RT-PCR detection of porcine reproductive and respiratory syndrome virus based on the ORF5 gene in mainland China, 2012-2015

Between January 2012 and December 2015, 13,567 clinical samples were collected from healthy pigs and pigs with a history of respiratory symptoms and/or reproductive disorders in 29 provinces of mainland China to detect porcine reproductive and respiratory syndrome virus (PRRSV). From these samples, 7490 were PRRSV-positive (average value, 55.21%). The annual PRRSV detection rate from 2012 to 2015 for each year is 45.67%, 55.99%, 56.91%, and 59.07%, respectively. Phylogenetic analyses revealed that the percentage of highly pathogenic PRRSV strains had a decreasing yearly trend, whereas the vaccine-like strains showed the opposite trend during the years 2012-2015. These data indicate that while the vaccine contributes to PRRSV prevention in China, it might also lead to serious problems. Specifically, we identified 12 NADC30-like PRRSVs during the years 2014-2015, suggesting potential transmission of the newly emerged PRRSV strains in China. Our data contribute to new information about the epidemiology of PRRSV.