Characterization of Venezuelan Equine Encephalitis Emergence Sites Using GIS

Project institutions: The University of Texas Medical Branch at Galveston, Galveston, Texas; Central University of Venezuela, Caracas, Venezuela; and National Institute of Hygiene, Caracas, Venezuela

Principal investigator: Dr. Robert Tesh¹
Co-investigators: S. Weaver¹, R. Barrera², J. Freier³, J. Navarro², R. Salas⁴

¹ University of Texas Medical Branch at Galveston
² Central University of Venezuela,
³ USDA-Fort Collins
⁴ National Institute of Hygiene, Caracas

Venezuelan equine encephalitis (VEE) is a classical emerging arboviral disease that represents a threat throughout most of the Americas, including the United States. This virus has caused repeated epidemics and equine epizootics since the 1920s, involving up to hundreds of thousand of equines and tens of thousands of people with severe morbidity and mortality. The source of these epidemic/epizootic viruses was recently identified as the enzootic variety ID VEE, strains that circulate in sylvatic transmission foci in South America and Panama. Three recent outbreaks in South America and Mexico underscore the continued threat of VEE emergence from enzootic progenitors.

This proposal is a pilot study to develop remote sensing and geographic information systems (GIS) to identify locations of potential VEE emergence. The specific aims are:

1. Identify environmental factors that are correlated with the distribution of enzootic variety ID VEE viruses. Hypothesis: The habitat that supports enzootic transmission of VEE variety ID viruses in Venezuela is unique and can be defined ecologically by field studies. Two known ID enzootic transmission foci will be studied in the Catatumbo region of western Venezuela; arbovirus and mosquito fauna, as well as dominant plant communities, will be characterized along with elevation, soil type, ground moisture and climate, using on-ground observations. These data well be included as a layer in GIS analyses.

2. Use remotely sensed data from satellite imagery to identify a spectral reflectance pattern, or "signature," for the ID virus transmission habitat. Hypothesis: Ecological descriptions of ID transmission foci generated in aim 1 can be compared to remotely sensed satellite spectral data to develop reflectance patterns, or "signatures," specific for enzootic VEE virus transmission habitats. By correlating ground truth data obtained in aim 1 with Landsat data derived from multi-spectral scanners, we will begin to define spectral "signatures" for VEE ID virus biotopes. This pilot study will later be extended to generate a map of landscape elements for the entire Catatumbo region, allowing us to locate additional enzootic virus transmission foci where VEE emergence could occur. This will lead to improvements in our ability to detect locations of potential epidemic/epizootic VEE emergence.

This GIS data begun in this project will benefit VEE surveillance throughout the Americas, and will be useful in assessing the impact of future ecological changes on enzootic virus ecology. In addition to developing tools for studying emergence mechanisms of an important New World pathogen, these studies will serve as a model system for epidemiological studies of other arthropod-borne and zoonotic viral diseases.

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