RT-PCR differential diagnosis technique for variant and classical strains of PRRSV and its clinical application

[Objective]The studies were conducted to establish the RT-PCR assay for the differential diagnosis of the highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV)(variant strain) and classical PRRSV in order to provide control measures for PRRS. [Method]A pairs of specific primers was designed on the basis of Nsp2 gene sequences of PRRSV collected from GenBank to amplify PRRSV genes using RT-PCR for differentiating the variant and classical strains of PRRSV. The specificity and sensitivity test were performed and clinical applications were carried out. [Result]The fragments of 332 and 241 bp were amplified from classical and variant strains of PRRSV using RT-PCR, respectively, which could be differentiated on the basis of their sizes. The sensitivity test results demonstrated that as little as 100 fg of the classical strain of PRRSV RNA, and 10 fg of the variant strain of PRRSV RNA could be detected by RT-PCR. The clinical application of RT-PCR showed that, out of 37 suspicious disease samples, 24.32 and 51.35% belonged to classical and variant strains of PRRSV, respectively, while the others showed negative. [Conclusion]The established RT-PCR differential diagnosis technique was found to differentiate the classical and variant strains of PRRSV effectively, and showed highly specific and simple assay, which may be widely used in clinical diagnosis.