Mycobacterium leprae

Background

Microbiology

• Slow-growing acid-fast bacillus

Epidemiology

• About 1 million cases worldwide each year, but is rare in North America
  • Number may be underestimated due to difficulties with reliable diagnosis
• Most commonly occurs in Southeast Asia (especially India) and Brazil
• Decreasing incidence over the past several decades, likely due to short-course multidrug therapy starting in 1982
• Humans are thought to be the main reservoir, but it has been found in animals as well (particularly armadillos)
• Transmitted most likely by respiratory droplets, though can also be transmitted by direct contact, transplacentally, through breast milk, and after animal exposure

Risk Factors

• Age, with peaks in adolescence and ≥30 years
• Adult men (compared to adult women)
• Duration of contact with an infected patient, and the burden of bacilli in the patient

Clinical Presentation

• Following exposure, about 95% clear it spontaneously
• For those who do not, there is an incubation period of 3-5 years (with wide range) that is usually followed by indeterminate leprosy
  • Single, ill-defined, hypopigmented skin lesion
  • About 75% sponetaneously resolve, with the other 25% progressing
• Classic presentation is anaesthetic hypopigmented skin lesion with thickened nerves

Spectrum of disease

• Clinical spectrum can be classified based on the number of lesions and burden of mycobacteria
  • Paucibacillary (PB) disease has 1 to 5 skin lesions, without bacilli on skin slit smear
  • Multibacillary (MB) disease has more than 5 skin lesions, with or without nerve involvement or bacilli on slit-skin smear (regardless of number of lesions)
• Can also be classified based on general clinical appearance
  • Tuberculoid leprosy (TT) corresponds to paucibacillary
  • Borderline tuberculoid leprosy (BT)
  • Borderline leprosy (BB)
  • Borerdline lepromatous leprosy (BL)
  • Lepromatous leprosy (LL) corresponding to multibacillary disease

Type I reaction

• A cell-mediated hypersensitivity reaction that can develop in the course of treatment
• Also known as a reversal reaction due to the apparent worsening of the lesion
• Occurs most commonly in the borderline cases and may signal progression to the cell-mediated tuberculoid end of the clinical spectrum

Type 2 reaction

• A humorally-mediated hypersensitivity reaction that can develop in the course of treatment
• Also known as erythema nodosum leprosum
• Characterized by systemic illness and immune-complex deposition that appears as groups of tender subcutaneous nodules
• May have other signs of vasculitis, including fevers, arthralgias, neuralgia, lymphadenopathy, orchitis, and dactylitis

Management

Disease	Treatment
Paucibacillary	6 months of rifampin, dapsone, and clofazimine
Multibacillary	12 months of rifampin, dapsone, and clofazimine
Rifampin resistance	6 months of at least two second-line drugs with clofazimine, followed by 18 months of one second-line drug with clofazimine
Quinolone resistance	As for rifampin resistance, but without a fluoroquinolone

Second-line antibiotics

• Clarithromycin
• Minocycline
• Fluoroquinolones