Leprosy is a chronic, progressive bacterial infection caused by the bacterium Mycobacterium leprae. It primarily affects the nerves of the extremities, the skin, the lining of the nose, and the upper respiratory tract. Leprosy is also known as Hansen’s disease.

Leprosy produces skin ulcers, nerve damage, and muscle weakness. If it isn’t treated, it can cause severe disfigurement and significant disability.

Leprosy is one of the oldest diseases in recorded history. The first known written reference to leprosy is from around 600 B.C.

Leprosy is common in many countries, especially those with tropical or subtropical climates. It’s not very common in the United States. The Centers for Disease Control and Prevention (CDC) reports that only 150 to 250 new cases are diagnosed in the United States each year.

The main symptoms of leprosy include:

The skin lesions result in decreased sensation to touch, temperature, or pain. They don’t heal, even after several weeks. They’re lighter than your normal skin tone or they may be reddened from inflammation.

The bacterium Mycobacterium leprae causes leprosy. It’s thought that leprosy spreads through contact with the mucosal secretions of a person with the infection. This usually occurs when a person with leprosy sneezes or coughs.

The disease isn’t highly contagious. However, close, repeated contact with an untreated person for a longer period of time can lead to contracting leprosy.

The bacterium responsible for leprosy multiplies very slowly. The disease has an average incubation period (the time between infection and the appearance of the first symptoms) of five years, according to the World Health Organization (WHO).

Symptoms may not appear for as long as 20 years.

According to the New England Journal of Medicine, an armadillo native to the southern United States and Mexico can also carry the disease and transmit it to humans.

There are three systems for classifying leprosy.

1. Tuberculoid leprosy vs. lepromatous leprosy vs. borderline leprosy

The first system recognizes three types of leprosy: tuberculoid, lepromatous, and borderline. A person’s immune response to the disease determines which of these types of leprosy they have:

  • In tuberculoid leprosy, the immune response is good. A person with this type of infection only exhibits a few lesions. The disease is mild and only mildly contagious.
  • In lepromatous leprosy, the immune response is poor. This type also affects the skin, nerves, and other organs. There are widespread lesions, including nodules (large lumps and bumps). This form of disease is more contagious.
  • In borderline leprosy, there are clinical features of both tuberculoid and lepromatous leprosy. This type is considered to be between the other two types.

2. World Health Organization (WHO) classification

WHO categorizes the disease based on the type and number of affected skin areas:

  • The first category is paucibacillary. There are five or fewer lesions and no bacterium detected in the skin samples.
  • The second category is multibacillary. There are more than five lesions, the bacterium is detected in the skin smear, or both.

3. Ridley-Jopling classification

Clinical studies use the Ridley-Jopling system. It has five classifications based on severity of symptoms.

ClassificationSymptomsDisease response
Tuberculoid leprosyA few flat lesions, some large and numb; some nerve involvementCan heal on its own, persist, or may progress to a more severe form
Borderline tuberculoid leprosyLesions similar to tuberculoid but more numerous; more nerve involvementMay persist, revert to tuberculoid, or advance to another form
Mid-borderline leprosyReddish plaques; moderate numbness; swollen lymph nodes; more nerve involvementMay regress, persist, or progress to other forms
Borderline lepromatous leprosyMany lesions, including flat lesions, raised bumps, plaques, and nodules; more numbnessMay persist, regress, or progress
Lepromatous leprosyMany lesions with bacteria; hair loss; more severe nerve involvement with peripheral nerve thickening; limb weakness; disfigurementDoesn’t regress

There’s also a form a leprosy called indeterminate leprosy that isn’t included in the Ridley-Jopling classification system. It’s considered to be a very early form of leprosy where a person will have only one skin lesion that’s just slightly numb to the touch.

Indeterminate leprosy may resolve or progress further to one of the five forms of leprosy within the Ridley-Jopling system.

Your doctor will conduct a physical exam to look for telltale signs and symptoms of the disease. They’ll also perform a biopsy in which they remove a small piece of skin or nerve and send it to a laboratory for testing.

Your doctor may also perform a lepromin skin test to determine the form of leprosy. They’ll inject a small amount of leprosy-causing bacterium, which has been inactivated, into the skin, typically on the upper forearm.

People who have tuberculoid or borderline tuberculoid leprosy will experience a positive result at the injection site.

WHO developed a multidrug therapy in 1995 to cure all types of leprosy. It’s available free of charge worldwide.

Additionally, several antibiotics treat leprosy by killing the bacteria that causes it. These antibiotics include:

  • dapsone (Aczone)
  • rifampin (Rifadin)
  • clofazimine (Lamprene)
  • minocycline (Minocin)
  • ofloxacin (Ocuflux)

Your doctor will likely prescribe more than one antibiotic at the same time.

They may also want you to take an anti-inflammatory medication such as aspirin (Bayer), prednisone (Rayos), or thalidomide (Thalomid). The treatment will last for months and possibly up to 1 to 2 years.

You should never take thalidomide if you are or may become pregnant. It can produce severe birth defects.

Delayed diagnosis and treatment can lead to serious complications. These can include:

The best way to prevent leprosy is to avoid long-term, close contact with an untreated person who has the infection.

The overall outlook is better if your doctor diagnoses the leprosy promptly before it becomes severe. Early treatment prevents further tissue damage, stops the spread of the disease, and prevents serious health complications.

The outlook is typically worse when diagnosis occurs at a more advanced stage, after an individual has significant disfigurement or disability. However, proper treatment is still necessary to prevent any further body damage and prevent the spread of the disease to others.

There may be permanent medical complications despite a successful course of antibiotics, but your physician will be able to work with you to provide proper care in order to help you cope with and manage any residual conditions.