Causes of Disease
- What are pathogens?
- How do pathogens enter the body?
- How do pathogens cause disease?
Pathogens are microorganisms (general term for a single-celled organisms that is too small to see without the use of a microscope) that cause disease. Disease is not a single thing but rather a description of certain symptoms, either physical or mental (or both). Disease suggests a malfunction of body or mind which has an adverse effect on good health.
For a microorganism to be considered a pathogen it must:
- gain entry to the host
- colonise the tissues of the host
- resist the defences of the host
- cause damage to the host tissues.
Pathogens include bacteria, viruses and fungi. If a pathogen gets into the host and colonises its tissue an infection results. Disease occurs when an infection leads to recognisable symptoms in the host. When a pathogen is transferred from one individual to another it is known as transmission.
A microorganism normally gets into the body by penetrating one of the organisms' interfaces (a surface or boundary linking…