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Abstract

Background: Vector-borne diseases are the most dreaded worldwide health problems. Although many campaigns against it have been conducted, Dengue Fever (DF) and Dengue Haemorrhagic Fever (DHF) are still the major health problems of Thailand. The reported number of dengue incidences in 1998 for the Thailand was 129,954, of which Sukhothai province alone reported alarming number of 682. It was the second largest epidemic outbreak of dengue after 1987. Government arranges the remedial facilities as and when dengue is reported. But, the best way to control is to prevent it from happening. This will be possible only when knowledge about the relationship of DF/DHF with climatic and physio-environmental agents is discovered. This paper explores empirical relationship of climatic factors rainfall, temperature and humidity with the DF/ DHF incidences using multivariate regression analysis. Also, a GIS based methodology is proposed in this paper to explore the influence of physio-environmental factors on dengue incidences. Remotely sensed data provided important data about physical environment and have been used for many vector borne diseases. Information Values (IV) method was utilised to derive influence of various factors in the quantitative terms. Researchers have not applied this type of analysis for dengue earlier. Sukhothai province was selected for the case study as it had high number of dengue cases in 1998 and also due to its diverse physical setting with variety of land use/land cover types.

Analyzing the spatio-temporal relationship between dengue vector larval density and land-use using factor analysis and spatial ring mapping

“…Land-cover for 1860 classes was merged into 171 classes following Land Development Department Thailand rules of classification codes, based on similar class structures. The resultant classes were further contracted to 27 classes representing all types of major and mixed classes, as reported in the literature about the relationship of dengue with land-use type [7,11,15] (Figure 7). Successive contractions of land-cover classes were carried out to reduce the redundancy of similar patterns to clearly determine the comprehensive phenomena of vector-borne disease (dengue).…”

“…Successive contractions of land-cover classes were carried out to reduce the redundancy of similar patterns to clearly determine the comprehensive phenomena of vector-borne disease (dengue). Considering the maximum mosquito flight range during its life span around the village, a buffering operation of one-kilometer was performed using GIS software for the 92 villages [15]. This helped to indicate the environmental conditions around the observed locations, i.e.…”

“…), as indicators that can be adopted to compare their individual relationships with each of the habitat parameters [4,12]. The relationship between number of dengue virus infections (cases) and climatic factors has been reported by many researchers using several indices, and it has been concluded that climatic conditions have a strong influence on dengue infection [13-15]. However, drawbacks associated with the use of dengue case data include the occurrence of asymptomatic infections which cannot be used to support a real-time indication of a forthcoming disease scenario, as can be predicted using larval density data [16].…”

“…tree holes, plant axils, cut bamboo stumps and opened coconuts, but also in outdoor artificial containers, i.e. rubber tyres, water storage barrels, glass and plastic bottles, and jars located up to one-kilometer diameter [15,18]. …”

“…pathogen dispersal might be highly localized, vectors or reservoirs for pathogens might be spatially restricted, or susceptible hosts might be clumped [19]. In addition to the reported relationship between climatic conditions and dengue infection [13,15], understanding the contribution of land-use type to dengue vector breeding ability is directly required to unveil the underlying scenario comprehensively. A few previous studies have emphasized the analysis of land-use and land-cover types due to their relevance with mosquito breeding habitat and people’s living style.…”