TEMPLATE DESIGN © 2008

www.PosterPresentations.com

System Dynamic Modeling & Decision Tree Analysis to capture uncertainties of intervention choices and weather patterns on West Nile Virus disease outcomes

Karen Yee1, Dr. Nathaniel Osgood2, Judith Wright3, and Dr. Lisa Lix1

Introduction

Human Cases of WNV in Canada 2002-2007

Human Diagnosis and Clinical Manifestation System Dynamic (SD) Modeling Mosquito and Human WNV Disease Progression PHC 1, 2, 3, 4, 6

Decision Tree Analysis PHC 2, 3, 6

Relevant Public Health Competencies (PHC)

Contact informationKaren Yee, MPH CandidateSchool of Public Health. Health Sciences Building107 Wiggins Road. University of SaskatchewanSaskatoon, SK. S7N 5E5; Email: karen.yee@usask.ca

Summary

School of Public Health, University of Saskatchewan1

Department of Computer Science, University of Saskatchewan2

Saskatoon Public Health Observatory, Public Health Services, Saskatoon Health Region3

Source: Penn State University

SusceptibleMosquitoes

Density

EndogeneouslyCalculated Infectious

Mosquito Density

Death of SusceptibleMosquitoes Death of Infectious

Mosquitoes

Larval FemaleMosquitoes

Density

Exposed FemaleAdult Mosquitoes

Density

Death From LarvalFemale Mosquitoes

Death of ExposedFemale AdultMosquitoes

Natural Death Rate OfLarval FemaleMosquitoes

Mean Time toLarval Maturation

<Mean Time toLarval Maturation>

<Natural Death Rate OfLarval FemaleMosquitoes>

Birth Rate For LarvalFemale Mosquitoes

Maturation ofLarvae

Pathogen TransmissionFrom Infected Bird to

Susceptible Mosquitoes

Probability Of VirusTransmission to Mosquito,

Per Infectious Bite

Disease Incubation

Virus IncubationRate

Susceptible Humans

AsymptomacticallyInfected Humans

Hospitalized West NilePatients with Meningitis and

Encephalitis

Non-Hospitalized Neurological West NilePatients Under Recovery

Recoveryfrom M and E

Deaths fromSusecptible

Humans

Deaths fromAsymptomacticallyInfected Humans

Deaths ofNeurological

WNV Patientsunder Recovery

Deaths due toWNV-induced

Entrants ofHumans

Per Bite Probability oftransmission from infected

mosquito to human

<Number of bitings ofsusceptible humans by infected

mosquitoes per day>

Recruitment rate ofsusceptible humans

Mean Time toRecovery for M and E

Patients

WNV-induced deathrate for humans

Death rate for adultMosquitoes

<Death rate for adultMosquitoes>

<Death rate for adultMosquitoes>

<Death rate for adultMosquitoes>

Biting Rate onInfectious Juvenile

Biting Rate onInfectious Adults

<Fraction of infectiousjuvenile birds density>

<Fraction ofinfectous Adult birds

density>

VaccinatedHumans

VaccineLoss Immunity ofVaccinated Humans

Vaccine Rate

Rate of Loss Immunityof Vaccinal Humans

<Biting Rate onJuvenile>

<Biting Rate onAdult>

Mosquitoes

Humans

Hospitalized West NilePatients with Fever (WNF)

Hospitalized West NilePatients with Meningitis

Hospitalized West NilePatients with acute flaccid

paralysis

Recovery fromparalysis

Recovery frommeningitis

Number of adultblood meals per

day

Non-Hospitalized WNF PatientsUnder Recovery

Discharge of WNFCases from Hospital

Recovered andWNV Immune

Patients

Recovery ofWNF Patients

Egg Laying Rate for AdultFemale Mosquitoes

Egg DensityBirth of Mosquito

Larvae

<Total adult femalemosquitoes density>

Egg Laying by AdultFemale Mosquitoes

Density

Mean Time as Egg

CurrentTemperatureInCentigrade

Pupae FemaleMosquitoes

Density

Maturation ofPupae

Mean Time toPupal Maturation

Mean Time inHospital for

Meningitis Patients

Mean Time inHospital for Patients

with Paralysis

Mean Time inHospital for WNF

Patients

Loss of Immunity of Recovered andWNV Immune Patients

Recovery ofNeurological WNV

Patients

Deaths of WNFPatients under

Recovery

Mean Time toWaning Immunity

Mean Time toRecover for

PostHospital WNFPatients

Mean Time toRecovery forPostHospital

Neurological Cases

<Mean Time toWaning Immunity>

Mean Time to LarvalMaturation for Given

Temperature

<CurrentTemperatureInCentigrade>

Virus IncubationThreshold

Temperature

Recovery ofAsymptomatically Infected

Patients

CumulativeWNVSymptomaticCases

New SymptomaticCases

InterventionSelected

AdulticidingDeath Rate

Natural death rate forAdult Mosquitoes

Source Reduction DeathRate of Larval Female

Mosquitoes

Larvacide Reduction DeathRate of Larval Female

Mosquitoes

Death Rate for LarvalFemale Mosquitoes

Mean Time inHospital forNeurological

Patients

Average lifespan ofa human

<Average lifespanof a human>

<Average lifespan ofa human>

<Average lifespanof a human>

Mean Time to Recover forAsymtomatically Infected

Patients

<InterventionSelected>

Death from PupalFemale

Mosquitoes

Natural Death Rate ofPupal FemaleMosquitoes

Natural Death Rate ofImmature Female

Mosquitoes

Larvacide Reduction DeathRate of Pupal Female

Mosquitoes

<Larvacide Reduction DeathRate of Larval Female

Mosquitoes>

<InterventionSelected>

Source Reduction DeathRate of Pupal Female

Mosquitoes

Source Reduction DeathRate of Immature Female

Mosqutioes

Death rate for pupalfemale mosquitoes

Exposed Humans

Newly InfectedPre-symptomatic Human

Cases

AsymptomaticInfection

Mean Time Until WNVIncubates in Humans

Number of Human Cases perDay Completing WNV

Incubation

Progression to Non-Hospitalized WNF

Hospitalized forWNF

Hospitalized formeningitis

Hospitalized for M and E

Hospitalized forparalysis

<Fraction of ExposedHumans present with M

and E>

<Fraction of ExposedHumans that remain

asymptomatic>

<Fraction of ExposedHumans present with

paralysis>

<Fraction of ExposedHumans present with

meningitis>

<Fraction of Exposed Humanswith NonHospitalized WNF>

<Fraction of ExposedHumans with WNF that are

hospitalized>

<Progression toNon-Hospitalized

WNF>

<Hospitalized forM and E>

<Hospitalized formeningitis>

<Hospitalized forparalysis>

<Hospitalized forWNF>

<VaccinatedHumans>

Number of adult bloodmeals per day for Given

Temperature

Area Under Study

Egg Laid perBlood Meal

Birth Coefficient

Force of Infectionfor Humans

NegativeOfCumulativeWNVSymptomaticCases

Deaths of Recovered andWNV Immune Patients

<Average lifespan ofa human>

Current temp = 20oC

Current temp = 30oC

Adulticiding = 3

Current temp = 20oC

Current temp = 30oC

Larvaciding = 2

Current temp = 20oC

Adulticiding = 3

Current temp = 20oC

Current temp = 30oC

Larvaciding = 2

Larvaciding = 2

Do Nothing = 0

Current temp = 20oC

Current temp = 30oC

Larvaciding = 2

Do Nothing = 0

Current temp = 20oC

Current temp = 30oC

Current temp = 20oC

Current temp = 20oC

Current temp = 30oC

Larvaciding = 2

Do Nothing = 0

Current temp = 15oC

Current temp = 20oC

Current temp = 15oC

Current temp = 30oC

Current temp = 20oC

Current temp = 30oC

Current temp = 20oC

Current temp = 30oC

Current temp = 30oC

Current temp = 20oC

Current temp = 30oC

Current temp = 20oC

Do Nothing = 0

Larvaciding = 2

Do Nothing = 0

Time (weeks)

Week 1 Week 2

Larvaciding = 2

Adulticiding = 3

Source Reduction = 1

…. same as below

…. same tree structure as the “do nothing” branch

…. same tree structure as the “do nothing” branch

• Organizes decisions/actions into a logical tree structure taking into account uncertainties and consequences.

• Consequences (outcomes) can be derived from running the SD model on particular scenarios of decisions that are made when faced with uncertainty.

• Backward induction will enable the decision maker to identify the optimal decision rules to bring about the most desired outcome.

• Takes into consideration present and historical uncertainties (e.g., temperature)

• SD modeling is a computer tool used to understand complex issues and problems often associated with many causal forces that create the problem or positively/negatively contribute to it.

• Takes into account delays (e.g., time from contact to symptoms of a disease), interactions (e.g., chronic diseases with infectious diseases), feedbacks (e.g., behavioral changes from altered risk perceptions), nonlinear relationships (e.g., risk, costs), and heterogeneities (e.g., differences in infection rates between sexes)

• SD models are not about forecasting the future, but rather on how actions in the present can trigger plausible reactions over time

• New insights (e.g., on clinical disease progression of WNV) and changing conditions (e.g., weather patterns) or goals (e.g., target host for vaccination) are incorporated into SD models

Hospitalized West Nile Patients with Meningitis and Encephalitis

0.02

0.015

0.01

0.005

03 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

2 22

22

22

22

22

22

22

22 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

1 11

1

1

1

1

1

1

1

1

1

1

11

11

11

11

11

11

1 1 1 1 1 1 1 1 1 1 1 1 1 1

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100Time (Day)

Hospitalized West Nile Patients with Meningitis and Encephalitis : InfectiousMosquitoDensity_0006 person1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Hospitalized West Nile Patients with Meningitis and Encephalitis : InfectiousMosquitoDensity_0003 person2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

Hospitalized West Nile Patients with Meningitis and Encephalitis : InfectiousMosquitoDensity_0001 person3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

Computer simulation showing the proportion of humans hospitalized for meningitis and encephalitis as the infectious mosquito density is raised 3 (red line) and 6 fold (blue line) from baseline (green line).

Key Public Health of Canada Competencies addressed during theWNV portion of this project with Saskatoon Public Health Observatory,Public Health Services SHR & Dr. Nathaniel Osgood include: 1.0 Public Health Sciences; 2.0 Assessment and Analysis3.0 Policy and Program Planning, Implementation and Evaluation;4.0 Partnerships, Collaboration and Advocacy 6.0 Communication

• Saskatchewan suffered the highest incidence of WNV in the country in 2003 and 2007

• Saskatoon Health Region (SHR) reported 6.5% and 25% of the provincial cases in 2003 and 2007, respectively

Source: PHAC, 2006

• West Nile Virus (WNV) belongs to a group of disease-causing viruses called flaviviruses, which include yellow fever, Japanese encephalitis and dengue

• Found in both tropic and temperate regions• Two genetic lineages:

lineage 1 strains are found in North America, Europe, Africa, Asia, and Australia; Can lead to severe inflammation of spinal cord (meningitis) and/or brain (encephalitis). lineage 2 strains have been isolated only in sub-Saharan Africa and Madagascar. Little severe human disease.

WNV Transmission Cycle

WNV Control Planning PHC 3, 4, 6

• WNV control in Saskatchewan: Integrative pest management (IPM) approach larval source reduction surveillance and monitoring of larval vector species

public messages about increasing disease transmission, and personal protective equipment (e.g., use of DEET repellent, wearing long sleeves, and avoiding outdoor activities at dusk/dawn). use of ultra-low volume (ULV) malathion spraying for the control of adult mosquitoes (adulticiding) as last resort.

• WNV sensitivity registry feasibility study: involved collecting information on sensitivity registries and telephone information lines for SHR to assist them in making informed decisions on the usefulness of each for fulfill the obligation to protect the public’s health in the context of adult mosquito control programs.

Source: www.azstarnet.com/metro/295104 Source: www.comosquitocontrol.com/Mosquito_Biology.html

Source: unknown

This project provides:• multiple stakeholders with useful information & computer tools for

understanding the dynamics of WNV• ability to use current and historic uncertainty to make informed

decisions on optimal intervention measures for improved health outcomes.

• an in-depth review of sensitivity registries and telephone information lines for informing the public regarding adulticiding should it ever be necessary to control for WNV

• amalgamated mosquito trap data from 2003-present in a format suitable for easy communication of health risk to the public

WNV Surveillance & Risk Communication PHC 2, 3, 4, 6

This research was kindly supported by the Research Alliance for the Prevention of Infectious Disease (RAPID) Network created through a grant from the Saskatchewan Heath Research Foundation

Mosquito AdultMosquito PupaMosquito Larvae

• Birds: Passive - specimens turned in by public to Canadian Cooperative Wildlife Health Centre are tested for WNV

• Mosquitoes:Larval testing presence & geographic location of Culex tarsalis mosquito (this species of primary concern in Saskatchewan for transmission of WNV) Adult trapping presence of C. tarsalis in proportion to other mosquito speciesPool testing testing batches of Culex mosquitoes for WNV

• Environment: Growing degree days the # of days the average nightly temperature above 15°C, ideal for mosquito breeding; 300-350 GDD enough heat accumulation for 4 to 5 generations of mosquitoes over the summer

• Horses: Passive - veterinary reports• Humans: Active - physician reporting (reportable disease)

• Incubation period of WNV is believed to range from 3 to 14 days • 80% of WNV infections asymptomatic• > 95% symptomatic infections are non-neurological (e.g., West

Nile Fever)• < 1% symptomatic infections are neurological (e.g. meningitis

and/or encephalitis)

Highest risk of transmission to humans when: 1) WNV in birds; 2) WNV in C. tarsalis; 3) increase in average # C. tarsalis / trap night; 4) % C. tarsalis high relative to other mosquito species

Risk communication include weekly average # C. tarsalis, minimum infection rate, maximum likelihood estimate, & risk index provided to SHR weekly from province. Part of this project involved amalgamating 2003-present data relevant for SHR into a single database for easy public messaging & surveillance.