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Histoplasma
Etiology

Inhalation of Histoplasm capsulatum from dust contaminated with bird dropping
Pathogenesis

Inhale the microconidia (small spores)
Dimorphic fungus with conidia and yeasts at body temperature and hyphae outside the body
Yeasts and conidia bind LFA-1 and MAC-1
Phagocytosed by macrophages (obligate intracellular parasites)
Killed by T cells that recognize the antigens as well as TNF-alpha,
Epidemiology

Frequent in individuals living along the Ohio and Mississippi rivers
Also frequent in individuals living in the Carribean
General Gross Description

Granulomatous lesions that fibrose to form round, well demarcated firm gray white lesions
Apical and pleural involvement may occur
Diffuse pneumonic process in the immunocompromised host
•Examples:
General Microscopic Description

Epithelioid granulomas that caseate, then fibrose (resemble lesions of Mycobacteria tuberculosis)
Immunocompromised patient may lack the ability to form granulomas but show diffuse macrophage proliferation containing organisms.
•Examples:
Histoplasma Infection of Lung (GMS stain 40X))
Clinical Correlation

May be incidental finding in the immunocompetent patient.
Immunocompromised patient may have diffuse pneumonia with respiratory distress
References

Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th edition. Philadelphia, W.B. Saunders, 1994, pp. 327-28.

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Histoplasma
Synopsis by: Melinda Sanders M.D. (T28000E41450)[352]
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