Leprosy

Leprosy (Hansen's disease) is a chronic infection caused by the bacterium Mycobacterium leprae that 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.

Because of the visible disfigurement in untreated people, people with leprosy have long been feared and shunned by others. Although leprosy is not highly contagious, does not cause death, and can be effectively treated with antibiotics, the disease still causes widespread anxiety. As a result, people with leprosy often suffer psychologic and social problems.

More than 1 million people worldwide have leprosy. Leprosy is most common in Asia (especially India and Nepal), Africa, Latin America, and the islands of the Pacific Ocean. About 4,000 people in the United States are infected, most of them in California, Hawaii, and Texas. Almost all cases of leprosy in the United States involve people who emigrated from developing countries. The infection can start at any age but most commonly begins in the 20s and 30s.

It is not clear how leprosy is spread. However, one way the disease is likely passed from person to person is through droplets expelled from the nose and mouth of an infected person and breathed in or touched by an uninfected person. But even with the bacteria in the air, 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 do 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. Other potential sources of Mycobacterium leprae are soil, armadillos, and possibly bedbugs and mosquitoes.

About 95% of people who are exposed to Mycobacterium leprae do not develop leprosy because their immune system fights off the infection. In people who do develop the disease, the infection can range from mild (tuberculoid leprosy) to severe (lepromatous leprosy). The tuberculoid form of leprosy is not contagious.

Symptoms

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

Leprosy mainly affects the skin and peripheral nerves. The skin develops characteristic rashes and bumps. Infection of the nerves makes the skin numb or the muscles weak in areas controlled by those nerves.

Leprosy is categorized as tuberculoid, lepromatous, or borderline according to the type and number of skin spots. The type of leprosy dictates the long-term prognosis, likely complications, and how long antibiotic treatment is needed.

In 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.

In 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.

Borderline leprosy shares features of both tuberculoid and lepromatous leprosy. If not treated, borderline leprosy may improve to resemble the tuberculoid form or worsen to become more like the lepromatous form.

The most severe symptoms of leprosy result from infection of the peripheral nerves, which causes a deterioration of a person's 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, at times resulting in clawing of the fingers and a "drop foot" deformity. Skin infection can lead to areas of swelling and lumps, which can be particularly disfiguring on the face.

People with leprosy also may develop sores on the soles of the feet. Damage to the nasal passages can result in a chronically stuffy nose and, if untreated, complete erosion of the nose. Eye damage may lead to blindness. Men with lepromatous leprosy may experience erectile dysfunction (impotence) and become infertile, because the infection can reduce the amount of testosterone and sperm produced by the testes.

During the course of untreated or even treated leprosy, the body's immune response may produce inflammatory reactions. These reactions can produce fever and inflammation of the skin, peripheral nerves, and less commonly the lymph nodes, joints, testes, kidneys, liver, and eyes.

Diagnosis

The symptoms (such as distinctive skin rashes that do not disappear, loss of the sense of touch, and deformities that result from muscle weakness) provide strong clues to the diagnosis of leprosy. Microscopic examination of a sample of infected skin tissue confirms the diagnosis. Because leprosy bacteria will not grow in the laboratory, tissue cultures and blood tests are not useful.

Prevention and Treatment

In the past, the deformities caused by leprosy led to ostracism, and people with the disease often were isolated in institutions or colonies. In some countries, this practice is still common. Isolation, however, is unnecessary. Leprosy is contagious only in the untreated lepromatous form, and even then the disease is not easily transmitted to others. Once treatment has begun, the disease cannot be passed to others. Furthermore, most people are naturally immune to leprosy, and only those who have close, long-term contact with an infected person are at risk of developing an infection. People at risk should be monitored by a doctor, but preventive antibiotics are not used. The BCG vaccine, which is used to prevent tuberculosis, offers some protection against leprosy--but is not often used.

Antibiotic treatment can stop the progression of leprosy but does not reverse any nerve damage or deformity. Thus, early detection and treatment are vitally important. Because some leprosy bacteria may be resistant to certain antibiotics, doctors prescribe more than one drug. The standard combination is dapsone and rifampin. Dapsone is relatively inexpensive and generally safe to use; it only occasionally causes allergic skin rashes and anemia. Rifampin, which is more expensive, is even stronger than dapsone; its most serious side effects are damage to the liver and flu-like symptoms. Clofazimine is often added to the treatment regimen for severe cases. Other antibiotics that may be given to people with leprosy include ethionamide, minocycline, clarithromycin, and ofloxacin.

Antibiotic therapy must be continued for a long time, because the bacteria are difficult to eradicate. 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 for people with lepromatous leprosy.