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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: [email protected]
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.