Environmental Determinants Influencing the Diversity of Snail Intermediate Hosts of Schistosomes in Burkina Faso

The diversity of snail intermediate hosts of schistosomes and infection rates are influenced by environmental determinants. Knowledge of these local environmental determinants is an important basic step in epidemiology for the control of schistosomiasis. In this study, we investigate the local environmental determinants of the diversity of snail intermediate hosts of schistosomes in 24 sites in the Sudano-Sahelian and Sudanian zones of Burkina Faso based on accessibility and epidemiological data. The study was conducted every two months between November 2020 and September 2021. Samples were collected at each sampling point using flexible forceps and an Eckman grab by two surveyors on all available supports for 15 minutes. The collected samples were preserved in 75% ethanol and then transported to the laboratory for identification and enumeration. The BRT-optimised model was used to model species abundance as a function of local variables. A total of 14,587 snails belonging to seven families and 21 species were collected. Five intermediate host species of human schistosomes, namely Bulinus truncatus, Bulinus forskalii, Bulinus globosus, Bulinus senegalensis and Biomphalaria pfeifferi, were collected with relative abundances ranging from 7% for B. globosus to 42% for B. truncatus. The occurrence of B. truncatus was positively correlated with conductivity, pH, and latitude and negatively correlated with altitude. The occurrence of B. forskalii was positively correlated with vegetation, while the occurrence of Bi. pfeifferi and B. senegalensis was positively correlated with temperature and altitude but negatively correlated with ammonium and total iron. The optimised BRT model explained 43.36%, 77.047%, 73.906%, 48.169%, and 23.23% of the variation in abundance of B. senegalensis, B. truncatus, B. globosus, B. forskalii, and Bi. pfeifferi, respectively. The nature of the water regime (24.9%) and the vegetation cover (18.6%) were relatively more important in explaining the abundance of B. globosus. The most important parameters to explain the abundance of B. senegalensis, B. truncatus, B. forskalii, and Bi. pfeifferi were all physicochemical parameters.