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Multi-host, multi-parasite Multi-host, multi-parasite

Multi-host, multi-parasite - PowerPoint Presentation

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Multi-host, multi-parasite - PPT Presentation

dynamics Andy Dobson Many thanks to Peter Hudson Mercedes Pascual and Stefano Allesina Anieke van Leeuwen amp Claire Standley Kevin Lafferty Jennifer Dunne and Giulio ID: 927794

th1 th2 multiple species th2 th1 species multiple parasite food competition aicd parasites levels dynamics hosts life work initial

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Slide1

Multi-host, multi-parasite dynamics – Andy Dobson

Many thanks to Peter HudsonMercedes Pascual and Stefano AllesinaAnieke van Leeuwen & Claire StandleyKevin Lafferty, Jennifer Dunne, and Giulio de Leo Many, many NCEAS working groups

 Ancient cures for diseases will reveal themselves once more. Mathematical discoveries glimpsed and lost to view will have their time again.” 

― 

Tom Stoppard

Arcadia

Slide2

Tom Stoppard, Arcadia

“It's the best possible time to be alive, when almost everything you thought you knew is wrong.” “It's the wanting to know that makes us matter.” “We're better at predicting events at the edge of the galaxy or inside the nucleus of an atom than whether it'll rain on auntie's garden party three Sundays from now.” 

Slide3

Outline

Parasite diversity and food websParasites with multiple hostsParasites with sequential multiple hostsParasite communities : dynamics x immunity.“The unpredictable and the predetermined unfold together to make everything the way it is.” ― Tom Stoppard, Arcadia

Slide4

Food webs and parasites.Carpinteria salt marsh, California

Traditional resource-consumerweb. Trophic levels = 3.77

Food web that incudes

b

asic parasite links

Trophic levels = 5.68

Dunne et al,

PLoS

Biology, (2013)

Slide5

Parasites are central to healthy ecosystems!! (Hudson et al, 2005)

Number of trophic levels = 7.16 Includes parasite trophic

links

Free-living species – red :

Macroparasites

– blue

Not yet added

microparasites

or “

microbiome

Dunne et al, 2013,

PLoS

Biology.

Slide6

Parasites and food webs

Food webs are even more complex when we include parasites: Many more species -> more linksSimple cascade model is instantly falsifiedHow does this effect May’s (1973) stability-complexity paradigm?Main focus of this talk is to consider how work since “Ro or Not Newton” has developed insights into this central problem in Ecology.

Slide7

S

Allesina

& S Tang

Nature

000

,

1

-

4

(2012) doi:10.1038/nature10832

.

Stability

Diversity - Number of Species

Stability criteria for different types of interaction

Slide8

Multiple host species I.

What happens when multiple host species share the same pathogen ?Rinderpest would be classic example here – eradicated since last Newton…Also rabies and other species that jump between hosts.Can be modeled with coupled sets of SI and SIR equations

Slide9

Walter Plowright

Walter Plowright, CMG, FRS[1], FRCVS (born 20 July 1923, Holbeach, Lincolnshire – 19 February 2010 London[2]) was an English veterinary scientist who devoted his career to the

eradication

of the cattle plague

rinderpest

. Dr

Plowright

received the 1999

World Food Prize

for his development of tissue culture

rinderpest

vaccine (TCRV), the key element in the quest to eliminate

rinderpest

.

[3]

Rinderpest

became the first animal disease to be eliminated worldwide

Slide10

Multiple host species I.

What happens when multiple host species share the same pathogen ?Rinderpest would be classic example here – eradicated since last Newton…Also rabies and other species that jump between hosts.Can be modeled with coupled sets of SI and SIR equations

Slide11

A cartoon of the talk…..

Slide12

Rinderpest – Serengeti

Slide13

Basic model structure..

Susceptibles

Infecteds

Within

Between

Scale virulence

as a proportion

of life expectancy

Between species transmission

Allometric scaling of all birth and death rates

Slide14

De Leo and Dobson (1996)

Slide15

Time

Susceptible density

Between sps. transmission

Buffering: dynamics in DD case

Slide16

Buffering: dynamics in DD case

Between/within species transmissionMax./Min. susceptible density

Slide17

Multiple hosts species II

Obligatory and sequential use of multiple hosts to complete complex life cycleCan next-generation methods be useful here?Food-web perspective Long loops ‘may’ be stabilizingOften multiple alternative hosts on same trophic levelTypes of pathogen where most likely to see dilution effects

Slide18

Cestodes of the Serengeti (host)

Slide19

Multiple definitive hosts

Slide20

Multiple intermediate hosts

Slide21

Slide22

Beetles….

Cestodes

of the Serengeti….

Slide23

Insight:

There are multiple ways to go around the life cycle…

Slide24

Insight 2: Ro is a root of the sum of all possible routes

around the life cycle…..

hmmmm

!

But why does the magnitude of the root keep changing

Slide25

..then a pattern began to emerge…

Although these expressions look at first sight slightly incongruous, they both have the same properties in that they define R0 as the ‘n-th’ root of the sum of all the possible transmission routes around the life cycle; notice that ‘n’ is the number of trophic levels that the parasite passes through in the course of its life cycle. This creates a beautiful link to the need to study complex life cycles parasites within a food-web context.

Slide26

ScienceArt.com

Ribeiroia ondatrae

Flatworm Life Cycle Contact Elizabeth Morales

Slide27

Convert to a more theory friendly format….

Slide28

Slide29

Multiple Parasite species

Communities of parasites that share the same hosts speciesInitial work by Robert’s and Dobson at NewtonMuch current interest in role that immunity playsBUT, current work tends to ignore earlier work on aggregation and persistence.So need to find a framework to bring the two together!

Slide30

Anderson and May macroparasite models – with multiple parasites

Original two parasite version developed by Dobson (1985), extended to n-species by Roberts and Dobson (1995)Simple graphical ways for initially considering this with two speciesMulti-parasite version has underlying structural similarities to Hubbell’s Neutral theory.

Slide31

Phase plane for simple competition

Coexistence requires

And vice versa for B

2

and B

1

Thus coexistence requires k’>>1

Both species have to be aggregated

Slide32

Interference competition

eg (nearly) all immunological interactions!!

Here we assume competition

is asymmetrical:

B can exclude A,

but not vice versa.

Coexistence still requires

A

2

>A

1

and B

2

>B

1

Slide33

Synergistic interactions

most of the other immunological interactions

Coexistence still requires

A2>A1 and B2>B1

So we need to know how immunity impacts virulence and aggregation

Slide34

N-species of parasite

Note – curiously related to “Neutral theory of Ecology - Hubbell……

Slide35

Intrinsic growth rate of parasite species 1.

Intrinsic growth rate of parasite species 2

Both parasite species co-exist

Slide36

Slide37

Slide38

Stomach

Small Intestine

Large Intestine

Worm 1

Worm 3

Worm 2

Worm 4

Food -ve

Space

-ve

Direct competition

Excreta -ve

When should we expect competition?

Applying the findings from community ecology…this should be greater when parasites are related

Interestingly this contrasts with exploitation competition

Parasite Community Dynamics

2. Interference competition

What is the nature of competition?

Competition for space

Competition for food

Competition via excreted material

Food

-ve

appears

+ve

Isabella

Cattadori’s

work on

helminth

Communities in rabbits with and w/o

Myxomatosis

– P. Hudson on Thursday

Slide39

Mixed macro and micro parasite models

Some initial work by Andy Fenton.

Slide40

Slide41

Slide42

Within Host dynamics of

parasite communities will be driven by Immunological dynamics regulated by Th1-Th2 cytokine interactionsJoint work with my Post-Docs : Anieke van Leeuwen and earlier explorations with Claire Standley

Slide43

Background

Th1 cytokines -> microparasite infection control [viruses, bacteria, fungi, protozoa]Th2 cytokines -> macroparsite infection control [helminths, nematodes]Th1 and Th2 responses are supposed to have mutual inhibitory effects (competition)Hosts are often co-infected with multiple parasite species (e.g. Fenton & Pedersen 2007)How does the interaction of the th1 and th2 immune responses work out?=> Mathematical modeling

Slide44

Th1

Th2Th1

Th2

Th

APC

IL-4

IL-10

+

-

IFN-

γ

+

IL-12

+

-

-

IFN-

γ

IFN-

γ

+

IL-2

+

TGF-

β

IL-10

IL-4

-

-

IFN-

γ

+

IL-2

+

IL-2

+

IL-2

+

IL-4

+

-

TGF-

β

AICD

AICD

After Yates et al. 2000 - JTB

Processes in detail

Slide45

Tempting to think of this as a food-web

Slide46

Th1

Th2Th1

Th2

Th

APC

+ -

+

-

-

+

+

+

+

AICD

AICD

Simplified representation

After Yates et al. 2000 - JTB

Slide47

Activation

Th1

Th2

Th1

Th2

Th

APC

+ -

+

-

-

+

+

+

+

AICD

AICD

Yates et al. 2000 - JTB

Th1

Th2

Slide48

Proliferation

Th1

Th2

Th1

Th2

Th

APC

+ -

+

-

-

+

+

+

+

AICD

AICD

Yates et al. 2000 - JTB

Slide49

Mortality

Th1

Th2

Th1

Th2

Th

APC

+ -

+

-

-

+

+

+

+

AICD

AICD

Yates et al. 2000 - JTB

Slide50

Model equations

Th1

Th2

Th1

Th2

Th

APC

+ -

+

-

-

+

+

+

+

AICD

AICD

Yates et al. 2000 - JTB

Slide51

Model dynamicsbifurcation over Th2 activation parameter,

σ2Th1Th2

Slide52

Parameterization

σ1 = 1.5π1 = 2.0δ1 = 0.1

σ

2

= varied

π

2

= 2.0

ρ

= 0.1

δ

2

= 0.0

σ

2

= 0.4

Model dynamics

Scenario 1: low Th2 activation level

a

b

initial levels: Th1

: low

Th2: low

initial levels: Th1: high Th2: low

Slide53

a

b

Parameterization

σ

1

= 1.5

π

1

= 2.0

δ

1

= 0.1

σ

2

= varied

π

2

= 2.0

ρ

= 0.1

δ2 = 0.0σ2 = 0.6

Model dynamicsScenario 2: intermediate Th2 activation level

initial levels: Th1: low Th2: low

initial levels: Th1: high Th2: low

Slide54

a

b

Parameterization

σ

1

= 1.5

π

1

= 2.0

δ

1

= 0.1

σ

2

= varied

π

2

= 2.0

ρ

= 0.1

δ2 = 0.0σ2 = 1.2

Model dynamicsScenario 3: high Th2 activation level

initial levels: Th1: low Th2: low

initial levels: Th1

: high Th2: low

Slide55

LP1

BPx2

BPx1

H

LP2

bistability:

Th1-Th2

: damped oscillations

Th1

dominance

Th1

dominance

bistability:

Th1-Th2

: cycles

Th1

dominance

Th1-Th2

cycles

Th1-Th2

damped oscillationsTh2 dominance

bistability:Th1-Th2: cyclesTh2

dominance

δ1 = 0.1δ

2 = 0.0θ1,2 = 0.0χ0 = 0.0

ρ = 0.1

Slide56

Ultimately we need to know how activation energies of Th1, Th2 impact virulence and aggregation!

Slide57

Conclusions

Parasite diversity and food websParasites look increasingly viable as the ‘missing links’ in food webs, the ‘dark matter’ that helps stabilize otherwise unstable structures.Parasites with multiple hostsStrong form of frequency dependent selection for stability if within species transmission < between.Parasites with sequential multiple hostsPossible powerful use of next generation matricesParasite communities : dynamics x immunity.Rapidly developing area, but needs to resolve how diversity in immune response impacts aggregation as well as abundance.

Slide58

Penultimate word from Tom Stoppard

“We shed as we pick up, like travellers who must carry everything in their arms, and what we let fall will be picked up by those behind. The procession is very long and life is very short. We die on the march. But there is nothing outside the march so nothing can be lost to it. The missing plays of Sophocles will turn up piece by piece, or be written again in another language. Ancient cures for diseases will reveal themselves once more. Mathematical discoveries glimpsed and lost to view will have their time again. You do not suppose, my lady, that if all of Archimedes had been hiding in the great library of Alexandria, we would be at a loss for a corkscrew?” ― Tom Stoppard, Arcadia

Slide59

Deconstructing this..

What did I take away from Newton meeting 20 years ago?Collaborations in small mixed groups is the best way to do new scienceMathematics will constantly find new, innovative and exciting ways to solve old problems in disease and ecologyBut…. there are still a whole bunch of unexamined questions out there in Nature and mathematics is the best way to focus those questions. So go into the field, talk to people and find ways to turn problems of disease, ecology and evolution into new problems.Ecologists now see parasites as central to EcologyHard to interpret the bit about the corkscrew, but they have been known to come in useful as social facilitators!

Slide60

Thank you!