Porcine reproductive and respiratory syndrome virus (PRRSV) is a widely disseminated, macrophage-tropic arterivirus that exhibits profound genetic and pathogenic heterogeneity. The present study was conducted to determine the complete genome sequences of two novel Korean lineage 1 PRRSV-2 strains, KNU-1901 and KNU-1902, which were isolated from vaccinated pig farms experiencing unusually high morbidity and mortality. Both isolates contained notable discontinuous 423-nucleotide deletions (DELs) within the genes encoding nonstructural protein 2 (nsp2) and GP3 when compared with the prototype strain VR-2332. In particular, the nsp2 DEL viruses had unique quadripartite discontinuous DEL signatures (111-1-19-9) in nsp2; this is an expanded version of the tripartite 111-1-19 DEL previously identified in virulent lineage 1 PRRSV-2 strains. Phylogenetic analysis revealed that both novel nsp2 DEL viruses belong to the Korean clade (KOR C) of lineage 1 isolates based on ORF5 but cluster with lineage KOR A strains based on the nsp2 or complete genome sequence. Recombination detection analysis suggested that both novel isolates are recombinants and may have evolved via natural inter-lineage recombination between circulating KOR A and KOR C strains. Interestingly, compared with the prototype VR-2332 virus, the novel nsp2 DEL variants were less efficient at promoting the expression of immune response genes in porcine alveolar macrophage culture. Taken together, we conclude that KNU-1901 and KNU-1902 are recently evolved recombinant variants of the virulent lineage 1 family that caused the regional severe PRRS outbreaks.

猪繁殖与呼吸综合征病毒（PRRSV）是一种广泛传播的嗜巨噬性小动脉病毒，具有深远的遗传和致病性异质性。本研究旨在确定两种新型韩国谱系1 PRRSV-2株KNU-1901和KNU-1902的完整基因组序列，它们是从发生异常高发病率和死亡率的疫苗接种猪场中分离出来的。与原型菌株VR-2332相比，两个分离株在编码非结构蛋白2（nsp2）和GP3的基因中均包含明显的不连续的423个核苷酸缺失（DEL）。特别是，nsp2 DEL病毒在nsp2中具有唯一的四方不连续DEL签名（111-1-19-9）；这是先前在毒性谱系1 PRRSV-2菌株中鉴定的三方111-1-19 DEL的扩展版本。系统发育分析表明，这两种新的nsp2 DEL病毒均属于基于ORF5的谱系1分离株的韩国进化枝（KOR C），但与基于nsp2或完整基因组序列的谱系KOR A株成簇。重组检测分析表明，这两种新分离株都是重组体，并且可能是通过循环的KORA A和KORC菌株之间的自然种系重组进化而来的。有趣的是，与原型VR-2332病毒相比，新型nsp2 DEL变体在促进猪肺泡巨噬细胞培养物中免疫反应基因表达方面效率较低。综上所述，我们得出的结论是，KNU-1901和KNU-1902是最近进化的有毒谱系1家族的重组变异体，导致了区域严重PRRS暴发。