Leprosy is a chronic infection usually caused by the bacteria Mycobacterium leprae or Mycobacterium lepromatosis. 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 and throat.
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.
People with untreated leprosy become visibly disfigured and often have significant disability, thus 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 has considerable social stigma attached to it. As a result, people with leprosy and their family members often have psychologic and social problems.
Worldwide, the number of leprosy cases is declining. In 2020, about 130,000 new cases were reported, and about 73% of them occurred in India, Brazil, and Indonesia.
In 2020, 159 new cases were reported in the United States. In the United States, most leprosy cases occur in people who worked in or emigrated from countries where leprosy is common. Over 70% of cases occurred in six states: California, Florida, Hawaii, New York, Texas, and Louisiana. Many of these cases occurred in people in southern states who had direct contact with nine-banded armadillos, which carry leprosy bacteria.
Leprosy can develop at any age. Older age is a risk factor for leprosy, but the infection appears to develop most often in people aged 5 to 15 years or over 30 years.
It is estimated that most 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.
Transmission of leprosy
Leprosy 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 develop leprosy. About half of the people with leprosy probably contracted it through close, long-term contact with an infected person. Casual contact and short-term contact do not seem to spread the disease. Leprosy cannot be contracted by simply touching someone with the infection, as is commonly believed. Health care workers often work for many years with people who have leprosy without developing the infection.
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Armadillos are the only confirmed source other than people, although other animal and environmental sources may exist.
Classification of leprosy
Leprosy can be classified by the type and number of skin areas affected:
Paucibacillary: People with paucibacillary leprosy have 5 or fewer affected skin areas. No bacteria can be detected in samples taken from these areas.
Multibacillary: People with multibacillary leprosy have 6 or more affected skin areas and/or have bacteria detected in samples taken from an affected area.
Leprosy can also be classified based on the symptoms people have and other findings:
Tuberculoid: People with tuberculoid leprosy typically have few skin areas affected (paucibacillary), and the disease is milder, less common, and less contagious.
Lepromatous: People with lepromatous leprosy typically have more skin areas affected (multibacillary), and the disease is more severe, common, and contagious.
Borderline: People with borderline leprosy have features of tuberculoid leprosy and lepromatous leprosy.
In both classifications, the type of leprosy determines the following:
How well people fare in the long term
What complications are likely
How long antibiotic treatment is needed
Symptoms of Leprosy
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 but may take 20 to 30 years. Once symptoms begin, they progress slowly.
Leprosy affects mainly the skin and peripheral nerves (the nerves outside the brain and spinal cord). Characteristic rashes and bumps develop. They are not itchy. 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.
Tuberculoid leprosy: A rash appears, consisting of one or a few flat, lighter areas with sharp, raised borders. Areas affected by this rash are numb because the bacteria damage the underlying nerves.
Lepromatous leprosy: Many small or larger raised bumps 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. In affected men, the breasts may enlarge. People may lose their eyelashes and eyebrows.
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.
Complications of leprosy
The most severe complications 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 foot drop. Infected nerves may enlarge so that during a physical examination, doctors can feel them.
Tuberculoid leprosy causes a rash consisting of lighter areas with sharp, raised borders. Areas affected by this rash are numb because the bacteria damage the nerves underneath.
CNRI/SCIENCE PHOTO LIBRARY
In this person, leprosy has caused part of the fingers of both hands to be lost.
Image courtesy of Arthur E. Kaye via the Public Health Image Library of the Centers for Disease Control and Prevention.
In this person, leprosy has caused the cartilage in the nose to disintegrate.
Image courtesy of Dr. Andre J. Lebrun via the Public Health Image Library of the Centers for Disease Control and Prevention.
Tuberculoid leprosy causes a rash consisting of lighter areas with sharp, raised borders. Areas affected by this rash are numb because the bacteria damage the nerves underneath.
CNRI/SCIENCE PHOTO LIBRARY
In this person, leprosy has caused part of the fingers of both hands to be lost.
Image courtesy of Arthur E. Kaye via the Public Health Image Library of the Centers for Disease Control and Prevention.
In this person, leprosy has caused the cartilage in the nose to disintegrate.
Image courtesy of Dr. Andre J. Lebrun via the Public Health Image Library of the Centers for Disease Control and Prevention.
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:
Kidneys: The kidneys may malfunction. In severe cases, kidney failure may occur.
Leprosy reactions
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 reactions can also contribute to nerve damage. The skin around bumps may swell and become red and painful, and the bumps may form open sores. People may have a fever, swollen lymph glands, and painful joints.
Diagnosis of Leprosy
Examination of a sample of infected skin tissue
Doctors may suspect leprosy based on symptoms, such as distinctive rashes that do not disappear, enlarged nerves, loss of the sense of touch, and deformities that result from muscle weakness. But in the United States, doctors may not think of leprosy right away because it is rare and they are unfamiliar with its symptoms.
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. (Antibodies are produced by the immune system to help defend the body against a particular attacker, including leprosy bacteria.)
Prevention of Leprosy
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.
The best way to prevent leprosy is to
Avoid contact with bodily fluids from and the rash on infected people.
Avoid contact with armadillos.
People who are contacts of people who have leprosy and who are over 2 years of age can be given a single dose of the antibiotic rifampicin as preventive treatment. This drug is given only after doctors have ruled out leprosy and tuberculosis and have determined that people have no other issues that would prevent them from taking the drug.
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 of Leprosy
Antibiotics
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 leprosy bacteria become resistant to an antibiotic if it is used alone, doctors prescribe more than one drug.
Because the bacteria are difficult to eradicate, antibiotics must be continued for a long time. Depending on the severity of the infection, antibiotics are taken for 6 to 12 months and sometimes for up to 2 years.
The drugs chosen depend on the type of leprosy. All of them are taken by mouth (orally):
Multibacillary:
Paucibacillary:
is relatively inexpensive and generally safe to use. It occasionally causes allergic rashes and anemia.
Clofazimine is extremely safe. The main side effect is temporary skin pigmentation, which may take months to disappear.
Leprosy reactions are treated with oral corticosteroids. Mild skin inflammation does not require any treatment.
