Bech-Nielsen S, Jorgensen J B, Ahrens P, Feld N C
National Veterinary Diagnostic Laboratory, Copenhagen, Denmark.
J Clin Microbiol. 1992 Mar;30(3):613-8. doi: 10.1128/jcm.30.3.613-618.1992.
The purpose of this study was to describe the responses of sera from five groups of cattle to an enzyme-linked immunosorbent assay (ELISA) for paratuberculosis by using serum absorbed with Mycobacterium phlei at a single working dilution. The infection status of the cattle was determined by fecal culture. Cattle with different levels of exposure (high versus low prevalence and test negative) and disease manifestation (clinically suspect infection versus subclinical infection) were examined, as follows: (i) two paratuberculosis-negative herds; (ii) a fecal culture-confirmed, clinically suspect cases of paratuberculosis; (iii) cows from a paratuberculosis-infected herd with a high infection rate, as determined by fecal culture, but with no clinical cases at the time of sampling; (iv) cows from three paratuberculosis-infected herds known to have paratuberculosis diagnosed on the farm (low infection rate determined by fecal culture); and (v) one fecal culture-negative herd with known serologically positive cattle. Results generally showed a decreased ELISA response when absorbed rather than nonabsorbed serum from each animal was used. The results of the fecal culture confirmed clinically suspect cases, which were analyzed in relation to the amount of colonies isolated from the animals on fecal culture (0, +, ++,+++ , ++++, and above). There was a significant increase in the ELISA response for animals with heavy Mycobacterium paratuberculosis shedding ( ++++ or above), when both unabsorbed and absorbed sera were used, compared with the response in animals that were fecal culture negative or that shed M. paratuberculosis at lower levels (less than +) (P less than 0.05). The effects on sensitivity and specificity by using different cutoff points for the five groups of cattle with different levels of exposure is described, since sera were not discretely segregated into distinct groups of positive and negative samples. The specificity of the ELISA in the two fecal culture-negative herds was 100% at an ELISA cutoff of an optical density (OD) of 0.1 and above for absorbed serum. For unabsorbed serum the specificity was 62.9% at a similar cutoff value. Similarly, the specificity of the fecal culture-negative, serologically positive herd increased from 37.5 to 72.2 at an ELISA cutoff value of 0.1 to 0.2 (OD) by using absorbed versus unabsorbed serum from 75.0 to 94.4 at an ELISA cutoff value of 0.2 to 0.3 (OD).
本研究的目的是描述五组牛的血清对用于副结核病的酶联免疫吸附测定（ELISA）的反应，方法是使用在单一工作稀释度下用草分枝杆菌吸收的血清。通过粪便培养确定牛的感染状况。检查了具有不同暴露水平（高患病率与低患病率以及检测阴性）和疾病表现（临床疑似感染与亚临床感染）的牛，如下：（i）两个副结核病阴性牛群；（ii）粪便培养确诊的临床疑似副结核病例；（iii）来自粪便培养确定感染率高但在采样时无临床病例的副结核感染牛群的奶牛；（iv）来自三个已知在农场诊断出患有副结核病的副结核感染牛群的奶牛（粪便培养确定感染率低）；（v）一个粪便培养阴性但血清学检测已知阳性的牛群。结果总体显示，使用每只动物吸收后的血清而非未吸收的血清时，ELISA反应降低。粪便培养结果证实了临床疑似病例，并根据从动物粪便培养中分离出的菌落数量（0、+、++、+++、++++及以上）进行了分析。与粪便培养阴性或副结核分枝杆菌排出量较低（少于+）的动物相比，当使用未吸收和吸收后的血清时，副结核分枝杆菌大量排出（++++及以上）的动物的ELISA反应显著增加（P小于0.05）。由于血清未被离散地分为明显的阳性和阴性样本组，因此描述了对五组不同暴露水平的牛使用不同临界值对敏感性和特异性的影响。对于吸收后的血清，在ELISA临界值光密度（OD）为0.1及以上时，两个粪便培养阴性牛群中ELISA的特异性为100%。对于未吸收的血清，在类似临界值时特异性为62.9%。同样，通过使用吸收后的血清与未吸收的血清，粪便培养阴性、血清学阳性牛群在ELISA临界值从0.1至0.
