A spherule stage is seen in humans infected with what organism?
a. Blastomyces dermatitidis
b. Coccidioides immitis
c. Histoplasma capsulatum
d. Paracoccidioides brasiliensis

Verified step by step guidance

Step 1: Understand the term 'spherule stage' in the context of fungal infections. A spherule is a large, thick-walled structure containing endospores, characteristic of certain dimorphic fungi during infection in humans.

Step 2: Review the life cycles and morphological forms of the listed fungi when infecting humans: Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum, and Paracoccidioides brasiliensis.

Step 3: Recall that Blastomyces dermatitidis typically forms broad-based budding yeast in tissue, not spherules.

Step 4: Recognize that Histoplasma capsulatum appears as small intracellular yeasts within macrophages, not spherules.

Step 5: Identify that Coccidioides immitis is known for forming spherules filled with endospores in human tissue, which is a distinctive diagnostic feature.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Spherule Stage in Fungal Life Cycles

The spherule is a specialized, thick-walled structure formed by certain fungi during infection in humans. It contains endospores and is a key diagnostic feature, especially in tissue samples. Understanding which fungi produce spherules helps identify the causative agent of specific fungal infections.

Coccidioides immitis and Coccidioidomycosis

Coccidioides immitis is a dimorphic fungus that causes coccidioidomycosis (Valley fever). In the human host, it transforms into spherules filled with endospores, which rupture to release new infectious particles. This spherule stage is unique to Coccidioides among the listed fungi.

Differentiation of Dimorphic Fungi

Dimorphic fungi like Blastomyces, Histoplasma, and Paracoccidioides have distinct morphological forms in the environment and in human tissue. Recognizing their specific tissue forms—such as yeast, intracellular forms, or spherules—is essential for accurate diagnosis and treatment.

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