H. capsulatum, a dimorphic fungus, is found in soil heavily contaminated with bird droppings. Which of the following statements best describes the presence of the organism in tissue biopsies?
**Core Concept**
Histoplasma capsulatum is a dimorphic fungus that exists in two forms: a soil-dwelling mycelial form and a yeast-like form found in tissues. The transition from the mycelial to the yeast form is temperature-dependent, occurring at body temperature. This dimorphism is a key characteristic of H. capsulatum.
**Why the Correct Answer is Right**
In tissue biopsies, H. capsulatum appears as small, intracellular yeast-like structures, often within macrophages. This is because the organism has undergone the temperature-dependent transition from the mycelial to the yeast form upon entering the human body. The yeast cells are typically 2-4 μm in diameter and can be seen within the cytoplasm of infected macrophages.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the appearance of H. capsulatum in tissue biopsies. While H. capsulatum can cause a granulomatous response, the organism itself is typically seen as small yeast-like structures within macrophages.
* **Option B:** This option is incorrect because it does not accurately describe the growth form of H. capsulatum in tissue biopsies. H. capsulatum is typically seen as yeast-like structures, not as mycelial forms.
* **Option D:** This option is incorrect because it does not accurately describe the cellular location of H. capsulatum in tissue biopsies. H. capsulatum is typically seen within the cytoplasm of infected macrophages, not within the extracellular space.
**Clinical Pearl / High-Yield Fact**
Histoplasmosis is a significant occupational hazard for individuals who work with soil, particularly in areas where the soil is heavily contaminated with bird droppings. Workers in these environments should wear protective masks and follow proper safety protocols to minimize their risk of exposure.
**Correct Answer:** C.