Porcine circovirus type 2 (PCV2) is the etiological agent of post-weaning multisystemic wasting syndrome (PMWS). The original prevalent genotype, PCV2a, has been replaced by genotypes 2b and 2d in the swine population worldwide. The Rep protein is critical for viral replication. Comparison of a large number of Rep protein amino acid (aa) sequences showed that three sites distinguish genotype 2b from genotype 2d. In order to analyze the effect of exchanging the amino acids (asparagine and serine) at position 6 in the Rep proteins of PCV2b and PCV2d, two wild-type and two mutant viruses were rescued. Real-time quantitative PCR and a one-step growth curve were used to determine the viral load to assess the replication ability of the rescued viruses. The results showed that there was no significant difference in in vitro performance between the wild-type PCV2b and the mutated virus, while the mutation of PCV2d enhanced viral replication.

猪圆环病毒 2 型 (PCV2) 是断奶后多系统衰竭综合征 (PMWS) 的病原体。在全世界的猪群中，最初流行的基因型 PCV2a 已被基因型 2b 和 2d 所取代。Rep 蛋白对病毒复制至关重要。大量Rep蛋白氨基酸（aa）序列的比较表明，三个位点将基因型2b与基因型2d区分开来。为了分析交换 PCV2b 和 PCV2d Rep 蛋白中第 6 位氨基酸（天冬酰胺和丝氨酸）的影响，拯救了两种野生型病毒和两种突变型病毒。实时定量 PCR 和一步生长曲线用于确定病毒载量，以评估获救病毒的复制能力。结果表明，在体外没有显着差异 野生型 PCV2b 和突变病毒之间的性能，而 PCV2d 的突变增强了病毒复制。