A 45-year-old man who eats raw fish regularly develops progressive numbness and tingling of the feet along with pallor. Haemogram shows macro-ovalocytes and hypersegmented neutrophils with low serum vitamin B12. Stool examination reveals broad proglottids and operculated eggs. The cause of his anaemia is:

• A Toxin-mediated suppression of erythropoiesis
• B Chronic occult blood loss from the intestinal mucosa
• C Autoimmune destruction of gastric parietal cells
• D Competitive uptake of vitamin B12 by the worm's absorptive surface ✓

Explanation

Diphyllobothrium latum, the fish tapeworm, is the longest human tapeworm and selectively absorbs vitamin B12 through its tegument, sometimes splitting up to 80 percent of dietary B12, causing megaloblastic anaemia in a minority of carriers. Operculated eggs distinguish it from Taenia species, whose eggs are not operculated. Blood loss causes iron deficiency rather than megaloblastic change, and parietal cell autoimmunity defines pernicious anaemia, unrelated to the tapeworm.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.