Genetic and antigenic characterization of complete genomes of Type 1 Porcine Reproductive and Respiratory Syndrome viruses (PRRSV) isolated in Denmark over a period of 10 years

Lise K Kvisgaard,Charlotte K Hjulsager,Charlotte S Kristensen,Klara T Lauritsen,Lars E Larsen

doi:10.1016/j.virusres.2013.10.009

Abstract

Porcine Reproductive and Respiratory Syndrome (PRRS) caused by the PRRS virus (PRRSV) is considered one of the most devastating swine diseases worldwide. PRRS viruses are divided into two major genotypes, Type 1 and Type 2, with pronounced diversity between and within the genotypes. In Denmark more than 50% of the herds are infected with Type 1 and/or Type 2 PRRSV. The main objective of this study was to examine the genetic diversity and drift of Type 1 viruses in a population with limited introduction of new animals and semen. A total of 43 ORF5 and 42 ORF7 nucleotide sequences were obtained from viruses collected from 2003 to February 2013. Phylogenetic analysis of ORF5 nucleotide sequences showed that the Danish isolates formed two major clusters within the subtype 1. The nucleotide identity to the subtype 1 protogenotype Lelystad virus (LV) spanned 84.9–98.8% for ORF5 and 90.7–100% for ORF7. Among the Danish viruses the pairwise nucleotide identities in ORF5 and ORF7 were 81.2–100% and 88.9–100%, respectively. Sequencing of the complete genomes, including the 5′- and 3′-end nucleotides, of 8 Danish PRRSV Type 1 showed that the genome lengths differed from 14,876 to 15,098 nucleotides and the pairwise nucleotide identity among the Danish viruses was 86.5–97.3% and the identity to LV was 88.7–97.9%. The study strongly indicated that there have been at least two independent introductions of Type 1 PRRSV in Denmark and analysis of the full genomes revealed a significant drift in several regions of the virus.

Highlights

Porcine Reproductive and Respiratory Syndrome (PRRS) is considered one of the most devastating and economically challenging diseases to the swine industry worldwide (Holtkamp et al, 2013)
There has been a gap in knowledge regarding the diversity of PRRS virus (PRRSV) Type 1 circulating in Denmark since the latest available information was obtained on viruses isolated in the late 1990s
We report an extensive analysis of ORF5 and ORF7 of 43 viruses and full genome sequences of 8 Type 1 PRRS viruses isolated over almost two decades which to our knowledge makes this study the most extensive full-length Type 1 study published globally

Summary

Introduction

Porcine Reproductive and Respiratory Syndrome (PRRS) is considered one of the most devastating and economically challenging diseases to the swine industry worldwide (Holtkamp et al, 2013). ORF1a and ORF1b covers the first three quarters of the PRRSV genome and encode two long non-structural polyproteins, pp1a and pp1ab, where the latter is expressed after a ribosomal frameshift (Snijder and Meulenberg, 1998). ORF2b fully embedded in ORF2 and ORF5a partially overlapping ORF5 encodes the non-glycosylated proteins E and ORF5a protein (Wu et al, 2001; Johnson et al, 2011; Firth et al, 2011). Genetic nucleotide sequence comparisons of viruses isolated in Europe and North America respectively revealed only 50–60% identity between viruses; PRRSV was divided into two major genotypes, Type 1 and Type 2 (Allende et al, 1999).

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Conclusion