| Porcine circovirus is a member of Circoviraceae Circoviridae, it was add in sixth Report of virus classification in International Committee on the Taxonomy of Viruses (ICTV), according to difference between antigenicity and genetic constitution it can be divided into two types, nonpathogenic PCV1 and pathogenic PCV2. research indicate that PCV1 is ubiquitous and nonpathogenic for pigs, whereas PCV2 is main initiation for postweaning multisystemic wasting syndrome (PMWS), it becomes including pig immunosuppression aspects disease to continue Porcine reproductive and respiratory syndrome. PMWS has made a huge economic loss for world's swine industry and aroused people's attention.PCV confirmed by means of respiratory tract infection in pigs in different age groups, with 5 to 12-week-old early weaned piglets and adult pigs the most sensitive. It was also suggested that PCV transmitted to sow through to semen of boar, and then infected to piglets, discharges to the virus such as nasal fluid and waste, so the wide dissemination and it exists of PMWS, was a worldwide trend in Europe, the Americas, Asia countries in the region all have been reported. With in-depth study, PCV2 not only the main cause PMWS, but cause Porcine Dermatitis and Nephropathy Syndrome, Congenital Tremor type AII, Swine Respiratory disease syndrome, Sow Reproductive disorders at the same time and performance related to clinical symptoms and the corresponding changes in anatomical pathology. It can be said that after the farm infected PCV at once, it will be difficult to completely eliminate the virus, which has become a major problem for the pig farming industry.Recently, it had established a number of PCV2 detection methods after a large number of researches and practices. Including viral isolation assay, Immunofluorescence assay, Enzyme-linked Immunosorbent assay, Polymerase Chain Reaction, In Situ nucleic acid Hybridization and so on, can be used to test DNA of virus or antibody levels in tissue sample and serum. According to the specific circumstances of each laboratory, these tests were used widely. The PCV genome studies have shown that Both PCV1 and PCV2 were known that they contain two major open reading frames (ORFs) that are ORF1 and ORF2 which were most important of all its. ORF1 (945bp) it major founction is encodes a viral replication protein (Rep protein). Rep protein of PCV1 shares about 85% identity with PCV2 through homology comparison, that is the most important reason of PCV1 and PCV2 have cross-reaction of antigenicity. ORF2 (702bp) it major founction is encodes a major structural protein of virus. They shares about 68% identity to contrast two types virus; however, they have no cross-reaction of antigenicity is observed between themslf. Therefore, the ORF2 protein is always used to distinguish PCV1 and PCV2, and have greater significance for porcine circovirus disease diagnosis and porcine circovirus vaccines.Epidemiological investigation in this article part, through testing 76 samples from Beijing area, 44 samples of Hebei, 60 samples of Shandong region, 33 in Shanxi region, for a total of 213 tissue samples were detected by PCR, test results: positive for the virus in Beijing was 34.2%, Hebei 22.7%, Shanxi region 24.2%, Shandong region was 35% positive rate. In order to determine the various regions, PCV2 distribution of the prevalence in the large-scale pig farm for clinical medicine, and further rationalization of the recommendations provided to the pig farm, modify the immune comprehensive prevention and control procedures provide an important basis for measures. Then the focus of this study is the findings from the epidemiological, select positive sample to carry out DNA cloning, sequencing, analysis of the prevalence of PCV2 strain region ORF1, ORF2 gene sequences, compared to homology: PCV2 ORF1 shares about 97.8% ~ 99.4% range; PCV2 ORF2 shares about 91.4% ~ 99.7% of the range. Internal and abroad compared the prevalence of homology between the strains, internal reference strain as the strain of Heilongjiang (HLJ-AY122275), Beijing(BJ-AY177626), Jiangsu(JS-AY686762) and the Guangdong(GD-AY65185 ); abroad for the American strain (AMA-AF264038), the Canadian strain (CAN-AF109399), the German strain (GER-AF201311), France strain (FRA-AJ623306), the Korean strain (KRO-AY672600) of ORF1, ORF2 between gene sequence comparison, the results are: PCV2-ORF1 homology was 97.4% ~ 100%; PCV2 ORF2 homology was 91.3% ~ 100%. The results showed that a strain of PCV2 variation between ORF1 little difference between ORF2 and abroad mainly in between the strains, which results with the basic line. Through genetic analysis of phylogenetic trees found in different parts of the four PCV2-ORF2 sequences are closely related, indicating that these four areas of genetic variation may come from the same strain. |
