Chronic Wasting Disease Research at the USGS-Wisconsin Cooperative Wildlife Research Unit

Spatial and demographic analysis of CWD prevalence and transmission rate

We are using statistical models to characterize the probability of deer being infected with CWD (prevalence) and to estimate the rate that uninfected animals become infected (transmission).  Prevalence varies in space and with age and sex of the deer (see figures).  Transmission rate may also vary in space and may vary with age of the deer.  We are estimating these parameters by fitting mathematical models to age-prevalence data.  Observed prevalence of CWD appears to increase with age faster in males than in females.  Prevalence is highest in the center of the Disease Eradication Zone, and then declines with distance.  These models will allow assessment of the Wisconsin DNR CWD management and surveillance efforts and to monitor changes in CWD prevalence with time.

Comparing CWD outbreaks between SW-Wisconsin and SE-Wisconsin/ Northern Illinois

The CWD outbreaks in SW Wisconsin and SE Wisconsin/Northern Illinois appear to differ in spatial patterns.  The SW Wisconsin outbreak is confined to a central area with prevalence declining with distance.  This spatial pattern implies that the disease was recently introduced and is spreading out from the original point of introduction.  The spatial patterns in SE Wisconsin/Northern Illinois are not as clear.  One difference between these areas is deer habitat fragmentation.  Deer habitat in the SW Wisconsin area is relative contiguous; whereas, deer habitat is the SE area is highly fragmented and consists most of river corridors.  Because deer have been shown to disperse farther in fragmented habitats, one hypothesis for the different patterns is that deer disperse farther from a central disease area.  Statistical models are being developed that will help identify disease clusters and estimate prevalence and transmission rates.  These parameters will then be compared between which those of the disease outbreak in SW Wisconsin.

Spatial analysis of deer density and removal

The primary management tool used by the Wisconsin Department of Natural Resources to control and eliminate CWD is the removal of deer by hunters.  Hunting seasons have been liberalized for deer in the two disease outbreak areas.  Increased harvest can help control disease by shifting the age structure of the population to younger animals and by reducing the total number of infected deer.  In order to assess deer numbers, the Wisconsin Department of Natural resources counts deer from helicopters each winter.  We are using statistical techniques to determine the power of these counts to detect an actual decline in deer numbers and to model deer numbers in areas that were not surveyed.  We are also using statistical models to assess the factors that determine deer removal and whether deer removal or densities affect CWD transmission rates.

Assistant Scientist: Dr. Erik Osnas

Back to Landscape Page

Back to Introduction