A Bayesian analysis of a Test and Vaccinate or Remove study to control bovine tuberculosis in badgers (Meles meles)

Abstract

A novel five year Test and Vaccinate or Remove (TVR) wildlife research intervention project in badgers (Meles meles) commenced in 2014 in a 100km2 area of Northern Ireland. It aimed to increase the evidence base around badgers and bovine TB and help create well-informed and evidence-based strategies to address the issue of cattle-to-cattle spread and spread between cattle and badgers. It involved real-time trap-side testing of captured badgers and vaccinating those that tested negative for bTB (BadgerBCG–BCG Danish 1331) and removal of those that tested bTB positive using the Dual-Path Platform VetTB test (DPP) for cervids (Chembio Diagnostic Systems, Medford, NY USA). Four diagnostic tests were utilised within the study interferon gamma release assay (IGRA), culture (clinical samples and post mortem), DPP using both whole blood and DPP using serum. BCG Sofia (SL222) was used in the final two years because of supply issues with BadgerBCG. Objectives for this study were to evaluate the performance of the DPP in field conditions and whether any trend was apparent in infection prevalence over the study period. A Bayesian latent class model of diagnostic test evaluation in the absence of a gold standard was applied to the data. Temporal variation in the sensitivity of DPP and interferon gamma release assay (IGRA) due to the impact of control measures was investigated using logistic regression and individual variability was assessed. Bayesian latent class analysis estimated DPP with serum to have a sensitivity of 0.58 (95% CrI: 0.40–0.76) and specificity of 0.97 (95% CrI: 0.95–0.98). The DPP with whole blood showed a higher sensitivity (0.69 (95% CrI: 0.48–0.88)) but similar specificity (0.98 (95% Crl: 0.96–0.99)). The change from BCG Danish to BCG Sofia significantly impacted on DPP serum test characteristics. In addition, there was weak evidence of increasing sensitivity of IGRA over time and differences in DPP test sensitivity between adults and cubs. An exponential decline model was an appropriate representation of the infection prevalence over the 5 years, with a starting prevalence of 14% (95% CrI: 0.10–0.20), and an annual reduction of 39.1% (95% CrI: 26.5–50.9). The resulting estimate of infection prevalence in year 5 of the study was 1.9% (95% CrI: 0.8–3.8). These results provide field evidence of a statistically significant reduction in badger TB prevalence supporting a TVR approach to badger intervention. They give confidence in the reliability and reproducibility in the DPP Whole Blood as a real time trap-side diagnostic test for badgers, and describe the effect of vaccination and reduced infection prevalence on test characteristics.

Test and vaccinate or remove: Methodology and preliminary results from a badger intervention research project

“…This issue is dealt with in a parallel paper. 33 Any badger intervention using cage trapping is resource intensive given the staff requirement, and this was the case in this study. 44 Trapping activities broadly equated to 3 weeks per field person per km 2 .…”

“…However, the apparent prevalence indicated, taking no account of the DPP test characteristics, would result in misclassification of a proportion of tested badgers as either false positives or false negatives. This issue is dealt with in a parallel paper 33 …”

“…During 6 weeks of year 1 (2014), DPP tests were not available to carry out field testing of badger samples, and shortages in their supply were also experienced throughout the study. However, serum samples from each badger were stored for retrospective DPP testing during the entire project, which were used (along with other diagnostic tests) to estimate the DDP test characteristics and annual badger M. bovis prevalence 33 . For the rest of year 1, DPP testing was carried out on a daily batch basis within a nearby field laboratory.…”

“…However, serum samples from each badger were stored for retrospective DPP testing during the entire project, which were used (along with other diagnostic tests) to estimate the DDP test characteristics and annual badger M. bovis prevalence. 33 For the rest of year 1, DPP testing was carried out on a daily batch basis within a nearby field laboratory. The sample was declared positive when a visible pink/purple line was observed at line 1 and/or line 2 within the test area of the assay (Figure 2).…”

Genomic epidemiology ofMycobacterium bovisinfection in sympatric badger and cattle populations in Northern Ireland

“…The study was conducted in a small 100 km 2 area of Northern Ireland (Figure 1A), using data from a recently completed (2014-2018) wildlife intervention. The ‘test and vaccinate or remove’ (TVR) selective culling protocol applied to the local badger population (Arnold et al 2021; Menzies et al 2021) provided an important opportunity to systematically sample sympatric cattle and badger populations for M. bovis , and to apply WGS, phylogenetic and population genetic methods to attempt to determine the roles that both cattle and badgers play in the local disease dynamics.…”