Identification of radically different variants of porcine reproductive and respiratory syndrome virus in Eastern Europe: towards a common ancestor for European and American viruses

Abstract

We determined 22 partial porcine reproductive and respiratory syndrome virus (PRRSV) ORF5 sequences, representing pathogenic field strains mainly from Poland and Lithuania, and two currently available European-type live PRRSV vaccines. Also, the complete ORF7 of two Lithuanian and two Polish strains was sequenced. We found that Polish, and in particular Lithuanian, PRRSV sequences were exceptionally different from the European prototype, the Lelystad virus, and in addition showed a very high national diversity. The most diverse present-day European-type PRRSV sequences were from Poland (2000) and Lithuania (2000), and exhibited only 72n2% nucleotide identity in the investigated ORF5 sequence. While all sequences determined in the present study were clearly of European type, inclusion of the new Lithuanian sequences in the genealogy resulted in a common ancestor for the European type virus significantly closer to the American-type PRRSV than previously seen. In addition, the length of the ORF7 of the Lithuanian strains was 378 nucleotides, and thus intermediate between the sizes of the prototypical EU-type (387 nucleotides) and US-type (372 nucleotides) ORF7 lengths. These findings for the Lithuanian PRRSV sequences provide support for the hypothesis that the EU and US genotypes of PRRSV evolved from a common ancestor. Also, this is the first report of ORF7 protein size polymorphism in field isolates of EU-type PRRSV.

Characterization of Emerging European-Like Porcine Reproductive and Respiratory Syndrome Virus Isolates in the United States

“…Forsberg et al (19) confirmed the scant isolate variation in these countries but found diversity to be high among type 1 PRRSV when isolates from Italy and Denmark were included in the analysis. ORF 5 phylogenetic analysis also revealed a tight clustering of isolates from The Netherlands, Great Britain, France, and Belgium around LV, but quite divergent strains were shown to be present in Eastern Europe (67). Although high genetic variability is common among North American type 2 isolates, these new U.S. type 1 isolates cluster around the LV isolate despite their wide geographic distribution, suggesting a common source of entry into the United States.…”

“…Several members of the nidovirus order have been shown to undergo high-frequency recombination (50,81,83). Because of unique recombinatorial properties (81,83), widespread persistence, intermingling of virus types, and changes in swine management, PRRSV has been a key subject of evolutionary interest (17,18,19,33,39,67,69).…”

Significance of the oligosaccharides of the porcine reproductive and respiratory syndrome virus glycoproteins GP2a and GP5 for infectious virus production

“…Actually, the N-glycan at position 46 is very close to Cys 50 , the residue presumed to be involved in GP 5 -M protein linkage (Verheije, 2002). In this respect it is remarkable that the sole PRRSV strains known to lack the N-glycan at position 46 instead have a nearby glycosylation site at position 37 (Mateu et al, 2003;Stadejek et al, 2002), suggesting that these glycans can adopt each other's function. As GP 5 -M disulphide-bond formation is essential for arterivirus assembly (Snijder et al, 2003;Verheije, 2002), an effect of the GP 5 -N46Q mutation on this process might explain the reduced mutant virion production levels.…”

Restriction fragment length polymorphism of ORF6 and ORF7 genes of porcine reproductive and respiratory syndrome virus (PRRSV) vaccine strains registered in the Czech Republic

“…Until recently, the European type isolates have been considered as less variable. However, the latest studies show a significant genetic heterogeneity within the European type isolates (Indik et al, 2000;Stadejek et al, 2002). Radically different variants of PRRSV in Eastern Europe support the hypothesis that the European and American genotypes of PRRSV evolved from a common ancestor (Stadejek et al, 2002).…”