Abstract: Two porcine reproductive and respiratory syndrome virus (PRRSV) strains which named YN-1 strain and YN-2 strain, were isolated by inoculating into Marc-145 cell. The two isolated strains can induce Marc-145 cell stack together, pull net, formation of plaque, and other typical lesions for 4 blind passage, with TCID₅₀ 10^-3.6/0.1 mL. RT-PCR based on NSP2 gene showed that there were 90 nucleotides deletion than Ch-1a strain, the typical gene characteristic of highly pathogenic PRRSV. Genetic evolution of ORF5 showed the two isolated strains were in a small branch with high identity 99.5%. They were in a branch with Shandong strain JN-HS,Hennan-1 and Vietnam 347-T-KSA strain with identity 99.2% to 99.8%. The two isolated strains were in a different branch with Ch-1a and VR-2332 strains,the identity were 94.4% to 94.5%, and the identity 98% to 99% with other Chinese highly pathogenic strains, the two isolated strains belonged to the high-pathogenic strain.

Key words: PRRSV; isolation; identification; ORF5 gene; genetic evolution