Mod 7- T1 Matrix

• Infectious diseases


  Diseases caused by pathogens that enter the body and can be transmitted from one organism to another
• Types of pathogens

  • Bacteria
  • Viruses
  • Fungi
  • Prions
  • Protozoa
  • Macro-parasites
• Bacteria


  • Unicellular prokaryotes that have a cell wall but lack membrane-bound organelles
• Viruses


  • Non-cellular and non-living agents that require a host to reproduce, consist of nucleic acids (DNA or RNA) and a protein coat only
• Fungi


  • Unicellular or multicellular eukaryotes, possesses a cell wall made of chitin
• Prions

  • Misfolded proteins that are non-living and non-cellular
• Protozoa


  • Unicellular eukaryotes that lack a cell wall, macro-parasites: parasites visible to the naked eye
• Prions


  • Mad cow disease, scrapie, CJD
• Viruses


  • AIDS, influenza, measles, smallpox
• Bacteria


  • Tetanus, tuberculosis, syphilis, cholera
• Protozoans

  • African sleeping sickness, malaria
• Fungi


  • Ringworm, Athlete's foot, thrush
• Macro-parasites


  • Tapeworm disease, guinea worm disease
• Spontaneous generation


  Theory that living things could spontaneously generate from non-living matter
• The work of scientists Robert Koch and Louis Pasteur disproved spontaneous generation and replaced it with Germ Theory - that diseases are caused by tiny microbes
• Louis Pasteur


  • Carried out experiments proving that microbes in the air cause contamination in food and are also responsible for causing diseases in humans
• Louis Pasteur's swan-neck flask experiment

  1. Microbes in the air are responsible for food contamination

  2. This led to the process of food pasteurisation to destroy microbes using heat
• Robert Koch


  • Established the link between specific microbes and specific diseases by formulating Koch's Postulates
• Koch's Postulates


  1. The microorganism must be present in diseased organisms and absent in healthy organisms

  2. The microorganisms must be isolated from the diseased organism and grown in pure culture

  3. The cultured microorganism must produce the same disease upon inoculation into a healthy organism

  4. The microorganism must be re-isolated and re-cultured form the inoculated organism, and upon culturing, it should be identical to the original isolated microorganism
• Culturing techniques


  1. Inoculating nutrient agar plates with a sample

  2. Incubating the plates at a constant temperature

  3. Observing and recording the number of microbial colonies after the incubation period

  4. Repeating the experiment at least three times and averaging the results
• Sterile techniques


  • A Bunsen burner should be used to sterilise the inoculating loop and once the plate is inoculated it must remain sealed to prevent the release of harmful pathogens into the environment
• Chain of infection


  Shows how infectious diseases result from interactions between the pathogen, the host and the environment
• Components of the chain of infection

  • Reservoirs
  • Portals of exit
  • Modes of Transmission
  • Portals of Entry
  • Susceptible hosts
• Modes of transmission


  • Direct contact
  • Indirect
  • Vector
• Direct contact transmission


  Physical contact between an infected and a susceptible individual, e.g. hand shaking or coughing directly on someone
• Indirect transmission


  Touching of contaminated objects, airborne transmission (e.g. airborne virus) or animal to person (handling of animal faeces)
• Vector transmission


  Pathogen is transmitted through a bite of an insect e.g. mosquitoes carrying the Plasmodium parasite that causes malaria in humans
• Pathogens can infect almost every part of the human system, and our innate and adaptive immune responses protect us against pathogens
• Pathogens such as bacteria and viruses have developed adaptations to facilitate their entry into and transmission between hosts, such as the use of vectors to bypass the skin barrier
• Bacterial adaptations


  • Formation of a sticky biofilm
  • Production of kinase enzymes
  • Production of toxins
  • Fimbriae appendages
  • Flagellum
• Biotrophic pathogens


  Feed on living plant tissue
• Necrotrophic pathogens


  Produce toxins which kill plant cells before they feed on them
• Plant diseases


  • Oak mildew
• Oak mildew


  • Fungal infection that results in powdery blotches and produces effects like inhibition of photosynthesis and chlorophyll production, blocking of stomata and wilting
• The lack of genetic diversity in crop plants make the entire crop susceptible to a single pathogen, affecting agriculture by reducing crop yield and causing major economic loss
• Animal diseases


  • Mad cow disease
• Mad cow disease


  Caused by prions that damage the cow's central nervous system, can spread amongst animals and on to humans through consumption of infected meat
• Once the disease is detected, all potentially infected cows must be destroyed to prevent further spread, affecting the agricultural industry by causing major economic loss and often resulting in banning of livestock exportation from affected regions