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Dynamics of egg counts and circulating antigen levels in a recent Schistosoma mansoni focus in northern Senegal

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Serum circulating anodic antigen (CAA) levels were compared with faecal egg counts in four subsequent population samples, randomly selected at 8-month intervals, in a recent Schistosoma mansoni focus in northern Senegal. In all four samples, antigen levels showed the same age-intensity profiles as egg counts, with a strong decline in adults. Also across population samples, a consistent relationship was found between egg counts and antigen levels. Assuming the level of CAA to be a direct reflection of worm burden, these findings support the idea that the observed egg count patterns and levels indeed reflect dynamics of worm burdens, and not of egg excretion or worm fecundity. Remarkably similar levels of both egg counts and CAA were observed in the first and last sample, collected in the same season (August–September), but 2 years apart. This suggests that a steady state of S. mansoni infection had already been reached shortly after the onset of the epidemic in this focus (3 years). Significantly lower infection levels were found in the intermediate population samples collected in January and April. The differences in infection levels across the four population samples may be because of seasonal transmission patterns. They would indicate a substantial turnover of worm populations, with an estimated average life span of only 7 months, probably less, in this recently emerged, intense S. mansoni focus.
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Keywords: Schistosoma mansoni; Senegal; circulating anodic antigen (CAA); faecal egg counts; seasonality; worm longevity

Document Type: Research Article

Affiliations: 1: Department of Parasitology, Leiden University Medical Centre, Leiden, The Netherlands 2: Department of Public Health, Erasmus University Rotterdam, Rotterdam, The Netherlands 3: Région Medicale de St Louis, St Louis, Senegal 4: Department of Medical Statistics, Leiden University Medical Centre, Leiden, The Netherlands 5: Prince Leopold Institute of Tropical Medicine, Antwerp, Belgium

Publication date: 2001-07-01

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