TABLE 2.
Number of animals positive for subclinical paraTB by IFN-γ test and estimated specificity with different antigen stimulations and different interpretation criteria
| Interpretation criterion for paraTB | No. of cows positive (% specificity)
|
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|---|---|---|---|---|---|---|
| 5 noninfected herds (n = 116)
|
10 infected herds (n = 249)
|
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| PPDj | PPDa | PPDj + PPDaa | PPDj | PPDa | PPDj + PPDa | |
| Fixed difference from no-antigen stimulation | ||||||
| 1. PPDxb-PBS > 0.05 | 23 (80)c | 53 (54) | 20 | 169 | 193 | 164 |
| 2. PPDx-PBS > 0.1 | 12 (90)c | 36 (69) | 12 | 137 | 163 | 135 |
| 3. Estimated difference from no-antigen stimulation | ||||||
| PPDj-PBS > 0.254 | 2 (98) | 83 | ||||
| PPDa-PBS > 0.453 | 6 (95) | 1 | 84 | 74 | ||
| 4. Relative to no-antigen stimulation, 2 and PPDx/PBS > 4 | 7 (95) | 24 (79) | 5 | 114 | 143 | 109 |
| Relative to control antigen | ||||||
| 5. 1 and PPDx > PPDb | 6 (95) | 42 (64) | 4 | 127 | 171 | 124 |
| 6. 2 and PPDx > PPDb | 2 (98) | 27 (77) | 2 | 112 | 149 | 109 |
| 7. 3 and PPDx > PPDb | 1 (99) | 6 (95) | 1 | 75 | 82 | 67 |
| IDEXX | ||||||
| 8. 1 and PPDb/PPDx < 0.71 | 3 (97) | 29 (75) | 2 | 93 | 141 | 90 |
| 9. 2 and PPDb/PPDx < 0.71 | 2 (98) | 22 (81) | 2 | 89 | 127 | 85 |
| 10. 3 and PPDb/PPDx < 0.71 | 1 (99) | 4 (97) | 1 | 64 | 75 | 57 |
a
PPDj + PPDa indicates the number of animals with paraTB-positive results in both PPDj and PPDa tests.
b
PPDx relates to either PPDj or PPDa as a stimulant in whole-blood cultures.
c
An estimate of test specificity for bovine paraTB was calculated as [N −n(pos)]/N × 100, where N is the number of tested animals (N = 116) and n(pos) is the number of (false) test-positive animals.