Serological survey of neutralizing antibodies to eight major enteroviruses among healthy population

Seasonal Testing, Results, and Effect of the Pandemic on Coxsackievirus Serum Studies

Coxsackieviruses (CVs) are common causes of infections and can be life-threatening. Unfortunately, rigorous studies guiding the clinician in interpreting CV serum antibody titer testing is lacking. To explore the epidemiology of circulating CVs and the serological test utility in aiding diagnosis of CV infections in our community, we obtained results of CV immunologic diagnostic tests between 2018 and 2022 from a regional healthcare database. For CV type A, rare individuals had positive CF (complement fixation) tests whereas all 16 individuals with IFA testing showed at least one positive serotype. For CV type B CF testing, 52.2% of 222 patients had at least one serotype positive, with B5 being most common and also the most common with higher titers (14.8% with ≥1:32). We found a significant reduction in seropositivity rate during the pandemic in 2020 compared to 2018, which continued through 2022 (OR: 0.2, 95% CI: 0.08-0.49, p-value < 0.001). During the pandemic, the seasonal pattern of positive tests varied from the pre-pandemic pattern. Testing for CVs was increased after the first year of the pandemic. Overall, the variability by month and seasonal change in our data support that CF testing can be used to identify recent CVB infection.

Humoral and cellular immunogenicity and efficacy of a coxsackievirus A10 vaccine in mice

Coxsackievirus A10 (CV-A10) has become one of the major pathogens of hand, foot and mouth disease (HFMD), and studies on the vaccine and animal model of CV-A10 are still far from complete. Our study used a mouse-adapted CV-A10 strain, which was lethal for 14-day-old mice, to develop an infected mouse model. Then this model was employed to establish an actively immunized-challenged mouse model to evaluate the efficacy of a formaldehyde-inactivated CV-A10 vaccine, which was prepared from a Vero cell-adapted strain. CV-A10 vaccine at a dose of 0.5 or 2.0 μg was inoculated intraperitoneally in neonatal Kunming mice on the third and ninth day. Then the mice were challenged on day 14. The survival rate of mice immunized with 0.5 or 2.0 μg vaccine were 90% and 100%, respectively, while all Alum-inoculated mice died. Compared to those in the two vaccinated groups, the Alum-inoculated mice showed severe pathological damage, strong viral protein expression and high viral loads. The antisera from vaccinated mice showed high level of neutralizing antibodies against CV-A10. Meanwhile, three potential T cell epitopes located at the carboxyl-terminal regions of the VP1 and VP3 were identified and exhibited CV-A10 serotype-specific. The humoral and cellular immunogenicity analysis showed that immunization with two doses of the vaccine elicited CV-A10 specific neutralizing antibody and T cell response in BALB/c mice. Collectively, these findings indicated that this actively immunized-challenged mouse model will be invaluable in future studies on CV-A10 pathogenesis and evaluation of vaccine candidates.

Non-small cell lung cancers (NSCLCs) oncolysis using coxsackievirus B5 and synergistic DNA-damage response inhibitors

With the continuous in-depth study of the interaction mechanism between viruses and hosts, the virus has become a promising tool in cancer treatment. In fact, many oncolytic viruses with selectivity and effectiveness have been used in cancer therapy. Human enterovirus is one of the most convenient sources to generate oncolytic viruses, however, the high seroprevalence of some enteroviruses limits its application which urges to exploit more oncolytic enteroviruses. In this study, coxsackievirus B5/Faulkner (CV-B5/F) was screened for its potential oncolytic effect against non-small cell lung cancers (NSCLCs) through inducing apoptosis and autophagy. For refractory NSCLCs, DNA-dependent protein kinase (DNA-PK) or ataxia telangiectasia mutated protein (ATM) inhibitors can synergize with CV-B5/F to promote refractory cell death. Here, we showed that viral infection triggered endoplasmic reticulum (ER) stress-related pro-apoptosis and autophagy signals, whereas repair for double-stranded DNA breaks (DSBs) contributed to cell survival which can be antagonized by inhibitor-induced cell death, manifesting exacerbated DSBs, apoptosis, and autophagy. Mechanistically, PERK pathway was activated by the combination of CV-B5/F and inhibitor, and the irreversible ER stress-induced exacerbated cell death. Furthermore, the degradation of activated STING by ERphagy promoted viral replication. Meanwhile, no treatment-related deaths due to CV-B5/F and/or inhibitors occurred. Conclusively, our study identifies an oncolytic CV-B5/F and the synergistic effects of inhibitors of DNA-PK or ATM, which is a potential therapy for NSCLCs.

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

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

Development of a rapid neutralization testing system for Rhinovirus C15 based on the enzyme-linked immunospot assay

Human Rhinoviruses (RVs) are dominant pathogens causing a wide range of respiratory tract diseases, posing a huge threat to public health worldwide. Viruses belonging to the RV-C species are more likely to cause severe illnesses and are strongly associated with asthma onset or exacerbations than RV-A or RV-B. Rapid and sensitive detection of neutralizing antibodies (NAbs) against RV-C can promote the development of vaccines and antiviral drugs and help in the diagnosis of viral infection. In this study, a rapid neutralization testing system for RV-C15, based on an enzyme-linked immunospot assay (Nt-ELISPOT) was developed. A monoclonal antibody (MAb), named 9F9, with high binding efficacy for RV-C15 conjugated to horseradish peroxidase (HRP), was used to detect RV-C15-infected cells at a concentration of 2 μg/ml. The optimal infectious dose of RV-C15 was set at 1 × 10⁴ TCID₅₀/well and the cells were fixed with 0.5% formaldehyde diluted in PBS after incubation for 20 h. Compared with the traditional cytopathic effect (CPE)-based neutralization assay (Nt-CPE), Nt-ELISPOT significantly shortened the detection period and showed good consistency with the detection of neutralizing titers of both sera and NAbs. Using Nt-ELISPOT, three anti-RV-C15 NAbs were obtained with IC₅₀ values of 0.16, 0.27, and 11.8 μg/ml, respectively. Moreover, 64 human serum samples collected from a wide range of age groups were tested for NAb against RV-C15 by Nt-ELISPOT. The total seroprevalence was 48.4% (31/64) and the positive rate was lowest in the group under 6 years old. Thus, the Nt-ELISPOT established in this study can be used as a high-throughput and rapid neutralization assay for the screening of NAbs and for seroepidemiological investigation against RV-C15.

Comparison of Neutralizing Antibody Response Kinetics in Patients with Hand, Foot, and Mouth Disease Caused by Coxsackievirus A16 or Enterovirus A71: A Longitudinal Cohort Study of Chinese Children, 2017-2019

Hand, foot, and mouth disease (HFMD), which is mainly caused by coxsackievirus A16 (CVA16) or enterovirus A71 (EV-A71), poses a serious threat to children's health. However, the long-term dynamics of the neutralizing Ab (NAb) response and ideal paired-serum sampling time for serological diagnosis of CVA16-infected HFMD patients were unclear. In this study, 336 CVA16 and 253 EV-A71 PCR-positive HFMD inpatients were enrolled and provided 452 and 495 sera, respectively, for NAb detection. Random-intercept modeling with B-spline was conducted to characterize NAb response kinetics. The NAb titer of CVA16 infection patients was estimated to increase from negative (2.1, 95% confidence interval [CI]: 1.4-3.3) on the day of onset to a peak of 304.8 (95% CI: 233.4-398.3) on day 21 and then remained >64 until 26 mo after onset. However, the NAb response level of EV-A71-infected HFMD patients was much higher than that of CVA16-infected HFMD patients throughout. The geometric mean titer was significantly higher in severe EV-A71-infected patients than in mild patients, with a 2.0-fold (95% CI: 1.4-3.2) increase. When a 4-fold rise in titer was used as the criterion for serological diagnosis of CVA16 and EV-A71 infection, acute-phase serum needs to be collected at 0-5 d, and the corresponding convalescent serum should be respectively collected at 17.4 (95% CI: 9.6-27.4) and 24.4 d (95% CI: 15.3-38.3) after onset, respectively. In conclusion, both CVA16 and EV-A71 infection induce a persistent humoral immune response but have different NAb response levels and paired-serum sampling times for serological diagnosis. Clinical severity can affect the anti-EV-A71 NAb response.

[Enteroviral (Picornaviridae: Enterovirus) (nonpolio) vaccines]

Non-polio enteroviruses (NPEVs) are ubiquitous and are one of the main causative agents of viral infections in children. NPEVs most commonly infect newborns and young children, due to their lack of antibodies. In children, clinical manifestations can range from acute febrile illness to severe complications that require hospitalization and lead in some cases to disability or death. NPEV infections can have severe consequences, such as polio-like diseases, serous meningitis, meningoencephalitis, myocarditis, etc. The most promising strategy for preventing such diseases is vaccination. No less than 53 types of NPEVs have been found to circulate in Russia. However, of epidemic importance are the causative agents of exanthemic forms of the disease, aseptic meningitis and myocarditis. At the same time, the frequency of NPEV detection in the constituent entities of the Russian Federation is characterized by uneven distribution and seasonal upsurges. The review discusses the epidemic significance of different types of enteroviruses, including those relevant to the Russian Federation, as well as current technologies used to create enterovirus vaccines for the prevention of serious diseases.

Long-term high-dose immunoglobulin successfully treats Long COVID patients with pulmonary, neurologic, and cardiologic symptoms

Introduction

Long COVID is the overarching name for a wide variety of disorders that may follow the diagnosis of acute SARS-COVID-19 infection and persist for weeks to many months. Nearly every organ system may be affected.

Methods

We report nine patients suffering with Long COVID for 101 to 547 days. All exhibited significant perturbations of their immune systems, but only one was known to be immunodeficient prior to the studies directed at evaluating them for possible treatment. Neurological and cardiac symptoms were most common. Based on this data and other evidence suggesting autoimmune reactivity, we planned to treat them for 3 months with long-term high-dose immunoglobulin therapy. If there was evidence of benefit at 3 months, the regimen was continued.

Results

The patients' ages ranged from 34 to 79 years-with five male and four female patients, respectively. All nine patients exhibited significant immune perturbations prior to treatment. One patient declined this treatment, and insurance support was not approved for two others. The other six have been treated, and all have had a significant to remarkable clinical benefit.

Conclusion

Long-term high-dose immunoglobulin therapy is an effective therapeutic option for treating patients with Long COVID.

First seroepidemiological investigation of human enterovirus 71 in Iran

Background and Objectives:

Human Enterovirus 71 (EV-A71) is the causative agent for many dermal to neurological diseases especially polio-like paralysis outbreaks around the world. This study, the first of this kind in Iran, aimed to find neutralizing antibodies against EV-A71 in serum of healthy individuals in different age groups based on neutralization test (NT).

Materials and Methods:

In this cross-sectional study, 547 serum samples were collected from healthy individuals who were referring for routine checkup tests (aged from under 6 months to over 31 years old) to Imam-Khomeini Hospital in Tehran during January-December 2015. Serum samples were examined by NT in cell culture to detect neutralizing antibodies against EV-A71. In the next step, some of the positive samples were subjected to complete titration to determine the exact titer of anti-EV-A71 antibodies.

Results:

Of 547 samples, 310 (56.7%) were positive for EV-A71 neutralizing antibody. The presence of the antibody increased with age (p<0.001), and there was a significant statistical relationship between sex and the presence of antibody (p=0.009).

Conclusion:

Our results demonstrated an apparent but limited circulation of EV-A71 in our society. After the worldwide eradication of poliovirus, EV-A71 which can cause polio-likes syndrome, might be the new challenge for our health care system as regard more in depth research is however needed.

Seroprevalence of coxsackievirus A16 antibody among people of various age groups: a systematic review and meta-analysis

BACKGROUND

Coxsackie virus group A type 16 (CoxA16) is the main pathogen and usually an alternative to or joins in prevalence with enterovirus 71 (EV71) causing hand, foot and mouth disease (HFMD). The objective of this study was to estimate the seroprevalence of CoxA16 antibody among people of various age groups by a systematic review and meta-analysis.

METHODS

The literature of seroprevalence of CoxA16 antibody among people has been systematically searched through databases from the date of their establishment to Jan. 2021. Estimates of seroprevalence of CoxA16 antibody by gender and age groups have been summarized by using fixed- and random- effect models. All analyses have been conducted in STATA version 12.0 software.

RESULTS

A total of 14 publications with 9 in English and 5 in Chinese containing 9562 samples were finally included in the meta-analysis. The seroprevalence of CoxA16 antibody reported in different studies range from 24.85 to 76.92 %. Meta-analysis has revealed that the seroprevalence of CoxA16 antibody was 56.3 % (95 %CI: 47.7 %~64.9 %) in the overall population and 55.1 % (95 %CI: 44.1 %~66.1 %) in the Chinese population. Subgroup analysis by gender has revealed that the seroprevalence of CoxA16 antibody was 56.1 % (95 %CI: 45.2 %~67.1 %) in males and 60.0 % (95 %CI: 50.0 %~69.9 %) in females. Subgroup analysis by age groups has revealed that the seroprevalence of CoxA16 antibody was 49.1 % (95 %CI: 36.2 %~62.0 %) in the 0 ~ 5 age group and 63.9 % (95 %CI: 53.1 %~74.7 %) in the over 5 age group. Begg's funnel plots have suggested that there were no publication bias in all groups. Sensitive analysis has suggested that the result of the meta-analysis was stable.

CONCLUSIONS

The seroprevalence of CoxA16 antibody was closely related to age. Children under 5 years old were the main susceptible groups for CoxA16 and also the key groups for the prevention and control of HFMD.

Neutralising Antibodies against Enterovirus and Parechovirus in IVIG Reflect General Circulation: A Tool for Sero-Surveillance

Non-polio enteroviruses (NPEV) and parechoviruses (PeV) are widespread pathogens that cause significant morbidity. Surveillance is based on culturing or genotyping of virus strains found in clinical samples. Sero-surveillance, by measuring neutralising antibodies (nAb) through virus neutralisation assays (VNA), could provide additional information as it offers a more comprehensive overview of exposure to circulating types in the general population. In our study we evaluated Intravenous immunoglobulins (IVIG) to generate sero-surveillance data. We performed VNA of nineteen NPEV and PeV with Dutch IVIG batches from two different time points (2010 and 2017) and an IVIG batch from Vietnam (2011). We compared our findings with geno- and sero-surveillance data and evaluated changes over time and between the two countries. Our findings show a good correlation with what is known from geno-surveillance data. The highest nAb titres were found against strains from Enterovirus B, while we did not observe nAb titres against strains belonging to Enterovirus C. In conclusion, we demonstrated that sero-surveillance by means of IVIG can be used to obtain insight into circulation of EV and PeV genotypes. This is of particular interest for public health, to evaluate changes over time and population susceptibility to emerging genotypes.

Simultaneous enterovirus EV-D68 and CVA6 infections causing acute respiratory distress syndrome and hand, foot and mouth disease

Background

Although most enterovirus (EV) infections can be asymptomatic, these viral agents can cause serious conditions associated with central nervous system, respiratory disease and uncommon manifestations of hand, foot and mouth disease (HFMD). EV-coinfections have been rarely reported with development of complications and severe clinical outcome. An atypical case of a child presenting HFMD and severe acute respiratory syndrome, co-infected with EV-D68 and CVA6, is reported herein.

Case presentation

A 3-year-old boy was admitted in the emergency department unit showing fever, abdominal pain and tachycardia. Twenty-four hours after hospitalization the child developed severe clinical symptoms associated with HFMD and was discharged after recovery. Two days later, the child was readmitted with fever, cough and respiratory distress. RT-PCR and Sanger sequencing confirmed positivity for EV-D68 and CVA6 in oro and nasopharynges swabs and vesicles fluid, respectively. Phylogenetic analysis based on VP1 gene sequences suggested that CVA6 was closely related with HFMD viruses circulating in Turkey, while EV-D68 was genetically related to a Chinese strain.

Conclusions

To the best of our knowledge, this case is the first report of a double infection caused by CVA6 and EV-D68, which shed light on the pathogenesis of enterovirus infections. Further studies must be conducted to ascertain the role and clinical significance of EV co-infections, as well as a potential synergistic pathway between these viruses.

Seroprevalence of Neutralizing Antibodies Against Candidate Serotypes of Enterovirus Vaccines Among Korean Children

Hand, foot, and mouth disease (HFMD) is a pediatric public health concern in Asia. Surveillance data on the circulating serotypes of HFMD suggest that Enterovirus A71 (EV-A71) and coxsackieviruses A6, A10, and A16 (CVA6, CVA10, and CVA16) are the major serotypes causing HFMD. Asian countries, including Korea, are currently developing a multivalent vaccine targeting these serotypes. However, the immunity of children against specific serotypes, indicating past infection, should also be considered while selecting candidate serotypes for vaccine development. Therefore, we aimed to identify the age-stratified serological statuses of Korean children to determine candidate serotypes for HFMD vaccine development. This study included 220 participants, categorized into four age groups, 7 months-2 years, 3-5 years, 6-10 years, and 11-15 years. A neutralization test was performed to quantitate the neutralizing antibodies (NtAbs) in the sera of the participants. Only EV-A71 and CVA6 were found suitable as candidate serotypes for vaccine development, whereas further study is needed for CVA10 and CVA16. The highest seropositivity and NtAb titer ranges were observed for CVA6 in all age groups, suggesting that the participants had been predominantly exposed to CVA6. For EV-A71, seropositivity and NtAb titer ranges steadily increased with age, suggesting that children were currently exposed to EV-A71. For CVA10, the 3-5 years group showed the highest seropositivity rate and higher NtAb titer ranges than the older age groups, indicating that the exposure to CVA10 had mainly occurred in recent years. Future studies will identify whether the exposure to CVA10 was transient or will continue. For CVA16, seropositivity and NtAb titer ranges were generally low, indicating that only a few participants had been exposed to CVA16. We identified discrepancies between the sentinel surveillance data and our findings. This study provides a new perspective for HFMD vaccine development and policy making in Asian countries.

Muscle destruction caused by coxsackievirus A10 in gerbils: Construction of a novel animal model for antiviral evaluation

The morbidity and mortality of coxsackievirus A10 (CVA10)-associated hand, foot, and mouth disease (HFMD) have been increasing in recent years, while few studies on the vaccine and animal model of CVA10 have been reported. Here, we first established a CVA10-infected gerbil model and employed it to evaluate the immunoprotective effect of an inactivated CVA10 vaccine. The results showed that gerbils up to the age of 14 days were fully susceptible to CVA10, and all died within five days post-infection by intraperitoneal inoculation. Lethargy, wasting, hind-limb paralysis, and even death could be observed in the CVA10-infected gerbils. Pathological examination suggested that CVA10 has a strong tropism toward muscle tissue, and muscle bundle fracture and muscular fibers necrosis were observed in the limb muscles. Additionally, active immunization results showed that gerbils immunized with the inactivated CVA10 vaccine were 100 % protected from lethal CVA10 challenge. The antisera from vaccinated gerbils also showed high neutralizing titers against CVA10. Based on these results, the CVA10-infected gerbil model was a suitable tool for analyzing the pathogenesis of CVA10 and assessing the protective efficacy of CVA10 candidate vaccines.

Onychomadesis and potential association with HFMD outbreak in a kindergarten in Hubei province, China, 2017

BACKGROUND

In 2017, an outbreak of onychomadesis occurred in kindergarten H, Hubei province, China. We investigated the field to learn about the magnitude and reason of the outbreak.

METHODS

The case definition was that a child with onychomadesis or transverse ridging (Beau's line) in fingernails and toenails without previous traumatic or systemic disease in kindergarten H from Sep. 1st to Nov. 30th, 2017. A retrospective cohort study was carried out to analyze the epidemiological relationship between onychomadesis and the hand-foot-mouth disease (HFMD) in Primary Class #2, kindergarten H. We also performed a serological survey for neutralizing antibodies against coxsackie virus A6 (CVA6), coxsackie virus A10 (CVA10) among 15 cases and six healthy children in the kindergarten. Meanwhile, some children were carried out with routine blood, fungal microscopic and microelement tests. Indoor environment examinations had been done for all classes.

RESULTS

A total of 20 cases were identified in Kindergarten H. Seventy-five percent (15/20) cases occurred in Primary Class #2. Fifty-five percent of the cases (11/20) had suffered from HFMD within two months. The median time between onychomadesis and HFMD was 45 days (ranging from 31 to 58 days). A retrospective cohort study in Primary Class #2 showed the attack rate was 90.0% among 10 children who suffered from HFMD in the past two months compared to 30.0% among 20 children who didn't (Rate Ratio [RR] =3.0, 95% Confidence Interval [CI] =1.5-6.0). The positive rates of neutralizing antibodies were 66.7% for CVA6 and 26.7% for CVA10 in tested cases. The result of routine blood, fungal microscopic, microelements tests were normal in cases. The indicators of environment were within the normal range.

CONCLUSION

The results of this study suggested that the outbreak of onychomadesis in Hubei province was probably associated with HFMD epidemic within two months.

Acute Flaccid Myelitis in the United States: 2015-2017

BACKGROUND

Acute flaccid myelitis (AFM) is a neurologic condition characterized by flaccid limb weakness. After a large number of reports of AFM in 2014, the Centers for Disease Control and Prevention began standardized surveillance in the United States to characterize the disease burden and explore potential etiologies and epidemiologic associations.

METHODS

Persons meeting the clinical case criteria of acute flaccid limb weakness from January 1, 2015, through December 31, 2017, were classified as confirmed (spinal cord gray matter lesions on MRI) or probable (white blood cell count >5 cells per mm³ in cerebrospinal fluid [CSF]). We describe clinical, radiologic, laboratory, and epidemiologic findings of pediatric patients (age ≤21 years) confirmed with AFM.

RESULTS

Of 305 children reported from 43 states, 193 were confirmed and 25 were probable. Of confirmed patients, 61% were male, with a median age of 6 years (range: 3 months to 21 years; interquartile range: 3 to 10 years). An antecedent respiratory or febrile illness was reported in 79% with a median of 5 days (interquartile range: 2 to 7 days) before limb weakness. Among 153 sterile-site specimens (CSF and serum) submitted to the Centers for Disease Control and Prevention, coxsackievirus A16 was detected in CSF and serum of one case patient and enterovirus D68 was detected in serum of another. Of 167 nonsterile site (respiratory and stool) specimens, 28% tested positive for enterovirus or rhinovirus.

CONCLUSIONS

AFM surveillance data suggest a viral etiology, including enteroviruses. Further study is ongoing to better characterize the etiology, pathogenesis, and risk factors of this rare condition.

Enteroviruses: A Gut-Wrenching Game of Entry, Detection, and Evasion

Enteroviruses are a major source of human disease, particularly in neonates and young children where infections can range from acute, self-limited febrile illness to meningitis, endocarditis, hepatitis, and acute flaccid myelitis. The enterovirus genus includes poliovirus, coxsackieviruses, echoviruses, enterovirus 71, and enterovirus D68. Enteroviruses primarily infect by the fecal–oral route and target the gastrointestinal epithelium early during their life cycles. In addition, spread via the respiratory tract is possible and some enteroviruses such as enterovirus D68 are preferentially spread via this route. Once internalized, enteroviruses are detected by intracellular proteins that recognize common viral features and trigger antiviral innate immune signaling. However, co-evolution of enteroviruses with humans has allowed them to develop strategies to evade detection or disrupt signaling. In this review, we will discuss how enteroviruses infect the gastrointestinal tract, the mechanisms by which cells detect enterovirus infections, and the strategies enteroviruses use to escape this detection.

Hand, foot, and mouth disease associated with coxsackievirus A10: more serious than it seems

INTRODUCTION

Hand, foot, and mouth disease (HFMD) is a common viral childhood illness, that has been a severe public health concern worldwide, particularly in the Asia-Pacific region. According to epidemiological data of HFMD during the past decade, the most prevalent causal viruses were enterovirus (EV)-A71, coxsackievirus (CV)-A16, CV-A6, and CV-A10. The public health burden of CV-A10-related diseases has been underestimated as their incidence was lower than that of EV-A71 and CV-A16 in most HFMD outbreaks. However, cases of CV-A10 infection are more severe, and its genome is more variable, which has alerted the research community worldwide. Areas covered: In this paper, studies on the epidemiology, laboratory diagnosis, clinical manifestations, molecular epidemiology, seroepidemiology, animal models of CV-A10, and vaccines and antiviral strategies against this genotype are reviewed. In addition, the genetic evolution of circulating strains was analyzed. Expert opinion: Multivalent vaccines against EV-A71, CV-A16, CV-A6, and CV-A10 should be a next-step HFMD vaccine strategy.

Development of an efficient neutralization assay for Coxsackievirus A10

Coxsackievirus A10 (CVA10) recently has become one of the major pathogens of hand, foot, and mouth disease (HFMD) in children worldwide, but no cure or vaccine against CVA10 is available yet. Serological evaluation of herd immunity to CVA10 will promote the development of vaccine. The traditional neutralization assay based on inhibition of cytopathic effect (Nt-CPE) is a common method for measuring neutralizing antibody titer against CVA10, which is time-consuming and labor-intensive. In this study, an efficient neutralization test based on a monoclonal antibody (mAb) 3D1 against CVA10, called Elispot-based neutralization test (Nt-Elispot), was developed. In the Nt-Elispot, the mAb 3D1 labeled with horseradish peroxidase (HRP) was used to detect the CVA10-infected RD cells at a 1:4000 dilution and the optimal infectious dose of CVA10 was set at 10⁵ TCID₅₀/well when combined with a fixed incubation time of 14 h. Compared with the Nt-CPE, the Nt-Elispot method effectively shortened the detection period and presented a good correlativity with it. Using the Nt-Elispot, a total of 123 sera from healthy children were tested for neutralizing antibody against CVA10, demonstrating that the overall seroprevalence was 49.3% (54/123) and the geometric mean titer (GMT) had been calculated as 574.2. Furthermore, 2 anti-CVA10 neutralizing mAbs were obtained by screening via the Nt-Elispot. Overall, the established Nt-Elispot could be used as an efficient and high-throughput method for evaluating immunity to CVA10 and screening the neutralizing antibodies.

Population based hospitalization burden of laboratory-confirmed hand, foot and mouth disease caused by multiple enterovirus serotypes in Southern China

BACKGROUND

Hand, foot and mouth disease (HFMD) is spread widely across Asia, and the hospitalization burden is currently not well understood. Here, we estimated serotype-specific and age-specific hospitalization rates of HFMD in Southern China.

METHODS

We enrolled pediatric HFMD patients admitted to 3/3 county-level hospitals, and 3/23 township-level hospitals in Anhua county, Hunan (CN). Samples were collected to identify enterovirus serotypes by RT-PCRs between October 2013 and September 2016. Information on other eligible, but un-enrolled, patients were retrospectively collected from the same six hospitals. Monthly numbers of all-cause hospitalizations were collected from each of the 23 township-level hospitals to extrapolate hospitalizations associated with HFMD among these.

RESULTS

During the three years, an estimated 3,236 pediatric patients were hospitalized with lab-confirmed HFMD, and among these only one case was severe. The mean hospitalization rate was 660 (95% CI: 638-684) per 100,000 person-years for lab-confirmed HFMD, with higher rates among CV-A16 and CV-A6 associated HFMD (213 vs 209 per 100,000 person-years), and lower among EV-A71, CV-A10 and other enterovirus associated HFMD (134, 39 and 66 per 100,000 person-years respectively, p<0.001). Children aged 12-23 months had the highest hospitalization rates (3,594/100,000 person-years), followed by those aged 24-35 months (1,828/100,000 person-years) and 6-11 months (1,572/100,000 person-years). Compared with other serotypes, CV-A6-associated hospitalizations were evident at younger ages.

CONCLUSIONS

Our study indicates a substantial hospitalization burden associated with non-severe HFMD in a rural county in southern China. Future mitigation policies should take into account the disease burden identified, and optimize interventions for HFMD.

Sero-molecular epidemiology of enterovirus-associated encephalitis in Zhejiang Province, China, from 2014 to 2017

BACKGROUND

Recently, both sporadic and outbreak aseptic meningitis caused by enteroviruses have been reported in Zhejiang Province based on a surveillance system.

METHODS

This study analysed the epidemiologic features, phylogenetic characteristics and prevalence of enterovirus neutralizing antibodies (nAbs) from 2014 to 2017 in Zhejiang Province.

RESULTS

A total of 584 samples were collected. Males accounted for 66.07% while females accounted for 33.93%. The median age was 6 years (range: 1-15 years). Cases peaked in May and August (81.17%) and 162 cases (28.93%) occurred in June. We detected 15 serotypes, some of which (E6, E9, E18 and E30) were the dominant serotypes prevalent in different years and geographical regions. Phylogenetic results revealed that all of the isolates from this study belonged to the human enterovirus B family. A total of 329 subjects sampled from a healthy population were tested for nAbs against B5, E6 and E30 in Rui'an county in 2015. The seropositive rate of E30 in each age group was significantly higher than that of the other serotypes.

CONCLUSION

Enterovirus-associated encephalitis pathogens circulating in Zhejiang caused sporadic aseptic meningitis in children. The level of nAbs against human enterovirus reflects the history of previous infections in different age groups. Therefore, additional surveillance sites and more precise seroprevalence studies based on these populations are required to gain better insight into the epidemiology of enterovirus-associated encephalitis in Zhejiang Province.

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.

Discovery and structural characterization of a therapeutic antibody against coxsackievirus A10

Coxsackievirus A10 (CVA10) recently emerged as a major pathogen of hand, foot, and mouth disease and herpangina in children worldwide, and lack of a vaccine or a cure against CVA10 infections has made therapeutic antibody identification a public health priority. By targeting a local isolate, CVA10-FJ-01, we obtained a potent antibody, 2G8, against all three capsid forms of CVA10. We show that 2G8 exhibited both 100% preventive and 100% therapeutic efficacy against CVA10 infection in mice. Comparisons of the near-atomic cryo-electron microscopy structures of the three forms of CVA10 capsid and their complexes with 2G8 Fab reveal that a single Fab binds a border region across the three capsid proteins (VP1 to VP3) and explain 2G8's remarkable cross-reactivities against all three capsid forms. The atomic structures of this first neutralizing antibody of CVA10 should inform strategies for designing vaccines and therapeutics against CVA10 infections.

Molecular epidemiology of coxsackievirus A6 derived from hand, foot, and mouth disease in Fukuoka between 2013 and 2017

Coxsackievirus (CV)-A6 has been the primary causative agent of hand, foot, and mouth disease (HFMD) in Japan since 2011. In Fukuoka, CV-A6-associated HFMD caused epidemics in 2013, 2015, and 2017. This paper reports the genetic characteristics of the CV-A6 entire viral protein 1 (VP1) derived from patients with HFMD in Fukuoka between 2013 and 2017. CV-A6 was detected in 105 of 280 clinical specimens, and the entire VP1 sequences could be analyzed for 90 of the 105 specimens. Phylogenetic analysis revealed that the CV-A6 strains were classified into clade A and subgrouped into subclade A3 or subclade A4. Each subclade strain carried amino acid substitutions in the presumed DE and GH loops of the VP1, and no amino acid substitutions were identified as deleterious to the protein function. No significant difference was found in the clinical symptoms between the genetic subclades using statistical analyses. In conclusion, this study clarified the genetic diversity of CV-A6 in Fukuoka from 2013 to 2017. The emergence of the CV-A6 strains was classified into derived new subclades based on phylogenetic analysis of the VP1 gene that may cause CV-A6-associated HFMD epidemics approximately every 2 years.