Hansen's Disease

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Hansen's Disease (formerly known as Leprosy') is a chronic infectious disease caused by the bacterium Mycobacterium leprae. It usually affects the skin, peripheral nerves, and mucous membranes. Leprosy has a long history, and although feared as a highly contagious and devastating disease, it is now known that leprosy is not highly transmissible. Modern antibiotics make leprosy very treatable.

Leprosy in two boys, circa 1900. Source: National Park Service.


Other Names

  • Hansen's Disease


There are two kinds of leprosy: paucibacillary or multibacillary. Paucibacillary leprosy is milder and characterized by one or more hypopigmented (light-colored) skin macules. Multibacillary leprosy is associated with symmetric skin lesions, nodules, plaques, thickened dermis, and frequent involvement of the nasal mucosa resulting in nasal congestion and epistaxis (nosebleeds).

Signs and Symptoms

This chronic disease usually affects the skin and peripheral nerves but has a wide range of possible symptoms.

Initial symptoms are usually related to damage to nerves that supply the skin and muscles, resulting in the loss of innervation to sweat glands, hair follicles, and pigment-producing cells. This produces a lightening (or darkening) of the skin with a loss of feeling and sweating. As the disease progresses, patients experience paresthesias or "pins-and-needles" sensations or may have numb patches on the skin.

When patients finally lose the ability to sense pain, the body loses the reflexive ability to withdraw from painful stimuli. This can lead to extensive tissue injury and perhaps to loss of fingers and/or toes. Muscle paralysis can cause additional disfigurement. The inability to close the eyelids increases the chance of damage to the eyes in the form of ulceration, which can lead to blindness. Blindness can also result from direct invasion of the eyeball by bacteria.

People with leprosy can generally continue their normal work and other activities uninterrupted while they are under treatment, which may last several years, yet leprosy remains the most misunderstood human infectious disease. The stigma long associated with the disease still exists in most of the world and the psychological and social effects may be more difficult to deal with than the actual physical illness.


Mycobacterium leprae a slow growing, gram-positive bacterium causes leprosy. These bacteria mainly affect the skin, nerves, and mucous membranes. The organism has never been grown in bacteriologic media or cell culture, but has been grown in mouse foot pads.


Diagnosis is usually based on findings of the physical and neurological examination, or the organism may be identified from biopsy specimens. In some cases, molecular diagnosis based on the polymerase chain reaction can provide confirmation that M. leprae is present in a biological sample, and can also provide material for sequencing the organism's genome.


Leprosy is treated with antibiotics.

Multi-drug therapy has not been implemented in many endemic areas. Nerve damage must be recognized and managed. Relapse rate after completion of short course multi-drug therapy may rise.

Chances of Developing Hansen's Disease

In 2002, the number of new cases detected worldwide was 763,917. In 2002, 96 cases occurring in the United States were reported to CDC. In 2002, WHO listed Brazil, Madagascar, Mozambique, Tanzania, and Nepal as having 90% of cases.

Risk factors

Close contacts with patients with untreated, active, predominantly multibacillary disease, and persons living in countries with highly endemic disease.


Worldwide, 1-2 million persons are permanently disabled as a result of Hansen's disease. However, persons receiving antibiotic treatment or having completed treatment are considered free of active infection.

How Hansen's Disease is Spread

Although the mode of transmission of leprosy remains uncertain, most investigators think that M. leprae is usually spread from person to person in respiratory droplets.


Armadillos are used in leprosy research. Source: CDC.
Research on leprosy is difficult, as we are unable to grow Mycobacterium leprae in culture. The armadillo was the first animal model of leprosy, and the sooty mangabey model of leprosy confirmed that monkeys were more susceptible to leprosy when coinfected with the monkey version of the human virus that causes AIDS. [1]


The first mention of leprosy in recorded history dates to 1250 BC when it was mentioned as a curse in Shinto prayers. The disease was also mentioned in some Egyptian legends to explain the exodus of the Hebrews. Although leprosy has been afflicting humans throughout recorded history, it was not until 1873 that Armauer Hansen, with the aid of the newly-invented microscope, identified the causative organism.


  1. Hamilton HK, Levis WR, Martiniuk F, Cabrera A, Wolf J. The role of the armadillo and sooty mangabey monkey in human leprosy. Int J Dermatol. 2008 Jun;47(6):545-50. Abstract

External Links

Global Project on the History of Leprosy

Medpedia-logo.gif The basis of this article is contributed from Medpedia.com These articles are licensed under the GNU Free Documentation License It may have since been edited beyond all recognition. But we thank Medpedia for allowing its use.
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