Characterization of enzootic foci of Venezuelan equine encephalitis virus in western Venezuela.

The research investigates the distribution of Venezuelan equine encephalitis (VEE) virus in tropical forests of western Venezuela using remote sensing and geographic information system technologies. The observation implied a significant potential risk of severe disease to humans within the area from enzootic ID VEE viruses. At the same time, equines may become naturally vaccinated, preventing the emergence of epizootic IC VEE virus strains.

Investigation Methodology

• The researchers used Landsat 5 Thematic Mapper satellite imagery for the investigation. This technology was used to study the reflectance patterns of areas where the VEE virus was endemic. This data was then used to identify other locations with similar reflectance patterns.
• The researchers also captured wild vertebrates and exposed sentinel hamsters to mosquito bites for VEE virus surveillance in seven forests identified and located by means of satellite imagery.
• The researchers used unsupervised and supervised techniques to classify the satellite image into 13 validated classes of land use and vegetation types. This classification used raw digital values of near- and mid-infrared bands, Tasseled Cap indices of wetness, greenness, brightness, and the Normalized Difference Vegetation Index.
• Additional data layers included digitized maps of elevation and soil geomorphology, along with a digital layer of roads and georeferenced images for locating the study sites.

Findings

• The researchers were able to isolate VEE viruses worth noting from 48 of 1,363 sentinel hamsters in two different forests, both in dry and wet seasons.
• The cluster analysis of the above data revealed two main groups of dense forests separated by spectral properties, altitude, and soil geomorphology.
• The virus was found more frequently in forest types on flat flood plains of main rivers than in forest types found on the rolling hills of the study area.

Conclusions

• The spatial analysis suggested that mosquitoes carrying the enzootic viruses could reach 82-97% of the total land area by flying only 1-3 km from forests.
• The findings led the researchers to hypothesize that humans within that area could be at risk of severe disease caused by enzootic ID VEE viruses.
• However, the researchers also suggest that equines, through natural exposure to these viruses, could become naturally vaccinated against VEE, thereby preventing the local emergence of more dangerous epizootic IC VEE virus strains while indirectly protecting humans.