Module 4.1.1- Communicable diseases, disease prevention and the immune system

• Communicable disease


  a disease that is spread from one host to another caused by pathogens
• Vectors


  An organism that transmits disease by conveying pathogens from one host to another
• 2 ways bacteria can be identified

  by their basic shapes

  by their cell walls
• What colour do gram-positive bacteria and gram-negative bacteria appear under staining respectively


  purple blue (+) and red (-)
• Viruses


  smaller than bacteria and other pathogensinside the genetic material surrounded by a protein invade living cells in order to reproducewhen they invade, the cells are damaged or destroyed in the process of releasing new particles to infect other cells
• Protoctista


  unicellular and multicellular eukaryotic organisms

  may be auto or heterotrophic
• Fungi


  Kingdom composed of heterotrophs; many obtain energy and nutrients from dead organic matter (saprophytes)some are parasitic

  
• Bacteriophage


  A virus that infects bacteria
• How do viruses damage host tissues directly


  virus attaches to host cell

  insertion of viral nucleic acid

  replication of viral nucleic acid

  synthesis of viral protein

  assembly of viral particles

  lysis of host cell, spreading toxic particles to other cells

  
• How can toxins damage host tissues


  break down cell membranes

  damage or inactivate enzymes

  interfere with host cell genetic material
• Example of a plant and animal disease (bacteria)


  Ring rot and Tuberculosis or Bacterial meningitis
• Example of a plant and animal disease (virus)


  Tobacco mosaic virus and HIV/AIDS or Influenza
• Example of a plant and animal disease (fungus)


  Black sigatoka and Ring worm or Athletes foot
• Example of a plant and animal disease (protoctist)


  Potato blight and Malaria
• Direct methods of transmission


  direct contact - kissing, touching etc.

  inoculation - animal bite, break in skin etc.

  ingestion- contaminated food etc.
• Indirect methods of transmission


  fomites- inanimate objects such as socks

  droplet infection- minute droplets of saliva etc.

  vectors
• Factors affecting transmission of communicable diseases in animals

  overcrowded living and working conditions

  poor nutrition

  compromised immune system

  poor disposal of waste

  climate change

  culture and infrastructure

  socioeconomic factors
• Types of vectors


  wind

  water

  animals

  humans
• Factors affecting transmission of communicable diseases in plants


  planting crops susceptible to disease

  overcrowding

  poor mineral nutrition

  damp warm conditions

  climate change
• How do plants recognise an attack


  plant cells recognise molecules produced by pathogens

  when pathogen(ie enzymes) break down the plant cell wall, the breakdown products are recognised

  signalling molecules alert nucleus to attack:

  • polysaccharides (callose and lignin) made to strengthen cell wall)
  • alarm other cells before they are attacked
  • attack pathogen directly

  
• Function of callose


  deposited between cell walls and membranes to prevent pathogen entry

  block sieve plates in phloem sealing infected parts

  deposited in plasmodesmata to prevent spread
• Chemical defences of plants

  
  

  • insect repellents
  • insecticides
  • antibacterial compound
  • antifungal compound
  • anti-oomycetes
  • general toxins
• Non-specific defences animals- skin


  
  

  • covers the body preventing the entry of pathogens
  • has skin flora that outcompete pathogens for space on body surface
  • skin also produces sebum which inhibits pathogen growth
• Non-specific defences animals- mucous membranes


  many of the body tracts are lined by this

  secrete sticky mucus trapping microorganisms and contains lysozymes and phagocytes
• Non specific defences animals- lysozymes


  found in tears, urine and the acid in the stomach

  contains hydrolytic enzymes to break down pathogens
• Blood clotting and wound repair


  cut detected by platelets thromboplastin is released

  serotonin is released clot dries and scabs form epidermal cells below the scab grows sealing wound damaged blood vessels regrowing collagen fibres deposited to give strength scab falls off

  
• Thromboplastin (blood clotting)


  an enzyme that triggers a cascade of reactions resulting in the formation of a blood clot
• Serotonin (blood clotting)


  makes the smooth muscle in the walls of the blood vessels contract, so they narrow and reduce the supply of blood to the area
• Inflammatory response (non specific animal defence)


  localised response to pathogens resulting in inflammation at the site of a wound activating mast cells releasing histamines and cytokines
• Mast cells


  Cells that release chemicals (such as histamine or cytokines) that promote inflammation.
• Histamine role (in inflammation)


  make blood vessels dilate causing localised heat and redness

  temperature raised to prevent pathogens reproducing

  make blood vessel walls leaky so blood plasma is forced out as tissue fluid causing swelling and pain
• Cytokines (in inflammation)


  attract white blood cells (phagocytes) to the site

  they dispose of pathogens by phagocytosis
• Fever (non specific response)


  when pathogen invades body

  cytokines stimulate hypothalamus to increase temperature

  higher temperatures inhibit pathogen reproduction

  specific immune system works faster at higher temperatures
• Why is increasing body temperature good for fighting off pathogens

  higher temperatures inhibit pathogen reproduction

  specific immune system works faster at higher temperatures
• 2 types of phagocytes


  neutrophils and macrophages
• Phagocytosis stages (neutrophil)


  
  

  • Pathogens produce chemical that attracts phagocytes and recognise it as non-self by then binding to it
  • Phagocyte engulfs pathogen to form phagosome
  • Phagosome binds with lysosome to form phagolysosome
  • Lysosome enzymes digest and destroy the pathogen
• Phagocytosis stages (macrophage)


  After lysosome digests the pathogen, it combines antigens from the pathogen surface membrane with the major histocompatibility complex (MHC)

  The MHC complex moves pathogen antigens to the macrophage's surface membrane to become an antigen-presenting cell (APC)
• Antigen-presenting cells (APCs)


  cells such as B cells, macrophages, and dendritic cells that can present exogenous antigens to naive or memory T cells, activating them
• Cytokines


  act as cell-signalling molecules, informing other phagocytes that the body is under attack and stimulating them to move to the site of infection or inflammation
• Opsonins


  chemicals that bind to pathogens and tag them so they are recognised more easily by phagocytes, e.g. antibodies.