Virus detection: interference: 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 · Virus detection: interference

Sample item

Rubella virus from a throat swab is inoculated into African green monkey kidney cells, and no cytopathic effect appears. When ECHO 11 virus is added, the cells are also unaffected, whereas control cells without rubella show destruction. Which phenomenon allows rubella detection here?

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

The answer and the reasoning

C. Viral interference

Rubella virus often grows without cytopathic effect, but cells infected with it resist superinfection by a challenge virus such as ECHO 11 because of interference. Protection against the challenge virus, therefore, shows indirectly that rubella is present. Interferon and receptor competition may mediate the effect.

Option by option

  • A. Complementation

    Complementation involves one virus supplying a missing function to a defective virus.

  • B. Haemadsorption

    Haemadsorption relies on red cells sticking to infected cells, not on resistance to a challenge virus.

  • C. Viral interference (correct)

    Correct. Resistance to the challenge virus reveals the non-cytopathic virus.

  • D. Phenotypic mixing

    Phenotypic mixing involves envelope or capsid swapping in dual infection.

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 C, Viral interference. Rubella virus often grows without cytopathic effect, but cells infected with it resist superinfection by a challenge virus such as ECHO 11 because of interference.

Why is "Complementation" not the answer?

Complementation involves one virus supplying a missing function to a defective virus.

Why is "Haemadsorption" not the answer?

Haemadsorption relies on red cells sticking to infected cells, not on resistance to a challenge virus.

Why is "Phenotypic mixing" not the answer?

Phenotypic mixing involves envelope or capsid swapping in dual infection.

What concept does this question test?

It tests Virus detection: interference in Microbiology. Protection against the challenge virus, therefore, shows indirectly that rubella is present. Interferon and receptor competition may mediate the effect.

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 Virus detection: interference?

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.