DIAGNOSIS OF TUBERCULOSIS DUE TO MYCOBACTERIUM-BOVIS IN NEW-ZEALAND RED DEER NECRVUS-ELAPHUS) USING A COMPOSITE BLOOD-TEST AND ANTIBODY-ASSAYS

A blood test for tuberculosis in deer was developed as an ancillary te st to clarify the status of skin test-positive deer, with non-specific sensitisation following exposure to saprophytic mycobacteria. The blo od test incorporates the measurement of the relative humoral and cellu lar immunological responses to Mycobacterium bovis and M. avium antige ns to provide a composite test with high levels of sensitivity (>95%) and specificity (>98%). The specificity of the test has allowed it to be used in parallel with the skin test to salvage thousands of tubercu losis-free deer with non-specific skin test-positive reactions, while its high sensitivity has consistently identified M. bovis-specific rea ctivity in tuberculous skin test-positive animals. The rules for estab lishing the diagnostic parameters for the cellular and antibody assays were developed by retrospective analysis of the laboratory results us ing blood samples from many thousand tuberculous or disease-free deer. The sensitivity of the blood test was tested in this study using 150 animals with tuberculosis diagnosed by the isolation of M. bovis. It h ad sensitivity values of 95.7-95.9% in herds with a low (<2.0%) or a h igh (>30.0%) incidence of tuberculosis. The test had a specificity of 98.0% when tested on 218 disease-free animals, 118 of which were skin test-positive. An antibody test was developed to diagnose M. bovis in skin test-negative ''anergic'' deer from tuberculosis infected herds. When this test was used with deer blood taken 10 days after reading th e skin test, it had a sensitivity of 85.3% for 102 M. bovis-positive d eer. When used in combination with skin test, the antibody test comple mented the skin test to raise the sensitivity of the combined tests to 95.0%, when antibody-positive or skin test-positive tests were used t o diagnose tuberculosis. The specificity of the antibody test was 100% when used to evaluate 218 disease-free deer from non-infected herds.