Laurin Emilie L, Chaffer Marcelo, McClure J Trenton, McKenna Shawn L B, Keefe Greg P
Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI, C1A 4P3, Canada.
Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI, C1A 4P3, Canada.
J Dairy Sci. 2015 Jan;98(1):211-20. doi: 10.3168/jds.2014-8406. Epub 2014 Nov 7.
Mycobacterium avium ssp. paratuberculosis (MAP) is the causative organism of Johne's disease. Although fecal culture is considered the standard diagnostic test, the long incubation times, costs, and intermittent shedding of MAP hinder efficient screening programs based on culture results. The primary objectives of this study were to determine the detection ability of solid culture, broth culture, and real-time PCR (qPCR) for MAP in fecal samples and to assess how shedding patterns of MAP in feces vary with lactation stage and season. This knowledge could improve the use of these diagnostic assays in Johne's management programs. For this study, 51 MAP-infectious cows from 7 Atlantic Canadian dairy farms had fecal samples collected monthly over a 12-mo period. Samples were analyzed for MAP bacterial load via solid culture, broth culture, and qPCR. For all fecal samples, 46% [95% confidence interval (CI): 40 to 51%] were positive by solid culture, 55% (95% CI: 50 to 60%) by broth culture, and 78% (95% CI: 73 to 82%) by qPCR. Sensitivity of qPCR was numerically higher in the dry and postpartum lactation periods, and qPCR detection in summer and fall was 85% of that in winter and spring. Furthermore, culture-determined moderate or light shedding categories generally corresponded to qPCR cycle threshold values <35, but heavy shedding categories corresponded to qPCR values <29. Direct fecal qPCR is a MAP detection method that is quick and less costly than culture techniques, and it avoids the use of decontamination steps that could decrease numbers of bacteria in a sample below the detection limit. This study indicates that, for known MAP-positive cows, fecal qPCR had high sensitivity of MAP detection, thereby supporting the use of direct fecal qPCR as part of a Johne's herd control program.
副结核分枝杆菌(MAP)是副结核病的病原体。尽管粪便培养被认为是标准诊断测试,但MAP的长时间培养、成本以及间歇性排出,阻碍了基于培养结果的高效筛查计划。本研究的主要目的是确定固体培养、液体培养和实时荧光定量PCR(qPCR)对粪便样本中MAP的检测能力,并评估粪便中MAP的排出模式如何随泌乳阶段和季节而变化。这些知识可改善这些诊断方法在副结核病管理计划中的应用。在本研究中,来自加拿大7个大西洋沿岸奶牛场的51头感染MAP的奶牛在12个月期间每月采集粪便样本。通过固体培养、液体培养和qPCR分析样本中的MAP细菌载量。对于所有粪便样本,固体培养的阳性率为46%[95%置信区间(CI):40%至51%],液体培养为55%(95%CI:50%至60%),qPCR为78%(95%CI:73%至82%)。qPCR的敏感性在干奶期和产后泌乳期在数值上更高,夏季和秋季的qPCR检测率是冬季和春季的85%。此外,培养确定的中度或轻度排出类别通常对应于qPCR循环阈值<35,但重度排出类别对应于qPCR值<29。直接粪便qPCR是一种检测MAP的方法,比培养技术更快且成本更低,并且避免了使用可能使样本中细菌数量降至检测限以下的去污步骤。本研究表明,对于已知感染MAP的奶牛,粪便qPCR对MAP检测具有高敏感性,从而支持将直接粪便qPCR作为副结核病畜群控制计划的一部分。