BOVINE TUBERCULOSIS IN A BACTRIAN CAMEL HERD: CLINICAL, THERAPEUTIC, AND PATHOLOGIC FINDINGS

Tuberculosis, caused by Mycobacterium bovis, was diagnosed in two of 19 Bactrian camels (Camelus bactrianus) in an established herd, based on pathologic findings and correlative postmortem cultures. From 1974 to 1984, tuberculosis was a concern because of positive reactions to intradermal tuberculins in many camels in the herd, but the disease was not diagnosed in 12 postmortem examinations. Following the diagnosis of tuberculosis in a 3-yr-old male camel, the remaining camels were tested with intradermal tuberculins with inconclusive results. An ELISA test indicated antibodies to M. kansasii, M. scrofulaceum, and M. bovis in all of the camels with positive intradermal tests. Of 13 camels tested by fused rocket immunoelectrophoresis, all had antibodies to antigens of four other atypical mycobacteria. These immunologie tests suggest that camels may frequently harbor different mycobacteria, thus explaining why false-positive tuberculin reactions are relatively common. Following a second confirmed case of M bovis in an aged camel that was euthanized, the remaining 17 camels were treated with isoniazid (INH), which was incorporated into pelleted feed (2.4 mg/kg). Within 6 wk, three young camels died with purpuric hemorrhages and agranulocytosis attributed to INH-induced bone marrow toxicity. Attempts to minimize the INH toxicity with supplemental pyridoxine (vitamin B6) failed, and three more camels died from bone marrow suppression-associated anemia and severe leukopenia. The remainder of the herd was euthanized because of the lack of reliable antemortem diagnostic tests for tuberculosis and the failure of the treatment with INH. Of 19 camels necropsied, M. avium was cultured from bronchial lymph nodes of one, and another had histologie lesions of resolving tuberculosis, but no acid-fast bacteria (AFB) were observed or isolated. The lesions seen in camels with tuberculosis differ from those of domestic ruminants in that grossly they appear sarcomatoid and histologically they form solid pyogranulomas with few giant cells and AFB are rarely evident.