口蹄疫病毒3ABC单抗阻断ELISA抗体检测方法应用

正根据新型口蹄疫疫苗生产工艺,用灭活疫苗免疫的动物不会产生病毒非结构蛋白3ABC抗体。因此,采用口蹄疫病毒非结构蛋白3ABC单抗阻断ELISA试验,可以区分免疫抗体与自然感染抗体。1材料与方法1.1实验材料1.1.1实验动物随机抽取基地牧场3-4月龄经过口蹄疫灭活三价疫苗免疫健康犊牛30-40头。1.1.2试验试剂盒采用中国农业科学院兰州兽医研究所口蹄疫病毒3ABC单抗阻断ELISA抗体检     

口蹄疫3ABC非结构蛋白抗体检测试剂盒适用范围探讨

为了调查口蹄疫3ABC非机构蛋白抗体在临床诊断健康的动物体内是否存在,以及探索3ABC抗体检测试剂盒的适用范围,设计此试验。随机选取新乡市辖区范围内的猪场4个、牛场12个、羊场9个,采集动物全血,分离血清,利用间接ELISA方法(3ABC-I-ELISA)和荧光PCR方法分别检测免疫过口蹄疫疫苗的健康猪、牛、羊体内非结构蛋白3ABC抗体存在情况和血清中口蹄疫病毒存在情况。结果发现,临床健康动物也会产生口蹄疫3ABC非结构蛋白抗体,且动物日龄越大,产生抗体的比例越高。表明口蹄疫3ABC非结构蛋白抗体不仅在野毒感染动物(包括隐性感染动物)体内产生,而且在健康动物中由于免疫频率的增加和免疫剂量的加大也会产生。因此,口蹄疫3ABC非结构蛋白抗体检测试剂盒只适用于对口蹄疫疫情的初筛,且在日龄较小或免疫口蹄疫疫苗次数较少的动物更加适用。     

科技

<正>兰州兽医所科研团队建立口蹄疫感染和免疫鉴别诊断技术体系近日,从中国农业科学院兰州兽医研究所获悉,经十余年的努力,该所科研团队建立了口蹄疫感染和免疫鉴别诊断技术体系。该体系包括研发了口蹄疫病毒非结构蛋白3ABC抗体检测ELISA试剂盒;口蹄疫病毒非结构蛋白2C3AB抗体检测试纸条;口蹄疫病毒非结构蛋白3ABC单抗阻断ELISA抗体检测试剂盒;口蹄疫病毒五种非结构蛋白抗体检测免疫印迹技术等。     

口蹄疫灭活疫苗的免疫效果及其对鉴别诊断的干扰

灭活疫苗免疫是防控口蹄疫的重要措施,但是灭活疫苗的免疫效果及其对感染与免疫鉴别诊断的干扰一直是口蹄疫免疫无疫区建设评估需要明确的重要问题。本研究中选择了3个企业（代号A、B与C）的4组口蹄疫O型与A型二价灭活疫苗,分别免疫口蹄疫抗体阴性健康未成年牛,免疫3～4次,测定免疫前后结构蛋白和非结构蛋白抗体的应答水平。结果显示：（1）结构蛋白抗体合格率：a1组（A企业多批次疫苗）4次免疫后O型和A型均为100%;a2组（A企业同批次疫苗）一~三免O型为36.7%、98.3%与100%,A型为15%、86.7%与100%;b组（B企业疫苗）一~三免O型为18.3%、97%与100%,A型为1.7%、45%与53.3%;c组（C企业疫苗）一~三免O型为26.7%、96.7%与100%,A型为21.7%、71.7%与100%。（2）非结构蛋白3ABC抗体阳性率（两种方法复核结果）：a1组一~四免分别为0.7%、1.4%、9.5%与4.8%;a2组和c组三次免疫均未检测到阳性;b组仅三免后阳性率为0.6%。3组灭活疫苗首次免疫牛的抗体合格率远不及70%,但加强免疫后抗体合格率均显著提高;非结构蛋白抗体检测结果表明有3组疫苗的抗原纯净度符合OIE的要求,但a1组灭活疫苗免疫后,仍然对感染与免疫鉴别诊断存在干扰;采用两种非结构蛋白抗体检测方法进行复核检验,可以提高感染与免疫鉴别诊断的准确性。本研究为口蹄疫免疫无疫评价方案的制定提供了科学依据。     

用口蹄疫病毒非结构蛋白鉴别感染动物与疫苗免疫接种动物

口蹄疫是由口蹄疫病毒引起的发生于偶蹄类动物的一种急性、热性传染病,曾多次在世界上发生过大流行。疫苗接种是防控口蹄疫暴发的有效措施之一,而要控制口蹄疫的流行,首先要将病毒感染动物从疫苗接种群体中区分开来。以口蹄疫病毒非结构蛋白(NSPs)为抗原,分别利用口蹄疫病毒非结构蛋白2C、3B、3AB和3ABC作为鉴别诊断抗原,检测动物体内的NSPs抗体,可有效的区分感染动物与疫苗免疫接种动物。目前,许多实验室已展开此项工作的研究,这为防控口蹄疫打下了良好的基础。     

口蹄疫病毒3ABC非结构蛋白抗体检测结果分析

随机选取猪、牛、羊场不同日龄动物血清,利用间接ELISA方法（3ABC-Ⅰ-ELISA）检测接种口蹄疫病毒疫苗的健康猪、牛、羊体内非结构蛋白3ABC抗体存在情况.结果发现临床健康动物也会产生3ABC非结构蛋白抗体,且动物日龄越大,产生抗体的比例越高.这可能与日龄越大的动物在生长过程中感染口蹄疫的概率越大有关,或与多次疫苗免疫后导致产生非结构蛋白抗体有关.因此,口蹄疫3ABC非结构蛋白抗体检测适用于对口蹄疫疫情的初筛,且对日龄较小或免疫口蹄疫疫苗次数较少的动物比较适用.     

口蹄疫病毒非结构蛋白2C基因在昆虫细胞中的表达及应用

研究口蹄疫病毒(FMDV)非结构蛋白(NSP) 2C在区分灭活疫苗免疫动物与自然感染动物方面的意义.本研究将FMDV NSP 2C基因,克隆到穿梭载体pFast-bac- HT-B,将其转入含骨架载体Bacmid的DH10Bac,经蓝白斑筛选得到重组骨架质粒Bacmid-2C.将Bacmid-2C转染昆虫细胞Sf9,鉴定正确后,经3次增殖获得高滴度的P-3代病毒后,在High Five细胞中进行目的蛋白的表达.SDS-PAGE结果显示在High Five细胞中得到了相对分子质量约为38.93 ku的目的蛋白2C,Western blotting及Dot-ELISA结果显示,该表达产物对FMDV感染动物阳性血清有良好的反应性.以电泳纯化的2C蛋白为抗原建立间接ELISA,检测健康非免疫动物、免疫动物及FM-DV试验感染动物血清,结果表明2C-ELISA不但能区分免疫动物和感染动物的血清,而且还能检测FMDV感染早期动物血清中的2C抗体.说明昆虫细胞表达的2C蛋白可作为FMDV疫苗免疫动物与自然感染动物鉴别诊断的良好抗原.2C基因在Bac-to-Bac系统中的成功表达为建立通过检测几种NSP抗体,筛查感染及隐性带毒动物,净化畜群的方法奠定了基础.     

免疫猪群口蹄疫非结构蛋白抗体与免疫剂量的关系

为了鉴别免疫猪群3ABC抗体阳性猪是免疫动物受到病毒感染引起的,还是疫苗中残留的非结构蛋白引起的,通过检测免疫动物体内的3ABC抗体和病毒感染情况,探讨3ABC抗体的出现与免疫剂量的关系。选取60日龄保育猪20头,分成A、B、C、D 4个组,分别注射猪口蹄疫O型灭活疫苗(OS/99株)1、2、4、6m L/头。每组猪分别在免疫前1 d以及免疫后3、7、14、30和60 d,采集血清和鼻咽拭子,使用口蹄疫3ABC间接ELISA检测试剂盒、口蹄疫多重RT-PCR检测试剂盒以及病毒分离试验,检测3ABC抗体和病毒感染情况,发现保育猪在低剂量(1 m L/头或2 m L/头)免疫后没有检测到非结构蛋白抗体,而高剂量(4 m L/头或6m L/头)免疫后出现非结构蛋白抗体阳性率升高,而且出现非结构蛋白抗体阳性的动物中没有检出病毒感染或病毒核酸。检测结果提示这些免疫猪群非结构蛋白抗体的形成与免疫剂量有关。     

口蹄疫O型、A型二价3B蛋白表位缺失灭活疫苗免疫安全性和抗体消长规律研究

为摸清口蹄疫O型、A型二价3B蛋白表位缺失灭活疫苗免疫安全性和抗体消长规律,对试验猪群进行免疫,观察其健康状况,采用口蹄疫非结构蛋白ELISA检测非结构蛋白抗体,采用液相阻断ELISA检测O型和A型口蹄疫抗体。结果显示,疫苗免疫后,猪群健康状况良好,各时间点口蹄疫非结构蛋白抗体均为阴性;免疫前、一免后29 d、61 d、95 d、123 d,二免后30 d、64 d、92 d,A型口蹄疫抗体阳性率分别为7.14%、100%、100%、100%、100%、100%、100%和100%,O型口蹄疫抗体阳性率分别为0、100%、100%、100%、100%、100%、100%和100%。表明该疫苗免疫猪只后,安全性好,不会诱导动物机体产生口蹄疫非结构蛋白抗体,诱导产生的高水平A型、O型口蹄疫抗体可以维持较长时间,实施一免可维持至少4个月,实施二免可维持至少3个月。     

口蹄疫病毒抗体检测

口蹄疫是一种急性、高度接触性、烈性的传染病,是由口蹄疫病毒引起的,常常发生在偶蹄动物,偶尔也见于人和其它动物。世界动物卫生组织已经将该病列为法定申报传染病,我国将其列为一类动物疫病。我国主要通过实施强制免疫来预防控制该病,疫苗免疫之后所产生的抗体水平是评价免疫效果的重要手段,也可以根据免疫后的效果来制定合理免疫程序。本实验室主要通过口蹄疫液相阻断和3ABC非结构蛋白抗体检测试剂盒来进行抗体检测。     

Developments in diagnostic techniques for differentiating infection from vaccination in foot-and-mouth disease

Foot-and-mouth disease (FMD) is a highly contagious and economically significant disease of cattle, pigs, sheep, goats and wild ruminant species. The FMD virus genome encodes a unique polyprotein from which the different viral polypeptides are cleaved by viral proteases, including eight different non-structural proteins (NSPs). Both structural and non-structural antigens induce the production of antibodies in infected animals. In contrast, vaccinated animals which have not been exposed to replicating virus will develop antibodies only to the viral antigens in the inactivated material. Vaccination against FMD is a key element in the control of the disease in addition to slaughter and movement restrictions. However, countries that vaccinate in the event of an outbreak will have to re-establish their FMD free status to the satisfaction of their trading partners.Because currently available vaccines stimulate the production of antibodies indistinguishable from those produced by infected animals in response to live virus and because vaccinated animals can be infected and become carriers of FMD virus, efforts have been made to develop diagnostic test that can differentiate vaccinated animals from those that are convalescent and from those that have been vaccinated and become carriers following subsequent contact with live virus. Currently the detection of antibodies to non-structural protein's (NSPs) is the preferred diagnostic method to distinguish virus infected, carrier, animals from vaccinated animals. However this is currently only possible at the herd level because of the great variability in the initiation, specificity and duration of the immune response in individual animals to the NSPs shown in many studies. Considerable effort and attention is now being directed toward the development of new methods and techniques for the rapid and accurate detection of anti-NSP antibodies, harmonization and standardization of current diagnostic techniques, as well as the production of defined reagents.     

Presence of antibodies to non-structural proteins of foot-and-mouth disease virus in repeatedly vaccinated cattle

For the purpose of removing infected animals by detecting humoral immune responses to non-structural proteins of the foot-and-mouth disease (FMD) virus, antibodies induced by contaminated residual non-structural proteins contained in less pure FMD vaccine can be problematic for serological screening. The aim of the present study was to measure the possible presence of antibodies against these non-structural proteins in repeatedly vaccinated calves and beef cattle. Five imported FMD vaccines were examined using two commercial ELISA kits, UBI FMDV NS EIA and Ceditest FMDV-NS, for serological testing. After five doses of vaccination, the serum of one calf tested positive, and two vaccines induced a significant increase in anti-3ABC antibodies in calves. This finding demonstrated that a positive reaction to non-structural proteins due to impurities in the FMD vaccine was detectable using commercial tests. A low percentage of field sera sampled from beef cattle in Kinmen also tested positive, but the key factor resulting in the positive reactions could not be positively identified based on our data.     

Comparable sensitivity and specificity in three commercially available ELISAs to differentiate between cattle infected with or vaccinated against foot-and-mouth disease virus

Three commercially available ELISAs for the detection of antibodies to the non-structural proteins of foot-and-mouth disease virus (FMDV) were evaluated, using sera from uninfected, vaccinated, infected, inoculated, first vaccinated and subsequently infected, and first vaccinated and subsequently inoculated cattle. We compared antibody kinetics to non-structural proteins, sensitivity, and specificity. One of the ELISAs had a higher sensitivity and much lower specificity than the other two, therefore we established standardised cutoff values for the compared assays using receiver operated characteristic (ROC) curves. Using the standardised cutoff values, all three ELISAs produced comparable results with respect to sensitivity and specificity. Antibody development to non-structural proteins after infection and after vaccination/infection was not significantly different. Development of antibodies, however, both neutralising and directed to non-structural proteins, was significantly delayed after intranasal inoculation as compared to intradermolingual infection. Based on results of sera obtained after vaccination and experimental infection all three assays can be used for testing sera collected between 4 weeks and 6 months after infection. More information is needed on the prevalence of positive reactors in a situation where emergency vaccination has been used and FMD transmission was still observed.     

Anti-3AB antibodies in the Chinese yellow cattle infected by the O/Taiwan/99 foot-and-mouth disease virus.

The O/Taiwan/99 foot-and-mouth disease virus (FMDV), a South Asian topotype of serotype O, was introduced into Taiwan in 1999. The Chinese yellow cattle infected by the virus did not develop clinical lesions under experimental and field conditions. A blocking enzyme-linked immunosorbent assay (ELISA) kit with the 3AB antigen, a polypeptide of FMDV non-structural (NS) proteins, was used to evaluate the development and duration of anti-3AB antibodies, proving active viral replication, in the Chinese yellow cattle. The specificity of the assay was 99%, as was established with negative sera from regularly vaccinated and from na?ve cattle. The sensitivity tested with sera from naturally infected animals was approximately 64% and it was lower than that obtained by serum neutralization (SN) test. Under experimental infection, the Chinese yellow cattle developed lower anti-3AB antibodies than that developed in other species. Duration of anti-3AB antibodies was traced in two herds of naturally infected animals, indicating that anti-3AB antibodies persisted for approximately 6 months after outbreaks. On the basis of this study, we propose that the Chinese yellow cattle may have natural resistance, which limits viral replication and reduces the development of anti-3AB antibodies.     

Differentiating infection from vaccination in foot-and-mouth-disease: evaluation of an ELISA based on recombinant 3ABC

Recent devastating outbreaks of foot-and-mouth disease (FMD) in Europe have reopened the discussion about the adequacy of the non-vaccination strategy implemented by the EU in 1991. Here we describe the evaluation of a new commercially available test kit for the discrimination between vaccination and infection. The test is based on the detection of antibodies against the recombinant non-structural (NS) protein 3ABC. In contrast to immunization with vaccines free of 3ABC, these antibodies are elicited as a consequence of infection. Testing more than 3600 negative sera from several countries revealed a specificity of > 99% for bovine, ovine, and porcine samples. Antibodies specific for 3ABC can be detected as soon as 10 days post-infection. As compared with the occurrence of antibodies against structural proteins of FMDV, anti-3ABC antibodies can be detected 5-10 days later, depending on the species. No anti-3ABC antibodies were detected in sera from vaccination experiments or in field sera from vaccinated animals. However, anti-3ABC antibodies can be detected in vaccinated animals upon challenge. These results provide evidence that this test can facilitate the use of vaccines in new strategies against FMD.     

Detection of carriers of foot-and-mouth disease virus among vaccinated cattle

To investigate and optimise detection of carriers, we vaccinated 15 calves with an inactivated vaccine based on foot-and-mouth disease virus (FMDV) A Turkey strain and challenged them and two further non-vaccinated calves with the homologous virus four weeks later. To determine transmission to a sensitive animal, we put a sentinel calf among the infected cattle from 60 days post-infection until the end of the experiment at 609 days post-infection. Samples were tested for the presence of FMDV, viral genome, specific IgA antibodies, antibodies against FMDV non-structural (NS) proteins or neutralising antibodies. Virus and viral genome was intermittently isolated from probang samples and the number of isolations decreased over time. During the first 100 days significantly more samples were positive by RT-PCR than by virus isolation (VI), whereas, late after infection more samples were positive by virus isolation. All the inoculated cattle developed high titres of neutralising antibodies that remained high during the entire experiment. An IgA antibody response was intermittently detected in the oropharyngeal fluid of 14 of the 17 calves, while all of them developed detectable levels of antibodies to NS proteins of FMDV in serum, which declined slowly beyond 34 days post-infection. Nevertheless, at 609 days after inoculation, 10 cattle (60%) were still positive by NS ELISA. Of the 17 cattle in our experiment, 16 became carriers. Despite frequent reallocation between a different pair of infected cattle no transmission to the sentinel calf occurred. It remained negative in all assays during the entire experiment. The results of this experiment show that the NS ELISA is currently the most sensitive method to detect carriers in a vaccinated cattle population.     

Cedivac-FMD can be used according to a marker vaccine principle

In this study, we investigated whether Cedivac-FMD, an emergency vaccine against foot-and-mouth disease (FMD), is suitable for use conjointly with a screening program intended to confirm freedom from disease in vaccinated herds based on evidence of virus replication in vaccinates. Different sets of sera were tested using the Ceditest FMDV-NS ELISA for the detection of antibodies against non-structural proteins (NSPs) of FMD virus. During a vaccine safety study, serum samples were collected from 10 calves, 10 lambs and 10 piglets following administration of a double dose and a repeat dose of high payload trivalent Cedivac-FMD vaccine. All serum samples collected both 2 weeks following the administration of a double dose as well as those collected 2 weeks after the single dose booster (given 2 weeks after the double dose) were negative in the Ceditest FMDV-NS ELISA. In a series of vaccine potency experiments, serum samples were collected from 70 vaccinated cattle prior to and following exposure to infectious, homologous FMD virus. When testing cattle sera collected 4 weeks after vaccination with a regular dose of monovalent >6 PD(50) vaccines, 1 of 70 animals tested positive in the NSP antibody ELISA. After infection with FMD virus, antibodies to NSP were detected in 59 of 70 vaccinated cattle and 27 of 28 non-vaccinated control animals within 7 days. Cedivac-FMD vaccines do not induce NSP antibodies in cattle, pigs or sheep following administration of a double dose or a repeat dose. FMD-exposed animals can be detected in a vaccinated group within 7-14 days. Because Cedivac-FMD does not induce NSP antibodies, the principle of 'marker vaccine' applies.     

A Bayesian evaluation of six diagnostic tests for foot-and-mouth disease for vaccinated and non-vaccinated cattle

The sensitivity and specificity of six ELISA tests for foot-and-mouth disease (FMD) to discriminate between sero-converted (for non-structural FMD virus proteins) and non-sero-converted cattle were evaluated for vaccinated and unvaccinated cattle. Since none of the tests could be considered as a proper reference test and for about half of the tested sera the true status (sero-converted or not for non-structural proteins, i.e. presence of antibodies) of the animals was unknown, a Bayesian analysis employing a latent class model was used that did not rely on the use of a reference test or gold standard. Prior information about prevalence for subsets of the data and specificity of the tests was incorporated into the analysis. The specificity of the six tests for vaccinated and non-vaccinated cattle ranged from 96 to 99%. For vaccinated cattle, one test stood out with an estimated sensitivity of 94% (95% CI from 89.8 to 98.1%). Second best for vaccinated cattle were two tests with estimated sensitivities of 85% (95% CI from 78.9 to 89.7%) and 92% (95% CI from 86.2 to 95.6%). For non-vaccinated cattle, the sensitivities of these three tests were around 97%. The remaining three tests showed lower estimated sensitivity for vaccinated cattle, ranging from 57 to 79%.     

Non-structural protein 3A for differentiation of foot-and-mouth disease infected and vaccinated animals in Haryana (India)

There are severe international trade restrictions on foot-and-mouth disease (FMD) affected areas. Because of endemic nature of FMD, India started FMD control programme (FMD-CP) using mass vaccination in selected states including Haryana (year 2003). Although no significant incidence of the disease was reported after launching FMD-CP in the state but in order to participate in international trade of animal and animal products, veterinary authorities have to prove that there is no FMD virus (FMDV) circulation in the animal population, for which it is necessary to differentiate the FMD infected and vaccinated animals. For this purpose, an in-house indirect ELISA utilizing baculovirus-expressed FMDV non-structural protein (NSP) 3A was used to find evidence for virus circulation (prevalence of anti-NSP 3A-specific antibodies) by examining serum samples that were collected either before start of FMD-CP or after completion of third phase (Pre-4th) of vaccination in Haryana (India). A significant reduction (P < 0.01) in prevalence of anti-NSP 3A-specific antibodies (possibly carriers) was observed 2 years after launching FMD-CP in Haryana. However, in cattle the percentage of animals with anti-NSP 3A-specific antibodies was found to be significantly higher (P < 0.01) than buffalo, both before (P < 0.01) and after (P < 0.01) launching FMD-CP in the state. The findings of this study suggest that use of FMDV vaccine in cattle and buffaloes in endemic areas reduces virus circulation (carriers) in the vaccinated herds and that the current 3ANSP-ELISA can be successfully used to monitor the FMDV circulation in endemic areas.     

Differentiation of foot-and-mouth disease-infected pigs from vaccinated pigs using antibody-detecting sandwich ELISA

The presence of serum antibodies for nonstructural proteins of the foot-and-mouth disease virus (FMDV) can differentiate FMDV-infected animals from vaccinated animals. In this study, a sandwich ELISA was developed for rapid detection of the foot-and-mouth disease (FMD) antibodies; it was based on an Escherichia coli-expressed, highly conserved region of the 3ABC nonstructural protein of the FMDV O/TW/99 strain and a monoclonal antibody derived from the expressed protein. The diagnostic sensitivity of the assay was 98.4%, and the diagnostic specificity was 100% for na?ve and vaccinated pigs; the detection ability of the assay was comparable those of the PrioCHECK and UBI kits. There was 97.5, 93.4 and 66.6% agreement between the results obtained from our ELISA and those obtained from the PrioCHECK, UBI and CHEKIT kits, respectively. The kappa statistics were 0.95, 0.87 and 0.37, respectively. Moreover, antibodies for nonstructural proteins of the serotypes A, C, Asia 1, SAT 1, SAT 2 and SAT 3 were also detected in bovine sera. Furthermore, the absence of cross-reactions generated by different antibody titers against the swine vesicular disease virus and vesicular stomatitis virus (VSV) was also highlighted in this assay's specificity.