The epidemiology of a recent focus of mixed Schistoroma haematobium and Schistosoma mansoni infections around the 'Lac de Guiers' in the Senegal River Basin, Senegal

A village with mixed Schistosoma mansoni and S. haematobium infections (pro bably in a early endemic phase) was identified around the Lac de Guiers in the Senegal River Basin. In documenting the epidemiology of both schistosom es, we focused on prevalence and intensity of infection, transmission patte rns and the impact of treatment. S. mansoni prevalences (near 100%) and egg counts overall geometric mean eggs per gram of faeces (epg) of 589 were hi gh in all age groups, with 35% of individuals excreting > 1000 epg, and sho wing a slow decline in egg output only after the age of 30 years. The overa ll prevalence (28 %) and egg counts (2% > 50 eggs/10 mi) of S. haematobium were low, with mean counts of 6.3 eggs/10 mi. Maximal mean S, mansoni egg c ounts were found in 5-9 year-old boys and in 15-19 year-old girls; S. haema tobium maximal counts in 1-4 year-old boys and in girls aged 5-9. Extremely high Biomphalaria Pfeifferi infection ratios were recorded over the whole year. Following a single treatment, re-infection was rapid with prevalences and mean egg counts of both Schistosoma species reaching pretreatment leve ls within 7 months.