Communicable diseases

• Peptidoglycan

  A structural component of bacterial cell walls
• Cell wall

  Maintains shape and prevents the cell from bursting
• Bacteria share genetic material through plasmids
• Bacteria

  • Can contain plasmids
  • Have pili
  • Have a nucleoid
  • Have a peptidoglycan cell wall
  • 70s ribosomes
  • Flagellum
  • Capsule
  • Can reproduce by binary fission
• Pili

  Hair-like structures that help bacteria attach to surfaces
• Gram positive

  Looks purple/blue under a light microscope (stained with Crystal Violet)
• Gram negative

  Looks red under a light microscope (stained with safranin)
• Shapes of bacteria

  • Coccus
  • Bacillus
  • Vibrio
  • Spirillum
• Bacterial reproduction- binary fission 


  1. Duplication of chromosomes

  2. continued growth of cell

  3. Division into two cells
• One bacterium can divide into two new bacteria every 20 minutes
• One bacterium can divide into two new bacteria every 20 minutes after 4 hours, there would be 4096 bacteria
• Bacterial diseases

  • Tuberculosis (TB)
  • Bacterial meningitis
  • Ring rot
• Tuberculosis (TB)

  Damages lung tissue and suppresses the immune system
• Bacterial meningitis

  Destroys the meninges of the brain
• Ring rot

  Affects potatoes, tomatoes
• There is no cure for ring rot once a field is infected
• Viruses

  Pathogens that invade living cells
• Bacteriophage lytic cycle

  1. Virus attaches to a specific host cell and binds to a receptor

  2. Injects DNA, RNA into host cell

  3. Makes copies of the virus due to viral genes

  4.Host cell splits open, cell membrane bursts
• HIV is an example of a retrovirus
• Retrovirus replication

  • Fusion and entry
  • Reverse transcription- creates DNA from virus RNA
  • Integration- virus genetic information is within hosts DNA
  • Transcription- viral RNA is synthesised by host cell
  • Host cell is able to make new viruses which travel to the hosts membrane to be released
• Viral diseases

  • HIV/AIDS
  • Influenza virus
  • Tobacco Mosaic Virus
• HIV/AIDS

  Targets T-helper cells in the immune system
• Influenza virus

  Infects ciliated epithelial cells in the respiratory system
• Tobacco Mosaic Virus

  Damages leaves, tubers, and fruit in plants. It can also cause stunned growth
• Fungal diseases

  • Cattle ringworm
  • Athlete's foot
  • Black sigatoka
• Cattle ringworm

  Causes a grey-white, crusty, infectious area on the skin
• Athlete's foot

  A fungal infection that causes cracking and scaling of the skin
• Black sigatoka

  Affects banana plants, causing leaves to turn black
• Protoctista diseases

  • Malaria
  • Blight in potatoes/tomatoes
• Malaria

  Caused by Plasmodium, invades red blood cells, the liver and eventually the brain
• Blight in potatoes/tomatoes

  Destroys leaves, tubers, and fruit
• Means of transmission of animal communicable pathogens

  • Direct transmission
  • Indirect transmission
• Direct transmission

  • Direct contact
  • Inoculation
  • Ingestion
• Indirect transmission

  • Fomites
  • Droplet infection
  • Vectors
• Vectors can be animals or water
• Factors that increase the transmission of communicable disease in animals

  • Overcrowded living
  • Poor nutrition
  • Poor sanitation
  • Climate change
  • Compromised immune system (HIV or needing immunosuppressants)
  • Cultural effects
  • Socioeconomic factors
  • Infrastructure
• Non-Specific defence

  • Inflammation
  • Fever
  • Phagocytes
• Inflammation process

  1. Mast cells release histamines and cytokines

  2. Histamines cause blood vessels to dilate and become leaky

  3. Cytokines attract phagocytes

  4. Cytokines raise body temperature
• Fever: cytokines are released. The hypothalamus detects this and increases body temp. Most pathogens reproduce best at 37°C or below.
• Phagocytes

  Cells that engulf and destroy pathogens