Published on 3 April 2020
Since its inception in 1948, World Health Day has been celebrated on April 7th. This year, its celebration will take place in the midst of one of the most destructive pandemics in recent history: the rampant spread of COVID-19, the disease caused by the novel coronavirus.
In recent years, researchers and decision makers alike have been employing Earth observation (EO) data in their quest to improve global health. One significant contribution of EO is in the field of spatial epidemiology, particularly in regions where epidemiological data are scarce. Remotely sensed data can provide accurate descriptions of demographic, socio-economic and epidemiological profiles at very detailed spatial scales. This information can direct relevant authorities, organizations and stakeholders, both at identifying the populations most susceptible by infectious diseases but also understanding the drivers behind their spread. One of the most devastating infectious diseases is malaria.
Environments suitable for malaria mosquito vectors can be detected from satellite imagery. A snapshot of a very high resolution Pléiades satellite image over an urban region surrounded by marshes and wetlands in Dakar, Senegal.
Malaria is a vector-borne disease transmitted to humans by Anopheles mosquitoes that carry the Plasmodium parasite. Until fairly recently, the disease was found in large parts of the world all the way up to the Arctic circle, but today it has been eradicated in the Western world, although it is still prevalent in large parts of the tropics and subtropics, notably in Africa. According to the World Health Organisation, Sub-Saharan Africa is hit the hardest, with over 90 % of all malaria-related casualties coming from that region.
Source: World Health Organisation (www.who.int)
Most of these deaths are children under five, since they are most vulnerable to the disease. Malaria is known as a rural disease, with most initiatives by governments, scientists and international organizations being focused on non-urban environments.
In urban areas, high population density combined with poverty may result in more people being exposed to malaria risk
However, since the past few decades, the urbanization rates across the sub-Saharan region have been dramatically increasing and by 2050, about 50% of its population is estimated to be living in cities. Nowadays, the majority of sub-Saharan urban residents live in crowded informal housing, often built on inadequate land (e.g., floodplains, marshy areas, dumpsites) with inadequate water supply, sanitation and waste disposal, which poses serious health threats. Malaria can persist and thrive in these newly shaped environments as the conditions that made the disease dominant in rural areas now exist in several Sub-Saharan cities.
This heterogeneity of intra-urban risk is not captured in continental malaria risk mapping initiatives, nor is it considered as part of current national control strategies that focus on protecting less densely populated rural communities.
Adult mosquito habitat suitability in Dakar, Senegal using multicriteria analysis on Earth Observation and ancillary spatial datasets.
The STEREO III project REACT (Remote Sensing for Epidemiology in African Cities) brings together an international consortium of four universities and aims to contribute to the use of EO for tackling urban health issues. In the project, a wide suite of satellite images at different spatial resolutions are harnessed to derive variables and examine in detail the predictability of intra- and inter-urban variations of malaria infection risk and vector suitability. The spatial epidemiology of malaria is investigated at a sub-continental scale in a set of 24 large cities. The project is based on malaria case studies and aims to develop generic methods that can be adapted to other vector-borne diseases (e.g., dengue fever).
Members of the REACT project team