Summary
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.
Similar content being viewed by others
References
Appleton, C.C.: Observations on the thermal regime of a stream in the Eastern Transvaal, with reference to certain aquatic Pulmonata. S. Afr. J. Sci.72, 20–23 (1976)
Austin, F.G., Stirewalt, M.A., Danziger, R.E.:Schistosoma mansoni: stimulatory effect of rat skin lipid fractions on cercarial penetration behaviour. Exp. Parasitol.31, 217–224 (1972)
Bolwig, N.: An experimental study of the behaviour and host-recognition in schistosoma cercariae. S. Afr. J. Sci.51, 338–344 (1955)
Deschiens, R., Delas, S.: L'extension géographique de la bilharziose àSchistosoma intercalatum en Afrique tropicale. Trans. roy. Soc. trop. Med. Hyg.63, (Suppl.) 57–65 (1969)
Pitchford, R.J., Du Toit, J.F.: The shedding pattern of three little known African schistosomes under outdoor conditions. Ann. trop. Med. Parasitol.70, 181–187 (1976)
Schwetz, J.: Role of wild rats and domestic rats (Rattus rattus) in schistosomiasis of man. Trans. roy. Soc. trop. Med. Hyg.50, 275–282 (1956)
Southgate, V.R.: Observations on the epidermis of the miracidium and on the formation of the tegument of the sporocyst ofFasciola hepatica. Parasitology,61, 177–190 (1970)
Southgate, V.R., van Wijk, H.B., Wright, C.A.: Schistosomiasis at Loum, Cameroon:Schistosoma haematobium, S. intercalatum and their natural hybrid. Z. Parasitenkd.49, 145–159 (1976)
Wright, C.A., Southgate, V.R., Knowles, R.J.: What isSchistosoma intercalatum Fisher, 1934? Trans. roy. Soc. trop. Med. Hyg.66, 28–64 (1972)
Wright, C.A., Knowles, R.J.: Studies onSchistosoma haematobium in the laboratory III. Strains from Iran, Mauritius and Ghana. Trans. roy. Soc. trop. Med. Hyg.66, 108–118 (1972)
Wright, C.A., Southgate, V.R., van Wijk, H.B., Moore, P.J.: Hybrids betweenSchistosoma haematobium andSchistosoma intercalatum in Cameroon. Trans. roy. Soc. trop. Med. Hyg.68, 413–414 (1974)
Wright, C.A., Southgate, V.R.: Hybridisation of schistosomes and some of its implications. In: Genetic aspects of host-parasite relationships. A.E.R. Taylor and R. Muller eds., Symp. Brit. Soc. Parasitol.14, 55–86 (1976)
Van Wijk, H.B.:Schistosoma intercalatum infection in schoolchildren of Loum, Cameroon. Trop. geogr. Med.21, 375–382 (1969)
Van Wijk, H.B.:Schistosoma intercalatum infection in Mungo Department, Cameroon. Thesis, University of Amsterdam, 1–154 (1975)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
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
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00930749