Introduction

1. Current temp = 15oC Adulticiding = 3 …. same tree structure as the “do nothing” branch Current temp = 20oC Do Nothing = 0 Current temp = 30oC Larvaciding = 2 …. same tree structure as the “do nothing” branch Current temp = 15oC Larvaciding = 2 Source Reduction = 1 Current temp = 20oC …. same as below Current temp = 20oC Current temp = 30oC Do Nothing = 0 Current temp = 30oC Current temp = 20oC Current temp = 20oC Current temp = 20oC Larvaciding = 2 Do Nothing = 0 Current temp = 20oC Do Nothing = 0 Do Nothing = 0 Current temp = 30oC Current temp = 30oC Current temp = 20oC Larvaciding = 2 Current temp = 30oC Current temp = 30oC Current temp = 20oC Larvaciding = 2 Current temp = 30oC Current temp = 20oC Current temp = 20oC Adulticiding = 3 Current temp = 30oC Larvaciding = 2 Current temp = 20oC Larvaciding = 2 Current temp = 30oC Current temp = 30oC Current temp = 20oC Time (weeks) Adulticiding = 3 Week 1 Week 2 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 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 School of Public Health, University of Saskatchewan1 Department of Computer Science, University of Saskatchewan2 Saskatoon Public Health Observatory, Public Health Services, Saskatoon Health Region3 Human Diagnosis and Clinical Manifestation System Dynamic (SD) Modeling Mosquito and Human WNV Disease Progression PHC 1, 2, 3, 4, 6 Introduction Decision Tree Analysis PHC 2, 3, 6 • 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) • 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 Surveillance & Risk Communication PHC 2, 3, 4, 6 • 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 species • Pool 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) Human Cases of WNV in Canada 2002-2007 • 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) 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. Summary • 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 • 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 accountdelays (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 Source: PHAC, 2006 • 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 WNV Control Planning PHC 3, 4, 6 WNV Transmission Cycle Mosquito Larvae Mosquito Pupa Mosquito Adult Source: unknown Source: www.comosquitocontrol.com/ Mosquito_Biology.html Source: www.azstarnet.com/metro/295104 Relevant Public Health Competencies (PHC) • 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. Key Public Health of Canada Competencies addressed during the WNV 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 Analysis 3.0 Policy and Program Planning, Implementation and Evaluation; 4.0 Partnerships, Collaboration and Advocacy 6.0 Communication 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). Contact information Karen Yee, MPH Candidate School of Public Health. Health Sciences Building 107 Wiggins Road. University of Saskatchewan Saskatoon, SK. S7N 5E5; Email:karen.yee@usask.ca Source: Penn State University