The use of GIS in Research and Control of Malaria
Thisula Abeysekera, D.M. Goonewardena, Gamini Jayasundera, Lal Muthuwatte,
P.Kumr Kotta1, Thilak Senanayake2,
Richard Carter3 Kamini N. Mendis, A.R. Wickremasinghe4
Malaria Research Unit, Faculty of Medicine, University of Colombo.
1SACEP, Anderson Road, Colombo 4.
2Mahaweli Authority of Sri Lanka, Polgolla.
3Division of Biological Sciences, University of Edinburgh, Scotland, U.K.
4Deparment of Community Medicine and Family Medicine, Faculity of Medical Science, University of Sri Jayawardenepura
Introduction
Malaria is a disease transmitted by mosquitoes of the Anopheles species. Its distribution in Sri Lanka Corresponds to the climatic zones of the island with the dry zone carrying the highest case load, the intermediate less, and the wet zone being almost free of the disease except during epidemic periods. Malaria transmission varies seasonally corresponding toe monsoonal rainfall. The distribution of malaria is not homogeneous even within climatic zones, and scattered pockets of high transmission are found mainly in the dry zone. Malaria is affected greatly by environmental factor such s h u mediate and altitude which affect the survival and longevity of the vector mosquito, and the presence of water bodies which are its breeding sites. It has an association with large scale agricultural development projects due to creation of breeding sites and he migration of labour from non-malarious area, they being more prone to disease due to low levels of immunity.
The Malaria Research Unit (MRCU) of the Faculty of Medicine, University of Colombo has been conducting research on malaria and its control over the last 15 years. A
geographic Information system (GIS) laboratory was established in the MRU in 1994. The objectives of the programme is to establish a GIS for health with emphasis on malaria. Since the establishment of the GIS laboratory at the MRU, research has focussed on two major projects: The first project is on the micro-epidemiology of malaria, where the unit the analysis was the household. The second project is on macro-epidemiology in which the objective is to determine environmental an land use pattern correlates of malaria at the Grama Niladhari Divisional level and beyond.
1. The Micro -Epidemiology Project.
The purpose of this study was to determine the association between the incidence of malaria and the distance to sources of water and the forest controlling for the type of house construction, the latter shown by us previously to be a risk factor for malaria. The study was carried out in 8 adjoining villages in Kataragama, situated in the Moneragala District of Sri Lanka. The study units consisted of 423 households and a population of 1875. Malaria data was collected over a period of 18 months from January 1992 to June 1993. All individuals were individuals were identified by a unique identification number and it was possible to link each malaria case to a particular house in the area. The detection of malaria was carried out at the field station located in the area by trained personnel. We assume that almost all the malaria infections that occurred in the area detected by us.
The study area was mapped using aerial photographs of 1:5,000 magnification, obtained from the Survey department and field checked by the project personnel. The maps were digitized using the Arc/Info software package. Coverages of roads, streams, the landuse pattern and houses were digitized separately and overlaid to obtain the final map. Data on individual households was linked to the point attribute table (PAT) final map. Data on individual households was linked to the point attribute table (PAT ) files of houses that are generated by Arc/Info. Two varieties i.e. the Incidence Rate and the House Type, were used for analysis. The incidence rate was calculated as the number of malaria cases in a household that occurred during the 18 month period of the study divided by the number of members of the household. Household with 2
persons or less were eliminated for statistical reasons. House type was classified into two according to the type of house construction namely the walls and roofs; 'good' houses had brick walls and tiled roof and the 'poor' house and mud walls and cadjan roofs. It was shown that the malaria incidence rate of 'poor' house was significantly higher (2.5 times) than that of 'good' house.
Distances between individual houses and water bodies and the edge of the forest were obtained using the NEAR command IN Arc/Info. There was no association between the incidence of malaria and the distance from a house to the forest edge after controlling for house type. There was a significant negative correlation between the incidence of malaria and the distance from a house to a water body only in the case of 'poor' house. A buffer zone of 200 meters around water bodies was simulated, from which, we eliminated the 'poor' houses and relocated them outside the buffer zone. The reduction in the incidence of malaria that this intervention would yield was estimated to be approximately 30%.
