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Leprosy: A Broad Overview as of 2023

Written by Leeon Maher, Peer Reviewed by Xiaochen Liu, Edited by Courtney Coleman


Leprosy, also known as Hansen's disease, is a chronic infectious disease primarily affecting the skin and nerves. It is caused by the bacterium Mycobacterium leprae and has been a health concern for centuries.

Causes and Transmission:

The exact mode of transmission of the disease is not fully understood, but many researchers believe it to be spread through respiratory droplets when an infected person coughs or sneezes. Additionally, animals, such as armadillos, are natural carriers of bacteria and have been known to transmit the disease to humans, in rare cases. Although leprosy can affect individuals of all ages, it is more commonly found in people between 10-14 years old. (1)

The risk factors for contracting leprosy include poor living conditions, inadequate access to healthcare, malnutrition, and a weakened immune system. While the disease is highly contagious, only some people exposed to the bacteria will develop the disease. According to the World Health Organization (WHO), about 95% of people are naturally immune to the disease; however, those who develop the disease may experience a range of symptoms, from mild skin lesions to severe nerve damage. (2)


Leprosy is a slow-progressing disease, and it can take up to 20 years for symptoms to appear after infection (1). There are two types of leprosy: tuberculoid and lepromatous. Tuberculoid leprosy is milder, whereas lepromatous leprosy is more severe (3).

Symptoms of tuberculoid leprosy usually include a small number of pale-colored skin patches with well-defined edges (1). These patches may be numb to the touch due to nerve damage (3). Tuberculoid leprosy may also cause nerve damage, leading to muscle weakness or paralysis in the affected area (4).

Lepromatous leprosy, on the other hand, can cause widespread skin lesions that may appear darker than the person's natural skin color. The lesions usually appear on the face, ears, and buttocks (1). The disease can also cause lumps on the face and ears, dry and scaly skin, and nerve damage, leading to muscle weakness or paralysis (3).

Both types of leprosy can cause damage to the nerves, resulting in a loss of sensation in the fingers and toes, and a lack of sweat or oil gland function, leading to dry and cracked skin (4). In advanced cases, leprosy can also cause blindness, disfigurement of the face, and a loss of fingers and toes (1).


Leprosy is often diagnosed through physical examinations, especially if the patient has cutaneous manifestations, such as hypopigmented or reddish plaques, nodules, or ulcers. Moreover, physicians may conduct skin smears and biopsy samples to identify acid-fast bacilli (AFB) and observe nerve damage. Nerve damage is crucial in the diagnosis of leprosy. According to the World Health Organization (WHO), clinicians should use a combination of clinical, histopathological, bacteriological, and diagnostic tests to diagnose leprosy accurately (1).


Currently, the treatment for leprosy is multi-drug therapy (MDT), provided free of charge by the WHO. MDT is highly effective in curing leprosy, with most patients responding well to treatment within the first few weeks; however, MDT cannot reverse the nerve damage that has already occurred, which can lead to permanent disabilities (1). Thus, early diagnosis and treatment are crucial in preventing long-term complications. In addition to providing treatment, taking preventive measures to control the spread of leprosy is essential.

Preventive measures include early diagnosis and prompt treatment of leprosy patients, screening of high-risk populations, such as family members and close contacts of leprosy patients, and immunization with the Bacille Calmette-Guérin (BCG) vaccine. The BCG vaccine is not a specific leprosy vaccine, but it has shown a reduction in leprosy incidence in some populations (1).

Current Global Status:

Although leprosy is no longer a public health problem in most countries, it remains a concern in some parts of the world. According to the World Health Organization (WHO), in 2020, there were 146,994 new cases of leprosy reported globally. India had the highest number of new cases (57.5%), followed by Brazil (13.3%) and Indonesia (8.4%). These three countries accounted for 79.2% of the world's new leprosy cases (5). While the prevalence of the disease is declining, the stigma associated with leprosy remains a significant problem. As a result, people affected by leprosy may face discrimination and exclusion from society. Therefore, several organizations, including the WHO and the International Federation of Anti-Leprosy Associations (ILEP), are working to raise awareness for the disease and eliminate its stigma (6).

The figures below show more data as of 2021. The colors of each country represent the number of leprosy cases reported that year. The pie chart illustrates the proportions of these cases globally (7).


In conclusion, leprosy is a debilitating infectious disease caused by Mycobacterium leprae. It mainly affects the skin and nerves, leading to disfigurement and disabilities. Despite being curable, leprosy remains a significant health concern, particularly in low-income countries, where stigma, lack of awareness, and inadequate healthcare systems hinder prevention and control efforts.; however, with early diagnosis, prompt treatment, and preventive measures, leprosy can be effectively managed and eventually eradicated.


Works Cited

(1) World Health Organization. "Leprosy." World Health Organization, 2022,

(2) World Health Organization. "Leprosy Fact Sheet." World Health Organization, 2020,

(3) Mayo Clinic. "Leprosy." Mayo Foundation for Medical Education and Research, 2021, 0375075.

(4) National Institute of Allergy and Infectious Diseases. "Hansen's Disease (Leprosy)." U.S. Department of Health and Human Services, 2021,

(5) "Global Leprosy Update, 2021: Moving towards a leprosy-free world." Weekly Epidemiological Record, vol. 96, no. 35, 2021, pp. 469-488, 21-vol-96-no-35-2021.

(6) World Health Organization. "Leprosy - An Overview." World Health Organization, 2021,

(7) “Number of New Leprosy Cases: 2021.” World Health Organization, World Health Organization, 2021,


This post is not a substitute for professional advice. If you believe that you may be experiencing a medical emergency, please contact your primary care physician, or go to the nearest Emergency Room. Results from ongoing research is constantly evolving. This post contains information that was last updated on April 13,2023.


Leeon Maher is currently a Molecular and Cell Biology major undergraduate at UC Berkeley.

Xiaochen Liu is a 5th year Ph.D. student in Epidemiology focusing on the genomic risk factorin Alcoholic-associated Hepatitis at UC Irvine.

Courtney Coleman is a master's degree candidate in biology at Harvard and Co-President of Students vs Pandemics.

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