A woman leper at Rawalpindi Leprosy Center in Pakistan. Mycobacterium leprae is the causative agent of leprosy. It is chronic disease, and progressive if left untreated. It is a disease of the peripheral nerves, and upper respiratory tract. The most prominent symptom are skin lesions. Contrary to myth, leprosy is not highly contagious. The historical practice of establishing leper colonies to isolate the victims has diminished greatly, as we have come to understand the true nature of the affliction.