Mycobacterium leprae in the context of "Ziehl–Neelsen stain"

Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria Mycobacterium leprae or Mycobacterium lepromatosis. Infection can lead to damage of the nerves, respiratory tract, skin, and eyes. This nerve damage may result in the loss of nociception, which can lead to the loss of parts of a person's extremities from repeated injuries or infection through unnoticed wounds. An infected person may also experience muscle weakness and loss of eyesight. Leprosy symptoms may begin within one year or take 20 years or more.

Leprosy is spread between people, although extensive contact is necessary. Leprosy has a low pathogenicity, and 95% of people who contract or who are exposed to M. leprae do not develop the disease. Spread is likely through a cough or contact with fluid from the nose of a person infected by leprosy. Genetic factors and baseline immune function play a role in how easily a person catches the disease. Leprosy is not spread during pregnancy to the unborn child or through sexual contact. Leprosy occurs more commonly among people living in poverty. There are two main types of the disease—paucibacillary and multibacillary, which 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 skin patches. The diagnosis is confirmed by finding acid-fast bacilli in a biopsy of the skin.

Mycobacterium lepromatosis is an aerobic, acid-fast bacillus (AFB), and the second known causative agent of Hansen's disease (leprosy). It was discovered in 2008. Analysis of the 16S rRNA gene confirms that the species is distinct from Mycobacterium leprae.

Mycobacteriaceae is a family of bacteria in the phylum Actinomycetota. Its name is derived from the Mycobacterium genus, which includes pathogens known to cause serious diseases in mammals, including tuberculosis (M. tuberculosis) and leprosy (M. leprae) in humans. The Greek prefix myco- means 'fungus', alluding to the mold-like appearance of these organisms on agar plates.

A leper colony, also known by many other names, is an isolated community for the quarantining and treatment of lepers, people suffering from leprosy.

M. leprae, the bacterium responsible for leprosy, is believed to have spread from East Africa through the Near East, Europe, and Asia by the 5th century before reaching the rest of the world more recently. Historically, leprosy was believed to be extremely contagious and divinely ordained, leading to enormous stigma against its sufferers. Other severe skin diseases were frequently conflated with leprosy and all such sufferers were kept away from the general public, although some religious orders provided medical care and treatment. Recent research has shown M. leprae has maintained a similarly virulent genome over at least the last thousand years, leaving it unclear which precise factors led to leprosy's near elimination in Europe by 1700. A growing number of cases following the first wave of European colonization, however, led to increased attention towards leprosy during the New Imperialism of the late 19th century. Following G. A. Hansen's discovery of the role of M. leprae in the disease, the First International Leprosy Conference held in Berlin in 1897 renewed interest and investment in the isolation of lepers throughout the European colonial empires.