Effective diagnostic tests are a crucial element of any disease eradication programme. The Irish bTB eradication programme uses two main diagnostic tests for live animals:
- The single intradermal comparative tuberculin test (SICTT), often referred to as the skin test, which is the test most widely used in an Irish context.
- The gamma interferon test (a blood test) which is used as an adjunct to the SICTT in known infected herds.
These are the two tests recognised under EU regulation 64/432, which is the basis for enabling our cattle to trade within the EU.
Additionally, another blood test, the Tb ELISA test, is also used where necessary as a tool where there are intractable TB breakdowns to try to identify chronically infected individual animals which are still clinically normal but whose immune system is not capable of reacting to the tuberculin skin test.
For samples taken from animals suspected of having TB lesions detected at routine slaughter, such samples are tested using bacteriological culture and histopathological examination.
My Department has for many years supported and funded research and development of new diagnostic tools for bTB, and continues to do so. This includes work to validate new molecular diagnostic techniques such as polymerase chain reaction (PCR) on post-mortem samples, research into the use of novel antigens to improve the performance of the gamma interferon test on blood samples and research into immunological variations in cattle affecting the response to bTB. This work involves collaborations with UCD and Teagasc, with private sector companies seeking to validate tests, and with research groups in other countries such as the UK which face similar challenges to us in respect of bTB.
When performed correctly, the TB skin test continues to be the best and most accurate diagnostic screening test available for use in cattle. In particular, it has an exceptionally high specificity i.e. the rate of false positive results with the Tb skin test is very low - less than 1 in 5,000 tests gives a false positive result. While the possibility of human error cannot be eliminated, my Department has a robust quality control programme in place to ensure accuracy and consistency in relation to test performance. Testing can only be carried out by authorised veterinary practitioners and the authorisation process includes taking part in a DAFM training course. The performance of Tb tests by veterinary practitioners is subject to unannounced inspection and supervision by DAFM Veterinary Inspectors.
An IT system is used to evaluate and measure the testing performance of individual veterinary practitioners, using a number of test performance quality indicators including the number of positives detected in comparable groups, and the results of this evaluation is communicated to each veterinary practitioner. The results of this evaluation is also used as the basis for risk-based inspections of testing veterinarians by DAFM Veterinary Inspectors. As an additional layer of quality control on the accuracy and standard of skin testing, a significant number of reactor animals are blood tested using the gamma interferon blood test. Sanctions, including suspension from testing, are applied where veterinary practitioners are found where significant non compliances are found. In relation to the rotation of personnel, in general the individual farmer who pays for the herd test chooses the veterinary practitioner who carries out his annual herd test. In relation to other testing (reactor retests, contiguous tests etc), my Department assigns some of those tests to other veterinary testers on a risk basis as a result of epidemiological investigations, area risks, test risks and herd risks.
