Causes of disease

• Define health

  A state of complete physical, mental and social wellbeing (as defined by the WHO)
• Disease


  A disorder of the body or mind that negatively affects an individual’s health
• Communicable disease


  • A disease that is directory passed between individuals

  • Caused by a pathogen
• Pathogen

  A disease-causing organism e.g. virus, fungi, bacteria, protists
• Non-communicable disease 


  • A disease that cannot be transmitted between individuals

  • Generally long lasting with a slow-onset

  • Cause by lifestyle, environmental conditions, genetic mutations etc
• Symptom


  A change experienced by an organism that indicates disease
• Why does having an illness make an individual more likely to contract another disease?

  A disease may weaken an individual’s immune system making them increasingly susceptible to other infections
• Cholera


  • Caused by a bacterium

  • Spread by drinking water or washing in water that has been contaminated with infectious faeces

  • SYMPTOMS —> diarrhoea, vomiting
• How can the incidence of cholera be reduced?

  • Access to clean water

  • Improved sanitation (sewage disposal etc.)
• Describe tuberculosis (TB)

  • Caused by a bacterium

  • It is an airborne bacteria spread by droplet infection

  • SYMPTOMS —> lung damage, chesty cough, wheezing
• How can the transmission of TB be reduced?

  • Improved hygiene (washing hands, sneezing into tissues etc.)

  • Infected individuals should avoid crowded areas

  • Increased ventilation in the individual’s home
• Describe Chalara ash dieback

  • Causes by a fungus that infects ash trees

  • Spread via airbourne spores which are carried by the wind

  • Causes dark lesions on bark and blackened leaves which wilt and eventually die
• How can the transmission of chakra ash dieback be reduced?

  • Control the movement of ash trees

  • Kill infected plants

  • Replant with a different species
• Malaria


  • Caused by a protist

  • Spread by mosquito vectors which pick up the protist when feeding on the blood of an infected organism and transmit malaria to other organisms during feeding

  • Flu-like symptoms, damage to red blood cells, liver damage
• How can the incidence of malaria be reduced?

  • Mosquito nets

  • Insect repellant

  • Cover arms and legs
• HIV


  • Caused by human immunodeficiency virus

  • Spread by direct contact with infected bodily fluids e.g. blood, semen, breast milk

  • Destroys white blood cells making the individual immunodeficient and increasingly susceptible to other diseases

  • Leads to AIDS
• How can the spread of HIV be reduced?

  • Use of condoms and protected sex

  • Needle exchange

  • Screening blood for HIV

  • Deterring infected mothers from breastfeeding
• Chlamydia 


  • Caused by a bacterium

  • Spread through sexual contact or direct contact with infected genital fluids

  • Can result in infertility
• How can the transmission of chlamydia be reduced?

  • Use of condoms and protected sex

  • Screening