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PubMed1979

A longitudinal study of schistosome vector snail populations in Liberia.

Seasonal changes in populations of Biomphalaria pfeifferi and Bulinus globosus were observed at 62 locations in Liberia, West Africa. All varieties of water in both urban and rural locations were sampled. A wet season decrease and dry season increase of B. globosus populations in both urban and rural locations, similar to that reported elsewhere in West Africa, was observed. Similar fluctuations of B. pfeifferi populations were noted. The prevalence of schistosome infected vector snails varied markedly between rural and urban locations. At rural sites parasite prevalence followed the appropriate vector snail prevalence. At urban sites a portion of the vector snail population appeared relatively unaffected by seasonal changes. This stable population harbors a reservoir of infected snails that sustain year round transmission. Human infection was sampled in school children in the study area and prevalence of approximately 50% was found for both Schistosoma mansoni and S. haematobium. Added to the malacologic information this suggests less than hyperendemic transmission. The data suggest that urban environments should receive priorities for control programs.

Animals↗

PubMed1976

The use of a molluscicide in conjunction with chemotherapy to control Schistosoma haematobium at the Barombi Lake foci in Cameroon. II. Urinary examination methods, the use of niridazole to attack the parasite in man, and the effect on transmission from man to snail.

The use of niridazole, in conjunction with snail control, in an attempt to control the transmission of Schistosoma haematobium at 2 Cameroon crater-lake villages is described. Quantitative examinations of urines for S. haematobium eggs were made on the whole population before control began, at intervals during the maintenance of control, and again after control ceased. The methods and difficulties are described, and their accuracy is discussed. After each examination all accessible egg-passers were treated or re-treated with niridazole. The drug was well tolerated and effective. Most treated patients ceased to pass live eggs, and most of those who later became positive again were thought to represent reinfections rather than relapses. During the maintenance of snail control, niridazole treatment of the 'whole' community reduced the total load of S. haematobium eggs passed to less than 1 per cent of the pre-control figure; and repeated subsequent treatments maintained a level of the same order. Despite this, there remained at different times 0.6-50.9 per cent of persons passing small quantities of live eggs, and these were an important source of continuing transmission. The possibility that more than one strain of S. haematobium was involved is discussed. An index of transmission from man to snail is proposed and discussed in relation to determining the level of the "break-point" in transmission. Although combined niridazole/molluscicide control reduced transmission from man to snail by about 3 log cycles, the "break-point", which is thought to lie 4 or more log-cycles lower, was not reached. When control was stopped, transmission built up again, with the prevalence rate in man rising more rapidly than the intensity of infections.

Adolescent↗

PubMed1976

The freshwater snail lymnaea rubiginosa as an experimental host of Angiostrongylus malaysiensis: a preliminary report.

Preliminary studies have shown that Lymnaea rubiginosa, a common fresh-water snail in Peninsular Malaysia, which is easily colonized and reared in the laboratory, is a capable experimental intermediate host for Angiostrongylus malaysiensis. Overall 73% of the snails tested became infected following 6 hours exposure to infective rat faeces. Higher infection rates, up to 100%, and heavier worm loads, occurred among the larger sized snails. Snail attrition was low except when very heavy worm loads were acquired.

Animals↗

PubMed2000

SDS-PAGE-separated tissue proteins of Biomphalaria alexandrina snails in the presence and absence of Schistosoma mansoni.

SDS-PAGE was used to separate tissue proteins of control and trematode-infected Biomphalaria alexandrina snails. The separated profiles demonstrate the occasional appearance of protein fractions and the remarkable increase of concentration of certain molecular masses in infected snails at one week interval over four weeks post exposure to Schistosoma mansoni. Proteins of molecular masses of 44, 56, 65 and 144 KDa were among these occasionally appeared protein masses. Post exposure to S. mansoni larval infection, a protein mass of 36 KDa was predominant giving a markedely higher absorbance (> 1) compared to control (0.0166). This was identified as lactate dehydrogenase enzyme. Moreover, a protein of 56 KDa mass was identified as Pyruvate kinase. The predicted induction of these two enzymes could be either of host and/or parasitic origin. This study revealed that S. mansoni- B. alexandrina complex has a completely different protein pattern compared to control with very low similarity coefficient "S" value. A correlation between the snail tissue protein or separation patterns and the metabolic redirection of the snail host by the developing sporocyst was discussed.

Animals↗

PubMedDate not supplied

[Search of natural occurrence of xiphidiocercariae (trematoda) in fresh water snails of nine countries from São Paulo State, Brazil].

Xiphidiocercariae, aquatic larval stages of some trematodes are considered a potential instrument for biological control of mosquitoes. In this study we evaluated its natural occurrence in Campinas region and two places in Vale do Ribeira (Registro and Miracatu), São Paulo State. Snails were obtained from fresh water collections from September 1996 to February 1999. The species collected were Lymnaea columella, Physa marmorata, Biomphalaria tenagophila, Biomphalaria sp., Drepanotrema cimex, D. lucidum and Drepanotrema sp. Fasciola hepatica, xiphidiocercariae (Haematoloechidae) and echinostomatid cercariae were detected in the lymnaeids snails from Miracatu, SP. In the same locality were found planorbids snails parasitized by furcocercariae, echinostomatid cercariae and xiphidiocercariae. The xiphidiocercariae found in the planorbids were different from those obtained from lymnaeids. One Biomphalaria sp. infected with furcocercariae was found in Louveira, SP. In the ROSA place (Campinas, SP) an individual of Biomphalaria sp. and one of L. columella were found infected by the furcocercariae and echinostomatid cercariae, respectively. In the place UNI-I, in Campinas, one L. columella was infected by furcocercariae. Double infection in snails from Miracatu was also observed.

Animals↗

PubMed2002

Morphological and ecological studies on Lymnaea natalensis the snail vector of Fasciola gigantica in Egypt.

Lymnaea natalensis were collected from several localities in Giza Governorate (El-Mansouria, Kafr Hakim and The Nile). The collected snails were examined for cercarial shedding and measurement of shell was carried out using a virner caliper. A total of 217 Lymnaea was collected from all habitats and 24 snails were found to shed Fasciola gigantica cercariae with infection rate 11.1%. The ratio of shell height to shell width (H/W) ranged 1.7-2.1. The ratio between length of aperture to shell height (A/H) was almost constant ranged 0.7-0.8. While the ratio between length of aperture and shell width (A/W) ranged from to 1.8. There was a significant positive correlation between shell height and both shell width and length of aperture (p<0.001). The same relation was clearly indicated between shell width and length of aperture. Also, when the aperture length increased the ratio between height and width increased (p<0.05). While, the following ratios (H/W), (A/H) and (A/W) remained somewhat constant irrespective to the number of whorls. There was a positive correlation between number of whorls and each of aperture length, shell length and shell height. On maintaining L. natalensis in different pH values, the results showed that at pH 3 and pH 11, all snails maintained at these pH values died after one day of maintenance. While snails survived and laid eggs in the range of pH 5-9.

Animals↗

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.

Animals↗

PubMed1992

Effects of excretory-secretory products of Echinostoma paraensei larvae on the hematopoietic organ of M-line Biomphalaria glabrata snails.

Responses of the hematopoietic organ (HO) in Biomphalaria glabrata snails to extracts and excretory-secretory (E-S) products of Echinostoma paraensei larvae were studied to understand the HO-activating mechanism. M-line B. glabrata snails were injected with materials from E. paraensei larvae, and the size of the HO was ascertained in histological sections. The size of HO in snails injected with extracts and E-S products from sporocysts and rediae was significantly larger than that in snails injected with culture medium. E-S products of sporocysts were fractionated using ultrafiltration membranes, polyacrylamide gel electrophoresis, and electrophoretic elution. Examination of fractionated E-S products of sporocysts revealed that specific components of E-S products were responsible for HO-stimulating activity.

Animals↗

PubMed2005

Modeling the distribution of Schistosoma mansoni and host snails in Uganda using satellite sensor data and Geographical Information Systems.

The potential value of MODIS satellite sensor data on Normalized Difference Vegetation Index (NDVI) and land surface temperatures (LST) for describing the distribution of the Schistosoma mansoni-"Biomphalaria pfeifferi"/Biomphalaria sudanica parasite-snail system in inland Uganda, were tested by developing annual and seasonal composite models, and iteratively analysing for their relationship with parasite and snail distribution. The dry season composite model predicted an endemic area that produced the best fit with the distribution of schools with > or =5% prevalence. NDVI values of 151-174, day temperatures of 26-36 degrees C, and night temperatures of 15-20 degrees C were used as criteria for the prediction model. Using the same approach with host snail data indicated that most of Uganda is suitable "B. pfeifferi"/B. sudanica habitat, except for possibly the north-eastern region of the country. The parasite, however, appears to be restricted in its distribution in both the north-eastern and the south-western regions of Uganda. The absence of disease in the south-west can not be attributed to the absence of snail hosts. Results suggest a combination of satellite sensor data on temperature and standard climate data on precipitation, as the best ecological determinants of the S. mansoni-"B. pfeifferi"/B. sudanica system. Satellite composite models and logistic regression analysis, suggest low night time temperature as one of the significant factors inhibiting S. mansoni transmission in the south-western highland areas of Uganda. The developed models are, however, unique, representing species-specific ecologic preferences of the S. mansoni-"B. Pfeifferi"/B. sudanica system in inland Uganda. Further validation studies are needed to test the value of the model in other countries in East Africa.

Animals↗

PubMed2002

[Studies upon behaviour of snails in anthropogenically changed water environment. 1. Locomotor activity of Lymnaea stagnalis (L.), with regard to subpopulations infected with developmental stages of digeneans].

The aim of the paper was to analyse the locomotor activity of snails, Lymnaea stagnalis, with regard to physico-chemical properties of water in an inhabited reservoir and parasitic infection. The material was collected in selected anthropogenic water environments situated in the Upper Silesian Industrial Region (sinkhole ponds, sand- and clay-excavations). The locomotor activity of each snail was analysed in laboratory conditions by designation of number of penetrated segments, marked in tanks filled with water originating from a given reservoir, during 15', with intervals of 1'. It was observed the significant relationship between locomotor activity of examined snails and the water carbonaceous hardness (r = -0,812, at range of the independent variable 173.0-863.5 mg CaCO3/dm3). Correlation coefficients with other physico-chemical parameters of water were close to zero. Locomotion of snails infected with developmental stages of digenetic trematodes was significantly lower comparing to non-infected individuals. Locomotor activity of these former ones was dependend more on degree of the digestive gland damage by the parasite than on the infection agent.

Animals↗

PubMed2006

Identification of an avian schistosome recovered from Aythya novaeseelandia and infectivity of its miracidia to Lymnaea tomentosa snails.

A partial life cycle involving miracidia hatched from the eggs of Trichobilharzia sp. recovered from New Zealand scaup (Aythya novaeseelandia) to the release of furcocercariae by laboratory snails (Lymnaea tomentosa) was accomplished. Challenges with five and ten miracidia per snail were lethal. Challenge with three miracidia resulted in development to the daughter sporocyst stage and death in five, development to furcocercarial stage and death in one, and shedding of furcocercariae in one of seven snails. Observed lethality of schistosome miracidia to L. tomentosa may explain the low infection prevalence observed in the wild. Future work should plan challenge exposures of three or fewer miracidia to ensure snail survival and successful recovery of furcocercariae. The Trichobilharzia sp. found in the New Zealand scaup does not key morphologically to the literature. It may be a new species and further work is needed.

Animals↗

PubMed2006

Molluscicidal activities of aqueous extract of the sea anemone Parasicyonis actinostoloides against vector snails Bulinus truncatus and Lymnaea natalensis.

The aqueous extract of the sea anemone Parasicyonis actinostoloides showed molluscicidal effect against vector snails of Schistosoma hacematobium and Fasciola gigantica after 24 hours of exposure. LC50) and LC90 values for P. actinostoloides were 40 & 78.6 ppm for B. runcatus and 46.6 & 86.5 ppm for L. natalensis respectively. The effect of continuously exposure of B. truncatits and L. naltlensis to sublethal aqueous extract concentrations (LC0, LC10 & LC25) on survival rate, egg production and on infectivity of miracidia to infection with S. haematobium and F. gigantica were studied. The data showed that no B. truncatus survived more than 42, 32 & 27 days after exposure with a mean life span of 18.5, 13.3 & 11.1 days respectively. The death rate of B. truncatus with LC0 was highly significant as compared to treatment with LC10 & LC25 (p < 0.01). L. natalensis were more susceptible to the effect of aqueous extract than B. truncatus. LC0, LC10 & LC25, extract killed all L. natalensis through 32, 27 & 22 days. The mean life span of those exposed to LC0 was 12.37 days, high significant when compared with treated LC10 & LC25 ones (p < 0.01). The cumulative mortality rates of B. truncatus and L. natalensis in controls during the experimental study (52 days) was 60% & 75%, respectively. Egg production of B. truncatius and L. natalensis was not affected by sublethal concentrations. Control snails layed significantly higher no. of eggs than treated ones. B. truncatus stopped egg laying 17 days after exposure to LC25. those treated with LC10 & LC0 ceased to deposit eggs after 22 & 27 days respectively. The percent reduction in egg laying capacity of B. truncatus treated with LC0, LC10 & LC25 compared to controls was 77.1%, 93.2% & 92.8% respectively (p < 0.01). Similar reduction in egg production of treated L. natalensis cornpared to controls occurred, the percent reduction in egg production of snails treated with LC0, LC10 & LC25 in relation to controls was 78.4%, 92.4% & 94.7% respectively. Sublethal concentrations of aqueous extract of P. actinostoloides affected hatchability of B. truncatus and L. natalensis eggs. The data showed that eggs of B. truncatus and L. natalensis can hatch in all tested concentrations but with different rates. The eggs' hatchability in snails exposed to LC0, LCIo & LC25 extract at 5 days old was 44%, 38% & 30% in B. truncatus respectively. In L. natalensis eggs, the corresponding rates were lower 28%, 24% & 18% respectively. The infection of B. truncatuts and L. natalensis with S. haematobium n and F. giganlica miracidia was greatly reduced by the sublethal concentrations of aqueous extract of P. actinostoloides. The reduction of infection rate increased with the increased of sublethal concentrations. In B. truncatus the reduction was 43.2%, 57.6% & 76.6% compared to controls and in L. natalensis was 56.3%, 70.2% & 77.4%, respectively.

Animals↗

PubMed2006

Influence of certain fertilizers on the activity of some molluscicides against Biomphalaria alexandrina and Lymnaea natalensis snails.

Effect of the fertilizers (ammonium nitrate, potassium sulphate and urea) on molluscicidal activity of the molluscicides (copper sulphate, niclosamide & mollutox) against B. alexandrina and L. natalensis was investigated. The molluscicides were more potant than fertilizers. Snails were exposed for 24 hr to a fertilizers using LC0 (1/10 & LC50) then, to molluscicides. Pre-exposure to potassium sulphate caused a synergistic action with copper sulphate, niclosamide and mollutox on L. natalen-sis. Pre-exposure to urea caused an additive effect with niclo-samide and mollutox against L. natalensis and B. alexandrina respectively. Pre-exposure to ammonium nitrate caused an additive action to niclosamide on L. natalensis. Snails were exposed for 24hr to one molluscicide, then exposed to fertilizers, showed that pre-exposure to niclosamide or mollutox caused an additive effect with ammonium nitrate and potassium sulphate. Pre-exposure to mollutox caused an additive effect with urea on the two snails' sp. juvenile or adult B. alexandrina were ex-posed to LC0 of molluscicide-fertilizer mixture, showed that urea when mixed with each molluscicides showed greatly reduced on the growth rate percent (0.00), survival rate and snail fecundity. Molluscicides and fertilizers mixed at different ratios of LC (40:10, 30:20, 25:25, 20:30 & 10:40), the toxicity of the mixtures caused antagonistic effect on adult B. alexandrina, but a mixture of niclosamide-ammonium nitrate caused a potent effect (synergism or additive) except at ratio 20:30 which showed an antagonism on L. natalensis. Mixtures of copper sulphatepotassium sulphate (10:40), niclosamide-potassium sulphate (20:30), mollutox-ammonium nitrate (25:25) revealed an additive effect on L. natalensis.

Animals↗

PubMed1989

Geographical distribution and habitat preferences of the invader freshwater snail species Lymnaea columella (Mollusca: Gastropoda) in South Africa.

The present geographical distribution of Lymnaea columella, as recorded in the National Freshwater Snail Collection, is described and discussed. It appears that L. columella is the most successful colonist of all the freshwater snail species in South Africa, and, together with Bulinus tropicus and Lymnaea natalensis, it forms the most widely distributed freshwater snail species in the region. Data regarding the 2,341 discovery sites of L. columella recorded by collectors during surveys are analysed. L. columella cluster mainly in rivers or streams with perennial, slow flowing, or stagnant freshwater with many plants and a mud substrate. L. columella is regarded as a more effective intermediate host for the transmission of fascioliasis than the indigenous snail species. The economical implications of this are discussed briefly in the light of its success as an invader species.

Animals↗

PubMed1985

Snails and aquatic vegetation in Gezira irrigation canals.

All 38 minor canals in a limited area of the Gezira Irrigated Area were surveyed four times over a 2-year period to determine the aquatic and semi-aquatic vegetation types found and their distribution. A more detailed 2-year study of the correlation between snail density and aquatic vegetation was carried out in 18 of these canals. A total of 22 different species of weed were recorded, with floating and submerged weeds being more widespread and dense in the clear, slow-moving water at the end of the irrigation season in March/April, than in the turbid flood waters in October. The schistosome vector snails Biomphalaria pfeifferi and Bulinus truncatus were found in conjunction with aquatic weeds and B. pfeifferi in particular increased in numbers as weed growth continued. In the second season of the study when mechanical weed clearing and regular focal mollusciciding was being carried out there was a noticeable reduction in weed density but repopulation was rapid. Snail numbers were reduced by mollusciciding and/or weed clearance in four canals, but outside the focal target canal stretches the weed clearance alone did not substantially reduce the snail populations.

Agriculture↗

PubMedDate not supplied

Population genetics of Biomphalaria straminea in Hong Kong. A neotropical schistosome-transmitting snail recently introduced into China.

Since its introduction in the early 1970s Biomphalaria straminea (Gastropoda: Planorbidae) has spread rapidly and is locally the most abundant fresh water snail in Hong Kong. Studies of 19 electrophoretically detected loci in four populations show that the colonists retain high levels of variability (P = 0.26, H = 0.056 - 0.097), comparable with those found in autochthonous samples of related species. Genotype frequencies at the five polymorphic loci, and a comparison of maternal and progeny genotypes of individual field-collected snails, revealed no evidence for self-fertilization in these functional hermaphrodites. F statistics indicated minimal genetic structuring, presumably because of outcrossing and recency of origin of the populations. Geographic distribution of various alleles and their frequencies suggest that two southern populations were derived from the original colonists by dispersal but that a northern population represents a second introduction in about 1982. This interpretation (based on genetics) is consistent with the known history of the various populations. The Asian populations of this South American snail are interpreted as being in the "flush" phase of the colonization process. Finally, the probability of the secondary spread of this snail from Hong Kong, and the probability of its parasite, the human blood fluke Schistosoma mansoni, being introduced to Asia are discussed.

Alleles↗

PubMed1995

Killing of Schistosoma mansoni sporocysts in Biomphalaria glabrata implanted with amoebocyte-producing organ allografts from resistant snails.

Schistosome-susceptible National Institutes of Health (NIH) albino Biomphalaria glabrata were implanted with the amoebocyte-producing organ (APO) from 4 types of donors: (1) exposed-resistant (eR), i.e., schistosome-resistant 13-16-R1 snails that had been exposed to miracidia of Schistosoma mansoni 30 or more days previously in order to verify their resistance, (2) exposed-susceptible (eS), i.e., NIH albino snails that had been similarly exposed to miracidia, (3) unexposed-resistant (uR), and (4) unexposed-susceptible (uS). Allograft recipients, along with unimplanted NIH albino and 13-16-R1 controls (cS and cR, respectively), were then challenged with 100 miracidia each of Schistosoma mansoni at 14-15 days postimplantation. Histological sections of tentacles fixed at 3 days postchallenge (PC) showed significantly fewer normal sporocysts and more numerous developmentally retarded sporocysts in cR snails than in the other 5 treatment groups, and significantly more killed sporocysts in both cR snails and recipients of eR APOs than in the other 4 groups. In addition, the histological condition of eR allografts in both unchallenged (at 1, 3, 7, 10, and 14 days postimplantation) and schistosome-challenged (at 3 days PC) NIH albino recipients was examined. Viable hematopoietic cells were found in 96% of implants, and in 86% of implants low numbers of mitotic figures were found among these cells, although no increased mitotic activity occurred in challenged recipients. These data suggest that lowered susceptibility to infection with S. mansoni in recipients of APO allografts results primarily from hemocyte-mediated resistance.

Animals↗

PubMed1997

Effect of UV-irradiation, gamma irradiation and praziquantel on infected Biomphalaria alexandrina snails.

Schistosomiasis control represent the main target of many research programme allover the world. Effect of physical (UV- and gamma-irradiation) treatment as well as chemical (PZQ) treatment on infected laboratory bred Biomphalria alexandrina snails have been studied. Gamma irradiation and PZQ-treatment induced high rate of mortality than UV-irradiated and non-treated control snails. The cercarial production was severely reduced as a result of UV-, gamma-irradiation and PZQ-treatment. Pre-patent period was significantly increased in gamma-irradiated and PZQ-treated groups than UV-irradiated and control groups. Gamma irradiation and PZQ-treatment showed severe effects on hermaphrodite gland and cercariae. Trials of experimental infection in swiss albino mice revealed that low rate of infection (9.7% and 1.3%) was induced by cercarial shedding from UV-irradiated and PZQ-treated snails respectively. Whereas, cercarial production of gamma-irradiated snails failed to induce infection in swiss mice.

Animals↗