Diagnosis: Mycobacterium bovis
• The discriminatory phenotypic methods that can distinguish Mycobacterium tuberculosis from M. bovis are niacin, nitrate, thiophene-2-carboxylic acid hydrazide (TCH), susceptibility or resistance to pyrazinamide (PZA), and colonial morphology (see the table).
• Molecular methods for identifying M. tuberculosis and M. bovis provide rapid results. These include DNA sequence analysis of direct repeat regions or single nucleotide polymorphisms. In addition, the presence of absence of particular deletions can be discriminatory. Intrinsic resistance to PZA can also be detected using DNA sequence analysis.
• M. bovis is the etiologic agent for tuberculosis in warm-blood animals, mainly cattle. It can be transmitted from animal-to-human and person-to-person through inhalation of infectious droplet nuclei. Patients most susceptible to M. bovis infection include those born outside the United States, of Hispanic ethnicity, younger than 15 years, and with HIV infection.
• Abdominal tuberculosis is more often caused by M. bovis than M. tuberculosis, and is transmitted to humans through the ingestion of unpasteurized, contaminated dairy products, such as Mexican cheese. M. bovis is prevalent in dairy herds in some parts of Mexico, whereas it has been nearly eradicated in U.S. and Canadian cattle herds.
• Distinguishing between M. tuberculosis and M. bovis is important for determining epidemiologic profiles to track the incidence and transmission of M. bovis. In addition, treatment of M. bovis infection is the same as that for M. tuberculosis, except for PZA in M. bovis due to intrinsic resistance.
