MOLECULAR VARIATION IN THE NUCLEOPROTEIN GENE (ORF7) OF THE PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS (PRRSV)

The nucleoprotein gene (ORF7) of 15 European isolates of porcine repro ductive and respiratory syndrome virus (PRRSV) was sequenced and compa red with corresponding sequences of other PRRSV isolates (2 European a nd 13 American) and one isolate each of other arteriviruses (the lacta te dehydrogenase elevating virus (LDV), the simian haemorrhagic fever virus (SHFV) and the equine arteritis virus (EAV)). Their phylogenetic relationships were established using neighbour-joining and parsimony methods. Four lineages (PRRSV, LDV, SHFV and EAV) were discriminated. Two genotypes of PRRSV, European and American, could be further identi fied. The European genotype of PRRSV was highly conserved. Analysis of the nucleotide and amino acid substitutions in PRRSV ORF7 revealed fo ur stable regions, probably conserved because of their requirement for nucleocapsid function and/or structure. No constant mutations accumul ation in the ORF7 could be determined precisely when either synonymous or non-synonymous mutations were studied. Passage of the European PRR SV in vivo had little in influence on the ORF7 sequence: only a small number of synonymous substitutions in ORF7 was detectable, confirming its low variability. (C) 1998 Elsevier Science B.V. All rights reserve d.