Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria Mycobacterium leprae or Mycobacterium lepromatosis. Initially, a person who is infected does not have symptoms and typically remains this way for 5 to 20 years. Infection can lead to damage of the nerves, respiratory tract, skin, and eyes. This nerve damage may result in a lack of ability to feel pain, which can lead to the loss of parts of a person's extremities from repeated injuries or infection due to unnoticed wounds. An infected person may also experience weakness and poor eyesight.
Leprosy is spread between people, although extensive contact is necessary. About 95% of people who contact M. Leprea do not develop the disease. Spread is thought to occur through a cough or contact with fluid from the nose of a person infected by leprosy. Leprosy is not spread during pregnancy to the unborn children or through sexual contact. Leprosy occurs more commonly among people living in poverty. Genetic factors and immune function play a role in how easily a person catches the disease. The two main types of disease – paucibacillary and multibacillary – differ in the number of bacteria present. A person with paucibacillary disease has five or fewer poorly pigmented numb skin patches while a person with multibacillary disease has more than five. The diagnosis is confirmed by finding acid-fast bacilli in a biopsy of the skin or by detecting the bacteria's DNA using polymerase chain reaction.
Leprosy is curable with multidrug therapy. Treatment of paucibacillary leprosy is with the medications dapsone, rifampicin, and clofazimine for six months. Treatment for multibacillary leprosy uses the same medications for 12 months. A number of other antibiotics may also be used. These treatments are provided free of charge by the World Health Organization. People with leprosy can live with their families and go to school and work. At the end of 2016, there were 173,000 leprosy cases globally, down from 5.2 million in the 1980s. The number of new cases in 2016 was 216,000. Most new cases occur in 14 countries, with India accounting for more than half. In the past 20 years, 16 million people worldwide have been cured of leprosy. About 200 cases per year are reported in the United States.
Leprosy has affected humanity for thousands of years. The disease takes its name from the Greek word λέπρᾱ (léprā), from λεπῐ́ς (lepís; "scale"), while the term "Hansen's disease" is named after the Norwegian physician Gerhard Armauer Hansen. Leprosy has historically been associated with social stigma, which continues to be a barrier to self-reporting and early treatment. Separating people affected by leprosy by placing them in leper colonies still occurs in some areas of India, China, and Africa. However, most colonies have closed, since leprosy is not very contagious. Some consider the word "leper" offensive, preferring the phrase "person affected with leprosy". Leprosy is classified as a neglected tropical disease. World Leprosy Day was started in 1954 to draw awareness to those affected by leprosy.