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 membranes of the nose.
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 have psychologic and social problems.
During 2007, over 250,000 new cases were reported. About 90% of these cases occurred in the following eight countries (listed 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.
Leprosy can be categorized by the type and number of skin areas affected. People with 5 or fewer affected skin areas have a type of leprosy called paucibacillary. No bacteria can be detected on samples from these areas. People with 6 or more affected areas have a type of leprosy called multibacillary. Bacteria may or may not be detected on samples from these areas.
Leprosy can also be classified as tuberculoid, lepromatous, or borderline based on 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 or borderline leprosy typically have more skin areas affected (multibacillary), and the disease is more severe, common, and contagious.
In both classifications, the type of leprosy determines how well people fare in the long term, what complications are likely, and how long antibiotic treatment is needed.
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.
Specific symptoms vary depending on the type of leprosy.
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:
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.
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.
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.
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:
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