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Schistosomiasis is a parasitic disease caused by flatworms that live in snail-infested fresh water. It is endemic to 74 countries and affects some 200 million people worldwide, causing an estimated 200,000 deaths annually . Schistosomiasis can affect the gastrointestinal tract and liver (S. mansoni and S. japonicum species), resulting in diarrhoeal disease and hepatic fibrosis, or the urinary tract (S. haematobium) where it causes haematuria, strictures, obstruction, super-infection and, ultimately, cancer. In children and vulnerable adults, systemic effects such as anaemia, malnutrition, stunted growth and impaired cognition can be profound. The association between this parasitic infestation and the development of bladder cancer literally took millennia to uncover. It is unusual for a parasitic disease to result in a fatal neoplastic process, and rarer still to have public health efforts, aimed at eradication of the parasitic menace, to result in a dramatic shift in the epidemiology of the most common cancer in a nation.
© 2010 THE AUTHORS. BJU INTERNATIONAL © 2010 BJU INTERNATIONAL.
Conflicting interpretations regarding the fecundity of schistosomes infecting human beings have arisen and are, in part, due to the inability to directly measure the parameters. The inability to experimentally manipulate human beings necessitates the use of surrogate variables, i.e., number of eggs per gram of feces, as an indicator of worm burden. This study reanalyzes data from quantitative autopsies performed in Egypt by Cheever and colleagues on individuals with active Schistosoma mansoni infections. Exploratory regression analysis of the relationship of female worms recovered to eggs/g of feces and of female worms to eggs retained in host tissues suggests a linear relationship in both cases. Over the observed range of female worms recovered from an individual human being, the estimated worm fecundity, as measured by the number of eggs either in feces or retained in tissues per female worm, is not significantly different from a constant value. Hence, density-dependent fecundity of S. mansoni in the human host, as suggested by others, is not demonstrated in these data.