A 45-year-old man who eats smoked freshwater fish develops progressive fatigue and paraesthesiae. Haemogram shows macrocytic anaemia with low serum vitamin B12 and a normal folate level. Stool examination reveals an operculated egg discharged unembryonated. The most likely causative agent is:

• A Taenia saginata
• B Diphyllobothrium latum ✓
• C Echinococcus granulosus
• D Hymenolepis nana

Explanation

Diphyllobothrium latum, the fish tapeworm, competes with the host for vitamin C12 by absorbing it through its broad proglottids, producing megaloblastic anaemia that can be severe enough to cause neurological signs. Its eggs are operculated and leave the body unembryonated, unlike any other human tapeworm egg. Taenia eggs are spherical with hooks and radially striated shells, Hymenolepis eggs have polar filaments, and Echinococcus eggs are indistinguishable from Taenia eggs.

Reference: Paniker's Textbook of Medical Parasitology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.