Pathogens and communicable diseases
What is a pathogen?
A is a microorganism that causes infectious disease. Diseases caused by pathogens are — they can be passed from one person, animal or plant to another. Pathogens can infect both plants and animals.
There are four main types of pathogen:
Key terms
How bacteria and viruses make us ill
are small cells that can reproduce very rapidly inside the body. Some produce poisons called , which damage tissues and make us feel ill.
are much smaller than bacteria and are not cells. They live and reproduce inside cells, and this causes cell damage — often the cell bursts, releasing new viruses to infect more cells.
are single-celled eukaryotes, and can be single-celled or made of thread-like hyphae that spread through tissue.
Key terms
How pathogens spread
Pathogens can be spread in three main ways:
- Direct contact — touching an infected person, animal or plant, or sexual contact (e.g. gonorrhoea, TMV).
- Water — drinking or eating contaminated water or food (e.g. salmonella).
- Air — breathing in droplets from coughs and sneezes (e.g. measles).
Some pathogens are carried by a — an organism, such as a mosquito, that transfers a pathogen from one host to another without getting the disease itself.
Key terms
Preventing the spread of disease
The spread of communicable disease can be reduced or prevented by:
- Being hygienic — washing hands, disinfecting surfaces and preparing food carefully.
- — e.g. using insecticides or draining standing water where mosquitoes breed.
- — so they cannot pass the pathogen on.
- — so people cannot develop the infection and pass it on.