Infectious Disease - causes of infectious disease

Question 1

List the infectious agents/pathogens - smallest to largest

Answer 1

1. prions
2. Viruses
3. Bacteria
4. Protozoans
5. Fungi
6. Macroparisites

Question 2

Prions

Answer 2

Prions are a non-cellular pathogen. They are Infectious proteins that do not contain any genetic material.
E.g CJD or mad cow disease

Question 3

Viruses

Answer 3

Viruses are non-cellular and non-living pathogens. They consist of a protein coat that encloses genetic material.
E.g. HIV

Question 4

Bacteria

Answer 4

Bacteria are single-celled prokaryotic organisms. They have a cell wall but no membrane-bound organelles.
Reproduction occurs through binary fission (division into two)
E.g E.coli

Question 5

Fungi

Answer 5

Fungi are eukaryotic organisms and can be unicellular or multicellular. They have a cell wall and reproduce both sexually/asexually
E.g. Athletes foot

Question 6

Protozoans

Answer 6

Protozoa are single-celled eukaryotic organisms. they have a membrane-bound nucleus/organelles and a cell membrane but no cell wall.
Reproduction occurs through binary fission (division into two)
E.g. Malaria

Question 6

Macroparisites

Answer 6

Macroparisites are multicellular and eukaryotic. They can be seen with the naked eye and reproduce sexually.
E.g ticks

Question 7

Modes of transmission - DIrect contact

Answer 7

(horizontal transmission) Transfer of the pathogen via exposure to infected skin or body secretions
E.g. kissing, touching, biting

(Vertical transmission) Transfer of the pathogen from mother to child prenatal/perinatal

Question 8

Modes of transmission - Indirect contact

Answer 8

(horizontal transmission) Transfer of pathogen to a new host via a non-living object
E.g. contaminated food, airborne transmission, infected surfaces

Question 9

Modes of transmission - Vector transmission

Answer 9

Transfer of pathogen via another organism
E.g mosquitos

Question 10

Modes of transmission - Vehicle Transmission

Answer 10

Transfer of a pathogen via a contaminated object (fomite)

Question 11

Robert Koch and louis Pasteur

Answer 11

Koch and Pasteur made some of the most significant discoveries in human history regarding the causes/spread of infectious disease.
Disproved spontaneous generation and replaced it with germ theory – germs (microbes) cause diseases and all micro-organisms come from pre-existing micro-organisms.

Question 12

Robert Koch

Answer 12

Koch discovered and established the criteria that must be met to determine whether a particular microorganism is responsible for causing a disease – Koch’s Postulates.

[COMMON, CULTURE, CAUSE, COMPARE]

Question 13

Kochs postulates

Answer 13

1. the microorganism or other pathogen must be present in all cases of the disease
2. the pathogen can be isolated from the diseased host and grown in pure culture
3. the pathogen from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal
4. the pathogen must be reisolated from the new host and shown to be the same as the originally inoculated pathogen

Question 14

Louis pasteur

Answer 14

Pasteur performed his swan neck flask experiments and disproved spontaneous generation and clearly demonstrated that microbes are airborne and thus could be transmitted from an infected to non-infected individual

Question 15

Swan neck flask experiment

Question 16

Effects on agricultural production

Answer 16

o Death of infected animals/livestock, which in turn reduces productivity
o Global crop production decreases and is lost
o Loss of international trading opportunities
o Loss of economic value of individual animals
Collectively these losses limit the availability of food, fibre, and dairy products

Question 17

plant disease

Answer 17

POTATO BLIGHT
Potato blight was caused by a mould (phytophthora infestans) that is a fungal pathogen found in potatoes and tomatoes, it destroyed crops and spread quickly. It spread quickly through spores that are frequently released and can be further dispersed by wind and soil.

Question 18

Animal disease

Answer 18

FLYSTRIKE
Flystrike is caused by several species of blow flies (macro parasite). The Australian blowfly (lucilia cuprina) is responsible for over 90% of flystrike in sheep.

Question 19

Adaptations of different pathogens - Prions

Answer 19

May attach to other proteins such as meat proteins to facilitate movement through the gut
E.g. scrapie in sheep

Question 20

Adaptations of different pathogens - Viruses

Answer 20

Entry - Contains a viral envelope to protect DNA and prevent recognition by host immune system

Transmission - Small and can remain suspended in the air on mucous droplets, thus highly effective at indirect transmission

Question 21

Adaptations of different pathogens - Bacteria

Answer 21

Entry - Pili on surface and production of biofilm makes them sticky and provides protection against hosts immune response and enzymes such as collagenase break down cell content.

Transmission - Induce vomiting and diarrhoea to expel them to other hosts E.g. E.coli and other food poisoning bacteria.

Question 22

Adaptations of different pathogens - Fungi

Answer 22

Entry - Cell wall and capsule protection provide protection from host attacks

Transmission - Microscopic spores are light and can travel through air and soil that can touch body surfaces or be inhaled, thus easy transmission.

Question 23

Adaptations of different pathogens - Protzozoan

Answer 23

Entry - Has several stages to their life cycle and thus prevents the immune system from initiating an effective response.

Transmission - Uses insect vectors (mosquitoes) which aids in fast transmission

Question 24

Adaptations of different pathogens - Macroparisites

Answer 24

Entry - highly specialised mouthparts are inserted into host skin to attach.

Transmission - Many can crawl/fly thus easy and effective transmission e.g. ticks