Evaluation of Reverse Transcription Loop-Mediated Isothermal Amplification assays for Rapid Detection of Human Enterovirus 71 and Coxsackievirus A16 in Clinical Samples

A sensitive reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for human enterovirus 71 (EV71) and Coxsackievirus A16 (CVA16) infection was further evaluated. The one step reaction was performed in a single tube at 65?C for 45 min for EV71 and 35 min for CVA16. The detection limits of RT-LAMP assays for both EV71 and CVA16 were 0.1 of a 50% tissue culture infective dose (TCID50) per reaction, based on 10—Fold dilutions of a titrated EV71 or CVA16 strain. The specific assay showed there were no cross-reactions with Coxsackievirus A (CVA) viruses (CVA 2, 4, 5, 7, 9, 10, 14, and 25), Coxsackievirus B (CVB) viruses (CVB 1, 2, 3, 4, and 5) or ECHO viruses (ECHO 3, 6, 11, and 19). In parallel with commercial quantitative real-time polymerase chain reaction (qRT-PCR) diagnostic kits for EV71 and CVA16, the RT-LAMP assay was evaluated with 515 clinical specimens, the results showed the RT-LAMP assay and the qRT-PCR assay were in complete agreement for 513/515 (99.6%) of the specimens. Two samples with discrepant results from two methods were further verified by nested reverse transcription polymerase chain reaction (nRT-PCR) assay and sequencing to be true positives for CVA16. In conclusion, RT-LAMP assay is demonstrated to be a sensitive and specific assay and have a great potential for the rapid and visual screening of EV71 and CVA16 in China, especially in those resource-limited hospitals and rural clinics of provincial and municipal regions.

Replication Kinetics of Coxsackievirus A16 in Human Rhabdomyosarcoma Cells

Coxsackievirus A16(CVA16),together with enterovirus type 71(EV71),is responsible for most cases of hand,foot and mouth disease(HFMD) worldwide.Recent findings suggest that the recombination between CVA16 and EV71,and the co-circulation of these two viruses may have contributed to the increase of HFMD cases in China over the past few years.It is therefore important to further understand the virology,epidemiology,virus-host interactions and host pathogenesis of CVA16.In this study,we describe the viral kinetics of CVA16 in human rhabdomyosarcoma(RD) cells by analyzing the cytopathic effect(CPE),viral RNA replication,viral protein expression,viral RNA package and viral particle secretion in RD cells.We show that CVA16 appears to first attach,uncoat and enter into the host cell after adsorption for 1 h.Later on,CVA16 undergoes rapid replication from 3 to 6 h at MOI 1 and until 9 h at MOI 0.1.At MOI 0.1,CVA16 initiates a secondary infection as the virions were secreted before 9 h p.i.CPE was observed after 12 h p.i.,and viral antigen was first detected at 6 h p.i.at MOI 1 and at 9 h p.i.at MOI 0.1.Thus,our study provides important information for further investigation of CVA16 in order to better understand and ultimately control infections with this virus.

接种EV-A71疫苗后对EV-A71IgM和CV-A16IgM检测结果影响的探讨

目的探讨接种肠道病毒71型(EV-A71)疫苗后对EV-A71IgM和柯萨奇病毒A16型(CV-A16)IgM检测结果的影响。方法采取手足口病患儿的静脉血,用酶联免疫法进行EV-A71IgM和CV-A16IgM检测,检测结果应用统计学软件进行比较分析。结果疫苗接种者与未接种者EV-A71IgM阳性率差异有统计学意义(P<0.01),CV-A16IgM阳性率差异无统计学意义(P>0.05)。接种疫苗者分组,120~<150组与未接种组阳性率差异无统计学意义(P>0.05);第1剂疫苗“<20d”组EV-A71IgM阳性率(50.0%)除“40~<60”组外与其他组差异有统计学意义(P<0.05);第2剂疫苗,各组之间差异无统计学意义(P>0.05)。结论接种EV-A71疫苗的手足口病患者的EV-A71IgM阳性率高于未接种者(P<0.01),尤其是第1剂接种后20d内,120d后差异无统计学意义(P>0.05),CV-A16IgM阳性率差异无统计学意义(P>0.05)。

重组EV71和CVA16型手足口病双价VLP疫苗构建及免疫保护效果评价

目的运用Bac-to-Bac杆状病毒表达系统表达EV71和CVA16的病毒样颗粒，并对纯化的重组EV71、CVA16双价病毒样颗粒疫苗进行免疫效果评价。方法构建重组杆状病毒Bacmid-P1-3CD，转染Sf9昆虫细胞，纯化EV71、CVA16的病毒样颗粒并检测其形态和生物特性；通过EV71、CVA16的病毒样颗粒免疫ICR雌鼠后，以EV71、CVA16强毒株腹腔攻击5日龄乳鼠，对重组EV71、CVA16型双价VLP免疫保护性进行评价。结果利用Bac-to-Bac杆状病毒表达系统成功构建并表达EV71和CVA16病毒样颗粒，颗粒大小约为23-30nm，存在Mr约39000VP1特异性蛋白表达。重组EV71、CVA16双价VLP疫苗免疫接种能够诱导小鼠机体产生高效价的特异性抗体（EV71中和抗体效价为1：960，CVA16中和抗体效价为1：624）并发挥优于单价VLP疫苗的有效免疫保护效果。结论重组EV71、CVA16型双价VLP疫苗免疫原性和保护性显著高于单价疫苗，为手足口病疫苗的研发提供了新的思路及实验基础。。

柯萨奇病毒A组16型研究进展

A组16型柯萨奇病毒(Coxsackievirus A16,CVA16)是引起手足口病(Hand,foot and mouth disease,HFMD)的主要病原体之一。近年来,HFMD在亚太地区暴发流行,已经成为重大的公共卫生问题之一。加强对CVA16生物学特征、流行病学特征、临床表现、实验室诊断、防治手段的认识,有助于防控HFMD的蔓延。

CA16滴度微量检测方法的建立及其验证

目的建立用Vero细胞检测柯萨奇病毒A组16型（CAl6）滴度的方法，并对其适用性进行初步验证。方法通过对细胞种类的选择、细胞接种浓度和细胞病变判定时间的优化，建立测定CAl6滴度的半数细胞感染剂量法（CCID50法），并对其进行初步验证。结果通过对病毒感染后细胞病变情况的观察，确定了以Vero细胞作为CAl6病毒滴度检定用细胞。Vero细胞的最佳接种浓度和结果判定时间分别为5×10^4-1×10^5细胞／mL（即96孔板内每孔加入的最终细胞量为5×10^3-1×10^4细胞）和7d。由4组人员对6批CAl6病毒液进行重复检测，实验结果表明不同实验人员测定结果的变异系数（CV）在1．739％-4．974％之间，说明该方法测定结果重复性好，准确度高。结论该法简便、稳定，可以灵敏、准确地检测CA16病毒的滴度，可用于相关疫苗生产过程中的质量控制。

柯萨奇病毒A组16型的研究进展

柯萨奇病毒A组16型(Coxsackievirus A group 16 strain,CA16)感染在中国很常见,CA16在流行过程中不断发生变异,其致病性与肠道病毒71型有明显差异。CA16可诱导产生多种微小核糖核酸,影响炎性信号通路的传导,导致病理损害的发生。目前已成功建立了小鼠、树鼩、猕猴CA16感染模型,可用于评估抗CA16药物和疫苗效果。检测方面,多重实时逆转录聚合酶链反应可针对手足口病进行高灵敏度检测和快速分型,胶体金免疫层析法可用于现场的快速诊断。多种单价、多价的CA16疫苗在动物实验中诱导出有效的免疫。

CD8^+T细胞在CA16感染手足口病中的表达变化及潜在作用

目的:对比分析15~24个月及2~5岁CA16感染的普通型与危重症手足口病(hand,foot and mouth disease,HFMD)患者外周血中CD8^+T细胞的表达情况,寻找发现与CA16致病有关的免疫病理因素。方法:收集2014年5-8月间昆明市儿童医院感染科确诊的儿童HFMD病例外周血标本共72例,其中普通型32例,危重症40例,采用流式细胞术对患者外周血CD8^+T淋巴细胞亚群进行检测分析。结果:15~24个月普通型HFMD患者外周血CD8^+T淋巴细胞百分比略高于正常健康儿童参考值,而危重症患者CD8^+T细胞略低于正常参考值。此外,与正常参考值相比,2~5岁普通型及危重症患者外周血中CD8^+T淋巴细胞百分比均减低,其中危重症患者略低于普通型患者。结论:CA16感染后,不同年龄、不同病情的HFMD患者外周血中CD8^+T细胞的表达变化不太明显,说明CA16感染后,患者体内的CD8^+T细胞基本能够发挥正常的抗病毒免疫效应。而在危重症时,两个年龄段患者CD8^+T细胞百分比略低或减低,说明CA16的持续性感染可能对机体CD8^+T细胞的表达产生了影响,使其杀伤病毒效应减低,这可能是CA16感染诱导神经系统并发症发生的免疫病理因素之一。

柯萨奇病毒A组16型抗原的ELISA定量检测方法建立

目的:建立柯萨奇病毒A组16型(CA16)抗原的双抗体夹心ELISA定量检测方法,用于CA16灭活疫苗的研发和生产过程的抗原定量检测。方法:以CA16中和单抗T26H12为包被抗体、NA14B9为标酶抗体,构建定量检测CA16抗原的双抗体夹心ELISA方法,并对方法的特异性、灵敏度、精密度、准确性、线性和稳定性进行分析。结果:建立了双抗体夹心定量检测CA16抗原的ELISA方法。方法的线性相关系数R2=0.998,线性范围为8～128 ng/ml,定量限度为8 ng/ml;变异系数CV<15%;回收率介于87.0%～113.8%之间;37℃6天的回收率>80%;与CA16以外的其他样本没有交叉反应。结论:构建的CA16抗原ELISA定量检测方法的各项性能符合定量检测需要,可用于CA16疫苗的研发和生产过程的抗原活性的定量检测。

柯萨奇病毒A组16型VP1蛋白的原核表达

目的构建重组质粒柯萨奇病毒A组16型(coxsackievirus group A type 16,CA16)VP1,并进行原核表达及鉴定。方法用PCR方法扩增CA16 VP1序列,构建其重组表达质粒pET21b-CA16 VP1,并转入大肠杆菌E.coli BL21(DE3)进行诱导表达及纯化,SDS-PAGE鉴定表达及纯化产物,间接ELISA方法检测重组蛋白CA16 VP1的抗原性和有效性。结果成功原核表达并纯化了CA16 VP1蛋白,可与小鼠抗CA16病毒血清特异性结合,与太原市老年人群中部分血清存在高反应性。结论 CA16 VP1蛋白获得成功表达,ELISA检测具有良好的抗原性和有效性,为CA16诊断试剂盒的研究奠定基础。

小鼠在柯萨奇病毒A组16型活病毒免疫原性评价中的应用

目的评价小鼠在柯萨奇病毒A组16型（CA16）活病毒感染中免疫原性的应用，为减毒活疫苗研究提供实验数据。方法以不同剂量的CA16活病毒通过皮下、腹腔和肌肉途径接种不同年龄的ICR和BALB／C小鼠，采集初次免疫7d、21d、28d以及加强免疫7d后的血样：通过微量细胞病变中和法检测中和抗体效价，细胞因子ELISA检测试剂盒检测6种细胞因子含量。结果初次免疫后28d，肌肉、腹腔和皮下途径免疫的小鼠血清抗体阳转率分别为83．33％、40．00％和0．00％，抗体几何平均效价（GMT）分别为1：169、1：32和0；加强免疫后，肌肉、腹腔和皮下途径免疫的小鼠血清抗体阳转率均达100％，抗体GMT分别为1：813、l：609和1：32，肌肉和腹腔途径免疫的小鼠血清抗体GMT平均增长4．8倍和19．0倍；加强免疫7d的抗体阳转率达100％；明显高于初次免疫28d和21d；BALB／c小鼠与ICR小鼠相比，前者的中和抗体效价和抗体阳转率明显高于后者，而小鼠年龄对中和抗体效价和抗体阳转率的影响不显著（P〉0．05）；免疫剂量对中和抗体效价和抗体阳转率的影响显著（P〈0．05），高剂量病毒免疫小鼠后中和抗体效价和抗体阳转率明显比低剂量高（P〈0．05）；细胞因子检测结果显示加强免疫7d后的白细胞介素100L-10）和肿瘤坏死因子α（TNF-α）的含量与初次免疫7d的相比显著增加。结论BALB／c和ICR小鼠可做为CA16活病毒免疫原性评价的动物模型，以4～6周龄的BALB/c小鼠最为敏感。

肠道病毒71型和柯萨奇病毒A16鼠源性广谱中和活性单克隆抗体的制备

目的制备可以同时阻断肠道病毒71型(EV71)及柯萨奇病毒A组16型(CV-A16)感染的中和活性单克隆抗体(mAb)。方法采用EV71病毒体蛋白1(VP1)羧基端的163~177位氨基酸(SP55)免疫BALB/c小鼠,通过杂交瘤技术制备mAb,用EV71中和抗原表位SP55以及高度同源的CV-A16 VP1羧基端的第163~177位氨基酸(PEP55)同时进行检测,筛选同时与EV71和CV-A16发生交叉反应的mAb,并进行体外中和试验检测对EV71和CV-A16的中和作用,并分析mAb的生物学特性。结果筛选获得1株可以同时中和EV71及CV-A16的mAb 6E5,其重链为IgG1亚类,轻链为Kappa链;细胞微量中和实验表明其抗EV71感染的中和效价为1∶128,抗CV-A16感染的中和效价为1∶32。结论成功获得1株能同时中和EV71及CV-A16的广谱中和活性mAb。

Dynamic change of mother-source neutralizing antibodies against enterovirus 71 and coxsackievirus A16 in infants

Background Enterovirus 71 （EV71） and coxsackievirus A16 （Cox A16） are major causative agents for hand, foot and mouth disease （HFMD）. Studies indicate that the frequent HFMD outbreaks result in a few hundreds children＇s death in China in recent years. The vaccine and other research for HFMD need to be developed urgently. The aims of our study were： to explore dynamic development of mother-source neutralizing antibodies against EV71 and Cox A16 in infants from Jiangsu Province, China, and to provide the fundamental data for further establishing of corresponding immunization course. Methods Peripheral blood samples were collected from 133 of parturient women once immediately before delivery and their infants at two and seven months of age. Method of micro-dose cytopathogenic effect was used to measure neutralizing antibodies against EV71 and Cox A16, respectively. Results Seropositive rates of anti-EV71 and anti-Cox A16 in prenatal women were 79.7% （106/133） and 92.5% （123/133）, respectively; geometric mean titers （GMTs） were 29.0 and 61.9; 75.9% （101/133） prenatal women were both positive in anti-EV71 and anti-Cox A16; seropositive rates of anti-EV71 and anti-Cox A16 were 25.6% （34/133） and 38.3% （51/133） in infants at two months of age; GMTs were 12.3 and 18.0, respectively. GMTs of anti-EV71 were significantly higher for infants at seven months （82.6） compared with that at two months （P 〈0.05）, showing infants had inapparently infected by EV71 during two to seven months. Although only one offspring （0.75%） at seven months was found having anti-Cox A16 transfered from maternal, this observation suggested no maternal antibody may remain in infants at seven months. Conclusions The prevalence of EV71 and Cox A16 were relatively high in Jiangsu Province. Bivalent vaccine against both EV71 and Cox A16 should be developed, and the ideal time point for prime immunization for infants is around 2-5 months of age.

Development and characterization of a clinical strain of Coxsackievirus A16 and an eGFP infectious clone

Coxsackievirus A16(CA16) is one of the major causes of hand, foot, and mouth disease(HFMD) worldwide, which is a common illness that affects children. The frequent occurrence of HFMD outbreaks has become a serious public health problem in Asia. Therefore, it is important to understand the pathogenesis and replication of CA16. In this study, a stable infectious c DNA clone of an epidemic strain of Coxsackievirus A16(CA16) was assembled, and subsequently a reporter virus(e GFP-CA16) was constructed by inserting the e GFP gene between the 5'-UTR and the N-terminus of VP4, with the addition of a 2A protease cleavage site(ITTLG) at its C-terminus. This was transfected into Vero cells to generate infectious recombinant viruses. The growth characteristics and plaque morphology, in vitro, in mammalian cells were found to be indistinguishable between the parental and recombinant viruses. Although the e GFP-CA16 showed smaller plaque size as compared to recombinant CA16, both were found to exhibit similar growth trends and EC50 of NITD008. In summary, this stable infectious c DNA clone should provide a valuable experimental system to study CA16 infection and host response. The e GFP-CA16 is expected to provide a powerful tool to monitor e GFP expression in infected cells and to evaluate the antiviral activity of potential antiviral agents in the treatment of CA16 infections.

Molecular epidemiology of coxsackievirus A16 circulating in children in Beijing, China from 2010 to 2019

Background Coxsackievirus A16(CVA16)is one of the major etiological agents of hand,foot and mouth discase(HFMD).This study aimed to investigate the molecular epidemiology and evolutionary characteristics of CVA16.Methods Throat swabs were collected from children with HFMD and suspected HFMD during 2010-2019.Enteroviruses(EVs)were detected and typed by real-ime reverse transcription-polymerase chain reaction(RT-PCR)and RT-PCR.The genotype,evolutionary rate,the most recent common ancestor,population dynamics and selection pressure of CVA16 were analyzed based on viral protein gene(VPI)by bioinformatics software.Results A total of 4709 throat swabs were screened.EVs were detected in 3180 samples and 814 were CVA16 positive.More than 81%of CVA 16-positive children were under 5 years old.The prevalence of CVA 16 showed obvious periodic fluctuations with a high level during 2010--2012 followed by an apparent decline during 2013--2017.However,the activities of CVA16 increased gradually during 2018-2019.All the Beijing CVA16 strains belonged to sub-genotype BI,and B Ib was the dominant strain.One B Ic strain was detected in Bejing for the first time in 2016.The estimated mean evolutionary rate of VPI gene was 4.49x 103 substitution/site/year.Methionine gradually fixed at site-23 of VP1 since 2012.Two sites were detected under episodic positive selection,one of which(site-223)located in neutralizing linear epitope PEP71.Conclusions The dominant strains of CVA 16 belonged to clade B lb and evolved in a fast evolutionary rate during 2010-2019 in Beiing.To provide more favorable data for HFMD prevention and control,it is necessary to keep attention on molecular epidemiological and evolutionary characteristics of CVA16.

An open conformation determined by a structural switch for 2A protease from coxsackievirus A16

Coxsackievirus A16 belongs to the family Picornaviridae,and is a major agent of hand-foot-and-mouth disease that infects mostly children,and to date no vaccines or antivi-ral therapies are available.2A protease of enterovirus is a nonstructural protein and possesses both self-cleavage activity and the ability to cleave the eukaryotic translation initiation factor 4G.Here we present the crystal structure of coxsackievirus A162A protease,which interestingly forms hexamers in crystal as well as in solution.This structure shows an open conformation,with its active site accessible,ready for substrate binding and cleav-age activity.In conjunction with a previously reported“closed”state structure of human rhinovirus 2,we were able to develop a detailed hypothesis for the conforma-tional conversion triggered by two“switcher”residues Glu88 and Tyr89 located within the bll2-cII loop.Substrate recognition assays revealed that amino acid residues P1′,P2 and P4 are essential for substrate specificity,which was verifi ed by our substrate binding model.In addition,we compared the in vitro cleavage effi ciency of 2A pro-teases from coxsackievirus A16 and enterovirus 71 upon the same substrates by fl uorescence resonance energy transfer(FRET),and observed higher protease activity of enterovirus 71 compared to that of coxsackievirus A16.In conclusion,our study shows an open conformation of coxsackievirus A162A protease and the underlying mechanisms for conformational conversion and substrate specifi city.These new insights should facilitate the future rational design of effi cient 2A protease inhibitors.

Improved plasmid-based recovery of coxsackievirus A16 infectious clone driven by human RNA polymerase I promoter

Dear Editor,Coxsackievirus A16(CA16)is one of the major viral pathogens associated with hand,foot,and mouth disease.CA16 belongs to the Enterovirus genus of the Picornaviridae family and possesses a single-stranded positivesense RNA genome(Mao et al.,2014).Reverse genetics is an important tool for CA16 research.Previously,a reverse genetics T7 polymerase-based system was de-

Epidemiology and genetic characteristics of coxsackievirus A16 associated with hand-foot-and-mouth disease in Yantai city,China in 2018-2021

In 2008,China launched a national surveillance system for hand‐foot‐and‐mouth disease(HFMD).Several million cases of HFMD are reported every year,coxsackievirus A16(CVA16)was the leading cause of HFMD epidemic in Yantai city,China in recent years,but the information of epidemiology and molecular characterization of CVA16 in Yantai is limited.The aim of this study is to investigate the epidemiological characteristics and pathogenic spectrum of HFMD,and most importantly,the molecular characterization of CVA16 in Yantai from 2018 to 2021.A total of 2,000 clinical samples were collected in Yantai city from 2018 to 2021 and the enterovirus typing was performed using real‐time reverse transcriptase–polymerase chain reaction(qRT‐PCR).VP1 coding regions of 41 CVA16 isolates were amplified and Sanger sequenced,and phylogenetic analysis was performed.During the study period,HFMD became prevalent from May to August each year.It peaked in June and declined in September.The incidence was highest in children aged 1 to 5 years,while more common in males than females.1,617 out of 2,000 clinical collection of samples were tested positive for enterovirus.Among them,614 were identified as CVA16,45 were enterovirus A71(EV A17),and 958 were other enterovirus serotypes.All 41 CVA16 strains belonged to the Bla and B1b genotypes.Homology analysis showed that 41 CVA16 isolates shared 83.2%–100%nucleotide and 93.7%–100%amino acid similarity among themselves.The results of this study update molecular epidemiology of CVA16 and provide a reference for HFMD prevention and control.

EV-A71和CV-A16感染正常人呼吸道上皮细胞诱导差异性IFN-I产生通路相关基因表达的研究

手足口病(hand,foot and mouth disease,HFMD)是一种全球性的传染病,其主要病原体为肠道病毒A组71型(Enterovirus group A 71,EV-A71)和柯萨奇病毒A组16型(cosackievirus A 16,CV-A16)。EV-A71感染易引发重症病例及死亡病例,而CV-A16感染所致的症状普遍较轻,且CV-A16容易引发重复感染,但目前其中的机理仍不清楚。本研究比较了EV-A71与CV-A16感染正常人呼吸道上皮细胞16HBE后I型干扰素(Type I interferon,IFN-Ι)产生相关基因的改变。结果发现EV-A71感染后TLR3、TLR7、RIG-I、MDA5、MAVS、MyD88、IRF3、IRF7、IFNα和IFNβ的基因表达量均发生了显著性地上调,而在CV-A16感染后仅MDA5显著性上调;TLR3和IRF3的基因表达水平显著性地下降,而其它基因表达水平均无显著性地变化。此外,病毒滴度和病毒拷贝数的检测结果显示,CV-A16在16HBE上的复制效率明显高于EV-A71。上述结果提示我们EV-A71和CV-A16感染16HBE对其IFN-I产生相关基因表达的影响完全不一样,且CV-A16更容易感染人呼吸道上皮细胞。本研究为EV-A71和CV-A16引起的临床症状差异的机理研究以及CV-A16重复感染的机理研究提供了线索。

CV-A16和EV-A71感染对肠道上皮细胞间连接分子排布和表达的影响

柯萨奇病毒A组16型(Coxsakievirus A 16,CV-A16)与肠道病毒71型(Enterovirus 71,EV-A71)是引发手足口病(Hand foot and mouth disease,HFMD)的两种主要病原体,然而两者的致病机理仍未完全被阐明。病毒感染对肠道上皮细胞间连接分子排布和表达直接与病毒感染造成的后果相关。本研究通过右旋糖苷穿透实验、免疫荧光以及蛋白免疫印迹等技术检测了CV-A16和EV-A71感染对肠道上皮细胞系(Intestinal epithelial cell)FHC后细胞通透性的变化以及细胞间连接分子排布和表达情况。研究结果表明,CV-A16和EV-A71感染FHC可导致其通透性显著增强、连接分子Nectin1、Claudin4、Claudin5、ZO-1以及E-Cadherin的排布被破坏,且表达量显著性降低。这一结果提示了CV-A16和EV-A71感染肠道FHC细胞并在细胞中复制引起肠道上皮细胞损伤,导致肠道上皮细胞间连接分子排布的改变和表达量的减少。