[Classification and concept of mycobacterial infections]

Mycobacterial infections are consisted of three categories; tuberculosis, nontuberculous mycobacterioses, and leprosy. Tuberculosis is a systemic infectious disease involving respiratory, genitourinary and lymphatic systems caused by Mycobacterium tuberculosis complex (Mycobacterium tuberculosis, M. bovis, M. africanum, and M. microti). Extrapulmonary tuberculosis remains a significant clinical problem because symptoms and signs may be difficult to recognize and to relate to tuberculosis. Miliary tuberculosis is responsible for up to 10% of predominantly extrapulmonary cases. HIV-related miliary tuberculosis is rapidly progressive and almost always fatal without treatment. Nontuberculous mycobacteria (NTM) have been commonly implicated as opportunistic pathogens in patients with underlying disease or immunosuppression including AIDS. M. avium complex (M. avium and M. intracellulare) and M. kansashii are most common causes of nontuberculous mycobacterial diseases in humans. M. leprae is the causative agent of leprosy, an infection of the skin, mucous membranes, and peripheral nerves. This disease is rare in Japan, yet it remains a major problem in some part of the world.