Response to Infections

• Pathogens


  Disease-causing organisms
• Communicable/infectious/transmissible diseases


  Diseases spread from one person to another
• Human body's defences


  • Prevent pathogens from entering the body
  • Deal with pathogens before they can cause symptoms
  • Enable recovery without medical intervention
• Common pathogens affecting the human body


  • Bacteria
  • Viruses
  • Fungi
  • Animal parasites
• The great majority of bacteria are harmless to humans; they are non-pathogenic
• Bacteria's role


  • Decomposition of organic material
  • Cycling of the elements
  • Used in industrial processes
• Bacteria used in industrial processes


  • Lactobacilli used to make yoghurt and sauerkraut
  • Bacteria used in cheese production
• Huge numbers of bacteria live on our skin, in our alimentary canal and in other parts of the body
• Bacteria have no ill effect on our health, yet there are others that may cause illness or death when present in relatively small numbers
• Bacteria's effects on the body


  • Producing toxins
  • Inducing an allergic response
• Viruses


  • 20 to 750nm in size
  • Too small to be seen with an ordinary light microscope
  • Discovered in 1938 using an electron microscope
  • Contain genetic material in the form of DNA or RNA, but never both
  • Surrounded by a coat of protein
  • Some have an external lipid envelope
• Viruses


  • Not living things
  • Infect a living cell and its DNA or RNA induces the cell to manufacture more virus particles
  • New virus particles leave the host cell to infect others
  • During this process the cells become damaged or changed, or die
• Bacteriophages


  Viruses that multiply in bacterial cells, causing the death of the bacterium