Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at January 27, 2016

Leprosy or Hansen's disease is a chronic bacterial infection caused by a slow-growing bacteria called Mycobacterium leprae. The disease has been around since Medieval times and it has long had a social stigma with patients in the past forced to live in colonies due to a mistaken belief that leprosy was highly contagious. While global elimination has been achieved, every year thousands of people are still diagnosed with this now curable infection.


Definition & Facts

Hansen's disease, better known as leprosy, is a chronic bacterial infection that may remain asymptomatic for up to twenty years. The bacillus Mycobacterium leprae, which multiplies very slowly, is responsible for the infection. Eventually, the infection causes the development of granulomas on the skin, eyes, respiratory tract, and nerves. Over time, this reduces the ability to feel pain, and repeated injuries that may go unnoticed.

When left untreated, leprosy can result in permanent damage to the eyes, limbs, skin, and nerves. The disease affects about 200,000 people around the world with about 150 new cases in the U.S. each year. It was once believed to be very contagious and people with leprosy were often ostracized and required to live in colonies. While curable, the social stigma of the infection remains.

Symptoms & Complaints

Hansen's disease progresses very slowly, and it may take anywhere from 2 to 20 years for symptoms to appear. Leprosy mostly causes symptoms of the mucous membranes, nerves, and skin. Early symptoms of Hansen's disease include skin spots that can appear red but may be lighter or darker than surrounding skin. Spots can become numb over time and lose hair. These spots usually appear on the back, arms, and legs at first.

With many people, the only early sign of leprosy is numbness in a single toe or finger. If untreated, this numbness can spread to the hands and feet as muscles paralyze, eventually causing curling of the toes or fingers. As the facial nerves become affected, the patient can lose the blinking reflex.

When the bacteria enters the mucous lining of the nose, it can cause damage and scarring that causes the nose to collapse. Eventually, leprosy can lead to blindness, deformity, loss of sweat gland function, loss of oil gland function, loss of strength in the feet and hands, paralysis of the hands and feet, and a loss of the ability to feel light touch sensations or pain sensations.


Leprosy is caused by the Mycobacterium leprae bacteria that infects the skin and nerves. It was first viewed under a microscope by Dr. Armauer Hansen in 1873. It isn't well understood how leprosy spreads, but it is known to spread mostly through sneezing and coughing. Leprosy is believed to be transmitted from human to human via respiratory droplets. Most people do not catch leprosy unless they are in long-term close contact with an untreated person with leprosy.

About 95% of the world's population has a natural immunity to the bacteria. While infected respiratory droplets are believed to be one way of catching leprosy, more than half of all people who develop the infection have no confirmed contact with an infected person at all. Factors that may affect who can develop leprosy include the extent of exposure to the bacteria, genetics, and environmental factors.

Diagnosis & Tests

People who have suspicious skin sores should visit a doctor to have the sores tested. If a doctor suspects leprosy, a sample of the abnormal skin growth or tissue will be taken and sent to a lab for examination. While a skin biopsy is the most common way to diagnose leprosy, a skin smear test can also be conducted. No bacteria can be detected with either method if the patient has paucibacillary leprosy, the mildest form of the infection. Someone with multibacillary leprosy, the most common form, will get a positive skin smear test.

Skin smears or biopsy material with acid-fast bacilli and a Fite stain or Ziehl-Neelson stain are used to diagnose leprosy. Less commonly used diagnostic tests include nerve biopsies, nasal smears, and blood tests. Once a diagnosis is made, the patient can be diagnosed with paucibacillary or multibacillary leprosy.

Another classification system is the Ridley-Jopling system with five categories describing a patient's presentation. This scale moves from tuberculoid leprosy (in which the person has a resistance to the bacteria) to borderline tuberculoid leprosy, mid-borderline leprosy, borderline lepromatous leprosy, and lepromatous leprosy.

Treatment & Therapy

Leprosy is a very curable infection. When treatment is provided during the early stages, disability can be avoided completely. The World Health Organization (WHO) provides multidrug therapy treatment free of charge to people around the world. Multidrug therapy has cured almost 16 million people of leprosy over the last two decades. In 2000, leprosy was eliminated from the world by dropping the prevalence rate to less than 1 documented case per 10,000 people. While rare today, it is still found in over 100 countries.

Multidrug therapy involves a combination of three antibiotics: dapsone, clofazimine, and rifampin. While people are no longer contagious after they have been on treatment for one week, treatment usually lasts 6 to 12 months or longer. Multidrug therapy causes what is known as the "leprosy reaction," which is the body's response to the dead bacteria. It can take years for all of the dead M. leprae bacteria to clear from the body, and the body may react with swelling and pain in the affected skin and nerves. About half of all people with leprosy have these reactions which do not mean the treatment is not working.

Prevention & Prophylaxis

Leprosy has been mostly eradicated, but it is still found in many areas of Africa and Asia as well as the United States. In the Gulf Coast region of the United States and parts of Mexico, leprosy can be spread by nine-banded armadillos. Armadillos are the only animal known in North America to carry the M. leprae bacteria, but research has suggested that humans cannot easily catch leprosy from armadillos as it requires more than skin contact. Leprosy cannot be transmitted through pregnancy or sexual contact, and there is no risk of catching it from someone who has been on multidrug therapy for a week.

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