Serology: 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 · Serology

Sample item

A traveller returns with high fever, retro-orbital pain and myalgia on the second day of illness. Which test is most useful at this stage to confirm dengue?

AIgG ELISA aloneBPaul-Bunnell testCNS1 antigen detection or RT-PCRDWeil-Felix test

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

The answer and the reasoning

C. NS1 antigen detection or RT-PCR

In the first few days of dengue, viraemia is high and NS1 antigen and viral RNA are detectable. IgM antibodies appear around day 5 onward, and IgG appears later (or rapidly in secondary infection), so serology alone is poor in early illness.

Option by option

A. IgG ELISA alone
IgG alone is unreliable early and cannot distinguish past infection.
B. Paul-Bunnell test
The Paul-Bunnell test detects heterophile antibodies of EBV infection.
C. NS1 antigen detection or RT-PCR (correct)
Correct. NS1 antigen and RT-PCR are positive during early viraemia.
D. Weil-Felix test
The Weil-Felix test is for rickettsial disease.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is C, NS1 antigen detection or RT-PCR. In the first few days of dengue, viraemia is high and NS1 antigen and viral RNA are detectable.

Why is "IgG ELISA alone" not the answer?

IgG alone is unreliable early and cannot distinguish past infection.

Why is "Paul-Bunnell test" not the answer?

The Paul-Bunnell test detects heterophile antibodies of EBV infection.

Why is "Weil-Felix test" not the answer?

The Weil-Felix test is for rickettsial disease.

What concept does this question test?

It tests Serology in Microbiology. IgM antibodies appear around day 5 onward, and IgG appears later (or rapidly in secondary infection), so serology alone is poor in early illness.

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 Serology?

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.