Molecular epidemiological investigation of porcine reproductive and respiratory syndrome virus in Northwest China from 2007 to 2010.

Porcine reproductive and respiratory syndrome (PRRS) is an economically important swine disease affecting swine worldwide. Northwest China has a sparse pig population and there is no comprehensive information currently available on PRRSV infection. In this study, we analyzed the epidemiological features and genetic diversity of PRRSV from this region. 322 field-isolated tissues or serum samples were collected from aborted pig fetuses or pigs with respiratory disease from 15 herds, twice over a period of 2 years. PRRSV infection was determined and virus strains were classified by the sequencing of GP5. We found that 35.9 % of the animals were PRRSV-positive, and the average prevalence in 2007-2008 and 2009-2010 was 46.5 and 29.3 %, respectively. To further investigate the genetic divergence of PRRSV samples collected from 2007 to 2010, 32 strains were isolated for GP5 sequencing and analysis, and phylogenetic trees were created based on GP5 amino acid sequences. All PRRSVs were of the North American genotype and belonged to the highly pathogenic HP-PRRSV subgenotype. Isolates from the Xinjiang province formed a tightly clustered branch and were closely related to an evolutionary intermediate subgroup isolate. Virus sequences from 2007 to 2008 were compared with those from 2009 to 2010 from the same herd. New mutations were found in isolates after 2009 and focused on nucleotides in the GP5 antibody decoy epitope. PRRSV strains in Northwest China from 2007 to 2010 were similar to those from other regions of China, with some regional characteristics. These results contribute to the knowledge of PRRSV epidemiology in China.