In the Garrett-Jones formula for vectorial capacity of a malaria vector, indoor residual spraying (IRS) with a persistent insecticide exerts its greatest effect on which component?

• A Man-biting habit (ma)
• B Duration of sporogony (n)
• C Probability of daily survival of the vector (p) ✓
• D Number of parasites ingested per blood meal

Explanation

Vectorial capacity varies with the square of daily survival probability (p raised to n, divided by minus loge p), making longevity the most sensitive component. IRS kills mosquitoes resting on treated walls after feeding, sharply reducing p even when biting rates remain unchanged. Sporogony duration depends on ambient temperature and biting habit is unaffected by wall spraying.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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