4.1.1 - communicable diseases

• The four groups of pathogen that can cause communicable diseases are:

  bacteria

  fungi

  protoctista

  viruses
• Tuberculosis is a bacterial disease that affects parts of the body and mainly the lungs.

  Caused by bacteria mycobacterium
• Baacterial meningitis is a bacterial disease that affects the Brain and nerves. Causes fever, cold sweat, rash, severe muscle pain.

  Caused by bacteria streptococcus pneumonia
• The three bacterial diseases are:

  meningitis

  tuberculosis

  ring rot
• The three viral diseases are:

  HIV / aids

  influenza

  tobacco mosaic virus
• The three fungal diseases are:

  athletes foot

  black Sigatoka

  ringworm
• The two protoctista are:

  malaria

  tomato late blight
• Ring rot is a bacterial disease in plants that causes decay in the vascular tissue, and a leaf wilting
• HIV is a viral disease that attacks cells in the immune system and compromises the immune response
• Influenza is a viral disease that attacks the respiratory system and causes muscle pains and headaches
• Tobacco mosaic virus is a viral disease that causes discolouration of leaves
• Black sigatoka is a fungal disease that causes leaf Spots on banana plants
• ringworm is a fungal disease that causes growth of fungus in skin with spores erupting to cause a rash
• Athletes foot is a fungal disease that causes growth under skin of feet and between the toes
• Tomato late blight is a protoctista that affects leaves and potato tubers
• Pathogens can be transmitted directly by

  inhalation (droplet infection)

  skin to skin contact or exchange of fluids

  penetrate skin actively using enzymes or through wounds.
• Direct transmission is passing a pathogen from host to new host with no intermediary
• Indirect transmission is passing a pathogen from host to new host via a vector
• Malaria is a protoctist disease that is a parasite in the blood that causes headaches, fever and may progress to a coma and death
• Pathogens can be transmitted indirectly by

  consumption of contaminated food and drink

  via a vector

  spores
• Lifestyle and living conditions can affect disease transmission:

  overcrowding increases direct transmission

  climate determines which organisms can survive

  social factors influence how quickly people are treated which can increase/decrease transmission
• Lifestyle factors that affect direct transmission include:

  Overcrowding

  poor ventilation

  poor health

  poor diet

  homelessness
• Indirect transmission involves fomites - inanimate objects that can transfer pathogens
• plant pathogens can be transmitted directly when pathogens are present in the soil and will infect plants by entering the roots
• Many fungi produce spores that may be carried by the wind for airborne transmission
• pathogens in leaves are distributed when the leaves are shed and carry the pathogen back to the soil
• Indirect transmission of plant pathogens occurs as a result of insect attack. Spores or bacteria become attached to a burrowing insect which has attacked an infected plant and then goes on to infected a healthy plant.
• Indirect transmission in plants is affected by

  wind

  water

  animals

  humans
• 4 physical barriers to pathogen entry in plants

  cellulose cell walls

  lignified layer

  waxy upper cuticle

  callose
• Two mechanical responses to infection in plants:

  guard cells close stomata

  callose is deposited between cell wall and membrane of plant cells
• Necrosis is when injury activates intracellular enzymes in plants that kill cells near site of infection to prevent pathogen from spreading.
• Necrosis of woody tissue is known as canker
• Some of the chemical defences plants use against pathogens are

  terpenoids

  phenols

  alkaloids

  defensins

  hydrolytic enzymes
• Terpenoids are essential oils that act as antibacterial
• Phenols inhibit insects from attacking by interfering with digestion
• Alkaloids are natural defences that deter herbivores because they taste bitter eg, caffeine
• defensins inhibit transport channels
• Hydrolytic enzymes break down cell wall of invading organisms eg, chitinases
• Five barriers to infection in animals are:

  skin

  blood clotting

  hydrochloric acid

  harmless bacteria

  mucous membranes
• The skin is a tough keratin layer