| Porcine Reproductive and Respiratory Syndrome is one of the most important infectious diseases and widespread in the current pig industry.The clinical symptoms of sows are mainly stillbirth,premature delivery and abortion;piglets in the weaning stage are mainly respiratory symptoms such as cough and dyspnea.PRRSV has continuous genetic variation in the epidemic process,and the vaccine can not play a good protective effect.Therefore,it is very important to monitor the PRRSV epidemic and analyze the genetic evolution.In this study,serological tests were carried out on the samples by ELISA.The results showed that the positive rate of antibody detection of PRRSV in vaccinatedpigs in Tianjin was 79.29%,and the positive rate of non-vaccinatedpigs was 25.63%.In addition,a molecular epidemiological survey of samples using differential RT-PCR showed an average detection rate of 40.47% and showed an increasing trend.The detection rate of NADC30-like was 28.74%,accounting for 71.01% of the total positive samples.At the same time,the mixed infection of PRRSV with other viruses and bacteria was studied.The test sample was sequenced for the ORF5 and Nsp2 hypervariable regions of PRRSV.The PAMs cells and Marc-145 cells were combined with CPE,RT-PCR and immunofluorescence to isolate and purify the dominant PRRSV strains,and the whole genome sequence was determined and genetically evolved.The genetic evolution analysis of ORF5 revealed that 12 strains of NADC30,such as TJjh1602,deleted an amino acid at position 34 of ORF5.Nsp2 genetic evolution analysis found that strains had the same type of "111+1+19" deletion pattern as the amino acid of NADC30 strain,and there were different point deletions.The genome-wide genetic evolution analysis of the isolated strains TJxq1701 and TJjh1602 indicated that the TJxq1701 strain was located in the branch of the HP-PRRSV strain,and TJjh1602 was located in the same branch as the NADC30-like strain.In summary,PRRSV is widely prevalent in Tianjin,and the immune effect of the vaccine is not good.The NADC30-like strain has become a major epidemic strain and is constantly mutating during the epidemic.A strain of NADC30-like strain TJjh1602 was successfully isolated and identified.The whole gene comparison found that one amino acid was deleted at position 34 of ORF5,and its biological significance needs further study. |
