2 - Host-Parasite interactions

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41 Terms

1
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List 3 ways parasites affect ecosystems

  • impact the distribution and abundance of host populations

  • affect community interactions

  • influence ecosystem functioning

2
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Give an example of how a parasitic infection could influence ecosystem functioning

parasites may have a role in regulating the populations of their hosts or may alter host behaviour to encourage spread infection

3
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Define pathogenicity

the ability to cause disease

4
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Define virulence

the degree of pathogenicity

5
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How can you calculate infection?

(# of organisms x virulence) / host resistance

6
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How is virulence measured?

experimentally by determining the lethal dose 50 (LD50) and infectious dose 50 (ID50)

7
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How many cells of salmonella are required to cause disease?

>1,000

8
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How many cells of campylobacter are required to cause disease?

~500-10,00

9
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How many cells of shigella are required to cause disease?

<10

10
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What is the ID50 of cutaneous anthrax?

10-50 endospores

11
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What is the ID50 of inhalation anthrax?

10,000-20,000 endospores

12
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What is the ID50 of gastrointestinal anthrax?

250,000-1,000,000 endospores

13
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List the 6 components of the chain of infection

  • infectious agent

  • reservoirs

  • portal of exit

  • means of transmission

  • portal of entry

  • susceptible host

14
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What can reservoirs be split into?

animate reservoirs (biotic) and inanimate reservoirs (abiotic)

15
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List 5 portals of exit

  • excretions

  • secretions

  • skin

  • droplets

  • body fluid

16
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List 4 portals of entry

  • GI tract

  • GU tract

  • respiratory tract

  • broken skin

17
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List 5 virulence factors of bacteria

  • capsule

  • cell wall

  • enzymes

  • antigenic variation

  • biofilm

18
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List 4 mechanisms of bacterial damage to host

  • using host nutrients

  • causing direct damage in immediate vicinity of invasion (localised)

  • producing toxins, transported by blood and lymph, that damage sites away from original site of invasion (systematic)

  • by producing hypersensitivity reactions

19
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What are exotoxins?

proteins produced inside pathogenic bacteria that are secreted into the surrounding medium during log phase

20
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What are endotoxins?

lipid portions of lipopolysaccharides that are part of the outer cell wall of bacteria. They’re liberated when bacteria die and the cell wall lyses

21
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What are exotoxins often released from?

gram positive bacteria

22
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What are endotoxins often released from?

gram-negative bacteria

23
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How do viruses avoid host immune response?

by growing inside cells

24
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How do viruses gain access to host cells?

attaching via complimentary attachment sites for host cell receptors

25
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What are cytopathic effects?

visible signs of viral infection

26
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What are cytocidal effects?

cell death

27
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What are non-cytocidal effects?

cell damage but no death

28
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List 4 cytopathic effects

  • cessation of mitosis

  • lysis

  • chromosomal changes

  • cell fusion

29
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List 3 ways that fungal infections can be caused

  • capsules

  • toxins

  • allergic responses

30
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How do protozoa and helminths cause infection? (2 points)

  • causing mage to host tissue

  • harmful metabolic waste products of the parasite

31
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How do some algae cause infection?

producing neurotoxins that cause paralysis when ingested by humans

32
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Define resistance

the ability to limit pathogenic burden

33
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Define tolerance

the ability to limit health impact of a given pathogenic burden

34
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Are pathogens under selective pressure when a host has high resistance and why

yes, when the host’s immune system is able to recognise pathogenic antigens and destroy them, there is a selective pressure to become resistant

35
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Are pathogens under selective pressure when a host has high tolerance and why

no because infection still occurs but the main focus is limiting health impact as opposed to destroying the infectious agent

36
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Define microevolution

small, random genetic changes hat occur over generations to drive either speciation or extinction (both macroevolution)

37
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List 3 classes of pathogenic evolution

  • drug resistance

  • immune iscape

  • adaptation to new hosts

38
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Explain red queen dynamics

to hold your space, you always have to run

39
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Link red queen dynamics to evolution

suggests coevolution between host and parasite drives a constant cycle of adaptation

40
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List 2 methods of transition between a one and two host-life cycle

  • upward incorporation of a definitive host

  • downward incorporation of an intermediate host

41
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Why do we see periodic epidemics of influenaz when new strains emerge

antigenetic drift leads to new strains with different HA/NA antigens that are able to infect people resistant to other strains