Schistosomiasis in the Senegal River Basin: before and after the construction of the dams at Diama, Senegal and Manantali, Mali and future prospects

AbstractEcological changes in the Senegal River Basin (SRB) resulting from the construction of a barrage at Diama, Senegal on the Senegal River to prevent the intrusion of sea water into the river, and a dam at Manantali, Mali on the Bafing River to control the flow of water and to generate electricity, have been responsible for changes in the epidemiology of human schistosomiasis. The introduction of Schistosoma mansoni into the Lower and Middle Valleys of the SRB and subsequent spread of the parasite in the human population is recorded with regard to prevalence and intensity. New foci of S. haematobium are described. The reduction in salinity and change from an acidic to an alkaline environment in the water are beneficial to both the fecundity and growth of freshwater snails and transmission of the parasite. The creation of new irrigation canals and expansion of the rice fields have provided new habitats for intermediate hosts to colonize. The evidence for praziquantel resistance/tolerance by populations of S. mansoni and the possibilities of the development, production and testing of a vaccine against human schistosomiasis are discussed. Future studies will monitor the spread of human urinary and mesenteric schistosomiasis in the SRB, will evaluate further the presence of praziquantel resistance/tolerance in S. mansoni, will examine the heavily infected human population for pathological symptoms and determine the most appropriate methods to control this severe outbreak of human schistosomiasis.</jats:p

Infectivity of a Cambodian isolate of <i>Schistosoma mekongi</i> to <i>Neotricula aperta</i> from northeast Thailand

AbstractAll three strains of Neotricula aperta (Gastropoda: Pomatiopsidae) sampled from populations in northeast Thailand were found to be compatible with a Schistosoma mekongi isolate from Kratié District, eastern Cambodia. The infection rates were: 3.0%, α-strain; 6.0%, β-strain; and 20.5%, γ-strain. The greater infectivity to the γ-strain, over both the α- and β-strains, was statistically significant. Comparisons of infectivity patterns for the Kratié isolate, with those described in earlier studies using S. mekongi isolates from southern Laos, revealed differences among the strains. The γ-strain of N. aperta is responsible for endemic transmission of human schistosomiasis in southern Laos and at Kratié. Consequently, the findings of this study are of use in the prediction of changes in the distribution of Mekong schistosomiasis, particularly its introduction to northeast Thailand from the neighbouring countries, Cambodia and Laos.</jats:p

Mating interactions between Schistosoma haematobium and S. mansoni

Schistosoma haematobium and S. mansoni are two medically important schistosomes, commonly occurring sympatrically in Africa and so potentially able to infect the same human host. Experiments were designed to study the mating behaviour of these two species in mixed infections in hamsters. Analysis of the data obtained showed that both heterospecific and homospecific pairs readily form. No significant difference was seen between the two species in their ability in forming pairs, however, S. mansoni showed a greater homospecific mate preference. Analysis of the data using the Mantel-Haenszel test suggests that mating competition does occur between S. haematobium and S. mansoni, the former being the more dominant species. Both species appeared to be able to change mate, with S. haematobium showing a greater ability in taking S. mansoni females away from S. mansoni males when introduced into a pre-established S. mansoni infection highlighting the competitiveness of S. haematobium. The significance of the results is discussed in relation to the epidemiological consequences occurring in Senegal, and other areas where both species are sympatric.</jats:p