A 40-year-old man who frequently eats raw freshwater fish develops paraesthesiae of the feet. Haemogram shows macrocytic anaemia, and serum vitamin B12 is markedly low. Stool examination reveals broad proglottids and operculated eggs with a rosette shaped uterus. What is the mechanism of his anaemia?

• A Competition with the host for absorption of dietary folate
• B Chronic mucosal bleeding at the site of scolex attachment
• C A secreted toxin that suppresses bone marrow erythropoiesis
• D The worm splits the vitamin B12 and intrinsic factor complex and absorbs B12 through its own surface ✓

Explanation

Diphyllobothrium latum, acquired from plerocercoid larvae in raw freshwater fish, grows to many metres with broad craspedote proglottids and produces operculated eggs with a rosette uterus. The worm preferentially occupies the ileum, releases factors that dissociate the vitamin B12 intrinsic factor complex, and takes up B12 across its tegument, causing megaloblastic anaemia that can be severe enough to produce neurological signs. Blood loss is negligible compared with hookworm, ruling out option B.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.