Estimating the seroprevalence of tuberculosis (Mycobacterium bovis) infection in a wild deer population in southwest England

Bovine tuberculosis (bTB) is a major disease of cattle that is subject to an eradication strategy in England. To inform control policies and manage the epidemic, all potential sources of infection for cattle must be identified and understood. The causative agent of bTB, Mycobacterium bovis, has a wide host range including several deer species. While transmission between cattle and deer has been implicated in some localised endemic regions, the role of deer in the epidemiology of bTB in England is poorly understood. This paper presents the results of a serological survey to estimate the prevalence of M. bovis in a large wild deer population in the High bTB Risk Area of southwest England. Blood samples were collected post-mortem over a 12-month period from wild deer during annual deer management controls in the Exmoor area and tested for M. bovis serum antibodies. Overall, 432 samples were collected and 69 (16.0%) were seropositive. The true seroprevalence in our sample was estimated to be 29.2% (95% CrI 21.1-38.6%), using Bayesian Latent Class Analysis to account for imperfect diagnostic test accuracy. Prevalence did not appear to differ between sexes nor between species, although the sample was predominantly red deer. The lowest prevalence was observed in animals aged under 1-year. Whilst these results provide valuable insights into M. bovis seroprevalence in this wild deer population, they should be interpreted alongside other relevant information such as ecology, species-specific epidemiology and disease pathology, deer density and cattle management to inform potential transmission risks between cattle and wild deer.