Case of TB in a sheep caused by Mycobacterium bovis with transmission to another sheep and a steer in the same building

An adult sheep housed indoors developed chronic respiratory tract infection that was unresponsive to treatment and resulted in euthanasia. Granulomas were found in multiple organs and lymph nodes, which contained acid-fast bacilli identified in Ziehl-Neelsen stains, and Mycobacterium bovis was cultured from tissues, confirming tuberculosis. Tuberculin skin testing of other animals in the building subsequently identified another sheep as infected, which had been housed with the index case for 46 months, although no visible lesions were seen postmortem. A steer that shared common air space with the sheep in the same building was also identified as test reactor and M bovis was cultured from the retropharyngeal lymph node. Strain typing of the isolates from the index case and the steer revealed the same genotype, suggestive of transmission from sheep to steer. This is the first documented episode of M bovis transmission from sheep to cattle.