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

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

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

Vertical Transmission of Coxsackievirus A6 with Severe Congenital Pneumonia/Sepsis

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

Viral metagenomics reveals diverse viruses in the fecal samples of children with diarrhea

Diarrhea is the third leading cause of death in developing countries in children under the age of five. About half a million children die of diarrhea every year, most of which in developing countries. Viruses are the main pathogen of diarrhea. In China, the fecal virome of children with diarrhea has been rarely studied. Using an unbiased viral metagenomics approach, we analyzed the fecal virome in children with diarrhea. Many DNA or RNA viruses associated with diarrhea identified in those fecal samples were mainly from six families of Adenoviridae, Astroviridae, Caliciviridae, Parvoviridae, Picornaviridae, and Reoviridae. Among them, the family of Caliciviridae accounts for the largest proportion of 78.42%, following with Adenoviridae (8.94%) and Picornaviridae (8.36%). In addition to those diarrhea-related viruses that have already been confirmed to cause human diarrhea, the viruses not associated with diarrhea were also identified including anellovirus and picobirnavirus. This study increased our understanding of diarrheic children fecal virome and provided valuable information for the prevention and treatment of viral diarrhea in this area.

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Many DNA or RNA viruses associated with diarrhea were identified in this study.

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Viruses belonging to the family of Caliciviridae were the most main pathogen that induced children diarrhea.

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In addition to those diarrhea-related viruses, the viruses not associated with diarrhea were also identified.

A 10-Day-Old Murine Model of Coxsackievirus A6 Infection for the Evaluation of Vaccines and Antiviral Drugs

Coxsackievirus A6 (CVA6) is recognized as a major enterovirus type that can cause severe hand, foot, and mouth disease and spread widely among children. Vaccines and antiviral drugs may be developed more effectively based on a stable and easy-to-operate CVA6 mouse infection model. In this study, a wild CVA6-W strain was sub-cultured in newborn mice of different ages (in days), for adaptation. Therefore, a CVA6-A mouse-adapted strain capable of stably infecting the mice was generated, and a fatal model was built. As the result indicated, CVA6-A could infect the 10-day-old mice to generate higher levels of IFN-γ, IL-6, and IL-10. The mice infected with CVA6-A were treated with IFN-α1b at a higher dose, with complete protection. Based on this strain, an animal model with active immunization was built to evaluate antiviral protection by active immunization. The three-day-old mice were pre-immunized with inactivated CVA6 thereby generating IgM and IgG antibodies within 7 days that enabled complete protection of the pre-immunized mice following the CVA6 virus challenge. There were eight mutations in the genome of CVA6-A than in that of CVA6-W, possibly attributed to the virulence of CVA6 in mice. Briefly, the CVA6 infection model of the 10-day-old mice built herein, may serve as an applicable preclinical evaluation model for CVA6 antiviral drugs and vaccine study.

The Epidemiological and Clinical Characteristics of Hand, Foot, and Mouth Disease in Hangzhou, China, 2016 to 2018

Hand, foot, and mouth disease (HFMD) is most frequently caused by several serotypes of human enterovirus (EV) including Enterovirus 71 (EV-A71), coxsackievirus A16 (CV-A16), or other types of EV. The aim of this study was to determine the epidemiological characteristics of HFMD and to describe the epidemiologic characteristics of HFMD among severe and mild cases. We collected 4760 HFMD cases in Hangzhou from 2016 to 2018. Specimens from these cases were collected and tested for EV-A71, CV-A16, CV-A6, CV-A10, CV-A2, and CV-A5 by reverse transcriptase polymerase chain reaction. From 2016 to 2018, the prevalence of HFMD was seasonal each year. Among the 4760 probable HFMD cases, 3559 cases were confirmed (74.8%), including 426 cases of EV-A71 infections (8.9%), 249 cases of CV-A16 infections (5.2%), and 2884 cases of other EV infections (60.6%). The percentage of other EV infections was more than 80%, which increased year by year. Random selection of samples for detection of other EV infections in 2017 and 2018, among the 1297 cases, showed there were 835 (64.4%) cases of CV-A6 infections, 177 (13.6%) cases of CV-A10 infections, 100 (7.7%) cases of CV-A2 infections, 40 (3.1%) cases of CV-A5 infections, 3 (0.02 %) cases of mixed infections, and 11.0% untyped EV infections. Preschool children were still the primary population susceptible to HFMD. In severe cases, EV-A71 infection was the main cause. Characterizing the epidemiology and the relationship between severe and common cases of HFMD would provide relevant evidences for the prevention and treatment of HFMD.

A review and meta-analysis of the epidemiology and clinical presentation of coxsackievirus A6 causing hand-foot-mouth disease in China and global implications

Coxsackievirus A6 (CV-A6) has been associated with increasingly occurred sporadic hand-foot-mouth disease (HFMD) cases and outbreak events in many countries. In order to understand epidemiological characteristics of CV-A6, we collected the information describing HFMD caused by CV-A6 to describe the detection rate, severe rate and onychomadesis rate, which is defined as one or more nails defluvium, caused by CV-A6 from 2007 to 2017. The results showed that there was an outbreak of CV-A6 every other year, and overall trend of the epidemic of CA6-associated HFMD was increasing in China. The detection rate of CV-A6 in other countries was 32.0% (95% CI: 25.0%~40.0%) before 2013 and 28.0% (95% CI: 20.0%~36.0%) after 2013, respectively. Although the severe rate of HFMD caused by CV-A6 was low (0.10%, 95% CI: 0.01%~0.20%), CV-A6 can cause a high incidence of onychomadesis (28.0%, 95%CI: 21.9%-34.3%). Thus, it would be worthwhile to research and develop an effective multivalent vaccine for CV-A6 to achieve a more powerful prevention of HMFD.

VP1 of Enterovirus 71 Protects Mice Against Enterovirus 71 and Coxsackievirus B3 in Lethal Challenge Experiment

Enterovirus and Coxsackievirus are the major viruses that cause hand, foot, and mouth disease (HFMD) outbreaks worldwide. Several studies have shown the potential of viral envelope protein 1 (VP1) on providing protective effects from viral strains of different genotypes. However, whether VP1 has the cross-protection in Enteroviruses or Coxsackievirus has not been studied in-depth. In this study, the vp1 gene of Enterovirus 71 (EV71) and Coxsackievirus B3 (CB3) was inserted into the vector pET22b (+) to form the respective expression plasmids pEVP1 or pCVP1, and then transformed into Escherichia coli strain BL21 (DE3). The recombinant EVP1 or CVP1 protein was overexpressed successfully and effectively purified to homogeneity. Then, we identified that EVP1 and CVP1 protein could generate effectively specific humoral immunity and cellular immunity in mice, what's more, we determined the cross-protection of VP1 between EV71 and CB3 in a murine model. The results showed that immunization with EVP1 could effectively induce specific IgG and secretory IgA against CVP1 and the sera from EVP1-immunized mice could neutralize CB3 with mean titers 1:440. In contrast, no measurable neutralizing antibodies to EV71 were detected in CVP1-immunized mice. Then, newborn BALB/C mice, whose mother was immunized with EVP1 or CVP1, were administered with different lethal doses of EV71 or CB3. The EVP1 immunized group showed a 90% protective efficacy for a CB3 dosage of 120 LD₅₀, but the CVP1 immunized group showed no significantly different protective efficacy against 15 LD₅₀ of EV71 compared with the BSA immunized group. Hence, EVP1 is a promising subunit vaccine candidate against Enterovirus 71 and Coxsackievirus B3 caused HFMD.

Development and comparison of forecast models of hand-foot-mouth disease with meteorological factors

Hand-foot-mouth disease (HFMD) is an acute intestinal virus infectious disease which is one of major public health problems in mainland China. Previous studies indicated that HFMD was significantly influenced by climatic factors, but the associated factors were different in different areas and few study on HFMD forecast models was conducted. Here, we analyzed epidemiological characteristics of HFMD in Yiwu City, Zhejiang Province and constructed three forecast models. Overall, a total of 32554 HFMD cases were reported and 12 cases deceased in Yiwu City, Zhejiang Province. The incidence of HFMD peaked every other year and the curve of HFMD incidence had an approximately W-shape. The majority of HFMD cases were children and 95.76% cases aged ≤5 years old from 2008 to 2016. Furthermore, we constructed and compared three forecast models using autoregressive integrated moving average (ARIMA) model, negative binomial regression model (NBM), and quasi-Poisson generalized additive model (GAM). All the three models had high agreements between predicted values and observed values, while GAM fitted best. The exposure-response curve of monthly mean temperature and HFMD was approximately V-shaped. Our study explored epidemiological characteristics of HFMD in Yiwu City and provided accurate methods for early warning which would be great importance for the control and prevention of HFMD.

Application of a combined model with seasonal autoregressive integrated moving average and support vector regression in forecasting hand-foot-mouth disease incidence in Wuhan, China

Hand-foot-mouth disease (HFMD) is a serious public health problem with increasing cases and substantial financial burden in China, especially in Wuhan city. Hence, there is an urgent need to construct a model to predict the incidence of HFMD that could make the prevention and control of this disease more effective.The incidence data of HFMD of Wuhan city from January 2009 to December 2016 were used to fit a combined model with seasonal autoregressive integrated moving average (SARIMA) model and support vector regression (SVR) model. Then, the SARIMA-SVR hybrid model was constructed. Subsequently, the fitted SARIMA-SVR hybrid model was applied to obtain the fitted HFMD incidence from 2009 to 2016. Finally, the fitted SARIMA-SVR hybrid model was used to forecast the incidence of HFMD of the year 2017. To assess the validity of the model, the mean square error (MSE) and mean absolute percentage error (MAPE) between the actual values and predicted values of HFMD incidence (2017) were calculated.From 2009 to 2017, a total of 107636 HFMD cases were reported in Wuhan City, Hubei Province, and the male-to-female ratio is 1.60:1. The age group of 0 to 5 years old accounts for 95.06% of all reported cases and scattered children made up the large proportion (accounted for 56.65%). There were 2 epidemic peaks, from April to July and September to December, respectively, with an emphasis on the former. High-prevalence areas mainly emerge in Dongxihu District, Jiangxia District, and Hongshan District. SARIMA (1,0,1)(0,0,2)[12] is the optimal model given with a minimum Akaike information criterion (AIC) (700.71), then SVR model was constructed by using the optimum parameter (C = 100000, =0.00001, =0.01). The forecasted incidences of single SARIMA model and SARIMA-SVR hybrid model from January to December 2017 match the actual data well. The single SARIMA model shows poor performance with large MSE and MAPE values in comparison to SARIMA-SVR hybrid model.The SARIMA-SVR hybrid model in this study showed that accurate forecasting of the HFMD incidence is possible. It is a potential decision supportive tool for controlling HFMD in Wuhan, China.