12. Communicable Disease

• Communicable disease

  A disease that can spread between organisms.
• Host


  The organisms in which the pathogen lives.
• Vector


  Carries and spreads pathogens.
• Pathogen

  A microorganism that causes disease.
• What does the pathogen gain?

  Nutrients, shelter, and the ability to reproduce.
• What happens to a host infected with a pathogen?

  It has nutrition taken from it.

  Damage is also caused, which can be considerable.
• Mutualistic


  Both organisms benefit.
• Commensal


  Where one species of organism lives harmlessly in or on the obdy of a larger species.
• Parasitic


  Only benefits the parasite.
• Types of pathogen:

  1. Bacteria
  2. Virus
  3. Fungi
  4. Protoctista/Protozoa
• All pathogens are parasites. Some become pathogenic if there are changes to the host’s health or if the infect an unnatural host.
• Direct contact between animals

  • Exchange of bodily fluids
  • Skin to skin contact
  • Microorganisms from faces to hands
• Inoculation

  • Through a break in the skin
  • Animal bites
  • Puncture wounds or shared needles
• Ingestion

  • Contaminated food or water.
• Direct transmission

  Direct contact; inoculation; ingestion
• Physical barriers are the physical characteristics of the body that prevent pathogens from entering.
• Examples of physical barriers in plants

  Cellulose cell walls; lignin thickening of cell walls; waxy cuticle; bark; stomatal closure.
• Cellulose cell wall

  Acts as a physical barrier and can contain a variety of chemical defences that can be activated when a pathogen is detected.
• Lignin thickening of cell walls

  Compound that is waterproof and almost completely indigestible.
• Waxy cuticle

  Prevents water collecting on the cell surfaces.
• Bark


  Most contain a variety of chemical defences that work against pathogenic organisms.
• Stomatal closure

  Controlled by guard cells which will close the stomata when pathogens are detected.
• Tuberculosis


  Bacterium; affects animals, typically humans and cattle.
• Bacterial meningitis


  Bacteria; humans
• Ring rot


  Bacteria; potatoes, tomatoes
• HIV/AIDS


  Virus; humans
• Influenza


  Virus; animals, including humans
• Tobacco mosaic virus


  Virus; Plants
• Black sigatoka


  Fungus; banana plants
• Ringworm


  Fungus; cattle
• Athlete's foot


  Fungus; humans
• Potato/potato blight


  Protozoa; potatoes/tomatoes
• Malaria


  Protozoa; animals, including humans
• Inoculation


  Through breaks in the skin.
• Fomites


  Inanimate object which can transfer pathogens.
• Vecotrs


  Transmits communicable pathogens from one host to another.
• Overcrowded living conditions increase the transmission of many communicable diseases.
• Climate can also affect the spread of communicable diseases as it can affect the availability of clean water and food and can increase frequency of conditions in which pathogens are easily spread.
• Social factors like healthcare and education also affect the transmission of disease.
• Skin


  Acts as a physical barrier, blocking pathogens from entering the body. It also acts as a chemical barrier by producing antimicrobial chemicals and can lower pH.