Video

• Communicable diseases are caused by pathogens including bacteria, viruses, protoctista, and fungi
• Pathogens cause harm by directly damaging tissue or releasing toxins
• Examples of diseases caused by different pathogens

  • Bacterial diseases
  • Viral diseases
  • Protoctista diseases
  • Fungal diseases
• Prokaryotic cells


  Classified by shape or cell wall
• Shapes of prokaryotic cells

  • Rods
  • Spherical
  • Comma
  • Spiraled
  • Corkscrew
• Gram-positive and gram-negative bacteria

  Determined by cell wall type
• Tuberculosis


  • Caused by Mycobacterium tuberculosis or Mycobacterium bovis
  • Damages lung tissue and suppresses immune system
  • Can be cured with antibiotics
  • Can be prevented through vaccination
• Bacterial meningitis


  • Caused by Streptococcus pneumoniae or Neisseria meningitidis
  • Infects the meninges (protective layers around the brain)
  • Very serious, spreads quickly causing septicemia
  • Can be cured with antibiotics if diagnosed early
  • Some forms can be vaccinated against
• Ring rot


  • Caused by Clavibacter michiganensis
  • Infects potatoes, tomatoes, and aubergines
  • Gram-positive bacteria that damages leaves, tubers, and fruit
• Viruses

  • Non-living, acellular, smaller than bacteria, consist of genetic material, capsid, and attachment proteins
  • Can only replicate inside host cells
• Bacteriophages


  Viruses that infect bacteria
• HIV


  • Consists of capsid, core with RNA and reverse transcriptase, envelope with lipids from host, and attachment proteins
  • Transported in blood, uses CD4 proteins to attach to helper T cells
  • Reverse transcriptase copies viral RNA into DNA which enters host cell nucleus
  • Destroys helper T cells, leading to AIDS when immune system is compromised
• Influenza


  • Caused by Orthomyxoviridae
  • Infects ciliated cells in gas exchange surfaces
  • Can kill these cells, leading to harmful secondary infections like pneumonia
  • Young, elderly, and immunocompromised are most at risk
• Tobacco mosaic virus


  • Infects tobacco plants, causes damage to leaves resulting in mosaic pattern
  • Affects photosynthesis and plant growth
  • No cure, but resistant plant strains have been developed
• Protoctista


  Eukaryotic, single-celled or colonial organisms, few are pathogenic but very dangerous
• Malaria


  • Caused by Plasmodium protoctista
  • Transmitted by mosquitoes
  • Infects red blood cells and liver in humans
  • No vaccine or cure, but preventative medicines exist
• Potato blight


  • Caused by Phytophthora infestans protoctista
  • Fungus-like protoctista that causes damage to leaves and fruit of potatoes and tomatoes
  • No cure, but resistant plant strains have been developed
• Fungi


  Eukaryotic, mainly cause plant diseases, can be multicellular or single-celled, parasitic
• Black Sigatoka


  • Caused by Mycosphaerella fijiensis fungus
  • Infects banana leaves, prevents photosynthesis and plant growth
  • Fungicides can kill the fungus, resistant strains have been developed
• Ringworm


  • Caused by Trichophyton verrucosum fungus
  • Infects many mammals including humans, causes white crusty circles on skin
  • Not harmful but can cause itching and discomfort
  • Can be cured using antifungal creams
• Athlete's foot


  • Caused by Tineapedis fungus
  • Type of ringworm that infects human feet, especially between toes
  • Causes cracked, scaly, itchy skin
  • Can be cured using antifungal creams
• Factors that increase disease transmission


  • Hot climates
  • Poverty/developing countries
  • Lack of infrastructure (sewage, fresh water, sanitation)
  • Overcrowding
  • Lack of medicines/vaccines
• Modes of disease transmission

  • Direct transmission (contact, inoculation, ingestion)
  • Indirect transmission (vectors, droplets, fomites)
• Plant defenses against pathogens

  • Physical barriers (bark, cuticles)
  • Antibacterial chemicals and proteins
  • Repelling insects (vectors)
  • Physical defenses to prevent spread between cells
• Animal primary defenses against pathogens

  • Skin as physical barrier
  • Skin flora
  • Blood clotting
  • Mucus membranes and ciliated cells
  • Lysozymes
  • Sneezing, coughing, vomiting
  • Inflammation
• Phagocytosis


  1. Pathogens release cell signaling chemicals

  2. Phagocytes attracted to site

  3. Phagocytes bind to and engulf pathogens

  4. Lysosomes fuse with phagosomes to digest pathogens

  5. Phagocytes present pathogen antigens
• Adaptive immune response

  • Involves B cells and T cells
  • B cells mature in bone marrow
  • T cells mature in thymus
  • Receptors bind to specific antigens
  • Rapid cell division to produce clones
• Immune response


  1. Pathogen engulfed and destroyed by phagocyte

  2. Phagocyte becomes antigen presenting cell

  3. T helper cells bind to antigen on antigen presenting cell

  4. T helper cells produce interleukins

  5. T helper cells divide by mitosis (clonal expansion)

  6. T helper cells differentiate into different cell types (T helper, T memory, T killer, T regulator)
• Antigen presenting cells


  Cells that present a non-self antigen on their surface, e.g. infected body cells, phagocytes that have engulfed a pathogen, transplanted organ cells, cancer cells
• T helper cells


  Have receptors that bind to complementary shaped antigens on antigen presenting cells, produce interleukins to activate other immune cells
• T killer cells (cytotoxic T cells)


  Destroy abnormal or infected cells by releasing perforin to create pores in the cell membrane, causing the cell to dry out and die or burst
• Humoral immune response


  1. T helper cells bind to and activate B cells

  2. B cells rapidly divide by mitosis (clonal expansion)

  3. B cells differentiate into memory B cells or plasma cells

  4. Plasma cells produce antibodies
• Antibodies


  Globular quaternary structure proteins with variable regions that bind to specific antigens, can cause agglutination, act as opsonins, or act as antitoxins
• Primary immune response


  First exposure to pathogen, takes days to produce enough antibodies, can get symptoms
• Secondary immune response


  Reinfection with same pathogen, memory B cells rapidly produce antibodies, minimal or no symptoms
• Active immunity


  Immunity gained by being exposed to a pathogen or antigen, either naturally or through vaccination
• Passive immunity


  Temporary immunity gained by direct introduction of antibodies, e.g. from placenta or breast milk
• Cells are labeled with unique proteins to enable self/non-self recognition by the immune system
• Autoimmune disease


  Immune system identifies the body's own cells as non-self and attacks them
• Autoimmune diseases


  • Rheumatoid arthritis
  • Lupus