Causes of Disease

What is disease?

• A disease is defined as a physical or mental disorder or malfunction with a characteristic set of signs or symptoms.
• Diseases may be caused by a single factor such as a pathogenic microorganism or be multifactorial and have many causes some of which may depend on lifestyle.

Pathogens

• Pathogenic microorganisms include bacteria, viruses and fungi.
• Each pathogen has a specific method by which it causes disease.  Some such as the influenza virus damage host cells whereas others, such as Vibrio cholera produce toxins which have a harmful effect on the body.
• The ability of the pathogen to cause disease depends on
  • Location - what tissue is colonised
  • Infectivity - how easily a bacterium can enter the host cell
  • Invasiveness - how easily a bacterium or its toxin spreads within the body
  • Pathogenicity - how a bacterium causes disease
• Common entry points for pathogens are the gas exchange and digestive system.

Lifestyle

• A healthy lifestyle involves:
  • Maintaining a healthy weight
  • Taking regular exercise
  • Eating a balanced diet
  • Drinking a limited amount of alcohol
  • Not smoking
• Lifestyle has an effect on human health:
  • Exposure to carcinogenic chemicals (i.e. those found in tobacco smoke) or radiation (i.e. X-rays) may increase a person's chance of contracting cancer
  • Coronary heart disease is associated with diets that are rich in fat and a sedentary lifestyle
  • Alterations to a person’s lifestyle can have a dramatic effect on the likelihood of them contracting these conditions