Abstract: To isolate and identify porcine circovirus type 2 (PCV2)strains,and investigate its' characteristic of vitro propagation, polymerase chain reaction (PCR) was utilized in this study to detect the specimens of suspected PMWS cases collected from Shangdong, Shangxi, Beijing and Hebei province, the positive samples were dealt with and inoculated into the PCV-free PK15A cells which were then propagate continuously to isolate PCV2 strains. The cytopathic effect (CPE) was examined each time and the cultures of the 3rd time were identified by PCR and indirect immunofluorescence assay (IFA). The genome of each isolates were then cloned and sequenced. The sequence was submitted to the GenBank. Based on the sequence phylogenetic tree analysis was made too, subsequently these PCV2 strains' characteristic of vitro propagation were studied by propagated continuously to the 20^th generation, and the 5^th, 10^th,15^th and 20^th generation's titer known as 50% tissue culture infectious dose (TCID₅₀) were detected. These results showed that there were five strains of PCV2 were isolated and identified named PCV2 DBN-SD02,DBN-SX07,DBN-BJ08, DBN-HB12 and DBN-HB13 respectively, and the GenBank submission number were FJ660967, FJ660968, FJ660969, FJ660970,FJ660971,respectively. The genome of five isolates was all 1767 bp. Four of five isolates were belong to the PCV2b genotype and share a 98.5%-99.7% identity except PCV2 DBN-BJ08 strain which belong to the PCV2a genotype. The vitro propagation study showed that the TCID₅₀ increase obviously with the times of propagation.

Key words: porcine circovirus type 2; isolation; identification; characteristic of propagation