Spatial Risk Factors for West Nile Virus Positivity in Mosquitoes in Indiana

Spatial Risk Factors for West Nile Virus Positivity in Mosquitoes in Indiana StateKrishna ThakurHu Suk Lee

1OutlineIntroductionGIS questions?ObjectivesMaterials and MethodsResultsDiscussionConclusions

2What is WNV?West Nile virus (WNV) is a Flavivirus which causes neurological disease in humans, horses and other animals

Birds develop substantial viremia and are considered a major reservoir host

Humans and horses are dead-end hosts

WNV was first detected in 1999 in the United States (New York State)

3Transmission by MosquitoesWNV is an Arbovirus transmitted by several mosquito speciesMost important vector: Culex spp.

Mosquito abundance is associated with environmental and anthropogenic factorsStanding WaterVegetation overgrowthUrbanizationHost population (Humans and Horses)

4GIS question?Why some of the counties in Indiana State have high positive cases of mosquitoes for WNV compared with other counties?

5ObjectivesUse GIS to compare counties in Indiana in terms of high and low positive cases of WNV toHuman population densityHorse population densityPercent of wetlandPercent of urbanPercent of different types of land usesIdentify areas with high risk and make a risk map for WNV in Indiana using Ordinary least square regression model(OLS)

6MaterialsData sourcesWNV mosquito cases by county in Indiana State in 2010http://diseasemaps.usgs.gov/wnv_in_mosquito.html

Indiana State map by county from Statewidedanpatch.ecn.purdue.edu\asm540\data\tippecanoe\statewide

Wetland Datahttp://inmap.indiana.edu/dload_page/hydrology.html

Land coverdanpatch.ecn.purdue.edu\asm540\data\tippecanoe\landcover

7MaterialsData sourcesHuman population (Census block)http://inmap.indiana.edu/dload_page/demographics.html

Horse populationhttp://www.ces.purdue.edu/extmedia/ID/ID-320-W.pdf

Census urban Area danpatch.ecn.purdue.edu\asm540\data\tippecanoe\statewide

Other related references

8Methods

9MethodsNormalization by area of countyHuman populationHorse populationArea of wetlandArea of land use type

Recombination and reclassificationForest= Deciduous + Evergreen + MixedWetland= Herbaceous + Woody

10Methods

FINAL MODEL

11MethodsNormalization by area of county Human populationHorse populationWetland areaLand cover valuesReclassification and recombination of Land cover valuesForest= Deciduous + Evergreen + MixedWetland= Woody wetland+ Emergent herbaceous wetland

12Initial Analysis

13Initial Analysis

14Ordinary Least Square Regression Result

15Random spatial pattern of under and over prediction

16Real cases vs. Predicted cases

17Comparison of Counties with High and Low WNV

18DiscussionWNV cases in mosquitoes are related withHuman density

This model explains 28% of variation in WNV cases in mosquito indicating some variables are still missing in the model

Predicted cases are not spatially autocorrelated indicating random pattern and model significance

19DiscussionGISOLS tool and Spatial correlation tool work well in comparing and modeling multiple spatial factors

Good Visualization tool to understand the distribution of disease and associated risk factors

Useful to obtain spatial data for other studies

20ConclusionRequired more factors in order to explain the WNV cases in mosquito

Obtained data can be analyzed using robust statistical software

Helpful to design mosquito control program

Acquaintance with GIS application in spatial epidemiology

21Thank you for your attention

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