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Disease Dilemmas

Temperature, rainfall, relief and water supply as controls on disease

  • 3 things to know
  • Component 03

Overview

Recall questions on why malaria is confined to warm regions and limited by altitude, standing water and heavy rainfall, drought and water-borne disease, schistosomiasis and irrigation schemes, river blindness beside fast rivers, the African meningitis belt and the Harmattan, relief and access to healthcare, humidity, and tropical rainfall patterns.

What you need to know

Answer each one before you reveal it.

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Key term

Why is malaria largely confined to warm regions?

Key term

How does altitude limit the distribution of malaria?

Key term

Why is standing water essential to mosquito-borne disease?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why is malaria largely confined to warm regions?

    Model answer

    The Plasmodium parasite can only complete its development inside the mosquito where temperatures stay above about 18°C, so transmission fails in cooler places.

  2. 2

    How does altitude limit the distribution of malaria?

    Model answer

    Temperature falls by roughly 6.5°C for every 1,000 m of ascent, so land above about 2,000 m is usually too cold for the parasite to develop, which is why highland cities such as Nairobi and Addis Ababa were historically free of malaria.

  3. 3

    Why is standing water essential to mosquito-borne disease?

    Model answer

    Mosquito larvae develop in water, so pools, paddy fields, irrigation ditches and storage containers provide the breeding sites without which the adult population collapses.

  4. 4

    Explain why very heavy rainfall can reduce mosquito numbers in the short term.

    Model answer

    Torrential rain flushes out the small pools in which larvae develop and washes them away, so numbers fall before rising again once the water settles into stagnant pools.

  5. 5

    How does drought increase the risk of water-borne disease?

    Model answer

    As sources dry up people crowd around the few that remain and use contaminated supplies, and there is too little water for washing, so diseases spread by the faecal-oral route and infections such as trachoma increase.

  6. 6

    Which disease is caught from freshwater snails living in slow-moving water?

    Model answer

    Schistosomiasis, also known as bilharzia.

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