Common infections

Health, disease and the development of medicines · Pathogens and infections · note 2 of 4

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In short

Common infections include cholera, tuberculosis, Chalara ash dieback, malaria and HIV. Cholera is caused by a bacterium and causes diarrhoea, and tuberculosis is caused by a bacterium and causes lung damage. Chalara ash dieback is caused by a fungus and damages ash trees. Malaria is caused by a protist, and HIV is a virus that destroys white blood cells.

Infections you need to know
Disease	Pathogen type	Effect on the host
Cholera	Bacterium	Causes diarrhoea
Tuberculosis	Bacterium	Causes lung damage
Chalara ash dieback	Fungus	Causes leaf loss and bark lesions in ash trees
Malaria	Protist	Causes damage to the blood and liver
HIV	Virus	Destroys white blood cells, leading to the onset of AIDS

Triple only

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

Triple only infections
Disease	Pathogen type	Effect on the host
Stomach ulcers (Helicobacter)	Bacterium	Causes stomach ulcers
Ebola	Virus	Causes haemorrhagic fever

Triple only

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

Haemorrhagic fever means a fever with bleeding.

Written and checked against the Edexcel GCSE Combined Science (1SC0) 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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