Lack of Demonstrable Density-Dependent Fecundity of Schistosomiasis Mansoni: Analyses of Egyptian Quantitative Human Autopsies

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  • * Department of Epidemiology and Public Health, Yale University School of Medicine
  • Departments of Epidemiology and Social Medicine and Pediatrics, Albert Einstein College of Medicine-Montefiore Medical Center
  • G. H. Sergievsky Center, Columbia University College of Physicians and Surgeons

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.