Mod 7 - Infectious Diseases

• Infectious Disease

  Diseases that are transmissible from one organism to another and are caused by pathogens
• Pathogens


  Disease causing agents that are living matter, or contain components of living things (DNA), and can be microscopic or macroscopic
• Types of Pathogens

  • Cellular
  • Non-Cellular
• Cellular Pathogens

  • Prokaryotic (bacteria)
  • Eukaryotic (protists, fungi, parasites)
• Non-Cellular Pathogens

  • Contains some proteins and genetic materials (DNA/RNA), requires host to reproduce, specialised by host
• Non-Cellular Pathogens

  • Virus
  • Prions (damaging proteins)
• Bacteria

  Unicellular, cell wall made up of peptidoglycan
• Bacterial Diseases

  • Tuberculosis (caused by Mycobacterium tuberculosis)
  • Golden Staph (caused by Staphylococcus aureus)
• Virus

  Non-cellular, extremely rapid reproduction rate, requires host, consist of nucleic acids and protein coat
• Viral Diseases

  • Covid-19 (caused by SARS-COV-2)
  • Ebola Hemorrhaging Fever (caused by Ebola Virus)
• Fungi

  • Microscopic eukaryotic (unicellular and multicellular), spread through spores (release harmful enzymes), mainly affect plants, usually chronic: because it is slow growing
• Fungal Diseases

  • Ringworm (caused by a range of fungi)
  • Black Spot (plant) (caused by Diplocarpon Rosae)
• Types of Fungal Infection

  • Systemic (deep in body, internal)
  • Cutaneous (skin)
  • Subcutaneous (fatty-tissue beneath skin, very rare)
• Protists

  • Unicellular or colony-forming eukaryotic, live in water/soil, complex life cycles, different locomotion (movement) (cilia, pseudopod, flagellum)
• Protist Diseases

  • Amoebic Dysentery (caused by Entamoeba Histolytica)
  • Malaria (caused by Plasmodium, transmitted by Anopheles Mosquitoes)
• Macroscopic Parasites

  Visible with naked eye, including Helminths (parasitic worms) and Arthropods (insects, fleas, ticks)
• Types of Parasites

  • Ectoparasite (live on organism)
  • Endoparasite (live in organism)
• Prions


  Misfolded proteins that transmit misfolding to healthy proteins and trigger cellular death, change to structure = change in function
• Prion Diseases

  • Kuru (Transmissible Spongiform Encephalopathy (TSE))
  • Mad Cow Disease (Transmissible Spongiform Encephalopathy (TSE))
• Modes of Transmission

  • Direct (person to person, animal to person, mother to unborn-child)
  • Indirect (touching contaminated surface)
  • Vectors (carries the pathogen but not impacted by it)
• Portals of Entry

  • Skin surface
  • Respiratory tract
  • Gastrointestinal tract
  • Urogenital tract
• Epidemic

  Spread rapidly in an area
• Pandemic


  Spread rapidly across countries or the world
• Endemic


  Consistently present in a population with low spread
• Spontaneous Generation Theory (Abiogenesis)


  Living organisms could arise from non-living matter, used to explain how people get sick
• Germ Theory


  Disease is caused by pathogens, germs invade host and cause damage to target tissue, germs are microscopic and hard to identify
• Louis Pasteur

  French microbiologist who discovered principles of vaccinations, pasteurisation and microbial fermentation, used to disprove Spontaneous Generation Theory
• Robert Koch

  German microbiologist who discovered bacteria that causes tuberculosis through postulates
• Koch's Postulates

  • Microorganism must be present in diseased organism and absent in healthy organisms
  • Microorganism must be isolated from diseased organism and grow in pure culture
  • When healthy organism is inoculated, it must develop the same symptoms as the sick organism
  • Isolate and regrow the micro-organism from the new infected organism. If it is identical to the organism cultured, it has been identified as the cause of the disease.
• Sanitisation

  Reduces the number of microorganisms to a safe level
• Sterilisation


  Removes all microorganisms from an item
• Aseptic


  Free from contamination caused by harmful bacteria, viruses, or other microorganisms; surgically sterile or sterilized
• Citrus Canker is a plant disease caused by the bacteria Xanthomonas citri subsp. that affects citrus species and related plants, leading to decreased fruit production and trade bans
• Karnal Bunt of Wheat is a plant disease caused by the fungus Tilletia indica that attacks the flower and wheat kernel, causing quarantine and rejection of grains in international markets
• Flystrike is an animal disease caused by the parasitic fly Lucilia cuprina that lays eggs in damaged sheep wounds, leading to decreased productivity and painful death
• Anthrax is an animal disease caused by the bacteria Bacillus anthracis that can be fatal, with blood tests for identification and antibiotics used in early stages
• Reservoir


  Where an infectious agent lives and grows
• Portal of Exit


  Where the pathogen leaves the reservoir to infect other organisms
• Portal of Entry

  Way that pathogens enter the host
• Susceptible Hosts


  Hosts that are vulnerable to infection