Animal Plant Health Agency
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Private vets must ask for permission from the Animal and Plant Health Agency (APHA) before carrying out any TB testing.
You must not do a tuberculosis test on an animal unless you have permission from APHA. You must report the test result immediately to APHA. This is set out in Article 10 of The Tuberculosis in Animals (England) Order 2021.
The only ante mortem tests currently approved for statutory cattle tuberculin (TB) testing in England are the:
- comparative intradermal tuberculin skin test
- supplementary interferon-y (IFN-y) blood test
An understanding of the performance of any diagnostic test is needed before it can be officially approved for routine veterinary use, usually following validation to the standards set out by the World Organisation for Animal Health (WOAH).
Private vets can carry out other non-validated or unapproved TB tests:
- with permission from the Animal and Plant Health Agency (APHA)
- on an exceptional basis
This applies to any TB test other than the skin and IFN-y tests cited in current EU legislation.
Non-validated or unapproved TB tests cannot be used to replace the current statutory TB testing regime.
Private vets can also consider using the IFN-y test on a voluntary basis, at the herd owners expense, if:
- a herd does not qualify for mandatory IFN-y testing
- APHA will not pay for the test on a discretionary basis
Read the guidance on private IFN-y testing.
What non-validated or unapproved tests can be used for
These tests can only be used to identify additional infected animals in herds with chronic TB breakdowns with lesion and/or positive PCR (or culture) cattle that have not been resolved by repeated short interval skin testing or IFN-y parallel testing.
They cannot be used to negate or question positive results to official tests on animals awaiting slaughter that are:
- skin test reactors
- IFN-y test positive
Non-validated or unapproved TB test types
There are 2 categories of unofficial tests for TB in individual cattle herds:
- WOAH-validated kits such as the IDEXX ELISA and the Enferplex TB antibody test
- novel, semi-experimental assays that have not been validated in cattle, such as the Polymerase Chain Reaction (PCR) on faecal samples and the Actiphage blood assay
The IDEXX ELISA test for M. Bovis
The bovine IDEXX ELISA antibody assay (IDEXX Laboratories, Maine, USA) can be used to measure circulating antibodies in cattle with advanced M. bovis. It is approved by WOAH to supplement the skin test for detection of TB-infected cattle and it was added to WOAHs Register of Validated Diagnostic Kits in June 2012. Its performed at APHA Starcross.
Antibody assays are not currently approved for official, regular TB testing of bovine animals in England. However, APHA may use the IDEXX ELISA test as a third-line test in exceptional circumstances in for herds that have chronic or persistent TB breakdowns that have not resolved after already been through:
- multiple rounds of short interval skin testing
- the IFN-y parallel test
Supplementary IDEXX testing carried out by APHA in England requires prior consent and a written agreement from the owner to allow the removal of any TB seropositive animals, with statutory compensation payments.
The IDEXX ELISA is a relatively simple and inexpensive assay that uses a combination of 2 M. bovis recombinant antigens (MPB83 and MPB70) that can provide test results in 2 hours and has:
- a moderate test sensitivity of 65%
- a specificity of 98% in cattle
To achieve maximum sensitivity in this test, a prior TB skin test must be performed. APHA then requires that blood samples for government-funded IDEXX testing are taken for 10 to 30 days following the skin test.
The Enferplex test for M. Bovis
The Enferplex TB test is another antibody test for TB in cattle that was validated to WOAH standards more recently (Enfer Diagnostics). This test achieved WOAH approval and was added toWOAHs Register of Validated Diagnostic Kitsfor the detection of TB in cattle in May 2019.
This test is currentlynotapproved by Defra, Scottish and Welsh Governments for official government-funded supplementary antibody testing of cattle. It can be used on a private basis in England subject to prior permission from APHA.
The Enferplex TB test is a multiplex enzyme immunoassay designed to detect the presence of antibodies to an array of 11M. bovisantigens. Any antibodies present in serum (and potentially milk) samples are detected simultaneously by a multiplex immunoassay.
Information in the WOAH data sheet indicates:
- a high test sensitivity of 71.4% (non-boosted) and 94.2% (boosted by a prior intradermal injection of tuberculin)
- a specificity of 99.7% for this test using a high specificity setting
As for the IDEXX test, the highest sensitivity of the Enferplex TB test is also dependent on a prior tuberculin skin test, which triggers the anamnestic (memory) antibody response in infected cattle. APHA strongly recommends that blood samples for Enferplex testing of cattle are taken within 10 to 30 days following a skin test.
Conditions for getting permission to test
You must get permission from APHA before carrying out any private non-validated or unapproved TB test.
APHA will only give permission for the test if the:
- herd has undergone mandatory IFN-y testing (if the herd is eligible under current Defra policy)
- herd owner has given informed, written consent
Informed consent from herd owners
Before testing, the private vet must get written consent from the herd owner to show they have informed them that:
- the tests are not validated or approved by Defra for routine use in cattle
- the test results may be unreliable and difficult to interpret, meaning the test may not offer any certainty about the animals true infection status
- the herd owner is responsible for all removal and slaughter costs, unless:
- the animals become positive after a subsequent government-funded TB test
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