opisthorchis viverrini transmission models *-5mm

Opisthorchis viverrini Transmission Models

Christine Burli1,2, Helmut Harbrecht2, Peter Odermatt1,2, Somphou Sayasone1,2,3,Nakul Chitnis1,2

1Swiss Tropical and Public Health Institute, Basel, Switzerland2Universitat Basel, Basel, Switzerland3National Institute of Public Health, Vientiane, Lao People’s Democratic Republic

Swiss TPH Winter Symposium 2017Helminth Infection – from Transmission to ControlBasel, Switzerland, 8 December 2017

Department of Epidemiology and Public Health

Infectious Disease Modelling Unit

Opisthorchis viverrini

DogsCats

Humans

Eggs

SnailsCercariaeFish

2017-12-08 2

O. viverrini in South East Asia

Forrer et al. (2012)

2017-12-08 3

Modelling Framework

Basic Model

if

wh

is

Reservoir Host Model

if

wh

wc

wd

is

2017-12-08 4

Reproductive Numbers

The basic reproduction number R0 is the average number of new cases of an infection(or number of parasite offspring) caused by one typical infected individual (or oneparasite), from one generation to the next, in a population with no pre-existinginfections.

Type-reproduction numbers provide a threshold for whether certain host types canmaintain transmission on their own.

Ui is the host-specific type reproduction number.

Qi is the host-excluded type reproduction number.

2017-12-08 5

Data from Southern Champasack Province

Species Tested Positive Prevalence

Humans: 994 603 61%Dogs: 68 17 25%Cats: 64 34 53%Fish: 628 129 21%

Snails: 3102 9 0.29%Vonghachack et al. (Submitted)

2017-12-08 6

Data on Intensity of Infection in Humans

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000Eggs per gram

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Dens

ity

#10-3

OV eggs per gramNegative Binomial

2017-12-08 7

Numerical Simulations

Basic Model

0 50 100 150 200Time (years)

0

5

10

15

20

25

30

35

Num

ber

of p

aras

its33.289w

h

0 50 100 150 200Time (years)

0

0.05

0.1

0.15

0.2

0.25

0.3

Pre

vale

nce

0.003

0.269is

if


0 50 100 150 200Time (years)

0

5

10

15

20

25

30

35

Num

ber

of p

aras

its

33.289

1.292

13.875

wh

wd

wc

0 50 100 150 200Time (years)

0

0.05

0.1

0.15

0.2

0.25

0.3

Pre

vale

nce

0.003

0.269is

if

2017-12-08 8

The Basic Reproductive Number R0

Basic Model

0 2 4 6 8 10 12R

0

0

50

100

150

200

Fre

quen

cy

2.2715

R0

R0=1

median


0 2 4 6 8 10 12R

0

0

50

100

150

200

250

300

Fre

quen

cy

1.7965

R0

R0=1

median

2017-12-08 9

Sensitivity Analysis of R0

Basic Model

-1 -0.5 0 0.5 1

-fs

-sh

Ns

Nh

-hf

Nf

7f

7ph

7s

Parameter Descriptions


-1 -0.5 0 0.5 1

7pd

-sd

Nd

-df

Nc

-cf

-sc

7pc

Nh

-sh

-hf

Ns

-fs

Nf

7ph

7f

7s

2017-12-08 10

Sensitivity Analysis of Endemic Mean Worm Burden in Humans

Basic Model

-1 -0.5 0 0.5 1

-sh

-fs

Nh

Ns

7f

7s

Nf

-hf

7ph


-1 -0.5 0 0.5 1

-fs

7f

Ns

Nd

Nf

-df

7pd

-sd

Nc

-sc

-cf

-hf

7pc

7ph

Nh

-sh

7s

2017-12-08 11

Human Reproductive Numbers

Only Human Transmission

0 2 4 6 8 10 12U

h

0

5

10

15

20

25

30

Fre

quen

cy

1.6886

Uh

Uh=1

median

P (Uh > 1) = 0.92

No Human Transmission

0 1 2 3 4 5Q

h

0

5

10

15

20

25

30

Fre

quen

cy

0.87307

Qh

Qh=1

median

P (Qh > 1) = 0.38

2017-12-08 12

Cat Reproductive Numbers

Only Cat Transmission

0 1 2 3 4 5U

c

0

5

10

15

20

25

30

Fre

quen

cy

0.81406

Uc

Uc=1

median

P (Uc > 1) = 0.33

No Cat Transmission

0 2 4 6 8 10 12Q

c

0

5

10

15

20

25

30

Fre

quen

cy

1.7015

Qc

Qc=1

median

P (Qc > 1) = 0.94

2017-12-08 13

Dog Reproductive Numbers

Only Dog Transmission

0 0.5 1 1.5 2 2.5U

d

0

5

10

15

20

25

30

Fre

quen

cy

0.41912

Ud

Ud=1

median

P (Ud > 1) = 0.03

No Dog Transmission

0 2 4 6 8 10 12Q

d

0

5

10

15

20

25

30

Fre

quen

cy

1.7879

Qd

Qd=1

median

P (Qd > 1) = 0.99

2017-12-08 14

Control Interventions

DogsCats

Humans

Eggs

SnailsCercariaeFish

ImprovedSanitation

(Id)

Mass DrugAdministration

(Im)

EducationCampaigns

(Ie)

2017-12-08 15

Effects of Interventions on Reproductive Number

0 0.2 0.4 0.6 0.8 1

Intervention coverage

0.2

0.4

0.6

0.8

1

Rep

rodu

ctio

n nu

mbe

rR

c(I

e)

Rc(I

d)

Rc(I

m)

Rc = 1

R0

2017-12-08 16

Effects of Interventions on Worm Burden in Humans

Education Campaigns

0 5 10 15 20Time (years)

0

10

20

30

40

Num

ber

of p

aras

ites

no interventionIe= 0.2

Ie= 0.4

Ie= 0.6

Improved Sanitation

0 5 10 15 20Time (years)

0

10

20

30

40

Num

ber

of p

aras

ites

no interventionId= 0.4

Id= 0.6

Id= 0.8

Annual Treatment

0 5 10 15 20Time (years)

0

10

20

30

40

Num

ber

of p

aras

ites no intervention

Im

= 0.4

Im

= 0.6

Im

= 0.8

2017-12-08 17

Elimination Dynamics

0 0.18 0.36 0.54 0.72 0.9Intervention coverage

0

10

20

30

40

50

Tim

e to

elim

inat

ion

(yea

rs)

0 0.18 0.36 0.54 0.72 0.9Intervention coverage

0

0.2

0.4

0.6

0.8

1

Pro

babi

lity

of e

limin

atio

n

Ie

Id

Im

twice a year

Im

once a year

Im

every 2 years

Im

every 3 years

Im

every 4 years

2017-12-08 18

Conclusions and Outlook

Conclusions

Transmission is unlikely to persist without humans.

Humans can maintain transmission on their own.

Education and improved sanitation require a very high coverage to eliminate.

Best strategy is a medium coverage of humans with treatment and as high aspossible with education campaigns and improved sanitation.

Outlook

Calibrate model with age-dependence in humans.

Model seasonality in fish and snail population dynamics.

Model heterogeneity and morbidity in humans.

Model intensity of infection in fish.

2017-12-08 19

Acknowledgements

NIOPH

Somphou Sayasone

Youth Vonghachack

Swiss TPH

Christine Burli

Nakul Chitnis

Peter Odermatt

Thomas Smith

University of Basel

Helmut Harbrecht

Funding

Swiss National Science Foundation

2017-12-08 20

opisthorchis viverrini transmission models *-5mm

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