Phylogenetic analysis and molecular characteristics of 17 porcine reproductive and respiratory syndrome virus isolates in Southern China from 2010 to 2011.

We analyzed the complete genomic sequences of 17 porcine reproductive and respiratory syndrome virus (PRRSV) isolates from Southern China obtained between 2010 and 2011 and found that four of seven isolates from 2011 were closely related to the JXA1-R strain (vaccine virus of JXA1). This close relationship between field isolates and China domestic vaccine viruses has not been reported to date. The occurrence of vaccine-like viruses potentially creates a threat for the pig breeding industry and brings difficulties for control of this disease.