Biology: Mod 7 - Infectious Diseases

what are the 6 types of pathogens that cause infectious diseases?

prions, viruses, bacteria, fungi, protozoans, macrorganims

what are the two types of organisms within macroorganisms?

endoparasites: inside the body

ectoparasites: outside the body

what is the structure of prions?

• Proteinaceous infectious particles

• Has no genetic material

• Non-cellular 

• 10𝜇m 

how do prions transmit diseases?

• Abnormally folded protein: transmits the misfolded protein to other cellular proteins

• Transmitted through ingestion of infected tissues, contaminated surgery etc.

• The disease caused is called spongiform diseases, as the infected individuals brain resembles a sponge with holes

  

name two diseases caused by prions?

CJD disease: a rapidly progressive and fatal brain disease - from eating infected cows, humans

Mad Cow Disease: brain disease for cows

what is the structure of viruses?

• Non-cellular: they can crystallise

• 100-200 nm (viewed with electron microscope)

• Have nucleic acids surrounded by a protein coat (capsin) and pass on hereditary information

• Can only reproduce and metabolise in a host cell

what is a virion

single viral particle

what is adenovirus

• DNA viruses

what is retroviruses?

• RNA viruses (injects RNA into host cell)

what are the 4 shapes of viruses?

how do viruses transmit diseases?

why is it difficult to treat viruses diseases?

Sometimes treatment is difficult as by killing viruses, you kill the host cell

name two diseases caused by viruses?

Influenza: fever, muscle aches, chills

HIV/AIDS: weakens immune system

structure of bacteria

• Unicellular prokaryote (no membrane bound organelles - has cell wall + DNA)

• Reproduce through binary fission

• 0.2-10𝜇m 

what are the three shapes of bacteria

how does bacteria transmit diseases?

• Can be beneficial (symbiotic) or harmful (parasitic)

• Transmitted through in/direct contact of host organisms

• Some form endospores that allow them to lie dormant for years

• Managed through antibiotics

what is a disease caused by bacteria?

Whooping Cough: runny nose, sneezing, cough that makes “whoop sound” 

Salmonella: food poisoning, vomit, diarrhoea, dehydration

what is the structure of fungus?

• uni/multicellular, eukaryotic, has a cell wall + DNA

• micro/macroscopic

• Heterotrophs (eats autotrophs), decomposers

• Reproduce a/sexually

  

how do funguses transmit diseases?

• Infections can be cutaneous (outer skin), subcutaneous (beneath skin), systemic (affect internal organs)

• Opportunistic: affect individuals with weakened immune systems/constant diseases

• Transferred via close contact between host or contaminated objects

• Main causes of plant infectious diseases

what does opportunistic mean?

• affect individuals with weakened immune systems/constant diseases

examples of fungal diseases?

Thrust (yeast infection): associated with long-term asthma inhalants, long-term use of antibiotics

Tinea (athlete’s foot): redness, swelling, breaking down of toe nails

Mildew (plant disease): powdery growth on plant

structure of protozoa

• Unicellular, eukaryotic organism (no cell wall)

• Heterotrophic: absorb nutrients from hosts

• Produced by binary fission

• 1-300𝜇m

• 

what are the types of protozoa?

• Hold structures to aid motility: flagellates (tail), ciliates (cilia), amoebae (cytoplasm), sporozoa (don't move)

how does protozoa transmit diseases?

• Secrete toxins, invade cells, and form colonies to disrupt cell and tissue function

• Transmitted through insect bites, contaminated water

what are diseases caused by protozoa

Malaria: transmitted through mosquitoes - fever, fatigue, headaches

Dysentery: spread through contaminated food/water - inflammation of intestines, bloody stool

what is the structure of macro-organisms?

• Visible to the naked eye

• Multicellular, eukaryotes

• Endoparasites = live inside the body of the host

• Ectoparasites = live outside the body

  • Fleas, ticks, lice, mites

how do macro-organisms transmit diseases?

• Invade, destroy cells + create competition for nutrients

• Some cause diseases, some act as vectors

examples of diseases caused by macro-organisms?

Endoparasite: tapeworm disease - red/itchy anus, lack of appetite, worms/blood in stool

Ectoparasite: fleas acted as a vector for the bacteria that caused bubonic plague

what is the chain of infection

infectious organism —> reservoir —> portal of exit —> mode of transmission —> portal of entry —> vulnerable host —> infectious organism

define reservoir

place where a microorganism lives and thrives

define portal of exit

how to microorganism leaves the reservoir

define mode of transmission

how the micro-organim transmits from one person/place to another

what is direct contact?

Transfer to new host via physical contact

what are the two types of mode of transmission

1. direct contact

2. indirect contact

what are the two types of direct contact?

Horizontal Transmission: between organisms that aren’t mother/child

• Touching, kissing, sex, contact with body fluids

• Touching soil/vegetation that holds infectious organisms

• Zoonotic disease: animal to human

Vertical Transmission: contact between offspring and mother

• Prenatal (before/during prego)

• perinatal (at time of birth)

what is a zoonotic disease

transfers from an animal to a human

examples of direct contact diseases

HIV/AIDS/ Herpes/ Ringworm/Whooping Cough

what is indirect contact?

Infection occurs from a reservoir created outside of the host 

• Contaminated material/obj

what are the types of indirect contact?

Vehicle Transmission: transmission through vehicles that passively carries pathogen/provides pathogen with environment to grow

• Fomites = inanimate obj that carries infection (clothes, door knob)

• Waterborne Transmission

• Airborne Transmission

• Foodborne Transmission

• vector transmission

what are fomites?

• inanimate obj that carries infection (clothes, door knob)

what is airborne transmission?

• small (≤5𝜇m) droplets may have settled then re-suspended after movement

• Small droplets can stay suspended longer and travel farther

what is vector transmission?

a type of indirect transmission

occurs through arthropods (mosquitoes, ticks, fleas), infected plants, fungi and some mammals (bats, pigs)

• Transmission occurs when pathogen is transferred by biting the host’s blood or if the arthropod is swallowed

what are the two types of vector transmission?

• Mechanical Vector: organism carries pathogen on its body from one host to another host

• Biological Vector: pathogen carried from one host to another after becoming infected itself (malaria)

what is waterborne transmission caused by?

poor sanitation

what is foodborne transmission caused by?

• improper handling of food

  • good environment for spores to reactivate and produce toxins in e.g. canned food

what is an example of a waterborne disease?

Dysentery, particularly amoebic dysentery, can spread when people drink or use water contaminated with fecal matter from an infected person

what is an example of an airborne disease?

• Measles: viral infection spread through airborne transmission → red blotchy rash, hacking cough

what is an example of a vector disease?

• Malaria: infection spread through biological vector transmission (female mosquito) from the Plasmodium parasites → fever, nausea, rapid heartbeat, diarrhoea

how does malaria affect an individual?

what is an example of a foodborne disease?

salmonella - a bacterial infection spread through contaminated food (usually by eating raw/undercooked meat, eggs or milk) = diarrhoea, fever, vomiting

what is the historical understanding of why diseases occurred?

The Theory of Spontaneous Generation

• Life (maggots in rotting flesh) arose spontaneously from nonliving things 

• Early experiments (Redi and Spallanzani - scientists) showed that some form of living matter had to be present before other living things could appear  (WASN’T WIDELY ACCEPTED)

what was Koch’s postulates?

what was the conclusion from Koch’s postulates?

Showed that the anthrax spores he had obtained from the pure cultures he had grown could cause the disease in other animals and kill them = each disease is caused by a specific microorganism

• added further weight to the germ theory of disease, showed that a microorganism grown outside the body caused a disease.

what did Pasteur present and disprove?

• Pasteur disproved the theory of spontaneous generation → established the germ theory of diseases: states germs (microbes) cause diseases 

  • All microorganisms arise from pre-existing microorganisms

what was Louis Pasteurs’s experiment that proved his germ theory?

• Bacterial growth also occurred if the flask was tilted to let the broth go into the swan-neck

  • Allowed broth to reach the curve where microorganisms were trapped

• Result: that microbial growth was a result of particles in the air, and could not arise spontaneously in sterile environments.

  • contributed to our understanding of disease → scientific community began to accept that infectious diseases must be a result of microorganisms, originating from some external source.

to infect a host, a pathogen must:

1. enter the host

2. multiply within host tissues

3. resist host defence mechanism (not get detected by it)

4. damage host

what are types of adaptations pathogens do the enter the host

1. attatchment to host tissue

2. ability to withstand harsh environment

3. biofilms

4. binding to host cells

5. produce toxins

6. survive in blood cells

how do pathogens attatch to host tissues?

produce protein called adhesion → allows them to bind to host cells → resists washing actions of secretion

how do pathogens withstand harsh environments?

E.g Helicobacter pylori secrete an enzyme which converts urea to ammonia to combat stomach’s acidity → causes stomach ulcers

how does biofilm allow bacteria to exist and enter the host?

99% of bacteria exist in colonies called biofilms: allows them to exist in 

• A dormant state with a reduced metabolism

• Become resistant by transferring genetic information in colony

• Prevents antibiotic penetrations by surrounding themselves in a slime-like matrix

E.g. Staphylococcus aureus → difficult to treat with antibiotic

how does binding to host cells allow pathogen to enter the host?

• Intracellular pathogens bind to receptor molecules on the surface of host cells

• Virus particles can bind in a complementary manner with the surface receptor molecule = they are taken into the cell

E.g. COVID-19

how does producing toxins allow pathogens to enter the host? + example

• Secrete toxins to destroy cells of host = weakens host defence system

E.g. Whooping Cough produce toxins to destroy respiratory tract lining → reduces changes of fighting infection

how does surviving in blood cells allow pathogens to survive in host?

• Pathogens can survive within the WBCs sent to destroy them

• Some pathogens infect and deplete the WBCs that coordinate the immune system

E.g HIV

give an example of an australian plant’s response to a disease

Myrtle Rust (first detected 2010 and spread across eastern Australia)

Affects plants in the Myrtaceae family (eucalypts, bottlebrushes, tea trees, lilly pilly) Fungal infection: attacks soft, new growth (leaves, shoot tips and young stems of plants) Infection begins as small purple spots on leaves → bright yellow spores form inside of bulbous pustules Spreads by releasing spores, which are easily dispersible by wind =  high degree of transmission over a short time

Plant Defences Mechanical barriers (bark, thick cell walls composed of pectin and lignin, and leaf cuticles) At infection sites: cell walls become reinforced by deposition of additional structural protein, secretory cells and glands transporting defensive substances Production of antimicrobial peptides

do plants have an immune system

no, they have defence systems

what are passive defences?

physical and chemical barriers

what are plant’s physical barriers (passive defence)

 thick cuticle (prevent chemicals from breaking cuticle down) , cell walls, small stomata = inhibit pathogen entry

what are plant’s chemical barriers (passive defence)

Chemical Barriers: presence of chemicals reduce pathogen growth

• E.g glucosides, saponins

• PAMPS (pathogen-associated molecular patterns) detect pathogens and activate the next stage of defence

what are the plant’s active defence steps?

targeted response

1. pathogen recognition

2. rapid active response (minutes to hours)

3. delayed active responses (days) = limits spread of pathogens

what do plants do for pathogen recognition

• Plants recognise pathogens through chemical/physical signals (fragments of their cell wall) by pattern recognition receptors (PRR) → located on the surface of plant cells

• Genes within the cells are thought to regulate plant responses

what do plant’s do for rapid active response?

1. Pathogen recognition → increased cell membrane permeability → ions move into cell → triggers activation of certain genes → releases hydrogen peroxide (H₂O₂) = oxidative burst → kills microbes

2. Reinforcement of cell wall near a defect in the wall = cell wall apposition 

3. Programmed cell death = apoptosis: cluster of dead cells gather around pathogen → isolates it → cells release antimicrobial compounds

what do plant’s do for delayed active response (days)

Delayed Active Response (days) = limits spread of pathogen

1. Repairs wounds in the bark (cork cell production, gum secretion)

2. Systemic Acquired Resistance: lysozyme like chemicals are released (antimicrobial), salicylic acid is a signalling agent → helps the plant to remember the particular pathogen → limits severity of subsequent infections

what is an innate immunity?

A type of simple immunity which is inbuilt at the time of birth (genetically determined)

what is the purpose of innate immunity?

• To prevent pathogen entry

• To kill pathogens before spread

• Physical & chemical barriers (1)

• Cellular responses (2)

what is the response, specificiy and memory of innate immunity?

fast, non-specific, no memory

what is the definition of acquired/adaptive immunity?

A type of complex immunity which is developed through a lifetime.

what is the purpose of adaptive immunity?

• To kill pathogens to prevent further spread

• To prevent pathogen further attack

what is adaptive immunity’s response, specificity and memory?

slow, specific, stores memory

what is an antigen?

antibody generator: molecule on the surface of a cell that an organism recognises as foreign→ triggers an immune response

• Stimulate (3) line of defence

what does an antigen have as a structure?

• On the surface of cells in the body, there are ‘marker’ molecules (epitope) that identify the cell as belonging to the body (‘self’) = protects the body from attacking itself.

• Particular lymphocytes will recognise a particular epitope as they have complementary binding sites = antigen receptors

what are white blood cells?

• Helps in both innate and adaptive responses to pathogens

• Different based on: size, do they have granules in their cytoplasm, colour of their granules, shape of nucleus

what are mast cells, their location and their role in the immune system?

• Blood vessel dilation

• Releases heparin, histamines

• Recruits neutrophils + macrophages

• Involved in allergic reactions

location: Connective tissues and mucous membranes

what is a dendritic cell (WBC), its role in the immune response and its location + analogy?

Dendritic Cell

Presents antigen Triggers adaptive immune response

Epithelial tissues - migrates to lymph nodes if activated

🛑Signal Man (relays information)

what is a macrophage (WBC), its role in the immune response and its location + analogy?

Macrophage

Phagocytosis of pathogens + cancer cells Presents antigens

Migrates from blood vessels to tissue

🚨Riot police (lasts longer)

what is a monocyte (WBC), its role in the immune response and its location + analogy?

Monocyte

Differentiates into phagocytic cells (dendritic, macrophages)

Stored in spleen - moves to infected tissues

what is a neutrophil (WBC), its role in the immune response and its location + analogy?

Neutrophil

Most common WBC at infection Releases toxins to kill/inhibit pathogen → die after killing a few (makes pus) Recruits other immune cells to infection

Migrates from blood vessels to tissue

👮🏻‍♀️Street Cop (rapid response + quick death)

what is a basophil (WBC), its role in the immune response and its location + analogy?

Basophil

Defence against parasites Releases histamines = inflammation

Circulates in blood - moves to tissue

🧑🏻‍🚒Fireman (inflammation)

what is a eosinophil (WBC), its role in the immune response and its location + analogy?

Eosinophil

Releases toxins that kill pathogens

Circulates in blood - moves to tissue

🤿Fumigator (kills parasites)

what is a lymphocytes (WBC), its role in the immune response and its location + analogy?

Lymphocytes

Produce specific antibodies to target specific antigens present Slowest to respond B Cells: antibody secreting plasma cells T Cells: mediate B cell activity Destroy virus-infected body cells with cytotoxic T cells and natural killer cells

More common in lymphatic system

🥷🏽Special force soldiers (slower, specific targeted response)

what WBCs are involved in innate immunity?

neutrophil, eosinophil, basophil, macrophage

what WBCs are involved in adaptive immunity?

lymphocytes —> B cells, T Cells

what does the first line of defence in humans consist of?

physical and chemical barriers

what are human’s physical barriers?

skin, mucous membranes, tight junctions, peristalisis

what are human’s chemical barriers?

Stomach acid	Kills ingested pathogens
Lysozyme Enzyme	Present in actions of secretion: urine, mucus, tears Breaks bacterial cell walls through antimicrobial peptides to kill pathogens
microbiome	The microbes on the body that have a symbiotic relationship with the body Microbes get food, habitat, conditions to survive → will inhibit growth of pathogen (competition)

what are the steps for the 2nd line of defence

1. inflammation

2. phagocytosis

3. natural killer cells

how is the 2nd line of defence activated

if the 1st line of defence is breached

how is inflammation triggered?

 tissue damage/presence of pathogens

what is the aim of inflammation?

eliminate pathogen, clear necrotic cells from infection, initiate tissue repair

what are the steps for inflammation?

Actions: 

1. mast cells and basophils release histamine=

   1. Vasodilation: increased blood flow 

   2. Increased capillary (blood vessels) permeability = plasma, clotting factors, WBCs leave blood vessels - enter tissues 

2. Mast cells release cytokines= recruit neutrophils (type of WBCs) for phagocytosis

   1. Stimulates fever in the hypothalamus

   2. Results in redness, heat, swelling, pain = isolate and eliminate pathogen

what is the purpose of fever?

• purpose of fever: increases body temp to activate heat shock proteins → suppress microbial growth and propagation

• Increases metabolic activity in body cells 

• Up to a certain point fever is beneficial → but too high will cause damage to the body’s enzymes