The Genetic Diversity of European Type PRRSV Is Similar to That of the North American Type but Is Geographically Skewed within Europe

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is a recently emerged pathogen. Two PRRSV genotypes exist, North American and European, which are only 55-70% identical at the nucleotide level. Previous studies have shown high nucleotide diversity in the North American genotype and low nucleotide diversity in the European genotype. Here, we analyzed the ORF5 and ORF7 genes for a large number of new European type PRRSV isolates in conjunction with existing database sequences. This new analysis showed that contrary to previous assumptions, genetic diversity is at least as high in the European genotype as in the North American genotype. Furthermore, we showed that genetic diversity of European type PRRSV has a marked geographical pattern, with exceptionally high genetic diversity among Italian sequences. The geographical pattern of diversity in relation to the epidemiology of PRRSV in Europe is discussed. Discrepancies between ORF5- and ORF7-based genealogies were observed, and further analysis of the data set confirmed the presence of recombination. We were therefore able to report the first observation of recombination in wild-type isolates of European genotype PRRSV.

Porcine reproductive and respiratory syndrome virus: Genetic diversity of recent British isolates

“…Furthermore, the finding of a field virus which had undergone recombination with a vaccine or vaccine-like virus highlights an additional mechanism for the generation of ever-more diverse viruses. Such recombination events between field strains have previously been proposed for PRRSV (Yuan et al, 1999;Forsberg et al, 2002;Liu et al, 2011).…”

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

“…This high level of identity was not expected for two type 1 PRRSV field isolates of a virus known to undergo a high rate of recombination and mutation and known to evolve rapidly (18, 19, . Considering the immense diversity of PRRSV isolates found worldwide, the 10-year interval between identification of isolates LV and EuroPRRSV, and the fact that EuroPRRSV was isolated in North America, we were anticipating much greater dissimilarity between the two strains (18,19,21,25). As a likely circumstance, the Minnesota Veterinary Diagnostic Laboratory sequenced 242 type 2 (NA) isolates in 1999, yet less than 16% displayed 95% or greater similarity to the type 2 prototype VR-2332, which was isolated at approximately the same time as strain LV.…”

“…For evolutionary studies, the nucleotide sequences corresponding to ORF 3, 5, or 7 were aligned to previously published database sequences (10,17,18,19,30,36,46,69) by using CLUSTAL X (gap opening penalty, 15; gap extension penalty, 6.66) (71). Following alignment, the phylogeny of the isolates was estimated by using the TREE-PUZZLE program and yielded the phylogenetic trees shown in Fig.…”

“…In another study, ORF 5 and 7 genes from 46 Europeantype PRRSV isolates were also sequenced and combined with existing database sequences to determine ORF 5-and 7-based genealogies (19). In this study, we expanded the data sets presented in those papers to include sequences from several PRRSV type 1 sequences generated from U.S. swine herds ( Table 1).…”

“…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).…”