In Brazil, around 30 million people are exposed to the risk of contracting schistosomiasis, and it is estimated that 4–6 million individuals are infected with S. mansoni[1, 2]. The northeastern region of the country is markedly the most endemic area, and for many years, schistosomiasis was considered to be a characteristic ailment of rural areas[4–6]. However, over recent decades, there has been increasing incidence of cases in urban and coastal areas[7–14]. One of the factors noted in this process of expansion of schistosomiasis is the migratory flow of the infected rural population, which, attracted by employment opportunities in urban and coastal localities, has ended up becoming established in peripheral agglomerations where the lack of sanitation and basic infrastructure result in fecal contamination of aquatic environments, with consequent infection of intermediate host and emergence of new foci of schistosomiasis transmission[8, 14].
Within this perspective, it is crucial to understand the environmental factors that give rise to occurrences of schistosomiasis in coastal areas, in order to identify the mechanisms for transmission and maintenance of this endemic disease. For this, remote sensing is becoming a valuable tool for identifying environmental changes that may directly or indirectly influence on occurrences of a disease. Studies using this technique have been shown to be effective for predicting the risk of infection, thereby enabling greater completeness of understanding about the large-scale ecology and distribution patterns of schistosomiasis, and also highlighting the influence of the determining factors within the microenvironment (parasite and snail) relating to transmission of this disease. Environmental changes can be viewed and measured using this technique, thus indicating that controlling the transmission and monitoring the areas at risk can be backed up through knowledge of changes to the plant coverage, topography and water courses, from before to after episode of flooding, by means of spatial models of geographical information systems and remote sensing.
The urbanization process has also been highlighted as a determining factor for occurrences of helminthiasis, given that this has a direct impact on the environment. Disorderly occupation of peripheral areas is characterized by overcrowding in improvised constructions and inadequate sanitary conditions, and this may be associated with increased transmission of helminthiasis and schistosomiasis. These authors pointed out that the risk of infection was higher for immigrants coming from non-endemic areas, thus emphasizing the need for studies on the impact of the urbanization process on schistosomiasis and their importance for understanding the factors that have led to expansion of this disease. In this regard, it has been estimated that by 2030, around 60% of the world’s population will be living in cities and that 93% of urban growth will be occurring in developing countries.
This urbanization process can be detected and the environmental degradation, defined in this paper as any change or disturbance to the natural environment, as for example: reduction of mangrove and vegetation areas, can be analyzed through remote-sensing techniques. These make it possible to measure the changes in occupation of natural areas over the course of time, by using data such as normalized difference vegetation index (NDVI), thermal index, digital elevation model (DEM) and using of land, from satellites image. Together with Geographic Information System (GIS), satellite image data have been used to correlating the transmission of schistosomiasis in China[16, 20] by analyzing the hydrographical transportation of intermediate host snails, and also the impact of irrigation system and seasonal flood on snail dispersal and the transmission of schistosomiasis. In Africa, satellite data have been used for surrogates of climate data in the development of environmental risk models for schistosomiasis, and in Brazil, similar studies were conducted by using GIS and remote sensing techniques to evaluate the risk of schistosomiasis and also to establish a statistical model for estimating its prevalence[22–24], which demonstrates the importance of those methods to evaluate the transmission and maintaining this ailment.
In Brazil, other studies have shown relationships between occurrences of schistosomiasis and environmental factors, highlighting the patterns of contact between at-risk populations and contaminated water accumulations[7, 25]. It was also reported the relation between snail breeding sites and the unorganized urbanization process, where no sanitation and stormwater drainage provide all conditions to the increase of temporary breeding sites of B. glabrata. However, models for estimating the transmission risk from temporal and spatial perspective are necessary in order to construct future scenarios in which the planning for healthcare action might be more effective, thereby minimizing the transmission and damage to health among individuals exposed to risk of this parasitosis.
The present study sought to identify environmental changes that have taken place as consequences of the process of occupation and urbanization of a locality, where the population increase was observed through the increase of housing construction from 2000 to 2010. However, this increase was not followed by sanitary infrastructure of households, which characterizes a disorderly occupation of space. Therefore, by means of spatial-temporal analysis based on satellite images and malacological and epidemiological data we sought to correlate these changes with the process of expansion and endemization of schistosomiasis in a coastal region of Brazil.