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