Studies on transmission and schistosome interactions in Senegal, Mali and Zambia
Vercruysse, J.; Southgate, V.R.; Rollinson, D.; De Clercq, D.; Sacko, M.; De Bont, J.; Mungomba, L.M.
Tropical and Geographical Medicine 46(4 Spec No): 220-226
1994
ISSN/ISBN: 0041-3232 PMID: 7825224 Document Number: 423868
The transmission and interaction of schistosomes in the Senegal River Basin in Mali 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. curassoni as well as the following potential intermediate hosts: Biomphalaria pfeifferi, Bulinus globosus, B. umbilicatus, B. truncatus, B. senegalensis 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 dams at Diana and Mananatali on the Senegal River, such as reduction in salinity, more stable water flow, creation of irrigation canals and development and extension of rice culture, have contributed towards the occurrence of new outbreaks of both intestinal and urinary schistosomiasis in the Senegal River Basin. In Mali, the four main area of high prevalence of S. haematobium are Office du Niger (irrigation areas), Bandiagara (small dams), Selingue' (dam areas) and Baguineda (irrigation areas). Apart from the Office du Niger, S. mansoni infections are rare. Surveys were carried out in the Dogon Country (Bandiagara District) in an attempt to confirm the recent independent reports of the presence of S. intercalatum. Data based on egg morphology and Ziehl Neelsen straining of egg shells suggested the possible occurrence of S. haematobium times S. intercalatum hybrids. Potential factors affecting the focal endemicity of S. haematobium in Mali are discussed. Five species of schistosomes are present in Zambia: S. mansoni, S. haematobium, S. mattheei, S. margrehowiei and S. leiperi. S. haematobium and S. mattheei are the msot widely distributed species and hybridization between these is known to occur. Examination of adult schistosomes from infected cattle by isoelectric focusing electrophoresis showed that S. mattheei was most prevalent (75%), followed by S. leiperi (12%) and S. margrebowiei (2%). Interestingly, the remaining 11% of worms gave two distinct heterozygote patters, indicating possible interactions between S. haematobium and S. mattheei and/or S. leiperi and S. mattheei. Examination of eggs passed in human urine collected in two different (town and village) transmission sites, demonstrated the presence of polymorphic shaped eggs in the samples from the village, indicating possible hybridization between S. haematobium and S. mattheei. Studies are contributing with the aim of unravelling the complexities of the transmission and interactions of schistosomes of the S. haematobium group in Senegal, Mali and Zambia.