The influence of anhydrobiosis on the infestation of Biomphalaria glabrata by Schistosoma mansoni miracidium

410 Biomphalaria glabrata (Caribbean strain of Guadeloupe) have been infected with one miracidium of Schistosoma mansoni, 110 snails, used as controls have been kept into water; the survival rate was 96.4% after 4 weeks and 25.4% produced cercariae. 300 snails were kept on wet soil, and submitted for 6 weeks to progressive desiccation. The survival rate was 23.4% but only 9 of them produced cercariae. Periodic variations of the production of male and female larvae have been shown by the weekly test of the cercariae productions. In previously desiccated snails, the production of male and female cercariae is similar while in controls the production of female larvae is more important. In experimental snails, the larval development seems to be stopped during anhydrobiosis. The production of cercariae is just delayed for the length of the dry keeping.     

Transient cellular reaction in Biomphalaria glabrata (Mollusca) to heterotopic isografts

Heterotopic isografts consisting of pieces of digestive gland were implanted into the cephalopedal sinuses of speciments of a strain of Biomphalaria glabrata from Brazil. Histological examination at 2, 24, 48, and 192 hr post-transplantation revealed that only the first phase of the encapsulation process, as defined by Jourdane and Cheng (1987), occurred. Furthermore, the cellular reaction was patchy and occurred only at 2, 24, 48, and 72 hr at sites where the surfaces of the grafts had been damaged. Death of isografts was not observed. In fact, regeneration of digestive gland acini probably occurred at 72 hr and later. By comparing the reported results with those involving allografts (Jourdane and Cheng, 1987), it is concluded that this strain of B. glabrata can discriminate between heterotopic iso- and allografts.     

The snail (Biomphalaria glabrata) genome project

In 2001, ideas for a snail genome project were discussed at the American Society of Parasitologists meeting (New Mexico) and a snail genome consortium was subsequently established (the first consortium meeting was held in 2005). A proposal for sequencing the snail genome was submitted to the National Human Genome Research Institute, and Biomphalaria glabrata was prioritized as a non-mammalian sequencing target in 2004. The sequencing of the genome of this medically important snail is now underway.     

Effects of eugenol and derivatives on Biomphalaria glabrata

Biomphalaria glabrata snails and egg-masses were exposed, for six to twenty-four hours to concentrations of 1, 10, 100 and 1000 ppm of Eugenol, O-methyleugenol, O-benzyleugenol and dehydrodieugenol. Only at 10 ppm O-benzyleugenol enhanced mortality of snails and egg-masses. The other substances showed ovicidal and molluscicidal activity only at 100 and 1000 ppm concentrations, causing a significant cardiac frequency reduction in snails after 6 to 24 hours of exposure as well as perduring low cardiac rates until 24 hours afterwards. Two specimen exposed to 100 ppm O-methyleugenol presented anesthetic effect and extrusion of copulator and urethral organs. No schistosomicide or anesthetic effects were observed in mice experimentally infected with Schistosoma mansoni and treated during 5 days with oral doses of 150 mg/kg of Eugenol, O-methyleugenol and O-benzyleugenol.     

The effect of schistosome excretory-secretory products on Biomphalaria glabrata hemocyte motility

Excretory-secretory (E-S) products contained in supernatants from in vitro cultured Schistosoma mansoni primary sporocysts were assayed for their effects on the in vitro motility of Biomphalaria glabrata hemocytes. Both whole (unfractionated) and fractionated E-S products were tested in modified Boyden chemotaxis chambers. E-S product fractionation was accomplished using both membrane ultrafiltration (MF) and high-pressure liquid chromatography (HPLC). Transformation (Tr) products, but not those products released by 8-day sporocysts, significantly inhibited the random motility of hemocytes from an S. mansoni susceptible strain (M-Line) of B. glabrata. This activity was found in both high and low MF fractions of Tr but not in an intermediate MF fraction. In an effort to isolate the active component(s) of the high MF fraction, HPLC was used to separate components based on size exclusion. Although each of four HPLC fractions displayed some inhibitory activity, the greatest consistent activity was found in fraction 3, which was composed, predominantly, of a 108-kDa protein. In contrast to the response of M-Line cells to Tr E-S products, the motility of hemocytes from an S. mansoni-resistant strain (10-R2-OK) of B. glabrata was not significantly reduced from controls. The high MF fraction, however, elicited a slight positive chemokinetic response, while the low MF fraction reduced 10-R2-OK hemocyte motility slightly but not significantly. While three HPLC fractions significantly reduced 10-R2-OK hemocyte motility, this effect was significantly less than that produced by the same HPLC fractions on M-Line hemocyte motility. These data suggest that S. mansoni sporocyst Tr E-S products differentially affect the random motility of M-Line and 10-R2-OK snail hemocytes. Although the significance of this differential effect on the in vivo defenses of B. glabrata is not known, it could be important in the host-parasite interaction which leads to either resistance or susceptibility.     

The significance of the amoebocyte-producing organ in Biomphalaria glabrata

In molluscs, internal defence against microorganisms is performed by a single cell type, i.e., the haemocyte or amoebocyte. The origin of these cells in Biomphalaria glabrata was initially thought to be localised within the vasculo-connective tissue. More recently, origin from a single organ, termed the amoebocyte-producing organ (APO), has been postulated based on the occurrence of hyperplasia and mitoses during Schistosoma mansoni infection. The present investigation represents a histological, immuno-histochemical and ultra-structural study of the B. glabrata APO, whereby histological identification was facilitated by means of collecting epithelial basophilic cells. These cells were comprised of single-cell layers that cover a portion of the stroma, which contains many small, round cells and haemolymph sinuses, as well as a small area of the pericardial surface of the reno-pericardial region. On occasion, this epithelial component vaguely resembled the vertebrate juxtaglomerular apparatus, which reinforces its presumed relationship to the kidney. Both in normal and infected molluscs, mitoses were only occasionally found. The present quantitative studies failed to demonstrate the presence of APO cellular hyperplasia, either in normal or schistosome-infected B. glabrata. Conversely, several structural details from the APO region in B. glabrata were found to be consistent with the hypothesis that the APO is a filtration organ, i.e., it is more closely related to the kidney rather than the bone marrow, as has been suggested in the literature.     

The galactan-degrading enzymes in the snail Biomphalaria glabrata.

1. Embryonic snails incorporate from the perivitelline fluid in which they are embedded a polysaccharide, called galactan, which is composed entirely of D-, or D- and L-galactose. In this investigation the p-nitrophenyl-beta-D-galactoside degrading enzyme of Biomphalaria glabrata which was assumed to be involved in the degradation of the galactans was purified almost to homogeneity and its specificity was studied. 2. It has a mol. wt of 135,000 and is composed of two identical subunits. 3. It could be shown that p-nitrophenyl-beta-D-fucoside was hydrolysed eight times faster, but native galactan was neither decomposed nor was it inhibitory for the hydrolysis of p-nitrophenyl-glycosides. 4. Thus, it is most likely that this galactosidase is not involved in the galactan metabolism. 5. However, a membrane-bound enzyme complex was revealed which was able to metabolize the native galactan of Biomphalaria glabrata completely and which showed graded reactivity towards galactans of other species. 6. Since no intermediate degradation products were found it must be assumed that they were metabolized further in the mitochondria.     

Biomphalaria glabrata in the state of Piaui

The occurrence of Biomphalaria glabrata is recorded for the first time in the state of Piaui, where it was collected from several breeding places in the city of Parnaíba. Examination of 694 specimens showed that a part of them were infected with trematodes other than Schistosomatidae. So far no autochthonous cases of schistosomiasis have been identified in the city. The presence of B. glabrata in Parnaíba extends by 20 km eastward its range on the Northern Coastal Region of the Great Northeastern Region of Brazil, where it had been found as far as Araioses, on the eastern extreme of the state of Maranh?o.     

Molluscicide activity of some natural products on Biomphalaria glabrata

The molluscicide activity of aqueous (macerated and boiled), hexanic and ethylic extracts of Aristolochia brasiliensis, Caesalpinia peltophoroides, Caesalpinia pulcherrima, Delonix regia, Spathodea campanulata and Tibouchina scrobiculata was evaluated in the laboratory. The solutions obtained from those extracts were tested on adults and egg masses of Biomphalaria glabrata reared in the laboratory at 1, 10, 20, 100 and 1000 ppm concentrations. The most active of the extracts studied was D. regia flowers' (flamboyant) ethylic extracts which presented molluscicidal activity on adult snails at 20 ppm.     

Schistosoma mansoni: influence of Biomphalaria glabrata size on susceptibility to infection and resultant cercarial production

Biomphalaria glabrata snails of the same age, but different sizes, were used to determine size-related susceptibility to Schistosoma mansoni miracidial infection and the influence of snail size on total cercarial production. Snails with shell diameters from less than 5 to greater than 17 mm were individually exposed to one or several miracidia, depending on the experiment. In snails exposed to multiple numbers of miracidia, the percentage of snails which developed patent infections was lower in snails with larger shell sizes. This was also reflected by fewer primary sporocysts per infected snail found in tissues of the larger snails. Upon determining cercarial production in these groups over a 1-month period there were no statistical differences between any groups in the numbers of cercariae produced per snail. However, upon determining the number of successful primary sporocysts found in cohort snails of each size group, cercarial production increased as a function of the number of successful primary sporocysts. This was verified by examining cercarial production in various size snails with known monomiracidial infections. Our data therefore confirm and extend earlier work using snails infected with unknown numbers of miracidia and clearly show that total S. mansoni cercarial development and decreased susceptibility of snails is a direct reflection of snail size and not necessarily age of the snail.     

The food-finding orientation mechanism of Biomphalaria glabrata (Say)

An experimental procedure involving the use of time-lapse cinematography for accurately recording pathways was used to investigate the responses of Biomphalaria glabrata (Say) to a stimulus source of plant chemicals. This allows a more detailed analysis of the orientation mechanism than is the case with the Y-maze method. Snails of this species, which are essentially herbivorous, respond either by klinotaxis or tropotaxis or both to a source of plant chemicals. It was not possible to demonstrate the involvement of kinesis in the orientation mechanism.     

Schistosoma mansoni modulation of phagocytosis in Biomphalaria glabrata

Both short-term (3 hr) exposure of Biomphalaria glabrata snails (M-line and 13-16-R1) to Schistosoma mansoni (PR1) miracidia and in vitro incubation of parasite sporocysts with host hemolymph components altered host phagocytic ability. Hemocytes obtained from susceptible (M-line) snails that had been exposed to parasite miracidia for 3 hr showed reduced levels of phagocytosis of yeast cells in vitro compared to hemocytes from unexposed individuals. Incubation of whole hemolymph with sporocysts in vitro also reduced yeast phagocytosis in this susceptible strain. In contrast, resistant (13-16-R1) hemocytes showed increased levels of yeast phagocytosis after in vitro incubation with the parasite, and the opsonic properties of 13-16-R1 plasma were greater after exposure of snails to miracidia. These strain-specific effects of S. mansoni on host hemocyte phagocytosis and plasma opsonization were seen only when both plasma and hemocytes were present at the time of exposure to the parasite.     

On the origin of the Biomphalaria glabrata hemocytes

A histologic, morphometric and ultrastructural study performed on Biomphalaria glabrata submitted to infection with Schistosoma mansoni miracidia failed to provide significant evidences that the so-called amebocyte-producing organ (APO) is really the central organ for hemocyte production. In infected snails no general reactive changes appeared in the APO, the mitoses were seen only occasionally, and the possibility of cellular hyperplasia was ruled out by morphometric measurements. Under the electron microscope the APO cells presented an essentially epithelial structure, without features indicative of transition toward hemocytes. On the other hand, the present findings pointed to a multicentric origin for the mollusc hemocytes, as earlier studies had indicated. Dense foci of hemocyte collections appeared sometimes around disintegrating sporocysts and cercariae in several organs and tissues of the infected snails, including a curious accumulation of such cells inside the ventricular cavity of the heart. In the heart and other sites, features suggestive of transformation of vascular space endothelial lining cells into hemocytes were apparent. To some extent, the postulated multicentric origin for B. glabrata hemocytes recapitulates earlier embryologic findings in vertebrates, when mesenchymal vascular spaces generate the circulating and phagocytic blood cells.     

Internal defenses of the snail Biomphalaria glabrata.

We describe three distinct types of cells among Biomphalaria glabrata hemocytes: large cells with a tubulo-vesicular compartment, a component of the endocytic system, and with numerous mitochondria and large aggregates of glycogen particles; medium-size cells poor in organelles and glycogen; and small cells with organelles and few secretory granules. Other small hemocytes can be interpreted as juvenile cells. B. glabrata hemocytes contain few enzymes and do not show specific secretory granules, except for a subpopulation of large cells richer in acid phosphatase vesicles. Hemocytes have different aspects corresponding to different physiological states and their transitions: in quiescent hemocytes, the cell cortex is narrow and organelles are scattered in the cytoplasm, both in circulating cells characterized by thin-folded filopods and large macropinocytic vacuoles and in sedentary cells in which extended filopods connect to the extracellular matrix. In stress-activated hemocytes, the cortical region is thickened by polymerization of actin, and organelles are gathered around the nucleus. Fixed phagocytes are components of the connective tissue; the presence of numerous lysosomes and residual bodies and of acid phosphatase and peroxidase activities suggests a high phagocytic activity.     

Effect of manganese on Biomphalaria glabrata infected with Schistosoma mansoni

This paper discusses observations on the emergence of Schistosoma mansoni from the snail Biomphalaria glabrata exposed to manganese sulfate. Such treatment, when snails were exposed to a short pulse of light, terminated cercarial emergence. However, with 6 hr of light, a relatively large number of cercariae emerged, indicating that a long photoperiod can override manganese inhibition. Manganese also inhibited emergence of cercariae from the sporocyst and retarded maturation of developing cercariae. Coincidental observations indicated that manganese exerts a prolonged anesthetic and relaxing action on the snail.