AGE-DEPENDENT REDUCTION OF SCHISTOSOME FECUNDITY IN SCHISTOSOMA-HAEMATOBIUM BUT NOT SCHISTOSOMA-MANSONI INFECTIONS IN HUMANS

Understanding the dynamics of schistosome infections is problematic be cause direct measurements of worm burden are not possible. Hitherto, t he relative intensity of infection has been estimated by the number of parasite eggs excreted. Egg excretion is assumed to have a consistent relationship with worm burden with duration of infection. We have tes ted this assumption in Schistosoma mansoni- and S. haematobium-infecte d populations by looking at the relationships between a circulating pa rasite antigen, egg excretion level, host age, and parasite density, T he study was carried out in two populations because experimental model s suggested that S. haematobium but not S. mansoni suffers immune-medi ated reduction of fecundity. The results were consistent with this obs ervation, showing that S. mansoni egg output remains stable irrespecti ve of host age or infection intensity while S. haematobium has a subst antially reduced egg production with host age. This,information is fun damental to understanding the immunology and epidemiology of human sch istosomiasis and thus practical approaches to disease control.