Mycobacterium leprae is a bacterium that causes leprosy, also known as "Hansen’s disease", which is a chronic infectious disease that damages the peripheral nerves and targets the skin, eyes, nose, and muscles.Leprosy can occur at all ages from infancy to elderly, but is curable in which treatments can avert disabilities. It was discovered in 1873 by the Norwegian physician Gerhard Armauer Hansen, who was searching for the bacteria in the skin nodules of patients with leprosy. It was the first bacterium to be identified as causing disease in humans.