Abstract

Two porcine reproductive and respiratory syndrome virus (PRRSV), respectively named YN-1 and YN-2 strains, were isolated by inoculation into Marc-145 cell. The two isolated strains induce Marc-145 cell stack together, pull net, form plaque and other typical lesions after 4 blind passages. With extracted viral RNA of fourth generation, reverse transcriptase (RT)-PCR based on open reading frame 5 (ORF5)gene showed that there was porcine reproductive and respiratory syndrome virus in Marc-145 cell of fourth generation. TCID50 of isolate measured by Reed-Muench method was 10^-3.6/0.1 ml. Genetic evolution of ORF5 indicated that the two isolated strains were in a small branch with high identity of 99.5%. They were in a branch with Shandong strain JN-HS, Hennan-1 and Vietnam 347-T-KSA strain with identity of 99.2 to 99.8%. The two isolated strains were in a different branch with Ch-1a and VR-2332 strains having identity of 94.4 to 94.5%.

Key words: Porcine reproductive and respiratory syndrome virus (PRRSV), isolation, ORF5 gene, genetic evolution