Abstract: The ORF6 and ORF7 genes of two highly pathogenic PRRSV SX,ZQ,derived from Shandong,were amplified by RT-PCR.The products were sequenced after cloning into pMD18-T vector respectively .The sequences were analysed using DNAStar and compared with those of VR-2332,LV and other strains isolated from China and circumjacent Country.The homologous of ORF6,ORF7 Nuclear acid was 91.1％～100％ with North American(VR-2332) and 66.2％～70.7％ with European(LV) viruses, The homologous of ORF6,ORF7 deduced amino acid was 91.2％～100％ with North American(VR-2332) and 62.3％～82.3％ with European(LV) viruses,indicating that the two new shandong isolates were related to the North American PRRSV genotype. The ORF6,ORF7 Nuclear acid of SX shared 99.8%,100% identity with highly pathogenic PRRSV JXA1,while The ORF6,ORF7 Nuclear acid of ZQ shared 99.6%,99.7% identity with highly pathogenic PRRSV JXA1.

Key words: highly pathogenic PRRSV; ORF6; ORF7; clone; sequence analysis