A Conserved Stem-Loop Structure within ORF5 Is a Frequent Recombination Hotspot for Porcine Reproductive and Respiratory Syndrome Virus 1 (PRRSV-1) with a Particular Modified Live Virus (MLV) Strain

The emergence of recombinant PRRSV strains has been observed for more than a decade. These recombinant viruses are characterized by a genome that contains genetic material from at least two different parental strains. Due to the advanced sequencing techniques and a growing number of data bank entries, the role of PRRSV recombinants has become increasingly important since they are sometimes associated with clinical outbreaks. Chimeric viruses observed more recently are products of PRRSV wild-type and vaccine strains. Here, we report on three PRRSV-1 isolates from geographically distant farms with differing clinical manifestations. A sequencing and recombination analysis revealed that these strains are crossovers between different wild-type strains and the same modified live virus vaccine strain. Interestingly, the recombination breakpoint of all analyzed isolates appears at the beginning of open reading frame 5 (ORF5). RNA structure predictions indicate a conserved stem loop in close proximity to the recombination hotspot, which is a plausible cause of a polymerase template switch during RNA replication. Further research into the mechanisms of the stem loop is needed to help understand the PRRSV recombination process and the role of MLVs as parental strains.

Automated summary

The emergence of recombinant PRRSV strains, which contain genetic material from at least two different parental strains, has become increasingly important due to advanced sequencing techniques. Recent chimeric viruses are a result of PRRSV wild-type and vaccine strains. Analysis of three PRRSV-1 isolates revealed that they are crossovers between different wild-type strains and the same modified live virus vaccine strain, with the recombination breakpoint consistently appearing at the beginning of open reading frame 5 (ORF5). Further research is needed to understand the role of MLVs as parental strains and the mechanism of the conserved stem loop near the recombination hotspot.