Tickborne Diseases: Background
The geographic ranges of many tick species have expanded over the past several decades, and several new tickborne zoonoses have emerged.
Two of these diseases are human monocytotropic ehrlichiosis (HME), caused by Ehrlichia chaffeensis; and human granulocytic anaplasmosis
(HGA) caused by Anaplasma phagocytophilum. Maps of these and other emerging pathogens can play an important role in the assessment of regional
public health. However, reliable data on the presence of vectors or pathogens is typically only available at isolated sample locations.
We used pathogen distribution data derived from serology of white-tailed deer combined with geospatial datasets describing climate, land
cover, soils, and deer density to map the distributions of E. chaffeensis and A. phagocytophilum. We used geographically-weighted regression
(GWR) to quantify spatial variability in the influences of climate and land cover on pathogen distributions across the southern United States
(Wimberly et al. 2007).
The results of this study showed that climate was primary correlate of pathogen distributions in the Southeast, whereas
forest cover and fragmentations constrained the western range boundaries in the south-central states. We also assessed fined-scale relationships
between pathogens and land cover within the Mississippi Alluvial Valley and found that environmental variables related to both flooding and
forest/nonforest land cover were related to pathogen distributions
(Manangan et al. 2007). Finally, we used hierarchical Bayesian models to
develop predictive maps of pathogen distributions
(Wimberly et al. 2008). The predictive accuracy of these models was increased by using
spatially explicit methods that incorporated either spatial autocorrelation (the tendency for pathogen distributions to be clustered in space)
or spatial heterogeneity (the potential for environmental influences on pathogens to vary predictably in space). This research was supported
by a grant from the National Institutes of Health, National Institute of Allergy and Infectious Diseases (1R03AI062944). The work was conducted by
Dr. Mike Wimberly from the
GISc Center of Excellence at South Dakota State University in collaboration with
Dr. Michael Yabsley from the
Southern Cooperative Wildlife Disease Survey (SCWDS) at the University of Georgia.
The following pages provide web access to the final pathogen distribution maps via several internet mapping tools.
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| Blacklegged Tick () (courtesy USGA ARS) |
Lone-Star Tick () (courtesy CDC) |
