A 34-year-old HIV-positive man from northeastern India presents with fever, weight loss, hepatosplenomegaly, and multiple umbilicated skin papules. Bone marrow smear shows intracellular yeasts of 3 to 5 micrometre size with a central transverse septum. What is the causative organism?
- A Histoplasma capsulatum, replicating by narrow-based budding
- B Cryptococcus neoformans var. grubii with narrow-necked budding
- C Penicillium marneffei (Talaromyces marneffei), a dimorphic fungus dividing by fission ✓
- D Leishmania donovani amastigotes with kinetoplasts
Correct answer: C. Penicillium marneffei (Talaromyces marneffei), a dimorphic fungus dividing by fission
Explanation
Intracellular yeasts showing a central transverse septum formed during reproduction by binary fission are pathognomonic of Talaromyces marneffei, a dimorphic fungus endemic to Southeast Asia and southern China that is an AIDS-defining infection in the region. Histoplasma yeasts divide by budding and lack a transverse septum. Cryptococcus is larger with a capsule and buds narrowly. Leishmania amastigotes show a nucleus and kinetoplast, not a fission septum.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.