The Molecular Epidemiological Investigation Of PRRSV In Hebei Province And The Isolation And Identification Of Its Epidemic Strain

Porcine Reproductive and Respiratory Syndrome(PRRS)is a potent infectious disease caused by Porcine Reproductive and Respiratory Syndrome Virus(PRRSV),which is characterized by dyspnea in different ages of pigs and reproductive disturbance in swine.Since the disease was first discovered in 1987,it has swept the world in just a few years.Almost every country and region has suffered from the invasion of PRRS,causing varying degrees of losses to the pig farming industry.In order to ascertain the prevalence of PRRS in Hebei Province and provide data support for the prevention and control of PRRS in Hebei Province,this study has carried out preliminary molecular epidemiology for PRRSV in Hebei Province and isolated and identified the epidemic strains in the province.The main research works were as following: 1.A total of 208 suspected cases of PRRSV were collected from the seven prefecture-level cities in Hebei Province.The detecting results showed that the total positive rate of PRRSV was 50.48%(105/208),including the 13.94%(29/208)positive rate of HP-PRRSV,and the 40.86%(85/208)positive rate of NADC30-like.The positive rate of mixed infection of HP-PRRSV and NADC30-like strains was 4.33%(9/208).19 strains of the nsp2 gene of PRRSV were amplified and sequenced from these positive samples.The alignment of the obtained 19 nsp2 gene sequences was produced.The results demonstrated that 6 nsp2 gene sequences of 19 were highly homologous to the HP-PRRSV strain and the other 13 nsp2 gene sequences were highly homologous to the NADC30 strain.This study indicated that PRRSV is ubiquitous in Hebei province,and the infection of the NADC30-like strain is predominant.More importantly,the PRRSV prevalent strains are constantly evolving,suggesting that PRRSV prevention and surveillance in this province should be strengthened.2.Virus isolation was performed on the collected samples from a pig farm in Qinhuangdao City.After three generations on PAMs,the collected samples were transferred to Marc-145 cells.And obvious lesions appeared on the Marc-145 cells.All passaging samples were PRRSV-positive by RT-PCR and indirect immunofluorescence tests.This PRRSV strain was isolated and named PRRSV QHD1.3.The whole genome sequence of PRRSV QHD1 was obtained by sequencing.The analysis showed that the PRRSV QHD1 is a North-American strain,and it has low homology with the European strains Lelystad virus and EuroPRRSV,with 60.3% and 60.4% similarity,respectively;the highest homology with the whole genome of the North American type NADC30 strain with 94.2% similarity.The recombination analysis demonstrated that the QHD1 strain is a recombinant strain,in which two recombination regions were found between 7 913-8 015 nt and 12 780-13 158 nt.This strain is a recombinant of the NADC30 strain and the vaccine strain RespPRRS MLV strain.The PRRSV NADC30-like strain is the most recent variant strain in China,and it is prone to reorganization and should be given sufficient attention.