In recent years, reports indicated that PCV3 may be involved in porcine dermatitis and nephropathy syndrome (PDNS)-like disease similar to that linked to PCV2. A total of 2,125 porcine samples from 910 cases were collected during 2016-2018 and tested for presence of PCV3 and PCV2 by real-time PCR assays. Results showed high prevalence of PCV3 and PCV2: 28.4% samples from 41.2% cases were PCV3 positive and 16.4% samples from 16.7% cases were PCV2 positive. The overall coinfection rate was 5.4% and 8.4% at the sample and case level, respectively. Temporal analysis indicated that PCV3 positive case rate increased from 31.6% in 2016, 40.9% in 2017, to 55.6% in 2018. Although its prevalence was lower, PCV2-positive case rate in 2018 (28.8%) doubled that in 2017 (14.4%). The coinfection case rate also increased from 3.4% in 2016, 8.0% in 2017 to 16.1% in 2018. The high positive rate of PCV3 (56.9%) and PCV2 (33.8%) in oral fluids, PCV3 in foetuses (57.1%) and PCV2 in tonsils (54.8%) implied viral transmission route and tissue tropism. In phylogenetic analysis, two small PCV3 clusters (1 and 2) were separated but others were clustered with low bootstrapping values indicating overall low genetic diversity. Genotypes, PCV2a-h, were confirmed by analysing 2,944 strains, with a new genotype proposed as PCV2i. In this study, 61 PCV3 unique whole genomes were sequenced; 12 belonged to a separate cluster that were characterized by five consistent amino acid changes in the capsid protein (24V, 27K, 56D, 98R and 168K) and may be associated with potential differences in immunogenicity. Among the 43 unique PCV2 whole genomes sequenced, 31 belonged to PCV2d, 7 to PCV2a and 5 to PCV2b. Thus, our study demonstrates that PCV2d is the predominant genotype and PCV3 is widely circulating in the Midwest of the USA.

中文翻译：

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2016-2018年期间，美国中西部地区3型猪圆环病毒（PCV3）和2型猪圆环病毒（PCV2）的遗传多样性和患病率。

近年来，有报道表明PCV3可能参与了猪皮炎和肾病综合征（PDNS）样疾病，类似于与PCV2相关的疾病。在2016年至2018年期间，共收集了910例病例的2125份猪样本，并通过实时PCR分析检测了PCV3和PCV2的存在。结果显示PCV3和PCV2的患病率很高：来自41.2％病例的28.4％样本为PCV3阳性，来自16.7％病例的16.4％样本为PCV2阳性。在样本和病例水平上，总体合并感染率分别为5.4％和8.4％。时间分析显示，PCV3阳性病例率从2016年的31.6％，2017年的40.9％增加到2018年的55.6％。尽管其流行率较低，但2018年PCV2阳性病例率（28.8％）是2017年（14.4％）的两倍）。合并感染病例率也从2016年的3.4％，2017年的8.0％增加到16年。2018年为1％。口腔液中PCV3（56.9％）和PCV2（33.8％），胎儿PCV3（57.1％）和扁桃体PCV2（54.8％）的高阳性率意味着病毒传播途径和组织嗜性。在系统发育分析中，分离了两个小的PCV3簇（1和2），但是其他的簇却具有较低的自举值，表明总体遗传多样性较低。基因型PCV2a-h通过分析2944株菌株得到确认，并提出了一种新的基因型PCV2i。在这项研究中，对61个PCV3独特的完整基因组进行了测序。12个属于单独的簇，其特征在于衣壳蛋白（24V，27K，56D，98R和168K）中的五个一致的氨基酸变化，并且可能与免疫原性的潜在差异有关。在43个独特的PCV2全基因组序列中，有31个属于PCV2d，7个属于PCV2a，5个属于PCV2b。从而，