Abstract
Plague is a zoonotic infectious disease present in great gerbil populations in Kazakhstan. Infectious disease dynamics are influenced by the spatial distribution of the carriers (hosts) of the disease. The great gerbil, the main host in our study area, lives in burrows, which can be recognized on high resolution satellite imagery. In this study, using earth observation data at various spatial scales, we map the spatial distribution of burrows in a semi-desert landscape.The study area consists of various landscape types. To evaluate whether identification of burrows by classification is possible in these landscape types, the study area was subdivided into eight landscape units, on the basis of Landsat 7 ETM+ derived Tasselled Cap Greenness and Brightness, and SRTM derived standard deviation in elevation.In the field, 904 burrows were mapped. Using two segmented 2.5m resolution SPOT-5 XS satellite scenes, reference object sets were created. Random Forests were built for both SPOT scenes and used to classify the images. Additionally, a stratified classification was carried out, by building separate Random Forests per landscape unit.Burrows were successfully classified in all landscape units. In the ‘steppe on floodplain’ areas, classification worked best: producer's and user's accuracy in those areas reached 88% and 100%, respectively. In the ‘floodplain’ areas with a more heterogeneous vegetation cover, classification worked least well; there, accuracies were 86 and 58% respectively. Stratified classification improved the results in all landscape units where comparison was possible (four), increasing kappa coefficients by 13, 10, 9 and 1%, respectively.In this study, an innovative stratification method using high- and medium resolution imagery was applied in order to map host distribution on a large spatial scale. The burrow maps we developed will help to detect changes in the distribution of great gerbil populations and, moreover, serve as a unique empirical data set which can be used as input for epidemiological plague models. This is an important step in understanding the dynamics of plague.
Highlights
Plague, a disease mainly spread by rodents, was responsible for the deaths of nearly one-third of the European human populationL.I
Much of our knowledge of disease dynamics in natural populations is gained from investigations using epidemiological models (Hudson et al, 2001)
Eight landscape units were distinguished in the Balkhash basin resulting from the landscape stratification using the layers TC-Brightness, TC-Greenness and Digital Elevation Model (DEM)-SD (Table 2 and Fig. 4)
Summary
A disease mainly spread by rodents, was responsible for the deaths of nearly one-third of the European human population. L.I. Wilschut et al / International Journal of Applied Earth Observation and Geoinformation 23 (2013) 81–94 about 2000 diagnosed human cases annually, of which the majority occur in Africa (World Health Organization, 2005). Much of our knowledge of disease dynamics in natural populations is gained from investigations using epidemiological models (Hudson et al, 2001). The spatial distribution of hosts may determine local host connectivity, which when increased enhances the likelihood of successful disease spread (Keeling, 1999). Model studies suggest that the spatial distribution of hosts influences disease dynamics in different ways, but empirical data on the spatial distribution of infected and susceptible hosts on a population scale is scarce
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