Circulating anodic antigen levels in two areas endemic for schistosomiasis mansoni indicate differences in worm fecundity

Serum levels of the adult schistosome circulating anodic antigen (CAA) were compared in 2 populations, both living in an area with extremely high transmission levels of Schistosoma mansoni. In one focus (Maniema, eastern Zaire) transmission has been established for several decades, while in the other focus (Ndombo, northern Senegal) transmission started only recently. While parasite egg counts in the 2 populations were virtually similar, including analogous age-related distributions, serum levels of CAA were approximately 5 times higher in the chronically exposed community. This difference in antigen level was most pronounced in adolescents and adults. As the level of CAA is assumed to be a direct reflection of worm burden, these findings suggest higher parasite fecundity in the recently exposed community. It is not very likely that these observations could be explained solely by differences in clearance mechanisms caused by a variation in experience of infection. The relationship between circulating antigen levels and egg counts was consistent for all age groups in the Maniema population, while in the Ndombo population only children showed a pattern similar to that in the chronically exposed community.