What is leprosy?
Leprosy, also termed Hansen's disease, is a chronic infection caused by the bacterium Mycobacterium leprae, a rod-shaped organism that stains reddish when an acid-fast stain is applied. Historians suggest leprosy was recognized as a disease as early as 600 BC; because of the disfigurement of individuals with untreated leprosy, people with leprosy have been shunned and isolated for many centuries. Fortunately, current multidrug therapy (MDT) has reduced leprosy so effectively that only a few countries still have individuals with this disease. Currently, the disease is rarely seen in the United States.
Leprosy has been classified into two major types: tuberculoid and lepromatous. However, there are intermediate subtypes (borderline, mid-borderline, and others). Tuberculoid leprosy has a more limited disease pattern and relatively few bacteria located in the infected tissue, while patients with lepromatous leprosy have widespread disease and much larger numbers of bacteria in infected tissue. These terms are still seen in the literature but are being replaced by the terms paucibacillary (for tuberculoid) and multibacillary (for lepromatous) types.
Mycobacterium leprae can infect armadillos that are indigenous to the southwest United States; occasionally, people can get leprosy if they handle these animals. Another form of leprosy is seen in dogs and cats (canine leprosy). Although canine leprosy is caused by Mycobacterium species, there is no good evidence that canine leprosy is transmitted to humans by pets.
Is leprosy contagious?
Leprosy is contagious but is considered to be only mildly contagious. However, acquisition of the disease usually occurs after long-term (months to years) contact with an untreated individual with the disease. It is passed from person to person via droplets from the nose and mouth during close and frequent contact with an untreated individual with leprosy.
Leprosy Risk Factors
People at highest risk are those who live in the areas where leprosy is endemic (parts of India, China, Japan, Nepal, Egypt, and other areas) and especially those people in constant physical contact with infected people. In addition, there is some evidence that genetic defects in the immune system may cause certain people to be more likely to become infected (region q25 on chromosome 6).
What is the incubation period for leprosy?
The bacteria are slow-growing; the incubation period for leprosy is about five years (two to 10 years), and it can take as long as about 20 years before symptoms and signs of leprosy (skin lesions, nerve damage, for example) develop in some patients.
How will I know if someone has leprosy?
Because symptoms appear so slowly after infection (from about two to 10 years), it may be difficult to tell that someone has leprosy. Skin lesions (lumps, bumps, or sores), loss of eyebrows, and numbness in the skin where lesions are present are often among the first signs and symptoms of leprosy. Other signs and symptoms include thick dry skin, muscle weakness or paralysis, nosebleeds, ulcers (especially on the feet), numbness, and/or severe pain. As the disease progresses, extremities may be slowly lost (for example, toes, fingers, and nose). The diagnosis of leprosy can be made by scraping lesions and staining the skin scrapings of lesions and/or mucous secretions with an acid-fast stain to demonstrate the presence of Mycobacterium leprae.
How is leprosy transmitted?
Leprosy (Hansen's disease) is spread from person to person. This spread can occur with direct person-to-person contact and/or by contaminated droplets that are released during coughing or sneezing. Individuals who inhale the contaminated droplets can develop leprosy.
How will I know someone is cured of leprosy?
Before the 1940s, there was no effective cure for leprosy. Since that time, antimicrobial medications have been used to stop or limit the disease. The key to the cure of leprosy is early treatment before irreparable damage to the patient occurs. Currently, leprosy is treatable with combination antibiotic therapy that lasts for about six months to two years, depending on the extent of the disease in an individual patient. Most individuals can be cured of leprosy; this occurs when all of the slow-growing Mycobacterium leprae bacteria are killed by the antibiotic treatment and the patient's immune response. However, even though the person is cured of leprosy by antibiotic treatment, damage to organ systems (nerve damage, tissue loss) that has occurred during the infection will not be repaired.
Diseases and Conditions: Diseases Making a Comeback
When should I contact a medical caregiver about leprosy?
Individual should contact medical caregiver if they have a high risk of exposure to leprosy and develop any symptoms or signs of the condition. For example, individuals who live in a country where leprosy is endemic, like Brazil, India, Nepal, the Marshall Islands, and several other countries (see references for an extensive list), have a higher chance of developing leprosy.
Armadillos, commonly found in the southern United States, can be naturally infected and carry Mycobacterium leprae. It is possible to become infected after handling these animals. People who handle armadillos and develop any signs or symptoms of leprosy should inform a physician about their contact with armadillos.
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Medically reviewed by Robert Cox, MD; American Board of Internal Medicine with subspecialty in Infectious Disease
Switzerland. World Health Organization (WHO). "Leprosy." May 2015. <http://www.who.int/mediacentre/factsheets/fs101/en/>.
United States. Centers for Disease Control and Prevention. Morbidity and Mortality weekly report, "Incidence of Hansen's Disease -- United States, 1994-2011." MMWR 63.43 Oct. 31, 2014: 969-972. <http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6343a1.htm>.