Mycobacterium leprae: Difference between revisions
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Mycobacterium leprae
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== Background == |
== Background == |
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=== Microbiology === |
=== Microbiology === |
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* Slow-growing [[Has Gram stain::acid-fast]] [[Has shape::bacillus]] |
* Slow-growing [[Has Gram stain::Gram-positive]] and [[Has Gram stain::acid-fast]] [[Has shape::bacillus]] |
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=== Epidemiology === |
=== Epidemiology === |
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=== Pathophysiology === |
=== Pathophysiology === |
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* The clinical spectrum of disease depends on the host immune response to infection |
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* A robust Th1 CD4 response causes tuberculoid leprosy, which is paucibacillary and well-controlled |
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** Requires interferon-γ |
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* A Th2 CD4 response causes lepromatous leprosy, which is multibacillary and more progressive |
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== Clinical Presentation == |
== Clinical Presentation == |
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Revision as of 19:48, 27 November 2019
Background
Microbiology
- Slow-growing Gram-positive and 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
Pathophysiology
- The clinical spectrum of disease depends on the host immune response to infection
- A robust Th1 CD4 response causes tuberculoid leprosy, which is paucibacillary and well-controlled
- Requires interferon-γ
- A Th2 CD4 response causes lepromatous leprosy, which is multibacillary and more progressive
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
Management of reactions
| Reaction | Management |
|---|---|
| Reversal reaction limited to skin | monitor clinically |
| Reversal reaction involving nerves | corticosteroids with slow taper, and rifampin changed to monthly from daily |
| Other reversal reaction | corticosteroids based on clinical judgment |
| Erythema nodosum leprosum with neuritis | prednisone 1 mg/kg/day (40 to 60 mg/day), tapered over 2 to 4 weeks, possibly with thalidomide or clofazimine as a steroid-sparing agent |
| Mild erythema nodosum leprosum | thalidomide 50 to 100 mg nightly |
