Recent cases of porcine reproductive and respiratory syndrome virus (PRRSV) infection in United States swine-herds have been associated with high mortality in piglets and severe morbidity in sows. Analysis of the ORF5 gene from such clinical cases revealed a unique restriction fragment polymorphism (RFLP) of 1-7-4. The genome diversity of seventeen of these viruses (81.4% to 99.8% identical; collected 2013–2015) and the pathogenicity of 4 representative viruses were compared to that of SDSU73, a known moderately virulent strain. Recombination analyses revealed genomic breakpoints in structural and nonstructural regions of the genomes with evidence for recombination events between lineages. Pathogenicity varied between the isolates and the patterns were not consistent. IA/2014/NADC34, IA/2013/ISU-1 and IN/2014/ISU-5 caused more severe disease, and IA/2014/ISU-2 did not cause pyrexia and had little effect on pig growth. ORF5 RFLP genotyping was ineffectual in providing insight into isolate pathogenicity and that other parameters of virulence remain to be identified.

在美国猪群中最近发生的猪繁殖与呼吸综合症病毒（PRRSV）感染病例与仔猪高死亡率和母猪严重发病有关。对来自此类临床病例的ORF5基因的分析显示，其独特的限制性片段多态性（RFLP）为1-7-4。将其中17种病毒的基因组多样性（81.4％至99.8％相同； 2013-2015年收集）和4种代表性病毒的致病性与已知的中度毒株SDSU73进行了比较。重组分析揭示了基因组结构和非结构区域的基因组断裂点，并证明了谱系之间发生重组事件。分离株之间的致病性各不相同，且模式不一致。IA / 2014 / NADC34，IA / 2013 / ISU-1和IN / 2014 / ISU-5造成了更严重的疾病，和IA / 2014 / ISU-2不会引起发热，对猪的生长影响很小。ORF5 RFLP基因分型不能有效地提供对分离株致病性的洞察力，而毒力的其他参数仍有待确定。