Combining Google Earth and GIS mapping technologies in a dengue surveillance system for developing countries

Abstract

Background: Dengue fever is a mosquito-borne illness that places significant burden on tropical developing countries with unplanned urbanization. A surveillance system using Google Earth and GIS mapping technologies was developed in Nicaragua as a management tool.

Methods and results: Satellite imagery of the town of Bluefields, Nicaragua captured from Google Earth was used to create a base-map in ArcGIS 9. Indices of larval infestation, locations of tire dumps, cemeteries, large areas of standing water, etc. that may act as larval development sites, and locations of the homes of dengue cases collected during routine epidemiologic surveying were overlaid onto this map. Visual imagery of the location of dengue cases, larval infestation, and locations of potential larval development sites were used by dengue control specialists to prioritize specific neighborhoods for targeted control interventions.

Conclusion: This dengue surveillance program allows public health workers in resource-limited settings to accurately identify areas with high indices of mosquito infestation and interpret the spatial relationship of these areas with potential larval development sites such as garbage piles and large pools of standing water. As a result, it is possible to prioritize control strategies and to target interventions to highest risk areas in order to eliminate the likely origin of the mosquito vector. This program is well-suited for resource-limited settings since it utilizes readily available technologies that do not rely on Internet access for daily use and can easily be implemented in many developing countries for very little cost.

Figure 1

Bluefields, Nicaragua: Google Earth Satellite Imagery. Jpeg images from Google Earth were compiled as a mosaic to create this base map to be use in the high performance mapping program ArcGIS.

Figure 2

Example of Printed Satellite Map for Data Collection in Neighborhood Beholden. Public health workers mark maps like this printed in black and white on 8.5 × 11 inch paper to denote the location of potential larval development sites during their routine epidemiologic surveillance. Each neighborhood block is denoted with its corresponding number.

Figure 3

Bluefields, Nicaragua with the locations of potential larval development sites overlaid. Dengue risk factors such as abandoned lots, cemeteries, landfills, and garbage dumps that act as locations for mosquito breeding and disease transmission are noted by different symbols on the map.

Figure 4

Bluefields, Nicaragua with the locations of reference points overlaid. Reference points can be helpful in areas with unplanned urbanization to localize patient homes as the address systems may be underdeveloped. In Nicaragua, addresses are giving based on landmarks such as "the home two blocks towards the lake from the church" so we found it useful to collect information of common reference points in Bluefields.

Figure 5

Bluefields, Nicaragua close-up of reference points. Here the baseball field, a church, and the home of a health promoter can be visualized.

Figure 6

Bluefields, Nicaragua with Suspected Cases from January 2009 overlaid on indices of infestation by neighborhood block. Suspected cases of dengue are cases with clinical symptoms of dengue that are awaiting serologic confirmation. Yellow areas indicate optimal control, with home indices less than 1%, light orange areas indicate good control, with home indices between 1–5%, dark orange areas indicate alarm levels with indices of 5–10%, and red areas indicate emergency levels with home indices greater than 10%. The cases are shown in green and generally correlate spatially with the locations of high indices of infestation.

Figure 7

Emergency Spatial Fumigation performed on 7/9/09 during a Dengue Epidemic. This map was constructed using the track function on the GPS unit to collect information on the path taken by the fumigation truck as it drove through areas of Bluefields. The map was then sent to the Ministry of Health in Managua to communicate the activities of the day and plan for control interventions for the following day. This map also demonstrates areas that cannot be reached by truck as the streets are two narrow. These areas are of particular risk as both the fumigation truck cannot enter and the garbage truck does not enter. Therefore, further resources are needed to send public health workers into these neighborhoods to fumigate with handheld devices, to clean up garbage, and to educate people about the importance of carrying their garbage out to a site where the garbage can be properly disposed of.