Parasitology: filariasis 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: filariasis diagnosis

Sample item

A farmer from an endemic area has a hydrocele and swollen leg. A blood smear collected at noon shows no microfilariae. Which test can still demonstrate Wuchereria bancrofti infection during the day?

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

The answer and the reasoning

A. Immunochromatographic card test for circulating filarial antigen

Wuchereria bancrofti microfilariae show nocturnal periodicity, appearing in peripheral blood mainly between about 10 pm and 2 am. The immunochromatographic card test detects circulating adult worm antigen at any time of day, and ultrasound may show the filarial dance sign in scrotal lymphatics. Skin snips are for Onchocerca, and the Casoni test was used for hydatid disease.

Option by option

  • A. Immunochromatographic card test for circulating filarial antigen (correct)

    Correct. The card test detects antigen independent of microfilarial periodicity.

  • B. Casoni test

    The Casoni skin test is an old test for hydatid disease.

  • C. Repeat Giemsa film at midday

    A midday film repeats the sampling error because microfilariae are absent from blood then.

  • D. Skin snip microscopy

    Skin snip is the method for onchocerciasis, not Wuchereria.

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, Immunochromatographic card test for circulating filarial antigen. Wuchereria bancrofti microfilariae show nocturnal periodicity, appearing in peripheral blood mainly between about 10 pm and 2 am.

Why is "Casoni test" not the answer?

The Casoni skin test is an old test for hydatid disease.

Why is "Repeat Giemsa film at midday" not the answer?

A midday film repeats the sampling error because microfilariae are absent from blood then.

Why is "Skin snip microscopy" not the answer?

Skin snip is the method for onchocerciasis, not Wuchereria.

What concept does this question test?

It tests Parasitology: filariasis diagnosis in Microbiology. The immunochromatographic card test detects circulating adult worm antigen at any time of day, and ultrasound may show the filarial dance sign in scrotal lymphatics. Skin snips are for Onchocerca, and the Casoni test was used for hydatid disease.

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 Parasitology: filariasis 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.