Biology Module 7

A disease can be infectious meaning that it is able to be transmitted from one organism to another and is caused by a pathogen (a disease-causing agent).

Pathogens are agents that can cause disease, including bacteria, viruses, fungi, protozoa, prions and macroparasites.

Cellular - Bacteria, fungi, protozoa and macroparasites are cellular (made from cells and considered living)

Non-Cellular - Prions and Virus (not made from cells and considered non-living)

Virus - Genetic material in a capsid. Intracellular parasites that rely on a host to survive and reproduce. Eg; HIV

Prions - Misfolded proteins, this abnormal folding leads to the development of neurodegenerative disease like CJD

Transmission of a disease involves the transfer of a pathogen from an infected host to a non-infected organism

a "chain of infection" must be present, which includes a host that is susceptible to the disease, an agent that can cause the disease (pathogen) and a mode of transmission (a way to get from one host to another).

1. Direct tranmission
2. Indirect Tranmission
3. Vector Transmission

This requires physical contact between the host and the non-infected organism. Examples include touching, sexual contact, kissing, biting, direct contact with blood or other body fluid Diseases caused by direct transmission include HIV/AIDS, ringworm

This does not require physical contact between the host and the non-infected organism. Infections occur from the reservoir outside the host e.g. contaminated surfaces/foods/water or airborne transmission (sneezing/coughing droplets in the air)

Diseases caused by this include COVID, Influenza etc

A type of indirect transmission in which a pathogen is transferred from one host to another via an intermediate host or vector. The list of vectors is extensive, but it mainly includes

- Mosquitoes (Malaria, dengue, Ross River virus, etc.)

Robert Koch was a physician who introduced germ theory through his postulates

1. The same pathogen must be present in every case of the disease.
2. The pathogen must be isolated from the diseased host and grown in pure culture.
3. The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible host
4. The pathogen must be isolated from the inoculated animal and must be shown to be the original organism.

He proved that a specific microorganisms (pathogen) cause specific diseases

Considered the 'Father of modern microbiology' due to his work in disproving spontaneous generations, developing pasteurisation and overall proving the germ theory

showed microbes caused fermentation & spoilage
disproved spontaneous generation
developed pasteurization
demonstrated the germ theory of diease

The Swan Necked flask experiment disproved spontaneous generation as the straight necked flasks became cloudy and spoiled whereas the swan-necked flasked remained clear and unspoiled.

Agriculture involves growing crops and raising animals for the purpose of providing food and other resources for humans. Due to our isolation, Australia is free from many diseases that impact agricultural production in other parts of the world. Additionally, we have strict biosecurity measures that reduce the risk of disease transmission. Thus, our agricultural products are highly sought after and important for our economy. Introduction of diseases to Australia could be devastating for this industry.

Unlike animals, plants do not have an immune system. However, they are able to respond to limit the spread and growth of pathogens with some well-developed "lines of defence". Plants that can prevent the pathogen from invading their cells or prevent it from reproducing are said to be resistant to the pathogen

1. Passive defences
2. Active defences

Physical barriers: can inhibit entry of the pathogen e.g. thick cuticle, cell walls, small stomata, bark, vertical hanging leaves (don't accumulate a water film that acts as a reservoir for pathogens)

Chemical barriers: chemical compounds in tissues of plants reduce fungal and bacterial growth or enzymes to break down toxins from pathogens. Chemical receptors on plant cells can also detect the presence of a pathogen and activate the next line of defence.

- Pathogen recognition: Plants are able to recognise pathogens through certain chemical and physical signals

- Rapid active response (minutes to hours): Quick responses provided by the plants typically to help seal off any wounds
EG: Programmed cell death (apoptosis) causes a cluster of dead cells to accumulate around the pathogen to trap it, followed by secretion of antimicrobial compounds.

- Delayed active response (days): Occurs after days of infection and limits the spread of the invading pathogen and involves complex chemical signalling
EG: Salicylic acid acts as a signalling agent after infection playing a role in plant memory of a pathogen

Complex, multicellular organisms have multilayered systems to defend against infection and colonisation by pathogens. The immune system of animals is highly organised and involves three "lines of defence".

The first and second lines of defence are known as the innate immune system - it is what an animal is born with.

The third line of defence is known as the adaptive immune system as it develops throughout the organism's life time.

It is a non-specific system of protection it involves:

Physical barriers - Skin, hair, mucus, stomach acid digestive enzymes etc

Internal Defences - Inflammatory response, phagocytosis (macrophages), Natural Killer Cells (NK) and fever symptons

Specific defensive system (learnt) that eliminates pathogens and abnormal cells.

Developed throughout the lifetime of an organism and is specific to pathogens. The adaptive immune response (or third line of defence) is activated when the innate immune response is unable to clear a pathogen from the body. The main cells responsible for the adaptive immune response are lymphocytes (B and T cells)

1. The production & release of Antibodies
2. Cell-Mediated response (T Cells)
3. Humoral immune response (B Cells)

Cell-mediated response is responsible for eliminating pathogens that are inside host cells. Antibodies are unable to access pathogens inside cells and so these cells are targeted by special T lymphocytes (T cells) which kill the cell and destroy the pathogen along with it

T cells are made in the bone marrow and they mature in the thymus glan. The main ones include:
- Helper T Cells - Activate B cells and Cytotoxic cells
- Cytotoxic T Cells - Kills the cell/pathogen with cytokines
- Suppresor T Cells - Stop the adaptive responses after the pathogen has been killed
- Memory T Cells - remain in the body to respond to future exposure from the same pathogen

Strategies to target and inactivate pathogens that are outside the cells (in body fluids). B lymphocytes (or B cells) are primarily responsible for this response.

B cells are made and mature in the bone marrow. These mature B cells are stored in the lymph nodes and tissues and circulate in the blood.

B Cells once activated by T Cells, differentiate into two cells:
- Plasma Cells (short-lived cells that secrete antibodies)
- Memory Cells (long-lived cells stored for future infection)

Leukocytes (white blood cells) coordinate the defence against infectious disease:

1. Neutrophils - Must abundant WBC, first to respond, undergo phagocytosis
2. Monocyte - Undergo Phagocytosis (macrophages). Largest type of WBC, slower to respond but last longer
3. Lymphocytes (part of the adaptive immune system) responsible for the production of antibodies and include B and T Cells

An antigen is a molecule that is capable of producing an immune response

Antibodies are Y-shaped protein molecules produced by your immune system to attack and fight off antigens.

Local factors usually relate to a neighbourhood, village, town or city. Factors that may impact spread of disease include:
- sanitation, especially waste and sewage disposal
- overcrowding
- local cultural or spiritual practices may influence spread of disease or access to healthcare

- Increased mobility of people aroud the world (travel)
- The rise of antibiotic resistant strains of bacteria
- Poor living conditions (lack of health care/vaccinations)

Local:
- Immunisation programs released by local governments
- The creation of supportive environments
Regional:
- Limiting direct transimission through border control/quarantine measures
Global:
- The release of global vaccination programs and the coordination of community and local public health measures

Hygiene is a set of practices performed to maintain good health and minimise the spread of pathogens. Good hygiene can be personal, communal or food/water related

Refers to the practices that an individual performs to minimise the risk of infection
- Frequent bathing
- Handwashing with soap and water
- Correct respiratory hygiene when coughing and sneezing (not coughing into the air)

refers to the practices performed at the local level to minimise disease spread
- Water purification systems
- Sewerage and garbage infrastructure and removal systems
- Sterilisation of equipment at local medical orgranisations (dentists, hospitals, surgeries etc)

refers to hygiene practices in which relate to food/water and prevent poisoning
- Keeping raw and cooked foods separate avoiding contamination
- Cooking foods for the appropriate time and temperature
- Using clean water for cooking
- Storing food at a recommended temperature (refrigerators)

Quarantine → Public health measure imposed to prevent the spread of disease or unwanted animals or plants through strict isolation periods
- Form of biosecurity
- minimse the risk of exotic pests/disease

Animal:
- Quarantine stations for up to 40 days to ensure they are disease free
Plant:
- Examining all plants for signs of pest and/or disease
Human: (regionallobal levels)
- Limiting/controlling human mobility through travel restictions and quarantine periods

injection of an attenuated (weakened) form of a pathogen to trigger a immune response.

By doing this the individual does not get the disease yet immunisation is still achieved

The process by which a person develops immunity to a disease-causing organism

Active acquired immunity occurs when the immune response occurs and memory cells are produced. This can occur naturally when the body is exposed to an antigen in a natural setting, or artificially when antigens are introduced through the use of vaccines.

Passive aquired immunity is when a person is given antibodies to a disease rather than producing them through his or her own immune system. Eg: A newborn baby acquires passive immunity from its mother through the placenta.

Public Health Campaigns are advertised and/or provided to the public to convey a health message to persuade the community to engage in behaviours that will improve their health or have them refrain from the behaviours that are unhealthy. It provides Health promotion information focusing on behavioural risk/protective factors of transmitting a disease.

EG: encouraging people to wear mask, sanitise, stay home to mitigate the spread COVID-19

1. The grim reaper campaign
- Australian TV commercial aimed at raising public awareness of the dangers of HIV/AIDS
- The campaign was a great success, contributing to the mass decline of incidence rates a decade after

2. The HPV vaccination program
- HPV is a common virus affecting both men and women
- HPV is spread through sexual contact
- Extensive trials demonstrated that vaccinating young women with the HPV vaccine significantly reduces the risk of cervical cancer
- As a result, a free national HPV vaccination program was released

Pesticides are chemicals used to kill the pests of plants and animals which include both pathogens and the vectors that transfer them between organisms.

Example: DDT (dichlorodiphenyltrichoroethane)
- DDT insecticide was used to kill Anopheles Mosquito, which is a vector for malaria disease as it carries the plasmodium pathogen.
- However, the effectiveness of DDT was reduced as mosquitoes developed resistance to it due to natural selection.
- However, despite the inevitable development of resistance by the pesticides and pesticides' negative impact on human health and the environment, alternative solutions are currently being researched.

Genetic engineering involves altering the genetic composition of an organism. One of the reasons that scientists do this is to make the organism resistant to diseases, preventing illness and transmission of the disease.

Example: CRISPR Cas-9 (Mosquiote borne diseases)
By using the new gene editing technology called CRISPR Cas-9, a gene can be introduced to a mosquito's genome causing death in the late larval stage. As the mosquitoes don't survive to adulthood, they are unable to transmit the disease or reproduce, thus reducing the vector populations.

A class of medication used to treat viral infections. The aim of antiviral therapy is to minimize the symptoms and to shorten the duration of illness. These drugs act by arresting the viral replication cycle at various stages.

Drugs that kill or prevent the growth of bacteria without killing healthy body cells.

- Selectively Toxic
- Do not work on viruses (non-cellular/no metabolism)
- Reduce mortality and disease rates
- Effectiveness has diminished due to bacteria evolving/conferring resistance (overuse) = limitation

Effectiveness has diminished due to bacteria evolving and conferring resistance (e.g. Golden Staph)

People get infected with Ebola through direct contact, this includes:
- infected animals when preparing, cooking or eating them
- body fluids of an infected person such as saliva, urine, faeces

Ebola enters the body through cuts in the skin or when touching one's eyes, nose or mouth.

Environmental control — facilities for barrier nursing, hand hygiene, waste management (leak proof bags, covered bins), PPE (masks, gloves, waterproof boots, respirator, suit), surfaces sterilised every day.

Quarantine — isolate patients in single room/at least 3m between patient beds. Same clinical staff and equipment assigned to single patients. Restricted visits

The incidence of a disease is the number of new cases of the disease in a given time period.
(No. of new cases/Size of the population at risk at start of the period) x 100

The prevalence of a disease is the proportion of the population that have the disease at a particular point in time
{ (All new cases + previous cases)/ Population during the time period } x100

Mortality is the number of people who die from a disease.

Mobility refers to the geographic movement of people from their usual place of residence. As air travel has become more affordable and accessible, the mobility of the population has increased which has led to the spread of disease across the globe.

Mosquito-borne tropical disease caused by dengue virus
● Infection results in fever, headache, joint pain and rashes
● May lead to the development of dengue haemorrhagic fever (DHF)
● Common in south-east asia and the western pacific

● 390 million infections globally per year
● 75% of global population exposed to DF live in the Asia-Pacific region

● Found in tropical and sub-tropical climates
● Most countries in south-east Asia experience a higher burden of DF or DHF with frequent cyclical
epidemics (3-5 year cycles)
● Typically affects children (2-15 years old) at a higher rate than adults
● Expected rate of DF will increase over time due to viral evolution, climate change, globalisation,
travel/trade and settlement and socioeconomic factors.

Epidemiology is the study of the incidence, prevalence, causes and control of disease and other factors relating to health

● Mid 1800s → Pasteur and Koch predicted spread of disease was caused by pathogens

● 1854, John Snow successfully used a 'spot map' to identify the relationship between people affected with cholera and contact with polluted sewage water from a local river.
- Before then, it was believed that cholera is due to contact with miasma, but after it was found to be the Broad St Pump

Different cultures would have different traditional methods in treating diseases passed down through generations.
For example, the Aboriginal People of Australia have acquired extensive knowledge in using native Australian flora to treat diseases. (Bush medicine)

● Ensuring, monitoring and supply of clean water
● Appropriate handling and treatment of sewage waste.
● Antibiotics & Anti-viral drugs.
● Vaccines
● Public Health Campaigns
● Quarantine (Isolation in hospitals etc)
● Pesticides
● Genetic Engineering

For thousands of years, Indigenous Australians have used native plants to treat wounds, bites and illnesses. This is referred to as "bush medicine".

There has been renewed interest in traditional Aboriginal medical knowledge, with many groups gathering data to ensure that the knowledge is not lost.

A plant that has been used for healing by Indigenous Australians for thousands of years. Pharmaceutical companies are also investigating the uses of this plant and its potential to be used to treat cancer and HIV/AIDS

- Adhesion or the ability to attach to host tissue
- The ability to withstand harsh internal/external environments (secrete enzymes to better suit the environment by making it less toxic)
- Antigen Variation - Changing these antigens allows pathogens to avoid detection from the hosts immune system (viruses acquiring immunity from antibodies)

- Using a vector (a vector is any agent that carries and transmits an infectious pathogen to another organism)
- Airborne/Waterborne - Pathogens that are resistant to drying out (dessication) may survive outside a host for a long period of time
- Vomitting and Diarrhoea