Mycobacterium leprae is a slow-growing bacterium that causes leprosy, also known as Hansen's disease. It primarily affects the skin, nerves, and mucous membranes. The bacterium is transmitted through prolonged close contact with an infected person, but it is not highly contagious. Symptoms can take years to appear and may include skin lesions, numbness, and muscle weakness. Leprosy has been known since ancient times and is often associated with social stigma. Early diagnosis and treatment with antibiotics, such as dapsone, can effectively manage the disease and prevent complications. Public health efforts have significantly reduced the prevalence of leprosy worldwide.