COMPARISON OF NUCLEIC AND AMINO-ACID-SEQUENCES AND PHYLOGENETIC ANALYSIS OF OPEN READING FRAME-3 AND FRAME-4 OF VARIOUS EQUINE ARTERITIS VIRUS ISOLATES

The genetic variation in equine arteritis virus (EAV) protein-encoding open reading frames (ORFs) 3 and 4 genes was investigated. Nucleic an d deduced amino acid sequences from seven different EAV isolates (one European, one American and five Canadian isolates) and the Arvac vacci ne strain were compared with those of the Bucyrus reference strain. OR F 3 nucleotide and amino acid sequence identities between these isolat es (including the Arvac vaccine strain) and the Bucyrus reference stra in ranged from 85.6 to 98.8%, and 85.3 to 98.2%, respectively, whereas ORF 4 nucleotide and amino acid sequence identities ranged from 90.4 to 98.3%, and 90.8 to 97.4%, respectively. Phylogenetic analysis and e stimation of genetic distances based on the ORF 3 nucleic acid sequenc es showed that the European Vienna isolate could be classified into a genetically divergent group from all other isolates and the Arvac vacc ine strain. In contrast, the nucleic acid sequences of ORF 4 were foun d to be less variable, with a closer phylogenetic relationship evident among the EAV isolates and the Arvac vaccine strain.