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Reporting Obligations

Individuals who have or may have leprosy shall be reported to the local Health Unit.

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Aetiologic Agent

Mycobacterium leprae (M. leprae) is the bacterium which causes leprosy. It is an obligate intracellular, acid-fast bacillus that can be Gram-stain variable.

Clinical Presentation

A chronic bacterial disease characterized by the involvement primarily of skin as well as peripheral nerves and the mucosa of the upper airway. Clinical forms of the disease represent a spectrum reflecting the cellular immune response to M. leprae. The following characteristics are typical of the major forms of the disease:

  • Tuberculoid: one or a few well-demarcated, hypopigmented and anesthetic skin lesions, frequently with active spreading edges and a clearing centre; peripheral nerve swelling or thickening also may occur;
  • Lepromatous: a number of erythematous papules, plaques, or nodules or an infiltration of the face, hands and feet with lesions in a bilateral and symmetrical distribution that progress to thickening of the skin, possible with reduced sensation;
  • Borderline (dimorphous): skin lesions characteristic of both the tuberculoid and lepromatous forms; and
  • Indeterminate: early lesions, usually hypopigmented macules, without developed tuberculoid or lepromatous features.

Modes of Transmission

The bacterium may be transmitted from close contact with nasal mucosa, possibly through respiratory secretions by untreated cases or individuals incubating subclinical infections, but the exact mechanism of transmission is not clearly understood. Indirect transmission is unlikely, although the bacillus can survive up to 7 days in dried nasal secretions.

Incubation Period

Incubation has been reported from as short as a few weeks to 30 years; however, the average incubation period is between 3 to 10 years.

Period of Communicability

Infectiousness is lost in most instances within a day of treatment with multidrug therapy.

Risk Factors/Susceptibility

Infection among close contacts of cases is frequent. Several human genes have been identified that are associated with susceptibility to M. leprae, and fewer than 5% of people appear to be genetically susceptible to the infection. People with human immunodeficiency virus (HIV) infection do not appear to be at increased risk of becoming infected with M. leprae. However, concomitant HIV infection and leprosy can lead to worsening of leprosy symptoms. Onset of leprosy is associated increasingly with use of anti-inflammatory autoimmune therapies and immunologic senescence among elderly patients. The disease is rarely seen in children younger than 3 years.

Diagnosis and Laboratory Testing

Laboratory confirmation of infection with clinically compatible signs and symptoms:

  • Demonstration of characteristic acid fast bacilli in slit-skin smears and biopsies prepared from the ear lobe or other appropriate site, such as elbow, knee, or skin lesion OR
  • Histopathological report from skin or nerve biopsy compatible with leprosy OR
  • Clinically compatible signs and symptoms with detection of Mycobacterium leprae (M. leprae) DNA in biopsy material
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Treatment and Case Management

Treatment should be under the direction of an infectious disease specialist; refer to World Health Organization (WHO) treatment recommendations. Medications are provided at no cost in Ontario.

No restrictions in employment or attendance at school are indicated for persons whose disease is regarded as non-infectious.

Contacts are defined as persons who have been in close, continuous household contact with a new patient up to 3 years prior to diagnosis or during any period of inadequate treatment. Persons residing with cases in areas of endemicity are particularly vulnerable.

Initial examination of contacts should take place, but long-term follow-up of asymptomatic contacts is not warranted.

Additional Resources

World Health Organization “Guidelines for the Diagnosis, Treatment and Prevention of Leprosy”

World Health Organization. “Leprosy.”


Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2022.