Gamma interferon tests aim to clamp down on TB

Although the announcement of wider use of the gamma interferon test alongside the tuberculin skin test has come as a welcome one, questions remain over what it will mean at farm level.

Independent vet consultant Tony Andrews says this blood test will result in fewer false reactions, picking up infected animals far earlier, but it will be dependent on prompt interpretation of test results and the ability of labs to provide a rapid turnaround.

“But, because the blood test will improve sensitivity of the testing regime and identify more infected animals quickly, farmers should be prepared to lose more animals in an infected herd than would have been picked up with the skin test alone,” he adds.

NFU adviser Alex Dinsdale says the test will be a valuable tool in helping keep clean areas clean, which is one of DEFRA’s major objectives.

“As infected cattle will be identified at a much faster rate, there will be less risk from infected cattle remaining on a holding long enough to infect wildlife populations and neighbouring cattle.”

Under this new policy the g-IFN test will be applied in mainly three and four-year testing parishes in an attempt to ensure infection in such areas doesn’t become established in cattle or wildlife.

From October this year, use of the test will be mandatory and will be used in the following circumstances as outlined by DEFRA.

All confirmed new incidents in three or four-year parish testing intervals, including those that fail to resolve through repeated skin tests or where complete or partial depopulation is contemplated.

The test will also be used when confirmed incidents failing to resolve (with visible lesions), despite taking biosecurity precautions in one and two-year parish testing intervals, including herds where a complete or partial depopulation is contemplated.

Furthermore, it will be used at the first inconclusive reactor retest in herds in one and two-year testing.

Additionally, DEFRA have said the test will be used occasionally to enhance specificity with non-specific reactors for unconfirmed breakdowns in two, three or four-year testing intervals and for suspected fraudulent reactors.

But Gloucestershire dairy producer Jan Rowe says that although wider use of the test should be encouraged by farmers, more should be done by DEFRA to address the issue of spread of infection through wildlife and ever-expanding hotspot areas.

“I’m also concerned as to the specificity of the test as to whether it will be throwing up true positives, or other misleading sources of mycobacterium, particularly as larger numbers of infected cattle are likely to be reported with this test.”

NBA chairman Duff Burrell says the test will be particularly useful for breeders in low-TB areas who have been hit with the disease, possibly through translocation, and who want their herd swept for reactors that have been missed by the skin test.

“This means producers will be clear of movement restrictions much quicker.”

Mr Burrell adds that the other bonus will be that some blood tested herds will become TB-free earlier than they would be and risk of regular reinfection within the herd is either reduced or eliminated.