Recombination between North American strains of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV), a recently dis covered arterivirus swine pathogen, was shown to undergo homologous recombi nation. Go-infection of MA-104 cells with two culture-adapted North America n PRRSV strains resulted in recombinant viral particles containing chimeric ORF 3 and ORF 4 proteins. Nucleotide sequence analysis of cloned recombina nt PGR products, encompassing 1182 bases of the 15.4 kb viral genome, revea led six independent recombination events. Recombinant products persisted in culture for at least three passages, indicating continuous formation of re combinant viruses, growth of recombinant viruses in competition with parent al viruses, or both. The frequency of recombination was estimated from < 2% up to 10% in the 1182 b fragment analyzed, which is similar to recombinati on frequencies observed in coronaviruses. An apparent example of natural OR F 5 recombination between naturally occurring wild type viruses was also fo und, indicating that recombination is likely an important genetic mechanism contributing to PRRSV evolution. (C) 1999 Elsevier Science B.V. All rights reserved.