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List 3 ways parasites affect ecosystems
impact the distribution and abundance of host populations
affect community interactions
influence ecosystem functioning
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
Define pathogenicity
the ability to cause disease
Define virulence
the degree of pathogenicity
How can you calculate infection?
(# of organisms x virulence) / host resistance
How is virulence measured?
experimentally by determining the lethal dose 50 (LD50) and infectious dose 50 (ID50)
How many cells of salmonella are required to cause disease?
>1,000
How many cells of campylobacter are required to cause disease?
~500-10,00
How many cells of shigella are required to cause disease?
<10
What is the ID50 of cutaneous anthrax?
10-50 endospores
What is the ID50 of inhalation anthrax?
10,000-20,000 endospores
What is the ID50 of gastrointestinal anthrax?
250,000-1,000,000 endospores
List the 6 components of the chain of infection
infectious agent
reservoirs
portal of exit
means of transmission
portal of entry
susceptible host
What can reservoirs be split into?
animate reservoirs (biotic) and inanimate reservoirs (abiotic)
List 5 portals of exit
excretions
secretions
skin
droplets
body fluid
List 4 portals of entry
GI tract
GU tract
respiratory tract
broken skin
List 5 virulence factors of bacteria
capsule
cell wall
enzymes
antigenic variation
biofilm
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
What are exotoxins?
proteins produced inside pathogenic bacteria that are secreted into the surrounding medium during log phase
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
What are exotoxins often released from?
gram positive bacteria
What are endotoxins often released from?
gram-negative bacteria
How do viruses avoid host immune response?
by growing inside cells
How do viruses gain access to host cells?
attaching via complimentary attachment sites for host cell receptors
What are cytopathic effects?
visible signs of viral infection
What are cytocidal effects?
cell death
What are non-cytocidal effects?
cell damage but no death
List 4 cytopathic effects
cessation of mitosis
lysis
chromosomal changes
cell fusion
List 3 ways that fungal infections can be caused
capsules
toxins
allergic responses
How do protozoa and helminths cause infection? (2 points)
causing mage to host tissue
harmful metabolic waste products of the parasite
How do some algae cause infection?
producing neurotoxins that cause paralysis when ingested by humans
Define resistance
the ability to limit pathogenic burden
Define tolerance
the ability to limit health impact of a given pathogenic burden
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
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
Define microevolution
small, random genetic changes hat occur over generations to drive either speciation or extinction (both macroevolution)
List 3 classes of pathogenic evolution
drug resistance
immune iscape
adaptation to new hosts
Explain red queen dynamics
to hold your space, you always have to run
Link red queen dynamics to evolution
suggests coevolution between host and parasite drives a constant cycle of adaptation
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
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