Tuberculosis in the wild boar: Frequentist and Bayesian estimations of diagnostic test parameters when Mycobacterium bovis is present in wild boars but at low prevalence

The Eurasian wild boar (Sus scrofa) is increasingly considered as a relevant actor in the epidemiology of animal tuberculosis (TB). Therefore, monitoring TB in this species is key when establishing comprehensive control schemes for this disease still present in Europe. No data are available on direct and indirect TB diagnostic methods in wild boars in epidemiological contexts where TB is endemic in cattle and detected in wild boars at low prevalence. We aimed to estimate and compare sensitivity and specificity values for bacterial culture, PCR and three commercial ELISAs, i.e. the TB ELISA-VK (using the bPPD antigen), INgezim TB Porcine and IDEXX M. bovis Ab Test (both using the MPB83 and MPB70 antigens), under field conditions in France. We used frequentist methods, with bacteriology as the gold standard, and a Bayesian formulation of the latent class analysis (LCA), without using a gold standard. Submandibular lymph nodes and sera from 495 wild boars hunter-harvested in three endemic areas (Aquitaine region, Cote d'Or region, and Corsica region) were collected between 2014 and 2016. Only eight individuals were positive for M. bovis by bacteriology (1.61%; CI95% 0.70-3.51%). The LCA method provided high specificities (99.2%; CI95% 98.2-99.8% for INgezim TB Porcine and 99.7%; CI95% 98.8-100% for IDEXX M. bovis Ab Test) and sensitivities (78.5%; CI95% 65.1-88.8% for INgezim TB Porcine and 83.9%; CI95% 58.9-97.2% for IDEXX M. bovis Ab Test) for both ELISAs using the MPB83 and MPB70 antigens. Bacterial culture showed limited sensitivity (42.8%; CI95% 19.0-70.6%), estimated as the probability of a positive result in an animal exposed to M. bovis. PCR and ELISA using the bPPD antigens demonstrated high specificities, and sensitivities intermediates between culture and the ELISAs using the MPB83 and MPB70 antigens. These results suggest that ELISA tests using the MPB83 and MPB70 antigens are useful to detect and monitor TB exposure of wild boar populations in field conditions in France.