Buddle B M, Ryan T J, Pollock J M, Andersen P, de Lisle G W
AgResearch, Wallaceville Animal Research Centre, P.O. Box 40063, Upper Hutt, New Zealand.
Vet Microbiol. 2001 May 3;80(1):37-46. doi: 10.1016/s0378-1135(00)00375-8.
The whole blood interferon-gamma (IFN-gamma) test has proven to be a practical ancillary test for re-testing cattle for bovine tuberculosis 8-28 days following tuberculin skin testing. An improvement in the specificity of the IFN-gamma test could further reduce culling of false positive animals. The primary aim of this study was to evaluate a single mycobacterial antigen, ESAT-6 in the IFN-gamma test for use in skin test-positive cattle. These skin test-positive cattle comprised 51 Mycobacterium bovis-infected animals from tuberculosis-infected herds and 85 non-infected animals from tuberculosis-free herds. The test based on ESAT-6 had a higher specificity than the test based on purified protein derivative (PPD) tuberculin, but this was offset by a small decrease in sensitivity. Use of a lower cut-off in the ESAT-6-based test improved the sensitivity, while still maintaining a very high specificity. A secondary aim in the study was to assess the ESAT-6 and PPD-based tests for detecting bovine tuberculosis in skin test-negative animals from a persistently infected herd. The PPD-based test detected the majority of the lesioned or M. bovis-culture positive animals, while the ESAT-6-based test detected a smaller proportion. The false negatives in the IFN-gamma test from both the skin test-negative and positive groups were predominantly M. bovis-culture positive animals with no visible lesions. The current study has shown that a defined specific antigen such as ESAT-6 can markedly improve the specificity of the IFN-gamma test for re-testing skin test-positive animals. An ESAT-6-based IFN-gamma test could be particularly useful to reduce the false positive rate, yet still maintain an acceptable level of sensitivity.
全血干扰素-γ（IFN-γ）检测已被证明是一种实用的辅助检测方法，用于在结核菌素皮肤试验8-28天后对牛进行牛结核病复检。提高IFN-γ检测的特异性可进一步减少对假阳性动物的扑杀。本研究的主要目的是评估在IFN-γ检测中用于皮肤试验阳性牛的单一分枝杆菌抗原——早期分泌性抗原靶6（ESAT-6）。这些皮肤试验阳性牛包括来自结核病感染牛群的51头牛分枝杆菌感染动物和来自无结核病牛群的85头未感染动物。基于ESAT-6的检测比基于纯化蛋白衍生物（PPD）结核菌素的检测具有更高的特异性，但这被敏感性的小幅下降所抵消。在基于ESAT-6的检测中使用较低的临界值可提高敏感性，同时仍保持非常高的特异性。该研究的第二个目的是评估基于ESAT-6和PPD的检测方法在检测来自持续感染牛群的皮肤试验阴性动物中的牛结核病情况。基于PPD的检测方法检测出了大多数有病变或牛分枝杆菌培养阳性的动物，而基于ESAT-6的检测方法检测出的比例较小。皮肤试验阴性和阳性组的IFN-γ检测中的假阴性主要是牛分枝杆菌培养阳性但无可见病变的动物。当前研究表明，一种确定的特异性抗原如ESAT-6可显著提高IFN-γ检测对皮肤试验阳性动物复检的特异性。基于ESAT-6的IFN-γ检测对于降低假阳性率可能特别有用，同时仍保持可接受的敏感性水平。
