Walsh & Hoyt: Histoplasma Capsulatum (Histoplasmosis)

Histoplasma capsulatum exists in the soil in the mycelial phase but converts to a yeast phase at the body temperature of mammals: 37C. The mycelial form consists of septate branching hyphae that bear spores at both lateral and terminal positions. The hyphae measure 12 micrometers in width, and the spores range in size from 2 14 micrometers in diameter. Spores of all sizes readily become airborne, and their size is such that they easily reach the small bronchioles or alveoli once inhaled. The resulting infection is called histoplasmosis.