Skip to content
    • Biologybiology Biology
    • 14-16
    • 16+
    • 55

Infectious diseases - pathogens

  of  10

What are pathogens?

Microorganisms that cause diseases are called pathogens. They are specialised to infect body tissues where they reproduce and cause damage that gives rise to the symptoms of the infection. The body fights back by mobilising its immune system to fight off the infection. Modern medicine has also developed many successful treatments to assist the body's natural defences.

Types of microorganisms

There are four main types of microorganisms:

  • bacteria
  • fungi
  • viruses
  • protozoa

In this resource, you can find out general information about these microorganisms and you can discover examples of diseases that they cause in the diseases resource.

Microorganisms in a water sample from a stream
Courtesy: CDC/ Janice Haney Carr