- Leprosy is a chronic infectious disease caused by *Mycobacterium leprae*, primarily transmitted via prolonged close contact with an untreated infected individual.
- The bacillus spreads through respiratory droplets, making close household or social contact the main risk factor for acquiring the disease.
- Other factors like consumption of unpasteurized milk, living at high altitude, or tobacco use do not contribute to transmission.
- Early identification of contacts is crucial for control and prevention.

Reference: Davidson’s Principles and Practice of Medicine, 24th Edition, Chapter: Infections of the Nervous System, Page 708.