Mapping malaria Aruna Srivastava Assistant Director B.N. Nagpal Senior Research Officer Malaria Research Centre, 20 Madhuban, Delhi 110 092 arunas@ndf.vsnl.net.in Remote sensing technologies combined with GIS can describe local and landscape-level features influencing disease and disease vector distribution GIS allows spatial data handling, manipulation, and analysis with a new dimension and unparalleled flexibility. These systems provide more accurate base maps and redefine several methods of data capturing within accepted levels of accuracy. Functionality on the Web for integrating data from various sources, including photographs, video, and sound data has given a new perception to spatial data management and global information sharing. In the current day scenario, GIS is finding application in diverse fields including health. In any disease control programme, there are several factors involved, namely estimation of disease burden, monitoring of disease trend, identification of risk factors, planning, allocation of resources, implementation etc. and a common thread involved in all these activities is 'Geography'. Geographic Information System owing to its inherent ability to manage both spatial and non-spatial information provides an excellent framework for disease monitoring and control. Globally malaria clinical cases are reported as 300-500 million and 1.5-2.7 million deaths annually. The increasing trend of environmental change is dramatically changing malaria pattern at the local and as well as global scales. Malaria situation is worsening with large-scale epidemics and increasing mortality. There have been immense efforts to correlate malaria and the environment as the latter influences development of both parasite and the vector (http://www.who.ch/). Many parameters associated with environmental change can now be remotely sensed using remote sensing technologies and combined with geographic information system (GIS) can describe local and landscape-level features influencing disease and disease vector distribution. Here a brief review of the work a) Mapping of Vector distribution and b) development of GIS-based malaria surveillance system is presented. For other contributions one can refer to the enclosed list.  a) Mapping of An. sundaicus, a malaria vector in India There are six major vectors of malaria, they differ greatly in their biology, breeding habitats and distribution. Looking to the vast areas, the reports on vector distribution, which is an essential component of selective malaria control strategy are scanty and old. Manual surveys are very costly, cumbersome and time consuming. Therefore GIS was used to map distribution of coastal malaria vector An. sundaicus in India. In India, An. sundaicus has been reported from eastern coast, two localities of western coast (Gujarat) and Andaman and Nicobar islands. The species is well known for its close association with coastal conditions. Its major breeding sites are swamps, creeks and pits containing stagnant brackish water. It is the sole malaria vector in Andamans and Nicobar islands. Different vector species establish their population at different heights where ecology is suited for their survival. Impermeable soil allows water stagnation and creates grounds for mosquito breeding and thus favours malaria. Porous soil is devoid of stagnant water bodies, hence unfavourable for anopheline breeding. Longevity of vectors and the process of parasite development are sensitive to temperature. Vector species adapts to different temperature threshold depending on the area it occurs. Low temperature, when duration of parasite development in mosquitoes exceed 30 days i.e. beyond average life span of mosquitoes limits active malaria transmission. At higher temperatures the longevity of mosquitoes is exponentially reduced. The number of breeding sites is generally related to the amount of rainfall for most of the vector species but excessive rains cause flushing, thus killing immature stages. Considering the above close association of vector biology with ecological parameters, rainfall, soil, altitude and temperature were taken in the study. Survey of India topo sheets in the scale 1 : 6,000,000 were digitised to prepare thematic maps of these parameters. In Andaman and Nicobar Islands, the altitude ranges from sea level to 150 m, and the annual mean temperature is about 25 deg C. Since very high rainfall is not suitable for vector immature stages, areas having >= 1600 mm. rainfall were considered as unfavourable. Sandy soil is the characteristic of coastal area, therefore other categories of soil were taken as unfavorable. Altitude map was taken as the base map and other thematic layers were added. Suitable ecological conditions from the areas for reported distribution of vector existence were identified and similar areas were extracted from each thematic layer. In the overlaid maps intersection of regions favorable in different themes resulted in mapping of areas of occurrence of the vector species (Fig. 1). For validity of the results, a blow up of the Orissa state was taken. It shows Chilka lake falling in GIS analysed favourable zone and An. sundaicus was reported from this lake. A little in south is Vishakha Pattanam of Andhra Pradesh state, it is also found in favourable GIS zone and the species has been recorded earlier from this area. Still down below on western coast Kerala state is situated and GIS studies revealed that a part of south Kerala is favourable for An. sundaicus but till date no survey has been conducted in this area. A comparison of GIS analysed map with reported distribution reveals a good spatial coherence. Since it is a coastal species, the comparison was restricted to coastal areas only (Fig. 2). There are a few obvious advantages of this technique i) The technique is good for covering vast areas, ii) It can map distribution at macro and as well as micro level, iii) Through GIS vector distribution in inaccessible and unsurveyed areas can be mapped, iv) once the desired scale maps are ready the information can easily be updated and analysed quickly. The technique is fast, reliable and good to study vast geographic areas to identify regions for specific distribution of vectors for planning cost-effective control strategy to interrupt malaria transmission.
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