Department of Health Management, University of Prince Edward Island, Charlottetown, PE, Canada C1A 4P3.
Department of Production Animal Health, University of Calgary, Calgary, AB, Canada T2N 4N1.
J Dairy Sci. 2018 Aug;101(8):7463-7470. doi: 10.3168/jds.2018-14458. Epub 2018 May 24.
In herds with typical moderate to low within-herd prevalence, testing for Mycobacterium avium ssp. paratuberculosis (MAP), the infectious agent of Johne's disease, will be more cost-effective if individual fecal samples are cultured in composite pools. However, sensitivity to classify a pool containing 1 or more positive individual samples as positive may depend on pool size and number of individual positive samples within a pool. Fecal samples collected from 994 dairy cows sampled at slaughter were cultured to detect MAP. Culturing was done both individually and as composite pooled samples using the TREK ESP Culture System II broth medium (Thermo Fisher Scientific, Trek Diagnostic Systems Inc., Cleveland, OH). Composite samples consisted of pools containing feces from 3, 5, 8, 10, or 15 cows. The number of individual fecal culture-positive cows within each pool ranged from 0 to 4. Culture of individual fecal samples detected MAP in 36 (3.6%) of the 994 cows. Individual samples that were detected within the first 50 d by TREK ESP Culture System II were more likely to lead to a positive pool result. In total, 840 pooled fecal samples were examined for presence of MAP, and of those, 272 pools actually contained feces from fecal culture-positive cows. The crude sensitivity (proportion of pools that contained at least 1 fecal-positive cow that tested positive) for pools of 3, 5, 8, 10, and 15 was 47, 67, 44, 59, and 39%, respectively. Across pools, an increase of the number of fecal culture-positive samples from 1 to 2 enhanced overall crude sensitivity from 44 to 71%. However, sensitivity did not further increase for pools with 3 or 4 fecal culture-positive samples (63 and 60%, respectively). Additionally, a simulation analysis assessing probability of pooled fecal samples being positive in herds of 50 and 100 cows was conducted. The simulation assumed that 1, 2, or 5 cows per herd were MAP fecal culture-positive and that pools of 5 and 10 were used. This low-prevalence herd simulation indicated that weighted mean herd probabilities of detecting a positive herd ranged between 52 and 99.3%, with the lowest probability for pools of 10 with 1 positive cow in the herd and the highest probability for pools of 5 with 5 positive cows in the herd. However, overall, pools of 5 and 10 had similar diagnostic capabilities, enabling cost savings by utilizing pools of 10.
在中等至低度群体内流行率的畜群中，如果对分枝杆菌 avium ssp. 进行个体粪便样本的复合培养，则对 paratuberculosis（MAP）进行检测更具成本效益，paratuberculosis 是约翰氏病的传染性病原体。然而，将包含 1 个或多个阳性个体样本的池分类为阳性的敏感性可能取决于池的大小和池内阳性个体样本的数量。从屠宰时采样的 994 头奶牛中收集粪便样本进行 MAP 培养。使用 TREK ESP 培养系统 II 肉汤培养基（Thermo Fisher Scientific，Trek Diagnostic Systems Inc.，克利夫兰，俄亥俄州）分别进行个体培养和复合 pooled 样本培养。复合样本由含有 3、5、8、10 或 15 头奶牛粪便的样本池组成。每个池内粪便培养阳性奶牛的个体数量从 0 到 4 不等。TREK ESP 培养系统 II 检测到 994 头奶牛中有 36 头（3.6%）存在 MAP。在 TREK ESP 培养系统 II 的前 50 天内检测到的个体样本更有可能导致阳性池结果。总共检查了 840 个 pooled 粪便样本是否存在 MAP，其中 272 个池实际上含有粪便培养阳性牛的粪便。包含至少 1 个粪便阳性牛的粪便阳性池的粗敏性（粪便培养阳性牛的比例）分别为 3、5、8、10 和 15 池的 47%、67%、44%、59%和 39%。在所有池中，粪便培养阳性样本数量从 1 增加到 2 ，总体粗敏性从 44%提高到 71%。然而，对于含有 3 或 4 个粪便培养阳性样本的池，敏感性没有进一步提高（分别为 63%和 60%）。此外，还进行了一项模拟分析，评估了在 50 头和 100 头奶牛的畜群中 pooled 粪便样本呈阳性的概率。该模拟假设每群中有 1、2 或 5 头奶牛为 MAP 粪便培养阳性，并使用 5 和 10 个 pooled。这种低流行率畜群的模拟表明，检测阳性畜群的加权平均畜群概率在 52%至 99.3%之间，畜群中含有 1 个阳性奶牛的 10 个 pooled 的概率最低，畜群中含有 5 个阳性奶牛的 5 个 pooled 的概率最高。然而，总体而言，5 个 pooled 和 10 个 pooled 的诊断能力相似，通过使用 10 个 pooled 可以节省成本。
