A 21-year-old man from a village near Raipur, Chhattisgarh, who regularly bathes in a stagnant community pond, presents with nasal obstruction and recurrent epistaxis for six months. Anterior rhinoscopy shows a painless, friable, pedunculated reddish polyp whose surface is studded with tiny white dots, giving a strawberry-like appearance. Histopathology of the excised mass shows numerous large, thick-walled spherical structures, up to about 300 µm across, packed with hundreds of endospores. Attempts to culture the organism fail. What is the most likely causative agent?
Answer: C. Rhinosporidium seeberi. A strawberry-like, bleeding nasal polyp in a young person who bathes in ponds, with large endospore-filled sporangia on histology, is classic rhinosporidiosis. India and Sri Lanka carry most of the world's cases, with Chhattisgarh, Tamil Nadu and Kerala reporting many. Rhinosporidium seeberi has never been cultured; it was long treated as a fungus but molecular studies place it among aquatic protistan parasites (class Mesomycetozoea). Diagnosis rests on histopathology (H&E, PAS, mucicarmine), and treatment is wide surgical excision with cauterisation of the base; recurrence is common and dapsone is sometimes added.
A. Coccidioides immitis also forms endospore-containing spherules, but these are smaller (about 20 to 80 µm) with fewer, smaller endospores; it causes pulmonary disease in the arid Americas and grows readily in culture.
B. Conidiobolus coronatus causes rhinoentomophthoromycosis: a firm, painless swelling of the nose and face, with broad, sparsely septate hyphae and a Splendore-Hoeppli reaction, not sporangia.
D. Aspergillus flavus causes chronic granulomatous sinusitis in India, showing narrow, septate hyphae with acute-angle branching, and grows readily in culture.
