This study addressed the need in Great Britain for supplementary blood tests for deer and pig herds under movement restrictions due to confirmed Mycobacterium bovis infection—to enhance the overall sensitivity and reliability of tuberculosis (TB) testing and contribute to an exit strategy for these herds. We evaluated four antibody tests (lateral flow DPP VetTB Assay for Cervids, M. bovis IDEXX ELISA, Enferplex Cervid and Porcine antibody tests and an in-house comparative PPD ELISA) using serum samples from defined cohorts of TB-infected and TB-free deer and pigs. TB-infected deer included two separate cohorts; farmed deer that had received a tuberculin skin test less than 30 days prior, and park deer that had received no prior skin test. In this way, we were able to assess the effect of the skin test anamnestic boost upon antibody test sensitivity. We tested a total of 402 TB-free pigs and 416 TB-free deer, 77 infected farmed deer and 105 infected park deer, and 29 infected pigs (including 2 wild boar). For deer, we found an equivalent high performance of all four tests: specificity range 98.8–99.5% and sensitivity range 76.6–85.7% for skin test-boosted infected deer, and 51.4–58.1% for non-boosted infected deer. These data suggest an overall approximate 25% increase in test sensitivity for infected deer following a skin test boost. For pigs, the tests again had equivalent high specificity of 99–99.5% and a sensitivity range of 62.1–86.2%, with substantial agreement for three of the four tests. Retrospective application of the ELISA tests to individual culled park deer and wild boar that showed no obvious evidence of TB at larder inspection identified a significant seropositivity within wild boar suggestive of low-level M. bovis infection that would otherwise not have been detected. Overall this investigation provided a robust evaluation of four antibody tests, which is essential to generate confidence in test performance before a wider deployment within TB control measures can be considered.

Background: Bovine tuberculosis (bTB) is an infectious disease which causes significant damage to the farming industry and remains a disease of global significance. Although control strategies have focused on a test and cull approach primarily based around specific cell-mediated immune responses, serological assays are increasingly being used as a supplementary test alongside skin testing and interferon-gamma release (IGRA) assays. The UK is moving towards the use of the Bacillus Calmette–Guérin (BCG) vaccination of cattle as an additional targeted control tool against bTB. However, there are concerns over its potential impact on the outcomes of bTB diagnostic tests and other non-TB assays, such as serological tests for Mycobacterium avium subsp. paratuberculosis (MAP). Methods: We investigated the performance of commercially available serology tests designed to detect bTB and MAP using serum samples from BCG-vaccinated animals which were subsequently infected with Mycobacterium bovis (M. bovis). Results: BCG vaccination per se did not significantly impact the specificity of serological diagnostic tests for bTB or Johne’s disease. However, increased numbers of false-positive responses in bTB serology tests were seen in BCG-vaccinated animals 3 weeks following a tuberculin skin test, where up to 23% and 54% of animals gave a positive result in IDEXX and Enferplex tests, respectively. Furthermore, M. bovis infection gave rise to false-positive test results for Johne’s disease, irrespective of the animals’ prior BCG vaccination status. Conclusions: Caution should be taken when assessing results from serology tests for bTB if tuberculin skin testing has occurred shortly before collection of blood from BCG-vaccinated cattle. Furthermore, these results highlight the potential for misdiagnosis of MAP infection when using serology tests in bTB-infected cattle.