Mycobacterium leprae are the bacteria that cause leprosy, a skin disease. Leprosy has been around for a very long time; it was a common ailment in the bible.It is characterized by skin sores and nerve damage, with a tendency to get progressively worse without treatment. Some symptoms of leprosy include lesions on the skin, numbness in the extremities, and muscle weakness.eprosy has been around for a very long time; it was a common ailment in the bible. It is characterized by skin sores and nerve damage, with a tendency to get progressively worse without treatment. Some symptoms of leprosy include lesions on the skin, numbness in the extremities, and muscle weakness.