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Mycobacterium leprae

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Mycobacterium leprae 

  • Characteristics
    • Acid fast rod
      • All mycobacterium are acid fast rods
    • Reservoir in the US is the armadillo
      • Otherwise far more common in developing world
  • Causes Leprosy - 2 forms:
    • Typically affects skin and superficial nerves
      • Grows best in temperatures below core body temperature
      • Typically found in extremities (skin, superficial nerves, eyes, etc.)
    • Tuberculoid (less severe)
      • Strong Th1 cell response and activation of macrophages kill bacteria, causing low bacterial load
      • Well-demarcated hypopigmented, hairless skin plaques with decreased sensation
        • Caused by local inflammation secondary to immune system activation
      • Lepromin skin test: raised nodule (like PPD)
        • M. leprae antigen injected intradermally
        • Demonstrates cellular response
    • Lepromatous (more severe, disseminated)
      • Largely Th2 cell response fails to kill bacteria, causing high bacterial load
      • Diffuse, poorly-demarcated skin lesions
      • Leonine facies (lion-like)
        • Caused by coalescence (merger) of skin lesions
        • Loss of nose and digits of extremities can occur
      • Lepromin skin test: non-reactive
        • M. leprae antigen injected intradermally
        • Demonstrates lack of cellular response
  • Diagnosed via skin biopsy or tissue PCR
  • Treatment 
    • Dapsone and Rifampin for tuberculoid form
    • Dapsone, rifampin, plus Clofazimine for lepromatous form