用荧光定量RT-PCR方法检测猪瘟病毒

为了建立能特异检测不同基因型猪瘟病毒(Classical swine fever virus,CSFV),同时又能区分其他瘟病毒的基因检测方法,本实验针对CSFV基因组5′端非编码区设计并合成了简并引物和TaqMan探针,在优化反应条件的基础上,成功地建立了特异检测CSFV的荧光定量RT-PCR检测方法。再以已知滴度的CSFV石门株血毒总RNA反转录产物建立标准品,该标准品可以用于定量临床样品中的CSFV滴度,所建立的荧光定量PCR方法可以灵敏地检测出10~(-0.82)个TCID_(50)病毒含量。最后用建立的方法对108份临床样品进行检测并同时进行病毒分离,荧光定量PCR方法检测出73份阳性样品且与病毒分离的符合率为100%,而常规RT-PCR只检测出54份阳性样品,表明本荧光定量RT-PCR法在检测猪瘟病料上具有潜在的应用价值。     

Evaluation of real-time RT-PCR assay for the routine intra vitam diagnosis of classical swine fever

The aim of the study was to evaluate the diagnostic quality of the real-time RT-PCR assay described by Hoffmann et al. [Hoffmann, B., Beer, M., Schelp, C., Schirrmeier, H., Depner, K., 2005. Validation of a real-time RT-PCR assay for sensitive and specific detection of classical swine fever. J. Virol. Methods 130, 36-44] for the routine intra vitam diagnosis of classical swine fever (CSF). We compared the assay with conventional diagnostic methods by using defined diagnostic material from an animal experiment with pigs showing different clinical forms of CSF. Compared to virus isolation and antigen ELISA an enhanced sensitivity of the real-time RT-PCR could be shown. We were able to detect all infected pigs regardless of the clinical course of CSF. CSF infection was detected already during the incubation period, during the entire clinical phase as well as at the beginning of convalescence when the first antibodies were detected and no virus could be isolated any more. In most cases, positive PCR results were obtained 2 days earlier than with virus isolation and 2-4 days earlier than with the antigen ELISA.     

Development of a triplex TaqMan real-time RT-PCR assay for differential detection of wild-type and HCLV vaccine strains of classical swine fever virus and bovine viral diarrhea virus 1

In this study, genomic sequences of pestiviruses available in GenBank were aligned to design three primer pairs and TaqMan probes: two targeting the NS5A region of the viral genome of classical swine fever virus (CSFV) for the differentiation of wild-type CSFV and hog cholera lapinized vaccine (HCLV) vaccine, and one targeting the 5'-untranslated region of bovine viral diarrhea virus 1 (BVDV-1). With these primers and probes, a triplex TaqMan real-time RT-PCR assay was developed for differentiating wild-type CSFV, the HCLV strain, and BVDV-1. The detection limit of the assay was 4.5 TCID(50) for wild-type CSFV, 10 TCID(50) for HCLV-strain CSFV, and 3.2 TCID(50) for BVDV-1. The triplex real-time RT-PCR had at least 98% (248 samples) agreement with other RT-PCR methods. The assay provides a sensitive tool for simultaneous detection and differentiation of wild-type CSFV and HCLV from BVDV-1.     

Classical swine fever virus: a second ring test to evaluate RT-PCR detection methods

Six laboratories participated in a study to compare the sensitivity and specificity of RT-PCR tests for the detection of classical swine fever virus (CSFV). Sets of coded samples were prepared by serial dilution of positive samples and then distributed to each of the laboratories. One set comprised 25 samples of random primed cDNA, synthesised from viral RNA representative of different pestiviruses. The other set comprised samples of blood and serum obtained from virus-free or CSFV-infected pigs. Each laboratory tested the samples using PCR/RT-PCR according to a set of standardised protocols that specified the exact conditions and requirements for inclusion of control samples. Two types of test were evaluated. One amplified a part of the 5'-non coding region of the pestivirus genome by means of a closed, one-tube RT-nested PCR. The other amplified a part of the NS5B gene using non-nested RT-PCR. The results of the laboratories were compared with one another, and with those obtained earlier when similar samples were tested by the same laboratories using non-standardised methods [Paton et al., Classical swine fever virus: a ring test to evaluate RT-PCR detection methods, Vet. Microbiol., in press]. Standardisation of the protocols resulted in a more consistent test sensitivity. Three laboratories avoided significant false positive results. Others that did not, could nevertheless recognise that test specificity was inadequate from the results obtained with the control samples. Minimum requirements for the inclusion of adequate controls and periodic proficiency testing are proposed.     

荧光定量RT-PCR法对犬瘟热病毒PS株感染犬血清和粪便中病毒的检测

为研究犬人工感染犬瘟热病毒(CDV)后病毒在血清和粪便中的含量及变化,本实验根据CDV核衣壳蛋白(NP)基因序列设计一对特异引物,扩增NP基因.并以NP基因重组质粒作为阳性标准品,建立检测CDV的SYBR GreenⅠ荧光定量RT-PCR方法.结果表明,该方法102拷贝～109拷贝范围内具有良好的线性关系,相关系数为R2=0.998,扩增效率为E=98.3％,敏感度高,最低检测限为6.1拷贝/μL,重复性检测变异系数低于2.62％.该方法与常规RT-PCR方法比较,其敏感性提高102倍.两只人工感染CDV PS强毒株的犬,分别于接种后17d、19d发病死亡,采用荧光定量RT-PCR方法对人工感染犬的血液和拭子液中的病毒核酸栽量进行定量检测以及对收集的22份临床样本拭子液进行检测,均检测到CDV.本研究结果表明,该方法可以用于CDV核酸定量检测,为该病毒的致病机理及病毒传播途径的研究提供了一种快速和敏感的检测手段.     

How molecular methods change our views of FeLV infection and vaccination

FeLV was discovered 40 years ago and vaccines have been commercially available for almost two decades. So far, most FeLV pathogenesis and vaccine studies were conducted assaying parameters, such as virus isolation and antigen detection. Accordingly, regressive infection was characterized by transient or undetectable viremia, while persistent viremia is typically observed in cats with progressive infection. Using real-time polymerase chain reaction assays, the spectrum of host response categories to FeLV infection was recently refined by investigating proviral and plasma viral RNA loads. Cats believed to be immune to FeLV infection were found to turn provirus-positive after virus exposure. Moreover, efficacious FeLV vaccines were found unable to prevent provirus-integration and minimal viral replication. Remarkably, no difference was found in initial proviral and plasma viral RNA loads between cats with different infection outcomes. Only subsequently, the infection outcome is associated with FeLV loads. FeLV provirus was found to persist for years; reoccurrence of viremia and disease development was observed in some cats. Thus, aviremic provirus-positive cats are FeLV carriers and, following reactivation, may act as an infection source. However, integrated viral DNA may also be essential for solid protection and long-lasting maintenance of protective immunity. In conclusion, real-time TaqMan PCR and RT-PCR assays are highly sensitive and specific. They yield a more sensitive measure for FeLV exposure than antigen detection, virus isolation or immunofluoresence assays. We recommend the use of real-time PCR assays to identify FeLV exposed cats, particularly in catteries, and investigate obscure clinical cases that may be FeLV-associated. The use of sensitive molecular methods will contribute to a more in-depth understanding of the FeLV pathogenesis.     

Comparison of five diagnostic methods for detecting bovine viral diarrhea virus infection in calves.

Five diagnostic techniques performed on skin biopsies (shoulder region) and/or serum were compared for detection of bovine viral diarrhea virus infection in 224 calves 0-3 months of age, 23 calves older than 3 months but younger than 7 months, and 11 cattle older than 7 months. The diagnostic methods used were immunohistochemistry (IHC), 2 commercial antigen ELISAs, 1 commercial antibody ELISA, and real-time RT-PCR. Results of 249 out of 258 skin and serum samples were identical and correlated within the 3 antigen detection methods and the real-time RT-PCR used. Twenty-six of these 249 samples were BVDV-positive with all antigen detection methods and the real-time RT-PCR. Nine out of 258 samples yielding discordant results were additionally examined by RT-PCR, RT-PCR Reamplification (ReA), and antigen ELISA I on serum and by immunohistochemistry on formalin fixed and paraffin-embedded skin biopsies. Virus isolation and genotyping was performed as well on these discordant samples. In 3 cases, transiently infected animals were identified. Two samples positive by real-time RT-PCR were interpreted as false positive and were ascribed to cross-contamination. The antigen ELISA II failed to detect 2 BVDV-positive calves due to the presence of maternal antibodies; the cause of 2 false-positive cases in this ELISA remained undetermined. Only persistently infected animals were identified in skin samples by IHC or antigen ELISA I. The 3 antigen detection methods and the real-time RT-PCR used in parallel had a high correlation rate (96.5%) and similar sensitivity and specificity values.     

牛传染性鼻气管炎病毒实时荧光定量PCR检测方法的建立

根据牛传染性鼻气管炎病毒(IBRV)保守基因gB和gE序列,分别设计两对引物及其相应的TaqMan探针,建立、优化反应体系后,利用10倍稀释的病毒进行扩增以检测其灵敏度,同时对伪狂犬病病毒(PRV)、马立克病病毒(MDV)、鸭瘟病毒(DPV)进行特异性检测.结果显示,建立的扩增gB和gE基因的荧光PCR可用于检测IBRV,其灵敏度为0.02 TCID50,而与PRV等非IBRV无交叉反应.本研究所建立的荧光PCR具有快速、灵敏、准确、低污染等优点,可用于IBRV的检测.     

Bluetongue virus serotype 8 (BTV-8)-associated brain malformations in two calves

Congenital brain malformations such as hydranencephaly as well as internal and external hydrocephalus combined with porencephaly were diagnosed in two calves which were born in spring 2008. In both calves bluetongue virus was detected by real-time PCR. Teratogenic pestiviruses were not found by serological, molecular or immunohistological methods. A causal relationship between the malformations and the bluetongue serotype 8 epidemic in 2007 has to be considered.     

Evaluation of a novel proximity ligation assay for the sensitive and rapid detection of foot-and-mouth disease virus

A novel proximity ligation assay (PLA) using a pan-serotype reactive monoclonal antibody was developed and evaluated for the detection of foot-and-mouth disease virus (FMDV) in clinical samples collected from field cases of disease. The FMDV-specific PLA was found to be 100 times more sensitive for virus detection than the commonly used antigen capture-ELISA (AgELISA). As few as five TCID50 were detected in individual assays, which was comparable with the analytical sensitivity of real-time RT-PCR. Although this assay was capable of detecting diverse isolates from all seven FMDV serotypes, the diagnostic sensitivity of the PLA assay was lower than real-time RT-PCR mainly due to a failure to detect some SAT 1, SAT 2 and SAT 3 FMDV strains. In conclusion, this new PLA format has high analytical sensitivity for the detection of FMDV in clinical samples and may prove valuable as a rapid and simple tool for use in FMD diagnosis.     

猪瘟病毒RT-PCR核酸检测与ELISA抗原检测试验应用研究

本试验根据NCBI公布的猪瘟病毒石门毒株E2基因序列,设计、合成了1对检测猪瘟病毒E2基因的PCR引物。以120份疑似猪瘟病料为试验材料,使用RT-PCR核酸检测与ELISA抗原检测2种方法,分别用这2种方法检测疑似病料,并且比较这2种方法在猪瘟病料检测中的实际差别。通过猪瘟病毒RT-PCR核酸检测结果及ELISA抗原检测结果相互印证,为云南猪瘟的诊断及防制提供了技术支持。