Porcine Reproductive and Respiratory Syndrome Virus Comparison: Divergent Evolution on Two Continents

TLDR

Porcine reproductive and respiratory syndrome virus (PRRSV) is a recently described arterivirus causing disease in swine worldwide, and its near‑simultaneous global emergence from divergently evolved strains suggests that changes in swine husbandry and management may have contributed to its spread. The study aimed to elucidate PRRSV evolution and pathogenicity by sequencing the 5′‑terminal region of VR‑2332 and comparing it to LV and other arteriviruses. The authors sequenced the 12,066‑base 5′‑terminal region of VR‑2332 and compared it to the corresponding region in LV and other arteriviruses. Comparative analysis revealed marked differences in the 5′ leader, ORF1a, and ORF1b regions, extensive variation in subgenomic mRNA processing and leader‑body junction usage, and overall genomic divergence, indicating that PRRSV has evolved independently on separate continents.

Abstract

ABSTRACT Porcine reproductive and respiratory syndrome virus (PRRSV) is a recently described arterivirus responsible for disease in swine worldwide. Comparative sequence analysis of 3′-terminal structural genes of the single-stranded RNA viral genome revealed the presence of two genotypic classes of PRRSV, represented by the prototype North American and European strains, VR-2332 and Lelystad virus (LV), respectively. To better understand the evolution and pathogenicity of PRRSV, we obtained the 12,066-base 5′-terminal nucleotide sequence of VR-2332, encoding the viral replication activities, and compared it to those of LV and other arteriviruses. VR-2332 and LV differ markedly in the 5′ leader and sections of the open reading frame (ORF) 1a region. The ORF 1b sequence was nearly colinear but varied in similarity of proteins encoded in identified regions. Furthermore, molecular and biochemical analysis of subgenomic mRNA (sgmRNA) processing revealed extensive variation in the number of sgmRNAs which may be generated during infection and in the lengths of noncoding sequence between leader-body junctions and the translation-initiating codon AUG. In addition, VR-2332 and LV select different leader-body junction sites from a pool of similar candidate sites to produce sgmRNA 7, encoding the viral nucleocapsid protein. The presence of substantial variations across the entire genome and in sgmRNA processing indicates that PRRSV has evolved independently on separate continents. The near-simultaneous global emergence of a new swine disease caused by divergently evolved viruses suggests that changes in swine husbandry and management may have contributed to the emergence of PRRS.