Leprosy

Leprosy, also known as Hansen disease, is a chronic infectious disease caused mainly by the bacterium Mycobacterium leprae (with rare cases caused by Mycobacterium lepromatosis). The disease is characterized by slow progression and primarily affects the skin, peripheral nerves, mucosa of the upper respiratory tract, and eyes. As a neglected tropical disease, leprosy continues to pose public health challenges in resource-limited settings despite being curable.

The disease manifests commonly through skin lesions and peripheral nerve involvement. Skin lesions typically present with different pigmentation than surrounding skin (hypopigmented or reddish) and may appear flat, raised, or nodular, either singly or in multiples, with definite loss of sensation. Nerve damage can result in loss of nociception, potentially leading to loss of extremities from repeated injuries or infections through unnoticed wounds, as well as muscle weakness and potential loss of eyesight. The incubation period is highly variable, with symptoms appearing within one year or taking as long as 20 years or more to develop. The disease course is highly variable among individuals depending on their immune response.

Leprosy is a neglected tropical disease that still occurs in more than 120 countries, with approximately 200,000 new cases reported annually. Global elimination as a public health problem (defined as prevalence of less than 1 per 10,000 population) was achieved in the year 2000 and in most countries by 2010. As of 2024 data, Brazil, India, and Indonesia continue to report more than 10,000 new cases each, while twelve additional countries (Bangladesh, Democratic Republic of the Congo, Ethiopia, Madagascar, Mozambique, Myanmar, Nepal, Nigeria, Philippines, Somalia, Sri Lanka, and United Republic of Tanzania) each reported between 1,000 and 10,000 new cases. Fifty-five countries reported zero cases, and 117 countries reported fewer than 1,000 new cases.

The disease is believed to be transmitted through inhalation of droplets from the nose and mouth of an untreated case of leprosy, following prolonged, close contact with the infected individual. The disease does not spread through casual contact such as shaking hands, hugging, sharing meals, or sitting next to each other. Importantly, the patient stops transmitting the disease upon initiation of treatment. The majority (approximately 95%) of people who are exposed to M. leprae do not develop leprosy, indicating low pathogenicity and the importance of host immune factors in disease development.

The greatest risk factor for developing leprosy is contact with another person infected with leprosy; people who are exposed to a person with leprosy are five to eight times more likely to develop the disease than the general population. Leprosy occurs more commonly among those living in poverty, and conditions that reduce immune function such as malnutrition may increase the risk of developing symptoms after exposure. However, not all people infected with M. leprae develop symptoms, and genetic factors play a role in susceptibility. Infection with HIV does not appear to increase the risk of developing leprosy.

Case detection and treatment with multidrug therapy alone have proven insufficient to interrupt transmission. The World Health Organization recommends contact screening of household, neighborhood, and social contacts, accompanied by administration of a single dose of rifampicin as post-exposure prophylaxis. Early diagnosis and prompt treatment with multidrug therapy (dapsone, rifampicin, and clofazimine) can prevent disabilities and halt disease progression.

Leprosy diagnosis is primarily clinical, based on the identification of at least one cardinal sign: definite loss of sensation in a pale (hypopigmented) or reddish skin patch; thickened or enlarged peripheral nerve with loss of sensation and/or weakness of muscles supplied by that nerve; or microscopic detection of bacilli in a slit-skin smear. Cases are classified as paucibacillary (five or fewer skin patches) or multibacillary (more than five skin patches) for treatment purposes. Laboratory-based services may be required for cases that are difficult to diagnose. Surveillance should account for the long incubation period when assessing transmission patterns and case clusters.

1. 1 WHO Health Topics. Leprosy (Hansen disease).
2. 2 WHO Fact Sheet. Leprosy.
3. 3 WHO Q&A. News.
4. 4 Wikidata. leprosy.
5. 5 Wikipedia. Leprosy - Wikipedia.

ICD-10

A30

ICD-11

1B20

Total cases

11K

Total deaths

15

Peak month

2013-01

Coverage

3 reporting countries · 2000-01-01 → 2026-05-09