Environmental health: indoor residual spraying: 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 · Environmental health: indoor residual spraying

Sample item

A malaria control programme sprays insecticide on the inner walls of houses once or twice a year. For this to work best, the target vector should show which habit?

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

The answer and the reasoning

C. Resting indoors on walls after a blood meal

Indoor residual spraying kills mosquitoes that rest on treated walls, so it works against endophilic vectors that feed on humans and rest indoors. It has little effect against exophilic mosquitoes that rest outdoors.

Option by option

  • A. Breeding in tree holes

    Tree-hole breeding is relevant to larval control and not to wall spraying.

  • B. Feeding only on animals

    A mosquito that feeds only on animals does not transmit human malaria.

  • C. Resting indoors on walls after a blood meal (correct)

    Correct. Indoor resting on walls brings mosquitoes into contact with the insecticide.

  • D. Biting and resting outdoors only

    Outdoor resting mosquitoes avoid the sprayed surfaces and are not controlled.

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 PSM question

What is the answer to this PSM question?

The best answer is C, Resting indoors on walls after a blood meal. Indoor residual spraying kills mosquitoes that rest on treated walls, so it works against endophilic vectors that feed on humans and rest indoors.

Why is "Breeding in tree holes" not the answer?

Tree-hole breeding is relevant to larval control and not to wall spraying.

Why is "Feeding only on animals" not the answer?

A mosquito that feeds only on animals does not transmit human malaria.

Why is "Biting and resting outdoors only" not the answer?

Outdoor resting mosquitoes avoid the sprayed surfaces and are not controlled.

What concept does this question test?

It tests Environmental health: indoor residual spraying in PSM. It has little effect against exophilic mosquitoes that rest outdoors.

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 Environmental health: indoor residual spraying?

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.