Bovine Tuberculosis: Testing

(asked on 18th August 2021) - View Source

Question to the Department for Environment, Food and Rural Affairs:

To ask the Secretary of State for Environment, Food and Rural Affairs, what estimate she has made of the total percentage of bovine TB tests involving the use of tuberculin that have produced false positives.


Answered by
Victoria Prentis Portrait
Victoria Prentis
Attorney General
This question was answered on 6th September 2021

The Single Intradermal Comparative Cervical Tuberculin test, commonly known as the ‘comparative skin test’, is the primary official antemortem test for tuberculosis (TB) in cattle in the UK and Ireland. This test has a very high specificity at standard interpretation of 99.98%, giving on average only one false positive result for every 5,000 to 6,000 uninfected cattle tested.

It is not possible to determine that a positive bovine TB (bTB) test in any species was actually a false positive result. However, the high specificity of the tests used, combined with the fact that they are often deployed in parts of the country with a high prevalence of bTB (or in herds with known or suspected infection), means that positive test results have a high predictive value. Post-mortem examinations of test positive animals do not always result in the detection of visible lesions of bTB and attempts to culture the bacterium in the laboratory may prove unsuccessful. In such cases this may be because the infection has not progressed to the stage at which definitive confirmation of disease is possible. In other words, absence of visible lesions of bTB at post-mortem examination or negative culture results do not indicate absence of infection in a bTB test-positive animal.

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