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PubMed2003

Miracidia of an Egyptian strain of Schistosoma mansoni differentiate between sympatric snail species.

The host-finding behavior of miracidia of 2 strains of Schistosoma mansoni from Egypt and Brazil was studied by recording their responses to snail-conditioned water (SCW) from the Egyptian sympatric snails, Biomphalaria alexandrina, Physa acuta, Lymnaea cailliudi, and Balinus truncatus, as well as from Biomphalaria arabica and Biomphalaria glabrata. Miracidia of the Egyptian strain significantly preferred SCW from their compatible hosts B. alexandrina and B. arabica and showed no or a weak response to SCW from the other sympatric species, whereas miracidia of the Brazilian strain did not differentiate between SCW from different snail species.

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PubMed1999

[Malacologic-schistosomal study of the refugee camps on the Plain of Ruzizi in the Democratic Republic of the Congo].

Bilharziasis due to Schistosoma mansoni is widespread in the eastern part of the People's Republic of the Congo, particularly in the Ruzizi plain area. The intermediate host is the fresh-water snail Biomphalaria pfeifferi whose ecology is now well documented. Bilharziasis due to Schistosoma haematobium and Schistosoma intercalatum have not yet been observed but the potential for this development is high given the presence of the intermediate hosts, i.e. Bulinus truncatus, Bulinus globosus, and Bulinus forskalii, and the migration of populations in the area. Malacological and cercariometric studies were undertaken in 3 refugee camps in 1995. Findings showed that Biomphalaria pfeifferi was present in all water systems tested but that levels varied from 21 p. 100 to 70 p. 100 from one camp to another. The rate of infestation by Biomphalaria pfeifferi varied from 37 to 20 p. 100 depending on the sampling site. Given the prevalence of Schistosoma mansoni in the population, extension of bilharziasis is likely in the Ruzizi plain area and its surroundings. Potential intermediary hosts for Schistosoma haematobium and Schistosoma intercalatum were of lower relative prevalence and were found in specific biotopes. The authors propose methods of controlling water snails and preventing infection of people and water systems.

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PubMed1992

A preliminary study on intermediate snail hosts of schistosomes in River Enyau, Arua district, Uganda.

A total of 1260 snail intermediate hosts of both Schistosoma mansoni and Schistosoma haemotobium were collected along the non-seasonal River Enyau which lies half a kilometre west of Arua, a north-western Uganda town. The snails collected were Biomphalaria pfeifferi 709: Biomphalaria choanomphala 457, Bulinus Bulinus tropicus 94. These were screened for cercariae shedding and 25 B. pfeifferi and 12 B. choanomphalal shed mammalian cercaricae while none of the Bulinus (Bulinus) tropicus shed any cercariae. River Enyau Biomphalaria snails were susceptible to a Schistosoma mansoni strain from Entebbe. Cercariae derived from these snails and also those found infected in the River Enyau were confirmed to be S. mansoni using laboratory mice.

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PubMed1996

The interactive effect of some molluscicides on the inermediate host of human bilharziasis and their associated zoosporic fungi in the river Nile, Egypt.

Biomphalaria alexandrina and Bulinus truncatus are the main vectors of human Bilharziasis in Egypt. The mycotic inhabitants of both control and treated snails were surveyed at 7 and 15 days intervals. The two molluscicides affected more on the mortality of Biomphalaria alexandrina than Bulinus truncatus. The highest population of zoosporic fungi was collected from Biomphalaria alexandrina, the lowest from Bulinus truncatus. Copper sulphate was more effective than Bayluscide on the fungal species of both snails. Achlya, Dictyuchus and Saprolegnia were the common genera while Leptolegnia caudata and Pythium ultimum completely missed from treated snails. The total colonies of zoosporic fungi were lowered after. 15 days of treatment. The two molluscicides inhibited the cell division of both tested snails.

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PubMed1997

[The distribution of freshwater molluscs the intermediate hosts of human schistosomas in Katan, south-Kivu].

In eastern Democratic Republic of Congo, the prevalence of bilharziasis due to Schistosoma mansoni is high along the Kivu lake shoreline where Biomphalaria pfeifferi, i.e. the intermediate host of Schistosoma mansoni, is the only snail that has been described until now. Although their occurrence has not been reported in the area, other schistosomas remain possible since their intermediate hosts are present. This study was carried out in 1992 to determine the distribution of intermediate host snails in freshwater systems in the region. Samples were collected according to the standardized harvest time unit method. Five species of intermediate host snails for human schistosomiasis were identified. By far the most prevalent species was Biomphalaria pfeifferi which was found in 75% of the freshwater systems studied. Given the presence of Schistosoma mansoni in the region, spread of this type of schistosome is likely. Ferrissia burnipi, the recognized intermediate host of Schistosoma haematobium, was observed in association with Biomphalaria pfeifferi. Snails of the Bulinus genus were confined to special environments. Factors preventing infestation by Schistosoma haematobium and Schistosoma intercalatum remain unclear. Control measures against snails and their larvae in fresh water systems in the region are needed to stop the spread of Schistosoma mansoni and prevent the appearance of Schistosoma haematobium and Schistosoma intercalutum.

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PubMed1998

Schistosomiasis in newly reclaimed areas in Egypt. 1-distribution and population seasonal fluctuation of intermediate host snails.

Two newly reclaimed areas located west & east of Suez Canal, namely El Manayef area and El Morra area, were studied for patterns of distribution and population seasonal fluctuation of Biomphalaria alexandrina and Bulinus truncatus, the intermediate host snails of Schistosoma mansoni and S. haematobium, respectively. In this study Geographic Information System (GIS) techniques were utilized for producing maps and analyzing the results. Habitats of the two vector snail species were categorized into suitability levels depending on the frequency with which snails were collected over a 12 months period. Data obtained from the most suitable habitats were only used for studying the seasonal fluctuation of snail population. The results showed that both study areas were almost similar in major physico-chemical parameters. However, oxygen content in canals was higher than in drains and conductivity was higher in drains than in canals. As regards snail distribution and density, most snails of both considered species were clustering in much fewer numbers of sites, more pronouncedly in the case of Biomphalaria than Bulinus. Population density of snails was significantly higher in El-Manayef area than in El-Morra area and in canals than in drains. Both species exhibited 2 population peaks/year, the peaks of Biomphalaria were in March-April & August in both study areas, while for Bulinus these peaks occurred in March-May and August in El-Manayef area and in May and March, respectively, in El-Morra area.

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PubMedDate not supplied

[Freshwater snails of the Campus of Manguinhos, Oswaldo Cruz Foundation, Rio de Janeiro, RJ].

A survey of freshwater gastropods of the Campus of Manguinhos, Fundação Oswaldo Cruz, Rio de Janeiro, was carried out during the last two years aiming to compare the current species with those found at the beginning of this century. Among 18 breeding sites in 880,000m2 of the surveyed area, 13 showed the following species: Antillorbis nordestensis; Biomphalaria glabrata; Biomphalaria straminea; Lymnaea columella; Melanoides tuberculatus; Physa cubensis; Pomacea glauca and Pomacea lineata. Notably, Biomphalaria tenagophila reported by Lutz in 1918, had disappeared and B. straminea and the Asiatic thiarid M. tuberculatus had been introduced. No specimens infected with Schistosoma mansoni were found.

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PubMed2002

Freshwater snails and Schistosomiasis mansoni in the State of Rio de Janeiro, Brazil: II--Centro Fluminense Mesoregion.

During the course of a survey carried out from 2000 to 2001 in the Centro Fluminense Mesoregion of the State of Rio de Janeiro 22 molluscan species were found. Many of the records are new due to the dearth of previous studies. Concerning the snail hosts of Schistosoma mansoni, the most frequently encountered species was Biomphalaria tenagophila, as it occurred in all the surveyed municipalities. There are new records of Biomphalaria straminea and Biomphalaria peregrina which is regarded as a potential intermediate host. Drepanotrema lucidum and Antillorbis nordestensis were found to be shedding echinostome cercariae and strigid cercariae respectively. An account about the current schistosomiasis transmission sites in this Mesoregion is presented as well.

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PubMed2004

Planorbidae, Lymnaeidae and Physidae of Ecuador (Mollusca: Basommatophora).

In the course of a trip to Ecuador I had the opportunity of collecting topotypic specimens of the following nominal species of pulmonate molluscs: Biomphalaria cousini Paraense, 1966; Planorbis equatorius Cousin, 1887; P. canonicus Cousin, 1887; Lymnaea cousini Jousseaume, 1887 and P. boetzkesi Miller, 1879. Additional findings were: Helisoma trivolvis (Say, 1817), Biomphalaria peregrina (Orbigny 1835), Drepanotrema anatinum (Orbigny, 1835), D. kermatoides (Orbigny, 1835), D. lucidum (Pfeiffer, 1839), D. surinamense (Clessin, 1884), Lymnaea columella Say, 1817 and Physa acuta Draparnaud, 1805. P. boetzkesi and P. canonicus are considered junior synonyms of Gyraulus hindsianus (Dunker, 1848) and Biomphalaria peregrina (Orbigny, 1835), respectively.

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PubMed2005

Habitat preference of freshwater snails in relation to environmental factors and the presence of the competitor snail Melanoides tuberculatus (Müller, 1774).

Our objective is to evaluate the habitat preference of freshwater snails in relation to environmental factors and the presence of the competitor snail Melanoides tuberculatus. In the first phase, snails was collected at 12 sites. This sampling sites presented a degree of organic input. In the second phase 33 sampling sites were chosen, covering a variety of lotic and lentic environments. The snail species found at Guapimirim, state of Rio de Janeiro, displayed a marked habitat preference, specially in relation to the physical characteristics of each environment. Other limiting factors for snail distribution at the studied lotic environments were the water current velocity and the amount of organic matter, mainly to Physa marmorata, M. tuberculatus, and Biomphalaria tenagophila. The absence of interactions between M. tuberculatus and another snails could be associated to the distinct spatial distribution of those species and the instability of habitats. This later factor may favor the coexistence of M. tuberculatus with B. glabrata by reduction of population density. In areas of schistosomiasis transmission some habitat modification may add to the instability of the environment, which would make room for the coexistence of M. tuberculatus and Biomphalaria spp. In this way, some of the usual measures for the control of snail hosts would prevent the extinction of populations of Biomphalaria spp. by M. tuberculatus in particular habitats.

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PubMed2001

[The model of statoconia distribution in the gravity receptors of shells in ontogenesis].

Based on the experimental data of Wiederhold et al., analyzed was distribution of statoconia in gravireceptors of Biomphalaria glabrata and Aplysia californica in ontogenesis. A mathematical model of size distribution of statoconia in statocyst Biomphalaria glabrata in ontogenesis has been developed. Growth of statoconia in size is described as a process of crystallization from solution. Hypothetically, redistribution of statoconia in ontogenesis is determined by generation of new statoconia and their linear growth in size. Comparison of the resultant analytical solution of the model with published experimental data revealed a number of characteristic stages in statoconia development. Generation of new statoconia if peculiar for stage 1 and proceeds till the shell diameter (D) becomes as large as 4 mm. At D > 6 mm, statoconia distribution is driven by their size growth at a permanent rate. In the interval of delta D = 4-6 mm, statoconia undergo redistribution which is probably connected with selective dissolution of big statoconia and ensuing period of linear growth. The model is in good agreement with the literature on experimental data and, therefore, is instrumental in evaluation of changes in statoconia distribution. The authors laid out plans of further experiments in order to test the model of statoconia distribution in Biomphalaria glabrata in ontogenesis, and to get quantitative description of statoconia distribution in the gravireceptor of Aplysia californica in ontogenesis.

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PubMed2003

A longitudinal study of schistosome intermediate host snail populations and their trematode infection in certain areas of Egypt.

Seasonal variation of Biomphalaria alexandrina and Bulinus truncatus populations and their infection rates with schistosome and other trematode cercariae were studied longitudinally in four water courses located in Giza and Faiyoum Governorates. Abundance of both species varied from year to year and according to the type of habitat. The mean prevalence of Schistosoma mansoni in Biomphalaria was 0.29%, that of S. haematobium in Bulinus was 1.36%. Seasonal variations of age structure of the 2 vector snails were monitored throughout the survey period. Infection rates with schistosome and other trematodes among Bulinus and Biomphalaria increased with the increase in snail size. Data suggest the occurrence of an antagonistic interaction between schistosome and non-human cercariae, especially echinostome, in infected snails.

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PubMedDate not supplied

Development of bait formulations for control of intermediate hosts of African schistosome species.

Exploration of methods of snail control indicated a need for a new method because many failures in control programmes are due to lack of contact between molluscicides and the target snail population. The incorporation of molluscicides inside food pellets that are attractive to and ingestible by the target snails is suggested. Different concentrations of alcoholic extracts of Ambrosia maritima, Cucumis prophetarum and Rhynchosia minima-molluscicides of plant origin-were compared with niclosamide (Bayluscide) which is a strong synthetic molluscicide. They were incorporated into attractive food pellets and the lethal doses were determined. The results showed that Biomphalaria alexandrina snails are sensitive to only bait formulations with low concentrations of molluscicides. Laboratory and semi-field trials were conducted to study the efficacy of the prepared bait formulations on Biomphalaria alexandrina snails. The stability of these bait formulations was studied and it was observed that their effectiveness was reduced after long storage periods (> 3 weeks). The results revealed that Ambrosia maritima was the most effective molluscicide.

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PubMed2001

Screening of Malian medicinal plants for antifungal, larvicidal, molluscicidal, antioxidant and radical scavenging activities.

A total of 78 different extracts from 20 medicinal plants belonging to 14 plant families from Mali were tested for their antifungal, larvicidal, molluscicidal, antioxidant and radical scavenging activities. Dichloromethane, methanol, water and ethanol extracts were used. TLC autobiography for antifungal activity was run with Cladosporium cucumerinum and Candida albicans. Extracts were also tested on the larvae of the mosquitoes Aedes aegypti, Anopheles gambiae and Culex quinquefasciatus. Molluscicidal activities were established with the snails Biomphalaria glabrata, Biomphalaria pfeifferi and Bulinus truncatus. beta-Carotene and DPPH solutions sprayed on TLC plates were used for antioxidant and radical scavenging assays. Of the extracts investigated, 20% were antioxidant and radical scavengers, 19% fungicidal, 30% were larvicidal and 11% were molluscicidal. Three of the plant extracts, from Cussonia barteri (Araliaceae), Glinus oppositifolius (Aïzoaceae) and Lannea velutina (Anacardiaceae) gave positive responses in all four tests.

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PubMed2000

Toxicity of Euphorbia milii latex and niclosamide to snails and nontarget aquatic species.

The toxicity of Euphorbia milii molluscicidal latex and niclosamide (NCL) to target snails (Biomphalaria glabrata and Biomphalaria tenagophila) and nontarget aquatic organisms is evaluated. Planorbidae snails were killed by very low concentrations of lyophilized latex (48-h LC(50), mg/L: B. glabrata, 0.12; B. tenagophila, 0.09; Helisoma duryi, 0.10). Latex was less toxic (48-h LC(50) or EC(50), mg/L) to oligochaeta (Tubifex tubifex, 0.31), planktonic crustacea (Daphnia similis, 0.38; C. dubia, 1.07; Artemia sp., 0.93), and fishes (Danio rerio, 0.96; Poecilia reticulata, 1. 39), and considerably less toxic to Ampullariidae snails (Pomacea sp. , 10.55) and frog tadpoles (Rana catesbeiana, 7.50). Latex (up to 100 mg/L) was not toxic to bacteria (P. putida and V. fischeri), algae (Selenastrum capricornutum and Chlorella vulgaris), and mosquito larvae (Anopheles albitarsis, Aedes aegypti, Aedes fluviatilis). NCL was very toxic (48-h LC(50) or EC(50), mg/L) to Planorbidae snails (B. glabrata, 0.15, B. tenagophila, 0.13; H. duryi, 0.10), T. tubifex (0.11), crustacea (D. similis, 0.19; Ceriodaphnia dubia, 0.47; Artemia sp. 0.18), fishes (D. rerio, 0.25; P. reticulata, 0.29), R. catesbeiana (0.16), and Pomacea sp. (0.76). NCL was toxic to bacteria, algae (96-h IC(50), mg/L: S. capricornutum, 0.34; C. vulgaris, 1.23) and slightly toxic to mosquito larvae. In conclusion, E. milii latex, as compared with the reference molluscicide niclosamide, presents a higher degree of selectivity toward snails which are intermediate hosts of Schistosoma trematodes.

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PubMed1975

The suitability of several aquatic snails as intermediate hosts for Angiostrongylus cantonensis.

Sixteen species of aquatic snails of four families were tested by quantitative technique under standardized conditions for their suitability as intermediate hosts for Angiostrongylus cantonensis. These species were the planorbid snails Biomphalaria glabrata, Biomphalaria alexandrina, Planorbis planorbis, Planorbis intermixtus, Bulinus truncatus, Bulinus contortus, Bulinus africanus, Bulinus tropicus and Helisoma sp.; the lymnaeid snails Lymnaea natalensis, Lymnaea tomentosa, Lymnaea stagnalis, and Stagnicola elodes; the physid snail Physa acuta (an Egyptian and a German strain) and the ampullariid snails Marisa cornuarietis and Lanistes carinatus. All these snail species proved to be susceptible to infection with A. cantonensis, and first stage larvae reached the infective third stage in all of them. However, the rate and intensity of infection varied with different species. B. glabrata was the most susceptible snail species with a 100% infection rate and an average percentage recovery of third stage larvae of 26.1. This was followed by S. elodes and B. africanus, with a 100% infection rate and an average percentage recovery of third stage larvae of 15.6 and 14.6 respectively. The rest of snail species proved to be less susceptible. For comparative evaluation of the suitability of the various snail species as intermediate hosts of A. cantonensis a "Capacity Index" was determined. This index should provide a useful method for the evaluation of the suitability of various snails as intermediate hosts of nematode parasites under standardized conditions in the laboratory.

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PubMed1980

The influence of environmental conditions and parasite-intermediate host-related factors on the transmission of Echinostoma liei.

Moderate freezing, desiccation, and pH levels of 5 and 6 killed the Echinostoma liei egg immediately or after only partial development, and increasing salinity levels above 3.79 0/00 and temperatures of 33 degrees C and 35 degrees C reduced the developmental potential. Temperatures of 6 degrees C and 8 degrees C and maintenance of eggs in mouse faeces arrested the development of the egg, and increasing temperatures decreaseds the time of development from 40 days at 18 degrees C to nine days at 35 degrees C. Maintenance of unembryonated eggs for 14 weeks in faeces at 12 degrees C and 22 degrees C and for 20 weeks in filtered pond water at 4 degrees C allowed a subsequent normal development, while embryonated eggs maintained at 4 degrees C only retained an unchanged hatchability for three weeks. A miracidium/snail density of 10:10 in 18 litres of water gave rise to an average level of parasitisation of 21%. Increasing miracidium/snail densities gave rise to increasing levels of parasitisation but to a level less than expected. The first intermediate host spectrum of E. liei was shown to be restricted to the genus Biomphalaria, but species variability in susceptibility within the genus and differences in survival of infected susceptible species was also demonstrated to exist. B. glabrata (Puerto Rico and St. Lucia), B. alexandrina (Qalyub), and B. pfeifferi (Malumfashi) were found to be susceptible, while B. camerunensis (Kinshasa) was almost refractory. Increasing size of B. glabrata (Puerto Rico) resulted in increasing daily cercarial production, but resistance to infection with increasing snail size was also demonstrated to exist. E. liei cercarial infectivity to the second intermediate host snail and the subsequent metacercarial infectivity to the mouse was found to be independent of the species of the first intermediate host and of the age of the infection in B. glabrata (Puerto Rico) for up to at least 6 1/2 weeks after the end of the prepatent period. No obvious peak in cercarial shedding fom the host snail occurred during the day. Five species of the genus Bulinus and Physa acuta (Egypt) were found to be highly susceptible as second intermediate host snails, whereas three species of the genus Biomphalaria, Planorbarius corneus (Rabat), Lymnaea natalensis (Egypt), and Helisoma duryi (Florida) all had a lower degree of susceptibility. On the other hand, E. liei metacercarial infectivity to the mouse was independent of the species and size of the second intermediate host snail. Also, the infectivity of metacercariae encysted on snail mucus, in snails harbouring patient redial infections, and in clean second intermediate host snails was comparable. Metacercarial infectivity remained unchanged for at least 12 and 18 weeks, respectively, when encysted in living B. glabrata (Puerto Rico) or when maintained in freshwater at 4 degrees C. Metacercariae in dead decaying B...

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PubMed1989

Biological control of the snail hosts of Schistosoma mansoni in the Caribbean area using Thiara spp.

Field observations and experiments using thiarid snails as competitors of Biomphalaria spp., potential intermediate hosts of Schistosoma mansoni in the Caribbean area, are reviewed. The parthenogenetic snails, Thiara granifera and T. (= Melanoides) tuberculata, were introduced to the Neotropical area in recent decades. In numerous islands and countries, these oriental species have demonstrated their capacity to colonize rapidly and densely many types of habitats while at the same time reducing and even eliminating populations of Biomphalaria spp. The results of field experiments, carried out in several Caribbean islands, have shown the efficiency as well as the limitations of T. tuberculata as a competitor of B. glabrata and B. straminea. In St. Lucia, B. glabrata was apparently eliminated from marshes and streams, 6 to 22 months after the introduction of the competitor. In Martinique, T. tuberculata was introduced into two groups of water-cress beds which constituted the last transmission sites of schistosomiasis on the island. In just less than three years after the introduction of the competitor, both B. glabrata and B. straminea have been eliminated from the transmission sites. In Guadeloupe, several introductions have been carried out in different types of habitat such as permanent ponds, canals, streams and temporary marshes. The findings of all field experiments have indicated that thiarid snails as competitors of pulmonates are favoured by the presence of permanent and stable habitats, preferably shallow, with emergent plants and well oxygenated. On the other hand, the competitor snails are at a disadvantage in waterbodies which are temporary, extremely deep, poorly oxygenated or with a dense mat of floating aquatic vegetation.(ABSTRACT TRUNCATED AT 250 WORDS)

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