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Dept for Environment Food and Rural Affairs

Answer

Andrew George: To ask the Secretary of State for Environment, Food and Rural Affairs what research she has evaluated on the specificity and sensitivity of the Bovigam gamma interferon test; and what conclusions she has drawn. [172550] Mr. Bradshaw: The Veterinary Laboratories Agency (VLA) has reviewed 13 papers reporting gamma- interferon (g-IFN) field trials in Australia, New Zealand, Northern Ireland, Republic of Ireland, Brazil, Italy, Spain and USA. Eight papers gave 20 estimates of sensitivity (80 per cent. were in the range 71-94 per cent.) and 8 papers gave 22 estimates of specificity (80 per cent. were in the range 89-99 per cent.). These estimates for sensitivity are similar to those for the skin test as practiced in the UK, but the estimates for specificity are lower. If the g-IFN test were used at the same time or shortly after the skin test and animals positive to either test were removed, the combined tests would have a greater sensitivity than the skin test alone. If used with the defined, more specific, antigens developed by VLA, the gamma interferon test can in certain circumstances identify uninfected animals that are positive to the skin test. The g-IFN assay is widely considered to be at least as sensitive as the skin tests and, in addition, will detect a proportion of infected cattle that fail to react to the skin tests. This is thought to be because the g-IFN test detects infection at an earlier stage that the skin test does, although there is also evidence that the two tests detect slightly different populations of tuberculous cattle. However, the g-IFN test is hardly ever used for mass TB screening on its own. This is because the test is relatively expensive, it does not detect all skin test-positive infected animals, it tends to be less specific than the SICCT (the single intradermal comparative cervical test, which is the version of the skin test used in the UK and Ireland) and, like the SICCT, it is unlikely to detect infected animals that are negative to the tuberculin test due to a depressed immune response to tuberculin (this can occur in cattle with advanced TB). The need to process samples within 24-30 hours of collection also poses some logistical problems for mass screening. In contrast, it has been postulated that the use of the g-IFN test in tandem with the skin test could allow the removal of more (but not necessarily all) infected cattle from particular breakdown herds than the skin test alone. If this is correct, use of the two tests in quick succession should speed up the elimination of infection from infected herds. Under this premise, the European Commission approved the g-IFN test in 2002 for use as an ancillary test in animals that fail to respond to the skin test and it now complements the skin tests in cattle herds with intractable, confirmed infection in many EU member states. It is worth noting that most of these member states use a version of the skin test different to that used in the UK and Ireland.

Secondary information

Type

Written question

Reference

172550; 421 c1104W

Session

2003-04

Subjects

Cattle Disease control Testing Bovine tuberculosis Skin

Link

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