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  • Title: Immuno-epidemiology of Schistosoma mansoni infections in a recently exposed community in Senegal.
    Author: Gryseels B, Stelma F, Talla I, Polman K, Van Dam G, Sow S, Diaw M, Sturrock RF, Decam C, Niang M.
    Journal: Mem Inst Oswaldo Cruz; 1995; 90(2):271-6. PubMed ID: 8531670.
    Abstract:
    Schistosoma mansoni was introduced in the Senegal basin around 1988, due to man-made ecological changes. Since 1991, we investigate a recent but very intense focus, Ndombo, a village near the city of Richard Toll where the outbreak was first described. Four cohorts, each a random sample (+/- 400 subjects each) from this community, were examined and followed up after treatment, starting at 8 month intervals over a 2-year period. Each cohort is examined parasitologically (Kato-Katz), clinically, serologically (circulating antigen and antibody profiles); treated with praziquantel 40 mg/kg; followed up 6-10 weeks, one and two years after treatment; and monitored for water contact patterns and local snail densities. In the first cohort, the prevalence was 91%, with a mean egg count of 663 epg. Prevalences are near 100% in all age groups, but egg counts decline strongly in adults. Antigen detection in serum and urine confirmed that the egg counts genuinely reflect variations of worm burdens, not e.g. of worm fecundity. This is surprising, as in this focus acquired immunity in adults should not have yet developed according to current hypothesis. The antigen detection assays (CAA/CCA) showed high sensitivity and quantitative power, and promising perspectives as a research tool and possibly as a method for non-invasive diagnosis and screening in urine. Epidemiological in subsequent cohorts were highly similar, although seasonal variations were observed possibly due to transmission fluctuations. Anti-AWA and anti-SEA IgE levels increased with age, while IgG4 peaked in the age-group 10 years and correlated well with egg counts.(ABSTRACT TRUNCATED AT 250 WORDS) 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.
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