Fungal and Parasitic Infections USMLE Step 1 Practice Question

A 6-year-old girl presents to the emergency department with a 2-week history of fever, nonproductive cough, and progressive fatigue. Her family recently relocated from Michigan to Ohio, where she spent considerable time exploring caves and playing outdoors. On examination, she has hepatosplenomegaly and mild lymphadenopathy. Vital signs: temperature 39.1°C, heart rate 115/min, respiratory rate 26/min, SpO2 97% on room air. Laboratory findings: hemoglobin 8.9 g/dL, white blood cells 6,200/μL, platelets 78,000/μL, AST 152 U/L, ALT 128 U/L. Blood and bone marrow cultures reveal small oval yeast organisms (2-4 μm) within macrophages and histiocytes. Chest X-ray demonstrates mild mediastinal lymphadenopathy without parenchymal infiltrates. Which of the following is the most likely diagnosis?