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Diseases and Immunity: Question 7

Syllabus 10.1

Structured Core 8 marks

A village has no sewage treatment system. Untreated waste from village toilets flows directly into the river, and this same river is also used by villagers as a source of drinking water and for washing food before it is cooked. Many villagers also prepare and sell food from open stalls beside the river, without any handwashing facilities nearby. Over one month, a large number of villagers become ill with a disease that causes vomiting and diarrhoea.

(a) Explain why allowing untreated sewage to enter the river that is also used for drinking water increases the risk of this disease spreading through the village. [2]

(b) State three measures, other than sewage treatment, that could be introduced in the village to help control the spread of this disease, and for each one explain how it helps to reduce transmission. [6]

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Worked solution

Part (a): Why untreated sewage in the drinking-water river increases risk

The disease is transmissible, meaning its pathogen can pass from one host to another. Untreated sewage from infected villagers’ toilets carries this pathogen, and because the sewage flows straight into the river without being treated, the pathogen is not removed before it reaches the water.

Since the same river is used as a source of drinking water, every villager who drinks from it, or uses it to wash food, risks swallowing water contaminated with the pathogen. Because so many people rely on this one water source, a single source of contamination can lead to a large number of people becoming infected. This is indirect transmission, by way of the contaminated river, rather than contact between infected people themselves.

Part (b): Three further measures to control the spread of the disease

  • A clean, treated water supply: treating the village’s drinking water (for example, by filtering or disinfecting it) before villagers drink it would remove or kill the pathogen, so people would no longer be swallowing it in their water.
  • Hygienic food preparation: washing food in clean water, keeping it covered, and cooking it thoroughly before it is sold would kill or remove any pathogen that had contaminated the food, stopping it being passed on to the people who eat it.
  • Good personal hygiene: encouraging villagers, especially those preparing or selling food, to wash their hands thoroughly with clean water after using the toilet and before handling food would stop the pathogen being carried from a person’s hands onto food or surfaces that other villagers then touch or eat.

Any three of these measures, properly explained, would be creditable; other reasonable community-level measures (such as improved waste disposal to keep sewage away from the river in the first place) would also be acceptable.

Final answers

  • (a) Untreated sewage carries the pathogen into the same river used for drinking water, so drinking or using this contaminated water spreads the pathogen to many villagers at once (indirect transmission via the river).
  • (b) Clean water supply (removes the pathogen from drinking water), hygienic food preparation (prevents contaminated food spreading the pathogen), good personal hygiene (stops the pathogen being carried on hands onto food or surfaces).