- The correct answer is Mycobacterium leprae because it is the acid-fast bacillus specifically responsible for causing Hansen's disease (leprosy).

- It primarily affects the skin and peripheral nerves, leading to characteristic symptoms.
- Unlike Mycobacterium tuberculosis, which causes tuberculosis, M. leprae has a unique predilection for nerve tissue.
- Other options like Nocardia asteroides and Corynebacterium diphtheriae cause different diseases and are not responsible for Hansen's disease.

Reference: Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, Volume 2, Chapter 123