A 40-year-old pig farm worker presents with bloody diarrhoea and lower abdominal pain. Stool wet mount shows large ciliated organisms measuring about 60 micrometers, oval in shape, with a cytostome and a single kidney-shaped macronucleus. This is the largest protozoan parasite infecting humans. The causative agent is:
- A Entamoeba histolytica
- B Isospora belli
- C Balantidium coli ✓
- D Giardia duodenalis
Correct answer: C. Balantidium coli
Explanation
Balantidium coli is the only ciliate and the largest protozoan parasitising humans. Its trophozoite is covered with cilia, possesses a cytostome and a prominent kidney-shaped macronucleus, and invades colonic mucosa causing balantid dysentery. Pigs are the natural reservoir, matching the occupational exposure. Amoebae and flagellates lack cilia, and Isospora is a sporozoan diagnosed by oocysts, so these options fail both morphologically and epidemiologically.
Reference: Paniker's Textbook of Medical Parasitology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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