Histoplasmosis
Histoplasma
capsulatum
Epidemiology and Etiology:
- Infection acquired
by inhalation
- Habitat:
- Soil contaminated
by bird or bat droppings
- Virulence factors:
- Heat-shock protein
60 (HSP60) binds to integrins on
macrophages
Common sites:
- Lungs
- Apices (secondary
lung disease)
- Mediastinum
- Adrenals
- Liver
- Meninges
- Disseminated
Gross features:
- Resembles TB
- Coin lesions on CXR
- May cavitate
- Fibrose and
calcify with resolution (tree-bark)
Histologic features:
- yeast:
- 3-5 micron
- thin-walled
- spherical to oval
- uninucleate
- narrow-based budding
(unusual but seen)
- often in clusters
- “darkly stained
foci” within (rarely) (similar to PCP)
- granulomas, usually
necrotizing
- resolution:
- fibrosis and
concentric calcification
- immunosuppressed:
- focal
accumulations of mononuclear phagocytes filled with fungal yeasts
Immunophenotype:
Marker:
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Sensitivity:
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Specificity:
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Molecular features:
Other features:
- fungus
- intracellular
parasite of macrophages
- clinically
resembles TB
References: