Leprosy (from the Greek lepi, meaning scales on a fish), or Hansen's disease (HD), is a chronic disease caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis.] Leprosy is primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract; skin lesions are the primary external symptom. Left untreated, leprosy can be progressive, causing permanent damage to the skin, nerves, limbs and eyes. Contrary to popular belief, leprosy does not directly cause body parts to fall off on their own accord; instead they become disfigured or amputated as a result of disease symptoms.[5]

Historically, leprosy has affected mankind since at least 4,000 years ago, and was well-recognized in the civilizations of ancient China, Egypt, and India,but it is unknown if it is the same disease mentioned in the Hebrew Bible. In 1995, the World Health Organization (WHO) estimated that between 2 and 3 million people were permanently disabled because of leprosy. In the past 20 years, 15 million people worldwide have been cured of leprosy.

The age-old social stigma associated with the advanced form of leprosy lingers in many areas, and remains a major obstacle to self-reporting and early treatment. MDT for multibacillary leprosy consists of rifampicin, dapsone, and clofazimine taken over 12 months. Dosages adjusted appropriately for children and adults are available in all Primary Health Centres in the form of blister packages.Single dose MDT for single lesion leprosy consists of rifampicin, ofloxacin, and minocycline. The move towards single dose treatment strategies has reduced the prevalence of disease in some regions since prevalence is dependent on duration of treatment.

International Leprosy Day was created to draw awareness to leprosy and its sufferers.

Mycobacterium leprae and Mycobacterium lepromatosis are the causative agents of leprosy. M. lepromatosis is only the causative agent in diffuse lepromatous leprosy, which can be lethal.

An intracellular, acid-fast bacterium, M. leprae is aerobic and rod-shaped, and is surrounded by the waxy cell membrane coating characteristic of Mycobacterium species.

Due to extensive loss of genes necessary for independent growth, M. leprae and M. lepromatosis are unculturable in the laboratory, a factor which leads to difficulty in definitively identifying the organism under a strict interpretation of Koch's postulates. The use of non-culture-based techniques such as molecular genetics has allowed for alternative establishment of causation.


The exact mechanism of transmission of leprosy is unknown: prolonged close contact and transmission by nasal droplet have both been proposed, and, while the latter fits the pattern of disease, both remain unproven. The only animal other than humans that is known to contract leprosy is the armadillo. The bacterium can also be grown in the laboratory by injection into the footpads of mice. There is evidence that not all people who are infected with M. leprae develop leprosy, and genetic factors have long been thought to play a role, due to the observation of clustering of leprosy around certain families, and the failure to understand why certain individuals develop lepromatous leprosy while others develop other types of leprosy. It is estimated that due to genetic factors, only 5% of the population is susceptible to leprosy.This is mostly because the body is naturally immune to the bacteria, and those persons who do become infected are experiencing a severe allergic reaction to the disease. However, the role of genetic factors is not entirely clear in determining this clinical expression. In addition, malnutrition and prolonged exposure to infected persons may play a role in development of the overt disease.

The incubation period for the bacteria can last anywhere from two to ten years.

The most widely held belief is that the disease is transmitted by contact between infected persons and healthy persons. In general, closeness of contact is related to the dose of infection, which in turn is related to the occurrence of disease. Of the various situations that promote close contact, contact within the household is the only one that is easily identified,

Two exit routes of M. leprae from the human body often described are the skin and the nasal mucosa, although their relative importance is not clear. It is true that lepromatous cases show large numbers of organisms deep down in the dermis. However, whether they reach the skin surface in sufficient numbers is doubtful. Although there are reports of acid-fast bacilli being found in the desquamating epithelium (sloughing of superficial layer of skin) of the skin,

The importance of the nasal mucosa was recognized as early as 1898 by Schäffer, particularly that of the ulcerated mucosa. The quantity of bacilli from nasal mucosal lesions in lepromatous leprosy was demonstrated by Shepard as large, with counts ranging from 10,000 to 10,000,000.Davey and Rees indicated that nasal secretions from lepromatous patients could yield as much as 10 million viable organisms per day.

The entry route of M. leprae into the human body is also not definitely known. The two seriously considered are the skin and the upper respiratory tract. While older research dealt with the skin route, recent research has increasingly favored the respiratory route. The CDC notes the following assertion about the transmission of the disease: "Although the mode of transmission of Hansen's disease remains uncertain, most investigators think that M. leprae is usually spread from person to person in respiratory droplets."

In leprosy both the reference points for measuring the incubation period and the times of infection and onset of disease are difficult to define; the former because of the lack of adequate immunological tools and the latter because of the disease's slow onset. Even so, several investigators have attempted to measure the incubation period for leprosy. The minimum incubation period reported is as short as a few weeks and this is based on the very occasional occurrence of leprosy among young infants. The maximum incubation period reported is as long as 30 years, or over, as observed among war veterans known to have been exposed for short periods in endemic areas but otherwise living in non-endemic areas. It is generally agreed that the average incubation period is between three and five years.


MDT remains highly effective, and patients are no longer infectious after the first monthly dose. It is safe and easy to use under field conditions due to its presentation in calendar blister packs.[7] Relapse rates remain low, and there is no known resistance to the combined drugs. The Seventh WHO Expert Committee on Leprosy, reporting in 1997, concluded that the MB duration of treatment—then standing at 24 months—could safely be shortened to 12 months "without significantly compromising its efficacy."

Persistent obstacles to the elimination of the disease include improving detection, educating patients and the population about its cause, and fighting social taboos about a disease whose patients have historically been considered "unclean" or "cursed by God" as outcasts. Where taboos are strong, patients may be forced to hide their condition (and avoid seeking treatment) to avoid discrimination. The lack of awareness about Hansen's disease can lead people to falsely believe that the disease is highly contagious and incurable.


In a recent trial, a single dose of rifampicin reduced the rate at which contacts acquired leprosy in the two years after contact by 57%; 265 treatments with rifampicin prevented one case of leprosy in this period. A non-randomized study found that rifampicin reduced the number of new cases of leprosy by 75% after three years

BCG offers a variable amount of protection against leprosy as well as against tuberculosis.