Phylogenetic relationships of European strains of porcine reproductive and respiratory syndrome virus (PRRSV) inferred from DNA sequences of putative ORF-5 and ORF-7 genes

The complete ORF-5 gene and a fragment of the ORF-7 gene from 14 different European porcine reproductive and respiratory syndrome virus (PRRSV) isolates were amplified by reverse transcriptase polymerase chain reaction (RT-PCR), and their nucleotide sequences were determined. The ORF-7 gene displayed nucleotide and amino acid identities of 94.1–99.6% and 95.3–100% among isolates from different countries. The ORF-5 gene showed higher nucleotide (87.1–99.2% identity) and amino acid (−88% identity) variability. The resulting sequences were aligned with other European and North American PRRSV strains and phylogenetic relationships among these strains were established by the maximum parsimony method. The phylogenetic trees inferred from both genes were in agreement and showed that European and North American PRRSV strains clearly represent two different genotypes. According to both trees, there is a perfect correlation between strains and the countries in which they were isolated. Additionally, the phylogenetic position of European and North American PRRSV strains within the recently proposed family Arteriviridae was also analyzed.