Methods
Study system Schistosomiasis, a global, tropical disease, is caused by schistosome blood flukes in the genus Schistosoma that cycle between freshwater snails and mammals and infect more than 200 million people worldwide (Hotez et al. 2014). Transmission is seasonal and relies on intermediate snail hosts primarily from three genera,Biomphalaria, Bulinus , and Oncomelania . Snails are infected by miracidia, the free-living juvenile stage of the schistosome that hatch from eggs excreted by humans into water bodies. Schistosomes reproduce asexually within the snail host and later emerge as aquatic cercariae. Humans become infected following dermal exposure to cercariae, which then mature into adults and lay eggs, completing the life cycle (Gryseels et al. 2006). Therefore, the density of schistosome cercariae in aquatic environments represents an important ecological dimension of the human risk of exposure.