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PubMed1982

Population structure in Biomphalaria glabrata: examination of an hypothesis for the patchy distribution of susceptibility to schistosomes.

It has been suggested that the patchy distribution of snail susceptibility to schistosomes might be due to genetic drift. Since direct estimation of genes for susceptibility is not feasible in population studies, electrophoretic techniques were used to examine this hypothesis for populations of Biomphalaria glabrata from Puerto Rico. These populations were characterized by relative genetic homogeneity within populations and differentiation among local populations. The data presented are consistent with the hypothesis that random genetic drift and low rates of migration might be responsible for the patchy distribution of small susceptibility to schistosomes.

Animals↗
PubMed1982

In vitro encounters between Schistosoma mansoni primary sporocysts and hemolymph components of susceptible and resistant strains of Biomphalaria glabrata.

Encounters between axenically transformed sporocysts of the Puerto Rican 1 strain of Schistosoma mansoni and hemocytes and plasmaaa components of susceptible "M line" and resistant 10-R2 and 13-16-1 strains of Biomphalaria glabrata were studied in vitro. After 24 hours of incubation in susceptible hemolymph components, 94.4% of 36 observed sporocysts retained normal structure, whereas 9l.6% of 48 sporocysts were destroyed after 24 hours of incubation in resistant hemolymph components. Sporocysts preincubated for 6 hours in susceptible plasm were destroyed when subsequently incubated with resistant hemocytes in susceptible plasma. Sporocysts preincubated in resistant plasma were not destroyed when subsequently incubated with susceptible hemocytes and plasma. Susceptible hemocytes preincubated in resistant plasma, and then incubated for 24 hours with sporocysts in the presence of susceptible plasma were incapable of inflicting damage. The simultaneous incubation of sporocysts with susceptible hemocytes and resistant plasma produced variable results. The predominant trend was sporocyst destruction in five replicates and lack of substantial damage in six replicates. Results of these and previous experiments imply that differences between susceptible and resistant strains of snails in their ability to destroy sporocysts in vitro can be attributed primarily to differences in their hemocytes, although plasma factors may alter these responses in some cases. The results also suggest that if sporocysts do acquire a coat of host plasma components, this strategy is by itself insufficient to account for the persistence of sporocysts in susceptible snails.

Animals↗
PubMed1987

Alkylphosphonates as unique compounds in the metabolism of the schistosomal vector Biomphalaria glabrata.

Examination of intact freshly laid egg masses of the schistosomal snail vector Biomphalaria glabrata by both 31P nuclear magnetic resonance spectroscopy and colorimetric phosphorus analysis indicated that 98% of the phosphorus in the egg masses was present in the form of alkylphosphonic acids. At least 87% of the total phosphorus originally present was comprised of 2-aminoethylphosphonic acid. During 11 days of embryonic development, alkylphosphonate-phosphorus decreased from 98% to 50% of the total phosphorus, indicating a possible role for phosphonate-phosphorus in the embryonic nutrition of these snails. Considering the relative uniqueness of the alkylphosphonates in nature, the very high concentration of these compounds in freshly laid eggs, and the reduction in their amount during embryonic development, the anabolic and catabolic pathways of alkylphosphonates may serve as sites for highly specific analogues in the control of these schistosomal vectors.

Aminoethylphosphonic Acid↗
PubMed1989

Schistosoma mansoni antigens recognized in Biomphalaria glabrata hemolymph by monoclonal antibodies.

In order to identify and characterize Schistosoma mansoni antigens in Biomphalaria glabrata, we examined 19 murine monoclonal antibodies (Mabs) for specific binding to schistosome larvae. None of the murine Mabs induced by infection or by immunization with a crude cercarial antigen (CCA) served this purpose. Two Mabs out of 9 (KCSme22-3 and KCSme22-4) induced by soluble egg antigens reacted with CCA but not with normal snail (NSN) extract. We selected these 2 for studies on detection and characterization of schistosomal antigens in snails. When employed in an ELISA, they differentially detected schistosomal antigens in extracts and cell-free hemolymph (plasma) of infected snails. The selected Mabs bind to cercarial surface as demonstrated by the indirect fluorescent antibody technique (IFAT) with paraformaldehyde-fixed cercariae. The epitopes corresponding to the selected Mabs are periodate sensitive, suggesting the glycoprotein nature of the antigens recognized. Immunoblotting analysis employing the selected Mab revealed 1 antigen in CCA (Mr = 205 kDa) and 3 antigens in snail plasma (Mr = 220 kDa, 180 kDa, and 135 kDa). Schistosomal antigens were first detectable in the snails' plasma 2 weeks after snail infection, and their quantity increased afterwards.

Animals↗
PubMed1992

Schistosoma mansoni infection in diapausing Biomphalaria glabrata snails: studies of temperature and genetic influences on diapausing behavior.

Snails that are capable of undergoing diapause can circumvent unfavorable environmental conditions, including long periods of drought. Studies were performed to investigate possible temperature and/or genetic factors that may trigger lamella formation and diapausing behavior. The influence of diapause in Biomphalaria glabrata snails on susceptibility to Schistosoma mansoni infection and levels of cercarial production was also investigated. Rearing temperatures of 23 degrees C or higher did not induce lamella formation or diapause, regardless of the parental phenotype. However, substantial percentages of progeny from lamellated or lamellated/diapausing parental snails developed lamellae at 18 degrees C and underwent diapause. Only a small percentage of offspring from nonlamellated parents formed lamellae at this temperature. Juvenile snails exposed just prior to diapause, or immediately following a diapause period of three weeks, were highly susceptible to infection by S. mansoni miracidia. Snails that underwent diapause produced comparable or only slightly fewer cercariae than did nondiapausing snails. These studies indicate that diapause in B. glabrata does little to decrease a snail's ability to act as an intermediate host for S. mansoni or to interrupt the development of the parasite. For these reasons, we believe that greater attention should be given to diapausing snail populations when planning field surveys or mollusciciding programs.

Animals↗
PubMed1997

Human schistosomiasis in Puerto Rico: reduced prevalence rate and absence of Biomphalaria glabrata.

A combined epidemiologic and malacologic survey of schistosomiasis in Puerto Rico was carried out in areas where previous surveys had reported the prevalence of the disease. This limited survey, with 495 persons examined, found a low prevalence (0.6%) of Schistosoma mansoni infections. The infections were restricted to three people more than 36 years of age. No infections were detected in children 16 years of age or less, and this cohort comprised 57.8% of the study group. Malacologic surveys of the four streams, 10 rivers, and eight lakes throughout the island revealed the absence of intermediate host Biomphalaria glabrata and the presence of Thiara granifera, a competitive species of B. glabrata and the predatory snail Marisa cornuarietis. We believe that the absence of B. glabrata is the primary reason for the sustained reduction in the prevalence of schistosomiasis in Puerto Rico.

Adult↗
PubMed1998

Transfection and heat-inducible expression of molluscan promoter-luciferase reporter gene constructs in the Biomphalaria glabrata embryonic snail cell line.

Studies were initiated to begin developing a genetic transformation system for cells derived from the freshwater gastropod, Biomphalaria glabrata, an intermediate host of the human blood fluke Schistosoma mansoni. Using a 70-kD heat-shock protein (HSP70) cDNA probe obtained from the B. glabrata embryonic (Bge) cell line, we cloned from Bge cells a complete HSP70 gene including a 1-kb genomic DNA fragment in its 5'-flanking region containing sequences indicative of a HSP promoter. Identified in the 5'-half (416 nucleotides) of this genomic fragment were TATA and CAAT boxes, two putative transcription initiation sites, and a series of palindromic DNA repeats with shared homology to the heat-shock element consensus sequence (Bge HSP70(0.5k) promoter). The 3'-half of this upstream flanking region was comprised of a 508-base intron located immediately 5' of the ATG start codon. To determine the functionality of the putative snail promoter sequence, Bge HSP promoter/luciferase (Luc) reporter gene constructs were introduced into Bge cells by N-(1-(2,3-dioleoyloxy) propyl)-N,N,N-trimethylammonium methylsulfate (DOTAP)-mediated transfection methods, and assayed for Luc activity 48 hr following a 1.5-hr heat-shock treatment (40 degrees C). Compared with control vectors or the Bge HSP70(0.5k/1.0k) promoter constructs at 26 degrees C, a 10- to 300-fold increase in Luc expression was obtained only in the Bge HSP70 promoter/Luc-transfected cells following heat-shock. Results of transfection experiments demonstrate that the Bge HSP70(0.5k) DNA segment contains appropriate promoter sequences for driving temperature-inducible gene expression in the Bge snail cell line. This report represents the first isolation and functional characterization of an inducible promoter from a freshwater gastropod mollusc. Successful transient expression of a foreign reporter gene in Bge cells using a homologous, inducible promoter sequence now paves the way for development of methods for stable integration and expression of snail genes of interest into the Bge cell line.

Animals↗
PubMed2001

Short report: Schistosoma mansoni miracidia are killed by the defense system of an Argentine strain of Biomphalaria straminea.

Biomphalaria straminea snails from Argentina fail to shed cercariae even if exposed to high doses of Schistosoma mansoni EC miracidia. Alternative explanations for this failure are that miracidia are unable to penetrate the snail's epithelium or that the miracidia are killed by the snail's defense system. To discriminate between these 2 possibilities, B. straminea snails were individually exposed to increasing doses of miracidia. Susceptible B. glabrata were used as controls. Exposed snails were fixed 12 hr after exposure, and histological sections of the whole specimens were examined. Miracidia were seen to penetrate the epithelium of B. straminea and B. glabrata at similar rates (14.7%), independent of the exposure level. Regardless of the miracidial dose, 94% of the penetrating miracidia appeared encapsulated by the B. straminea defense system, whereas in B. glabrata, only 42% of the miracidia underwent encapsulation. These results show that resistance of B. straminea to S. mansoni EC strain is due to an efficient defense system that destroys miracidia once they have penetrated.

Animals↗
PubMed1976

Influence of diet on breeding and infectivity in mass cultivation of Biomphalaria glabrata.

Under well defined laboratory conditions as troughs, room temperature, humidity, water and air supply Biomphalaria glabrata was bred and kept. In feeding trials powder of pellets for mice and commercial fish food were used as high protein diet in comparison to poor protein diet consisting of lettuce only. The high protein diet resulted in more clutches and eggs per snail than the lettuce diet. Also the yield of cercariae in the rish protein group was much higher than in the group fed on on lettuce alone. The optimal amount of snails could be obtained by feeding pellet powder, fish food and lettuce.

Animals↗
PubMed1976

Genetic variation in two natural populations of Biomphalaria tenagophila: esterases and alcohol dehydrogenase.

The polymorphism of two natural populations of snails, Biomphalaria tenagophila, from São José dos Campos, São Paulo State (SJ) and from Núcleo Bandeirante, Distrito Federal (BN), was studied with respect to esterase and alcohol dehydrogenase (ADH) zymograms. The two population zymograms do not differ qualitatively. However the high frequency of esterase a and b bands in SJ and of e,f and h in NB, is a diagnostic mark. Moreover, frequency of band e alone can be used to distinguish the two populations. The high frequency of 3-banded ADH phenotype is a diagnostic mark of the SJ population.

Alcohol Oxidoreductases↗
PubMed1999

Genetic diversity and recruitment pattern of Schistosoma mansoni in a Biomphalaria glabrata snail population: a field study using random-amplified polymorphic DNA markers.

Random-amplified polymorphic DNA markers have been used to assess the amount and the distribution of the genetic diversity of Schistosoma mansoni within a natural population of Biomphalaria glabrata at a transmission site of the murine schistosomiasis focus of Guadeloupe. Despite high infection rate and heavy schistosome load within the definitive hosts (Ratus rattus), prevalences within intermediate snails ranged from 0.2 to 4.8%. Whatever the transmission season may be (rainy vs. dry), most of the infected snails were spatially aggregated and 88.4% of them harbored a single parasite genotype indicative of a monomiracidial infection; 4.7% had dual sex infections and a parasite intensity not exceeding 3 miracidia per snail. A substantial resistance level toward the parasite and recruitment regulatory process within snails may explain in part the observed low parasite prevalences and intensities. Considering such a distribution pattern of larval S. mansoni genetic diversity among B. glabrata, mobility of the definitive hosts, or rapid turnover of infected snails, or both, are required to maintain genetic heterogeneity within adult schistosome populations.

Animals↗
PubMed1999

Some aspects of nitrogen metabolism in Biomphalaria alexandrina snails treated with selenium.

The toxicity of selenium on Biomphalaria alexandrina snails, intermediate host for Schistosoma mansoni, was traced by studying its effect on the protein profile, free amino acids (FAA) and some urea cycle enzymes, namely, ornithine aminotransferase, argininosuccinate synthetase and arginase in hepatopancreas of snails. The results revealed that treatment with 15 ppm selenium dioxide (SeO2) caused an elevation in the protein content and a variation in the percentage and number of the different polypeptides as obtained by gel electrophoresis, and a remarkable reduction in all FAA except arginine alanine and threonine. On the other hand, the activity of ornithine, aminotransferase was elevated whereas that of arginase was reduced. The study is a trial to focus some metabolic disorders caused by SeO2 on the physiological status of these intermediate host snails, which may greatly control parasite-host association and thus the life-cycle of the parasite within its respective host may be somewhat disturbed.

Animals↗
PubMed1999

Factors affecting adoptive transfer of resistance to Schistosoma mansoni in the snail intermediate host, Biomphalaria glabrata.

We examined potential variables affecting adoptive transfer of resistance to Schistosoma mansoni in Biomphalaria glabrata implanted with amebocyte-producing organs (APOs) from resistant snails. Transplants of 7 tissues other than the APO (heart, kidney, mantle, albumin gland, brain, digestive gland, and gonad) did not transfer resistance, suggesting a unique property of this structure. Only APOs from donors previously exposed to miracidia transferred resistance, although whether this is evidence for a priming effect or merely the elimination of susceptible donors is not known. Variability in the donor and in the implant itself apparently was unimportant, inasmuch as implants from small or large snails or from 2 separate donors all conferred similar levels of resistance. Recipients of APOs from 2 additional resistant strains of B. glabrata, 10-R2 and Salvador, also displayed resistance. However, no resistance was transferred by APOs from schistosome-refractory B. obstructa. Histological examination of implants removed from recipients that either did or did not show transferred resistance revealed no differences in mitotic activity. Furthermore, implanted APOs from B. obstructa displayed no mitotic activity. Finally, reexposure of snails with transferred resistance to a large dose of miracidia caused infection in 70%, suggesting that either transferred resistance is transitory or it can be overwhelmed.

Adoptive Transfer↗
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↗
PubMed1975

Distribution of the snail Biomphalaria glabrata, intermediate host of Schistosoma mansoni, within a St Lucian field habitat.

A total of 6360 mud samples were obtained, in 62 collections made with an exhaustive sampling device, from banana drains on the West Indian island of St Lucia during fortnightly samplings over a 2(1/2)-year period. Analysis of counts of the snail Biomphalaria glabrata from these samples showed that this species had a contagious distribution. This finding is consistent with other evidence that banana drains form a rigorous habitat for B. glabrata. Its distribution was more contagious than that of Oncomelania quadrasi in certain Philippine habitats and several species of aquatic snail in various African irrigation canals. The exact transformation for normalizing the snail counts for standard statistical techniques was z = x(0.287) but the more convenient cube root transformation is probably adequate. However, if too few snails are collected (15 or fewer per 100 samples) or if the frequency distribution of snail counts is discontinuous, with too many widely separated high frequency counts, neither transformation will be entirely satisfactory.

Animals↗
PubMed1976

The suppression, by Helisoma duryi, of the cercarial production of Schistosoma mansoni-infected Biomphalaria pfeifferi.

Biological control of the intermediate hosts of Schistosoma mansoni and S. haematobium by means of a competitor snail, Helisoma duryi, has been suggested. In the present laboratory study, the influence of H. duryi on the relationship between the parasite and the intermediate host was investigated. The results indicated that H. duryi behaves as a "decoy" if it is present when Biomphalaria pfeifferi is exposed to the miracidia of S. mansoni, and that the continued presence of H. duryi in the aquarium after B. pfeifferi has been exposed greatly reduces cercarial production. When these two species were present in equal numbers, cercarial production was reduced by 95.9% in comparison with a control group.

Animals↗
PubMedDate not supplied

[Susceptibility of Biomphalaria glabrata to Schistosoma mansoni from Venezuela and Brazil].

Schistosoma mansoni partially develops its life cycle into snails of the Family Planorbid. Biomphalaria glabrata represents an important host-intermediate. This paper reports experimental infection with miracidia vs. snail in sympatric and parapatric combination. The infection assay to sympatric combination were: BH snail (Belo Horizonte, Brasil) vs. a common geographic origin parasite, and Barbula, Carabobo State, Venezuela vs. SM Venezuela parasitic. The parapatric combination were: BH snail vs. SM; Barbula vs. BH; Caripe Monagas State, Venezuela vs. SM and Caripe vs. SM. During the study period was observed not miracid penetration. The infection percentage ranged from 88.89% in Barbula vs. SM combination to 0.00% in the Caripe vs. BH and BH vs. SM combination. We concluded which different existence of susceptibility from evaluated combination.

Animals↗
PubMed2000

Comparative studies for development of Schistosoma mansoni sporocysts in Puerto Rican and Brazilian Biomphalaria glabrata.

The development of sporocysts of Schistosoma mansoni was monitored in pigmented and albino Biomphalaria glabrata from Puerto Rico and Brazil. The snails were exposed individually to 20 miracidia, and sporocysts were allowed to develop for 3 to 12 weeks. Most of the immature sporocysts were found in the seminal receptacle sac and vas deferens during development. In contrast, mature daughter sporocysts were detected everywhere except in the foot at 12 weeks after exposure to the miracidia. It was found that mature daughter sporocysts formed more rapidly in the pigmented than in the albino snails, but no difference was observed in the formative time between the same types of Puerto Rican and Brazilian snails. It seems likely that there is a correlation between the infection rate and the time required for formation of mature daughter sporocysts in B. glabrata.

Animals↗