Diseases can be classified as infectious or non-infectious, depending on whether they are caused by a pathogen or not. Pathogens cause infectious diseases and range in size from the smallest sub-microscopic particles (prions) to multicellular organisms:
  • Prions (BSE or mad-cow disease)
  • Viruses (influenza, herpes, chicken-pox)
  • Bacteria (tuberculosis, tetanus, Staphylococcus, Salmonella)
  • Protozoans (malaria, amoebas)
  • Fungus (athlete’s foot, Candida)
  • Worms (tapeworm, nematodes)
  • Ticks and mites


You can find out more about pathogens and the immune system here:
It will also be useful to watch the “Life on Us” program at 8.30pm Sunday nighton SBS One. This two-part series has powerful imagery showing various microscopic pathogens that inhabit the human body – you can watch a shortpromotional video here.