Guangdong Key Laboratory of Animal Disease Prevention, Animal Disease Diagnostic Center, Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou, 510640, China.
Department of Biology and Microbiology, South Dakota State University, Brookings, SD, 57007, USA.
Virol J. 2017 Nov 13;14(1):222. doi: 10.1186/s12985-017-0892-4.
Porcine circovirus type 3 (PCV3), as an emerging circovirus species, was reported to be widely circulating in the United States, China, South Korea and Poland. Previous studies revealed that PCV3 was mainly concentrated in sick animals with respiratory disease, skin disease, reproductive disorders and so on. However, the circulating status of PCV3 in pigs with other clinical presentations (especilly asymptomatic or diarrhea) was not well established.
In this study, to conduct a comparative epidemiological survey of PCV3, 80 weaned pig serum samples with severe respiratory disease (SRD), 175 weaned pig serum samples with mild respiratory disease (MRD), 216 asymptomatic weaned pig serum samples, 35 diarrheal weaned pig samples and 35 non-diarrheal weaned pig samples were collected from eight provinces of China. Via qPCR testing, PCV3 was circulating in all sampling provinces, with total positive rates varying from 1.04% to 100%. Interestingly, the PCV3-positive rate was significantly higher in weaned pigs with SRD (63.75%, 51/80) than in those weaned pigs with MRD (13.14%, 23/175) and asymptomatic pigs (1.85%, 4/216) (P < 0.01). Similarly, the PCV3-positive rate was significantly higher in diarrheal weaned pigs (17.14%, 6/35) than in non-diarrheal weaned pigs (2.86%, 1/35) (P < 0.05). Moreover, the lower Ct values of qPCR were frequently found in those weaned pigs or fattening pigs with respiratory disease and diarrhea rather than that in asymptomatic pigs. Sequence analysis showed that low genetic diversity existed among those PCV3 sequences collected from pigs with different clinical presentations.
The present study further extends evidence that newly described PCV3 widely circulates in six additional provinces of Southern and Northern China and has high similarity to previously reported isolates. As an emerging virus of swine, although the present case-control study reveals that PCV3 has a potential association with swine respiratory disease and diarrhea, further investigations into the pathogenesis are needed to ascertain the role of PCV3 in swine health.
猪圆环病毒 3 型（PCV3）作为一种新兴的圆环病毒，据报道在美国、中国、韩国和波兰广泛传播。先前的研究表明，PCV3 主要集中在患有呼吸道疾病、皮肤病、生殖障碍等疾病的患病动物中。然而，PCV3 在其他临床表现（特别是无症状或腹泻）的猪中的流行情况尚不清楚。
在这项研究中，为了对 PCV3 进行比较流行病学调查，从中国 8 个省份采集了 80 份严重呼吸道疾病（SRD）断奶猪血清样本、175 份轻度呼吸道疾病（MRD）断奶猪血清样本、216 份无症状断奶猪血清样本、35 份腹泻断奶猪样本和 35 份非腹泻断奶猪样本。通过 qPCR 检测，PCV3 在所有采样省份均有传播，总阳性率为 1.04%至 100%。有趣的是，SRD 断奶猪的 PCV3 阳性率（63.75%，51/80）明显高于 MRD 断奶猪（13.14%，23/175）和无症状猪（1.85%，4/216）（P<0.01）。同样，腹泻断奶猪的 PCV3 阳性率（17.14%，6/35）明显高于非腹泻断奶猪（2.86%，1/35）（P<0.05）。此外，在患有呼吸道疾病和腹泻的断奶猪或育肥猪中，qPCR 的 Ct 值较低，而在无症状猪中则较低。序列分析表明，从不同临床表现的猪中采集的 PCV3 序列存在较低的遗传多样性。
本研究进一步证实，新描述的 PCV3 广泛流行于中国南方和北方的另外六个省份，与先前报道的分离株具有高度相似性。作为一种新兴的猪病毒，尽管本病例对照研究表明 PCV3 与猪呼吸道疾病和腹泻有潜在关联，但需要进一步研究其发病机制，以确定 PCV3 在猪健康中的作用。
