On factors possibly restricting the distribution ofSchistosoma intercalatum Fisher, 1934


Two hypotheses have been postulated explaining the limited distribution ofSchistosoma intercalatum.

The first hypothesis is correlated with physical factors and behaviour of cercariae. Histochemical and ultrastructural studies have shown that in response to increased temperature change the cercariae ofS. intercalatum form aggregates, unlike other schistosome cercariae of man, which are noninfective to the definitive host. The aggregates are formed by the release of the adhesive post-acetabular gland secretion which causes the cercariae to stick together. It is suggested that ifS. intercalatum spread from streams within tropical rain forest to pools and laybys of streams in the savannah, cercariae would be subjected to greater daily temperature changes thus triggering the release of post-acetabular gland secretion, thereby impairing invasion of the definitive host.

The second hypothesis is based on the natural occurrence of hybridisation betweenS. intercalatum andSchistosoma haematobium. With some strains of these two species there are no genetical isolating mechanisms. It is suggested that ifS. intercalatum extended into a savannah environment from tropical rain forest, hybridisation betweenS. intercalatum andS. haematobium would eventually occur. Experimental studies indicate that probably, as a result of introgressive hybridisation, a new strain ofS. haematobium would eventually supersede the originalS. intercalatum.

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Southgate, V.R. On factors possibly restricting the distribution ofSchistosoma intercalatum Fisher, 1934. Z. Parasitenkd. 56, 183–193 (1978). https://doi.org/10.1007/BF00930749

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  • Experimental Study
  • Temperature Change
  • Daily Temperature
  • Rain Forest
  • Physical Factor