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 isOften to a

similarEnvironment

(Related species)

But not always similar!

SARS virus apparently

Jumped from batsTo civets

To humans

Coinfection

• 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

20

02

-03

20

03

-04

Avian strain evolved

VirulenceIn dense

aggregations

Human strain evolved

With humanEnvironmental

background

Bats alsoA common

Source

Human strain evolved

With humanEnvironmental

background

2013: new outbreak of SARS - like virusIn 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

Awful Orange

Give one toUP TO 2

People YOU CAN REACHwithout standing

Green Goo

Give one toNext 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...

What happens when a dense population

with different demographics and

migration patterns...

Meets a sparse population that is

naïve to the pathogen?

Meets a sparse population that is

naïve to the pathogen?

Virulence associated w growth rate: uses host resource, by-product is

disease

Larger number people one interacts with

Vir

ule

nc

e

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