Leprosy: Fact Sheet


Leprosy is a chronic disease caused by a bacillus, Mycobacterium leprae (M. laprae). M. leprae multiplies very slowly and the incubation period of the disease is considered to be about five years.


Leprosy is transmitted by air through droplets from the nose and mouth, during close and frequent contacts with untreated cases. Leprosy is one of the least infectious diseases, because:

  • Over 99% of the population has adequate natural immunity;
  • Over 85% of the clinical cases are non-infectious, and
  • An infectious case is rendered non-infectious within one week, most often after the very first dose of treatment.


  • Leprosy mainly affects the skin and peripheral nerves.
  • If left untreated, it can lead to progressive and permanent damage of nerves, leading to loss of sensation and sweating in the extremities and paralysis of muscles in the hands, feet and face.
  • The disease is classified as paucibacillary (PB) or multibacillary (MB), depending on the bacillary load.
  • PB leprosy is a milder disease characterized by few (up to five) skin lesions (pale or reddish), whereas MB is associated with multiple (more than five) skin lesions, nodules, plaques, thickened dermis or skin infiltration.

History of the Disease

  • The first known written mention of leprosy is dated 600 BC.
  • Leprosy was recognized in the ancient civilizations of China, Egypt and India.
  • All countries of the South-East Asia Region were known to be endemic for leprosy.
  • Throughout history, the afflicted have often been ostracized by their communities and families. This situation has changed since leprosy is now completely curable and there is greater awareness about the disease.

History of Treatment

  • The first breakthrough occurred in the 1940s with the development of the drug dapsone, which cured the disease. But the duration of the treatment of leprosy was many years, even a lifetime, making it difficult for patients to be regular in their treatment.
  • In the 1960s, M. leprae started to develop resistance to dapsone, the world’s only known anti-leprosy drug at that time.

Treatment today

  • In 1981, a World Health Organization (WHO) Study Group recommended multi-drug therapy (MDT), a combination of three drugs.
  • MDT effectively kills the pathogen and cures the patient.
  • Treatment provided in the early stages averts disability.
  • With minimal training, leprosy can be easily diagnosed by clinical signs alone.

What is MDT

  • MDT comprises of three drugs, dapsone, rifampicin and clofazimine. Rifampicin and clofazimine were discovered in the early 1960s.
  • MDT is safe, effective and easily administered under field conditions.
  • MDT is available in convenient monthly calendar blister packs.
  • Since 1995, WHO has been providing free MDT for all patients in the world, initially through the drug fund provided by the Nippon Foundation and since 2000, through the MDT donation provided by Novartis and the Novartis Foundation for Sustainable Development.
  • Novartis has pledged free supply of MDT till 2010.

High effectiveness of Multidrug therapy

  • Transmission of leprosy is interrupted after the very first dose of MDT. In other words, patients are no longer infectious to others after being administered the first dose of the treatment regimen.
  • PB patients treated with MDT are cured within six months.
  • MB patients treated with MDT are cured within 12 months.
  • There are virtually no relapses, i.e. no recurrences of the disease after treatment is completed.
  • No resistance of the bacillus to MDT has been detected.
  • WHO estimates that early detection and treatment with MDT has prevented about four million people from becoming disabled.
  • MDT is very cost-effective as a health intervention, considering the economic and social losses averted.