Parasitology: malaria diagnosis: practice question

A Microbiology 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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Microbiology · Parasitology: malaria diagnosis

Sample item

A man treated for falciparum malaria 3 weeks ago is asymptomatic. A rapid test based on HRP-2 is positive, but two peripheral blood smears are negative. What is the most likely explanation?

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

The answer and the reasoning

A. Persistence of HRP-2 antigen in blood after parasite clearance

Histidine-rich protein 2 is released by Plasmodium falciparum and can persist for 2 to 4 weeks after parasites have been cleared, so HRP-2 rapid tests may remain positive in a recently treated patient with negative smears. Tests that detect parasite lactate dehydrogenase become negative sooner. Hypnozoites do not circulate and do not give HRP-2.

Option by option

  • A. Persistence of HRP-2 antigen in blood after parasite clearance (correct)

    Correct. Residual HRP-2 antigenaemia can persist for weeks after cure.

  • B. Treatment failure with sequestered adult parasites

    An asymptomatic patient with negative smears does not suggest treatment failure.

  • C. Cross reaction with dengue antibodies

    HRP-2 tests are not known to cross-react with dengue antibodies.

  • D. Co-infection with Plasmodium vivax hypnozoites

    Hypnozoites are liver forms and do not release HRP-2 into blood.

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.

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Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is A, Persistence of HRP-2 antigen in blood after parasite clearance. Histidine-rich protein 2 is released by Plasmodium falciparum and can persist for 2 to 4 weeks after parasites have been cleared, so HRP-2 rapid tests may remain positive in a recently treated patient with negative smears.

Why is "Treatment failure with sequestered adult parasites" not the answer?

An asymptomatic patient with negative smears does not suggest treatment failure.

Why is "Cross reaction with dengue antibodies" not the answer?

HRP-2 tests are not known to cross-react with dengue antibodies.

Why is "Co-infection with Plasmodium vivax hypnozoites" not the answer?

Hypnozoites are liver forms and do not release HRP-2 into blood.

What concept does this question test?

It tests Parasitology: malaria diagnosis in Microbiology. Tests that detect parasite lactate dehydrogenase become negative sooner. Hypnozoites do not circulate and do not give HRP-2.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Parasitology: malaria diagnosis?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.