Infectious diseases - 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 systemimmune system
The body's natural defence mechanism against infectious diseases.  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:

• bacteriabacteria
  Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus.
• fungi
• viruses
• protozoaprotozoa
  Protozoa are one-celled animals

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.