Biology module 7

• prion -> virus -> bacteria -> protists -> fungi -> macroparasites
• PRIONS

  • Protein only (misfolded protein)
  • No nucleic acid
  • Noncellular
  • Infects mammalian brain tissue
  • Reproduce via conformational remodelling (binding and inducing the misfolding of surrounding proteins
  • 1-10 nm
  • e.g. FFI, kuru, scrapie, mad cows disease, cjd
• VIRUSES

  • Noncellular and non-living
  • Contain rna OR dna
  • A strand of nucleic acid surrounded by a protein coat (capsid)
  • 30-300 nm
  • e.g. covid-19, influenza-A, HIV, dhengi fever, human papiloma virus
• BACTERIA

  • Prokaryotic cellular
  • Both nucleic acid
  • Heterotrophic
  • Treated with antibiotics (inhibit metabolic processes)
  • Lack a nucleus (nuclear region is the genophore/nucleoid)
  • 1-10 micrometers
  • e.g. tetanus (clostridium tetani)
• PROTOZOA/PROTISTS

  • Mostly unicellular
  • No cell wall
  • Eukaryotic cellular
  • Have both types of nucleic acids
  • 20-100 micrometers
  • e.g. giardia, malaria, sleeping sickness
• FUNGI

  • Heterotrophic
  • Multiceullar
  • Eukaryotic (with cell wall!)
  • e.g tinea, ringworm, thrush
• MACROPARASITES

  • Endo = lives internally within the host
  • Ecto = lives externally on the host
  • e.g. flatworms, roundworms, hydated cyst disease, head lice, scabies
• PLANT VIRUSES (and viroids)

  • Usually spread throughout the plant (systemic infection)
  • Symptoms: moisaic pattern of chlorosis/necrosis, strikes and streaking, vein clearing, vein banding, colour breaking of fruit, leaf rolling and curling
  • e.g. cauli
• PLANT BACTERIAL

  • Grow in the spaces between ells
  • Requires a would or natural opening to infect
  • Symptoms: galls, wilts, soft rots, scabs, cankers, spots, overgrowths
  • e.g. fire blight of apple, citrus canker
• PLANT FUNGAL

  • Biotrophs (colonise living tissue) or necrotrophs (kill and feed on dead tissue)
  • 80% plant diseases
  • Fungicides are fungal resistant strands of plants
  • Symptoms: evidence of fungal hyphae and spores
  • e.g. late potato blight, scherotina stem rot
• PLANT MACROPARASITES

  • e.g. Nematode worms infect root tissues, citrus leaf miner
• (1) DIRECT CONTACT

  • Infection of a new host via contact with an infected host (person-person transmission)
  • e.g. skin-skin, bodily fluids, mother-fetus transmission, droplet spread (close proximity ONLY)
  • e.g. meningococcal or influenza virus
• (2) INDIRECT CONTACT

  • Infection of a new host via an unaffected intermediatory
  • e.g. airborne transmission (without close proximity), fomites, food (e.coli via undercooked or contaminated meat), drinking water (giardia), zoonosis (toxoplasma gondii from cat faeces), environmental resourvoirs, vector transmission
• (3) VECTOR TRANSMISSION (type of indirect)

  • VECTORS are animals which transmits a pathogen from one person to another without being affected by the disease
  • Possible for all pathogens except prions and vertebrate macroparasites
  • e.g. female anophales mosquito transmits the plasmodium protozoan which causes malaria, aedes mosquito transmits dengue fever
• modes of transmission are direct contact, indirect contact, vector transmission
• ADAPTATIONS THAT FACILITATE ENTRY AND TRANSMISSION

  • Whooping cough bacteria can enter respiratory fluids, allowing them to be expelled in coughs and sneezes
  • Many bacteria and protozoa have flagella which give them to ability to move within host fluids
  • tapeworms have hooks and suckers that allow them to attach to the walls of hosts digestive systems
  •  vibrio cholera bacteria can survive for extended periods of time in water without a host
  • giardia (protozoa causing waterborne diarrheal illness) can switch to a cyst form when outside the host, which is more durable and allows it to survive
• FOOD AND WATER PRAC

  Method

  (1) sterilisation (ethanol spray + wash hands)

  (2) set up bunsen burner, sterilise inoculation loop in blue flame

  (3) dip loop in water, open agar plate lid at 45 degrees, quickly spread water over agar in a streaking pattern without breaking the agar

  (4) label with a date, sample and identity number

  (5) repeat as necessary (different water samples, repetitions of each)

  (6) incubate for 3 days at 25-30 degrees Celsius
• FOOD AND WATER PRAC Safety

  1. Sterilise work bench with ethanol spray before and after to PREVENT ingestion/exposure of pathogenic materials

  2. Seal and do not reopen agar plates, they will be melted down and destroyed to ensure pathogenic material is not released
• EPIDEMIOLOGY : The branch of medicine dealing with the incidence, distribution, and control of disease
• Sporadic = occurs infrequently and irregularly

  Endemic = exists permanently in a particular region

  Epidemic  = increase in number of cases above what is expected in that area

  Pandemic = GLOBAL increase in number of cases above what is expected
• Factors contributing to epidemics

  Occurs when a pathogenic agent and susceptible hosts are present in adequate numbers, and the agent has a successful method of transmission

  recent increase in quantity or virulence of agent

  introduction of an agent into a new environment

  enhanced mode of transmission

  • change in host susceptibility
• Features of an epidemiology question (TLC SMP)

  (1) Time frame (study for a long period of time, esp for non-infections)

  (2) large sample size (minimum of hundreds)

  (3) compiling data (including on incidence of disease, morbidity/mortality, information about affected persons)

  (4) statistically analyse

  (5) management plan (for affected individuals)

  (6) prevention and treatment plan (isolation, masks, social distancing)
• ROBERT KOCH

  Contributions

  development of the agar plate to culture bacteria/fungi outside the host

  identified anthrax in sheep as caused by anthrax bacillus, also discovered bacterial species responseible for cholera and TB

  determined that each disease was caused by a specific microorganism

  evidence for "germ theory" of disease

  • developed Koch's postulates (a method for linking a particular pathogen to the cause of disease)
• Koch's postulates (PIHS)

  1. the same microorganism must be present in every diseased host and not in unaffected hosts

  2. the microorganism must be isolated from a diseased host displaying symptoms and cultured, described, and recorded

  3. inoculated into a healthy host of the same species, and must display the same symptoms of disease as the original host

  4. microorganism must be isolated and cultured from the second host and identified as the same as the original species that caused disease
• Swan neck flasks

  (1) two flasks partially filled with equal volumes of beef broth

  (2) boiled for at least 20 minutes

  (3) neck of one is snapped, neck of other is bent into a swan shape

  (4) flasks are observed for evidence of decay after a period of time
• DISEASE IN AGRICULTURE

  Methods of prevention

  • Vaccination
  • Drenching
  • Dripping
  • Paddock rotation
  • Antibiotics in feed
  • Backup crops (non-monocultures)
  • Use of fungicides
• Intensive farming

  housing crops at higher densities, increasing direct contact between individuals, and consequently increasing the risk of infectious disease transmission.

  • etc spread of CJD was due to the practice of feeding living cattle with dead cattle meat to minimise resource consumption
• Artificial selection

  artificial selection lowers the genetic variation of the population, and in doing so it makes the population more vulnerable to disease

  Irish Potato Famine -> genetically identical potato crops all susceptible to the same fungal pathogen.

  • selection must be carefully controlled and farmers must use responsible breeding practices which promote biodiversity.
• LOUIS PASTEUR Contributions

  • Fermentation spoilage link with microbes (proved bacteria caused souring of wine)
  • developed pasteurisation (abnormal fermentation of wine prevented by heating to above 60C and cooling)
  • germ theory of disease (opposed to spontaneous generation)(swan neck flasks; sterilised cultures isolated from open air did not spontaneously generate)
  • linking microorganisms with disease (e.g. confirmed koch's isolation of bacillus anthrax)
• LOUIS PASTEUR Contributions

  • development of vaccines (used weakened versions of anthrax on farm animals, found that they became immune)
  • principle of immunity (found it possible to diminish microbes' virulence to immunise against disease)
• PLANT IMMUNITY (RESPONSE TO PATHOGENS)

  Basal resistance-> living plant cells become fortified against further infection

  Gene for gene resistance -> resistance from the proteins formed from the resistance gene and avirulence gene

  Hypersensitive response:  (limits pathogenic access to host)

  • Programmed cell death (apoptosis)
  • Increased lignification of plant cell walls
  • Plant cells produce compounds to destroy pathogenic cell walls

  Systemic Acquired Resistance -> nonspecific; the buildup of salicylic acid in the presence of pathogens
• MAMMALIAN IMMUNITY

  1st = innate resistance = physical barriers

  2nd = innate immunity = internal defences

  3rd = adaptive immunity = acquired immunity
• Physical barriers

  Skin

  Hair

  Cilia (respiratory track and ear canals)
• Chemical barriers

  Mucous membranes,Mucous/chemical secretions

  Digestive enzymes in mouth (saliva contains lysosome to destroy bacteria)

  Stomach acid + duodenum base + vagina acid
• Microbial barriers

  Natural microflora on skin, nose, mouth, throat, gastrointestinal and urogenital tract -> inhibit the growth and colonisation of other (pathogenic) microbes
• Innate Immunity

  [ histamine production, inflammation, phagocytosis, clotting elements, injured area walled off]

  1.Damaged cells release Chemotactic factors which attract leukocytes to infection site

  2. Mast cells identify foreign antigens and release histamine, blood vessels dilate (widen) to increase blood flow

  3. Phagocytes move from blood vessel to interstitial fluid through the capillary wall

  4. Phagocytes engulf pathogens by endocytosis

   

  Inflammation: heat, redness, pain, swelling, tenderness,
• NEUTROPHILS = kill the pathogen and then die (martyrs)

  MACROPHAGES = kill the pathogen and retain the antigens for antigen presentation

  
  

  they are phagocytes of the innate immune system
• adaptive immunity

  B-lymphocytes = antibody mediated immunity

  T-lymphocytes = cell mediated immunity
• Adaptive immunity process

  1. antigen presentation
  2. CD4 activation
  3. cytokine release
  4. antibody mediated response (B-cells)
  5. cell mediated response (T-cells)
• Antigen presentation (adaptive immunity)

  • Macrophages and dendritic cells hold the foreign antigen on their MHC II complex, presents it to the naïve CD4 T-cell (T helper), which becomes activated