Biology Module 7 - Infectious Diseases

Features of Bacteria

• Unicellular prokaryotes that risk causing disease

• no nucleus, no organelles, cell wall

• High reproduction rate asexually via binary fission

• cause disease by releasing endotoxins after death or producing exotoxins

• e.g. tuberculosis

Features of Fungi

• Eukaryotic, non-photosynthetic, uni or multicellular

• Often in form of moulds (tangles masses of filaments of cells) or yeasts (unicellular organisms whose colonies resemble those of bacteria)

• Impact via enzymes they produce

• e.g. thrush, grey mould

Features of Protists

• Eukaryotic organisms that are not plants, animals or fungi

• unicellular (w/cell wall)

• e.g. amoeba

Features of Viruses

• non-living infectious collection of genetic material surrounded by protein coat

• non-living (don't pass MRSGREN)

• non cellular

• injects dna into host cell so the host cell replicates its own and virus dna to create new viruses

• e.g. Influenza

Define Pathogens

Infectious organisms or agents that cause a disease

a) Define Prions b) Explain their process c) Identify a disease they cause d) How do they transmit?

• Infectious abnormally folded proteins, causing abnormal folding patterns when contacting other proteins, which changes their shape and structure and leaves them unable to perform their function

• Cause Mad Cow Disease, Kuru

• Often have to be ingested

Features of Viroids

• smallest pathogens

• small circular single-stranded RNA

• affects plants

• no protein coat (viruses have one)

• use host cells to replicate RNA to create new viroids e.g. Chrysanthemum Stunt Viroid

Identify the five ways bacterial infections may transmit

• airborne (e.g. via air currents)

• contact (e.g. skin to skin)

• droplet

• vectors (mosquito, tick, takes blood from infected and transfers pathogens to uninfected)

• vehicular (food and water)

Features of Macroparasites

• multicellular

• eukaryotic

• can be seen with human eye

• e.g. tapeworms

Direct contact

• physical contact between an infected and a susceptible individual e.g. kissing, fluid contact, touching

• causes HIV/AIDS

Indirect contact

• spread of an infectious disease from an infected person to another person via a medium they both touch e.g. airborne, contaminated surgical devices

• causes influenza

Vector Transmission

• an organism, typically a biting insect or tick, that transmits a disease or parasite from one animal or plant to another e.g. mosquito, ticks

• causes malaria

Lytic vs Lysogenic Cycle

LYTIC:

• host cell copies only virus dna

LYSOGENIC:

• host cell replicates virus dna within its own

Steps of Lytic Cycle

1. virus inserts genetic material into host cell

2. host cell replicates viral general material using its own resources

3. host cell lyses (breaks down and instantly releases new viruses)

4. viruses infect new host cells

Steps of Lysogenic Cycle

1. virus inserts genetic material into host cell where it is hidden

2. as cell replicates its own material and viral material in new cells

3. the lytic cycle is triggered (e.g. lack of food for host) and all cells with viral genetic material can assemble viruses

Chain of Infection steps

• infectious agent

• reservoir

• portal of exit

• mode of transmission

• portal of entry

• susceptible host

Explain how Louis Pasteur disproved spontaneous germination and developed the germ theory of disease

Pasteur took 2 swan neck flasks and heated liquid in both flasks to kill germs (sterilisation known as pasteurisation)

• Flask 1 sealed, flash 2 had exposed to air

• Flask 1 no microorganisms, flask 2 had airborne exposure and grew bacteriap

How was disease explained pre-Pasteur?

• miasma (bad air caused by rotting food and waste in the streets, everyone assumed it was the smell)

• religious punishment

• the humours

• spontaneous generation

Define pasteurisation

"the process of heating something, especially milk, at a controlled temperature for a fixed period of time in order to kill bacteria:"

Identify an achievement of Louis Pasteur

• disproved spontaneous generation theory

• proved vaccination worked through trialing on chickens

• developed anthrax and rabies vaccines

Explain Koch's Postulates and what they are used for

• purpose: verification on whether a specific pathogen causes a specific infectious disease by isolating and testing that particular pathogen

• separation from host

• grown in pure culture

• injected into healthy organism

• extracted and ensured it is the same as the original pathogen

Outline a bacterial adaptation in pathogens and how it facilitates their entry into and transmission between hosts

• Sticky biofilm --> provides protection against the host's immune system

• Toxin production to weaken the immune system and damage the tissue

• Flagellum enhance bacteria mobility/swimming ability

Outline a viral adaptation in pathogens and how it facilitates their entry into and transmission between hosts

• Antigenic Shift --> two different viruses combine to create a brand new virus with new antigens

• Antigenic Drift --> the virus accumulates random mutations that change the antigens so the immune system cannot recognise them

Identify a physical and chemical response of plants to pathogens

Physical --> leaf dropping Chemical --> Produces toxic chemicals to pathogens e.g. caffeine

Identify a physical response of animals to pathogens

• mucous membranes and cilia --> trap pathogens and cilia sweeps them out of lungs

• skin --> outer barrier

• peristalsis --> muscle contractions in muscle tract moving mucus or causing vomiting to eliminate pathogens

Identify a chemical response of animals to pathogens

• lysosomes in tears and salvia --> destroy bacterial cell walls

• high acidities e.g. in stomach acid --> kills pathogens

Compare innate and adaptive immunity

• Innate immunity is non-specific, non-specialised responses to pathogens and include the 1st and 2nd lines of defence (macrophages, phagocytes, physical and chemical defences). Does not include antigen responses or long-term immunity. No previous exposure needed

• Adaptive immunity, the 3rd line of defence. Specialised and confers long-term memory. Involves B and T cell lymphocytes for antigen responses. Takes longer to work

Describe the 1st line of defence in the immune response

• innate immunity -chemical and physical barriers prevent pathogen entry into the body

Describe the 2nd line of defence in the immune system

• innate non-specific responses when pathogen breaches into body

• inflammation, phagocytosis, fever

Explain the inflammation process in the 2nd line of defence

• a wound is found and pathogens enter the body

• platelets from the blood release blood-clotting proteins to close the wound. blood and plasma delivery increases

• white blood cells (neutrophils, macrophages) under phagocystosis

• macrophages produce hormones that call immune system cells to site for tissue repair

Explain the phagocytosis process

• phagocyte recognises anti-self proteins on pathogen

• engulfs pathogen

• lysosomes in phagocyte produce H202 to break down pathogen

• pathogen digested

• antigen delivered to messengers to send to T cells to prepare 3rd defence line

third line of defence

• T Helper cell activated

  • release chemical messagers to activate antigen-specific b cells which clone themselves specifically to the recognised antigen by the t cells

    • create memory cells for if the antigen returns the body will go immediately to third line for pathogen removal

    • create a large plasma B cell → pregnant, gives birth to antibodies made antigen-specific that only locks onto antigens

    • antibodies go through the blood to infection site and lock pathogen antigens → now pathogen antigens cannot attach to cells and harm

  • chemical messengers secreted activate T helper cell reproduction to make more T helper cells with receptors that have matched with the pathogen antigens

    • Create memory t cells which stay in the body and circulate, and will attack antigen directly if they see it

    • T cells: attack invaders inside cells

    • Some cloned helper T cells become cytotoxic killers, which migrate to site of infection and directly attack pathogens without antibodies; reproduce in large amounts

    • Create suppressor t-cells which prevent the constant creation of these cells (if not created, causes leukaemia). They regulate immune response and suppress b cells and cytotoxic t cells when antigens are all destroyed (like an off switch to get body back to balance)

Active vs Passive Immunity

Passive: receiving antibodies from another, e.g. mother --> child, less effective

Active: vaccination/disease exposure causes body to create antibodies and memory cells

Identify one method of disease prevention and outline its process

• vaccination

• public health campaigns

• genetic engineering

Identify one method of controlling disease and outline its process

• Quarantine

• Pesticides

• Hygiene practises

Identify one method of treating diseases and outline its process

• antivirals

• antibiotics

Hygiene Practises as a method of controlling disease. Explain:

• what the process entails

• pros and cons

• maintaining personal cleanliness to prevent the spread of infectious agents

• PROS: simple, cost-effective, widely applicable

• CONS: dependency on consistency

Quarantine as a method of controlling disease. Explain:

• what the process entails

• pros and cons

• isolation to ensure individuals are prevented from exposure to infectious disease

• PROS: can be effective in early stage of outbreaks and protects broader population

• CONS: compliance issues, emotionally challenging

Pesticides as a method of controlling disease. Explain:

• what the process entails

• pros and cons

• chemicals that harm pathogens and their insect vectors

• PROS: effective in preventing pest damage to agriculture

• CONS: environmental concerns, genetic resistance via natural selection = ineffective

Vaccination as a method of preventing disease. Explain:

• what the process entails

• pros and cons

• weakened pathogen exposed to immune system via injection or pill to allow the body to create memory cells of the pathogen's antigens

• PROS: allows body to adapt to fight disease, often accessible

• CONS: reliant on herd immunity, lengthy to immunise communities

Public health campaigns as a method of preventing disease. Explain:

• what the process entails

• pros and cons

• educational initiatives based on raising awareness of disease and healthy preventative habits

• PROS: Can reach large audiences

• CONS: dependent on effective messaging, can be difficult to sustain behaviour

Genetic engineering as a method of preventing disease. Explain:

• what the process entails

• pros and cons

• Genetic Engineering → insertion of genes from one organism to another; modification of an organism's genes to prevent or treat diseases, e.g. replacing faulty gene

• PROS: effective, broad range of uses (treating disease or providing medicine, e.g. creating cows for antibodies)

• CONS: still experimental, ethical concerns

Antivirals as a method of preventing disease. Explain:

• what the process entails

• pros and cons

• medication that prevents protein synthesis in viruses because viruses have protein coats and uses host ribosomes for protein synthesis

• PROS: effective in treating and reducing symptoms

• CONS: genetic resistance via natural selection

Antibiotics as a method of preventing disease. Explain:

• what the process entails

• pros and cons

• medication that treat bacterial infections by targeting bacterial features, e.g. breaking down bacterial cell walls

• PROS: easily produced, effective, CONS: antibiotic resistance via natural selection

Outline a strategy to control antibiotic resistance

• minimising the dependency on antibiotics and its misuse

• Avoid broad-spectrum antibiotics, use targeted narrow-spectrum antibiotics

Define Epidemic

increase in cases in an area above what is normally expected in that area

Named infectious disease: Malaria (fill in here!!)

Define Pandemic

an epidemic spread over several countries or continents

Define Prevalence and how to calculate it

percentage or total amount of people infected over a period of time

[number of total cases during a time period divided by size of population x 100]

Define Incidence and how to calculate it

rate of new cases developing for particular disease

[number of new cases during a time period divided by size of population at start of monitoring period x 100]

Identify two methods used to control an epidemic or pandemic

• Pre-preparedness and awareness

• Management of healthcare facilities e.g. PPE and special methods for handling infected patients

• Chemical spray and disinfectants in entry and exit facilities

• Biosecure disposal of contaminated medical materials

• Quarantine and isolation of individuals

• Exit screening at airports for individuals leaving infected countries

How does mobility influence disease?

The mobility of individuals who are immune or immunised impacts disease incidence and prevalence.

• white settlers introducing smallpox to aus indigenous, killing them. increase of prevalence and incidence

• urbanisation

• international travel

Outline an example of a modern strategy to control or predict disease

Surveillance: faster identification of patterns and epidemic frequency

Simulations: used to predict how a disease will progress and spread + the impacts of intervention attempts

Continued public health intervention: mass vaccination, education programs

Explain bush medicine and provide an example of its use in modern medicines

Bush medicine → use of herbs and plants to treat illness, e.g. tea tree oil as antiseptic

Smoke Bush in WA contains medicinal essential oils and has potential to kill viruses. Being studied for cancer research and HIV treatment

Describe the response of a named Australian plant to a named pathogen/disease

Eucalyptus (Fungal)

• Oidium eucalypti (fungal pathogen) causes powdery mildew disease in Eucalyptus.

  • Patches of white powdery growth on plants. Can stunt plants and cause withering

• Response → Barrier zones created in new healthy tissue to protect it from infected tissue

Banana (Viral)

• Banana bunchy top virus (BBTV) → single strand DNA viral disease transmitted by aphids (vector insects that suck sap from trees). Stunts leaf growth, leaving young leaves yellow and prevents the plant from producing fruit. Furthermore, the suckers (shoots out from base to grow into another plant) of infected plant will be diseased

• Human responses → quarantine measures prevent infected plants entering Aus, control of aphid vectors

Explain how the immune system responds after primary exposure to a pathogen

• memory B cells remember antigen and the antibodies used, creates new antibodies and immediately produces a faster and stronger response

Provide information on malaria as an infectious disease, including factors increasing its prevalence

• Malaria is one of the most common mosquito-borne diseases in Southeast Asia

• Vector transmission through mosquitoes

• Protozoan parasite

• Symptoms: High fever, Vomiting, Chills, Abundant sweating

• Morbidity and mortality are expected to increase with the rise in the global temperatures drug resistance and international travel

• Factors that contribute to increase in the incidence and prevalence of malaria include:

  • Resistance to chloroquine

  • Increased proliferation of low quality and counterfeit drugs that claim to cure malaria

  • Population movement and rapid urbanisation

  • Low community immunity due to high proportions of very young people in some (too young to immunise)

Identify an adaptation of malaria

• Parasite developed a mutation which made it resistant to chloroquine (antimalarial drug)

• Uses a host (mosquitos) to penetrate skin (physical barrier) and transmit disease

Describe forms of treatment, prevention and controls for malaria

consider global and local

• Insecticide DDT to wipe out mosquitoes implemented by WHO in the 50s, dropped by the early 70s. From the 70s, different antimalarial drugs but the parasite evolved to resistant form → ineffective. DDT discontinued

• Engineering the genes of vectors such as mosquitoes can control the spread of diseases including malaria

• Use mosquito nets when sleeping In places where malaria is present

• Use Mosquito Repellents

• Global controls:

  • closing off travellers from malaria endemic areas

  • informing and vaccinating travellers 

  • screening people entering the country

    • Testing travellers and closing borders will prevent the spread of the disease into new population groups)