A 5-year-old child returns from a week-long rural camp and develops acute watery diarrhoea with mucus (no blood) after 3 days. Microscopy of a fresh stool reveals oval cysts (8–12 µm), each containing 4 nuclei with eccentric karyosome and fibril-like axonemes (median bodies). What is the most likely pathogen and treatment of choice?
- A Entamoeba histolytica — treatment with metronidazole followed by luminal amebicide (diloxanide furoate)
- B Giardia duodenalis (intestinalis) — treatment with metronidazole (10 mg/kg TDS × 5 days) or tinidazole (single dose 50 mg/kg) ✓
- C Cryptosporidium parvum — treatment with nitazoxanide in immunocompetent children
- D Cyclospora cayetanensis — treatment with trimethoprim-sulfamethoxazole
Explanation
Giardia lamblia (duodenalis) cysts are oval, 8–12 µm, contain 4 nuclei with peripherally placed karyosome, and have 'claw-hammer' appearance with 2 median bodies (axonemes). Giardia typically causes watery/pale frothy diarrhoea, flatulence, and malabsorption without bloody stool. Treatment: metronidazole 10 mg/kg TID × 5 days or tinidazole single dose (50 mg/kg, max 2 g). E. histolytica cysts contain 1–4 nuclei with central karyosome and chromatoid bars. Cryptosporidium oocysts are round, acid-fast, 4–6 µm. Cyclospora oocysts are round, 8–10 µm, and auto-fluorescent.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.