Communicable diseases: influenza pandemic mechanism: practice question

A PSM 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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PSM · Communicable diseases: influenza pandemic mechanism

Sample item

A new influenza A virus carrying a haemagglutinin subtype to which the human population has no immunity spreads worldwide within months. Which process best explains the origin of such a virus?

AReassortment of gene segments between human and animal strainsBAcquisition of a toxin gene through lysogenic conversionCPhase variation of surface antigens during replicationDAccumulation of point mutations in the haemagglutinin gene

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

The answer and the reasoning

A. Reassortment of gene segments between human and animal strains

Pandemic influenza A strains arise by antigenic shift, a sudden major change caused by reassortment of the segmented genome between viruses of different hosts. Gradual point mutations cause antigenic drift, which explains seasonal epidemics and the need for yearly vaccine updates.

Option by option

A. Reassortment of gene segments between human and animal strains (correct)
Correct. Reassortment of segments produces a novel subtype and underlies pandemics.
B. Acquisition of a toxin gene through lysogenic conversion
Lysogenic conversion is a bacteriophage mechanism, as in toxin production by Corynebacterium diphtheriae.
C. Phase variation of surface antigens during replication
Phase variation is a bacterial mechanism, for example in Salmonella flagella.
D. Accumulation of point mutations in the haemagglutinin gene
Point mutations produce antigenic drift, which causes seasonal epidemics rather than pandemics.

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 PSM question

What is the answer to this PSM question?

The best answer is A, Reassortment of gene segments between human and animal strains. Pandemic influenza A strains arise by antigenic shift, a sudden major change caused by reassortment of the segmented genome between viruses of different hosts.

Why is "Acquisition of a toxin gene through lysogenic conversion" not the answer?

Lysogenic conversion is a bacteriophage mechanism, as in toxin production by Corynebacterium diphtheriae.

Why is "Phase variation of surface antigens during replication" not the answer?

Phase variation is a bacterial mechanism, for example in Salmonella flagella.

Why is "Accumulation of point mutations in the haemagglutinin gene" not the answer?

Point mutations produce antigenic drift, which causes seasonal epidemics rather than pandemics.

What concept does this question test?

It tests Communicable diseases: influenza pandemic mechanism in PSM. Gradual point mutations cause antigenic drift, which explains seasonal epidemics and the need for yearly vaccine updates.

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 Communicable diseases: influenza pandemic mechanism?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM 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.