NORCET -3 (Shift-2): Spraying kerosene on stagnant water shall kill Anopheles due to

NORCET -3 (Shift-2)

Community Health Nursing

Medium

Appeared in: NORCET -3 (Shift-2)

Explanation

Kerosene, a mineral oil, spreads as a thin film on the water surface when applied.
Mosquito larvae and pupae are aquatic but need to breathe atmospheric air from the surface through their spiracles.
The oil film creates a physical barrier that prevents the spiracles from making contact with the air.
This blockage of air supply leads to suffocation (asphyxiation) and death of the larvae and pupae.

Option B: The primary action is blocking access to air at the water's surface, not entering and physically blocking the internal respiratory tract. The barrier is external.
Option C: While oil may have some toxic properties, the main and most rapid cause of death is suffocation. Death occurs too quickly for diffusion and systemic toxicity to be the primary mechanism.
Option D: Kerosene does not 'burn' the body wall of the larvae in this context. It acts as a physical agent to cause suffocation, not as a corrosive or thermal agent.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Vector control methods, specifically the mechanism of anti-larval measures for mosquitoes as background academic context rather than a clinical decision trigger.
Understanding this mechanism is crucial for public health nurses involved in vector-borne disease control programs, such as the National Vector Borne Disease Control Programme (NVBDCP) in India.
Nurses educate communities on simple, effective methods like oiling stagnant water in drains, pits, and coolers to prevent the breeding of mosquitoes that transmit diseases like malaria (Anopheles), dengue (Aedes), and filariasis (Culex).
It is important to advise that oiling should not be done in water sources used for drinking or in ponds with fish, as it contaminates the water and harms aquatic life.

How to Approach the Question

First, identify the core subject of the question: a method of mosquito control (chemical larvicide).
Recall or deduce the life cycle of a mosquito, specifically that the larval stage is aquatic but requires atmospheric air to breathe.
Analyze the properties of kerosene on water: it is less dense and immiscible, so it will form a film on the surface.
Connect these two facts: the oil film on the surface will interfere with the larva's need to access air from the surface.
Evaluate the options based on this understanding. 'Prevention of spiracle to come in contact with air' directly describes this mechanism of suffocation.
Eliminate other options: 'entry into tract' is less precise, 'diffusion' is a secondary effect at best, and 'burning' is biologically incorrect.

Concept Tested & Keywords

Concept Tested: Vector control methods, specifically the mechanism of anti-larval measures for mosquitoes.
Stem keywords: Spraying kerosene, stagnant water, Anopheles, kill
Lead-in keywords: due to
Negative lead-in flag: false

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E6 Parks TextBook of Preventive & Social Medicine part 2 — Subpart B (pp 233-449 of 464) p. 88-90