QUIZ
Answer: Coccidioides posadasii/Coccidioides immitis. Figures 1a and b in the Photo Quiz depict the mold and yeast forms of Coccidioides posadasii/Coccidioides immitis, respectively. In tissue, C. posadasii/C. immitis are characterized by thick-walled spherules measuring up to 80 μm in diameter (1), which may contain multiple endospores, measuring 2 to 4 μm in diameter. These large spherules frequently fragment in tissue sections, releasing their endospores. When large, round, yeast-like organisms are observed in tissue sections, it is important to develop a broad differential diagnosis considering all possible etiologies, including Coccidioides, Candida species, Histoplasma, and Blastomyces. Since Coccidioides, Histoplasma, and Blastomyces are all causes of endemic mycoses, careful attention to the patient's travel history may be helpful. This patient presented with travel to both the southwest and the midwestern regions of the United States, in which Coccidioides and Blastomyces, respectively, are endemic. Though histologic differences between these organisms are generally apparent, these differences are not always obvious. Blastomyces is smaller (8 to 15 μm in diameter), exhibits broad-based budding, and lacks multiple endospores (1). Further, Blastomyces can rarely exhibit “giant” multinucleated yeast cells, mimicking Coccidioides (2). Fortunately, the mold forms of each pathogen are very different, and fungal culture is more sensitive and specific than histology. The mold form of Coccidioides exhibits barrel-shaped arthroconidia, whereas the mold form of Blastomyces exhibits septate hyphae with circular conidia on short conidiophores (often referred to as “lollipops”). Though not likely mistaken for Blastomyces, the mold of Coccidioides must be distinguished from other arthroconidium-forming molds. For this reason, confirmatory identification is typically performed via nucleic acid hybridization (1).
(See page 3727 in this issue [doi:10.1128/JCM.01134-11] for photo quiz case presentation)
REFERENCES
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