Journal Article•
The epidemiology of human and animal schistosomiasis in the Senegal River Basin.
TL;DR: A snail survey in various parts of the Senegal River Basin, including the SenegalRiver Basin, temporary rain-fed pools, swamps, irrigation canals and drains, ricefields and Lac de Guier was carried out, finding Bulinus guernei was the most common, occurring in permanent habitats, and Bulinus senegalensis occurring in laterite pools in the eastern part of the Middle Valley.
Abstract: The results of four field surveys in Senegal are reported. 1. A snail survey in various parts of the Senegal River Basin, including the Senegal River, temporary rain-fed pools, swamps, irrigation canals and drains, ricefields and Lac de Guier was carried out. Three species of snails were commonly found: Bulinus guernei was the most common, occurring in permanent habitats, Bulinus senegalensis occurring in laterite pools in the eastern part of the Middle Valley, and also in the ricefields of Guede Chantier and Lampsar; B. forskalii was found in small numbers in Lac de Guier and Richard Toll. Three B. guernei were found to be naturally infected with S. bovis. Neither B. jousseaumei, B. globosus nor B. umbilicatus were found in our surveys. 2. A survey for urinary schistosomiasis was carried out in 100 villages (walo, near the Senegal River) and 11 villages (diere, away from the river) by delivering questionnaires in schools and by direct examinations of haematuria samples. The prevalence of haematuria varied between 0 and 33%. Generally, walos showed low rates of haematuria with the exception of Lampsar and Guede Chantier, and dieres showed higher rates of haematuria. 3. Examination of 400 cattle at the abattoir St. Louis, revealed a prevalence of 80% of schistosome infection. Two species were present, S. bovis and less commonly S. curassoni. Sometimes high worm burdens were seen, but lesions appeared to be minimal because of high ratio of male to female worms. 4. Examinations of 5722 sheep and 1752 goats in the abattoir, Dakar revealed an overall prevalence of 2.1%. Of the infected animals, 97.3% were infected with S. curassoni and 2.7% with S. curasonni and S. bovis. Laboratory snail infection experiments showed that S. curassoni is marginally compatible with B. senegalensis, but incompatible with B. guernei.
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TL;DR: It is concluded that the development and management of water resources is an important risk factor for schistosomiasis, and hence strategies to mitigate negative effects should become integral parts in the planning, implementation, and operation of future water projects.
Abstract: An estimated 779 million people are at risk of schistosomiasis, of whom 106 million (13.6%) live in irrigation schemes or in close proximity to large dam reservoirs. We identified 58 studies that examined the relation between water resources development projects and schistosomiasis, primarily in African settings. We present a systematic literature review and meta-analysis with the following objectives: (1) to update at-risk populations of schistosomiasis and number of people infected in endemic countries, and (2) to quantify the risk of water resources development and management on schistosomiasis. Using 35 datasets from 24 African studies, our meta-analysis showed pooled random risk ratios of 2.4 and 2.6 for urinary and intestinal schistosomiasis, respectively, among people living adjacent to dam reservoirs. The risk ratio estimate for studies evaluating the effect of irrigation on urinary schistosomiasis was in the range 0.02-7.3 (summary estimate 1.1) and that on intestinal schistosomiasis in the range 0.49-23.0 (summary estimate 4.7). Geographic stratification showed important spatial differences, idiosyncratic to the type of water resources development. We conclude that the development and management of water resources is an important risk factor for schistosomiasis, and hence strategies to mitigate negative effects should become integral parts in the planning, implementation, and operation of future water projects.
1,933 citations
TL;DR: These data provide indisputable evidence for: the high occurrence of bidirectional hybridization between these Schistosoma species; the first conclusive evidence for the natural hybridisation between S. haematobium and S. curassoni; and demonstrate that the transmission of the different species and their hybrids appears focal.
Abstract: Background
Schistosomes are dioecious parasitic flatworms, which live in the vasculature of their mammalian definitive hosts. They are the causative agent of schistosomiasis, a disease of considerable medical and veterinary importance in tropical and subtropical regions. Schistosomes undergo a sexual reproductive stage within their mammalian host enabling interactions between different species, which may result in hybridization if the species involved are phylogenetically close. In Senegal, three closely related species in the Schistosoma haematobium group are endemic: S. haematobium, which causes urogenital schistosomiasis in humans, and S. bovis and S. curassoni, which cause intestinal schistosomiasis in cows, sheep and goats.
159 citations
TL;DR: Future studies will monitor the spread of human urinary and mesenteric schistosomiasis in the SRB, evaluate further the presence of praziquantel resistance/tolerance in S. mansoni, examine the heavily infected human population for pathological symptoms and determine the most appropriate methods to control this severe outbreak of human schistOSomiasis.
Abstract: Ecological 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.
123 citations
TL;DR: In this article, the authors conducted a study to determine the prevalence and intensity of Schistosoma mansoni and S. haematobium in the Senegal river basin (SRB), and to ascertain the distribution of the snail species acting as intermediate hosts for both species of schistosomes.
Abstract: Extensive water development has taken place in the north of Senegal over the last decade, resulting in a large increase in the amount of fresh water for irrigation. The objectives of the present study were to determine the prevalence and intensity of Schistosoma mansoni and S. haematobium in the Senegal river basin (SRB), and to ascertain the distribution of the snail species acting as intermediate hosts for both species of schistosomes. The schistosomiasis survey started in January 1994 and was completed in March 1995. Compared to studies before the construction of the Diama dam, there was a significant increase in both the prevalence and intensity of urinary and intestinal schistosomiasis in the human population in parts of the SRB. From the 9014 people who were registered from 180 villages and 4 towns (10 districts), 7750 were examined. S. mansoni was found in the lower valley (lower delta-Senegal river, lower delta-Lampsar river, upper delta, and diere ) but not in the middle valley. The mean prevalence ranged from 4.4% in the lower delta-Senegal River to 71.8% in the zone of Lac de Guiers, where prevalence and intensity of infection were higher on the eastern side of the lake (81.3% with a mean number of 2088 eggs/g of faeces) compared with the western side (50.3% with a mean 1111 eggs/g). S. haematobium was recorded throughout the area of study, ranging from a mean prevalence of 0.37% in diere (lower valley) to 41.5% in the lower valley (Lampsar river), where the mean egg count was 313/10 mL of urine. Physical and chemical changes to the environment have favoured the spread and increase in the populations of freshwater snails. The only snail involved in the transmission of S. mansoni was Biomphalaria pfeifferi . Five species of bulinid snails were present— Bulinus globosus, Bu. umbilicatus, Bu. senegalensis, Bu. forskalii and Bu. truncatus —but only the first 3 species were involved in the transmission of S. haematobium in the lower and middle valleys.
108 citations
TL;DR: Despite the optimism of health-assessment reports prepared prior to the construction of the Diama dam, the unexpected appearance and spread of intestinal schistosomiasis as well as an increase in the incidence of urinary schistOSomiasis have aggravated public health in the Senegal River basin.
Abstract: The ecological changes caused by projects for the development of water resources are known to affect the epidemiology of water-related diseases. The effects of the construction of the Diama dam (completed in 1986) in the Senegal River on the epidemiology of malaria, urinary and intestinal schistosomiasis, diarrhoea and dysentery were investigated in four districts in northern Senegal. To make allowance for any general trend in reported morbidity (caused by changes in demography or the healthcare system), the numbers of cases of these illnesses reported by the basic healthcare facilities before and after the completion of the dam were compared with those of respiratory disease. Prior to the construction of the dam, malaria was the most encountered water-related disease in the medical records of all districts, followed by diarrhoea, dysentery and urinary schistosomiasis. This order remained the same after the completion of the dam. Despite the optimism of health-assessment reports prepared prior to the construction of the Diama dam, the unexpected appearance and spread of intestinal schistosomiasis as well as an increase in the incidence of urinary schistosomiasis have aggravated public health in the Senegal River basin. It remains to be judged whether the economic benefits of the dam will counterbalance its adverse effects.
76 citations
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89 citations
TL;DR: In an endemic area on Lake Volta, Ghana, urinary blood and protein levels as determined by chemical reagent strips in persons infected with Schistosoma haematobium, particularly in children aged between 5 and 14, correlated positively with urinary egg counts.
Abstract: In an endemic area on Lake Volta, Ghana, urinary blood and protein levels as determined by chemical reagent strips in persons infected with Schistosoma haematobium, particularly in children aged between 5 and 14, correlated positively with urinary egg counts. Geometric mean S haematobium egg counts were 10 or more times higher in urine specimens with at least 10 mg/dl of protein and detectable haematuria than in those without detectable blood or protein. Chemical reagent strips were both specific and sensitive for detection of urinary blood associated with S haematobium infection. This simple technique could be useful for screening entire populations in which urinary schistosomiasis is endemic so that heavily infected persons needing specific treatment can be identified.
88 citations
TL;DR: The following proved and potential vectors of human schistosomiasis, identified by Dr. G. Mandahl-Barth, are reported from the Gambia and evidence is given of their role in transmission.
Abstract: 1. (1) The following proved and potential vectors of human schistosomiasis, identified by Dr. G. Mandahl-Barth , are reported from the Gambia : ◦ Bulinus jousseaumei ◦ Bulinus guernei ◦ Bulinus globosus ◦ Bulinus senegalensis ◦ Bulinus forskali ◦ Biomphalaria p. gaudi Observations on their ecology are recorded and evidence is given of their role in transmission. 2. (2) Wild specimens of B. jousseaumei, B. guernei and B. senegalensis have been shown to be shedding cercariae of S. haematobium. Wild specimens of B. senegalensis were also found to be shedding S. bovis cercariae. 3. (3) Laboratory-bred specimens of B. forskali proved to be receptive to both S. haematobium and S. bovis.
58 citations
TL;DR: A survey of 5722 sheep and 1752 goats at the abatoir in Dakar, Senegal showed that the overall prevalence of schistosomiasis was 2·1%, and this species is shown to be distinct from S. bovis and S. mattheei.
Abstract: A survey of 5722 sheep and 1752 goats at the abatoir in Dakar, Senegal showed that the overall prevalence of schistosomiasis was 2·1%. Of the 112 animals where identification of the schistosome species was possible, all were infected with Schistosoma curassoni, and 2·7% had mixed infections with S. bovis. The adult worms of S. curassoni are described, and on the basis of egg morphology this species is shown to be distinct from S. bovis and S. mattheei. Eggs of S. curassoni measured 146 μm ± 16·8 × 63·3 μm ± 4·5 from sheep and 149·4 μm ± 13·2 × 62·8 μm ± 4·9 from mouse liver, and appear to be indistinguishable from the eggs of S. haematobium Guede Chantier, Senegal which measure 153·1 μm ± 11·1 × 62·4 μm ± 12·1 from mouse liver. However, S. curassoni differs from S. haematobium in that it develops more quickly than S. haematobium in hamsters, uterine eggs becoming visible at least 20 days earlier; the adult worms of S. curassoni are nearly double the size of S. haematobium in hamsters at 70 days post infec...
30 citations
TL;DR: Surveys in the South Chad Irrigation Project Area have revealed the presence of substantial populations of the important potential snail host for Schistosoma haematobium, Bulinus senegalensis, the first confirmed record of this species outside the Senegambian region.
Abstract: Surveys in the South Chad Irrigation Project Area have revealed the presence of substantial populations of the important potential snail host for Schistosoma haematobium, Bulinus senegalensis. This is the first confirmed record of this species outside the Senegambian region and the habitats in which it occurs differ from those previously reported. The implications of this finding for the epidemiology of S. haematobium in the Sahel region are discussed.
26 citations