Dáil Éireann Debate, Tuesday - 18 May 2021
723. Deputy Denis Naughten asked the Minister for Agriculture, Food and the Marine if he will expand the use of the gamma interferon test to eradicate bovine TB in the national herd; and if he will make a statement on the matter. [26592/21]
Amharc ar fhreagraThe gamma interferon test (also referred to as the GIF test or IFN-gamma test) is a valuable tool for detecting TB infection in cattle. It has been widely used as a core part of the TB eradication programme in Ireland since 2015, following many years of it being researched and tested in specific problem herds.
Like all such tools, it is important to use it in ways which maximise its utility. Each diagnostic test has strengths and weaknesses and the way in which a test is used must take these into account. The key measures of a diagnostic test’s accuracy are sensitivity and specificity. As is the case with diagnostic tests for other diseases, none of the tests currently available for the diagnosis of bovine TB (bTB) allow a perfectly accurate determination of the M. bovis infection status of cattle.
The single intradermal comparative tuberculin skin test (SICCT), often referred to as the skin test, which is used in Ireland is universally regarded as the best screening test in a general population of animals. However, in a group of animals where TB infection is known to be present, the gamma interferon test is used because it can detect infected cattle at an earlier stage of infection than the skin test. Therefore, it can detect a higher proportion of infected cattle; in other words, it has higher sensitivity than the skin test. When used in parallel to the skin test, the gamma interferon blood test can help to resolve TB problems in a herd more quickly by identifying cattle at an early stage of infection before they can spread infection onwards.
The gamma interferon test is used as standard in herds which have experienced a significant TB breakdown (for example, five or more reactors, 5% of the herd, or where the investigating veterinary inspector deems it necessary on epidemiological grounds). In addition, the gamma interferon test is used as a quality control measure on SICTT reactors, providing additional confidence in the quality of the skin testing process.
Under the new Bovine TB Eradication Strategy a new strategy has been deployed whereby the gamma interferon test is used to reduce the risk posed by animals which test inconclusive to the skin test. Other new policies being developed under the TB Eradication Strategy, focussing on herds with chronic or recurrent TB problems, will also use the gamma interferon test as appropriate.
However, the gamma interferon test is not suitable for use as a general screening test, in the way the SICCT test is used, because it has lower specificity than the skin test. That means the proportion of truly non-infected cattle identified as negative is lower with the gamma interferon test than with the skin test. Using it in herds not thought to be TB-infected would lead to non-infected cattle testing false positive.
