Whitlock R H, Wells S J, Sweeney R W, Van Tiem J
New Bolton Center, University of Pennsylvania, 382 West Street Road, Kennett Square, PA 19348, USA.
Vet Microbiol. 2000 Dec 20;77(3-4):387-98. doi: 10.1016/s0378-1135(00)00324-2.
The sensitivity and specificity of the ELISA and fecal culture tests for paratuberculosis in dairy cattle are examined. ELISA and fecal culture data from seven dairy herds where both fecal cultures and ELISA testing was done concurrently are included. A cohort of 954 cattle including 697 parturient adults, cultured every 6 months from 10 herds followed over 4 years served as the basis to determine fecal culture sensitivity. The fecal culture technique utilized a 2g sample with centrifugation and double incubation. Of the 954 cattle cohort of all ages (calf to adult) that were fecal sampled on the first herd visit, 79 were culture positive. An additional 131 animals were detected as culture positive over the next seven tests at 6-month intervals. The sensitivity of fecal culture to detect infected cattle on the first sampling was 38%. Of the 697 parturient cattle cohort, 67 were positive on the first fecal culture, while an additional 91 adult cattle were culture positive over the next seven tests, resulting in a sensitivity of 42% on the first culture of the total animals identified as culture positive. Animals culled from the herds prior to being detected as infected and animals always fecal culture negative with culture positive tissues at slaughter are not included in the calculations. Both groups of infected cattle will lower the apparent sensitivity of fecal culture. Infected dairy herds tested concurrently with both fecal culture and ELISA usually resulted in more than twofold positive animals by culture compared to ELISA. The classification of infected cattle by the extent of shedding of Mycobacterium paratuberculosis in the feces helps define the relative proportion of cattle in each group and therefore the likelihood of detection by the ELISA test. ELISA has a higher sensitivity in animals with a heavier bacterial load, i.e. high shedders (75%) compared to low shedders (15%). Repeated testing of infected herds identifies a higher proportion of low shedders which are more likely to be ELISA negative. Thus, the sensitivity of the ELISA test decreases with repeated herd testing over time, since heavy shedders will be culled first from the herds.
对奶牛副结核病的酶联免疫吸附测定（ELISA）和粪便培养检测的敏感性和特异性进行了检查。研究纳入了七个奶牛群的ELISA和粪便培养数据，这些牛群同时进行了粪便培养和ELISA检测。一个由954头牛组成的队列，包括697头临产成年牛，来自10个牛群，在4年时间里每6个月进行一次培养，以此作为确定粪便培养敏感性的基础。粪便培养技术采用2克样本，经过离心和双重培养。在首次对牛群进行粪便采样时，对所有年龄段（从犊牛到成年牛）的954头牛进行了检测，其中79头培养呈阳性。在接下来每隔6个月进行的七次检测中，又有131头动物被检测为培养阳性。粪便培养在首次采样时检测出感染牛的敏感性为38%。在697头临产牛队列中，67头在首次粪便培养时呈阳性，而在接下来的七次检测中，又有91头成年牛培养呈阳性，在首次培养时，被确定为培养阳性的所有动物的敏感性为42%。在被检测出感染之前就被从牛群中淘汰的动物，以及在屠宰时粪便培养始终为阴性但组织培养呈阳性的动物，未纳入计算。这两组感染牛都会降低粪便培养的表观敏感性。同时进行粪便培养和ELISA检测的感染奶牛群，与ELISA相比，培养检测出的阳性动物通常多出两倍以上。根据粪便中副结核分枝杆菌的排出程度对感染牛进行分类，有助于确定每组牛的相对比例，从而确定ELISA检测出感染牛的可能性。ELISA在细菌载量较高的动物（即高排出量动物，敏感性为75%）中比低排出量动物（敏感性为15%）具有更高的敏感性。对感染牛群进行重复检测会发现更高比例的低排出量动物，这些动物更有可能ELISA检测呈阴性。因此，随着时间的推移，对感染牛群进行重复检测，ELISA检测的敏感性会降低，因为高排出量动物会首先被从牛群中淘汰。
