Immuno-epidemiology of Schistosoma mansoni infections in a recently exposed community in Senegal.

ABSTRACT

PIP: A cohort analysis was performed in Ndombo, Senegal, a community of about 4000, in the epicenter of the schistosomiasis outbreak. Four randomly selected cohorts of +or- 400 subjects were surveyed. Each cohort was examined parasitologically, clinically, and serologically (circulating antigen and antibody profiles); treated with praziquantel 40 mg/kg; and followed up at 6-12 weeks and at 1 and 2 years after treatment. The first cohort numbered 422 individuals, of which 91% had positive egg counts, with a mean egg count of 663 eggs per gram feces (epg). Quantitative egg counts in those aged 10-14 were 1409 epg and then declined to 632 epg in the age group 20-29 and to 266 epg in the age group over 40. In cohorts 2 and 3, examined in the spring and autumn, egg counts were substantially lower, particularly in adults, as compared with cohorts 1 and 4, which were both examined in the summer season. 94% of the subjects were positive in the serum circulating anodic antigen (CAA) ELISA, 83% in the serum CAA ELISA, and 95% in the urine circulating cathodic antigen (CCA) ELISA; CAA in urine was less sensitive, and was negative in half of the urine samples. Positivity rates for all assays increased with rising egg counts, and circulating antigen concentrations in both serum and urine correlated well with egg counts. IgE showed a significant increase with age, while IgG4 peaked in the age groups 10-15 and/or 15-19 years. A strong correlation between IgG, IgGl, and IgG4 against both crude antigens with pretreatment egg load was observed. Of the subjects in the first cohort, 61% reported abdominal pain, 33% diarrhea; only 16% showed mild hepatomegaly and only a few children had mild splenomegaly. In the first cohort, 82% of 298 reexamined subjects were still positive for S. mansoni 12 weeks after treatment with praziquantel 40 mg/kg. One year after treatment, cohort 1 showed mean egg counts in children (5-19 years) at 358 epg as compared with 1188 epg pretreatment.