A previously healthy man returns from a visit to Arizona with fever, dry cough, and erythema nodosum. Lung biopsy reveals large thick-walled structures measuring 30 to 100 micrometres filled with small endospores. At which temperature does this organism exist as the tissue form?
- A At 37 degrees Celsius it exists as a budding yeast
- B At 37 degrees Celsius it exists as a spherule containing endospores ✓
- C It remains a mould at all temperatures, forming arthroconidia in tissue
- D It converts to a yeast-like cell that divides by binary fission
Correct answer: B. At 37 degrees Celsius it exists as a spherule containing endospores
Explanation
Coccidioides immitis and C. posadasii are dimorphic fungi of the desert southwestern United States. In soil at room temperature they grow as moulds producing barrel-shaped arthroconidia, which are highly infectious when inhaled. In tissue at 37 degrees Celsius they form spherules that mature and rupture to release endospores, each of which enlarges into a new spherule. Budding yeast forms belong to Blastomyces and Histoplasma, and binary fission in tissue is characteristic of Talaromyces marneffei.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.