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

Background In England, transmission of Mycobacterium bovis between cattle and certain species of free-roaming, wild deer has been implicated in some endemic bovine tuberculosis (bTB) regions. However, there are still data and knowledge gaps regarding the role of deer in the epidemiology of this disease. This paper presents the results of a serological survey to estimate the prevalence of M. bovis infection in a large wild deer population in the bTB high-risk area of southwest England. Methods Blood samples were collected postmortem over a 12-month period from wild deer shot during annual population controls in the Exmoor area and tested for M. bovis serum antibodies. True seroprevalence of M. bovis infection in the study population was estimated by accounting for the imperfect diagnostic accuracy of the IDEXX test used. Results Overall, 432 individual animal samples were tested, predominantly from red deer (80.3%). Sixty-nine (16.0%) were seropositive, with the estimated true seroprevalence being 27.4% (95% confidence interval 19.9%-36.3%). Prevalence did not appear to differ between sexes or species. Few positive samples were observed in the youngest animals. Limitations As convenience sampling of deer carcases was used, a degree of bias in the results cannot be excluded. Estimation of true seroprevalence was affected by the imperfect performance of the IDEXX test in deer. Conclusions This study provides valuable insight into M. bovis seroprevalence in this wild deer population, which is at the upper end of prevalence estimates reported in deer worldwide. Our results should be interpreted alongside other relevant information, including species-specific ecology, epidemiology and disease pathology, to inform potential transmission risks between cattle and wild deer.