Leprosy is caused by slow-growing bacteria in the cooler body environments of the skin and peripheral nerves. The respiratory tract, eyes, and scrotum may also be affected. The World Health Organization has provided free therapy since 1995, and cases fell from 5.2 million in 1985 to 189,018 in 2012.

820 (US); 219,000 (Global)
Hansen's disease; Mycobacterium leprae infection;
3-10 years (average); from a few weeks to 30 years; [CCDM]
Skin lesions (hypo- or hyperpigmented macules or papules/nodules); May have enlarged nerves and sensory loss; [5MCC-2020] The incubation period is about 5 years, and symptoms take as long as 20 years to appear. [WHO website]
Standard; "Physicians and nurses caring for leprosy patients and the co-workers of these patients are not at risk for leprosy." [Harrison ID, p. 637]
Leprosy is caused by slow-growing acid-fast bacteria in the cooler body environments of the skin and peripheral nerves. The upper respiratory tract, eyes, and scrotum are also affected in the lepromatous form. Leprosy is classified as tuberculoid (TT) or lepromatous (LL) based on the strength of the infected patient's immune response. In the TT form, the immune response is strong, and few bacilli are found. In the LL form, acid-fast bacilli are numerous in infected tissues. [5MCC-2020] Tuberculoid leprosy is at the less severe end of the spectrum--patients have asymmetrical disease of skin and peripheral nerves. Most commonly affected nerves are the ulnar, posterior auricular, peroneal, and posterior tibial--both sensory and motor loss occur. Skin lesions in tuberculoid leprosy are hypopigmented, sharply demarcated, and have raised borders. They lose sensation in the early stages and are dry and scaly since they lack sweat glands and hair follicles. [Harrison ID, p. 637] Other areas involved in lepromatous leprosy are the upper respiratory tract (including larynx), eyes, lymph nodes, and testes. Patients may present with sensory loss, paresis, and muscular wasting. [Guerrant, p. 257] Tuberculoid leprosy and lepromatous leprosy are stable forms; they do not convert to other forms (tuberculoid, lepromatous, or borderline). [Cecil, p. 2015] Corneal scarring is a complication of leprosy that may lead to blindness. Renal failure secondary to amyloidosis occurs occasionally in lepromatous leprosy. [Merck Manual, p. 1662] Skin lesions are anesthetic at the tuberculoid end of the spectrum. Anesthesia and paralysis from nerve damage leads to disability from skin injury, disuse, contractures, secondary infection, and osteomyelitis. [ID, p. 1415, 1421] Patients with lepromatous leprosy may have leonine facies (thickening of facial skin) and loss of eyelashes and lateral eyebrows. [PPID, p. 3027]

"M. leprae transmission is favored by close contact." No longer transmitted by patients "within a day of beginning treatment"; [CCDM, p. 346] Transmission is by respiratory secretions and nasal discharge (lepromatous leprosy) and possibly by skin-to-skin contact. [ID, p. 1421] The World Health Organization has provided free multidrug therapy (MDT) since 1995. More than 14 million leprosy patients have been cured. Leprosy cases dropped from 5.2 million in 1985 to 189,018 in 2012. "Leprosy has been eliminated from 119 countries out of 122 countries where the disease was considered as a public health problem in 1985." [WHO website] Percentage of cases that are lepromatous: India and Africa (10%); Southeast Asia (50%); Mexico (90%). [Harrison ID, p. 636]

Before clofazimine was available, erythema nodosum leprosum (ENL) was more common. In addition to painful skin lesions, neuritis, lymphadenitis, and fever, this reaction may also include iritis, orchitis, arthritis, glomerulonephritis, anemia, and elevated liver enzymes. [Merck Manual, p. 1663] ENL affects patients at the lepromatous pole (lepromatous and borderline lepromatous). ENL findings may include erythematous subcutaneous nodules, fever up to 40 degrees C., arthralgia/arthritis, neuritis, nephritis, and leukocytosis. [PPID, 8th Ed, p. 2826] In severe cases of erythema nodosum leprosum, widespread skin nodules may form pustules and ulcerate. [Cohen, p. 958]

Two forms are tuberculoid (paucibacillary) and lepromatous (multibacillary). Tuberculoid skin lesions are generally large, 1-5 in number, hypopigmented or reddish, and anesthetic. Borders are irregular and distribution is asymmetric. Lepromatous skin lesions are more numerous, symmetric, and small. These hyperpigmented papules and plaques sometimes show loss of sensation. The clinical diagnosis is based on: 1) chronic skin lesions; and 2) peripheral nerve hypoesthesia, anesthesia, and paralysis; Most cases diagnosed clinically, but skin biopsy confirmation recommended; [CCDM, p. 344-7]
Fite stain for AFB in skin scrapings or biopsy; False (-) from Ziehl-Neelsen stain; For tuberculoid leprosy with no bacteria: noncaseating granuloma in nerve biopsy; PCR (www.hrsa.gov/hansens-disease/diagnosis/biopsy.html); [PPID, p. 3029]]
About 3/4 of cases in India, Brazil, and Indonesia; Highest prevalence rates in Marshall Islands, Micronesia, and Kiribati; [CCDM] India, Brazil, and Indonesia have the largest number of cases.; [Cecil, p. 2013]
  • >arthralgia
  • >fever
  • E epistaxis
  • E nasal ulcers
  • E rhinitis
  • G hepatomegaly
  • G liver function test, abnormal
  • H anemia
  • H hypergammaglobulinemia
  • H leukocytosis
  • H lymphadenopathy
  • H splenomegaly
  • N muscle weakness
  • N paresthesia
  • S cellulitis or rash, circinate
  • S lymphadenitis, acute
  • S papules or plaques
  • S pustule
  • S skin or subcutaneous nodule
  • S ulcer of skin
  • *acute renal failure
  • *arthritis
  • *blindness
  • *cranial neuropathy
  • *epididymo-orchitis
  • *erythema nodosum
  • *glomerulonephritis
  • *osteomyelitis
  • *paralysis
  • *peripheral neuropathy
  • *uveitis




Inhalation, Skin or Mucous Membranes (Includes Conjunctiva)
1. (US) Published in MMWR 2011 = 82; Use correction factor of 10 for reported diseases: 82 X 10 = 820;
2. (Global) 182,000 affected and 219,000 new cases in 2011; [Fact sheets from WHO 2013]