Emergence of novel European genotype porcine reproductive and respiratory syndrome virus in mainland China

Porcine reproductive and respiratory syndrome (PRRS) has a major negative economic impact on the swine industry worldwide. During the investigation of PRRS virus (PRRSV) in mainland China, European genotype (EU, type 1) PRRSV isolates were detected in swine herds both with and without clinical symptoms. Two complete genome sequences for Chinese type 1 PRRSV isolates were identified from viruses isolated from lung tissue and sera. The two viruses, designated BJEU06-1 and NMEU09-1, produced cytopathic effects in primary porcine alveolar macrophages but not in Marc-145 cells, and had a mean diameter of 55 nm, as measured by transmission electron microscopy . Comparative sequence analysis revealed that they shared 87.0-91.5% and 58.0-58.2% identity with the EU and North American genotype (NA, type 2) prototypic strains LV and VR-2332, respectively. Remarkably, these isolates, characterized by concomitant deletions within non-structural protein 2 (Nsp2) and ORF3 hypervariable regions, have never been described. Phylogenetic trees showed that all of the novel Chinese isolates of European genotype are in the pan-European subtype 1 that is predominant in Europe. However, they evolved from different ancestors. These novel viruses are predicted to be products of the divergent evolution of ancestor PRRSV isolates introduced from Europe. This is the first report of type 1 PRRSV wild isolates being in mainland China. Our findings confirm that the Chinese type 1 PRRSV isolates originated from diverse progenitors and the type 1 and type 2 PRRSV isolates, having different biological properties, have coexisted on the Chinese mainland for several years.