Isolation, Identification And Genetic Variations Of Porcine Reproductive And Respiratory Syndrome Virus Isolates Prevalent In China

Porcine reproductive and respiratory syndrome (PRRS) is a serious infectious disease of swine which is caused by porcine reproductive and respiratory syndrome virus (PRRSV). It is characterized by severe reproductive failure in sows and respiratory distress in piglets and growing pigs. Since its first reported in the United States in 1987, it has been spread to most countries and caused large economically lost. A highly pathogenic disease which is characterized by high-fever, high morbidity and mortality rate was outbreaked in the south of China in 2006, and then spread quickly to most provinces. Most experts believed that PRRSV mutant was one of the main etiologies.1 In this study, three porcine reproductive and respiratory syndrome virus were isolated in Guangdong province in 2005 which were named GD1~GD3, five porcine reproductive and respiratory syndrome virus were isolated in Jiangxi province in 2006 which were named JS1~JS5. The isolates were identified by RT-PCR and IFA test. TCID50 and physico-chemical property was tested on Marc-145 cells.2 Three strains JS1, JS5 and GD3 were selected for full genomes sequencing. The all cDNA fragments of these three isolates were amplified by RT-PCR and 5′Full RACE method and cloned into PMD-18T vector. The complete genomes were obtained by assembling these sequence. Nucleotide analysis showed that JS1 and JS5 strains have 30 acid deletions in Nsp2 gene, but GD3 had only one acid deletion. Sequence comparison suggested the three isolates belong to American type.3 Twenty-two ORF5 genes were obtained by RT-PCR. Analysis by molecular softwares showed that all of them belong to American type. There were 90~99% amino acids identity between these sequences and they shared 91.5~99% and 86.6~90.5% amino acids identity with CH-1a and VR2332. The phylogenetic tree indicated that the Chinese isolates could be divided into two subgroups: CH-1a, JXA1, HUN4 and some other strains fall into subgroup 1; VR-2332, BJ-4 belonged to subgroup 2.