Integration of Remote Sensing and GIS Techniques to Study the
Relationship Between Vector Borne Disease and Vegetation
Cover: A Case of Malaria Chanthaburi Province of Thailand
Dr. Kaew Nualchawee1 , Dr. Pratap Singhasivanon2
Dr. Krongthong Thimasarn3, Dr. Darasri Dowreang4
Dr. Kenneth Linthicum5, Ms. Ratana Sithiprasasna6
Mr. P.L.Rajbhandari7
1Coordinator, Space Technology Applications and Research Program,
Asian Institute of Technology, Bangkok
2 Head, department of Tropical Hygiene,
faculty of Tropical Hygiene Mahidol University, Bangkok,
3 Director, Malaria Region V,
Department of Communicable Disease Control,
Ministry of Public Health, Nonthaburi, Thialand
4 Research Scientist, Remote Sensing Division,
National research Council of Thialand, Bangkok, Thailand
5Chief, Department of Entomology,
US Army Medical Component, AFRIMS, Bangkok, Thialand
6Medical Research Technologist, Department of Entomology,
US Army Medical Component, AFRIMS, Bangkok
7 Research Associate,
Space Technology Applications and Research Program,
Asian Institute of Technology, Bangkok, Thialand
Abstract
An Epidemiological and ecological study had been conducted to determine the correlation between various factors contributing to malaria transmission. The vegetation cover is one factor that may affect malaria transmission. Entomological parameters of Anopheles virus related to malaria transmission and vegetation patterns were determined in malaria endemic areas located along the Thai-Cambodia borders using retrospective and prospective data. LANDSAT satellite imagery was used to produce a land cover map for 1995. Land cover changes between 1985, 1990 and 1995 were analyzed using a Geographic Information System(GIS). GIS is used as the Analysis tool to map parameters contributing to malaria transmission by creating overlays of epidemiological, entomological and environmental data on land cover data from different dates. Analysis of environmental factors related to malaria transmission were performed using correlation statistics on geo- coded data in the GIS. The results of this study show that there are changes in the incidence of malaria transmission and vegetation cover s between 1985, 1990 and 1995 in the study area. Many factors, including land cover class, affect malaria transmission. The working scale of he study area map also plays an important role for the study.
Introduction
Malaria remains one of the major public health problems in Thialand. After 40 years of national control program efforts, the mortality due to malaria has been greatly reduced from 350 per 100,000 populations in 1951 to 1.87 per 100,000 in 1992. This is in part due t the impact of improvement of health infrastructure and malaria clinic network. Although malaria morbidity has shown a downward trend, some fluctuations of malaria incidence have been observed. Factors such as parasite resistance to drugs, influence of political situation, population movement and environmental changes are found to be associated with changing of malaria incidence.
At present malaria transmission is concentrated along the mountainous, forest covered areas of the Thai-Cambodian border where movement between countries is extensive and the vegetation is largely forest (Fig.1). By contrast, in the central plain area which has been largely deforested, malaria has been eradicated for many years.
Fig.1 Distribution of malaria different parts of Thialand in different years.
The two main mosquito vectors are Anopheles virus and Anopheles minimus. Anopheles virus larvae are found in stagnant water in deep dense forests and rubber plantations, fruit orchards and some man made breeding places. This vector is prevalent along the Thai-Cambodian border. Anopheles minimus is present throughout the country and breeds in slow running streams in forests or forests fringes. This is a very important vector in areas of deforestation and changing vegetation cover to agricultural plantations (e.g. sugarcane, corn and cassava).
Entomological studies that were conducted in some of malaria endemic areas in Thailand found that changes in anopheline vector species composition, density and biology were attributable to environmental shifts (Rosenberg et. al. 1990). Malaria incidence is greatest in provinces located along the Burmese and Cambodian borders with forest cover greater cover greater than 35% of the area of the province based upon unsupervised vegetation classification schemes of NOAA/NDVI data.
Satellite Remote Sensing techniques have been recently used to monitor factors affecting disease transmission. Recent studies have demonstrated that satellite imagery, digitized land use maps and geographic information systems are promising for predicting changes in habitats of mosquito vectors (Hayes et. a. 1985)., and LANDSAT TM data, with a resolution of 30m, have been used to characterize immature habitats of flood-water mosquitoes (Pope et. a. 1992). The study uses 1995 land use maps generated from LANDSAT TM data and reclassified land-use maps from 1985 and 1989 to compare changes in land-use with changes in malaria transmission.
