Snail Hosts Of Schistosomiasis Research Articles

The economic impact of schistosomiasis

BackgroundThe economic impact of schistosomiasis and the underlying tradeoffs between water resources development and public health concerns have yet to be quantified. Schistosomiasis exerts large health, social and financial burdens on infected individuals and households. While irrigation schemes are one of the most important policy responses designed to reduce poverty, particularly in sub-Saharan Africa, they facilitate the propagation of schistosomiasis and other diseases.MethodsWe estimate the economic impact of schistosomiasis in Burkina Faso via its effect on agricultural production. We create an original dataset that combines detailed household and agricultural surveys with high-resolution geo-statistical disease maps. We develop new methods that use the densities of the intermediate host snails of schistosomiasis as instrumental variables together with panel, spatial and machine learning techniques.ResultsWe estimate that the elimination of schistosomiasis in Burkina Faso would increase average crop yields by around 7%, rising to 32% for high infection clusters. Keeping schistosomiasis unchecked, in turn, would correspond to a loss of gross domestic product of approximately 0.8%. We identify the disease burden as a shock to the agricultural productivity of farmers. The poorest households engaged in subsistence agriculture bear a far heavier disease burden than their wealthier counterparts, experiencing an average yield loss due to schistosomiasis of between 32 and 45%. We show that the returns to water resources development are substantially reduced once its health effects are taken into account: villages in proximity of large-scale dams suffer an average yield loss of around 20%, and this burden decreases as distance between dams and villages increases.ConclusionsThis study provides a rigorous estimation of how schistosomiasis affects agricultural production and how it is both a driver and a consequence of poverty. It further quantifies the tradeoff between the economics of water infrastructures and their impact on public health. Although we focus on Burkina Faso, our approach can be applied to any country in which schistosomiasis is endemic.Graphical

Freshwater snails and schistosomiasis mansoni in the state of Rio de Janeiro, Brazil: VI - Noroeste Fluminense Mesoregion

In this paper, the last of a series dealing with the survey of freshwater gastropods of the state of Rio de Janeiro, the results of collections carried out in the Noroeste Fluminense Mesoregion from 2002 to 2005 are presented and revealed the occurrence of 20 species: Antillorbis nordestensis; Biomphalaria glabrata; B. straminea; B. tenagophila; Drepanotrema anatinum; D. cimex; D. depressissimum; D. lucidum; Ferrissia sp.; Gundlachia ticaga; Gundlachia sp.; Heleobia sp.; Idiopyrgus sp.; Lymnaea columella; Melanoides tuberculatus; Physa acuta; P. marmorata; Plesiophysa guadeloupensis; Pomacea lineata; and Pomacea sp. Concerning the snail hosts of schistosomiasis the three natural vectors were identified and, although no specimens were found harbouring larval forms of Schistosoma mansoni, different kinds of cercariae had been observed.

Impact of Invasive Water Hyacinth (Eichhornia crassipes) on Snail Hosts of Schistosomiasis in Lake Victoria, East Africa

Invasive plants may change ecologic conditions to contribute to transmission of human diseases. This study examined whether water hyacinth (Eichhornia crassipes) had an effect on the snails Biomphalaria sudanica and B. choanomphala, hosts of the disease organism Schistosoma mansoni in Lake Victoria, East Africa. Eight 16-m2 enclosures were established in shallow shoreline areas and were paired for water depth, substrate, detrital build up, and distance from rooted vegetation, agricultural runoff, and human activity. In each enclosure, nine randomly selected sediment samples were collected by using a Petite Ponar Dredge, after which 50 water hyacinth rosettes were added to the experimental enclosure within each pair. Six weeks later, nine randomly selected sediment samples were again collected, as were two water hyacinth rosettes from the water column above each sampling point. During the 6 weeks, water hyacinth density had increased from 50 to approximately 2400 rosettes in each enclosure. Adult B. sudanica and unidentified snail egg masses were observed on sampled water hyacinth petioles. Biomphalaria sudanica density was significantly higher in enclosures with water hyacinth (P = 0.034); snail size suggested that this difference was due to passive or active immigration rather than increased reproduction, but snail emigration or greater predation in control enclosures may also have contributed.

Molluscicidal and antimicrobial activity of Solanum aculeastrum

The methanolic extract of the fresh root bark and berries of Solanum aculeastrum showed significant activity against host snails of schistosomiasis. The berries extract was more potent with 100% snail kill at 50 ppm. Fractionation increased activity with 100% mortality at 20 ppm. The aqueous and methanolic extracts of the berries showed moderate antimicrobial activity, increasing by fractionation.

Community participation as an interactive learning process: experiences from a schistosomiasis control project in Zimbabwe

A schistosomiasis control project was undertaken from 1994 to 1998 in Guruve District, Zimbabwe, based on the active involvement of local communities in the growing and application of the molluscicidal plant Phytolacca dodecandra as a supplement to other control measures such as chemotherapy and health education. The berries of P. dodecandra are highly molluscicidal to the intermediate host snails of schistosomiasis and is rapidly degradable in water. It was observed that plant care fluctuated during the study period. Only a few households participated in snail control activities, although 97% of respondents in a baseline survey had stated a willingness to take part. This invoked an investigation to explore the reality from a user perspective. Focus group discussions, semi-structured interviews and observations were used to solicit information. In spite of a cultural inclination for collective work, many reasons for low-level involvement emerged, inter alia the low perceived value of the project, demands for tangible benefits, inaccessible fields and weak leadership. This study shows that community participation is a complex process upon which a multiplicity of social and cultural determinants have an impact. If community participation is to become successful in development programmes it ought to be viewed as a mutual learning process where obstacles are identified and discussed and solutions shared among community members and project staff.

Human health and sustainable water resources development in Nigeria: Schistosomiasis inartificial lakes

In the last three decades, there has been an unprecedented upsurge in dam construction in Nigeria to store water for year‐round water supply, irrigation and fisheries. Out of a total of 323 dams identified in the literature, 246 (76.2%) were constructed since 1970. Although only 47 of the reservoir lakes have been surveyed for snail intermediate hosts and 11 of the 47 for human infection, the results obtained by the various workers are very revealing. Snail hosts of schistosomiasis were found in 20 (42.6%) of the 47 lakes and human infection in 10 (90.9%) of the 11 lakes investigated for the respective purposes. These findings show that dam construction is contributing to schistosomiasis transmission in Nigeria and, unless urgent steps are taken to reverse the situation, the adverse health consequences of the dams will more than balance their socio‐economic benefits. This paper discusses these problems in the context of existing institutional and legal frameworks in Nigeria and identifies appropriate measures, that could achieve sustainable water resources development in the future.

Invading freshwater snails and biological control in Martinique Island, French West Indies.

Eight alien freshwater snail species were introduced into Martinique Island during the last 50 years. The introduced snails include four planorbids (Biomphalaria straminea, Helisoma duryi, Amerianna carinata and Gyraulus sp.), three thiarids (Melanoides tuberculata, M. amabilis and Tarebia granifera) and one ampullarid (Marisa cornuarietis). Four of these species rapidly colonized the whole Martinican hydrographic system whereas the other four remained restricted to some particular sites. The invasion processes were documented during the last 20 years and showed (i) a rapid invasion of the island by several morphs of M. tuberculata at the beginning of the 80's; (ii) the introduction of T. granifera in 1991 and M. amabilis in 1997; and (iii) the rapid spread of these last two species throughout the island. In the years following its introduction, M. tuberculata was used in biological control experiments against the snail hosts of schistosomiasis, B. glabrata and B. straminea. Experiments were conducted with success in several groups of water-cress beds which constituted the latest transmission sites for schistosomiasis at the beginning of the 80's. A malacological survey carried out in 2000 all over the island showed the absence of B. glabrata but the presence of some residual populations of B. straminea. Long-term studies carried out in Martinique have shown that the thiarids are able to maintain relatively stable populations over a long period of time, thus preventing recolonization by the snail hosts. Within this context the invasion of the hydrographic system of Martinique by thiarid snails has resulted in an efficient and sustainable control of the intermediate hosts of schistosomiasis.

Nucleotide sequence differences reveal genetic variation in Neotricula aperta (Gastropoda: Pomatiopsidae), the snail host of schistosomiasis in the lower Mekong Basin

To investigate the phylogenetic relationships among the different strains of the polytypic snailNeotricula aperta , mitochondrial-DNA sequence data were sampled from six populations from central and southern Laos, eastern Cambodia, and northeast Thailand. Part of the cytochrome c oxidase subunit I gene was sequenced for 21 individuals from 7 populations, with a 598 bp sequence used in the analyses. Evolutionary distances were estimated as the Kimura two-parameter distance ×100 (D). The samples were taken from the Mekong, Mul and Xé Bang-Fai rivers of the lower Mekong Basin. The snail Tricula bollingi was used as an outgroup. The least amount of genetic divergence was found where the Thai γ-strain was compared with the other N. aperta samples (D, 1.6–6.4), and next for the Xé Bang-Fai river γ-strain sample when compared with the other N. aperta (D, 2.8–7.5). Large distances were apparent between the β-strain and all the γ-strain populations (D, 4.7–8.3). The γ-strain population of northeast Thailand comprised two cryptic taxa which were relatively well diverged (D=2.1). The findings agreed with those of earlier studies based on rRNA gene RFLP variation. The findings were consistent with earlier evidence suggesting dispersal of snails from highland streams in central Laos (e.g. Xé Bang-Fai) into the Mekong river of northeast Thailand; this is proposed as an explanation for the cryptic taxa in the region. The γ-strain of Cambodia and southern Laos has been shown to act as intermediate host for Schistosoma mekongi. Such findings are important in the limitation of Mekong schistosomiasis as they relate to the timing and location of snail control measures. A revised phylogeography is presented for the Triculinae on the basis of the present findings and current palaeoÍgeographic models for Southeast Asia.

Nucleotide sequence differences reveal genetic variation in Neotricula aperta (Gastropoda: Pomatiopsidae), the snail host of schistosomiasis in the lower Mekong Basin

To investigate the phylogenetic relationships among the different strains of the polytypic snailNeotricula aperta , mitochondrial-DNA sequence data were sampled from six populations from central and southern Laos, eastern Cambodia, and northeast Thailand. Part of the cytochrome c oxidase subunit I gene was sequenced for 21 individuals from 7 populations, with a 598 bp sequence used in the analyses. Evolutionary distances were estimated as the Kimura two-parameter distance ×100 (D). The samples were taken from the Mekong, Mul and Xe Bang-Fai rivers of the lower Mekong Basin. The snail Tricula bollingi was used as an outgroup. The least amount of genetic divergence was found where the Thai γ-strain was compared with the other N. aperta samples (D, 1.6–6.4), and next for the Xe Bang-Fai river γ-strain sample when compared with the other N. aperta (D, 2.8–7.5). Large distances were apparent between the β-strain and all the γ-strain populations (D, 4.7–8.3). The γ-strain population of northeast Thailand comprised two cryptic taxa which were relatively well diverged (D=2.1). The findings agreed with those of earlier studies based on rRNA gene RFLP variation. The findings were consistent with earlier evidence suggesting dispersal of snails from highland streams in central Laos (e.g. Xe Bang-Fai) into the Mekong river of northeast Thailand; this is proposed as an explanation for the cryptic taxa in the region. The γ-strain of Cambodia and southern Laos has been shown to act as intermediate host for Schistosoma mekongi. Such findings are important in the limitation of Mekong schistosomiasis as they relate to the timing and location of snail control measures. A revised phylogeography is presented for the Triculinae on the basis of the present findings and current palaeoIgeographic models for Southeast Asia.

Effects of Bayluscide WP 70 on the survival and water-leaving behaviour of Biomphalaria straminea, snail host of schistosomiasis in northeast Brazil.

The toxic and behavioural effects of niclosamide (Bayluscide WP 70) on Biomphalaria straminea from a highly endemic area of schistosomiasis in northeastern Brazil were investigated through laboratory bioassays. The LD50 and LD90 were 0.114 mg/l and 0.212 mg/l, respectively. Water-leaving behaviour occurred among 14% to 30% of the snails in the presence of sublethal doses of niclosamide and among 16% of the controls. It was concluded that both the relatively low susceptibility to niclosamide and water-leaving behaviour of local B. straminea may be responsible for the recolonization of transmission foci after mollusciciding. It was suggested that recently improved measures of snail control, such as controlled-release formulations of niclosamide and plant molluscicides should be considered in areas where snail control is recommended.

The snail hosts of schistosomiasis: some evolutionary and ecological perspectives in relation to control.

Despite opportunities for radiation provided by spatio-temporal isolation, the basic morphological plan of pulmonate snails has remained conservative. In consequence of the resulting dearth of morphological characters and their plasticity, there is a case for using biochemical characters such as exogenous chemicals released by the snails (e.g. amino acids) and their chemoreception niche as taxonomic aids to classify snails of medical importance. As these same chemicals are used by snails to distinguish conspecifics they could also be used as "environmental antibodies" in controlled release formulations (CRF's) designed to remove target snails in a specific, cost-effective and ecologically acceptable manner. The snails, surface-living bacteria, algae and macrophytic plants are considered as co-evolved, interactive modular systems with strong mutualistic elements. Recently, anthropogenic perturbations such as deforestation, and damming of flowing waters, have benefited these modules whereas others such as river canalization, acid deposition, accumulation of pesticide residues and eutrophication have harmed them. Research is needed to elucidate the factors which limit the growth of snails in primitive habitats, uninfluenced by man, as well as in those subject to harmful anthropogenic factors. The understanding thus gained could be applied to develop cost-effective primary health care strategies to reduce or prevent transmission of schistosomiasis and other water related diseases.

A study of the sugar chemoreception niches of two bulinid snail hosts of schistosomiasis.

Components of the sugar chemoreception niches of two host snails of urinary schistosomiasis, namely Bulinus globosus (Morelet) and Bulinus rohlfsi (Clessin), were measured by using a buccal mass olfactometer. Among the polysaccharides tested, amylose was found to be the strongest phagostimulant for adults and juveniles of both snail species. Other phagostimulants identified were maltose and xylose for B. rohlfsi and maltotriose for B. globosus. The a(1-4)-glucosidic linkage and the presence of glucose residues were found to be key factors in the stimulus recognition system of the snails. The possible use of these findings in the design of controlled-release formulations for the selective removal of schistosome host snails is considered. The ecological implications of these studies are also examined.

An attempt to establish Helisoma duryi, a possible competitor of intermediate snail hosts of schistosomiasis, in natural habitats in South Africa.

An attempt to establish Helisoma duryi, a possible competitor of intermediate snail hosts of schistosomiasis, in natural habitats in South Africa.

Interaction in the laboratory between Helisoma duryi, a possible competitor snail, and Biomphalaria pfeifferi, snail intermediate host of Schistosoma mansoni

The planorbid snail, Helisoma duryi, has been proposed as a possible biocontrol agent against the intermediate host snails of schistosomiasis. In an attempt to evaluate the possible effect of interference between H. duryi and Biomphalaria pfeifferi, life-tables were compiled for these two snail species maintained both in the presence of each other and separately. The calculated population parameters indicated that H. duryi had a higher innate capacity of increase, net reproduction rate and finite rate of increase as well as a longer lifespan than the target species. However, the biological potential of B. pfeifferi was not influenced by the presence of H. duryi, and the latter appears to be unable to act as competitor against B. pfeifferi under similar prevailing conditions. It is possible that the situation might change under conditions of crowding and starvation.

The snail host of schistosomiasis in São Tomé

The snail host of schistosomiasis in São Tomé

Distribution of Freshwater Snails in Irrigation Schemes in the Sudan

(1) This study had two aims. Firstly, to investigate the distribution of aquatic macrophytes and molluscan intermediate hosts of schistosomes in the following irrigation systems in the Sudan: the Gezira-Managil Agricultural Scheme (GMAS), the Rahad Agricultural Scheme (RAS) and the New Halfa Agricultural Scheme (NHAS). Secondly, to formulate hypotheses to account for the distribution observed and to evaluate the possibility that snail hosts of schistosomiasis may be excluded by other competitor snail species. (2) The most snail species were recorded from GMAS, where Biomphalaria pfeifferi (Krauss) and Bulinus truncatus (Audouin) were very abundant and equally frequent. In RAS, B. pfeifferi was less common than B. truncatus; the opposite was found in NHAS. (3) Density of the intermediate hosts and of submerged plants was high, particularly in the terminal section of minor canals. Chemical and physical characteristics of the water showed remarkable variation among sites, which was related to the composition and density of the aquatic vegetation. In GMAS, positive and negative associations between snail and plant species were found. (4) Contingency tests revealed no significant negative correlations between pairs of snail species. On the contrary, a number of positive correlations was found. In GMAS, B. pfeifferi was positively correlated with B. truncatus, Lymnaea natalensis Krauss, Cleopatra bulimoides (Olivier) and Lanistes carinatus (Olivier). In RAS, Melanoides tuberculata (Muller) was positively correlated with B. pfeifferi.

Structure and function of the spermatheca in a snail host of schistosomiasis, Biomphalaria glabrata.

The histochemistry and ultrastructure (SEM and TEM) of the spermatheca of Biomphalaria glabrata was investigated to elucidate the function of this organ and to compare its structure and function to similar organs found in other species. The spermatheca has a debris-filled lumen surrounded by a thin wall of tissue. The cells adjacent to the lumen are of three columnar epithelial cell types. Two cell types have abundant microvilli and mammalian cell-like organelle distribution and morphology. The above cell types differ in the electron density of their cytoplasms, nuclear morphologies, and organelle content. The third cell type differs from the other two in its cytoplasmic makeup. However, the most distinctive difference is the presence of large numbers of cilia at the apical surface with no evidence of microvilli. These columnar cells rest on a basal lamina adjacent to a two to three cell thick muscle layer. The entire organ is surrounded by an adventitia of unusual morphology. Histochemical investigation demonstrated that DNAase, RNAase, and protease are present in the lumen, alkaline phosphatase is associated primarily with the microvilli, small amounts of acid phosphatase are concentrated in the midcell area of the columnar epithelium, and ATPase activity is localized in the muscle cells and just below the absorptive surface of the microvillous cells. The luminal contents and adventitial areas are Sudan Black B positive, all areas of the lumen and organ wall are PAS positive, the cell nuclei and amorphous masses in the lumen showed Feulgen staining, and large vesicles in the columnar cells were Oil Red O positive. Apparently, the spermatheca of B. glabrata is both a digestive and absorptive structure. Although this organ shares functional similarities with those found in opisthobranchs and terrestrial pulmonates, the epithelia of the spermatheca differ dramatically in these groups.

Snail Hosts of Schistosomiasis and Other Snail-Transmitted Diseases in Tropical America: A Manual

Dr. Malek has, with this manual, updated the 1968 PAHO publication A Guide for the Identification of the Snail Intermediate Hosts of Schistosomiasis in the Americas. The 1968 work has been expanded to cover snail hosts of fascioliasis, paragonimiasis, and angio-strongyliasis. The manual is primarily concerned with schistosomiasis in the Neotropics, i.e., Schistosoma mansoni transmitted by various planorbid snails. This topic is the forte of the author and is covered with excellence. Schistosomiasis and snail hosts of Schistosoma mansoni occupies some 25% of the manual. This section includes the anatomy and ecology of the planorbid intermediate hosts and a key to the 18 species of neotropical Biomphalaria. An additional 13% of the manual covers how to collect, preserve and store snails, to rear and maintain living snails, and to control snails. Some 6% of the manual deals with lymnaeid snails and fascioliasis, 15% with hydrobioid snails and paragonimiasis, and 15% with land snails and angiostrongyliasis.

Ecological studies on the snail hosts of schistosomiasis in the South Chad Irrigation Project Area, Borno State, northern Nigeria

Qualitative and quantitative samples of aquatic snails were collected over a two year period in the South Chad Irrigation Project Area, northern Nigeria. The area and its climate are described. Lake Chad, the irrigation channels and temporary pools are defined as three major categories of snail habitat and an account of the seasonal abundance of their snail populations is given. Bulinus rohlfsi, Bulinus forskali, a form of Bulinus globosus and Biomphalaria sudanica occurred in Lake Chad. Bulinus rohlfsi, Bulinus forskali, Bulinus senegalensis and another form of Bulinus globosus were found in irrigation channels. Bulinus senegalensis was the only bulinid recovered from temporary pools. The seasonal patterns of the snails are considered in relation to climatic and habitat changes. The possible roles of the bulinids in Schistosoma haematobium transmission are discussed.

Population dynamics of aquatic snails in three farm ponds of Puerto Rico.

Abstract Three ponds containing Biomphalaria glabrata, the snail host of schistosomiasis, and other aquatic snails were studied in Puerto Rico for over a year to determine birth, death. and growth rates of the snails. A sampling system involving an Emergy dredge was used to estimate the total number of snails in the ponds as well as the amount of vegetation. In addition, water temperatures and pond size were recorded at each biweekly sampling. The results showed that B. glabrata lived less than 200 days in the field, about a third of their life span in the laboratory. In contrast, the ampllarid snail, Marisa cornuarietis, had a life span of over 500 days in the field, providing a partial explanation for its domination of one of the ponds to the exclusion of B. glabrata. It was also shown that adult B. glabrata were highly resistant to desiccation and that water temperature was an important environmental parameter influencing the number of snails in a habitat by controlling the seasonal pattern of reproduction.