Improving of the Nested PCR for Detection of Bovine Leukemia Virus

Abstract

Enzootic bovine leukosis caused by a bovine leukemia virus has a significant economic impact and is reported in World Organization for Animal Health(OIE). Aim. The purpose of our work was to improve the nested polymerase chain reaction (PCR) recommended by the OIE conducting it second-stage in real-time (RT) PCR. Such modification does not require the stage of gel electrophoresis and consequently reduces contamination risks and prevents false positive results. Methods. Primers that are recommended by the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals (OIE) were used for the first amplification stage. For the second stage of the proposed modification of nested PCR, the primers and probe were designed based on the alignment of the sequences envelope gene of different isolates of bovine leukemia virus including Ukrainian isolates. Amplification of the internal control was carried out for the second stage to prevent false negative results. Results. Comparative studies of 48 blood samples for bovine leukemia virus identification by a proposed nested RT-PCR, nested PCR recommended by the protocol of the OIE, and RT-PCR were conducted. The sample panel included both positive and negative samples. A 100% match of the results of the bovine leukemia virus presence in nested PCR proposed by the OIE and in our proposed nested RT-PCR was obtained. Comparative analysis of results that were obtained using the RT-PCR and the proposed nested RT-PCR showed that false-negative results in 5 samples and 3 doubtful results that require retesting were obtained by use of RT-PCR. The interpretation of the results using nested RT-PCR is more efficient than RT-PCR since the cycle threshold value of positive samples obtained using RT-PCR was in the range of 24–40 cycles, whereas in the case of nested RT-PCR using, the value of Ct was in the range of 4–20 cycles. Conclusions. Proposed nested PCR modification includes the combination of the OIE recommendation about nested PCR and the reduction of the risk of contamination by conducting the second stage in RT-PCR. Results of approbation of proposed nested RT-PCR give a reason to recommend it for the identification of bovine leukemia virus.