Use of ESAT-6 in the interferon-gamma test for diagnosis of bovine tuberculosis following skin testing.

Abstract

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.

• Authors: B M Buddle, T J Ryan, J M Pollock, P Andersen, G W de Lisle
• Journal: Veterinary microbiology (Vet Microbiol) Vol. 80 Issue 1 Pg. 37-46 (May 03 2001) ISSN: 0378-1135 [Print] Netherlands
• PMID: 11278121 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antigens, Bacterial
• Bacterial Proteins
• ESAT-6 protein, Mycobacterium tuberculosis
• Interferon-gamma

Topics

• Animals
• Antigens, Bacterial
• Bacterial Proteins
• Cattle
• Interferon-gamma
• Sensitivity and Specificity
• Skin Tests (veterinary)
• Tuberculosis, Bovine (diagnosis)