Genetic characteristics of human enterovirus 71 and coxsackievirus A16 circulating from 1999 to 2004 in Shenzhen, People's Republic of China

Non-neutralizing monoclonal antibody targeting VP2 EF loop of Coxsackievirus A16 can protect mice from lethal attack via Fc-dependent effector mechanism

Coxsackievirus A16 (CA16), a main causative agent of hand, foot, and mouth disease (HFMD), has become a serious public health concern in the Asia-Pacific region. Here, we generated an anti-CA16 monoclonal antibody, DMA2017, derived from an epidemic strain CA16. Surprisingly, although DMA2017 could not neutralize the original and circulating CA16 strains in vitro, the passive transfer of DMA2017 (10 μg/g) could protect suckling mice from a lethal challenge with CA16 in vivo. Then, we confirmed the protective effect of DMA2017 relies on the Fc-dependent effector functions, such as antibody-dependent cellular cytotoxicity (ADCC). The linear epitope of DMA2017 was mapped by phage display technique to a conserved patch spanning residues 143-148 (NSHPPY) of the VP2 EF-loop of CA16. DMA2017 could inhibit the binding of the antibodies present in the sera of naturally infected children to CA16, indicating that the epitope of DMA2017 is immunodominant for CA16. Our results confirm, for the first time, that a potential preventive and therapeutic effect could be mediated by a non-neutralizing antibody elicited against CA16. These findings bring a hitherto understudied protective role of non-neutralizing antibodies during viral infections into the spotlight and provide a new perspective on the design and evaluation of CA16 vaccines.

Recent advances in anti-coxsackievirus A16 viral drug research

Hand, foot and mouth disease, a childhood disorder caused by enteroviruses, is intermittently endemic in the Asia-Pacific region and endangers the lives of many infants and young children. Coxsackievirus A16 (CV-A16) is one of the major pathogens causing hand, foot, and mouth disease on occasion, resulting in catastrophic neurological sequelae and patient death. Currently, no clinical interventions are available that completely block the CV-A16 infection. Therefore, research on anti-CV-A16 treatment continues to be a significant focus of interest. This report provides a detailed background on and an introduction to CV-A16; a description of the viral gene and protein structures and a summary of the current advances in pharmaceutical targets, drug research and other related areas.

Clinical profile and molecular typing of viral etiological agents associated with Hand, Foot and Mouth Disease (HFMD): A study from Udhampur, Northern India

PURPOSE

Hand, Foot and Mouth disease (HFMD) is a contagious pediatric viral disease caused due to enteroviruses (EV) of the family Picornaviridae. Cases of HFMD were reported from a tertiary care health centre, Udhampur, (Jammu and Kashmir), Northern India. The present study highlights the clinical and molecular virological aspects of HFMD cases.

MATERIAL AND METHODS

Cases reported during August 2016-September 2017, and clinically diagnosed as HFMD of all age groups were included. Clinical, Biochemical and molecular virology aspects were compared. Clinical samples (n ​= ​50) such as vesicle swab, buccal and throat swabs were collected for enterovirus detection. EV-RNA was detected by 5'NCR based RT-PCR and genotyping by VP1 gene amplification and cycle sequencing.

RESULTS

Of the cases of HFMD enrolled (n ​= ​50), highest (84%) were of children aged <5 years, presented either or both anathemas and exanthemas with prodromal symptoms (fever, irritability). Clinical presentations involved mainly oral ulcers on lips and tongue (48%). Oral erosions were either single or multiple in numbers. Exanthemas were seen on hand and palm, widely spread up to buttocks, legs, arms and trunk. Of these, six patients were found anemic. Complete blood count (CBC) indicated lymphocytosis and C-reactive protein (n ​= ​10) in children aged <5 years. EV-RNA was detected in 78% (39/50) of the clinical samples. VP1 gene based typing indicated the presence of CV-A16, CVA6 and EV-A71 types.

CONCLUSIONS

The study highlights association of EVs in HFMD cases in the reported region. CV-A16, CV-A6 and EV-A71 types were reported for the first time from Udhampur (J&K), Northern India. No differences were observed in the clinical profile of EV strains detected. Circulation of the strains warrant and alarm outbreaks. More focused studies on HFMD and monitoring of viral strains is mandatory.

Effect of difference between EV-A71 virus epidemic strain and "vaccine strain" on neutralizing antibody titer

Hand, foot and mouth disease was mainly caused by EV-A71 virus. The main antigen structure of VP1 region of EV-A71 was easily varied. Here, we investigated the seroprevalence of EV-A71 based on a large group of healthy individuals in Beijing, China, in order to study the effectiveness of EV-A71 vaccine in a real-world setting. BrCr and the clinical strain isolated from the Chinese mainland in 2008 ("vaccine strain:"CMU4232/BJ/CHN/2008), EV-A71 C4 epidemic strains isolated in 2010, 2013, and 2016, were tested for neutralizing antibodies (NtAb) in every year. Phylogenetic tree analysis of the EV-A71 strains above, as well as amino acid composition homologous sequence analysis were applied. The "vaccine strain" has 83.0% homology with FY23, H07 and FY7VP5. It belongs to the same branch of C4a as 10 C4, 13 C4 and 16 C4, and differs from the amino acid sites 283 and 293 of 16 C4. Compared with "vaccine strains," there was a significant difference between the 50-59 years old age group when the NtAb titer of 16 C4 strain was 1:512-1:1024. Our results suggest that changes in the functional epitopes of NtAb caused by amino acid 283 and 293 loci in EV-A71 strains may affect the production of neutralizing antibodies.

Epidemiology of hand, foot, and mouth disease and the genetic characteristics of Coxsackievirus A16 in Taiyuan, Shanxi, China from 2010 to 2021

Hand, foot, and mouth disease (HFMD) is a common childhood infectious disease caused by human enteroviruses (EV). This study aimed to describe the epidemiological features of HFMD and the genetic characteristics of Coxsackievirus A16 (CVA16) in Taiyuan, Shanxi, China, from 2010 to 2021. Descriptive epidemiological methods were used to analyze the time and population distribution of HFMD and the genetic characteristics of CVA16. Except being affected by the COVID-19 epidemic in 2020, HFMD epidemics were sporadic from January to March each year, and began to increase in April, with a major epidemic peak from May to August, which declined in September, followed by a secondary peak from October to December. The prevalence of EV infection was the highest in children aged one to five years (84.42%), whereas its incidence was very low in children under one year of age (5.48%). Enterovirus nucleic acid was detected by real-time reverse transcription polymerase chain reaction in 6641 clinical specimens collected from patients with HFMD from 2010 to 2021, and 4236 EV-positive specimens were detected, including 988 enterovirus A71 (EV-A71), 1488 CVA16, and 1760 other enteroviruses. CVA16 remains prevalent and has co-circulated with other EVs in Taiyuan from 2010 to 2021. A phylogenetic tree constructed based on the VP1 region showed that all CVA16 strains belonged to two different clades of the B1 genotype, B1a and B1b. They showed a nucleotide similarity of 86.5-100%, and an amino acid similarity of 96.9-100%. Overall, these findings add to the global genetic resources of CVA16, demonstrate the epidemiological characteristics of HFMD as well as the genetic features of CVA16 in Taiyuan City during 2010-2021, and provide supporting evidence for the prevention and control of HFMD.

Genetic and Cross Neutralization Analyses of Coxsackievirus A16 Circulating in Taiwan from 1998 to 2021 Suggest Dominant Genotype B1 can Serve as Vaccine Candidate

Coxsackievirus A16 (CVA16) is well known for causing hand-foot-and-mouth disease (HFMD) and outbreaks were frequently reported in Taiwan in the past twenty years. The epidemiology and genetic variations of CVA16 in Taiwan from 1998 to 2021 were analyzed in this study. CVA16 infections usually occurred in early summer and early winter, and showed increased incidence in 1998, 2000-2003, 2005, 2007-2008, and 2010 in Taiwan. Little or no CVA16 was detected from 2017 to 2021. CVA16 infection was prevalent in patients between 1 to 3 years old. A total of 69 isolates were sequenced. Phylogenetic analysis based on the VP1 region showed that CVA16 subgenotype B1 was dominantly isolated in Taiwan from 1998 to 2019, and B2 was identified only from isolates collected in 1999 and 2000. There was a high frequency of synonymous mutations in the amino acid sequences of the VP1 region among CVA16 isolates, with the exception of position 145 which showed positive selection. The recombination analysis of the whole genome of CVA16 isolates indicated that the 5'-untranslated region and the non-structural protein region of CVA16 subgenotype B1 were recombined with Coxsackievirus A4 (CVA4) and enterovirus A71 (EVA71) genotype A, respectively. The recombination pattern of subgenotype B2 was similar to B1, however, the 3D region was similar to EVA71 genotype B. Cross-neutralization among CVA16 showed that mouse antisera from various subgenotypes viruses can cross-neutralize different genotype with high neutralizing antibody titers. These results suggest that the dominant CVA16 genotype B1 can serve as a vaccine candidate for CVA16.

Prototypes virus of hand, foot and mouth disease infections and severe cases in Gansu, China: a spatial and temporal analysis

Background

Little research has been conducted on the spatio-temporal relationship between the severe cases and the enteroviruses infections of hand, foot and mouth disease (HFMD). This study aimed to investigate epidemic features and spatial clusters of HFMD incidence rates and assess the relationship between Enterovirus 71 (EV71) and Coxsackievirus A16 (CoxA16) and severe cases of HMFD in Gansu province, China.

Methods

Weekly county-specific data on HFMD between 1st January and 31st December 2018 were collected from the China Infectious Disease Information System (CIDIS), including enterovirus type (EV71 and CoxA16), severe and non-severe cases in Gansu province, China. Temporal risk [frequency index (α), duration index (β) and intensity index (γ)] and spatial cluster analysis were used to assess epidemic features and identify high-risk areas for HFMD. Time-series cross-correlation function and regression model were used to explore the relationship between the ratios of two types of viruses (i.e. EV71/Cox16) (EC) and severe cases index (i.e. severe cases/non-severe cases) (SI) of HFMD.

Results

Some counties in Dingxi City, Gansu were identified as a hot spot for the temporal risk indices. Time-series cross-correlation analysis showed that SI was significantly associated with EC (r = 0.417, P < 0.05) over a 4-week time lag. The regression analysis showed that SI was positively associated with EC (β = 0.04, 95% confidence interval (CI) 0.02–0.06).

Conclusion

The spatial patterns of HFMD incidence were associated with enteroviruses in Gansu. The research suggested that the EC could be considered a potential early warning sign for predicting severe cases of HFMD in Gansu province.

Consolidating the potency of Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) in viral diagnosis: extrapolating its applicability for COVID diagnosis?

MALDI-TOF-MS has essentially delivered more than expected with respect to clinical pathogens. Viruses are the most versatile entities of clinical pathogens that have challenged well-established microbiological methodologies. This review evaluates the existing scenario with respect to MALDI TOF-MS analytical technique in the successful analysis of viral pathogens. The milestones achieved with respect to detection and identification of COVID-19 has been presented. The fact that only a handful of scattered applications for COVID-19 exist has been pointed out in the review. Further, the lapses in the utilization of the available state-of-the art MALDI-TOF-MS variants/benchmark sophistications for COVID-19 analysis, are highlighted. When the world is seeking for rapid solutions for early, sensitive, rapid COVID-19 diagnosis, maybe MALDI-TOF-MS, may be the actual ‘gold standard’. Reverting to the title, this review emphasizes that there is a need for extrapolating MALDI-TOF-MS for COVID-19 analysis and this calls for urgent scientific attention.

Coxsackievirus B4 sewage-isolate induces pancreatitis after oral infection of mice

Numerous serotypes which belong to the genus Enterovirus (EV) show variability in their virulence and clinical manifestations. They are also known to undergo changes caused by mutations and recombination during their circulation in the environment and the population. Various EV serotypes are prevalent in groundwater, wastewater and surface waters. Our previous studies showed that oral infection induces pancreatitis depending on specific conditions, such as gravidity, in an outbred murine model. Our aim in the present study was to further explore the pancreatic histopathology in an outbred mouse model following oral infection with clinical isolates from a patient who had aseptic meningitis and an isolate from a treated-sewage sample recovered from the residential area of the patient. The isolates were identified as coxsackievirus B4 (CVB4) in tissue culture. The CVB4 sewage-isolate induced pancreatitis after oral infection. In contrast, pancreatitis was absent following infection with the clinical isolates. Comparison of polyprotein sequences showed that the treated-sewage strains differed from the patient's isolates by 9 and 11 amino acids. We conclude that the isolates of clinical and environmental origin differed in their pathogenic properties and showed genetic variation.

Continuous detection of norovirus and astrovirus in wastewater in a coastal city of China in 2014-2016

Norovirus (NoV) and human astrovirus (HAstV) are important causative agents of acute gastroenteritis in children and adults. They are comprised of multiple genotypes and attention should be paid to genotype changes or emergence of new genetic variants. To study the prevalence and diversity of NoV GI, GII, and HAstV circulating in eastern China, we conducted a three-year environmental surveillance in a coastal city of Yantai. Thirty-six sewage samples were collected, processed, and examined for the presence of viral genomes by PCR. The results showed that NoV GI, GII, and HAstV were detected in all 36 samples. Six NoV GI genotypes, 11 NoV GII genotypes, and 5 HAstV serotypes were identified; GI.6, GII.17, and HAstV-5 were the most prevalent types, respectively. Persistent existence of NoV GII.17 Kawasaki 308 variant was observed during whole study period. Phylogenetic analysis reflected multiple transmission lineages in local population for both viruses. Our results reflect continuous presence of enteric viruses in sewage, improve our understanding on their molecular epidemiology, and demonstrate surveillance on sewage is an effective approach in understanding the local circulation of enteric viruses.

Optimization of Vero Cells Grown on a Polymer Fiber Carrier in a Disposable Bioreactor for Inactivated Coxsackievirus A16 Vaccine Development

At present, there are no vaccines available for hand, foot, and mouth disease, which is caused by Coxsackie virus A16 (CVA16) infection. In the present study, we isolated epidemic strains of CVA16 and optimized the production of the virus in Vero cells. The system comprised growing the infected cells on polymer fiber paper carriers in a serum-free medium containing 0.5% (w/v) lactalbumin hydrolysate a mini bioreactor. Disposable Bioflo310 and AmProtein Current perfusion bioreactors were used to monitor virus infection and Vero cell culture. The total number of cells increased from 1.5 × 10⁹ to 3.0 × 10¹⁰. In our optimized culture process, the virus titer reached 7.8 × 10⁷ TCID₅₀/mL at three days after infection. The inactivated CVA16 prepared from our optimized culture procedure elicited a slightly higher neutralizing antibody titer compared with that derived from routine culture procedures. These results will promote the large-scale production of inactivated CVA16 vaccines using nonwoven polymer fiber paper cell cultures.

Molecular epidemiology of enteroviruses associated with severe hand, foot and mouth disease in Shenzhen, China, 2014-2018

In this study, we investigated the epidemiology and molecular characteristics of enteroviruses associated with severe hand, foot and mouth disease (HFMD) in Shenzhen, China, during 2014-2018. A total of 137 fecal specimens from patients with severe HFMD were collected. Enterovirus (EV) types were determined using real-time reverse transcription polymerase chain reaction (RT-PCR), RT nested PCR, and sequencing. Sequences were analyzed using bioinformatics programs. Of 137 specimens tested, 97 (70.8%), 12 (8.8%), and 10 (7.3%) were positive for EV-A71, coxsackievirus A6 (CVA6), and CVA16, respectively. Other pathogens detected included CVA2 (2.9%, 4/137), CVA10 (2.9%, 4/137), CVA5 (0.7%, 1/137), echovirus 6 (E6) (0.7%, 1/137) and E18 (0.7%, 1/137). The most frequent complication in patients with proven EV infections was myoclonic jerk, followed by aseptic encephalitis, tachypnea, and vomiting. The frequencies of vomiting and abnormal eye movements were higher in EV-A71-infected patients than that in CVA6-infected or CVA16-infected patients. Molecular phylogeny based on the complete VP1 gene revealed no association between the subgenotype of the virus and disease severity. Nevertheless, 12 significant mutations that were likely to be associated with virulence or the clinical phenotype were observed in the 5’UTR, 2A^pro, 2C, 3A, 3D^pol and 3’UTR of CVA6. Eight significant mutations were observed in the 5’UTR, 2B, 3A, 3D^pol and 3’UTR of CVA16, and 10 significant mutations were observed in the 5’UTR, VP1, 3A and 3C^pro of CVA10. In conclusion, EV-A71 is still the main pathogen causing severe HFMD, although other EV types can also cause severe complications. Potential virulence or phenotype-associated sites were identified in the genomes of CVA6, CVA16, and CVA10.

National Epidemiology and Evolutionary History of Four Hand, Foot and Mouth Disease-Related Enteroviruses in China from 2008 to 2016

Hand, foot and mouth disease (HFMD) is a major public health concern in China. The most predominant enteroviruses that cause HFMD have traditionally been attributed to enterovirus A71 (EVA71) and coxsackievirus A16 (CVA16). Since its first large outbreak in 2008, the dominant HFMD pathogens are constantly changing. In 2013 and 2015, CVA6 exceeded both EVA71 and CVA16 to become the leading cause of HFMD in some provinces. However, there still lacks a comprehensive overview on the molecular epidemiology and evolution of HFMD-related enteroviruses at the national level. In this study, we performed systematic epidemiological analyses of HFMD-related enteroviruses using the data of 64 published papers that met the inclusion criteria, and conducted phylogenetic analyses based on 12,080 partial VP1 sequences identified in China before 31st June 2018. We found that EVA71 prevalence has decreased sharply but other enteroviruses have increased rapidly from 2008 to 2016 and that one subtype of each enterovirus is represented during the epidemic. In addition, four genotypes EVA71_C4, CVA16_B1, CVA6_D and CVA10_C are the most predominant enterovirus strains and collectively they cause over 90% of all HFMD cases in China according to the phylogenetic trees using representative partial VP1 sequences. These four major enterovirus genotypes have different geographical distributions, and they may co-circulate with other genotypes and serotypes. These results suggest that more molecular epidemiological studies should be performed on several enteroviruses simultaneously, and such information should have implications for virological surveillance, disease management, vaccine development and policy-making on the prevention and control of HFMD.

An adult gerbil model for evaluating potential coxsackievirus A16 vaccine candidates

A suitable animal model of CVA16 infection is crucial in order to understand its pathogenesis and to help develop antiviral vaccines or screen therapeutic drugs. The neonatal mouse model has a short sensitivity period to CA16 infection, which is a major limitation. In this study, we demonstrate that adult (60-day-old) gerbils are susceptible to CVA16 infection at high doses (10^8.0 TCID₅₀). A clinical isolate strain of CVA16 was inoculated intraperitoneally into adult gerbils, which subsequently developed significant clinical symptoms, including hind limb weakness, paralysis of one or both hind limbs, tremors, and eventual death from neurological disorders. Real-time RT-PCR revealed that viral loads in the spinal cord and brainstem were higher than those in other organs/tissues. Histopathological changes, such as neuronal degeneration, neuronal loss, and neuronophagia, were observed in the spinal cord, brainstem, and heart muscle, along with necrotizing myositis. Gerbils receiving both prime and boost immunizations of alum adjuvant inactivated vaccine exhibited no clinical signs of disease or mortality following challenge by CVA16, whereas 80% of control animals showed obvious clinical signs, including slowness, paralysis of one or both hind limbs, and eventual death, suggesting that the CVA16 vaccine can fully protect gerbils against CVA16 challenge. These results demonstrate that an adult gerbil model provides us with a useful tool for studying the pathogenesis and evaluating antiviral reagents of CVA16 infection. The development of this animal model would also be conducive to screening promising CVA16 vaccine candidates as well as further vaccination evaluation.

Manassantin B shows antiviral activity against coxsackievirus B3 infection by activation of the STING/TBK-1/IRF3 signalling pathway

Coxsackievirus B3 (CVB3) is an important human pathogen associated with the development of acute pancreatitis, myocarditis, and type 1 diabetes. Currently, no vaccines or antiviral therapeutics are approved for the prevention and treatment of CVB3 infection. We found that Saururus chinensis Baill extract showed critical antiviral activity against CVB3 infection in vitro. Further, manassantin B inhibited replication of CVB3 and suppressed CVB3 VP1 protein expression in vitro. Additionally, oral administration of manassantin B in mice attenuated CVB3 infection-associated symptoms by reducing systemic production of inflammatory cytokines and chemokines including TNF-α, IL-6, IFN-γ, CCL2, and CXCL-1. We found that the antiviral activity of manassantin B is associated with increased levels of mitochondrial ROS (mROS). Inhibition of mROS generation attenuated the antiviral activity of manassantin B in vitro. Interestingly, we found that manassantin B also induced cytosolic release of mitochondrial DNA based on cytochrome C oxidase DNA levels. We further confirmed that STING and IRF-3 expression and STING and TBK-1 phosphorylation were increased by manassantin B treatment in CVB3-infected cells. Collectively, these results suggest that manassantin B exerts antiviral activity against CVB3 through activation of the STING/TKB-1/IRF3 antiviral pathway and increased production of mROS.

A potential therapeutic neutralization monoclonal antibody specifically against multi-coxsackievirus A16 strains challenge

Coxsackievirus A16 (CA16) has caused worldwide epidemics of hand, foot and mouth disease (HFMD), particularly in infants and pre-school children. Currently, there are no vaccines or antiviral drugs available for CA16-associated disease. In this study, a CA16-specific monoclonal antibody (MAb) NA11F12 was derived with an epidemic CA16 strain (GenBank no. JX127258). NA11F12 was found to have high cross-neutralization activity against different CA16 subgenotypes but not EV71 using RD cells. The neutralizing titers of NA11F12 ranged from 1:1024 to 1:12288 against A, B1, B2 and C subgenotypes of CA16 and was less than 8 against EV71 strain. In the neonatal mouse model, a single treatment of NA11F12 showed effective protection with a dose- and time-dependent relationship against lethal challenge by CA16 strain (GenBank no. JX481738). At day 1 post-infection, administering more than 0.1 μg/g of NA11F12 could protect 100% newborn mice from mobility and mortality challenged by CA16. With dose of 10 μg/g of NA11F12, a single administration fully protected mice against CA16-associated disease within 4 days post-infection. And there were 80% and 60% mice protected by administering NA11F12 at day 5 post-infection and day 6 post-infection when the control mice had shown clinical symptoms for 1- and 2-day, respectively. Immunohistochemical and histological analysis confirmed that NA11F12 significantly prohibited CA16 VP1 expression in various tissues and prevented CA16-induced necrosis. In conclusion, a CA16-specific MAb NA11F12 with high cross-neutralization activity was identified, which could effectively protect lethal CA16 challenge in mice. It could be a potential therapeutic MAb against CA16 in the future.

The application of meteorological data and search index data in improving the prediction of HFMD: A study of two cities in Guangdong Province, China

Hand, foot and mouth disease (HFMD) is a public health issue in China, and its incidence in Guangdong Province is higher than the national average. Previous studies have found climatic factors have an influential role in the transmission of HFMD. Internet search technology has been shown to predict some infectious disease epidemics and is a potential resource in tracking epidemics in countries where the use of Internet search index data is prevalent. This study aims to improve the prediction of HFMD in two Chinese cities, Shantou and Shenzhen in Guangdong Province, applying both meteorological data and Baidu search indices to create a HFMD forecasting model. To this end, the relationship between meteorological factors and HFMD was found to be linear in both cities, while the relationship between search engine data and HFMD was not consistent. The results of our study suggest that using both Internet search and meteorological data can improve the prediction of HFMD incidence. Using comparative analysis of both cities, we posit that improved quality search indices enhance prediction of HFMD.

Predicting Intraserotypic Recombination in Enterovirus 71

Enteroviruses are well known for their ability to cause neurological damage and paralysis. The model enterovirus is poliovirus (PV), the causative agent of poliomyelitis, a condition characterized by acute flaccid paralysis. A related virus, enterovirus 71 (EV-A71), causes similar clinical outcomes in recurrent outbreaks throughout Asia. Retrospective phylogenetic analysis has shown that recombination between circulating strains of EV-A71 produces the outbreak-associated strains which exhibit increased virulence and/or transmissibility. While studies on the mechanism(s) of recombination in PV are ongoing in several laboratories, little is known about factors that influence recombination in EV-A71. We have developed a cell-based assay to study recombination of EV-A71 based upon previously reported assays for poliovirus recombination. Our results show that (i) EV-A71 strain type and RNA sequence diversity impacts recombination frequency in a predictable manner that mimics the observations found in nature; (ii) recombination is primarily a replicative process mediated by the RNA-dependent RNA polymerase; (iii) a mutation shown to reduce recombination in PV (L420A) similarly reduces EV-A71 recombination, suggesting conservation in mechanism(s); and (iv) sequencing of intraserotypic recombinant genomes indicates that template switching occurs by a mechanism that may require some sequence homology at the recombination junction and that the triggers for template switching may be sequence independent. The development of this recombination assay will permit further investigation on the interplay between replication, recombination and disease.IMPORTANCE Recombination is a mechanism that contributes to genetic diversity. We describe the first assay to study EV-A71 recombination. Results from this assay mimic what is observed in nature and can be used by others to predict future recombination events within the enterovirus species A group. In addition, our results highlight the central role played by the viral RNA-dependent RNA polymerase (RdRp) in the recombination process. Further, our results show that changes to a conserved residue in the RdRp from different species groups have a similar impact on viable recombinant virus yields, which is indicative of conservation in mechanism.

The mature EV71 virion induced a broadly cross-neutralizing VP1 antibody against subtypes of the EV71 virus

Enterovirus 71 (EV71) has emerged as a neurological virus causing life-threatening diseases in young children and infants. Although EV71 vaccines in development have presented promising results in several clinical trials, the identified key antigen for improving the broad protective efficacy of EV71 vaccines has not been well investigated. In this report, we show that different multiplicities of infection (MOIs) of the B4(E59) virus significantly affect EV71 vaccine production in a serum-free microcarrier bioreactor system. The antigens produced from high MOIs of 10⁻¹ and 10⁻² exhibited higher yield and more infectious full particle (FP) contents in the EV71 vaccines than those produced with low MOIs of 10⁻⁴ and 10⁻⁶, leading to better cross-neutralizing efficacy. The C4(E36) neutralization results showed that only antisera raised from EV71 FPs provided substantial neutralizing titers against C4(E36), whereas empty particles (EPs) of EV71 conferred no efficacy. Competitive ELISA showed that anti-FP mainly binds to FPs and that 20% of antibodies bind to EPs, whereas most anti-EP binds EPs, with only 10% antibodies binding to FPs. VP1-adsorbed anti-FP lost most of the virus neutralization efficiency, suggesting that the VP1 subunit of FP is the major immunogenic antigen determining the ability of the EV71 vaccine to elicit cross-neutralizing antibodies against EV71 virus subtypes. These findings demonstrate that the high-MOI production approach is significantly correlated with FP productivity, thereby improving the cross-neutralization efficacy of an EV71 vaccine and providing the basis for a better vaccine design against widespread EV71 viruses.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Spiramycin and azithromycin, safe for administration to children, exert antiviral activity against enterovirus A71 in vitro and in vivo

Hand-foot-mouth disease (HFMD) is a common viral disease in young children, mainly caused by enterovirus A71 (EV-A71) and coxsackievirus A16 (CV-A16). Specific antiviral agents are not commercially available yet. Here we report that the macrolide antibiotics spiramycin (SPM) and azithromycin (AZM) possess antiviral activities against EV-A71 and CV-A16. SPM significantly reduced EV-A71 RNA and protein levels, most likely through interfering with viral RNA replication. The SPM-resistant EV-A71 variants showed similar resistance to AZM, indicating a similar anti-EV-A71 mechanism by which these two drugs exert their functions. The mutations of these variants were reproducibly mapped to VP1 and 2A, which were confirmed to confer resistance to SPM. Animal experiments showed that AZM possesses stronger anti-infection efficacy than SPM, greatly alleviated the disease symptoms and increased the survival rate in a mouse model severely infected with EV-A71. In all, our work suggests that AZM is a potential treatment option for EV-A71-induced HFMD, whose proved safety for infants and children makes it even more promising.

Complete genome analysis demonstrates multiple introductions of enterovirus 71 and coxsackievirus A16 recombinant strains into Thailand during the past decade

Hand, foot, and mouth disease (HFMD) caused by enteroviruses remains a public health threat, particularly in the Asia-Pacific region during the past two decades. Moreover, the introduction of multiple subgenotypes and the emergence of recombinant viruses is of epidemiological importance. Based on either the full genome or VP1 sequences, 32 enteroviruses (30 from HFMD patients, 1 from an encephalitic patient, and 1 from an asymptomatic contact case) isolated in Thailand between 2006 and 2014 were identified as 25 enterovirus 71 (EV71) isolates (comprising 20 B5, 1 C2, 2 C4a, and 2 C4b subgenotypes) and 7 coxsackievirus A16 (CA16) isolates (comprising 6 B1a and 1 B1b subgenotypes). The EV71 subgenotype C4b was introduced into Thailand for the first time in 2006 and was replaced by subgenotype C4a strains in 2009. Phylogenetic, similarity plot and bootscan analyses of the complete viral genomes identified 12 recombinant viruses among the 32 viral isolates. Only one EV71-B5 isolate out of 20 was a recombinant virus with one region of intratypic or intertypic recombination, while all four EV71-C4 isolates were recombinant viruses having undergone double recombination, and all seven CA16 isolates were recombinant viruses. The recombination breakpoints of these recombinants are located solely within the P2 and P3 regions. Surveillance for circulating strains and subgenotype replacement are important with respect to molecular epidemiology and the selection of the upcoming EV71 vaccine. In addition, the clinical importance of recombinant viruses needs to be further explored.

Hand, foot and mouth disease and herpangina caused by enterovirus A71 infections: a review of enterovirus A71 molecular epidemiology, pathogenesis, and current vaccine development

Enterovirus A71 (EV-A71) infections are one of the main etiological agents of hand, foot and mouth disease (HFMD) and herpangina worldwide. EV-A71 infection is a life-threatening communicable disease and there is an urgent global need for the development of vaccines for its prevention and control. The morbidity rate of EV-A71 infection differs between countries. The pathogen’s genetic lineages are undergoing rapid evolutionary changes. An association between the occurrence of EV-A71 infection and the circulation of different genetic strains of EV-A71 virus has been identified around the world. In this review, we present and discuss the molecular epidemiology and pathogenesis of the human disease caused by EV-A71 infection, as well as current prospects for the development of an EV-A71 vaccine.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Epidemiological characteristics and influential factors of hand, foot, and mouth disease reinfection in Wuxi, China, 2008-2016

Background

Hand, foot, and mouth disease (HFMD) is a viral disease caused by human enteroviruses. Although HFMD reinfection is common, studies investigating this phenomenon are insufficient.

Methods

The present study focused on HFMD reinfection in Wuxi from 2008 to 2016 using surveillance system data.

Results

Of 107,677 cases included in the study, 6470 cases were classified as reinfections. The overall reinfection rate was 6.01% (6.37% male and 5.48% female patients), which decreased with increasing age (χ² = 1125.477, p < 0.001). The rate was 6.17 and 5.79% in urban and rural areas, respectively, and 7.83 and 5.98% of the cases were severe and mild, respectively. Multivariate logistic regression analysis showed that male sex, younger age, residence in an urban area, and severe disease were risk factors for HFMD reinfection. The case-severity rate in secondary infection cases was lower than that in non-reinfection cases (odds ratio 0.675, 95% confidence interval 0.526–0.866).

Conclusions

Boys younger than 4 years of age living in urban areas were more prone to reinfection. Specific health education and intervention should be developed to protect these susceptible populations.

Genetic characteristics of the P1 coding region of Coxsackievirus A16 associated with hand, foot, and mouth disease in China

Coxsackievirus A16 (CVA16) is one of the major etiological agents of hand, foot, and mouth disease (HFMD) in young children. To investigate the genetic characteristics of the P1 coding region gene of CVA16 associated with HFMD in China, we included the sequences of CVA16 specimens obtained from outbreak investigations and sporadic HFMD cases between 1998 and 2014 in China from GenBank, we genotyped the CVA16 sequences and analyzed P1 coding region sequences that encode structural proteins with bioinformatics software. CVA16 was classified into genotypes A and B1 based on the VP1 gene; the B1b and B1a subgenotypes were the major CVA16 strains and predominated in the coastal areas of China. Four strains were found to show inter- and intra-typic recombination in the P1 region. The amino acid identities of VP1, VP2, VP3, and VP4 proteins in all Chinese CVA16 strains were 88.2-100%, 83.0-100%, 87.6-100%, and 72.4-100%, respectively. A total of 251 amino acid substitution sites were detected in the structural proteins encoded by the P1 coding region gene. The amino acid sequences of the P1 coding region in Chinese CVA16 strains were highly conserved, although some amino acid mutations occurred with high frequency: VP1-T11A (10%), N14S (14%), L23M/V (11%), T98M (16%), V107A (14%), N102D (6.1%), E145V (8.8%), N218D (10%), E241K (22%), T248A/I (6.8%); VP2-I217V (22%), T226A (38%); VP3-N141S/G (5.4%), and N240D (15%). The genetic characteristics of CVA16 in the P1 coding region gene may provide a basis for developing a CVA16 vaccine and preventing and controlling HFMD in China.

Epidemiology Characteristics of Human Coxsackievirus A16 and Enterovirus 71 Circulating in Linyi, China, from 2009 to 2017

In China, a rapid expansion of hand, foot, and mouth disease (HFMD) outbreaks has occurred since 2004, and HFMD has become an important issue in China. There are more than 20 types of enterovirus causing HFMD, of which coxsackievirus A16 (CA16) and enterovirus 71 (EV71) are the most common. This study aimed to analyze the epidemiological characteristics of HFMD caused by EV71 and CA16 in Linyi, Shandong province, China, from 2009 to 2017. The stool specimens and throat samples of 5,324 patients with HFMD were obtained for nucleic acid detection of enterovirus. A total of 4,040 HFMD cases were caused by viral pathogens. Of these, 1,706 cases were positive for EV71 and 1,266 were positive for CA16. These 2 virus strains appeared alternately in Linyi city. The incidence of EV71-positive and CA16-positive cases was highest in children aged 0-5 years, with male patients being predominant. This outbreak of HMFD caused by EV71 and CA16 mainly occurred between April and July and appeared alternately between the years 2011 and 2017. These results demonstrated that the epidemiological analysis of EV71 and CA16 can provide a scientific basis for the prevention and treatment of the disease.

A neonatal murine model for evaluation of enterovirus E HY12 virus infection and pathogenicity

Backgrounds

HY12 viruses are enteroviruses recently isolated from cattle characterized by severe respiratory and digestive disease with high morbidity and mortality in China. While the viruses exhibit unique biological and molecular characters distinct from known enterovirus E, the pathogenicity and viral pathogenesis remains largely unknown.

Methods

Neonatal mice of Balb/C, ICR, and Kunming strain are infected with HY12 to determine the susceptible mouse strain. The minimal infection dose, the virus infection routes, the pathogenicity and tissue tropism for HY12 were determined by infecting susceptible mice with HY12 viruses, and confirmed by different approaches including virus isolation and recovery, virus detection, histopathology, and immunohistochemistry.

Results

A murine model for HY12 infection was successfully established and employed to investigate the pathogenicity of HY12 viruses. ICR mouse strain is the most susceptible strain for HY12 infection with a minimal infective dose as 2×10⁶TCID₅₀/mouse. HY12 viruses have the capability of infecting ICR suckling mice via all infection routes including intranasal administration, oral administration, intraperitoneal injection, subcutaneous injection, and intramuscular injection, which are confirmed by the isolation and recovery of viruses from HY12-infected mice; detection of viruses by RT-PCR; observations of pathological lesions and inflammatory cell infiltrations in the intestine, lung, liver, and brain; uncovering of HY12 virus antigens in majority of tissues, especially in intestine, lung, and infected brain of mice by immunohistochemistry assay.

Conclusions

A neonatal murine model for HY12 infection is successfully established for determining the susceptible mouse strain, the minimal infective dose, the infection route, the viral pathogenicity and the tropism of HY12, thus providing an invaluable model system for elucidating the pathogenesis of HY12 viruses and the elicited immunity.

Risk factors for death in children with critical and severe hand-foot-and-mouth disease in Chongqing, China: An observational study

Hand-foot-and-mouth disease (HFMD) is a common childhood infection that may lead to serious complications and even death. Globally, epidemics of HFMD are increasing each year, especially in China. This study aimed to identify risk factors for death in children with critical and severe HFMD in Chongqing, China.We performed an observational study involving patients with critical and severe HFMD admitted to the Children's Hospital of Chongqing Medical University from January 2009 to December 2016. Overall, 179 patients aged 2 months to 16 years, were included; 127 died (non-survival group) and 52 survived (survival group); the case-fatality rate was 70.94%. Data comprising demographic characteristics, clinical symptoms and signs, and laboratory findings were collected. Non-conditional logistic regression analysis was performed to determine the risk factors for death.Univariate analysis showed that sex, coma, light-reflex insensitivity, pulmonary rales, pulmonary edema or hemorrhage, cold extremities, tachycardia, hypotension, white blood cell count, blood glucose concentration, serum lactate level, creatine kinase-MB isoenzyme level, and acidosis were associated with death (P < .05). Logistic regression analysis identified female sex (odds ratio [OR] 9.6, 95% confidence interval [CI] 3.0-30.2), light-reflex insensitivity (OR 4.4, 95% CI 1.4-13.1), tachycardia (OR 1.05, 95% CI 1.03-1.07), and higher serum lactate levels (OR 1.14, 95% CI 1.19-1.69) as independent risk factors; and longer onset-to-hospitalization time (OR 0.43, 95% CI 0.28-0.66) as an independent protective factor for death in children with critical and severe HFMD.Female sex, light-reflex insensitivity, tachycardia, and higher serum lactate level are potential independent risk factors; and longer onset-to-hospitalization time is possibly an independent protective factor for death in patients with critical and severe HFMD.

A mutation-resistant deoxyribozyme OR gate for highly selective detection of viral nucleic acids

Highly selective probes hybridize only to fully complementary DNA or RNA sequences and, therefore, often fail to recognize mutated viral genomes. Here we designed a probe that possesses two seemingly incompatible properties: it tolerates some point mutations in genome, while it remains selective towards others. An OR deoxyribozyme logic gate was designed to fluorescently report the sequences of enterovirus 71 (EV71) covering ∼90% of all known EV71 strains. Importantly, sequences of closely related coxsackieviruses that differed by single nucleotides were reliably differentiated in 7 out of 8 cases.

Phylogeography of Coxsackievirus A16 Reveals Global Transmission Pathways and Recent Emergence and Spread of a Recombinant Genogroup

Coxsackievirus A16 (CV-A16; Picornaviridae) is an enterovirus (EV) type associated with hand, foot, and mouth disease (HFMD) in children. To investigate the spatial spread of CV-A16, we used viral sequence data sampled during a prospective sentinel surveillance of HFMD in France (2010 to 2014) and phylogenetic reconstruction. A data set of 168 VP1 sequences was assembled with 416 publicly available sequences of various geographic origins. The CV-A16 sequences reported were assigned to two clades, genogroup B and a previously uncharacterized clade D. The time origins of clades B and D were assessed in 1978 (1973 to 1981) and 2004 (2001 to 2007), respectively. The shape of the global CV-A16 phylogeny indicated worldwide cocirculation of genetically distinct virus lineages over time and across geographic regions. Phylogenetic tree topologies and Bayes factor analysis indicated virus migration. Virus transportation events in clade B within Europe and Asia and between countries of the two geographic regions were assessed. The sustained transmission of clade D viruses over 4 years was analyzed at the township level in France and traced back to Peru in South America. Comparative genomics provided evidence of recombination between CV-A16 clades B and D and suggested an intertype recombinant origin for clade D. Time-resolved phylogenies and HFMD surveillance data indicated that CV-A16 persistence is sustained by continuing virus migration at different geographic scales, from community transmission to virus transportation between distant countries. The results showed a significant impact of virus movements on the epidemiological dynamics of HFMD that could have implications for disease prevention.IMPORTANCE Coxsackievirus A16 is one of the most prevalent enterovirus types in hand, foot, and mouth disease outbreaks reported in Southeast Asia. This study is based on epidemiological and viral data on HFMD caused by CV-A16 in a European country. The phylogeographic data complemented the syndromic surveillance with virus migration patterns between geographic regions in France. The results show how viral evolutionary dynamics and global virus spread interact to shape the worldwide pattern of an EV disease. CV-A16 transmission is driven by movements of infected individuals at different geographic levels: within a country (local dynamics), between neighboring countries (regional dynamics), and between distant countries (transcontinental dynamics). The results are consistent with our earlier data on EV-A71 and confirm the epidemiological interconnection of Asia and Europe with regard to EV infections.

Epidemiological characterizations, pathogen spectrum and molecular characteristics of Coxsackievirus A16 from patients with HFMD in Yantai, Shandong, China between 2011 and 2015

This study aimed to investigate the epidemiological characterizations and pathogen spectrum of hand, foot, and mouth disease (HFMD) in Yantai City, Shandong Province, China, during 2011-2015, and to study the nucleotide evolution and amino acid variation of coxsackievirus A16 (CV-A16) epidemic strains that caused HFMD. The HFMD epidemic began to rise in March, and became prevalent from May to August, reached its peak in June, and then declined in September every year, children aged one to 5 years-old had the highest incidence rate whereas the incidence in children under 6 months was very low, and there were more males than females. Enterovirus nucleic acid detection using real-time reverse transcription polymerase chain reaction was performed on 2130 clinical specimens collected from patients with HFMD between 2011 and 2015, and 2012 enterovirus positive samples were detected, including 678 CV-A16, 639 EV-A71, and 695 other enteroviruses. In total, 60 CV-A16 isolates were randomly selected each year for virus isolation, of which 33 CV-A16 strains were randomly selected for further characterization because CV-A16 is the predominant serotype that caused HFMD in Yantai City, and a phylogenetic tree based on the VP1 region was constructed. All 33 CV-A16 strains belonged to the Bla and B1b genotypes, with a nucleotide similarity of 87.9-100% and deduced amino acid similarity of 98.6-100%. Compared with the reference strain Tainan/5079/98 (AF177911), amino acid mutations were identified at positions 11, 23, 25, 31, 99, 145, and 289, where differences were observed among 33 strains, indicating a unique mutation map of CV-A16 in Yantai City. Our findings demonstrate the etiologic characteristics of HFMD, provide supporting evidence for the prevention and control of HFMD, and open a promising avenue for vaccine development against HFMD, by targeting CV-A16.

Prevalence of enteroviruses in healthy populations and excretion of pathogens in patients with hand, foot, and mouth disease in a highly endemic area of southwest China

Etiological carriers and the excretion of the pathogens causing hand, foot, and mouth disease (HFMD) in healthy persons, patients, and asymptomatic persons infected with HFMD as ongoing infection sources may play an important role in perpetuating and spreading epidemics of HFMD. The aims of this study were to determine the carrier status of EV-A71 and CV-A16 in healthy populations, as well as the duration of EV-A71 and CV-A16 shedding in the stools of HFMD patients in an epidemic area of southwest China. A cross-sectional study and a follow-up study were conducted in three HFMD endemic counties of Yunnan Province. Six hundred sixty-seven healthy subjects were recruited to participate in the cross-sectional study, and two stool specimens were collected from each subject. Among the healthy subjects, 90 (13.5%) tested positive for viral isolation, but neither EV-A71 nor CV-A16 was detected in healthy individuals. Of the 150 patients with probable HFMD, 55.3% (83/150) tested positive for viral isolation with presented serotypes such as EV-A71 (51.81%, 43/83), CV-A16 (32.53%, 27/83), other EVs (13.25%, 11/83), and mixed EV-A71 and CV-A16 (2.41%, 2/83). The longest duration of EV-A71 and CV-A16 shedding in stool specimens from patients with HFMD was >46 days after onset. The positive rate of EV-A71 in the stool specimens of confirmed patients dropped to 50% by the end of the third week, and the same occurred with CV-A16 by the end of approximately the seventh week after onset. Although carriers of major causative agents of HFMD in healthy populations are fewer in number, the prolonged shedding of pathogens in patients with HFMD may serve as an important factor in perpetuating and spreading HFMD epidemics.

A neonatal mouse model of coxsackievirus A10 infection for anti-viral evaluation

Epidemiological data indicate that coxsackievirus A10 (CVA10) has become one of the main causative agents of hand, foot and mouth disease (HFMD) and in recent years has often been found to co-circulate with other enteroviruses, which poses a challenge for the prevention and control of HFMD. Although most CVA10-associated HFMD cases present mild symptoms, severe manifestations and even death can also occur. However, the study of the pathogenesis and the development of drugs and vaccines for CVA10 infection are still far from complete. In this study, we established a neonatal mouse model for anti-viral evaluation and characterized the pathology of CVA10 infection. To develop the mouse model, both inbred and outbred mouse strains were used to compare their sensitivity to CVA10 infection; then, one-day-old BALB/c mice were selected and inoculated intraperitoneally with a CVA10 clinical strain, CVA10-FJ-01. Clinical symptoms, such as wasting, hind-limb paralysis and even death were observed in the CVA10-infected mice. Moreover, pathological examination and immunohistochemistry staining showed that severe myonecrosis with inflammatory infiltration was observed in CVA10-infected mice, indicating that CVA10 exhibited strong tropism to muscle tissue. Using real-time PCR, we also found that the viral load in the blood and muscle was higher than that in other organs/tissues at different time points post-infection, suggesting that CVA10 had a strong tropism to mice muscle and that viremic spread may also contribute to the death of the CVA10-infected mice. Additionally, to evaluate the neonatal mouse model of CVA10 infection, female mice were immunized with formalin-inactivated CVA10 and then allowed to mate after the third immunization. The results showed that maternal antibodies could protect mice against CVA10 infection. In summary, the results demonstrated that the neonatal mice model was a useful tool for evaluating the protective effects of CVA10 vaccines and anti-viral reagents.

A novel enterovirus species identified from severe diarrheal goats

Backgrounds

The Enterovirus genus of the family of Picornaviridae consists of 9 species of Enteroviruses and 3 species of Rhinoviruses based on the latest virus taxonomy. Those viruses contribute significantly to respiratory and digestive disorders in human and animals. Out of 9 Enterovirus species, Enterovirus E-G are closely related to diseases affecting on livestock industry. While enterovirus infection has been increasingly reported in cattle and swine, the enterovirus infections in small ruminants remain largely unknown.

Methods

Virology, molecular and bioinformatics methods were employed to characterize a novel enterovirus CEV-JL14 from goats manifesting severe diarrhea with morbidity and mortality respectively up to 84% and 54% in China.

Results

CEV-JL14 was defined and proposed as a new Enterovirus species L within the genus of Enterovirus of the family Picornaviridae. CEV-JL14 had a complete genome sequence of 7461 nucleotides with an ORF encoding 2172 amino acids, and shared 77.1% of genomic sequence identity with TB4-OEV, an ovine enterovirus. Comparison of 5’-UTR and structural genes of CEV-JL14 with known Enterovirus species revealed highly genetic variations among CEV-JL14 with known Enterovirus species. VP1 nucleotide sequence identities of CEV-14 were 51.8%-53.5% with those of Enterovirus E and F, 30.9%-65.3% with Enterovirus G, and 43.8–51. 5% with Enterovirus A-D, respectively. CEV-JL14 was proposed as a novel species within the genus of Enterovirus according to the current ICTV demarcation criteria of enteroviruses.

Conclusions

CEV-JL14 clustered phylogenetically to neither Enterovirus E and F, nor to Enterovirus G. It was defined and proposed as novel species L within the genus of Enterovirus. This is the first report of caprine enterovirus in China, the first complete genomic sequence of a caprine enterovirus revealed, and the unveiling of significant genetic variations between ovine enterovirus and caprine enterovirus, thus broadening the current understanding of enteroviruses.

Pathologic and immunologic characteristics of coxsackievirus A16 infection in rhesus macaques

Coxsackievirus A16 (CV-A16) causes human hand, foot and mouth disease, but its pathogenesis is unclear. In rhesus macaques, CV-A16 infection causes characteristic vesicles in the oral mucosa and limbs as well as viremia and positive viral loads in the tissues, suggesting that these animals reflect the pathologic process of the infection. An immunologic analysis indicated a defective immune response, which included undetectable neutralizing antibodies and IFN-γ-specific memory T-cells in macaques infected with CV-A16. Furthermore, existing neutralizing antibodies in macaques immunized with the inactivated vaccine were surprisingly unable to protect against a viral challenge despite the presence of a positive T-cell memory response against viral antigens. The virus was capable of infecting pre-conventional dendritic cells and replicating within them, which may correlate with the immunological characteristics observed in the animals.

Virus-Like Particles Produced in Pichia Pastoris Induce Protective Immune Responses Against Coxsackievirus A16 in Mice

BACKGROUND Coxsackievirus A16 (CA16) is one of the main causative agents of hand, foot, and mouth disease (HFMD), and the development of a safe and effective vaccine has been a top priority among CA16 researchers. MATERIAL AND METHODS In this study, we developed a Pichia pastoris yeast system for secretory expression of the virus-like particles (VLPs) for CA16 by co-expression of the P1 and 3CD proteins of CA16. SDS-PAGE, Western blot, and transmission electron microscopy (TEM) were performed to identify the formation of VLPs. Immunogenicity and vaccine efficacy of the CA16 VLPs were assessed in BABL/c mouse models. RESULTS Biochemical and biophysical analysis showed that the yeast-expressed CA16 VLPs were composed of VP0, VP1, and VP3 capsid subunit proteins, and present spherical particles with a diameter of 30 nm, similar to the parental infectious CA16 virus. Furthermore, CA16 VLPs elicited potent humoral and cellular immune responses, and VLPs-immunized sera conferred efficient protection to neonatal mice against lethal CA16 challenge. CONCLUSIONS Our results demonstrate that VLPs produced in Pichia pastoris represent a safe and effective vaccine strategy for CA16.

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

Background

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

Methods

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

Results

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

Conclusion

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

The Current Status of the Disease Caused by Enterovirus 71 Infections: Epidemiology, Pathogenesis, Molecular Epidemiology, and Vaccine Development

Enterovirus 71 (EV71) infections have a major public health impact in the Asia-Pacific region. We reviewed the epidemiology, pathogenesis, and molecular epidemiology of EV71 infection as well as EV71 vaccine development. Previous studies were found using the search terms "enterovirus 71" and "epidemiology" or "pathogenesis" or "molecular epidemiology" or "vaccine" in Medline and PubMed. Articles that were not published in the English language, manuscripts without an abstract, and opinion articles were excluded from the review. The reported epidemiology of cases caused by EV71 infection varied from country to country; seasonal variations in incidence were observed. Most cases of EV71 infection that resulted in hospitalization for complications occurred in children less than five years old. The brainstem was the most likely major target of EV71 infection. The emergence of the EV71 epidemic in the Asia-Pacific region has been associated with the circulation of different genetic lineages (genotypes B3, B4, C1, C2, and C4) that appear to be undergoing rapid evolutionary changes. The relationship between the gene structure of the EV71 virus and the factors that ensure its survival, circulation, and evasion of immunity is still unknown. EV71 infection has emerged as an important global public health problem. Vaccine development, including the development of inactivated whole-virus live attenuated, subviral particles, and DNA vaccines, has been progressing.

Characterization of VP1 sequence of Coxsackievirus A16 isolates by Bayesian evolutionary method

BACKGROUND

Coxsackievirus A16 (CV-A16), a major etiopathologic cause of pediatric hand, foot, and mouth disease (HFMD) worldwide, has been reported to have caused several fatalities. Revealing the evolutionary and epidemiologic dynamics of CV-A16 across time and space is central to understanding its outbreak potential.

METHODS

In this study, we isolated six CV-A16 strains in China's Jilin province and construct a maximum clade credibility (MCC) tree for CV-A16 VP1 gene by the Bayesian Markov Chain Monte Carlo method using 708 strains from GenBank with epidemiological information. The evolution characteristics of CV-A16 VP1 gene was also analysed dynamicly through Bayesian skyline plot.

RESULTS

All CV-A16 strains identified could be classified into five major genogroups, denoted by GI-GV. GIV and GV have co-circulated in China since 2007, and the CV-A16 epidemic strain isolated in the Jilin province, China, can be classified as GIV-3. The CV-A16 genogroups circulating recently in China have the same ancestor since 2007. The genetic diversity of the CV-A16 VP1 gene shows a continuous increase since the mid-1990s, with sharp increases in genetic diversity in 1997 and 2007 and reached peak in 2007. Very low genetic diversity existed after 2010. The CV-A16 VP1 gene evolutionary rate was 6.656E-3 substitutions per site per year.

CONCLUSIONS

We predicted the dynamic phylogenetic trends, which indicate outbreak trends of CV-A16, and provide theoretical foundations for clinical prevention and treatment of HFMD which caused by a CV-A16.

Development and evaluation of a non-ribosomal random PCR and next-generation sequencing based assay for detection and sequencing of hand, foot and mouth disease pathogens

Background

Hand, foot and mouth disease (HFMD) has become a major public health problem across the Asia-Pacific region, and is commonly caused by enterovirus A71 (EV-A71) and coxsackievirus A6 (CV-A6), CV-A10 and CV-A16. Generating pathogen whole-genome sequences is essential for understanding their evolutionary biology. The frequent replacements among EV serotypes and a limited numbers of available whole-genome sequences hinder the development of overlapping PCRs for whole-genome sequencing.

We developed and evaluated a non-ribosomal random PCR (rPCR) and next-generation sequencing based assay for sequence-independent whole-genome amplification and sequencing of HFMD pathogens. A total of 16 EV-A71/CV-A6/CV-A10/CV-A16 PCR positive rectal/throat swabs (Cp values: 20.9–33.3) were used for assay evaluation.

Results

Our assay evidently outperformed the conventional rPCR in terms of the total number of EV-A71 reads and the percentage of EV-A71 reads: 2.6 % (1275/50,000 reads) vs. 0.1 % (31/50,000) and 6 % (3008/50,000) vs. 0.9 % (433/50,000) for two samples with Cp values of 30 and 26, respectively. Additionally the assay could generate genome sequences with the percentages of coverage of 94–100 % of 4 different enterovirus serotypes in 73 % of the tested samples, representing the first whole-genome sequences of CV-A6/10/16 from Vietnam, and could assign correctly serotyping results in 100 % of 24 tested specimens. In all but three the obtained consensuses of two replicates from the same sample were 100 % identical, suggesting that our assay is highly reproducible.

Conclusions

In conclusion, we have successfully developed a non-ribosomal rPCR and next-generation sequencing based assay for sensitive detection and direct whole-genome sequencing of HFMD pathogens from clinical samples.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0580-9) contains supplementary material, which is available to authorized users.

Clinical and Associated Immunological Manifestations of HFMD Caused by Different Viral Infections in Children

Hand, foot, and mouth disease (HFMD), with vesiculae on the hands, feet and mouth, is an infectious disease caused by many viral pathogens. However, the differences of immune response induced by these pathogens are unclear. We compared the clinical manifestations and the levels of immunologic indicators from 60 HFMD patients caused by different viral pathogens to analyze the differences in the immune response. It was shown that Th2 cytokines (IL-4 and IL-10) increased significantly in EV71-infected children; Th1 cytokines (IL-2 and IFN-γ) rose in CA16-infected children; both Th1 and Th2 cytokines elevated in non-EVG-infected children; only individual cytokines (such as IL-10) went up in EVG-infected children. Meanwhile, the antibodies induced by viral infection could not cross-interfere between the different pathogens. These differences might be due to variations in the immune response induced by the individual pathogens or to the pathogenesis of the infections by the individual pathogens.

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

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

Molecular epidemiology of human coxsackievirus A16 strains

The hand, foot and mouth disease (HFMD) epidemics have mainly been caused by human enterovirus 71 and human coxsackievirus A16 (CA16), which circulated alternatively or together in the epidemic area. The aim of the present study was to provide guidance in the prevention and control of HFMD from CA16 infection. The molecular epidemiology of the human CA16 strains was investigated. Overall, 1,151 specimens (throat swabs) were collected from 1,151 patients with HFMD symptoms. The results of the homology comparison in the VP1 of CA16 strains showed that the CA16 strains belonged to the B1b subgenotype. The difference of the 6 CA16 strains analyzed showed that the most prominent strain was the A genotype, and the most close strains were the B1 gene subtype, particularly the B1b gene subtype. With regards to the amino acids, in addition to the A genotype, the differences of amino acids with other gene subtype was not significant. The present data suggest that more effective and highly targeted intervention mechanisms could be developed for the prevention and control of HFMD.

Genetic evolution of Human Enterovirus A71 subgenotype C4 in Shenzhen, China, 1998-2013

BACKGROUND

Human Enterovirus A71 (EV-A71) is one of the severest enteroviruses that causes hand, foot, and mouth disease (HFMD) among children. This study identified the mutations of EV-A71 VP1 amino acid residues over a number of years and explored the possible association of identified mutations and HFMD epidemic outbreaks in Shenzhen, China.

METHODS

A total of 3760 stool specimens were collected from HFMD patients by Shenzhen Centers for Disease Control and Prevention (CDC) between 1998 and 2013. In total 289 VP1 strains were sequenced in this study, and amino acids mutation frequency was calculated. There were 2040 China nationwide sequences downloaded from Genebank as replication data.

RESULTS

In our samples, 1036 subjects (27.6%) were EV-A71 infected. Three amino acid positions on VP1 protein were found to have high mutation prevalence. These are Q22H, S283T, and A289H. Site 22 showed a fast mutation fixation in the year 2008, at the time of the large scale epidemic outbreak in Shenzhen. Analysis of the nationwide data replicated the same trend of mutation prevalence of the three sites.

CONCLUSION

The switching from Q to H on site 22 of the EV-A71 VP1 strain might be associated with the HFMD outbreak in Shenzhen in 2008. The identified amino acid sites 22, 283 and 289 provided information for developing anti-viral drugs against EV-A71 in the future.

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

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

Protein microarray-mediated detection of antienterovirus antibodies in serum

Objective

To utilize prokaryotic gene expression and protein microarray to develop and evaluate a sensitive, accurate protein microarray assay for detecting antienterovirus antibodies in serum samples from patients with hand, foot and mouth disease (HFMD). Enterovirus 71 (EV71) and coxsackievirus A16 (CA16), two common causative agents for HFMD, were used for assay development.

Methods

Serum was collected from patients with HFMD and healthy controls. EV71 and CA16 VP1 and VP3 genes were expressed in transfected Escherichia coli; the resultant VP1 and 3 proteins were used in a microarray assay for human serum EV71 and CA16 immunoglobulin (Ig) M and IgG. To validate the microarray assay, serum samples were tested for EV71 IgM using enzyme-linked immunosorbent assay (ELISA).

Results

Out of 50 patients with HFMD, EV71 IgM and CA16 IgM was detected in 80% and 44% of serum samples, respectively, using protein microarray, and EV71 IgM was detected in 78% of samples using ELISA. Protein microarray and ELISA showed 100% specificity for EV71-IgM detection.

Conclusion

The protein microarray assay developed in the present study shows potential as a sensitive technique for detecting EV71 IgM in serum samples from patients with HFMD.

Development of sandwich ELISAs that can distinguish different types of coxsackievirus A16 viral particles

Coxsackievirus A16 (CA16) is one of the major causative agents of hand, foot, and mouth disease (HFMD). No CA16 vaccine candidates have progressed to clinical trials so far. Immunogenicity studies indicated that different CA16 particles have much influence on the efficacy of a candidate vaccine. However, there are still no relevant reports on the methods of detecting different CA16 particles. In this study, we screened several monoclonal antibodies (mAbs) specific for different CA16 particles, and several sandwich enzyme-linked immunoassays (ELISAs) were developed to measure the different types of CA16 viral particles. The mAbs that could only bind denatured or empty capsids could not neutralize CA16. In contrast, the mAbs that could bind mature full particles or all types of particles showed obvious neutralizing activity. The thermal stability of different CA16 particles was evaluated using these sandwich ELISAs. The mature full particles were found to be more thermolabile than the other types of particles and could be stabilized by high concentrations of cations. These methods can be used to assist in the potency control of CA16 vaccines and will promote the development of a CA16 vaccine.