Leprosy is a chronic infectious disease, caused by the Mycobacterium leprae bacterium. It should be noted that, since 1940, leprosy has been fully curable, this being when antibiotics were discovered. Though this treatment cannot kill the bacteria, it is able to considerably slow down the disease progression, and eventually cure the disease if initiated early. Leprosy causes cutaneous and nerve lesions that can affect the skin, mucous membranes, and peripheral nerves. It is only slightly contagious.