Leprosy (Hansen's disease) is a chronic infection caused by the bacteria Mycobacterium leprae. It results in damage primarily to the peripheral nerves (the nerves outside the brain and spinal cord), skin, testes, eyes, and mucous membrane of the nose.

• Leprosy ranges from mild (with one or a few skin areas affected) to severe (with many skin areas affected and damage to many organs).
• Rashes and bumps appear, the affected areas become numb, and muscles may become weak.
• The diagnosis is suggested by symptoms and confirmed by a biopsy of the affected tissue.
• Antibiotics can stop leprosy from progressing but cannot reverse any nerve damage or deformity.

Because without treatment, people with leprosy are visibly disfigured and often have significant disability, they have long been feared and shunned by others. Although leprosy is not highly contagious, rarely causes death, and can be effectively treated with antibiotics, it still causes anxiety. As a result, people with leprosy and their family members often suffer psychologic and social problems.

During 2007, over 250,000 new cases were reported. About 90% of these cases occurred in the following eight countries (from the most cases to the least): India, Brazil, Indonesia, Congo, Bangladesh, Nigeria, Nepal, and Ethiopia. In 2006, 137 new cases were reported in the United States. Cases occurred in 30 states, but over half occurred in six states: California, Florida, Louisiana, Massachusetts, New York, and Texas. Almost all cases of leprosy in the United States involve people who emigrated from developing countries.

Leprosy can develop at any age but appears to develop most often in people aged 5 to 15 years or over 30.

How leprosy is spread is unclear. However, it may be passed from person to person through droplets expelled from the nose and mouth of an infected person and breathed in or touched by an uninfected person. But even after contact with the bacteria, most people do not contract leprosy. About half of the people with leprosy probably contracted it through close, long-term contact with an infected person. Casual and short-term contact does not seem to spread the disease. Leprosy cannot be contracted by simply touching someone with the disease, as is commonly believed. Health care workers often work for many years with people who have leprosy without contracting the disease. Armadillos are the only confirmed source other than people, although other animal and environmental sources may exist.

About 95% of people who are infected with Mycobacterium leprae do not develop leprosy because their immune system fights off the infection. People who develop leprosy may have genes that make them susceptible to the infection once they are exposed.

Classification: Leprosy can be categorized by the type and number of skin areas affected. Those with 5 or fewer affected skin areas have leprosy that is called paucibacillary. People should have no bacteria detectable on samples from those areas. Those with 6 or more affected areas have leprosy that is called multibacillary. People may or may not have bacteria detected on samples from those areas.

Leprosy can also be classified as tuberculoid, lepromatous, or borderline according to the symptoms people have and other findings. People with tuberculoid leprosy typically have few skin areas affected (paucibacillary), and the disease is milder, less common, and less contagious. People with lepromatous and borderline typically have more skin areas affected (multibacillary), and the disease is more severe, common, and contagious.

In both classifications, the type of leprosy dictates the long-term prognosis, likely complications, and how long antibiotic treatment is needed.

Tuberculoid Leprosy

Symptoms

Because the bacteria that cause leprosy multiply very slowly, symptoms usually do not begin until at least 1 year after people have been infected. On average, symptoms appear 5 to 7 years after infection. Once symptoms begin, they progress slowly.

Leprosy affects mainly the skin and peripheral nerves Characteristic rashes and bumps develop. Infection of the nerves makes the skin numb or the muscles weak in areas controlled by the infected nerves.

• Tuberculoid leprosy: A rash appears, consisting of one or a few flat, whitish areas. Areas affected by this rash are numb because the bacteria damage the underlying nerves.
• Lepromatous leprosy: Many small bumps or larger raised rashes of variable size and shape appear on the skin. There are more areas of numbness than in tuberculoid leprosy, and certain muscle groups may be weak. Much of the skin and many areas of the body, including the kidneys, nose, and testes, may be affected.
• Borderline leprosy: Features of both tuberculoid and lepromatous leprosy are present. Without treatment, borderline leprosy may become less severe and more like the tuberculoid form, or it may worsen and become more like the lepromatous form.

The most severe symptoms result from infection of the peripheral nerves, which causes deterioration of the sense of touch and a corresponding inability to feel pain and temperature. People with peripheral nerve damage may unknowingly burn, cut, or otherwise harm themselves. Repeated damage may eventually lead to loss of fingers and toes. Also, damage to peripheral nerves may cause muscle weakness that can result in deformities. For example, the fingers may be weakened, causing them to curve inward (like a claw). Muscles may become too weak to flex the foot—a condition called footdrop. Infected nerves may enlarge so that during a physical examination, doctors can feel them.

Skin infection can lead to areas of swelling and lumps, which can be particularly disfiguring on the face.

Other areas of the body may be affected:

• Feet: Sores may also develop on the soles of the feet, making walking painful.
• Nose: Damage to the nasal passages can result in a chronically stuffy nose and nosebleeds and, if untreated, complete erosion of the nose.
• Eyes: Damage to the eyes may lead to glaucoma or blindness.
• Sexual function: Men with lepromatous leprosy may have erectile dysfunction (impotence) and become infertile. The infection can reduce the amount of testosterone and sperm produced by the testes.
• Kidneys: The kidneys may malfunction. In severe cases, kidney failure may occur.

During the course of untreated or even treated leprosy, the immune system may produce inflammatory reactions. These reactions can cause fever and inflammation of the skin, peripheral nerves, and, less commonly, the lymph nodes, joints, testes, kidneys, liver, and eyes. The skin around bumps may swell and become red and painful, and the bumps may form open sores. People may have a fever and swollen lymph glands.

Diagnosis

Symptoms (such as distinctive rashes that do not disappear, enlarged nerves, loss of the sense of touch, and deformities that result from muscle weakness) provide strong clues to the diagnosis of leprosy.

Examination of a sample of infected skin tissue under a microscope (biopsy) confirms the diagnosis. Because leprosy bacteria do not grow in the laboratory, culture of tissue samples is not useful. Blood tests to measure antibodies to the bacteria have limited usefulness because antibodies are not always present.

Did You Know... Leprosy is not easily spread. If leprosy is severe, people may have to take antibiotics for the rest of their life.

Prevention

Because leprosy is not very contagious, risk of spread is low. Only the untreated lepromatous form is contagious, although even then the infection is not easily spread. Once treatment has begun, leprosy cannot be spread. Avoiding contact with bodily fluids from and the rash on infected people is the best prevention. The BCG (bacille Calmette-Guérin) vaccine, used to prevent tuberculosis, provides some protection against leprosy, but it is not often used to prevent leprosy.

Treatment

Antibiotics can stop the progression of leprosy but do not reverse any nerve damage or deformity. Thus, early detection and treatment are vitally important. Because some leprosy bacteria are resistant to certain antibiotics, doctors prescribe more than one drug. The drugs chosen depend on the type of leprosy:

• Multibacillary: The standard combination of drugs is dapsone, rifampin, and clofazimine. People take rifampin and clofazimine once a month under a health care practitioner's supervision. They take dapsone plus clofazimine once a day on their own. This regimen is continued for 12 to 24 months, depending on the severity of the disease.
• Paucibacillary: People take rifampin once a month with supervision and dapsone once a day without supervision for 6 months. People who have only a single affected skin area are given a single dose of rifampin, ofloxacin, and minocycline.

Dapsone is relatively inexpensive and generally safe to use. It occasionally causes allergic rashes and anemia. Rifampin, which is more expensive, is even more effective than dapsone. Its most serious side effects are damage to the liver and flu-like symptoms. Clofazimine is extremely safe. The main side effect is temporary skin pigmentation.

Because the bacteria are difficult to eradicate, antibiotics must be continued for a long time. Depending on the severity of the infection and the doctor's judgment, treatment continues from 6 months to many years. Some doctors recommend lifelong treatment with dapsone for people with lepromatous leprosy.

Last full review/revision October 2008 by Edward A. Nardell, MD