Infectious Disease - causes of infectious disease Flashcards
List the infectious agents/pathogens - smallest to largest
- prions
- Viruses
- Bacteria
- Protozoans
- Fungi
- Macroparisites
Prions
Prions are a non-cellular pathogen. They are Infectious proteins that do not contain any genetic material.
E.g CJD or mad cow disease
Viruses
Viruses are non-cellular and non-living pathogens. They consist of a protein coat that encloses genetic material.
E.g. HIV
Bacteria
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
Fungi
Fungi are eukaryotic organisms and can be unicellular or multicellular. They have a cell wall and reproduce both sexually/asexually
E.g. Athletes foot
Protozoans
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
Macroparisites
Macroparisites are multicellular and eukaryotic. They can be seen with the naked eye and reproduce sexually.
E.g ticks
Modes of transmission - DIrect contact
(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
Modes of transmission - Indirect contact
(horizontal transmission) Transfer of pathogen to a new host via a non-living object
E.g. contaminated food, airborne transmission, infected surfaces
Modes of transmission - Vector transmission
Transfer of pathogen via another organism
E.g mosquitos
Modes of transmission - Vehicle Transmission
Transfer of a pathogen via a contaminated object (fomite)
Robert Koch and louis Pasteur
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.
Robert Koch
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]
Kochs postulates
- the microorganism or other pathogen must be present in all cases of the disease
- the pathogen can be isolated from the diseased host and grown in pure culture
- the pathogen from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal
- the pathogen must be reisolated from the new host and shown to be the same as the originally inoculated pathogen
Louis pasteur
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
Swan neck flask experiment
Effects on agricultural production
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
plant disease
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.
Animal disease
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.
Adaptations of different pathogens - Prions
May attach to other proteins such as meat proteins to facilitate movement through the gut
E.g. scrapie in sheep
Adaptations of different pathogens - Viruses
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
Adaptations of different pathogens - Bacteria
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.
Adaptations of different pathogens - Fungi
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.
Adaptations of different pathogens - Protzozoan
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
Adaptations of different pathogens - Macroparisites
Entry - highly specialised mouthparts are inserted into host skin to attach.
Transmission - Many can crawl/fly thus easy and effective transmission e.g. ticks
