Leprosy (Hansen's disease)

Causes, transmission and clinical features

The bacterium is transmitted mainly through prolonged close contact, probably via respiratory droplets, although the precise mechanisms are not as efficient as for many respiratory infections. Many people (often cited around 95%) have natural resistance and never develop disease after exposure. The incubation period can be very long — commonly several years — so symptoms may appear long after infection.

Typical early signs include pale or reddish skin patches with reduced sensation, numbness, and nerve enlargement. If untreated, nerve damage can lead to muscle weakness, clawing of the hands or feet, ulcers, and deformities. Leprosy is not usually fatal; disability arises from nerve injury and secondary infections.

Diagnosis and classification

Diagnosis is clinical, supported by skin smears, biopsies and nerve assessments. Cases are often categorized for treatment purposes as paucibacillary (few bacteria) or multibacillary (many bacteria) depending on clinical findings and tests. This classification helps determine the duration and combination of antibiotic therapy.

Treatment, prevention and public health

Effective treatment is available: World Health Organization–recommended multi‑drug therapy (MDT) combines antibiotics that reliably cure the infection and prevent transmission. Early diagnosis and prompt treatment dramatically reduce the risk of permanent nerve damage. Some countries use BCG vaccination and contact surveillance as adjunct public‑health measures. Antibiotics widely used for other infections may also reduce undetected transmission in some settings; however, targeted MDT remains the cornerstone of control.

Epidemiology and modern distribution

Leprosy is now uncommon in most high‑income countries but persists in parts of Asia, Africa and the Americas. Historically most new cases have been reported from India and other developing nations; ongoing efforts aim to detect and treat cases early to interrupt transmission. Access to treatment and stigma reduction are central to global control strategies. Discussions about global case counts and trends can be found in public health reports and surveillance data.

History, stigma and notable facts

Throughout history leprosy has attracted strong social stigma, often linked to moral judgments and exclusion; in some eras it was viewed as divine punishment or a sign of sin. Leprosaria and legal isolation were common responses. Modern understanding emphasizes medical treatment and social reintegration. A related organism, Mycobacterium lepromatosis, has been identified in some cases, and laboratory propagation of the bacteria is difficult outside special models. For contemporary information on clinical care and policies, see resources linked below.

• Key organisms: Mycobacterium leprae (and related species)
• Named for: Gerhard Armauer Hansen
• Geography: Concentrated in parts of Asia, Africa and Latin America, including India
• Treatment: Effective multidrug regimens available — see drug guidance and general antibiotic information
• Social context: Historically associated with punishment and moral stigma

For summaries, clinical guidelines and public‑health advice consult authoritative health organizations and specialist literature using the links above as starting points.