COMPETITIVE-EXCLUSION IN HUMAN SCHISTOSOMES - THE RESTRICTED DISTRIBUTION OF SCHISTOSOMA-INTERCALATUM

A study on the immune and mating interactions between Schistosoma inte rcalatum and S. mansoni has been carried out. The immunologically medi ated interactions and mating patterns observed between the two species demonstrate that S. mansoni is competitively dominant over S. interca latum. When S. mansoni females are absent, S. mansoni males are more c ompetitive than S. intercalatum males at pairing with S. intercalatum females. The use of a mathematical model shows how the abundance of S. mansoni worms per host could dramatically affect the mating probabili ty of S. intercalatum females with their homologous males. It appears that the competitive exclusion between these two species of schistosom es may probably be an important factor restricting the distribution of S. intercalatum in Africa.