Disease and the Immune System

• Pathogens

  • Disease-causing microorganisms
• Communicable Diseases

  • Diseases that can be spread between organisms / Disease resulting from infection of a host organism.
• Pathogens (Main 4)

  • Bacteria
  • Fungi
  • Viruses
  • Protoctists
  • Disease caused by pathogens Is a major cause of death worldwide.
• Viruses

  • Human Immunodeficiency Virus (HIV)
  • Influenza
  • Tobacco Mosaic Virus (TMV)
• Fungi

  • Athlete's Foot
  • Ringworm
  • Black Sigatoka
• Bacteria

  • Tuberculosis
  • Bacterial Meningitis
  • Ring Rot
• Protoctista

  • Malaria
  • Late Blights
• Influenza

  • A Virus that Infects Animals, including humans (it does not impact other organisms).
  • There are 4 types of Influenza: A, B, C and D.
  • A-type influenza are the virus that causes pandemics (typically)
  • Transmission is is through water droplets released from the patient, the virus is suspended in the fluid.
• Athlete's Foot

  • Fungi that Infects mostly humans.
  • Transmitted through direct contact with pathogen whilst barefoot.
  • Individuals with diabetes have an increased risk of developing Athlete's Foot (Tinea pedis)
• Tuberculosis

  • Bacteria that Infects Animals.
  • Humans and guinea pigs have a high susceptibility to Tuberculosis.
  • Spread through Airborne means, such as the inhalation of droplets.
• Bacterial Meningitis

  • Bacteria that Infects Animals.
  • Humans have a high susceptibility.
  • Transmitted through direct contact and contact with water droplets.
• HIV

  • Virus that infects humans.
  • Spread through sexual contact and fluid exchange with infected patients (like use of unclean needles).
• Malaria

  • Protoctista that infects animals, including humans.
  • Spread through vector: Female mosquito when it bites.
  • Typically found in tropical environments.
• Ringworm

  • Fungi that infects Animals.
  • Transmitted by direct contact with a pathogen.
• Late Blight

  • Protoctista that infects potato and tomato plants.
  • Spread through contact with spores.
• Black Sigatoka

  • Fungi that infects banana plants.
  • Spread through contact with spores.
• Ring Rot

  • Bacteria that infects potatoes, tomatoes and peppers.
  • Spread through indirect contact, contaminated seed tubers and soil, inects and other vectors.
• Tobacco Mosaic Virus

  • Virus that infects over 350 different plant species.
  • Transmitted by direct contact with the disease.
• Transmission of Diseases

  • Diseases are spread by either direct or indirect contact transmission.
• Direct Contact Transmission

  • Where the disease enters the animal through breaks in the skin, or the plant via breaks in it's exterior.
  • Examples of methods of transmission in animals include: Kissing, fluid exchange, skin-to-skin contact.
• Indirect Contact Transmission

  • Spread of a disease from one organism to another through an intermediate (vector).
• Factors Affecting Transmission

  • Living Conditions
  • Social Factors
  • Climate
• Factors Affecting Transmission - Living Conditions

  • Overcrowded conditions lead to increased contact rate, which causes a higher transmission rate.
• Factors Affecting Transmission - Social Factors

  • Lack of good healthcare systems and education on disease can lead to greater disease transmission.
• Factors Affecting Transmission - Climate

  • Warm and Wet conditions lead to greater cultivation of disease, causing more Transmission.
• Pathogens can enter Organisms:

  • Through the skin.
  • Through the body openings (Like the mouth, open wounds, ureter, etc...).
• Primary Body Defences

  • Skin
  • Mucous Membrane
  • Blood Clotting
  • Inflammation
  • Expulsive Responses
  • Wound Repair
• Primary Defences - Blood Clotting

  • Blood clots occur to prevent blood loss and pathogens entering the body.
  • First, Platelets are attracted to collagen when the skin opens, then, fibrin also covers the platelets by forming a net-like structure, creating a Blood Clot.
• Primary Defence - Inflammatory Response

  • Inflammation of the body causes swelling, release of puss, pain in the swollen area, as well as heat and redness.
  • Inflammation occurs when the skin is broken and a pathogen enters the open wound.
• Inflammatory Response - Process

  • When the skin is broken and a pathogen enters, the pathogen is detected by a mast cell.
  • This causes the release of histamines, which cause the dilation of local arterioles, which allows more blood to the area (Vasodilation).
  • Volume of tissue fluid formed is increased as local capilaries are now leaky, this causes the area to swell and leak puss.
  • Chemokines that are release attract phagocytes to the area, the phagocytes carry out phagocytosis and rids of the pathogens.
• Primary Defences - Skin

  • Acts as both a physical and chemical barrier.
  • The skin produces antimicrobial chemicals that destroy or stunt the growth of microorganisms, typically bacteria.
  • The same chemicals can lower the skin surface pH, which inhibits the pathogen growth.
  • Skin cells secrete fatty acids like theic acid that can kill bacteria and also lower Skin pH.
  • Skin cells also secrete lysozyme, which is an enzyme that catalyses the breakdown of carbohydrates in the cell wall.
• Physical Plant Defences

  • Waxy Cuticle
  • Cell wall
  • Callose Production
• Chemical Plant Defences

  • Insect Repellents
  • Insecticides
  • Antibacterial compounds
  • Saponins
  • Phytolexins
• Plant Defences - Waxy Cuticle

  • Thin surface of a waxy material on Plant Stems and Leaves.
  • This creates a physical barrier plants have to work past.
  • Has hydrophobic qualities, which stops water collecting on the leaves, which reduces infection risk from water-borne pathogens.
• Plant Defences - Cell Wall

  • If pathogens make it past the waxy cuticle, the cell wall acts as an additional physical barrier against pathogens entering and infecting the cells.
• Plant Defences- Callose Production

  • A polysaccharide called callose is produced in the plant and synthesised within minutes of infection.
  • It's then deposited between the cell wall and plasma membrane of cells neighbouring the infected cells.
  • The callose layer acts as a physical barrier to further infection of the cells surrounding the site of infection.
  • Callose is also deposited in the plasmodesmata between infected cells and neighbouring cells, sealing healthy cells off from the infected cells.
• Plant Defences - Insect Repellants

  • Chemicals that released by plants which repel insects from going near the plant or eating it.
  • This prevents the plant's death by consumption but also prevents the transmission of pathogens to the plant by a vector.
  • For example, citronella in lemongrass is used by humans to create outdoor candles that, when burnt, produce aromas that repel insects.
• Plant Defences- Insecticides

  • Chemicals within the plants fruit, and sometimes other parts of the plant that are toxic to insects and fungi.
  • This prevents them being eaten, infection passed by a vector and becoming infected by Fungi.
  • For Example, Caffeine, which is toxic to insects and Fungi.
  • Another Example, is Pyrethrins, which are made by chrysanthemums and act as insect neurotoxins.
• Plant Defences - Antibacterial Compounds

  • Compounds that lay on the waxy cuticle or internal structure of a plant that kill and destroy bacteria.
  • Examples include Phenols and Gossypol.
• Plant Defences- Phenols

  • Antiseptic produced by many different plants.