WBR0186

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1]]]
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 etiologic agent?]]
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. The tissue forms are small intracellular yeasts with narrow neck on bud with no capsules.]]
Answer B	AnswerB::Blastomyces dermatitidis
Answer B Explanation	AnswerBExp::Blastomyces dermatitidis forms 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 with the hyphae breaking into arthroconidia. It forms spherules with endospores.
Answer D	AnswerD::Aspergillus fumigatus
Answer D Explanation	AnswerDExp::Aspergillus fumigatus is a monomorphic filamentous fungus, dichotomously branching septate hyphae at 45 degrees 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::This patient has Coccidioidomycosis, a fungal infection caused by coccidioides immitis. Coccidioides immitis resides in the soil in certain parts of the southwestern United States, most notably in California and Arizona. It is also prevalent in northern Mexico, and parts of Central and South America. It is dormant during long dry spells, then develops as a mold with long filaments that break off into airborne spores when the rains come. The spores, known as arthroconidia, are swept into the air by disruption of the soil, such as during construction, farming, or an earthquake. Infection is caused by inhalation of the particles. The disease is not transmitted from person to person. The infection ordinarily resolves leaving the patient with a specific immunity to re-infection. However, in some cases the infection may manifest itself repeatedly or permanently over the life of the host. Coccidioides immitis is a dimorphic saprophytic organism that grows as a mycelium in the soil and produces a spherule form in the host organism. Symptomatic infection usually presents as an influenza-like illness with fever, cough, headaches, rash, myalgia (muscle pain), and arthralgia (joint pain). The rash is maculopapular. Erythema nodosum on lower extremities, and erythema multiforme in necklace-like fashion can occur predominantly in women. Some patients fail to recover and develop chronic pulmonary infection or widespread disseminated infection (affecting meninges, soft tissues, joints, and bone). Severe pulmonary disease may develop in HIV-infected persons. Educational Objective: References: ]]
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