Space technologies for the delineation of potential habitats of Banticota indica rodents, Hantavirus hosts in Nakhon Pathom province (Thailand) 3. Methodology Each parameter, which can describe the presence of one rodent, was considered and integrated as a cover into a GIS. For a given point it will inform the physical, demographic, social and economic parameters, and also their spatial description. The information from the disease survey and especially the rodents survey were associated later. Principles of the spatial analysis of vector biology assessing the vector presence and the risks to get Hantavirus related diseases.  Firstly, we can identify the parameters defining the presence of Bandicota indica after describing its ecology. Secondly, we modelled the presence of Bandicota indica using the rodent sampling data, which show the importance of each parameter. This modelling allows to spatially define its distribution. Finally, from the regional distribution of Bandicota indica, we will be able to evaluate the potential risks for humans. This will involve the knowledge of the hantaviruses presence (from the hantaviruses found in the rodents analysis) and the assessment of the human presence close to these vectors (either field or household contacts). Then the objectives are to delimit coherent regions, which express same characteristics of the presence of Bandicota indica and further the emergence of hantavirus related diseases. Different regions can show different reasons of emergence. 4. Results Bandicota indica is a field rat then the study focused mainly on the description of physical parameters from the satellite images. We analysed the image with Multiscope 3.1, a remote sensing software developed by EADS Matra, which provides also photo interpretation tools and a set of GIS functions. We classified the land use in 14 classes significant for the description of rodent habitats. We vectorized this cover, exported it into a GIS software and rebuilt it in order to obtain one polygon for each category. Considering the ecology and the description of the catching places of Bandicota indica, the presence of this species can be directly assessed from the type of land use. This is a field species, which was rarely found inside (4.5%) or around houses (21%). The index assessing the presence of Bandicota indica was deducted from the percentage of rats found in each class of land use. We realized a buffering around the catching places to describe the close environment of each rat caught. The living area of one rodent is within a one-kilometer radius of the trap. Then by extracting these buffers from the land use cover, we calculated the repartition of each land use category in Bandicota indica living area and the index for its potential presence. Using the map of land use and this index of presence we realized the map of the potential presence of Bandicota indica in Nakhon Pathom province. To visualize the results we classified the values in five equidistant classes. This map clearly shows that Bandicota indica is a field rat, which can be found almost everywhere. The “mixed agriculture” class is affected by the index 1, which is meaning a high probability to find Bandicota indica. Only three classes are mainly represented. The first one (27.6% of all surfaces), which describes the areas with a low presence of Bandicota indica, corresponds to grasslands, plantations and wetlands. The second one (35.7% of all surfaces) groups together the urban and suburban areas. We know that Bandicota indica is also attracted by the human presence because humans mean for rodents the possibility to find food. The last class (36.6% of all surfaces) represents the agricultural fields themselves (crops or paddy) and some heterogeneous areas in transition between agricultural and urban classes. These areas are often bare lands or classified into mixed agriculture and are places where rats will find refuge in proximity to large fields. 5. Conclusion This study has helped in displaying the presence of Bandicota indica and was adapted to other rodent species with a medical interest in Thailand (especially Rattus species). We are now working on an extension to other study areas inside the country and enlarging the research to other rodent-borne diseases. These rodent species carry numerous of diseases and among them hantaviruses have a special importance nowadays because we expect their emergence in south-east Asia. Hantaviruses have already been identified in our samples. That’s why a map assessing the presence of rats means also the assessment of the presence of hantaviruses. This delineation is only valid for Nakhon Pathom province and even within this province further samplings should improve the results. The maps done for each rodent species are and will be useful tools to conduct next researches. 6. References
Page 2 of 2
| Previous | |