The etiologic agent of Hansen disease is which Mycobacterium?

• A. Mycobacterium bovis
• B. Mycobacterium fortuitum
• C. Mycobacterium leprae
• D. Mycobacterium tuberculosis

Answer: (C)

Hansen disease (leprosy) is caused by Mycobacterium leprae. This slow-growing, acid-fast bacillus preferentially infects cooler parts of the body, leading to skin lesions and peripheral nerve damage that characterizes the disease. It cannot be easily cultured in ordinary artificial media, which is a notable feature of M. leprae. The other organisms listed cause different infections: Mycobacterium tuberculosis causes tuberculosis, Mycobacterium bovis can also cause TB-like disease, and Mycobacterium fortuitum is a rapid-growing non-tuberculous mycobacterium associated with skin and soft tissue infections. Therefore, the causative agent of Hansen disease is Mycobacterium leprae.