The Isolation And Identification Of A Highly Pathogenic Porcine Reproductive And Respiratory Syndrome Virus And The Establishment Of The Differential Diagnosis Method

Porcine reproductive and respiratory syndrome (PRRS) is caused by porcine reproductive and respiratory syndrome virus (PRRSV). The main characteristcs is reproductive loss and respiratory diseases. The disease is initially recognized in 1987 in United States of America, and then it is also found in North America, Europe and Asia. Occurrence of the disease has caused huge economic losses to the world pig industry, become a serious viral diseases hazarding pig industry. In recent years, the disease has brought great enormous losses to China, and has become a tough problem for Chinese swine industry, especially from the occurrence of highly pathogenic PRRSV (HP-PRRSV).Firstly, clinical diagnosis was done to detect a dead pig that was suspected being infected by PRRSV. The case was preliminary diagnosed as PRRS, according to the pathogenesis condition, epidemiological and clinical symptoms. In order to investigate the pathogeny, a further analysis was performed with methods of pathology and etiology. Tissue sections were observed and we found that the lungs appear typical interstitial pneumonia, which was the typical pathological change of PRRS. More importantly, the separation of bacterium cultivation ruled out the possibility of bacterium mixed infection. Marc-145 cells were used for viral isolation and then observed the cells after CPE appeared. The virus particles those were like PRRSV were observed. The RT-PCR showed that there was HP-PRRSV in the cells but no CSFV or PCV. Based on these results, we can determine that the case's dead was due to infection of HP-PRRSV.All HP-PRRSVs show four conserved deletions, including a deletion of adenosine at position 122 in the 5'-untranslated region, a deletion of guanosine at position 15,278 in the 3'-untranslated region, and two discontinuous deletions in the Nap2. In this study, primers were designed based on the Nsp2 strain, and RT-PCR was conducted to detect HP-PRRSV and classical PRRSV. Two sections were got in the study, which consistent with the expected. Thus, a RT-PCR method was established to detect HP-PRRSV and classical PRRSV. Further study confirmed that the method is of strong specificity, high sensitivity and good repeatability. Furthermore, RT-PCR, viral isolation and ELISA were used to detect the same samples. The results show that RT-PCR has higher sensitivity.In conclusion, this study not only provides theory basis for clinical diagnosis of PRRSV, but also establishes a method of the RT-PCR differential diagnosis. Our works lay a foundation for clinical inspection, epidemiological survey and formulate the prevention measures for PRRS.