A 55-year-old man who frequently eats smoked and raw freshwater fish develops progressive fatigue and tingling in his feet. Peripheral smear shows hypersegmented neutrophils and macro-ovalocytes, and serum vitamin B12 levels are low. Stool examination reveals yellowish eggs measuring about 65 x 45 micrometers with an operculum but without opercular shoulders. Which parasite is responsible?

• A Diphyllobothrium latum ✓
• B Hymenolepis nana
• C Taenia saginata
• D Fasciolopsis buski

Explanation

Diphyllobothrium latum, the broad fish tapeworm, competes with the host for vitamin B12 by absorbing it through its surface, causing megaloblastic anaemia in up to 2 percent of carriers. Its unembryonated eggs are broadly oval, operculated, and lack true opercular shoulders. Taenia eggs are spherical, thick shelled and radially striated, so they cannot explain the B12 deficiency here.

Reference: Paniker's Textbook of Medical Parasitology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.