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Effects of Schistosoma mansoni on the nutrition of its intermediate host, Biomphalaria glabrata.

Biomphalaria glabrata infected with Schistosoma mansoni and maintained on an artificial diet of Spirulina alga displayed reduced growth during the 5 wk following patency. Food consumption per unit snail weight was unaffected. Infected snails also failed to lay eggs. No difference in percentage of assimilation was observed between control and infected individuals, but infected snails had significantly decreased gross conversion efficiencies. The effects of infection on nutrition of B. glabrata were similar to those observed in nutrient-deprived snails fed diets containing low Spirulina levels. Nutrient deprivation, however, did not alter conversion efficiency.

Animal Nutritional Physiological Phenomena↗

The effect of size of M line Biomphalaria glabrata on the course of development of Echinostoma paraensei.

M line Biomphalaria glabrata snails of 4-, 6-, 8-, 10-, 12-, or 20-mm shell diameter were individually exposed to 10 miracidia each of Echinostoma paraensei. Snails 10 mm in size or larger were found to be significantly less likely to harbor intraventricular sporocysts than snails in smaller size categories. The percentage of snails with intraventricular sporocysts that also developed hemocyte encapsulation responses generally increased with snail size, whereas the number of snails that ultimately became heavily parasitized with large numbers of daughter rediae decreased significantly with snail size. However, at least some snails in each size category developed such disseminated infections. Comparative histological study of 6- and 12-mm snails revealed that parasites readily penetrated both groups of snails, but were more likely to be encapsulated and destroyed in larger snails. Encapsulation reactions were noted from 1 to 15 days postexposure (dpe) in 12-mm snails, indicating that unlike other commonly studied models of trematode-gastropod interactions, snail resistance is not always manifested during the first few days following exposure. Upon infection with E. paraensei, both 6- and 12-mm snails showed significant increases in the number of circulating hemocytes/mm3 of hemolymph. In 6-mm snails, such increases occurred concurrently with successful parasite development. Hemocyte counts in 6-mm snails were significantly elevated from 4 to 15 dpe whereas in 12-mm snails they were significantly elevated from 2 to 30 dpe. A significant degree of resistance to E. paraensei develops as B. glabrata grows and attains sexual maturity. A mechanistic understanding of this phenomenon awaits further investigation.

Animals↗

The genetic variation of compatibility in Biomphalaria glabrata and Schistosoma mansoni.

Interactions between different Biomphalaria glabrata stocks and Schistosoma mansoni strains were studied. A series of inbred stocks of B. glabrata were characterized as to genetic variations in susceptibility at different ages to a series of different S. mansoni strains. A series of inbred strains of S. mansoni were characterized as to genetic variations in infectivity for B. glabrata stocks at different ages. Also described is a process of selection for substrains from a single S. mansoni isolate that differ genetically in snail infectivity.

Animals↗

The effect of seasonal temperature and experimental illumination on reproductive rate in the snail Biomphalaria glabrata.

1. Reproduction in the snail Biomphalaria glabrata, a vector of Schistosoma mansoni, was measured by egg production and other parameters such as number of clutches, eggs per clutch and egg hatching, under laboratory conditions. 2. Reproductive rates were highest in terms of total number of eggs, clutches and hatching under constant illumination, followed by conditions similar to the natural rhythm of illumination. The greatest reduction in reproduction occurred in constant darkness. In summary, reproductive rate was dependent on both the intensity of absolute illumination and the schedule of illumination exposure. 3. Seasonal variation in reproductive rate appeared to vary inversely with local temperature in Belo Horizonte, situated in a tropical zone (latitude 20 S) owing probably to a temperature preference of 20 to 25 degrees C by the snail. The highest reproductive rates occurred in winter, except for the parameter eggs per clutch which was maximal in autumn. Snail reproduction appeared to be most reduced during summer. There was no linear correlation between reproductive rate and temperature.

Animals↗

Characterization of the 31P NMR spectrum of the schistosome vector Biomphalaria glabrata and of the changes following infection by Schistosoma mansoni.

The 31P nuclear magnetic resonance (NMR) spectrum of the digestive gland-gonad complex (DGG) of the schistosome vector Biomphalaria glabrata was characterized and the effects of infection by Schistosoma mansoni noted. The in vivo spectrum was comprised of 11 peaks, 5 downfield and 6 upfield of an external 85% phosphoric acid standard. Based on a variety of analytical procedures, the upfield peaks from the standard were demonstrated to be composed of carbamoyl phosphate + a mixture of 3 phosphatides and sphingomyelin, the gamma + beta phosphorus resonances of nucleotide triphosphate (NTP) and nucleotide diphosphate (NDP), respectively, the alpha phosphorus resonances of NTP + NDP, NAD(H) + the phosphorus resonance of uridine phosphate from uridine diphosphoglucose (UDPG), the phosphorus resonance of glucose phosphate from UDPG and, last, the beta phosphorus resonance of NTP. The downfield peaks were assigned as glycerophosphoryl choline, intracellular inorganic phosphate (Pi), sugar phosphates + phosphoryl choline, aminoethyl phosphonate (AEP), and ceramide AEP. T1 values for the in vivo NMR components were determined by inversion recovery. Infection produced distinct alterations in the levels of nonnucleotide components of the in vivo 31P NMR spectrum and the spectra of tissue extracts. Specifically, the levels of phosphonate, phospholipids, and carbamoyl phosphate were markedly reduced, and the relative level of Pi was increased. The potential significance of these changes to the parasite-host relationship was discussed. In contrast, starvation resulted in a decreased level of phosphonate only. The pH of the intact DGG was estimated by titrating the inorganic phosphate component of tissue extracts. The mean pH was 6.9 for both control and infected material.

Animals↗

Alterations in Biomphalaria glabrata plasma induced by infection with the digenetic trematode Echinostoma paraensei.

Alterations in the noncellular hemolymph components of M line Biomphalaria glabrata snails infected with the trematode Echinostoma paraensei for 1, 2, 4, 8, 15, 30, or 60 days were monitored by direct microscopical examination, and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in conjunction with quantitative densitometry. A prominent particulate substance was first noted in the hemolymph of infected snails at 1 day postexposure (PE), persisted through day 15, and subsided by day 30. This substance, which was not observed in control snails, contained 2 major polypeptides of 190-200 and 80-120 kDa. Infection with E. paraensei also induced substantial changes in soluble hemolymph polypeptides. PAGE lanes loaded with plasma samples from M line snails infected for 4, 8, 15, and 30 days exhibited a generalized increase in staining intensity relative to controls. A diffuse band centered at approximately 100 kDa, but of variable width, was selectively enriched relative to control preparations in snails with 4-, 8-, 15-, and 30-day-old infections. Standard protein assays also indicated an increase in total protein content of plasma samples from snails infected for 2-60 days, with significant increases noted at 4, 8, and 30 days. Infected snails of the 10-R2 strain of B. glabrata also contained particulate material in their hemolymph. However, soluble hemolymph components of 10-R2 snails exhibited relatively little change, or declined, as a result of infection. For either strain, no new bands could be detected in plasma samples from infected snails, nor were any bands consistently deleted as a result of infection. Although both snail strains exhibit alterations in hemolymph components as a result of infection, their responses differ qualitatively and quantitatively.

Agglutinins↗

Interaction between the Biomphalaria glabrata-Schistosoma mansoni host-parasite system and the non-target molluscs: influence on cercarial production.

The cercarial production of Schistosoma mansoni by Biomphalaria glabrata (target mollusc: TM) was studied in relation to the presence of non-target molluscs (NTM). Nine species of NTM were tested. Whatever the type of TM-NTM association (lasting association, during prepatent period and production period, association only during the exposure of the molluscs to the miracidia), the presence of NTM involved a significant increase of S. mansoni cercarial production. This increased cercarial production was more or less pronounced according to the NTM species present.

Animals↗

Effects of environmental calcium on fecundity and cercarial production of Biomphalaria glabrata (Say) infected with Schistosoma mansoni Sambon.

Biomphalaria glabrata were reared in stock culture and subjected to either 7-day or 60-day acclimation periods in complex CaCO3 media with calcium values ranging from 1.5 mg/L to 75 mg/L. Following 60-day acclimation, snails from series I were each exposed to 8 miracidia of Schistosoma mansoni. Snails of series II were each exposed to a single miracidium. Snails of both experimental regimens were observed for mortality, growth, rate of infection, and number of cercariae shed. Series I snails were also monitored for fecundity during acclimation and following miracidial exposure. Calcium levels of 1.5 and 75 mg/L resulted in significant snail mortality. Shell growth and rates of infection were positively correlated with calcium maintenance level. Snails with high fecundity prior to miracidial exposure subsequently shed more cercariae. In contrast, post-exposure (PE) fecundity of snails reared in media with up to 30 mg/L Ca++ were negatively correlated with calcium level, infection rate, and number of cercariae shed. Maximal cercarial emergence occurred at 30 mg/L Ca++. These results suggest that environmental calcium affects both the distribution patterns of snail hosts of human schistosomes and the productivity of intramolluscan schistosome infection.

Animals↗

Isolation and partial characterization of shared antigens of Biomphalaria glabrata and Schistosoma mansoni and their evaluation by the ELISA and the EITB.

Serum from humans infected with Schistosoma mansoni, when reacted with a Biomphalaria glabrata soluble hepatopancreas antigen extract (BgSHA) yields 2 lines of precipitation by gel diffusion and 1 by immunoelectrophoresis. The IgG from the serum of a human infected with S. mansoni was coupled to CNBr-activated Sepharose 4B. BgSHA (8.0 mg) was then filtered through the gel and the bound antigens, denoted BgSm, eluted with HCl-glycine, pH 2.6. These bound antigens comprised 2.8% of the total BgSHA. BgSm was then applied to an anti-Fasciola hepatica column as above. The drop through in PBS (38% yield) and containing the BgSm antigens depleted of cross-reactivity with F. hepatica was then tested by the ELISA to evaluate its serodiagnostic potential. These antigens detected a primary S. mansoni infection by 4 wk but were less sensitive than SmSEA in the detection of a primary infection with S. mansoni. However, the BgSm-specific antigens were more specific than SmSEA and showed less cross-reactivity with the serum of mice infected with F. hepatica. At least 16 peptides were seen by silver staining following SDS-PAGE with 5-20% gradient gels. The 2 more prominent bands obtained were estimated to have molecular weights of 62 and 66 kd. Nitrocellulose strips blotted with BgSHA were incubated with the serum of mice infected with S. mansoni for 12 wk and developed 6 bands with molecular weights of 66, 57, 55, 50, 48 and 32 kd.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Schistosoma mansoni (Gezira) infection in Biomphalaria pfeifferi snails from Gezira and Jebel Marra.

The comparative susceptibility of Biomphalaria snails from Gezira and Jebel Marra to S. mansoni (Gezira) was investigated. Groups of laboratory-bred snails from the two localities were exposed to 0, 1, 2, 3 and 4 miracidia. The growth rate of the snails was followed over the experimental period by measuring the snails' shell size. Sub-groups of infected snails were examined for daughter sporocyst counts by crushing of the snails. Other groups of exposed snails were maintained until cercariae were shed. The exposed snails grew faster than the controls and growth was not dependent on the number of infecting miracidia. Jebel Marra snails grew faster than the Gezira snails and development of the daughter sporocysts within the snails was temperature dependent. Daughter sporocysts were first found on day 19 after exposure when the laboratory temperature ranged between 18 and 25 degrees C and on day 10 at a range of between 28 and 30 degrees C. Daughter sporocysts and cercarial counts overlapped in numbers per snail exposed to 1, 2, 3 and 4 miracidia for both Gezira and Jebel Marra snails. Nine out of 78 Jebel Marra snails were negative for daughter sporocysts, while all of the Gezira snails were positive. This might indicate greater susceptibility of the Jebel Marra snails to the parasite. Our experiments showed that snails from Jebel Marra are capable of supporting an S. mansoni infection from the Gezira until cercariae are shed. The epidemiological significance of the migrant labourers to the Gezira area in the transmission and spread of intestinal schistosomiasis in Jebel Marra is discussed.

Animals↗

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↗

31P NMR studies on adenylates and other phosphorus metabolites in the schistosome vector Biomphalaria glabrata.

31P nuclear magnetic resonance spectroscopy was applied successfully to whole intact and de-shelled snails and to the isolated digestive gland-gonad tissue complex as well as other tissues of Biomphalaria glabrata. Several phosphorus metabolites, including ATP and ADP, were observed. The mean ATP/ADP ratio calculated for the tissue complex was 3.1 and the ATP concentration was 0.73 nmoles/mg tissue fresh weight. Assignments for AMP, sugar phosphates, and inorganic phosphate peaks were tentatively made. A major phosphorus component was identified as a phosphonate and this metabolite was also present in egg masses and the albumin gland. Phosphoarginine was not observed in the tissue complex but was present in whole animals. Infection by Schistosoma mansoni resulted in marked alteration in the relative levels of phosphorus metabolites in the digestive gland-gonad complex during the course of infection. The decrease in phosphonate was particularly notable. The relative level of a metabolite occurring at -1.1 ppm was also decreased but its identity remained unknown. The ATP/ADP ratio was not affected by infection, but an increase in the relative level of inorganic phosphate suggested a possible decrease in phosphorylation potential.

Adenine Nucleotides↗

Laboratory observations on the biological control of Biomphalaria glabrata by a species of Pomacea (Ampullariidae).

Laboratory experiments have shown that medium-sized (30-50 mm in shell height) Pomacea sp. snails consumed the egg masses of Biomphalaria glabrata deposited either on glass or on the leaves of Salvinia, and that they also caused a high mortality rate among the newly hatched B. glabrata. When the two species of snail were kept in the same tank, the Pomacea sp. caused a reduction in the B. glabrata egg density in proportion to their relative numbers and the presence of Pomacea sp. prevented colonies of B. glabrata from becoming established. The identity of the Pomacea sp. has not yet been satisfactorily established.

Animals↗

The biology of Biomphalaria choanomphala and B. sudanica in relation to their role in the transmission of Schistosoma mansoni in Lake Victoria at Mwanza, Tanzania.

A study of the intermediate snail hosts of Schistosoma mansoni in Lake Victoria at Mwanza, Tanzania, was begun in October 1969, the main aims being to investigate the distribution and seasonal variations in population densities of Biomphalaria choanomphala and B. sudanica in relation to the nature of the lake bottom and the biological features of the lake shore, the factors influencing variations in the intensity of S. mansoni transmission along the Mwanza shoreline, and the age structure of populations of B. choanomphala. Field surveys were made at 70 sites near Mwanza and in nearby bays, B. choanomphala being collected from the lake bottom by means of a wire-mesh dredge. Variations in the distribution and population density of B. choanomphala were correlated with the nature of the bottom and its depth profiles at depths of 0.5-6.0 m. Approximately 1-20 snails/m(2) were found on mixed sand and mud but only about 1 snail/m(2) on the predominantly muddy bottom farther out from the shore. Seasonal variations in the age structure and fluctuations in the population densities of B. choanomphala of as much as 10-13-fold were observed. A large and a small form of B. choanomphala, possibly ecophenotypes, were found. S. mansoni infection rates in B. choanomphala ranged from 0.2% to 3.3%, suggesting a tendency to higher infection rates in mature snails.

Animals↗

Histochemical and electrophoretical studies in normal and infected Biomphalaria glabrata. II. Acid and alkaline phosphatase.

Various organs of normal and infected Biomphalaria glabrata were analysed, electrophoretically and histochemically, with respect to the acid phosphatase and alkaline phosphatase activity. In general, digestive gland, ovotestis and stomach show an increase in acid phosphatase activity in infected snails, whereas kidney and albumen gland show less activity. Alkaline phosphatase does not show any significant different in activity between normal and infected snails. Electrophoretically digestive glands of snails, twenty days after infection, show an extra faint band, whereas seven days after infection, the snails do not show any such extra band. Histochemically also after twenty days, infected snails show more activity in the sporocyst region, but those infected for only seven days, do not show any increase in acid phosphatase activity.

Acid Phosphatase↗

[Evaluation of a trial to control Biomphalaria glabrata in Guadeloupe by using a sterilizing trematode (author's transl)].

A trial of biological control of Biomphalaria glabrata was carried out in Guadeloupe by using Ribeiroia marini guadeloupensis Nassi, 1978, an autochtonal Trematode which sterilizes the snail vector of Schistosoma mansoni. The trial took place in a pond in which the population of B. glabrata presents an annual demographic cycle related to the alternation of dry and rainy seasons. About 8 millions eggs of R. marini were introduced in 15 months into the biotope. Despite the low yield of these introductions, due particularly to the high turbidity of the water, this trial gave positive results in the disappearance of almost all the snails. The analysis of the results concerning the evolution of the levels of the snails and of the prevalence shows that a comparable efficiency could be obtained by massive introductions of eggs during short periods.

Animals↗

Effect of Schistosoma mansoni infection on fecundity and perivitelline fluid composition in Biomphalaria glabrata.

Egg production in the snail, Biomphalaria glabrata, infected with Schistosoma mansoni declined on day 23 postinfection, and was significantly lower than uninfected control snails by day 28 and thereafter. Protein and galactogen content of eggs produced by infected snails did not change during the period of reduced fecundity. This suggests that decreased hemolymph nutrient levels (rather than depleted albumen gland reserves) are responsible for inhibition of snail egg production. Growth rates of infected and uninfected snails were indistinguishable from days 14 through 35 postinfection. The hatching success of eggs produced by infected snails decreased slightly beginning at day 21 postinfection.

Animals↗

Interactions between St. Lucian Biomphalaria glabrata and Helisoma duryi, a possible competitor snail, in a semi-natural habitat.

In artificial drains similar to those used in banana culture on St. Lucia, Helisoma duryi, the rams-horn snail, controlled Biomphalaria glabrata, intermediate host of schistosomiasis on that island. Time required for elimination of B. glabrata depended on environmental temperature and numbers of H. duryi initially introduced in the drains. Best fit to the data was given by the equation for the logistic curve rather than by an equation for unlimited growth. Multiple regression analyses of natality and mortality rates of both species of snails indicated that populations of B. glabrata were regulated by temperature rather than by density-dependent means while numbers of H. duryi were strongly influenced by numbers of rams-horn snails already present in the drains. Fitting of snail shell growth to von Bertalanffy equations showed that H. duryi shell diameter was uninfluenced by environmental temperatures or presence of B. glabrata while growth of the intermediate host was strongly affected both by temperature and numbers of H. duryi.

Animals↗