Histoplasmosis #28

medical microbiology disease of the week 12

Classification

Histoplasmosis

dimorphic fungus (yeast in tissues 37˚C; filamentous growth in soil and media)

intracellular macrophage parasite

requires cellular immunity for clearance

causative organism

Histoplasma capsulatum

epidemiology

reservoir- environment (soil with bird/bat droppings)

portal of entry- respiratory tract

transmission- inhaled spores (microconidia)

incubation

1-3 weeks

pathogenesis

inhaled microconidia colonize lung as yeast. macrophages phagocytize (not kill) yeast. immune cells form granulomas around infected cells and fungi. systemic infection causes immune compromised hosts

symptoms

respiratory infection

sometimes asymptomatic

resolves within 2 weeks (may last 3-5)

fever/chills

cough

fatigue

headache/body aches

chest pain

complications

chronic pulmonary infection (fibrosis; cavity lesions)

dissemination to other tissues (mortality 4-8% when hospitalized)

prevention

avoid exposure

wear mask

spray 3% formalin on guano deposits

prophylaxis with itraconazole for immuno-compromised

treatment

symptoms may go away without treatment

antifungal medication (itraconazole for 3-12 months)