Porcine circovirus 4 (PCV4) is a novel circovirus first discovered in China in April 2019. Here, we established an SYBR Green I-based real-time PCR for quantitative detection of PCV4. A pair of specific primers was designed based on the conserved region of Cap of PCV4. The standard curve of the established real-time PCR

assay showed a good linear relationship. The sensitivity of the established real-time PCR was 100 times greater than that of conventional PCR, and the detection limit of the assay was 3 × 10¹ copies. There was no cross-reactivity with other swine DNA viruses, showing good specificity. The intra-group variation coefficient was 0.37–0.78%, and the inter-group variation coefficient was 0.57–0.94%, indicating that the assay has good repeatability. Moreover, the analysis of clinical samples showed that the positive detection rate of PCV4 was 10.71% (18/168), while that of conventional PCR was 8.93% (15/168). Interestingly, co-infection with PCV2 or PCV3, or both PCV2 and PCV3, was also detected. In conclusion, the established SYBR Green I-based real-time PCR may be a cost-effective and rapid method for PCV4 clinical diagnosis.

猪圆环病毒4（PCV4）是2019年4月在中​​国首次发现的新型圆环病毒。在这里，我们建立了基于SYBR Green I的实时PCR定量检测PCV4。基于PCV4的Cap的保守区域设计了一对特异性引物。建立的实时PCR的标准曲线

测定显示出良好的线性关系。建立的实时荧光定量PCR的灵敏度是常规PCR的100倍，检测限为3×10 ¹副本。与其他猪DNA病毒没有交叉反应，显示出良好的特异性。组内变异系数为0.37–0.78％，组间变异系数为0.57–0.94％，表明该测定具有良好的重复性。此外，对临床样本的分析表明，PCV4的阳性检出率为10.71％（18/168），而常规PCR的检出率为8.93％（15/168）。有趣的是，还检测到与PCV2或PCV3或PCV2和PCV3的共同感染。总之，建立的基于SYBR Green I的实时PCR可能是PCV4临床诊断的一种经济高效的快速方法。