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Bovine Tuberculosis

Answer

The single intradermal comparative cervical tuberculin (SICCT) test, commonly known as the tuberculin skin test, is a well-established screening test for TB in cattle. It is a test approved and recognised by the EU Commission and the International Animal Health Organisation (OIE) as a primary, effective tool for the diagnosis of TB in cattle and other species, by virtue of its overall accuracy, robustness and relative simplicity (as demonstrated in several field evaluations conducted throughout the world).The accuracy of any test is measured in terms of its    specificity (proportion of uninfected animals identified as negative) and its sensitivity (proportion of infected animals detected as positive). The specificity for a correctly performed SICCT is above 99 per cent. Its sensitivity is between 77 per cent. and 95 per cent.The effectiveness of the tuberculin test depends on a host of controllable and uncontrollable variables such as the quality of the test reagent (tuberculins) employed, the operator performing the test, the animal/herd being tested, criteria for interpretation and the epidemiological situation. All batches of tuberculin undergo quality assurance testing at the Veterinary Laboratories Agency before release and their performance in the field is also monitored by epidemiological analyses. The quality of tuberculin testing work by approved local veterinary inspectors (LVIs) is assured by annual veterinary practice audits conducted by the State Veterinary Service (SVS), which ensure that LVIs are working to the most up to date operating procedures. The test certificates submitted by LVIs to the SVS are also audited for consistency with professional expectations. All concerns raised by farmers regarding the administration of the test are investigated by the SVS. A number of key TB epidemiological parameters (e.g. rate of reactors per 10,000 tests, disease confirmation rate in individual reactors, slaughterhouse case numbers, etc.) are also centrally monitored as indirect indicators of the effectiveness of the tuberculin testing programme.Provisional statistics indicate that 33.6 per cent¹ of all skin test reactors slaughtered in 2005 had demonstrable signs of TB (visible lesions on post mortem examination or a positive culture result for mycobacterium bovis). The purpose of post mortem examination and bacteriological culture of tuberculin test reactors is not so much the validation of skin test results on individual animals, but rather to determine for epidemiological purposes, (a) the severity of disease in infected animals and (b) the strain of mycobacterium bovis organism involved. Failure to find evidence of the disease by these means in a test reactor does not mean that the animal was not infected. In the early stages of infection, it is not always possible to see TB lesions with the naked eye, and, due to the fastidious nature of the organism, it is not possible to culture it from samples in every case."¹ Provisional data downloaded from the State Veterinary Service database on 7 March 2006. Subject to change as more data become available."

Secondary information

Type

Written question

Reference

4610; 680 c53-4WA

Session

2005-06

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Subjects

Standards Testing Bovine tuberculosis

Contains statistics

Yes

Link

View this Written question on www.publications.parliament.uk