Hypermutations in porcine respiratory and reproductive syndrome virus

Abstract

Porcine reproductive and respiratory syndrome (PRRS), which is caused by the PRRS virus (PRRSV), has resulted in large economic losses for the swine industry. The virus has shown remarkable genetic diversity since its discovery. In our study, we investigated mutation types in the evolution of PRRSV for both in vivo and in vitro passaging of the virus. Sequence alignment analysis demonstrated that the most common hypermutations expressed were A→G/U→C and G→A/C→U. The data provide a new theoretical basis for PRRSV evolution.

Figure 1

In vitro nucleotide-sequence analysis of hypermutations in strains of Porcine reproductive and respiratory syndrome virus (PRRSV). A — Comparison between 6 live-attenuated vaccine strains and their corresponding parental strains. B — Comparison of 2 pathogenic strains, JXA1 and TP, with corresponding strains sampled during their attenuating passages in Marc-145 cells. JXA1-F10, JXA1-F15, JXA1-F45, JXA1-F70, and JXA1-F80 were sampled 10, 15, 45, 70, and 80 d after infection along with JXA1; TP P60 and TP P90 were sampled at 60 and 90 d along with TP.

Figure 2

A — In vitro nucleotide-sequence analysis of hypermutations in 10 field-isolated highly pathogenic PRRSV (HP-PRRSV) strains relative to CH-1a, the Chinese PRRSV strain considered to be the predecessor of the epidemic strains. B — Statistical analysis of the mutation numbers depicted in panel A, done using GraphPad Prism (version 5.0; GraphPad Software, La Jolla, California, USA). A P-value < 0.05 was considered to be statistically significant. C — Detection of hypermutations in HuN4a isolated from blood samples taken 3, 7, and 14 d after inoculation of 4 piglets (#51, #53, #55, and #56) with this HP-PRRSV strain. Types and frequencies of substitution mutations in the GP5 structural gene and the Nsp2 nonstructural gene were calculated.