Mycobacterium leprae (M. leprae)

James Shipley - 09001862

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M.leprae is believed to be one of the only known bacterium that grows in the peripheral nervous system as well as growing on skin cells. M.leprae is a acid fast rod shaped bacillus that is closely related to the tuberculosis pathogen. The Discovery which was made in 1870 was one of the first made that made a link between a bacterium and a disease. The Organism has an optimum growth temperature at 30oC preferring the cooler parts of the human body. M.leprae survives phagocytosis by macrophages and invades the myelin sheath of the peripheral nervous system which the bacterium causes damage to the nerves caused by a cell mediated immune response.

The incubation period of M.leprae is about 3 - 5 years with a long generation time of around 12 days. Because M.leprae has never been artificially grown in a lab it makes it difficult to study in depth, however armadillos have been infected under lab conditions as, This is because armadillos have a body temperature around 30oC - 35oC along with the fact that armadillos can also contract the disease in the wild.

there are two types of leprosy, Tuberculoid (neural) leprosy which is a mild form of the disease which is a non progressive form of the disease which is associated with a delayed - type hypersensitivity reaction to antigens on the surface of M.leprae. there is also lepromatous (progressive) leprosy. where large numbers of M.leprae develop in skin cels, the bacteria kills skin tissue which leads to a loss of facial features, fingers, toes and other features.

The disease usually been found in tropical climates with the disease affecting an estimated 11 million people with most cases in Africa, Asia, Brazil along with an estimated 4000 cases in the USA with 100 new cases reported each year. Leprosy is not highly infectious and is believed to be transmitted by droplets from the nose and mouth during close and frequent contacts with untreated cases. If leprosy is left untreated it can can can cause progressive and permanent damage to the skin, nerves, limbs and eyes. Early diagnosis and treatment with multi drug therapy (MDT) remain the key elements in eliminating the disease as a public health concern.

A little history on M. leprae and leprosy.

Although leprosy has been a disesase which has been around for thousands of years, it was only uncovered that the disease was caused by bacteria, discovered by Norwegian scientist, Dr Gerhard Armauer Hansen in 1873. Over the past 40 years considerable research has been made so that in todays modern world the mayority of cases can be treated.

The disesase has had a reputation in the past of been linked to biblical leprosy which was classified as a skin disesease. it is possible that this cases may have been caused by something else, this could include : -

  • Psoriasis
  • Sypilis
  • Fungal inection
  • Smallpox

Key Facts.

  • M. leprae also known as Hansen's disease is a bacteria that is the cause of leprosy.
  • M. leprae is an acid - fast, rod shaped bacillus. the disease leporsy is a chronic infectious disease which mainly affects the skin, peripheral nervous system, the mucosa in the upper respiratory tract and the eyes, but has been known to target other structures of the body.
  • M. leprae is a slow at multiplying and has an incubation period of around 5 years, with symtoms taking as long as 20 years to appear on the infected.
  • The BCG (Bacillus Calmette - Guérin) vaccine for TB has been found to somewhat protective against leprosy.


  1. U.S. National library of Medicine. (2009) accessed(04/02/11).
  2. The World Health Organisation. (2011) accessed(04/02/2011).
  3. The World Health Organisation. (2011) accessed(01/03/11).
  4. Tortora GJ, Funke BR, Case CL. Microbiology An introduction, Tenth Edition, International (2010) pg619 - pg620.
  5. Willey JM, Sherwood LM, Woolverton CJ. Microbiology Seventh Edition, International (2008) pg966 - pg967.