WBR0186

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Infectious Disease
Prompt	[[Prompt::A 40-year-old woman presents to the physician’s office for several weeks of cough and intermittent fever. Initial work-up reveals a heterogeneous right lower lobe mass, hilar lymphadenopathy, and a left-sided pleural effusion on chest x-ray. Bronchoscopy with transbronchial biopsy reveals necrotic lung tissue with spherules containing hundreds of uninucleated endospores. Which of the following is the most likely causative organism?]]
Answer A	AnswerA::''Histoplasma capsulatum''
Answer A Explanation	[[AnswerAExp::Histoplasma capsulatum is a dimorphic fungus that forms hyphae with microconidia and tuberculate macroconidia. It does not form spherules with endospores. Histoplamsa microconidia are much smaller than the spherules of Coccidioides species. They can be observed inside macrophages as they grow and multiply in the phagosome.]]
Answer B	AnswerB::''Blastomyces dermatitidis''
Answer B Explanation	AnswerBExp::''Blastomyces dermatitidis'' form hyphae with nondescript conidia. The tissue form is a broad-based budding yeast.
Answer C	AnswerC::''Coccidioides immitis''
Answer C Explanation	AnswerCExp::''Coccidioides immitis'' is a dimorphic fungus that forms characteristic spherules with endospores inside host tissues.
Answer D	AnswerD::''Aspergillus fumigatus''
Answer D Explanation	AnswerDExp::''Aspergillus fumigatus'' is a monomorphic filamentous fungus that forms dichotomously branching septate hyphae at 45 degree angle.
Answer E	AnswerE::Cryptococcus neoformans
Answer E Explanation	AnswerEExp::''Cryptococcus neoformans'' is an encapsulated monomorphic yeast. It does not form spherules with endospores.
Right Answer	RightAnswer::C
Explanation	[[Explanation::Coccidioidomycosis is a fungal infection caused by the dimorphic fungus Coccidioides immitis. Coccidioidomycosis is most prevalent in the southwestern United States, particularly in Arizona, California, Nevada, and New Mexico. In the soil, the organism exists as a mold with septate hyphae. When inhaled, spores evolve into round structures called spherules that grow and divide forming smaller internal structures known as endospores. Spherules that are large enough may rupture and release their endospores, causing further spread of the infection. Coccidioidomycosis is not transmitted from person to person. The infection is often asymptomatic and ordinarily resolves leaving the patient immune to re-infection. Symptomatic coccidioidomycosis typically presents as a flu-like illness with cough, headache, arthralgias, myalgias, and skin rashes. Certain patients may manifest signs of chronic or relapsing disease. Severe pulmonary disease and disseminated infection may develop in HIV-infected persons. Educational Objective: Coccidioidomycosis is caused by the dimorphic fungus Coccidioides immitis. The tissue form (parasitic form) of this fungus appears as a spherule containing hundreds of uninucleated endospores. References: Stevens, D. A., Mandell, G. L., Douglas Jr, R. G., & Bennett, J. E. (1990). Coccidioides immitis. Principles and practice of infectious diseases., (Ed. 3), 2008-2017.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Coccidioides immitis, WBRKeyword::Coccidioidomycosis, WBRKeyword::Dimorphic fungi, WBRKeyword::Spherules, WBRKeyword::Endospores, WBRKeyword::Fungal infections, WBRKeyword::Fungus
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