Weather and West Nile Virus Threat in Illinois

Shown by Climate Division

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Experimental Climate Division WNV Threat Model

Since the 2001 introduction of West Nile Virus (WNV) into Illinois, it is estimated that more than 200,000 cases have occurred and Illinois has the 3rd highest number of the more severe human WNV neural disease cases. The risk of exposure to WNV appears to increase under hot / dry summertime conditions. WNV affects citizens across the state, and while two county-level predictive models exist (one for Cook-DuPage, and one for Champaign County) the model results cannot be easily extrapolated to other regions of Illinois. THe goal of this research is to develop and validate a WNV threat predictive model that can be used throughout the state of Illinois, eventually throughout the Midwest and US, and perhaps apply these same techniques to other climate-related health or issues.

Components of this model will include: 1) climate divisions as the basic spatial unit to aggregate non-homogenous WNV human and mosquito case sampling, as well as daily weather data. 2) Graphical displays of accumulated daily temperature and precipitation departures from normal for high and low WNV case years for comparison with current weather conditions, 3) Computation of statistics based on differences from daily 30-year averages, rather than based on degree days. 4) Incorporation of 10-day daily temperature and 3-day daily precipitation forecasts to increase the lead time of model usefulness.

The number of human cases is somewhat related to popoulation, with climae division 02 (including the Chicago Metro Area) having the largest population and climate divisons 03, 07 and 09 having the least popoulation. The years with high and low cases per climate division were selected after the number of cases were normalized by the 2009 population of CD_02. In addition to population, other non-climate effects such as mosquito habitat, use and effectiveness of mosquito control, as well as human, bird and mosquito behavior, can affect the number of cases, leading to uncertainy in year to year results and some subjectivity in selection of high and low case years.

As the summer season progresses, the web site may change to become more user-friendly. Click a climate division for season-to-date WNV weather and threat graphics.


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  • Jeff Blackford, Environmental Health Division, Champaign-Urbana Public Health District
  • Sam Dorevitch, Division of Environmental and Occupational Health Sciences, University of Illinois at Chicago School of Public Health Institute for Environmental Science and Policy
  • Linn Haramis, Division of Public Health, Illinos Department of Public Health
  • Rich Lampman, Medical Entomology Laboratory, Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign
  • Juma Muturi, Medical Entomology Laboratory, Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign
  • Marilyn O'Hara Ruiz, Geographic Information Systems and Spatial Epidemiology Lab, Department of Pathobiology, University of Illinois at Urbana-Champaign
  • Scott Scallion, Statistical Modeling Branch, Meteorological Development Laboratory, National Weather Service Office of Science & Technology, National Oceanic and Atmospheric Adminstraion (NOAA)