10.1.2Diseases and Immunity
Controlling the Spread of Disease — Cambridge IGCSE Co-ordinated Sciences 0654 - Biology Revision Notes & Topical Questions
5 min read 6 parts Lesson 3 of 7
Part 1 of 4The principle
Stop the pathogen reaching a host
- Stop the pathogen reaching a host The simplest way to avoid disease is to prevent pathogens from spreading in the first place.
- Hygiene and sanitation reduce the numbers of pathogens in water, food and the environment, and so contain them and dispose of them safely.
Why this works
- Why this works If pathogens cannot get from one host to the next, the chain of infection is broken even without any medical treatment.
Part 2 of 4Control measures and why they work
| Measure | What it involves | Why it helps |
|---|---|---|
| Clean water supply | Treating and filtering drinking water | Water free of pathogens prevents waterborne diseases such as cholera. |
| Hygienic food preparation | Washing hands with soap, cooking food thoroughly, keeping raw and cooked food apart | Prevents contamination of food with harmful bacteria and fungi. |
| Personal hygiene | Washing hands, using tissues for coughs and sneezes and binning them | Reduces the spread of diseases such as colds and influenza. |
| Waste disposal | Removing and treating household and food waste | Reduces pests such as flies, which can act as vectors. |
| Sewage treatment | Treating sewage before releasing it | Removes pathogens so rivers and drinking supplies are not contaminated. |
Part 3 of 4Breaking the chain
1Source of pathogens
- Source of pathogens An infected person or animal releases pathogens in faeces, droplets or body fluids.
2Route of transfer
- Route of transfer The pathogens travel through water, food, air or a vector.
3Measures block the route
- Measures block the route Sewage treatment, clean water, hygiene and waste disposal stop the pathogens from being carried.
4Fewer infections
- Fewer infections Fewer people become infected, so outbreaks are smaller or do not start.
Part 4 of 4Examples to remember
Spread controlled
Cholera
- Cholera A disease spread by water contaminated with sewage;
- controlled by sewage treatment and clean drinking water.
Colds and flu
- Colds and flu Spread by droplets; reduced by tissues and handwashing.
Food poisoning
- Food poisoning Reduced by cooking food thoroughly and preventing contact between raw meat and other foods.
Key terms
| Term | Meaning |
|---|---|
| Hygiene | Practices such as handwashing that keep people and food free of pathogens. |
| Sanitation | Systems for safe removal and treatment of sewage and waste. |
| Vector | An organism, such as a fly, that carries pathogens from one host to another. |
| Waterborne disease | A disease, such as cholera, spread through contaminated water. |
| Contamination | Presence of harmful microorganisms in food, water or on surfaces. |
Avoid these mistakes
1
Saying that these measures kill all pathogens. They reduce the numbers and stop transfer.
2
Naming a measure without explaining why it helps. Always state what it prevents.
3
Confusing prevention of spread with treatment. Handwashing prevents infection; antibiotics treat it.
4
Writing that flies cause cholera. Flies can carry pathogens, but the disease is caused by a bacterium.
5
Forgetting that sewage treatment protects both drinking water and rivers.
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