A 35-year-old previously healthy man returns from a holiday in Arizona and develops fever, dry cough, pleuritic chest pain, and erythema nodosum over the shins. Sputum microscopy after digestion shows large, thick-walled, spherical structures 20 to 80 micrometres in diameter filled with small endospores. The environmental form of this organism contains:
- A Conidia borne in chains on conidiophores
- B Barrel-shaped alternating arthroconidia ✓
- C Microconidia on tuberculate macroconidia
- D Single-celled conidia on flask-shaped phialides
Correct answer: B. Barrel-shaped alternating arthroconidia
Explanation
The clinical picture is acute pulmonary coccidioidomycosis (Valley fever), often accompanied by erythema nodosum. In tissue, Coccidioides immitis forms thick-walled spherules packed with endospores. In soil, it exists as a mould that fragments into barrel-shaped, alternating (disjunctor cell separated) arthroconidia, which become airborne and are highly infectious when inhaled. Tuberculate macroconidia belong to Histoplasma, and phialide-borne conidia are features of Aspergillus and other hyaline moulds.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.