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PubMed2001

Genetic variability and molecular identification of Brazilian Biomphalaria species (Mollusca: Planorbidae).

Freshwater snails belonging to the genus Biomphalaria are intermediate hosts of the trematode Schistosoma mansoni in the Neotropical region and Africa. In Brazil, one subspecies and ten species of Biomphalaria have been identified: B. glabrata, B. tenagophila, B. straminea, B. occidentalis, B. peregrina, B. kuhniana, B. schrammi, B. amazonica, B. oligoza, B. intermedia and B.t. guaibensis. However, only the first three species are found naturally infected with S. mansoni. The classical identification of these planorbids is based on comparison of morphological characteristics of the shell and male and female reproductive organs, which is greatly complicated by the extensive intra-specific variation. Several molecular techniques have been used in studies on the identification, genetic structure as well as phylogenetic relationships between these groups of organisms. Using the randomly amplified polymorphic DNAs (RAPD) analysis we demonstrated that B. glabrata exhibits a remarkable degree of intra-specific polymorphism. Thus, the genetics of the snail host may be more important to the epidemiology of schistosomiasis than those of the parasite itself. Using the simple sequence repeat anchored polymerase chain reaction (SSR-PCR) in intra-populational and intra-specific studies we have demonstrated that snails belonging to the B. straminea complex (B. straminea, B. kuhniana and B. intermedia) clearly presented higher heterogeneity. Using the low stringency polymerase chain reaction (LS-PCR) technique we were able to separate B. glabrata from B. tenagophila and B. tenagophila from B. occidentalis. To separate all Brazilian Biomphalaria species we used the restriction fragment length polymorphism (PCR-RFLP) of the internal transcribed spacer region (ITS) of the DNA gene. The method also proved to be efficient for the specific identification of DNA extracted from snail eggs. Recently we have sequenced the ITS2 region for phylogenetic studies of all Biomphalaria snails from Brazil.

Animals↗
PubMed2000

Molecular evidence supports an african affinity of the neotropical freshwater gastropod, Biomphalaria glabrata, say 1818, an intermediate host for Schistosoma mansoni.

Freshwater snails of the genus Biomphalaria, Preston 1910, are the most important and widely distributed intermediate hosts of Schistosoma mansoni, the blood fluke responsible for human intestinal schistosomiasis, in Africa and the Neotropics. S. mansoni is thought to have been imported repeatedly into the Americas during the last 500 years with the African slave trade. Surprisingly considering that the New and Old World separated 95-106 million years (Myr) ago, the disease rapidly became established due to the presence of endemic susceptible hosts. Reconstructing the phylogenetic relationships within Biomphalaria may provide insights into the successful intercontinental spread of S. mansoni. Parsimony and distance analyses of mitochondrial and nuclear sequences show African taxa to be monophyletic and Neotropical species paraphyletic, with Biomphalaria glabrata forming a separate clade from other Neotropical Biomphalaria, and ancestral to the African taxa. A west to east trans-Atlantic dispersal of a B. glabrata-like taxon, possibly as recently as the Plio-Pleistocene (1.8-3.6 Myr ago) according to a general mitochondrial clock, would fit these observations. Vicariance or an African origin for B. glabrata followed by multiple introductions to South America over the past 500 years with the African slave trade seem unlikely explanations. Knowledge of the phylogenetic relationships among important intermediate host species may prove useful in furthering control measures which exploit genetic differences in susceptibility to parasites, and in elucidating the evolution of schistosome resistance.

Africa↗
PubMed1993

Population dynamics and schistosomal infection of Biomphalaria alexandrina in four irrigation canals in Egypt.

The natural growth, reproductivity, mortality and schistosomal infection of Biomphalaria alexandrina, the snail vector of Schistosoma mansoni in Egypt, were studied for one year in four irrigation canals, namely El-Khassa and Radwan (Giza Governorate) and Sendebis and Sanafeer (Qalyoubiya Governorate). Radwan canal contains a considerably dense Biomphalaria population and three generations of snails (parents generation and autumn and spring generations) were recognized. Two phases of growth were distinguished in both autumn and spring generations, a faster phase followed by a slower one. The faster phase extends from January to May and from March to August in the autumn and spring generations, respectively. The daily mortality rate of snails was highest in the hot season (June--September) and lowest in the cold months (December--April). Continuous reproductivity of Biomphalaria snails was observed allover the year with highest values of reproduction index from November to March. Biomphalaria snails collected from El Khassa and Radwan canals were free of S. mansoni infection, while snails of Sanafeer canal carried patent infection in September and October. Prepatent infection was also found in Sanafeer canal in July and September and in Sendebis canal in September.

Animals↗
PubMed1996

[Survival of Bulinus truncatus and Biomphalaria pfeifferi in sewer water purified in stabilization ponds in a sudanese-saharan zone].

In subsaharan Africa wastewater purification to protect the health of the population could create stagnate water reservoirs for parasitic vectors such as snails which are intermediate hosts of bilharzia. Laboratory studies of the survival of Bulinus truncatus, an intermediate host of Schistosoma haematobium, and Biomphalaria pfeifferi, an intermediate host of Schistosoma mansoni, in waste water purified in stabilization ponds showed that Biomphalaria pfeifferi thrives to dirty water (60 mg/l < or = COD < or = 1060 mg/l) while Bulinus truncatus survived only in slightly cleaner water (60 mg/l < or = COD < or = 200 mg/l). Field studies showed that Biomphalaria pfeifferi disappeared after 48 hours as compared to 25 days in the laboratory. In both laboratory and field studies Bulinus truncatus survived only 24 hours in raw waste water. The duration of survival grew longer as quality of the water improved. Temperature variations, high amounts of organic material in water, high oxygen content in water, and absence of plant-life are factors which could limit the development of the intermediate snail hosts (i.e. Bulinus truncatus and Biomphalaria pfeifferi) in the waste stabilization ponds of the Interstate School of Rural Equipment Engineers in Ouagadougou, Burkina Faso.

Animals↗
PubMed1998

Effect of six non-target snails on Schistosoma mansoni miracidial host finding and infection of Biomphalaria alexandrina under laboratory conditions.

Six snail species naturally associated with Biomphalaria alexandrina, the snail host of Schistosoma mansoni in Egypt, were tested under standard laboratory conditions, for impact on miracidial host findings and infection of the snail host. These snails are the prosobranchs Melanoides tuberculata, Cleopatra bulimoides, Bellamys unicolor and Lanistes carinatus, the pulmonates Planorbis planorbis and Physa acuta. The tested snail ssp. reduced considerably the infection rate of Biomphalaria with S. mansoni especially at a ratio of 10 decoy snails to one Biomphalaria snail. The prosobranchs Melanoides, Cleopatra and Lanistes exhibited more reducing effect on Biomphalaria infection than Bellamya and the pulmonates Physa and Planorbis being 65.2%, 78.8%, 62.9%, 33.3%, 30.3% and 46.9%, respectively.

Animals↗
PubMed1979

Studies of the relationship between Schistosoma and their intermediate hosts. III. The genus Biomphalaria and Schistosoma mansoni from Egypt, Kenya, Sudan, Uganda, West Indies (St. Lucia) and Zaire (two different strains: Katanga and Kinshasa).

The compatibility between strains of Schistosoma mansoni from Egypt, Kenya, Sudan, Uganda, the West Indies, and Zaire (two strains which came from Katanga and from Kinshasa), and various species and strains of Biomphalaria, i.e. Biomphalaria pfeifferi, B. alexandrina, B. glabrata and B. camerunensis was investigated. Data as mortality, rate of infection of the surviving snails, duration of infection, cercarial production per day per positive snail, etc., were observed. The main emphasis was placed on determining the total cercarial production per 100 exposed snails for each snail population. It was possible to infect all the tested populations of B pfeifferi with the various strains of S. mansoni, but the observation as e.g. TCP/100 exposed snails varied greatly according to the population of snail and the strain of S. mansoni. The results for the remaining species of Biomphalaria varied greatly, depending on the combination, e.g. B. alexandrina was only susceptible to the local S. mansoni from Egypt. The highest TCP/100 exposed snails was more than 1 million for the strains of S. mansoni from Egypt, Kenya and the West Indies in B. alexandrina, B. pfeifferi and B. glabrata, respectively. The next group, with a TCP/100 exposed snails on 7--800 000 consists of S. mansoni from Sudan, Uganda and Zaire (Katanga) all in B. pfeifferi. The last tested strain of S. mansoni, Zaire (Kinshasa) yielded a cercarial production on 500 000 per 100 exposed snails in B. pfeifferi and B. camerunensis. The shortest prepatent period, 19 days, was observed for S. mansoni from Kinshasa, Zaire, in B. camerunensis, and the longest prepatent period, 25 days, was found for strains from Egypt and from the West Indies in B. alexandrina and B. glabrata, respectively. In general, a very long duration of infection, lasting up to 200 days, was observed.

Animals↗
PubMed2000

Phylogenetic relationships among Brazilian Biomphalaria species (Mollusca: Planorbidae) based upon analysis of ribosomal ITS2 sequences.

In spite of their abundance, widespread distribution and medical importance, the phylogenetic relationships among Biomphalaria snails have received relatively little attention. We have collected and studied 29 populations of snails obtained from different localities from Brazil. We have sequenced the ribosomal DNA second internal transcribed spacer (ITS2) from the following Biomphalaria species: B. glabrata, B. tenagophila tenagophila, B. occidentalis, B. straminea, B. peregrina, B. kuhniana, B. schrammi, B. amazonica, B. oligoza, B. intermedia and an outgroup species Helisoma duryi. The sequence from each species is unique. Three different methods of phylogenetic reconstruction were used (distance, maximum parsimony and maximum likelihood). The resulting phylogenetic trees obtained by these methods basically support current systematic relationships based on morphological characters alone. This study demonstrates that the ITS2 region contains markers useful for identification and determination of relationships among Biomphalaria species.

Animals↗
PubMed1992

Predation of Biomphalaria and non-target molluscs by the crayfish Procambarus clarkii: implications for the biological control of schistosomiasis.

The North American crayfish Procambarus clarkii was examined under laboratory conditions for its ability to prey on Biomphalaria pfeifferi and B. glabrata, molluscan intermediate hosts of human schistosomiasis, and other, non-target gastropod species. Both male and female adult crayfish significantly reduced survival of neonate snails, even though alternative animal and plant foods were both available. In subsequent experiments, no differences in snail consumption were detected, for either adult or juvenile crayfish, in the presence or absence of a plant food alternative. Both adult and juvenile crayfish were able to consume small (2.5 mm) and large (17.5 mm) B. glabrata, suggesting that no size refuge from predation exists. Both adult and juvenile crayfish consumed Biomphalaria egg masses, although this consumption was significantly greater for juveniles. Procambarus clarkii adults were unable to consume substantial numbers of the relatively thick-shelled prosobranch snails Pila ovata and Lanistes carinatus. Crayfish did consume a third prosobranch, Melanoides tuberculata, and the pulmonate snail Physa acuta, but at a lower rate relative to consumption of Biomphalaria. Physa acuta, itself of North American origin, responded to the presence of crayfish by rapidly leaving the water and thereby avoided predation. Implications of these results for the biological control of schistosome-transmitting snails in East Africa are discussed.

Animals↗
PubMed2004

Polymerase chain reaction and restriction fragment length polymorphism analysis of the ITS2 region for differentiation of Brazilian Biomphalaria intermediate hosts of the Schistosoma mansoni.

We sequenced the internal transcribed spacer 2 of the ribosomal DNA (ITS2-DNAr) from the three Schistosoma mansoni intermediate hosts in Brazil: Biomphalaria glabrata, Biomphalaria tenagophila and Biomphalaria straminea. Analysis of a restriction map from those sequences allowed us to select putative restriction enzymes able to identify the snail species under study. Four restriction enzymes were used and HpaII provided simple species-specific profiles easily visualized in polyacrylamide gels. The use of ITS2 is advantageous as it provides a small fragment of 460 bp which may be easily amplified by PCR. In the current work, we showed that the amplification of ITS2-DNAr together with HpaII enzyme restriction is an auxiliary molecular tool for the morphological identification of such snails as well as for taxonomic and phylogenetic studies of neotropical planorbids.

Animals↗
PubMedDate not supplied

[The characterization of Biomphalaria orbignyi Paraense, 1974, a mollusk of medico-epidemiological importance recently reported for Cuba].

The conchological, anatomical and radular characteristics of Biomphalaria orbignyi are described, as well as the morphometric ratio between maximal height and maximal diameter, in which the regression coefficient value is 0.9. The life tables of Biomphalaria orbignyi shows a life range (L phi = 10.37) much higher than in the rest of the species available in Cuba; the value of k = 0.17 is similar to that of Biomphalaria havanensis. It has 2 reproductive peaks at middle age. Differently from other species of the genus, it has lower mortality at early ages and the highest peak is seen when it reaches the adult stage, which means it is a strong species. The zymograms that have been obtained confirm this species is different from B. havanensis. Since there are no marked differences on an individual basis, its correct identification requires to take into consideration every biological and ecological evidence available.

Animals↗
PubMed1987

Experimental infection of Physa heterostropha, Helisoma trivolvis, and Biomphalaria glabrata (Gastropoda) with Echinostoma revolutum (Trematoda) Cercariae.

Gross and histologic studies were done on laboratory-raised Physa heterostropha, Helisoma trivolvis, and Biomphalaria glabrata snails exposed individually to 100 cercariae of Echinostoma revolutum. Cercariae showed a predisposition for the kidneys of snails. They entered the nephridiopore, migrated up the tubular kidney, and encysted in the saccular kidney within 2 hr. Considerably more cysts were in the kidney of B. glabrata at 24 hr than in H. trivolvis or P. heterostropha kidneys. Encysted metacercariae were not infective to domestic chicks at 2 hr, but were infective by 4 hr. Biomphalaria glabrata exposed to about 1,000 cercariae/snail and necropsied either 10 or 16 wk postexposure contained 300-500 cysts/kidney; about one-half the cysts were viable and infective to chicks. Biomphalaria glabrata is an excellent second intermediate host for the laboratory propagation of E. revolutum.

Animals↗
PubMed1997

Detection of Schistosoma mansoni in Biomphalaria using nested PCR.

A nested polymerase chain reaction (PCR) protocol was developed for detecting the presence of Schistosoma mansoni sporocysts in intermediate host snails of the genus Biomphalaria. To accomplish this, rDNA genes encoding the 18S rRNA of S. mansoni and Biomphalaria alexandrina from Egypt were sequenced, as were 18S-encoding genes of the 13-16-R1 and Salvador strains of Biomphalaria glabrata. Based on a comparison of host and parasite sequences, a nested set of PCR primers was designed to allow specific amplification of portions of S. mansoni 18S rDNA. These primers allowed detection of as little as 10 fg of S. mansoni DNA diluted in 100 ng of snail DNA and did not allow amplification of snail 18S sequences. Using nested PCR, the presence of a single S. mansoni sporocyst within an adult snail could be detected at 1 day postexposure. In DNA samples extracted from each of 74 snails of the M-line strain of B. glabrata exposed to from 1 to 10 S. mansoni miracidia for intervals ranging from 1 to 44 days, use of the outside primer pair alone detected the parasite's presence in 51% of the snails, whereas the sequential use of outside and nested primer pairs detected parasites in 92% of the snails. This approach has utility in determining if snails in endemic areas bear prepatent or inactive infections and in assessing the degree of compatibility between local snail and schistosome populations. It will also facilitate studies of resistance of snails to infection.

Animals↗
PubMed2004

Polymeric controlled release formulations of niclosamide for control of Biomphalaria alexandrina, the vector snail of schistosomiasis.

Schistosomiasis is one of the most important public health problems in many developing countries. The present study was conducted to investigate the effect of the polymeric niclosamide formulations against Biomphalaria alexandrina snails, the intermediate host of Schistosoma mansoni in Egypt. Three new polymeric formulations were prepared for the molluscicide niclosamide. The formulations were prepared either by the chemical modifications of poly(glycidyl methacrylate) or by physical entrapment of the niclosamide in calcium alginate beads. The release of the niclosamide from the polymeric formulations was investigated. The activity of the prepared formulations against Biomphalaria alexandrina was investigated. The results obtained revealed higher potency for polymerized niclosamide B3 than B1; the lowest potency was revealed for B2. After an exposure period of 24 hours, LC(50) values were 0.073, 0.098 and 1.09 ppm for B3, B1 and B2, respectively. In addition, the molluscicidal potency of the test polymeric niclosamide was age-dependent, where old snails were more tolerant to the test solutions than young and newly hatched snails. The results also indicated that the molluscicidal activity of B3 was extended for 21 days and 17 days for B1, compared with 5 days for free niclosamide. However, the molluscicidal potency of the polymerized niclosamide was increased after boiling for one hour, and was increased with increasing the pH of the medium to pH 9. In addition, their potency was increased with decreasing the water hardness concentrations (CaCO(3)).Molluscicidal activity of free niclosamide and its polymeric formulations vs. exposure time.

Animals↗
PubMed1993

Schistosoma mansoni: comparison of cloned tropomyosin antigens shared between adult parasites and Biomphalaria glabrata.

Rabbit antisera, raised against whole, homogenized hepatopancreas from uninfected Biomphalaria glabrata, were used to screen a cDNA library prepared from adult Schistosoma mansoni. Of 1.8 x 10(5) recombinants screened, 34 clones were specifically immunoreactive with the antisera. Twenty of the clones were subcloned for further analysis, and 13 of the 20 were demonstrated to hybridize to a cDNA probe encoding schistosome tropomyosin I (pSMTM) at high stringency (Xu et al. Experimental Parasitology 69, 373-392, 1989). One partial cDNA clone (pSM4), which failed to hybridize to pSMTM, was used to rescreen the adult worm cDNA library and a 1381-bp cDNA clone, SmTMII, was identified and characterized. SmTMII contained a single 284-amino acid open reading frame and was shown to be 65.8% homologous to SMTM. Computer-assisted analysis of the predicted protein structure depicted a hydrophilic molecule with the extensive alpha helical secondary structure characteristic of tropomyosins. SmTMII was expressed in Escherichia coli and the resulting 45-kDa fusion protein was recognized by both a polyclonal antiserum specific for SMTM and the antiserum of mice chronically infected with S. mansoni. Northern analysis showed the SmTMII mRNA in the adult stage to be about 1.6 kb in size. Analysis of the SmTMII gene by Southern blot revealed a complex hybridization pattern suggesting the presence of introns or multiple gene copies. The 650-bp EcoRI fragment of SmTMII was used to screen a cDNA library prepared from uninfected Biomphalaria glabrata and two clones, each encoding a novel snail tropomyosin, BgTMII, were isolated and characterized. The two clones, consisting of 2816 and 2314 bp, respectively, differed from each other only in the polyadenylation signal used and each contained a single and identical 284-amino acid open reading frame having 94.7% homology with the previously reported snail tropomyosin, BG39 (Dissous et al. Molecular and Biochemical Parasitology 43, 245-256, 1990). BgTMII was shown to have a higher amino acid homology with SMTM (68.3%) than with BG39 (65.1%) and a higher amino acid homology with SMTM than the two schistosome tropomyosins (SMTM and SmTMII) have with each other (65.8%). Implications of these observations in relation to the concept of host-parasite antigen mimicry are discussed.

Amino Acid Sequence↗
PubMed1994

Biomphalaria glabrata: extensive genetic variation in Brazilian isolates revealed by random amplified polymorphic DNA analysis.

To examine the extent of genetic variation in Biomphalaria glabrata, the intermediate host of Schistosoma mansoni, specimens from seven Brazilian isolates were studied. Regions of genomic DNA were amplified using short, arbitrarily selected oligonucleotide primers under low-stringency conditions (random amplified polymorphic DNAs--RAPDs) and analyzed by polyacrylamide gel electrophoresis followed by silver staining. The RAPD profiles of snails of the same isolate were relatively homogeneous, with the majority of bands being common to all individuals studied. In contrast, the profiles of snails from different isolates were quite distinct, with less than 10% of amplified DNA fragments being common to all of the specimens studied. This was found to be true irrespective of the primer, indicating that B. glabrata is remarkably genetically heterogeneous. The data are consistent with the view that genetic drift plays a major role in the genetic structure of populations of B. glabrata due to their ability to reconstitute populations from very small numbers of individuals by self-fertilization. The great variety of polymorphic genetic markers identified in this restricted survey indicates that RAPD analysis may make a major contribution to the study of the genetics of Biomphalaria.

Animals↗
PubMed1999

Schistosoma mansoni: continuous variation in susceptibility of the vector snail of schistosomiasis, Biomphalaria tenagophila I. Self-fertilization-lineage.

Mascara, D., Kawano, T., Magnanelli, A. C., Silva, R. P. S., Sant' Anna, O. A., and Morgante, J. S. 1999. Schistosoma mansoni: continuous variation in susceptibility of the vector snail of schistosomiasis, Biomphalaria tenagophila I. Self-Fertilization-Lineage. Experimental Parasitology 93, 133-141. Artificial selection of Biomphalaria tenagophila snails for susceptibility to infection by Schistosoma mansoni (Brazilian SJ strain) was carried out from natural populations. After five self-fertilization generations, two lineages were isolated and were designated as SUSC (highly susceptible 93-100%) and RES (nonsusceptible 5-0%). Length of the prepatent period, cercarial production, and mortality of the hosts in postexposure were determined in all generations (F(1)-F(8)) and were analyzed as quantitative traits related to host susceptibility. Distribution patterns of frequencies were observed within snail families (samples derived from one F(0) snail), these traits showing a significant influence by selection applied to susceptibility. The multiple quantitative classes were described in terms of continuous variation. During the selection of SUSC lineage, classes with higher values of prepatent length and lower cercarial production were eliminated, and the heritability calculated for these two traits was 0.811 and 0.709, respectively. Experimental results were correlated with an increase in the level of susceptibility in the generations selected and are discussed in relation to inheritance patterns as well as the quantitative variation of susceptibility.

Animals↗
PubMed1981

[Investigations on periodic phenomena in the snail Biomphalaria glabrata (author's transl)].

A method was developed to measure the locomotive activity of Biomphalaria glabrata over long periods of time. A snail, radioactively marked with a Co57-source, moves on a circular path. Beneath the experimental vessel a lead disc with a slit revolves (one revolution per minute) over a counter tube. Once every minute the amount of radioactivity emitted falls through the slit onto the counter tube. The position and thence the locomotive activity of the snail is determined from the intervals between the impulses. Under constant conditions the experiments show a distribution of crawling activity over the whole day that is the same for animals infected with Schistosoma mansoni and non-infected molluscs. The snails have more locomotive activity by day than by night, with a distinct maximum in the second hour after exposure to light. Experiments using food marked with I125-labelled fibrinogen revealed that feeding activity is three times as high at night as by day. The experiments also show that Biomphalaria glabrata tends to prefer night-time for egg laying. The results are compared with other known periodic phenomena in B. glabrata in a phase-chart.

Animals↗
PubMed2000

Galactan biosynthesis in snails: a comparative study of beta-(1--> 6) galactosyltransferases from Helix pomatia and Biomphalaria glabrata.

Adult snails synthesize in their albumen glands a polysaccharide which is composed exclusively of D- or D- and L-galactose (Gal) residues which are interglycosidically linked by 1 --> 3 and 1 --> 6 bonds. It is the only carbohydrate source for embryos and freshly hatched snails. Two galactosyltransferases are described in this study which are most likely involved in the biosynthesis of this polysaccharide. One identified in Helix pomatia acts on oligosaccharides and could be used to synthesize a tetrasaccharide when the branched trisaccharide D-Gal-beta-(1 --> 3)-[D-Galbeta-(1 --> 6)]-D-Galbeta-1 --> OMe was offered as acceptor. This enzyme, requiring Mg++-and Mn++-ions for activity, introduced a linear beta-(1 --> 6) linkage at the terminal non-reducing ends and was not detected in Biomphalaria glabrata. The other enzyme, which introduced beta-(1 --> 6) linkages at subterminal D-Gal residues, thus forming branching points in the polysaccharide, was found in H. pomatia, Arianta arbustorum and B. glabrata with comparable activities. With the enzyme preparation of H. pomatia, up to four D-Gal residues were introduced into vicinal positions, forming single-membered side chains, if a hexasaccharide with five linearly beta-(1 --> 3)-linked D-Gal residues was offered as a acceptor. The multiple-branched structure formed is typical for snail galactans, making this enzyme a prime candidate for the branching enzyme in galactan synthesis. The enzyme activity could be solubilized and purified by affinity chromatography. In SDS-polyacrylamide electrophoresis, the Helix-derived eluate displayed two bands (68, 37 kDa) and that of Biomphalaria five bands (68, 63, 17.5; 15; 13 kDa). The purified material showed only 8% of the total activity of the crude extracts, but it could be shown that a phosphatase present in the crude extract can degrade UDP formed in the transfer reaction and thus drive the reaction to completion.

Animals↗