Ecological Niche Modeling for the Chagas Disease Vector

Team Location: Mobile County Health Department, Mobile, Alabama

An ecological niche risk map for T. sanguisuga, centered on the Southeast United States, at 1-kilometer resolution. Image Credit: Gulf Coast Health and Air Quality Team, NASA DEVELOP National Program.

An ecological niche risk map for T. sanguisuga, centered on the Southeast United States, at 1-kilometer resolution. Image Credit: Gulf Coast Health and Air Quality Team, NASA DEVELOP National Program.



Authors:
Walt Clark, Project Lead (University of South Alabama)
Sid King (University of South Alabama)
Shikher Mishra (University of South Alabama)
James Pickett (University of South Alabama)

Mentors/Advisers:
Dr. Bernard Eichold (Mobile County Health Department)
Joe Spruce (Computer Sciences Corp.)
Kenton Ross, Ph.D. (NASA, DEVELOP National Science Adviser)

Abstract:
Chagas Disease is a chronic infection from the Trypanosoma cruzi protozoa, and is transmitted by the Triatominae subfamily of the Reduviidae family of true insects. These insects seek blood meals, often from mammals including humans. In species that are notably successful vectors, the disease is then transmitted through defecation soon after feeding. The insect displays a preference for the face, which offers ample infection routes through the eyes or mouth. The disease initially manifests itself with symptoms similar to the flu as the immature protozoa circulate through the bloodstream. But, a lack of treatment leads to a chronic phase in which the transmitted protozoa enter host cells, mature to reproductive stages of the life cycle, and begin to asexually multiply in embedded soft tissues, causing irreparable damage to the heart, intestines and possibly other organs. Presently, little attention is given to Chagas Disease in the U.S., despite the presence of vectors and a large reservoir population. Although it is hypothesized that better housing within the U.S. prevents rampant transmission, increases in wild-urban interaction and climate change may open up new habitats for Triatominae and transmission potential for Chagas by extension. Thus, the objective of this project was to determine the risk of contracting Chagas Disease in the rural Southeast. Because the project partner was primarily concerned with the health risk for residents of Alabama, this study focused on the species Triatoma sanguisuga because of its widespread habitat range, which spans the southeastern states, as west as Texas. Since this species has specific environmental needs, environmental suitability modeling was performed using spatial data with Stockwell and Peters’ Genetic Algorithm for Rule Set Production (GARP) to create species location maps. Shuttle Radar Topography Mission (SRTM) data was used to ascertain elevation and slope. Moderate Resolution Imaging Spectroradiometer (MODIS) data was used to calculate Normalized Difference Vegetation Indices Normalized Difference Water Indices and to discriminate between deciduous and evergreen vegetation, as T. sanguisuga has an affinity for elm, oak and hickory groves. Tropical Rainfall Measuring Mission data was used to calculate rainfall accumulations on a seasonal basis. These data and other parameters that are identified in literature specific to Triatomines were created, formatted and implemented in the GARP environmental niche model in order to predict optimal habitats of endemic Triatomine species. The species location maps derived from GARP results were used with U.S. Census Bureau Topologically Integrated Geographic Encoding and Referencing (TIGER) files to determine transmission risk. Additionally, project partners may use the produced niche maps to collect T. sanguisuga for testing of the protozoa.



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