T8: Infectious Disease Flashcards
(21 cards)
Pathogens
viruses
bacteria
parasitic microbes
Coevolutionary arms race
pathogens evolve to exploit hosts (us)
hosts evolve resistance
pathogens evolve to overcome resistance
Viruses
protein boxes that transport a viral genome from one cell to another
obligate intracellular parasites
divert host resources for viral reproduction
^destroys cells (cause of flu/cold symptoms)
Pathogens evolutionary advantage over host
- Rapid evolution
- short gen time
- horizontal transmission (bacteria) - massive population size - ^chance of beneficial mutations
- can live in greater range of enviros
Virulence
damage caused by infection due to the pathogen’s intrinsic properties (not host’s response)
Effects of infection on host
virulence + host response to infection
what effects virulence evolution
1.virulence-transmission trade-off
2.mode of transmission
3.new host/ old host
virulence-transmission trade-off
more virulent = less chance for transmission
and vice versa
overly virulent pathogens
dead / immobilized host = low transmission
optimal virulence equation
max # 2ndary infections from primary infection = transmission rate / total parasite mortality rate
Vertical transmission
parent - offspring
decreased virulence
cost to hosts = costs to pathogens
evolve towards chronic illness/commensal/beneficial
Horizontal transmission
-host to host (not offspring)
-increased virulence
-lower penalty for damaging hosts
-favours increased virulence to maximize transmission
pathogens going to humans from animals
- ‘emerging infectious diseases of animal origin’
2.Zoonoses
‘Emerging infectious disease of animal origin’
- Pathogens that make the jump to humans and then evolve to specialize on humans
- unpredictable virulence
Zoonotic diseases
an infection that’s naturally transmitted from vertebrate animals to humans (World Health Organization)
- Jumps to humans, but either doesn’t stay in a population or stays only transiently
ebola, SARS, rabies
‘reservoir’ host
an organism (or organisms) in which a pathogen naturally lives and reproduces
zoonotic disease virulence
- very fatal
- virulence not calibrated to humans
- If they don’t reproduce in us, reduced virulence doesn’t evolve
Bats
- feel few symptoms from viruses deadly to other hosts
protected immune system
- high resistance - limit viral load
- high tolerance - reduces symptoms of viral load
Black death
bubonic plague
single greatest mortality event
potential for very strong natural selection
elite controller
someone w hiv who doesnt need meds to control the infection
MHC
major histocompatibility complex
200 genes on chromosome 6
very variable
help immune system detect infections
HIV epidemics appear to generate selection for certain MHC alleles
