STUDIES ON TRANSMISSION AND SCHISTOSOME INTERACTIONS IN SENEGAL, MALIAND ZAMBIA

The transmission and interaction of schistosomes in the Senegal River Basin in Mall and Zambia are reviewed and some preliminary field data are presented. In the Senegal River Basin four species of schistosomes are prevalent: Schistosoma mansoni, S. haematobium, S. bovis and S. c urassoni as well as the following potential intermediate hosts: Biomph alaria pfeifferi, Bulinus globosus, B. umbilicatus, B. truncatus, B. s enegalensis and B, forskalii. The role of each of these species in the transmission of schistosomes in man and domestic stock is discussed, Recent ecological changes caused by the construction of darns at Diama and Mananatali on the Senegal River, such as reduction in salinity, m ore stable water flow, creation of irrigation canals and development a nd extension of rice culture, have contributed towards the occurrence of new outbreaks of both intestinal and urinary schistosmiasis in the Senegal River Basin. In Mall, the four main areas of high prevalence o f S. haematobium are Office du Niger (irrigation areas), Bandiagara (s mall dams), Selingue (dam areas) and Baguineda (irrigation areas). Apa rt from the Office du Niger, S. mansoni infections are rare. Surveys w ere carried out in the Dogon Country (Bandiagara District) in an attem pt to confirm the recent independent reports of the presence of S. int ercalatum. Data based on egg morphology and Ziehl Neelsen staining of egg shells suggested the possible occurrence of S. haematobium x S. in tercalatum hybrids. Potential factors affecting the focal endemicity o f S. haematobium in Mall are discussed. Five species of schistosomes a re present in Zambia: S. mansoni, S. haematobium, S. mattheei, S. marg rebowiei and S. leiperi, S. haematobium and S. mattheei are the most w idely distributed species and hybridization between these is known to occur, Examination of adult schistosomes from infected cattle by isoel ectric focusing electrophoresis showed that S. mattheei was most preva lent (75%), followed by S. leiperi (12%) and S, margrebowiei (2%), Int erestingly, the remaining 11% of worms gave two distinct heterozygote patterns, indicating possible interactions between S. haematobium and S. mattheei and/or S. leiperi and S. martheei. Examination of eggs pas sed in human urine collected in two different (town and village) trans mission sites, demonstrated the presence of polymorphic shaped eggs in the samples from the village, indicating Possible hybridization betwe en S. haematobium and S. mattheei. Studies are continuing with the aim of unravelling the complexities of the transmission and interactions of schistosomes of the S. haematobium group in Senegal, Mall and Zambi a.