Histoplasmosis (Ohio Valley Disease) | Figure 4.31
A: Histoplasma capsulatum,
tuberculate macroconidium
(Courtesy of Sandra Arduin,
Michigan Department of
Community Health)
B: Histoplasmosis*
C: Blastomyces dermatitidis*
*Courtesy of Dr. Paul Getz |
(Figure 4.31A, B) - Histoplasma capsulatum, soil saprophyte, frequently in bat/bird feces which can harbor infectious fungal spores, common in southeastern and central USA; transmission via inhalation of airborne spores (soil or caves)
- Contains pseudocapsule; striking resemblance to leishmaniasis but lack kinetoplast and distributed evenly throughout the cytoplasm
- Typically results in asymptomatic primary pulmonary infection with rare skin findings in healthy patients; HIV patients can present with umbilicated papules, nodules, pustules, ± ulceration (but oral ulcers common presentation with chronic disseminated disease)
- Histology: characteristic intracellular yeast (2–4 µm) surrounded by rim of clearing (unstained capsule)
- Culture: white cottony colony at 25°C; moist yeast colony at 37°C; pear-shaped microconidia; round, spiny tuberculate macroconidia
- Treatment: spontaneous healing if minimal disease; amphotericin B in severely ill patients; itraconazole or ketoconazole in less severe cases
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