The etiological agent of PRRS was caused by PRRS virus (PRRSV), a small enveloped, single-stranded, positive-sense RNA virus with an approximately 15.4 kb genome possessing a 5’-capped structure, a 3’-polyadenylated tail and encodes at least nine open reading frames (ORFs) flanked by 5’ and 3’ untranslated regions (UTR)