Written answers

Tuesday, 3 November 2020

Department of Agriculture, Food and the Marine

Tuberculosis Eradication Programme

Photo of Denis NaughtenDenis Naughten (Roscommon-Galway, Independent)
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70. To ask 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. [33290/20]

Photo of Charlie McConalogueCharlie McConalogue (Donegal, Fianna Fail)
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The 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 post-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.

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.

One of the recommendations made by the TB Forum was for additional focussing on herds with chronic or recurrent TB problems. Based on this recommendation my officials are developing policies which will involve additional uses of the gamma interferon test; these will be discussed in more detail at the TB Forum as part of the ongoing discussions on TB strategy.

Currently, there are two laboratories in Ireland carrying out gamma interferon TB testing for my Department; a tender for a third lab to provide additional testing capacity has recently closed and this is expected to support an increase in test capacity.


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