The performance of the test at high sensitivity and high specificity settings has been elucidated in both Bovine TB positive and negative populations in UK and Ireland. Any data pertaining to being ‘Boosted’ indicate that samples were collected and analysed within the 10—30 day window post tuberculin injection and thereby would be expected to have an improved sensitivity compared to non boosted samples. This 10-30 day window gives the highest sensitivity and would normally be expected to be used, thus the sensitivities displayed are appropriate to the expected performance of the test.
Specificity
Table 1:
Relative Diagnostic Specificity of the Enferplex Bovine TB Antibody test at the high sensitivity and high specificity settings using sera from bTB-free animals from UK.| Country | High Sensitivity Setting | High Specificity Setting | |
|---|---|---|---|
UK* | N DSp Cl | 2268 98.1% 97.5-98.6 | 2268 99.8% 99.6-100.0 |
* Herd SICCT negative for 8 years, no evidence of bTB and more than 10 km from nearest herd with bTB in previous 12 months, or OTF status of country/region
Specific work showed no cross reaction with Mycobacterium avium subsp. paratuberculosis, a common infection in UK dairy and beef herds.
Sensitivity
The following are the sensitivities found when tested against a defined sample set e.g. sera from animals confirmed to have bTB by M.bovis culture etc. It is therefore stating the sensitivity against that defined population.
M.bovis culture positive animals
Table 2
Diagnostic sensitivity of Enferplex Bovine TB Antibody Test at the high sensitivity and high specificity settings in samples from all M.bovis culture positive from the UK and Ireland| Test method under evaluation | Country | High Sensitivity setting | High Specificity setting | |
|---|---|---|---|---|
| Diagnostic sensitivity (Positive by M.bovis culture) | UK, IE Boosted | N DSn Cl | 208 94.2% 91.1-97.4 | 208 94.2% 91.1-97.4 |
Animals positive for bTB by the presence of VL in UK
Table 3
Relative Diagnostic sensitivity of the Enferplex Bovine TB Antibody test at the High Sensitivity and High Specificity settings using sera from animals positive for bTB by the presence of VL in UK.| Comparative Reference Test | Country | High Sensitivity setting | High specificity setting | |
|---|---|---|---|---|
VL Positive | UK Boosted | N DSn Cl | 309 94.5% 92.0-98.6 | 309 93.8% 91.2-96.5 |
Animals positive to the SICCT from the UK and Ireland
Table 4
Diagnostic sensitivity of the Enferplex Bovine TB Antibody Test at the high sensitivity and high specificity settings in TT positive animals from the UK and Ireland.| Test method under evaluation | Country | Target species - cattle High Sensitivity | Target species - cattle High Specificity | |
|---|---|---|---|---|
| Diagnostic sensitivity (vs TT) | UK, IE Boosted | N DSn Cl | 2076 92.6% 91.5-93.8 | 2076 89.6% 88.2-90.9 |
Detecting animals missed by SICCT and IFNγ tests
The diagnostic data for serum that shows that the test can detect M. bovis infected animals not detected by SICCT or IFNγ are shown in Tables 5 and 6.
Table 5
Relative Diagnostic sensitivity of the Enferplex Bovine TB Antibody Test using sera from TT negative, lesion positive animals as a positive reference standard| Test method under evaluation | Country | Target species - cattle High Sensitivity | Target species - cattle High Specificity | |
|---|---|---|---|---|
| Diagnostic sensitivity (TT negative, Bovine TB lesion positive) | UK, IE Boosted | N DSn Cl | 137 88.3% 82.9-93.7 | 137 82.5 76.1 - 88.8% |
Table 6
Diagnostic sensitivity of the Enferplex Bovine TB Antibody Test using IFNγ negative, Bovine TB lesion positive animals as a positive reference standard| Test method under evaluation | Country | Target species - cattle High Sensitivity | Target species - cattle High Specificity | |
|---|---|---|---|---|
| Diagnostic sensitivity (IFNy negative, Bovine TB lesion positive) | IE Boosted | N DSn Cl | 57 82.5% 72.6-92.3 | 57 75.4% 64.3-86.6 |
The data thus indicates that the Enferplex Bovine TB Antibody Test can be used to detect M. bovis infected animals not detected by SICCT or IFNγ.
Relationship between Number of Antigens recognised and the Presence of VL in animals seropositive by Enferplex Bovine TB Antibody Test
As with Johnes disease, it is well accepted that in bovine TB, as disease progresses, then the production of antibody increases and the strength of the cell mediated immune response wanes. Consequently we have analysed the correlation between antibodies, specifically the number of bTB antigens recognised by antibody-positive sera and the presence of VL at post mortem. In total, 2056 SICCT positive UK and Irish animals were tested in Enferplex Bovine TB Antibody Test at the high sensitivity setting.
The results were analysed, by animals being classified as to how many antigens they recognised, e.g. 2 or more, 3 or more, etc., and this was correlated with the percentage with VL and as a percentage of the total VL animals in the population. The results showed that just under 90% of all the VL detected were in animals that had 5 or more antigens recognised by the Enferplex Bovine TB Antibody Test.
This shows that the Enferplex Bovine TB antibody test, as with the MAP serological tests, can aid in the identification of epidemiologically important bTB positive animals as those with lesions tend to be those which are excreting bacteria and are therefore infectious, as has been suggested by others1
1 Casal et al Vet Microbiol. 2014 Jun 4;170(3-4):342-51