Importance of primer selection in the application of PCR technology to the diagnosis of bovine leukemia virus

PCR detection for syphilis diagnosis: Status and prospects

Syphilis, a re‐emerging public health problem worldwide caused by Treponema pallidum subsp pallidum (T. pallidum), usually induces systemic and chronic inflammation in hosts who do not receive timely therapy after exposing to high‐risk factors such as leprous sexual contact. Before the treatment, rapid and accurate detection of syphilis is essential. However, the existing detection methods, which focus on the treponemal or non‐treponemal antibody test, both have inherent limitations. For instance, both of them cannot distinguish the stage and severity of syphilis. Non‐treponemal test such as RPR, which is generally deemed to be used for assessing treatment response, is influenced by biological false positives. Therefore, it is imperative to seek out a new and effective diagnostic test. With recent advancements in molecular biology and whole‐genome sequencing, the molecular diagnosis has increased in popularity, especially the use of polymerase chain reaction (PCR). Here, we firstly present a mini‐review on the research of PCR detection methods used for syphilis diagnosis over the past decade, and we then compare these methodologies to assess their potential and the challenges faced. This information can provide a fresh perspective to help researchers address the current challenges.

Development of an improved real time PCR for the detection of bovine leukaemia provirus nucleic acid and its use in the clarification of inconclusive serological test results

With the aim to erradicate Enzootic Bovine Leukosis from Poland, a more sensitive real-time polymerase chain reaction was required and developed to detect proviral Bovine leukaemia virus (BLV) DNA, the causative agent of Enzootic Bovine Leukosis (EBL). This new method proved more sensitive for our needs, than the current protocols available in the public domain. DNA was extracted from peripheral blood leukocytes of 51 cattle, which had given rise to doubtful serological test results by ELISA, and from mesenteric lymph nodes of six cattle that were slaughtered as EBL suspect cases. Additionally, fourteen DNA samples were obtained from animals with a strong BLV antibody response by ELISA. All real-time data were compared to results obtained from three different nested PCR methods. All 14 strongly positive ELISA samples were positive in all PCR tests. The real-time assay in comparison to the conventional PCR methods detected 7.8% (4/51) more specimens positive for BLV nucleic acid and showed a detection limit down to one copy. These observations represent the first report in the value of using a real-time method to help elucidate the disease status of animals when inconclusive ELISA results are obtained in the diagnostic laboratory. Thus, this method should be recommended for use in countries which have implemented an EBL-eradication programme, where a low level of BLV infection is evident.

Evaluation of a new antibody-based enzyme-linked immunosorbent assay for the detection of bovine leukemia virus infection in dairy cattle

The objective of this study was to validate a new blocking enzyme-linked immunosorbent assay (ELISA) (designated M108 for milk and S108 for serum samples) for detecting bovine leukemia virus (BLV) infection in dairy cattle. Milk, serum, and ethylenediaminetetraacetic acid-blood samples were collected from 524 adult Holstein cows originating from 6 dairy herds in Central Argentina. The M108 and S108 were compared with agar gel immunodiffusion (AGID), polymerase chain reaction and a commercial ELISA. Because there is currently no reference test capable of serving as a gold standard, the test sensitivity (SE) and specificity (SP) were evaluated by the use of a latent class model. Statistical inference was performed by classical maximum likelihood and by Bayesian techniques. The maximum-likelihood analysis was performed assuming conditional independence of tests, whereas the Bayesian approach allowed for conditional dependence. No clear conclusion could be drawn about conditional dependence of tests. Results with maximum likelihood (under conditional independence) and posterior Bayes (under conditional dependence) were practically the same. Conservative estimates of SE and SP (with 95% confidence intervals) for M108 were 98.6 (96.7; 99.6) and 96.7 (92.9; 98.8) and for S108 99.5 (98.2; 99.9) and 95.4 (90.9; 98.1), respectively. The ELISA 108 using either milk or serum to detect BLV-infected animals had comparable SE and SP with the official AGID and a commercial ELISA test, which are currently the most widely accepted tests for the serological diagnosis of BLV infection. Therefore, ELISA 108 can be used as an alternative test in monitoring and control programs.

Sensitive and specific detection of proviral bovine leukemia virus by 5' Taq nuclease PCR using a 3' minor groove binder fluorogenic probe

Sensitive assays are required to detect proviral bovine leukemia virus (BLV) in donor cattle used for the in vivo preparation of Australian tick fever vaccines. 5' Taq nuclease assays using 3' minor groove binder DNA probes (TaqManMGB) were developed and compared to conventional PCR assays for sensitive detection of Australian BLV. Seven beef and dairy herds were screened using DNA prepared by a variety of protocols to evaluate these tests. Comparative sensitivities of PCR tests were determined by testing log(10) dilutions of plasmids with inserted BLV sequences. Animals were also screened by the BLV standard agar-gel immunodiffusion test (AGID) and commercial enzyme linked immunosorbent assays (ELISA) for antibodies, and an ELISA for detecting viral antigens expressed (VAE) in lymphocyte cultures. The TaqMan MGB assay based on the pol region was the most sensitive and specific for the detection of BLV. This is the first report of a sensitive BLV 5' Taq nuclease assay.

Sensitive and specific detection of bovine immunodeficiency virus and bovine syncytial virus by 5' Taq nuclease assays with fluorescent 3' minor groove binder-DNA probes

Sensitive assays are required to detect bovine retroviruses in donor cattle used for the in vivo preparation of Australian tick fever vaccines. 5' Taq nuclease assays using 3' minor groove binder DNA probes (TaqMan)MGB) were developed and compared to conventional PCR assays for the sensitive detection of bovine syncytial virus (BSV) and bovine immunodeficiency virus (BIV). Seven beef and dairy herds were screened to evaluate these tests. Comparative sensitivities of PCR tests were determined by testing log(10) dilutions of plasmids with inserts containing corresponding provirus sequences. Published PCR assays targeting BIV env sequences did not adequately amplify Australian BIV sequences. Pol sequences from Australian strains of BIV and BSV were used to design TaqMan MGB assays, which improved sensitivity 10-fold (BIV) and 100-fold (BSV), respectively, over conventional PCR tests. This is the first report of Australian sequences of BIV and BSV and the first 5' Taq nuclease assays described to detect these viruses. These methods could be applied to future studies requiring sensitive detection of these two bovine retroviruses.

Detection of bovine leukemia virus in blood and milk by nested and real-time polymerase chain reactions

Concerns about retroviruses in livestock and products derived from them have necessitated the development of tests to detect the bovine leukemia virus (BLV) in blood and milk from cattle. Dairy cattle (n = 101) from 5 different geographical areas were used for this study. A nested polymerase chain reaction (PCR) identified 98% of BLV seropositive cattle (n = 80) from blood and 65% from milk, whereas real-time PCR detected 94% of BLV seropositive cattle from blood and 59% from milk. Bovine leukemia virus was also detected by PCR in approximately 10% of seronegative cattle (n = 21), most likely because of early detection before seroconversion.

A rapid and sensitive diagnosis of bovine leukaemia virus infection using the nested shuttle polymerase chain reaction

Bovine leukaemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL). In Argentina, where a program to eradicate EBL has been introduced, sensitive and reliable diagnosis has attained high priority. Although the importance of the agar gel immunodiffusion test remains unchanged for routine work, an additional diagnostic technique is necessary to confirm cases of sera with equivocal results or of calves carrying maternal antibodies.Utilizing a nested shuttle polymerase chain reaction, the proviral DNA was detected from cows experimentally infected with as little as 5 ml of whole blood from BLV seropositive cows that were nonetheless normal in haematological terms. It proved to be a very sensitive technique, since it rapidly revealed the presence of the provirus, frequently at 2 weeks postinoculation and using a two-round procedure of nested PCR taking only 3 hours. Additionally, the primers used flanked a portion of the viral genome often employed to differentiate BLV type applying BamHI digestion. It is concluded that this method might offer a highly promising diagnostic tool for BLV infection.

Provirus variants of the bovine leukemia virus and their relation to the serological status of naturally infected cattle

Infection of cattle with the bovine leukemia virus (BLV) results in a strong permanent antibody response to the BLV antigens some weeks after infection. However, cattle may carry provirus and not have detectable antibody titers. To prove the occurrence of different BLV provirus variants in German cattle and to study the influence of special BLV variants on the immunoreaction, a 444-bp fragment of the env gene of 35 naturally BLV infected animals was analyzed. Seven different groups of BLV provirus variants were found on the basis of restriction fragment length polymorphism. Three BLV provirus variant groups and five additionally sequenced BLV isolates showed a high similarity to BLV provirus isolates from other geographical areas. The variation in nucleotide sequence of the five BLV isolates compared with nine previously sequenced BLV isolates ranged up to 5. 3%. While BLV provirus variant groups A, C, D, E, F, and G were clearly related to agar-gel immunodiffusion test (AGID)- and enzyme-linked immunosorbent assay (ELISA)-positive animals, BLV provirus variant group B was solely found in permanent AGID- and ELISA-negative or in transient ELISA-positive animals. Altogether, these results indicate that special BLV provirus variants may be responsible for atypical forms of BLV infection in cattle.

Laboratory diagnostic tests for retroviral infections in dairy and beef cattle

Detection of bovine retroviruses stretches our diagnostic creativity to its limits. The nucleic acid-based, PCR-amplified assays are finding increased clinical use as the veterinary and livestock industry seek earlier detection of infection for eventual corrective management decisions. We are evolving from a point of disease diagnosis by tumor identification through conventional histopathology, to molecular diagnostics for early identification of retroviral nucleic acid (provirus). The clinical use of antibody-based assays lies in the simplicity of testing large numbers of animals, the relative sensitivity of the assays, and the low cost of testing. Although the pathogenicity of bovine leukemia virus (BLV) for cattle has been well documented, the disease potential for bovine immunodeficiency-like virus (BIV) for cattle is still being determined. Nevertheless, pressure to test for retroviral infections of livestock and, when feasible, removal of these infected animals from the herd will be increased.