A 45-year-old man from coastal Karnataka who regularly eats raw fish develops progressive fatigue and paraesthesiae. Haemogram shows macrocytic anaemia with hypersegmented neutrophils and low serum vitamin B12. Stool examination reveals broadly oval, operculated eggs. The causative agent acquires its plerocercoid larval stage in:
- A Pig muscle
- B Cyclops (copepod)
- C Freshwater fish ✓
- D Freshwater crab
Correct answer: C. Freshwater fish
Explanation
Diphyllobothrium latum, the broad fish tapeworm, causes megaloblastic anaemia because the worm absorbs vitamin B12 in the jejunum. Its operculated egg releases a coracidium that is ingested by a copepod (first intermediate host), where it becomes a procercoid; the fish then ingests the copepod and harbours the plerocercoid, the stage infectious to humans eating raw fish. The copepod alone carries only the procercoid, and crabs are intermediate hosts of Paragonimus.
Reference: Paniker's Textbook of Medical Parasitology, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.