Leprosy, also known as Hansen's disease (HD), a chronic infectious disease caused by a Mycobacterium (Mycobacterium leprae) affecting especially the skin and marginal nerves. It is characterized by the formation of nodules or macules that enlarge and spread with loss of sensation and eventually paralysis, wasting of muscle, and production of deformities called also Hansen's disease. This infection is caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis . It is primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract, skin lesions are the primary external sign . If left untreated, leprosy can be progressive, causing permanent damage to the skin, nerves, limbs and eyes.