Causes of disease
What is 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. It has mental, physical and social aspects.
Pathogens are microorganisms that cause disease. 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 recgonisable symptoms in the host. When a pathogen is transferred from one individual to another it is known as transmission.
How do microorganisms get into the body?
Pathogens normally get into the body by penetrating one of the organism's interfaces with the environment. An interface is a surface or boundary linking two systems, in this case linking the external environment with the internal environment of the body. One of these interfaces is the skin. However, as the skin forms a thick, continuous layer…