PHYLOGENETIC ANALYSES OF THE PUTATIVE M(ORF-6)-GENE AND N(ORF-7)-GENEOF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS (PRRSV) - IMPLICATION FOR THE EXISTENCE OF 2 GENOTYPES OF PRRSV IN THE USA AND EUROPE

The putative membrane (M) protein (ORF 6) and nucleocapsid (N) protein (ORF 7) genes of five U.S. isolates of porcine reproductive and respi ratory syndrome virus (PRRSV) with differing virulence were cloned and sequenced. To determine the genetic variation and the phylogenetic re lationship of PRRSV, the deduced amino acid sequences of the putative M and N proteins from these isolates were aligned, to the extent known , with other PRRSV isolates, and also other members of the proposed ar terivirus group including lactate dehydrogenase-elevating virus (LDV) and equine arteritis virus (EAV). There was 96-100% amino acid sequenc e identity in the putative M and N genes among U.S. and Canadian PRRSV isolates with differing virulence. However, their amino acid sequence s varied extensively from those of European PRRSV isolates, and displa yed only 57-59% and 78-81% identity, respectively. The phylogenetic tr ees constructed on the basis of the putative M and N genes of the prop osed arterivirus group were similar and indicated that both U.S. and E uropean PRRSV isolates were related to LDV and were distantly related to EAV. The U.S. and European PRRSV isolates fell into two distinct gr oups, suggesting that U.S. and European PRRSV isolates represent two d istinct genotypes.