Aetiology, pathogenesis and diagnosis of Mycobacterium bovis in deer

Tuberculosis, caused by Mycobacterium bovis, is emerging as the most important disease affecting farmed deer. While the disease is usually found at a low incidence involving lesions in single lymph nodes, it may present as a rapidly spreading, fulminating disease, especially in animals exposed to stress. The unique susceptibility of cervidae to mycobacteria in general has meant that diagnosis of tuberculosis in deer using conventional intradermal tuberculin tests may be unsatisfactory. Tuberculin testing in deer is more technically demanding than in cattle, with the cervical region being the most sensitive area. False positive skin reactions occur widely in non-diseased deer while seriously infected animals may be "anergic" and fail to react (false negative). Comparative cervical tests have been used to improve test specificity but they suffer from reduced levels of sensitivity. A new blood test for tuberculosis (BTB) has been developed specifically for deer. This assay uses a combination of laboratory tests which measure lymphocyte transformation, antibody and inflammation. The composite BTB has a sensitivity of > 95% and a specificity of > 98% for diagnosis of M. bovis in cervidae.