Department of Veterinary Medicine Virology Laboratory, College of Veterinary Medicine and BK21 Program for Veterinary Science, Seoul National University, 599 Gwanangno, Gwanak-Gu, Seoul, 151-742, Republic of Korea.
Vet Microbiol. 2011 Jun 2;150(3-4):230-8. doi: 10.1016/j.vetmic.2011.01.025. Epub 2011 Feb 1.
This study was to investigate dynamic and evolution of PRRSV in a seed-stock farm by monitoring PRRSV status from 11 June 2009 to 4 August 2010. For laboratory test, around 18-24 umbilical cords from farrowed sows and 5-95 sera from nursery and grow/finish pigs were submitted around every 2 weeks interval during the study. The submitted samples were tested for PRRSV using IDEXX PRRS 2XR ELISA kit, RT-nested PCR. The PRRSV-positive samples were further sequences based on ORF5 and analyzed using MEGA 3.1 program and Beast 1.5.4 package. The surveyed farm was first infected with type II PRRSV but it was infected newly with type I PRRSV of unknown origin, showing rapid substitution to type I PRRSV as a dominant strain in 2 weeks. The type I PRRSV was first detected from umbilical cord of a farrowed sow in 12 January 2010, and secondly from nursery pigs in 26 January 2010. Although sudden increase of mean S/P ratio was found in grow/finish pigs around 2 months earlier than first type I PRRSV detection, no type I PRRSV viremia was found. Thirty three ORF5 full sequences from 14 type II to 19 type I PRRSVs were obtained chronologically in this farm and the genetic characteristics and evolution rates of those sequences were analyzed. The substitution rates (/site/day) of two types were 4.03×10(-5) (type I), 3.09×10(-5) (type II), respectively, which was more frequent than previous reports. The calculated divergence time of type I PRRSV was consistent with the time when the sudden elevation of serum IgG in grow/finish barn was first observed. This study provided fundamental data for type I PRRSV dynamic in a previously type II PRRSV-infected farm and suggested grow/finisher barn could be a primary site for PRRSV introduction.
本研究通过监测 2009 年 6 月 11 日至 2010 年 8 月 4 日期间的 PRRSV 状态，调查了种猪场 PRRSV 的动态和演变。在研究过程中，每隔 2 周左右，实验室会检测来自分娩母猪的约 18-24 根脐带和来自保育猪和生长/育肥猪的 5-95 份血清。提交的样本使用 IDEXX PRRS 2XR ELISA 试剂盒和 RT-巢式 PCR 进行 PRRSV 检测。对 PRRSV 阳性样本进行进一步的 ORF5 序列分析，并使用 MEGA 3.1 程序和 Beast 1.5.4 包进行分析。该调查农场最初感染了 II 型 PRRSV，但随后感染了来源不明的 I 型 PRRSV，在两周内迅速取代 I 型 PRRSV 成为优势株。I 型 PRRSV 于 2010 年 1 月 12 日首次从分娩母猪的脐带中检测到，其次于 2010 年 1 月 26 日从保育猪中检测到。尽管生长/育肥猪的平均 S/P 比值在比首次检测到 I 型 PRRSV 早约 2 个月时突然升高，但未发现 I 型 PRRSV 血症。在该农场，我们从 14 株 II 型到 19 株 I 型 PRRSV 中获得了 33 个 ORF5 全长序列，并对这些序列的遗传特征和进化率进行了分析。两种类型的替代率（/位点/天）分别为 4.03×10(-5)（I 型）和 3.09×10(-5)（II 型），这比之前的报道更为频繁。I 型 PRRSV 的计算分歧时间与首次观察到生长/育肥猪血清 IgG 突然升高的时间一致。本研究为先前感染 II 型 PRRSV 的种猪场 I 型 PRRSV 的动态提供了基础数据，并提示生长/育肥猪舍可能是 PRRSV 传入的主要场所。
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