APHA broadens scope of PCR testing for bovine TB

09 February 2024

A man pushing a cow through a cattle crush

Following the initial rollout of PCR testing for the bacterium responsible for bTB, Defra has said the PCR test will now be applied to a wider range of bTB post-mortem test samples. 

PCR (Polymerase Chain Reaction) testing began in March 2022 to aid rapid detection of the bacterium, Mycobacterium bovis (M. bovis) which is responsible for bTB.

From 14 February, the APHA will expand the use of PCR testing in England, Wales, and Scotland to include suitable post-mortem tissue samples collected from:

  • Cattle that have tested positive for bTB
  • DCs (Direct contacts)
  • Privately or compulsory slaughtered or dead IRs (inconclusive reactors).

From this date, the current method for bTB diagnostic testing of tissue samples, microbiological culture, will only be applied to specific PCR test-positive samples, either to aid disease investigations by obtaining Whole Genome Sequence information or if a valid PCR result is not achieved.

‘Significant step’

NFU Cymru TB Focus Group Chairman Roger Lewis described the expansion of PCR testing as a 'welcome step' which NFU Cymru has long-called for.

He said: "This is a welcome step forward that will speed up the time taken to detect bovine TB in post-mortem samples. Swift disclosure of test results is crucial and can help offer some certainty for all those involved in managing a breakdown on farm."

A major benefit of using PCR testing is the speed at which APHA can confirm results – an average of 3 weeks. 

The gold standard method for bTB diagnostic testing from tissue samples (of both bovine and non-bovine farmed animals) is traditional microbiological culture.

Although well established, the major disadvantage of this approach is the length of time it typically takes to obtain a result (six to 22 weeks).

This could help provide a timely resolution of a suspected TB breakdown or allow for swift intervention to tackle infection at the earliest opportunity.

The approach and procedures for managing a TB breakdown will remain unchanged. However, detecting M. Bovis in post-mortem samples should generally be achieved more quickly.

More information on how the PCR test is currently used and further information can be found on the TB hub which will be updated in due course.

How is PCR testing currently used?

The PCR test introduced in March 2022 is currently only used in the following situations:

  • TB slaughterhouse cases in cattle and non-bovines i.e. animals routinely sent for private commercial slaughter that have suspicious lesions of TB at routine meat inspection.
  • Non-bovine animals such as camelids, goats, pigs, sheep and farmed deer that are removed as TB test reactors, direct contacts or clinical TB suspects, and cases where TB lesions are identified on diagnostic post-mortem examination in a veterinary laboratory.
  • Domestic pets (cats and dogs) and exotic species of animals (e.g. in zoological collections) submitted to APHA for laboratory investigation.

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