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.