Introduction to the Enferplex TB Antibody Tests
The Enferplex TB Antibody Tests are a serological or milk assay which identifies the presence of antibody to Mycobacterium bovis, the causal agent of bovine Tuberculosis (bTB).
Different versions of Enferplex TB Antibody Tests have been developed specifically for individual species including cattle, camelids, goats, deer, badgers, pigs and a variety of zoological species.
There are a number of antigens used in a test may vary between species. No matter which species, if two or more antigens levels are above the pre-defined levels, the result is interpreted as positive.
As the number of positive antigens increase, the specificity of the test increases. The higher the number of red dots (antigen positives), the increased likelihood the animal will demonstrate lesions.
Fig. 1:
1 antigen is positive (red) - this result would be interpreted as negative to bTB.
Fig. 2:
2 antigens are positive - this result would be interpreted as positive to bTB.
Fig. 3:
4 antigens are positive in this sample - the result is interpreted as positive to bTB as two or more antigens are positive.
How does the Enferplex Bovine TB antibody test work?
The test detects the presence of antibodies within blood to Mycobacterium bovis (M. bovis), the cause of bTB, by use of individual antigens.
The different antigens used in the test are placed separately as individual spots within a well. The number of antigens used in a test may vary between species. If antibody to bTB is present in the blood sample being tested, then it will bind with the relevant antigen resulting in a chemiluminescent reaction, the light from which can be measured and quantified (see Figure 1 below which demonstrates an outcome from a cattle test which uses 11 separate antigens).
Figure 1
Images from three individual testing wells showing individual antigen spots that have bound antibody and are luminescent. This light is measured to produce a quantitative result as displayed in the table (RLU = Relative Light Units).
Thresholds are set for each individual antigen and if the level of Relative Light Units (RLU) is above this threshold, a positive reaction is deemed to have occurred. In all species a positive test result is when two or more antigens are shown to be above the thresholds set for the antigens.
In cattle there are two different thresholds set for each antigen, a high sensitivity setting and a high specificity setting. The high specificity setting requires a higher threshold to be reached for a positive reaction.
The timing of sampling after a tuberculin ‘skin’ test (SICCT test) significantly affects the sensitivity of detection of antibody. Samples taken between 10 and 30 days post–SICCT testing will benefit from an antibody ‘boosting’ effect due to an anamnestic response to the PPD antigens used in the test in animals infected with M. bovis. Samples taken outside this ‘window’ (non-boosted) will have lower levels of antibody and the test will be less sensitive.