Vitamins and minerals: fish tapeworm and cobalamin: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Vitamins and minerals: fish tapeworm and cobalamin

Sample item

A man from a lakeside community who regularly eats raw freshwater fish has macrocytic anaemia, low serum cobalamin and normal folate. Stool shows operculated eggs. How is the vitamin deficiency produced?

AFolate is trapped as methyltetrahydrofolateBBacteria in a blind loop consume the vitaminCAutoantibodies destroy intrinsic factorDThe worm takes up cobalamin in the gut lumen

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. The worm takes up cobalamin in the gut lumen

The broad fish tapeworm, Diphyllobothrium latum, absorbs dietary cobalamin in the lumen before the host can bind it to intrinsic factor. Treatment with praziquantel removes the worm and the vitamin is then replaced. Folate is normal, which argues against a primary folate defect.

Option by option

A. Folate is trapped as methyltetrahydrofolate
Methyl-folate trapping is a consequence of cobalamin lack, and folate is normal here.
B. Bacteria in a blind loop consume the vitamin
Blind-loop bacterial overgrowth also lowers cobalamin but follows surgical or motility disorders, not fish and eggs.
C. Autoantibodies destroy intrinsic factor
Autoimmune loss of intrinsic factor causes pernicious anaemia, which is not suggested by eggs in the stool.
D. The worm takes up cobalamin in the gut lumen (correct)
Correct. The parasite competes for luminal cobalamin and starves the host.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, The worm takes up cobalamin in the gut lumen. The broad fish tapeworm, Diphyllobothrium latum, absorbs dietary cobalamin in the lumen before the host can bind it to intrinsic factor.

Why is "Folate is trapped as methyltetrahydrofolate" not the answer?

Methyl-folate trapping is a consequence of cobalamin lack, and folate is normal here.

Why is "Bacteria in a blind loop consume the vitamin" not the answer?

Blind-loop bacterial overgrowth also lowers cobalamin but follows surgical or motility disorders, not fish and eggs.

Why is "Autoantibodies destroy intrinsic factor" not the answer?

Autoimmune loss of intrinsic factor causes pernicious anaemia, which is not suggested by eggs in the stool.

What concept does this question test?

It tests Vitamins and minerals: fish tapeworm and cobalamin in Biochemistry. Treatment with praziquantel removes the worm and the vitamin is then replaced. Folate is normal, which argues against a primary folate defect.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Vitamins and minerals: fish tapeworm and cobalamin?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.