Geographic Determinants of Human Schistosomiasis Transmission in the Sourou Valley, Burkina Faso

Schistosomiasis (also known as Bilharzia or Bilharziasis) is the second most prevalent neglected tropical disease (NTD) after hookworm and is caused by infection with blood flukes of the genus Schistosoma. More than 85% of the estimated 779 million people at risk worldwide are concentrated in Sub-Saharan Africa (SSA). Of the 207 million infested persons worldwide, more than 97% are concentrated in SSA. The geographic study of human schistosomiasis comes within the framework of geography of health with the target of putting into perspective the natural and social determinants of the states of health within an area of interest. The complexity and multiplicity of factors contributing to the endemicity of human schistosomiasis suggests that patterns are readily predicted at regional and national scales and that more complex models are required to predict patterns at local scales. This local fine scale approach was adopted in this research to assess schistosomiasis-susceptibility at the community level by integrating natural and social geographic determinants in Burkina Faso in general and the Sourou Valley in particular. Therefore, the present study, in its conception, aimed to collect useful background information for analysing human schistosomiasis ecology and diffusion as well as the access to health care services and associated infrastructures at the community level. This study tried to provide answers to three specific questions: i) what are the natural and social geographic determinants of the disease and how do they interact in terms of infestation of local populations? ii) how do the determinants of the disease interact in terms of local environmental contamination? and iii) could natural and social geographic determinants be integrated to geographically map high schistosomiasis-susceptible communities in the Sourou Valley in Burkina Faso? These research questions have three underlying specific hypothesis: i) human infestation depends on diverse natural and social geographic determinants occurring through multiple factors and complex interactions; ii) local environmental contamination depends on diverse natural and social geographic determinants through a complex of interactions between multiple factors; and iii) the comprehensive, rapid and accurate mapping of high schistosomiasis-susceptible communities and sub-communities in the Sourou Valley is depends on the integration of diverse natural and social geographic determinants collected at the community level. Three specific objectives were defined to verify these hypotheses: i) to identify natural and social geographic elements at the local community level in order to understand their complex interactions with respect to human infestation; ii) to identify natural and social geographic elements at the local community level for understanding their complex interaction with respect to environmental contamination; and iii) to integrate identified natural and social geographic elements for geographic mapping of schistosomiasis-susceptible communities in the Sourou Valley. The global and eco-systemic approach used in this work required us to dispose of a multitude of layers of information. In fact, the determination of communities favorable to schistosomiasis transmission requires the crossing of different spatialized data. Data gathering following the holistic perspective included geographic data (natural and social) as well as epidemiologic data. Some were readily available from archive sources, but most of them were ground collected data, particularly human and illness-related data. In this thesis, physical data were collected for assessing the heterogeneity and patterns of the vulnerability in time and space. Climatic variables were used to measure the temporal vulnerability of local populations while environmental layers were used to measure the spatial vulnerability of local populations. Human data such as population size and movement as well as access to infrastructures were collected to assess vulnerable communities within the AOI. Epidemiologic data was needed to assess and highlight the magnitude of the vulnerability to schistosomiasis at the community level. The spatial analysis followed a vertical approach. Sixteen geographic parameters were identified and integrated using GIS tool for mapping and understanding the varying pattern of schistosomiasis risk within the AOI. Several natural and social geographic determinants explain the dysfunction between local populations and their environment which results in human infestation by schistosomes. The study demonstrated that the access to clean water, education, health and other related socio-economic infrastructures was strongly influenced by the settlement functions and its population size. The clean water supply did not succeed in discouraging people from the use of contaminated freshwater. Local populations travel greater distances to reach water bodies than they do for hydraulic works in the study area. Furthermore, results indicated that within the same community and for the same gender, women were more vulnerable to schistosomiasis due to their involvement in domestic activities that enhance their chances of coming in contact with water bodies. Within the same community and for the same age group, children vulnerability to schistosomiasis through recreational swimming was critically influenced by variability in air temperature. The role played by water bodies in the daily life of the respondents could be linked to poverty, socio-professional status, location of the settlements, culture, age and gender. These geographic determinants interact in a complex way resulting in vulnerability of local populations to schistosomiasis infestation. Several natural and social geographic determinants influence defecation pattern of local populations which leads to environmental contamination. In the rural context, the defecation space utilization is mainly based on open air defecation. The demand for familial latrines in our AOI was strongly determined by land cover and proximity to the bush. In the peasant philosophy of defecation space utilization, defecation in the open air is a normal occurrence and feces encountered outdoors are mainly from children. Therefore, this defecation pattern contributes to environmental contamination. Children who are known to be heavily infected have less access to modern health care services. Traditional healers hold the monopoly for delivery of schistosomiasis treatment, hence, the expression “farafing fula (Blackman medicine) is preferred to tubabu fula (Whiteman medicine)”. The persistence of defecation in the open air is associated with poverty, socio-economic status, location of settlement, culture and age These geographic determinants interact in a complex that result in contamination of the local environment by its schistosomiasis-ill inhabitants Through the application of geographic methods and techniques, we were able to assess schistosomiasis risk by crossing several layers of information putting into perspective the complex dynamic and functional relationships between natural and social geographic elements which promote the development of the disease in the Sourou valley. Risk maps were able to categorize settlements with a North-South similarity along the Sourou River from those with an East-West difference as one goes away from the Sourou River. Our model pointed to lakeside settlements as high schistosomiasis-susceptible settings. Furthermore, we demonstrated that the illness based mapping was cost effective: 4.4 times cheaper than the disease based mapping. Despite its limitations, this study was able to reveal communities with high-risk of schistosomiasis transmission. Therefore, it could be an indication that MDA is needed for control of schistosomiasis in the Sourou Valley