How pathogens spread and how to control them

Health, disease and the development of medicines · Pathogens and infections · note 3 of 5

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In short

Pathogens spread in different ways, and spread is reduced by blocking each route. Cholera spreads in contaminated water, so clean water is provided. Tuberculosis is airborne, so infected people are isolated. Chalara ash dieback spreads by airborne spores, so infected trees are destroyed. Malaria is carried by a mosquito vector, so mosquito nets are used.

To explain how to reduce the spread of a disease, first state how it is spread, then say how that route can be blocked.

Spread and control of named diseases
Disease	How it spreads	How spread can be reduced or prevented
Cholera (bacteria)	In water contaminated with sewage containing the bacteria	Provide clean drinking water; treat sewage; wash hands and cook food thoroughly
Tuberculosis (bacteria)	Airborne: droplets from coughs and sneezes	Isolate infected people; cover the mouth when coughing; good ventilation; vaccination
Chalara ash dieback (fungi)	Airborne spores carried by the wind	Destroy infected trees; restrict movement and import of ash plants
Malaria (protists)	By an animal vector: the mosquito, which carries the protist from person to person	Control mosquitoes (drain standing water, use insecticides); mosquito nets; insect repellent

Triple only

Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean

Spread and control of Triple only diseases
Disease	How it spreads	How spread can be reduced or prevented
Stomach ulcers, Helicobacter (bacteria)	Oral transmission: swallowing the bacteria in food, water or from saliva	Good hygiene; handwashing; clean water and food preparation
Ebola (virus)	Contact with infected body fluids	Isolate patients; wear protective clothing; avoid contact with body fluids, including safe handling of bodies

A vector is an organism that carries a pathogen from one host to another without usually being harmed itself. The malaria vector is the mosquito. Killing or avoiding the vector breaks the chain.

Common mistake:

Mosquitoes do not cause malaria. The protist causes it. The mosquito is only the vector that carries the protist.

Cycle diagram of malaria spread: an infected person has protists in the blood, a mosquito bites and takes up protists, the mosquito bites a healthy person and passes on the protists, and that person develops malaria; the protist is the pathogen and the mosquito is the vector. — The mosquito is the vector: it carries the malaria protist from one person to the next.

Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026

Frequently asked questions

How do pathogens spread?

Pathogens spread in several ways: in contaminated water, like cholera; through the air in droplets or spores, like tuberculosis and Chalara ash dieback; by an animal vector, like the mosquito carrying malaria; and by sexual contact, like chlamydia and HIV. To reduce the spread, identify the route and then block it.

What is the difference between bacteria and viruses?

Bacteria are single-celled organisms with no nucleus, while viruses are not cells at all. Viruses are much smaller than bacteria and can only reproduce inside a host cell. Examples are the cholera bacterium and HIV. This is why antibiotics, which inhibit cell processes in bacteria, do not work on viruses.

How can the spread of malaria be reduced?

The spread of malaria can be reduced by controlling its vector, the mosquito, which carries the malaria protist from person to person. Draining standing water and using insecticides kill mosquitoes, while mosquito nets and insect repellent stop people being bitten. Mosquitoes do not cause malaria; the protist does.

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