, and Flu A. HBoV and NoV were detected in 75% of cases, with co-infection in 65% of patients, indicating their involvement in the gastro-respiratory illness. Genotyping of HBoV (HBoV-1), NoV (GII.4_Sydney[P16], GII.2[P16], and GII.4_Sydney[P31]), EV (Coxsackievirus A6), HAdV (species C, type 6), and PeV-A (genotype 1) showed local virus diversity. Phylogenetic analysis indicated no ongoing community outbreak, with distinct clusters observed. The findings highlight the overlap of respiratory and enteric diseases, revealing local viral diversity and high exposure to enteric viruses. This underscores the challenges in differential diagnosis and the need for syndromic surveillance.

Evaluation of the Enterovirus serotype monitoring approach for wastewater surveillance of hand foot and mouth disease using secondary epidemiological surveillance data

The serotypes of Enterovirus A (EVA) causing hand, foot, and mouth disease (HFMD) exhibit cyclical dominance, with the dominant serotypes being EVA71, Coxsackievirus A type 6 (CVA6), CVA10, and CVA16. In this study, a quadruplex digital polymerase chain reaction (dPCR) assay was developed for serotype-level monitoring in wastewater surveillance for HFMD. The quadruplex dPCR assay performance was comparable to that of the singleplex assays. Grab influent samples (n = 122) were collected weekly from a wastewater treatment plant in Yamanashi Prefecture, Japan, from March 2022 to July 2024. The dPCR results revealed that CVA6 had a lower prevalence in 2023 than in 2022 and 2024, while the detection ratio of EVA71 was significantly higher in 2023 than in 2022 (Chi-square test, P < 0.05). Triangulation of these results with a clinical report indicated the dominance of CVA6 in 2022 and 2024, but not in 2023, while EVA71 was found to be dominant in 2023. Secondary data revealed significantly higher HFMD cases in the catchment in the years when CVA6 was dominant and significantly lower in the years when EVA71 was dominant. The comparative analysis revealed a stronger correlation between CVA6 RNA concentrations and HFMD cases (r = 0.83) than that between a broad range of Enteroviruses, Pan-Enterovirus RNA concentrations (r = 0.47). Thus, serotype-level monitoring, particularly through quadruplex dPCR, provides valuable insights into EVA serotype dynamics, accurately reflects HFMD trends, and supports the monitoring of the cyclical patterns of EVA serotypes.

The Immunogenicity of Coxsackievirus A6 (D3a Sub-Genotype) Virus-Like Particle and mRNA Vaccines

In recent years, coxsackievirus A6 (CVA6) has surpassed enterovirus A71 to become the main pathogen causing severe Hand, Foot, and Mouth disease (HFMD) in China with a substantial disease burden. However, there is currently no commercial CVA6 vaccine. The D3a genotype of CVA6 is the predominant genotype in China. In this study, virus-like particles (VLPs) and mRNA vaccines based on the CVA6 sub-genotype D3a were successfully developed. The immunogenicity and protective effects of the VLP of CVA6 combined with Al(OH)3 and CpG adjuvant indicated that VLP-induced neutralizing antibodies against three CVA6 sub-genotype (D2, D3a, and D3b) strains in Institute of Cancer Research (ICR) mice, and the combination of the two adjuvants enhanced cellular immunity. Passive immunization with serum from mice immunized with VLPs protected suckling mice against CVA6 lethal challenge in both antiserum transfer and maternal immunization experiments. The immunogenicity and protective effects of the mRNA vaccine of CVA6 indicate that it induces robust T-cell immunity. T-cell immunity was found to cross-protect against coxsackievirus A10 infection in mice. This is the first trial of a CVA6 mRNA vaccine worldwide and the first comparison of the immunogenicity and protective effects of VLP and mRNA vaccines based on D3a CVA6. The study provides a theoretical basis for the development of enteroviruses vaccines and the formulation of immunization strategies.

Genetic Characteristics and Phylogenetic Analysis of Coxsackievirus A6 Isolated in Linyi, China, 2022-2023

Hand, foot, and mouth disease (HFMD) has become one of the most common infectious diseases in the past few decades. Since 2013, coxsackievirus A6 (CVA6) has replaced enterovirus A71 (EV-A71) and coxsackievirus A16 (CVA16), becoming the predominant pathogen responsible for HFMD in many areas of China. This study aimed to investigate the genetic characteristics and molecular epidemiology of CVA6 in Linyi between the years 2022 and 2023. In total, 965 patients with HFMD were enrolled in this study, and analyses based on VP1 nucleotide sequences were performed to determine the evolutionary trajectory of CVA6. In 2022, 281/386 (72.8%) patients were positive for enteroviruses (EVs) and 217/281 (77.2%) were CVA6 positive. In 2023, 398/579 (68.7%) samples were positive for EVs and 243/398 (61.1%) were CVA6 positive. Six sequences were selected each year for homology analysis. The results showed that the 12 strains isolated from Linyi were distant from the prototype strain (AY421764) and the first CVA6 strain reported in China (JQ364886). Phylogenetic analysis showed that the CVA6 strains isolated from Linyi belonged to the D3 sub-genotype. CVA6 is emerging as a common pathogen causing HFMD in Linyi and continuous surveillance of HFMD etiologies agents is necessary.

NLRP3 inflammasome activation contributes to acute liver injury caused by CVA6 infection in mice

BACKGROUND

Coxsackievirus (CV) A6 has emerged as an important causative agent in global outbreaks of hand, foot, and mouth disease (HFMD), which typically presents as a mild illness with a large generalized rash, herpes. However, some patients can develop encephalitis, pneumonia, myocarditis and liver injury. Our previous study took the view that CVA6 could replicate in mouse liver, leading to acute liver injury; however, the precise underlying mechanism remains elusive.

METHODS

10-day-old wild-type (WT, C57BL/6J) and NLRP3 knock-out (KO) mice were intraperitoneal (i.p.) inoculated with a lethal dose of the CVA6 strain. The muscle homogenate supernatant from normal mice was used to inoculate mock-infected mice. At 5 days post infection (dpi), the mouse liver was taken out for histopathological analyses and molecular biology experiments.

RESULTS

Our in vivo experiments demonstrated that CVA6 caused severe liver injury in mice, as evidenced by pathological changes in liver slices, elevated liver injury markers (e.g., AST, ALT, LDH) and pro-inflammatory cytokines (e.g., IL-6, MCP-1, TNF-α, IL-1β). Further results revealed the activation of NLRP3 inflammasome characterized by the increase in the expression of NLRP3, Cleaved-Casp-1 (p20), mature IL-1β and IL-18. Importantly, upon CVA6 infection, NLRP3 KO mice exhibited attenuated pathological damage and reduced levels of pro-inflammatory cytokines production (e.g., TNF-α and IL-1β) compared with WT mice. Finally, increased levels of blood ALT, AST, LDH were strongly correlated with the severity of CVA6 patients.

CONCLUSION

Collectively, our findings suggest that the activation of NLRP3 inflammasome is involved in CVA6 infection-induced acute liver injury, providing novel insights into CVA6 infection associated adverse clinical outcomes.

Molecular Evolutionary Dynamics of Coxsackievirus A6 Causing Hand, Foot, and Mouth Disease From 2021 to 2023 in China: Genomic Epidemiology Study

Background

Hand, foot, and mouth disease (HFMD) is a global public health concern, notably within the Asia-Pacific region. Recently, the primary pathogen causing HFMD outbreaks across numerous countries, including China, is coxsackievirus (CV) A6, one of the most prevalent enteroviruses in the world. It is a new variant that has undergone genetic recombination and evolution, which might not only induce modifications in the clinical manifestations of HFMD but also heighten its pathogenicity because of nucleotide mutation accumulation.

Objective

The study assessed the epidemiological characteristics of HFMD in China and characterized the molecular epidemiology of the major pathogen (CV-A6) causing HFMD. We attempted to establish the association between disease progression and viral genetic evolution through a molecular epidemiological study.

Methods

Surveillance data from the Chinese Center for Disease Control and Prevention from 2021 to 2023 were used to analyze the epidemiological seasons and peaks of HFMD in Henan, China, and capture the results of HFMD pathogen typing. We analyzed the evolutionary characteristics of all full-length CV-A6 sequences in the NCBI database and the isolated sequences in Henan. To characterize the molecular evolution of CV-A6, time-scaled tree and historical population dynamics regarding CV-A6 sequences were estimated. Additionally, we analyzed the isolated strains for mutated or missing amino acid sites compared to the prototype CV-A6 strain.

Results

The 2021-2023 epidemic seasons for HFMD in Henan usually lasted from June to August, with peaks around June and July. The monthly case reporting rate during the peak period ranged from 20.7% (4854/23,440) to 35% (12,135/34,706) of the total annual number of cases. Analysis of the pathogen composition of 2850 laboratory-confirmed cases identified 8 enterovirus serotypes, among which CV-A6 accounted for the highest proportion (652/2850, 22.88%). CV-A6 emerged as the major pathogen for HFMD in 2022 (203/732, 27.73%) and 2023 (262/708, 37.01%). We analyzed all CV-A6 full-length sequences in the NCBI database and the evolutionary features of viruses isolated in Henan. In China, the D3 subtype gradually appeared from 2011, and by 2019, all CV-A6 virus strains belonged to the D3 subtype. The VP1 sequences analyzed in Henan showed that its subtypes were consistent with the national subtypes. Furthermore, we analyzed the molecular evolutionary features of CV-A6 using Bayesian phylogeny and found that the most recent common ancestor of CV-A6 D3 dates back to 2006 in China, earlier than the 2011 HFMD outbreak. Moreover, the strains isolated in 2023 had mutations at several amino acid sites compared to the original strain.

Conclusions

The CV-A6 virus may have been introduced and circulating covertly within China prior to the large-scale HFMD outbreak. Our laboratory testing data confirmed the fluctuation and periodic patterns of CV-A6 prevalence. Our study provides valuable insights into understanding the evolutionary dynamics of CV-A6.

Detection of enteroviruses related to hand foot and mouth disease in wastewater of Asian communities

Hand, foot, and mouth disease (HFMD) is contagious and predominantly affects children below the age of five. HFMD-associated serotypes of Enterovirus A (EVA) family include EVA71, Coxsackievirus A type 6 (CVA6), 10 (CVA10), and 16 (CVA16). Although prevalent in numerous Asian countries, studies on HFMD-causing agents in wastewater are scarce. This study aimed to conduct wastewater surveillance in various Asian communities to detect and quantify serotypes of EVA associated with HFMD. In total, 77 wastewater samples were collected from Indonesia, the Philippines, Thailand, and Vietnam from March 2022 to February 2023. The detection ratio for CVA6 RNA in samples from Vietnam was 40 % (8/20). The detection ratio for CVA6 and EVA71 RNA each was 25 % (5/20) for the Indonesian samples, indicating the need for clinical surveillance of CVA6, as clinical reports have been limited. For the Philippines, 12 % (2/17) of the samples were positive for CVA6 and EVA71 RNA each, with only one quantifiable sample each. Samples from Thailand had a lower detection ratio (1/20) for CVA6 RNA, and the concentration was unquantifiable. Conversely, CVA10 and CVA16 RNAs were not detected in any of the samples. The minimum and maximum concentrations of CVA6 RNA were 2.7 and 3.9 log10 copies/L and those for EVA71 RNA were 2.5 and 4.9 log10 copies/L, respectively. This study underscores the importance of wastewater surveillance in understanding the epidemiology of HFMD-associated EVA serotypes in Asian communities. Long-term wastewater surveillance is recommended to monitor changes in dominant serotypes, understand seasonality, and develop effective prevention and control strategies for HFMD.

Emerging concerns of atypical hand foot and mouth disease caused by recombinant Coxsackievirus A6 variants in Henan, China

An increasing number of studies have reported that atypical hand, foot, and mouth disease (HFMD) is becoming a new concern for children's health. At present, there is no official definition for atypical HFMD, but some studies have defined that it occurs at anatomic sites not listed in the definition of HFMD issued by the World Health Organization. Several pathogens have been reported to cause atypical HFMD, such as Coxsackievirus (CV)A6. As one of the most prevalent enteroviruses in the world, CVA6 seems to affect a wider range of children and causes more severe and prolonged illness than other enteroviruses. The early lesions of atypical HFMD are very similar to the clinical presentations of other diseases, such as eczema, which poses a challenge for clinicians aiming to identify and diagnose HFMD in a timely manner. Here, we report on six atypical HFMD patients caused by recombinant CVA6 variants, and the atypical manifestations include eczema coxsackium, large herpes, rice-like red papules and herpes, purpuric rash, and onychomadesis, as well as and large red herpes on scalp, perianal, testicles, shoulders and neck, and other atypical eruption sites, hoping to draw the attention of other pediatricians. This study will provide scientific guidance for timely diagnosis of HFMD to prevent serious complications.