PATHOGENS

• Histoplasma capsulatum is a dimorphic fungus, one of the "endemic fungi." Grows as a small oval yeast (2-5 mu in diameter) at 37° C or in human tissue. Grows as a mycelium in nature.
• Primarily intracellular pathogen infecting macrophages and causing granulomatous inflammation.
• Soil-based fungus that thrives in moist, acidic soil with a high nitrogen content (high burden in birds and bat droppings).
  • Old abandoned buildings and caves can contain high levels.
  • Exposure can occur through activities that expose people to contaminated soil.
• In US, endemic in Ohio, Mississippi, St. Lawrence River valleys, and Puerto Rico. Also endemic in areas of the Caribbean, Southern Mexico, Central and South America with microfoci in Eastern US, southern Europe, Africa, S and SE Asia.
• Most cases sporadic but occasionally occur in outbreaks
• Worldwide, most common endemic mycosis infection in AIDS patients.