Molecular Epidemiological Survey And Genetic Variation Of Porcine Circovirus Type 2 In Eastern China

Porcine circovirus disease (PCVD) consists of a series of swine diseases caused by Porcine circovirus type 2 (PCV2), mainly including postweaning multisystemic wasting syndrome (PMWS) and Porcine dermatis and nephropathy syndrome (PDNS), and so on. With immunosuppression caused by PCV2 infection, immunity of swine decreased and secondary infection probably occurred, and PCVD has been considered to have a severe economic impact on swine industry. The importance of this disease has stimulated veterinarians to aim at it. In the present study, in order to know the molecular epidemiology of PCV2 infection in Eastern China,426 serum samples and tissue samples of pigs with PMWS collected from 2009 to 2011 in Eastern China have been detected by PCR; The main objective of this study was to characterize and determine the genetic diversity of PCV2 based on the isolates and comparison of ORF2 gene of isolates. This study includes two parts:1. Four hundred and twenty-six serum samples or tissue samples of pigs with PMWS obtained from different regions located in 7 provinces (Shandong, Anhui, Jiangsu, Shanghai, Zhejiang, Jiangxi and Fujian) in Eastern China from 2009 to 2011 were detected by PCR test. The results demonstrated that 230 of 426 samples were PCV2 positive and the positive rate was 54.0%. The samples of PCV2 could be tested positive in all the 7 provinces. The highest positive rate is 59.5% in Zhejiang and the lowest is 48.0% in Fujian. Therefore, PCV2 is prevalent in Eastern China with a highly positive rate.2. Twenty-four PCV2-positive samples from 7 provinces were inoculated on pK-15 cells to isolate viruses. The isolated viruses were identified by PCR and specific fragment was detected in 16 isolates. The resluts of indirect immunofluorescence assay (IFA) further proved that these 16 PCV2-positive isolates can proliferate in pK-15. The complete genomes of all isolates were amplified, cloned into vector, sequenced and analysed. The whole genomes of ORF2 gene of 16 isolates were compared with 24 PCV2 reference strains registered in GenBank to construct phylogenetic tree, homology analysis and sequence analysis of amino acids. The results of homology analysis demonstrated that the homology between 40 PCV2 strains were 83.7% to 100%, the homology between 21 strains in Eastern China were 88.0% to 100%, the homology between 16 isolates were 88.0% to 100%. The phylogenetic analysis indicated that there were three subgenotypes occured in Eastern China from 2009 to 2011, PCV2a, PCV2b and PCV2d. The PCV2d was more popular in Eastern China than PCV2a and PCV2b. But the distribution of PCV2 did not show apparent geographical characteristics. And the amino acid sequence alignment of the capsid protein encoded by ORF2 gene showed Chinese PCV2 strains exhibited three major regions of greater heterogeneity at residues 53-91aa、121-151aa and 190-215aa and some mutations in the epitopes residues. However, these mutations affect the biological characteristics of the virus requires further study.In this study, the epidemiology and the characteristics of PCV2 in Eastern China have been known detailed, which provided the scientific basis for screening vaccine strains and the theoretical foundation for prevention and control of PCVD.