12 Oct TB test methods

It may be helpful for OVs to have in mind the relative roles of the different tests available when discussing controls with their farming clients.

To remind ourselves:

Sensitivity is the measure of how often the test will be positive if the animal is genuinely infected while specificity is the measure of how often the test proves negative if the animal does not have the disease.

	Sensitivity (%)	Specificity (%)
Skin test read at standard	81	99.98
Skin test read at severe	85	99.9
Gamma interferon test	90	96.5

 

Or, put another way:

The skin test read at standard interpretation will miss 19 in every 100 infected animals but when positive only 2 in every 10,000 will be slaughtered wrongly.

At severe interpretation, 15 in every 100 infected animals are undiagnosed but only 1 in 1,000 animals diagnosed as infected are wrongly slaughtered.

For gamma tests only 10 infected animals in every 100 truly infected are missed but 7 in every 200 animals diagnosed are, in fact, uninfected.

The true cattle data for the antibody tests used in Camelids, such as Enferplex (SureFarm Ltd) are still being determined via Defra. It is hoped that this test could become part of the armoury of diagnostics available to practitioners to help their clients make sensible decisions following the skin or gamma tests.

It is also worth being aware that the gamma test is available as a private test provided suitable permissions are obtained via your local APHA veterinary teams.