Author: Palamy Changleuxai
Changleuxai, Palamy, 2019 Investigating the relationship between surface water and dengue fever incidence. A case study: Vientiane Capital, Laos, Flinders University, College of Science and Engineering
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Dengue fever is a mosquito-borne disease caused by the dengue virus, with a high global incidence. More than 70 % of the world’s population is living in areas that are vulnerable to dengue fever, and most of them are in tropical regions. One of the most affected regions in Southeast Asia, where cases of dengue fever and deaths associated with dengue fever account for 40% of globally reported dengue fever cases (data from 2010 to 2013). Vientiane, the capital of Laos, has a long history of dengue disease, with the first report of dengue fever in 1983, and large outbreaks recorded in 1985, 1987, 1995, 1996, 1998, 2003, 2010, 2013, 2017 and the present (2019), with over 1,000 cases. The emergence of this increasing incidence is presumably associated with several factors, one of them is likely to be surface water, including both artificial and natural water bodies. Water bodies act as an important component in the number of dengue mosquitos – Aedes aegypti, and Aedes albopictus. Several previous studies have found that water bodies, a vector breeding site, tend to result in dengue mosquito proliferation under favorable conditions of temperature and rainfall. Vientiane is a mix of urban and rural areas and is surrounded by plenty of standing water and streams. During rainy seasons, many areas encounter poor water drainage, and this has caused marshland development. Given the nature of dengue disease mosquito vectors, small surface water bodies are likely to facilitate the expansion of mosquito populations.
In this study, freely available satellite images were used to derive surface water throughout the year 2017. Before selecting the suitable images, a process of selecting satellite imageries was conducted. Sentinel-1 SAR, Sentinel-2, PlanetScope, and RapidEye were assessed. A field survey was also conducted in order to observe the sites within the study area, focusing on water body size and vectors breeding sites. Three main datasets were used in this project; the satellite imageries – PlanetScope, and RapidEye, dengue incidence in 2017, and rainfall data. Surface water extraction, normalized difference water index (NDWI), and normalized difference moisture index (NDMI) were the main methods used to detect water areas.
To determine the relationship between surface water and dengue incidence, Spearman correlation and regression were used. As surface water acts as the breeding habitats for the dengue virus carriers, expected mosquito life development time was defined from the onset date of dengue fever symptoms. Estimated surface water extracted from satellite images showed a relationship with dengue incidence, at a significant level, but many aspects may need to be considered. Rainfall data were also compared with dengue incidence and showed a positive correlation with the disease cases; however, surface water and rainfall were found not to associate with dengue vector populations.
Keywords: GIS, Remote Sensing, surface water, water bodies, Aedes aegypti, Aedes albopictus, rainfall, dengue fever, satellite images, NDWI, NDMI
Subject: Computer Science thesis
Thesis type: Masters
Completed: 2019
School: College of Science and Engineering
Supervisor: Kirstin Ross