Leprosy (Hansen’s Disease)

Mycobacterium leprae, a bacillus that mainly affects the skin, nerves, and mucous membranes, is the organism responsible for leprosy (also known as Hansen’s disease). Unless spotted and treated in its early stage, the disease may cause disfiguration of the face and limbs, affecting physical appearance. The number of reported cases have been declining globally. According to the World Health Organization's (WHO) official figures, there were 176,176 leprosy cases registered in 2015. In Japan, where leprosy is known as leper, the memory is still fresh in our minds of people being forcibly segregated in sanitariums.

< Foot of a leprosy patient >

Causes of Infection

Mycobacterium leprae grows on rodent footpads and inside the body of nine-banded armadillos. Although it is unknown how exactly the disease is transmitted, it is believed that the disease usually spreads in the form of respiratory droplets that travel from person to person in cases where an infected individual exhales, coughs, or sneezes in the immediate vicinity.
The bacteria that cause leprosy have low infectability and multiply very slowly (approximately every 13 days). It may take 2 to 10 years (or even 20 years) before signs and symptoms appear, which mostly affect the skin, nerves, and mucous membranes. It can cause disfigurement.

Disease Agent:Mycobacterium leprae

Reservoir Hosts:Rodents and nine-banded armadillos

< Microscopic view of Hansen’s bacillus on the skin from a leprosy patient > CDC


Leprosy is caused by bacterial infection and its effects can last over a long period. While the disease has a variety of symptoms, it mainly affects the skin, the peripheral nerves, mucosa of the upper respiratory tract, and the eyes. Patients can typically be classified into two groups: those with paucibacillary leprosy and those with multibacillary leprosy.

Paucibacillary leprosy

In the case of paucibacillary leprosy, the symptoms may be milder and are often characterized by hypopigmented skin macules (one or more) accompanied by loss of sensation or a reddish rash.

Multibacillary leprosy

The form of the disease known as multibacillary leprosy results in characteristically symmetric skin lesions (mostly pale red in color) in at least five locations as well as thickened dermis, nodules, plaques, and frequent involvement of the nasal mucosa, in turn resulting in nasal congestion and epistaxis. In some cases, these skin lesions might not exhibit loss of sensation.

Aside from the above symptoms, both paucibacillary leprosy and multibacillary leprosy can cause muscle decay, paralysis (particularly in limbs), eye disorders that could cause blindness, skin hypertrophy, and ulcers on the soles of the feet. If left untreated, this disease can cause nerve damage, leading to muscle weakness and atrophy, and permanent disability.

Diagnosis and Treatment

Early diagnosis and treatment can cure the disease completely.

Diagnostic Methods

WHO's(World Health Organization) Guide to Eliminate Leprosy as a Public Health Problem (1997) defines a case of leprosy as a person having one or more of the following, and who has yet to complete a full course of treatment:

  • hypopigmented or reddish skin lesion(s) with definite loss of sensation
  • thickening of the peripheral nerves, as demonstrated by loss of sensation and mobility of the hands, feet or face
  • positive skin smears.


Both paucibacillary leprosy and multibacillary leprosy can be treated with little difficulty through multidrug (dapsone, rifampicin and clofazimine) therapy (MDT) over 6–12 months.
Furthermore, this highly effective treatment has a low relapse rate and no known drug resistance has been reported to date. As with any medicine, however, some patients may have an allergic reaction to one or more of the drugs used in this treatment. In the majority of such cases, severe itching will occur accompanied by red or dark spots on the surface of the skin and the patient will be asked to cease MDT and referred to a hospital for observation.


To prevent leprosy and accompanying disabilities, it is essential to detect all cases as early as possible and to treat them with MDT.

Regions at High Risk of Infection

Worldwide, the number of cases is decreasing but there are pockets of high incidence in several countries, including India, Brazil, Indonesia, Angola, the Central African Republic, Congo, Madagascar, Mozambique, Nepal, Tanzania, and the Philippines. In particular, India has more than half of all reported cases, followed by Brazil and Indonesia.

Estimated Number of Infected People

According to data released from the Centers for Disease Control and Prevention (CDC) in 2010, worldwide 1 to 2 million people are permanently disabled by leprosy. While the number of new cases detected worldwide was 250,000 in 2008, the global registered prevalence of leprosy at the end of the first quarter of 2013 stood at some 190,000 cases, showing a clear declining trend. Of the 122 countries where leprosy had been a national problem in 1985, 119 countries have already eliminated this disease.

Estimated Number of the Deaths

While leprosy cannot be the direct cause of death, it leaves permanent disabilities when it is not properly treated or when the infection is not spotted early enough.


WHO- Neglected Tropical Diseases, accessed March 19, 2014,

CDC- Neglected Tropical Diseases, accessed March 19, 2014,

Editorial Supervisors
Tsutomu Takeuchi, Professor Emeritus of Keio University
Hiroyoshi Endo, Professor Emeritus of St. Luke's International University