Leprosy is a chronic, progressive bacterial infection caused by the bacterium Mycobacterium leprae. It primarily affects the nerves of the extremities, the lining of the nose, and the upper respiratory tract. Leprosy produces skin sores, 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. According to the World Health Organization (WHO), the first known written reference to leprosy is from 600 B.C.
Leprosy is common in many countries, especially those with tropical or subtropical climates. However, it’s not as common in the United States. The National Institute of Allergy and Infectious Disease reports that only 100 to 200 new cases are diagnosed in the United States each year.
There are three systems for classifying leprosy. The first system recognizes two types of leprosy: tuberculoid and lepromatous. A person’s immune response to the disease determines their type of leprosy.
The immune response is good and the disease only exhibits a few lesions (sores on the skin) in tuberculoid leprosy. The disease is mild and only mildly contagious.
The immune response is poor in lepromatous leprosy and affects the skin, nerves, and other organs. There are widespread lesions and nodules (large lumps and bumps). This disease is more contagious.
WHO categorizes the disease based on the type and number of affected skin areas. The first category is paucibacillary, in which five or fewer lesions with no bacteria are detected in the skin sample. The second category is multibacillary, in which there are more than five lesions, bacteria is detected in the skin smear, or both.
Clinical studies use the Ridley-Jopling system. It has six classifications based on severity of symptoms. They are:
- intermediate leprosy: a few flat lesions that sometimes heal by themselves and can progress to a more severe type
- tuberculoid leprosy: a few flat lesions, some large and numb; some nerve involvement; can heal on its own, persist, or may progress to a more severe form
- borderline tuberculoid leprosy: lesions similar to tuberculoid but smaller and more numerous; less nerve enlargement; may persist, revert to tuberculoid, or advance to another form
- mid-borderline leprosy: reddish plaques, moderate numbness, swollen lymph glands; may regress, persist, or progress to other forms
- borderline lepromatous leprosy: many lesions including flat lesions, raised bumps, plaques, and nodules, sometimes numb; may persist, regress, or progress
- lepromatous leprosy: many lesions with bacteria; hair loss; nerve involvement; limb weakness; disfigurement; doesn’t regress
Leprosy spreads through contact with the mucus of an infected person. This usually occurs when the infected person sneezes or coughs. The disease isn’t highly contagious. Close, repeated contact with an untreated person can lead to contracting leprosy.
The bacteria responsible for leprosy multiply very slowly. The disease has an incubation period (the time between infection and the appearance of the first symptoms) of up to five years. 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 can also carry and transmit the disease to humans.
The main symptoms of leprosy include:
- muscle weakness
- numbness in the hands, arms, feet, and legs
- skin lesions
The skin lesions have decreased sensation to touch, temperature, or pain. They don’t heal after several weeks and are lighter than your normal skin tone.
Your doctor will conduct a physical exam to look for telltale signs and symptoms of the disease. They’ll also perform a skin biopsy or scraping. Your doctor will remove a small piece of skin and send it to a laboratory for testing.
Your doctor may also perform a lepromin skin test to determine the form of leprosy. Your doctor will inject a small amount of leprosy-causing bacteria into the skin, typically on the upper forearm. People who have tuberculoid or borderline tuberculoid leprosy will experience irritation 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:
Your doctor may prescribe more than one antibiotic at the same time. They also may want you to take an anti-inflammatory medication such as aspirin, prednisone, or orthalidomide. 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:
- hair loss, particularly on the eyebrows and eyelashes
- muscle weakness
- permanent nerve damage in the arms and legs
- inability to use the hands and feet
- chronic nasal congestion, nosebleeds, and collapse of the nasal septum
- iritis (inflammation of the iris of the eye)
- glaucoma (an eye disease that causes damage to the optic nerve)
- erectile dysfunction and infertility
- kidney failure
The best way to prevent leprosy is to avoid long-term, close contact with an untreated, infected person.
The overall outlook is good if your doctor diagnoses the leprosy promptly. Early treatment prevents tissue damage, stops the spread of the disease, and prevents serious health complications. The outlook is worse when diagnosis occurs at a more advanced stage, after an individual has significant disfigurement or disability. It may be impossible to lead a normal life despite treatment in these cases.