The Epidemiological Research For The Postweaning Multisystemic Wasting Syndrome In Hebei Province

Porcine circovirus was firstly isolated from the cell line PK15 by Tisher at 1974. Porcine circovirus is an unenveloped DNA virus, belonging to the circoviridae which includes Human TTV, CAV and PBFDV additionally. The diameter of PCV virion is about 17-20nm, and it is the smallest animal virus that has been known. According to its antigenlity and the difference of genetic compenets, there are two gene types or serum type for PCV, that is PCV-1 and PCV-2. PCV-1 has no pathgenocity and is common in cell lines and healthy pigs. However, researches indicate that PCV-2 has tight relation with some new infectious diseases in the pigherd, including PMWS, PDNS , PRDC and A2CT. The disease PMWS was reported in many countries, including China, since it was firstly reported in Canada in 1991. In recent years, it brings great harm to the world pig farm due to its more and more popular.The nosogenesis for the virus is still unknown now, so the PCV-2 has been a hot spot for veterinary research both in China and aboard. This study includes:1. The recombinant plasmid pETORF2 containing the ORF2 gene of PCV-2 was transformed into E. coli BL21 (DE3) competent cell. The ORF2 gene was over expressed in when the conditions of culture and inducing expression, such as the furthest concentration of IPTG and inducing time, were optimized. The expression product was purified by affinity chromatography and detected by SDS-PAGE and Western-blot experiment. The indirect ELISA method detecting the antibody of PCV-2 was established using purified recombinant Cap protein as antigen when the conditions were optimized.2. The antibodies against PCV-2 from different pig herd in Hebei province were detected with indirect ELISA established with recombinant PCV-2 ORF2 protein expressed in E.Coli. It is indicated that there are 32 show PCV-2 infection during the 36 investigated countries and the average serological positive rate of whole province is 76.8%, and the average positive rate for the investigated pig farm is 88.8%. There are more positive samples in old pigs than in the young pigs, and also, there more pigs show positive in later year than in the years before. All of these indicates that the PCV-2 infection is very popular in Hebei province.3. Using pair of specific primenrs designed according to the neucletide sequence of PCV-2 in GenBank, the PCR method for the detdction of PCV-2 was then established. With this method , 38 samoles show PCV-2 positive among the 45 suspicious samples that were detected. At the same time, other diseases that can cause reproducetive failure, such as PRRSV, PPV, CSFV and PRV were detected with RT-PCR or PCR method. The result indicates that 15 samples show PRRSV and PCV-2 coinfection; 2 samples are PPV and PCV-2 coinfection. In addition, there are 3 samples show PRRSV, PPV and PCV-2 coinfection.4. The ORF2 gene of three isolated strains were amplified with PCR metnod with a pair of specific primer designed according to the PCV-2 nucleotide sequence in Genbank( ). Sequence analysis indicated that the inserted fragment of three recombant plasmids are all 702bp. In a phylogenetic tree based on the sequenced ORF2 gene, the identity among three fragment is 100%, and have strong relationship with PCV-2 in Genebank. The homology between them is 91.5-99.6% and the amino acid homology is 92.3%-99.1%, on the other hand, the homology with PCV-1 is only 60.2%, and the amino acid homology is 66.8%.