Module 7 - Infectious Disease

Question 1

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How can pathogens be classified?

Answer 1

• Prions
• Virus
• Bacteria
• Protozoans
• Fungi
• Parasites

Question 2

Describe prions and the disease it can cause

Answer 2

• defective form of protein molecule
• Non-living and non-cellular
• no DNA or RNA
• 10nm
• Mad cow disease

Question 3

Describe viruses and the disease it can cause

Answer 3

• Requires living host cell to repllicate
• Non-living and non-cellular
• contains DNA and RNA
• 500nm
• Influenza A

Question 4

Describe bacteria and the disease it can cause

Answer 4

• Cell wall surrounding cell
• Living
• Prokaryotic, unicellular
• 100um
• Salmonella enterica - Salmonella -> vomiting cramps, dehydration

Question 5

Describe protozoans and the disease it can cause

Answer 5

• Complex life cycle
• Living
• Eukaryotic, unicellular
• 50-150um
• Malaria - plasmodium sp.

Question 6

Describe Fungi and the disease it can cause

Answer 6

• Has cell wall and chitin
• Living
• Eukaryotic, unicellular or multicellular
• um-mm
• Athlete’s foot

Question 7

Describe macro-parasites and the disease it can cause

Answer 7

• arthropods or worms, internal or external
• Living
• Eukaryotic, multicellular
• mm-m
• Tapeworm - malnutrition

Question 8

Explain the modes of transmission of infectious diseases

Answer 8

Direct contact: person-to-person contact or droplets spread from an infected individual who touches or exchanges body fluids with another individuals through touching, kissing or coughing.
e.g. chickenpox

Indirect contact: Airoborne (suspended in air), contaminated objects, food, or water
E.g. E.coli

Vector transmission: uses living organism as a medium to spread disease through bites
e.g. Malria

Question 9

Explain the role of Koch’s postulates

Answer 9

Proved that specific microbes caused specfic diseases

1. Same microorganism should be found in all organisms suffering from disease
2. Microbe is extracted and cultured
3. Cultured agent is isolated and healthy host is infected
4. Same symptoms should be displayed in host
5. Cultured agent from infected host is compared to original microbe and should be identical

Question 10

Explain the role of Louie Pasteur

Answer 10

Established Germ Theory, disproved spontaneous generation, developed first vaccine, fermentation, pasteurisation

1. Two identical flasks of broth are prepared and boiled
2. One of the swan necks are removed from the flask while the other remains
3. Dust and bacteria in the air enters flask 1, causing microbial growth while flask 2 remains the same
4. Disproved the theory of spontaneous generation -> in the air surrounding us

Question 11

Assess the cause and effects of plant diseases on agricultural production

Answer 11

Fire Blight
Highly infectious worldwide disease caused by bacterium Erwinia amylovora and infecting pome fruits. This results in tissue death and bacterial ooze droplets which can be spread to health plants through rain, wind and insects.
Impact: This cost $AU20 million in revenue when found in Melbourne 1997. However, strict quarantine and biosecurity has removed the disease in Australia.

Question 12

Assess the cause and effects of animal diseases on agricultural production

Answer 12

Foot and mouth disease
Highly contagious disease infecting cloven-hoofed animals such as cattle, sheep and pigs and caused by FMD virus. This causes fever and blisters in the mouth and hooves, leading to severe production losses as heards become destroyed.
Impact: meat and live animals make up 29% of Austrlia’s agricultural exports. Countries will only import livestock free of FMD, causing severe economic consequences.

Question 14

Explain the response of a named Australian plant to a named fungal pathogen

Answer 14

Marri Gum is native to Western Australia and is vulnerable to an introduced water mould, P.cinnamomi. The fungal pathogen lives in soil, attacking the roots of plants and leaving them unable to absorb nutrients and water.
Response: Increased lignin production protecting cell wall from pathogens

Question 15

Analyse responses to the presence of pathogens by assessing the physical and chemical changes in animal cells and tissues

Answer 15

First line of defence - Innate, non-specific
Physical
* Skin: prevents pathogen penetration
* Mucous membrane: traps debris and microbes upon entrance
* Cilia: directs pathogen away from organs

Chemical
* Sweat: breaks down bacterial cell wall
* Amyalse and stomach acid: prevents growth and perforate most microbes,
* Urine: antimicrobal peptides along urinary tract prevent bacteria from growing

Question 16

Explain the second-line of defence in the immune system response

Answer 16

Inflammatory response: Mast cells in damaged tissues release histamine that triggers the dilation of blood vessels and increases vascular permeability, causing redness, swelling and fever. The increased temperature makes the environment inhabitable for the pathogen.

Phagocytosis: More white blood cells like macrophages and neutrophils move into damaged tissue to engulf the pathogen. This combines with lysosome containing protease which break down the antigen and later undergo apoptosis

Lymph system: picks up the remaining microbes and pus (dead cells) then traps them in lymph nodes to be destroyed by phagocytes

Granuloma: neighbouring cells die, forming a capsule with a wall of necrotic tissue surrouding the infected cells.

Question 17

Explain the third-line of defence in the immune system response

Answer 17

Specific defence - Adapative immunity
A unique helper T-cell recognises the MHC II antigens presented on infected cells, releasing cytokines to trigger the cloning of specific B-cells and T-cells with unique matching (BCR) or (CD3)

Antibody mediated response
* Plasma B cells: rapidly produce antibodies which bond with antigens, forming an antibody-antigen complex (agglutination and neutralisation)
* Memory B cells: remain stored in body reader for subsequent exposure

Cell mediated response
* Killer T-cells: inject perforins into infected cells causing apoptosis
* Memory T cells: remain in body read for subsequent exposure
* Supressor T cells: stop immune response when antigen is destroyed

Question 18

How can local, regional and global spread of infectious diseases be limited?

Answer 18

Covid-19
Local: online school, hospitals
Regional: aeroplans,
Global: transport, trading

Question 19

Analyse procedures that can be employed to prevent the spread of disease

Answer 19

• Hygiene practices: kills pathogens and reduces spread e.g. handwashing, cooking
• Quarantine: strict isolation prevents spread
• Vaccination: passive immunity (injection of antibodies for immediate protection, short-term as no memory) active immunity (inactivated version of pathogen leading to production of antibodies for specific antigen)
• Public health campaigns: health education to minimise spread
• Use of pesticides: chemicals preventing spread of pathogens
• Genetic engineering: modification of organism genome (inserting transgene) to create altered phenotype

Question 20

Assess the effectiveness of pharmaceuticals

Answer 20

Antivirals: treats viral infections by killing the virus or supressing its ability to replicate.
-> can damage host cell, expensive

Antibiotics: treats bacterial infections (penicilin) interfering with formation of cell membran and DNA replicatin.
-> treats infection, antibiotic resistance

Question 21

Explain environemental management and quarantine methods

Answer 21

Environemental
* Vacciantion
* Water supply
* Food Source
* Hygiene

Quarantine
* Inspection: entrance
* Regulation: rules
* Restriction of movement: travel ban
* Destruction of diseased organism