Classification: ICD-9 030; ICD-10 A30
Syndromes and synonyms: Hansen disease, multibacillary leprosy (ML), paucibacillary leprosy (PL), lepromatous leprosy, tuberculoid leprosy.
Agent: Mycobacterium leprae, a slow-growing, acid-fast, intracellular bacterium. It grows best at 27–30 °C, which explains the main target organs of M. leprae: skin, peripheral nerves, nasal mucosa, upper respiratory tract, and eyes.
Reservoir: Humans are the main reservoir. Subclinical infection is likely common in endemic areas, as M. leprae DNA can be found in nasal swabs in up to 5% of healthy individuals in Asian endemic regions. Subclinical infection generally does not develop into clinical disease. Natural infection occurs in armadillos and several primates.
Transmission: The precise mechanism is unclear: probably by aerosol spread of nasal secretions from a case to respiratory mucosa of close contacts. M. leprae cannot cross intact skin. The relative risk for leprosy disease in household contacts is 8 to 10 for multibacillary (lepromatous) leprosy and 2 to 4 for paucibacillary (tuberculoid) leprosy.
Incubation period: 3 to 5 years (range 9 months to >20 years); shorter for PL than for ML.
Clinical findings
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