Evolution of Porcine Reproductive and Respiratory Syndrome Virus during Sequential Passages in Pigs

Abstract

Porcine reproductive and respiratory syndrome (PRRS) viruses are recognized as possessing a high degree of genetic and antigenic variability. Viral diversity has led to questions regarding the association of virus mutation and persistent infection in the host and has raised concerns vis-à-vis protective immunity, the ability of diagnostic assays to detect novel variants, and the possible emergence of virulent strains. The purpose of this study was to describe ongoing changes in PRRS virus during replication in pigs under experimental conditions. Animals were inoculated with a plaque-cloned virus derived from VR-2332, the North American PRRS virus prototype. Three independent lines of in vivo replication were maintained for 367 days by pig-to-pig passage of virus at 60-day intervals. A total of 315 plaque-cloned viruses were recovered from 21 pigs over the 367-day observation period and compared to the original plaque-cloned virus by virus neutralization assay, monoclonal antibody analysis, and sequencing of open reading frames (ORFs) 1b (replicase), 5 (major envelope protein), and 7 (nucleocapsid) of the genome. Variants were detected by day 7 postinoculation, and multiple variants were present concurrently in every pig sampled over the observation period. Sequence analysis showed ORFs 1b and 7 to be highly conserved. In contrast, sequencing of ORF 5 disclosed 48 nucleotide variants which corresponded to 22 amino acid variants. Although no epitopic changes were detected under the conditions of this experiment, PRRS virus was shown to evolve continuously in infected pigs, with different genes of the viral genome undergoing various degrees of change.

Immunological and biochemical characterisation of 7ap, a short protein translated from an alternative frame of ORF7 of PRRSV

“…However, more conservative estimations put the mutation rate somewhere between 1.8 and 7 × 10 −3 /nucleotide/year (Chang et al, 2002;Forsberg, 2005), which still places PRRSV among the most rapidly evolving viruses known. Despite the rapidly changing codon sequences of the main ORFs, recently several positionally conserved alternative ORFs have been identified in the PRRSV genome and all of them proved to be protein coding: ORFs partially coding the nsp2TF and nsp2N proteins in the NSP2 region (Fang et al, 2012), ORF5a and ORF2b overlapping with the ORF5 and ORF2a genes (Wu et al, 2001;Firth et al, 2011), respectively.…”

Diagnostic Performance of Assays for the Detection of Anti-Porcine Reproductive and Respiratory Syndrome Virus Antibodies in Serum and Muscle Transudate (“Meat Juice”) Based on Samples Collected under Experimental Conditions

“…The specific virus isolate used was derived from a plaque-cloned virus recovered from the serum of a pig inoculated with VR-2332. 5 Virus propagation. To avoid the effects of cell passage, virus was inoculated into a 21-day-old pig.…”

Presence of free haptoglobin alpha 1S-subunit in acute porcine reproductive and respiratory syndrome virus infection

“…It has been reported previously only in serum of humans with ovarian cancer (Ye et al, 2003). In pigs, its appearance after PRRSV infection is rapid and peaks at 13-21 days of infection, which is later than the typical peak of viraemia at 3-10 days (Chang et al, 2002;Johnson et al, 2004). It is possible that PRRSV pathogenesis indirectly results in hepatocyte damage and release of cleaved Hp-…”