CHARACTERIZATION OF ATYPICAL CLASSICAL SWINE FEVER VIRUSES IN YUNNAN PROVINCE AND SEQUENCE ANALYSIS OF E0 AND E2 GENES

Five swine fever viruses were isolated from 17 samples,which were collected from 13 large farms in 10 districts of Yunnan province.The nucleotide sequence analysis showed 99.99% homology among 3 isolates from KunMing,YuXi and QuJing and between 2 isolates from DaLi and BaoShan.All of these 5 isolates belonged to Genegroup 2.The titers of 5 isolates were about 2×106 TCID50/mL in PK-15 cells and the viruses could be detected by using fluorescent antibody technique.The full-length sequences of E0 and E2 genes about 700 bp and 1200 bp were amplified by RT-PCR,and then cloned into pMD18-T vectors.Sequence analysis showed that the E0 and E2 nucleotide fragments were 697 bp and 1173 bp in length,respectively.The nucleotide and amino acid sequences revealed 95.4% and 96.6% homology in E0 gene and 82.5% and 84.3% homology in E2 gene with CSFV Shimen strain.Animal experimentation showed that two isolates did not cause typical clinical signs of CSF but induced persistent infection in the challenged pigs.