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evolutionary medicine
• diseases tracking hosts,
and jumping to new hosts
• virulence evolves
• resistance evolves
• antibiotics and
evolutionary responses
openclipart.org
Cytomegalovirus
pathogens tend to track
hosts
• Hosts are ENVIRONMENTS
• immune response, nutrients,
habitat density, physiological
limits
• Some pathogens are
specialists on narrow range
of hosts, others are
generalist, broader niche
Habitat shift is
Often to a similar
Environment
(Related species)
But not always similar!
SARS virus apparently
Jumped from bats
To civets
To humans
2003-04
Coinfection
2002-03
• Hemagglutinin evolution
in flu virus can evolve
through mutation as well
as horizontal gene
transfer from other virus
when in same host
• Required new vaccine to
be developed
Avian strain
evolved
Virulence
In dense
aggregations
Human strain
evolved
With human
Environmental
background
Bats also
A common
Source
Human strain
evolved
With human
Environmental
background
2013: new outbreak of SARS - like virus
In Middle East, appears again to originate in bats
Again, we figure this out
using PHYLOGENETICS
Virus artificial
selection
= vaccine
Variation (high
mutation rate, large
population size)
May be heritable
Differential survival
Ones that survive carry
genes that increased
fitness
How vaccine is developed using
adaptation as a tool
Green Goo
Awful Orange
Give one to
UP TO 2
People YOU CAN REACH
without standing
Give one to
Next nearest person
(However far)
Discuss
• what element of pathogen biology did we
simulate?
• what happened to each pathogen?
• what were the parameters in our model?
• what would you change?
What happens when a
dense population with
different demographics
and migration patterns...
Meets a sparse
population that is naïve
to the pathogen?
Virulence
Virulence associated w growth rate: uses
host resource, by-product is disease
Larger number people one interacts with
Why selection affects
virulence?
1. Population dies out if uses up resources before it
finds more (general, selection is at level of host
population)
2. Less quick-growing strain loses reproductive
advantage to faster (more virulent) strain, selection is
within host
3. Note selection (evolution) and competition (ecology)
are analogous ways to discuss differential
performance of diversity
Lateral gene
transfer
• Diversity effect
of sexual
recombination,
across diverse
microbial taxa
• SUPERBUGS
• Strategy to cycle different antimicrobials in
facility - helps population resistant to one
antibiotic now be exposed to a second (can
evolve)
• Instead different treatment for each patient
appears to have theoretical/model advantage
Bergstrom's work suggests using multiple drugs in random
design is probably best for limiting bacterial evolution
• Not just in
humans,
HUGE usage
in animals
leads to
resistant
strains in
livestock AND
US
no class thursday
• Away at funeral
• We will finish
chapter 18 (aging
and cancer among
the topics) next
Tuesday, stop
there
• Exam next
Thursday 11/21