Scientific Opinion on the use of a gamma interferon test for the diagnosis of bovine tuberculosis

The procedures for gaining, maintaining, suspending, withdrawing or re-gaining official bovine tuberculosis free herd status and for certification for intra-Union trade are based on the results of tuberculin skin tests. The skin test has a number of drawbacks, therefore the suitability of the gamma interferon test and other tests to be included by EU legislation was assessed. Suitability means that the test has a sensitivity equivalent or superior to the standard test currently used in the European Union and specificity not lower than that of the standard test with the lowest specificity used in the EU. Furthermore, there should be no foreseeable practical difficulties that could compromise test performance. It was concluded that purified protein derivative based gamma interferon tests can be included amongst the official tests for the purpose of demonstrating freedom. However, some results suggest that the specificity of the purified protein derivative based gamma interferon tests may not always be as high as the single intradermal tuberculin test. In case the test is included, the protocols for its use for this purpose should be harmonised in the EU. Based on the reviewed information, other tests should not yet be considered for inclusion in the official tests for the purpose of granting and retaining official tuberculosis free herd status. Further evaluation of the suitability of the gamma interferon tests test should study the influence of factors such as the presence of environmental mycobacteria, prevalence of bovine tuberculosis in the herd, the age type and bovine tuberculosis test history of the animals all of which may affect test specificity and hence the suitability of the test for demonstrating freedom from bovine tuberculosis in different situations.