Tissue reactions induced by Schistosoma mansoni in Biomphalaria glabrata

In Biomphalaria glabrata with a strong natural resistance, Schistosoma mansoni sporocysts are rapidly encapsulated by granulocytes and killed, mainly by the strong phagocytic activity of the cells. Irradiated Echinostoma paraensei sporocysts seem able to suppress the function of the granulocytes. Tissue reactions in snails with self-cure demonstrate: involvement of two types of cells, granulocytes and hyalinocyte-like cells; formation of amoeba-fibrous capsules; limited tendency of granulocytes to become attracted to the parasites; a slow process of parasite destruction; and a possible involvement of humoral factors. It seems that there is partial suppression of the granulocyte function in smails with self-cure.     

The identification of markers segregating with resistance to Schistosoma mansoni infection in the snail Biomphalaria glabrata

Both snail and parasite genes determine the susceptibility of the snail Biomphalaria glabrata to infection with the trematode Schistosoma mansoni. To identify molecular markers associated with resistance to the parasite in the snail host, we performed genetic crosses between parasite-resistant and -susceptible isogenic snails. Because resistance to infection in adult snails is controlled by a single locus, DNA samples from individual F2 and F1 backcross progeny, segregating for either the resistant or susceptible phenotypes, were pooled (bulked segregant). Genotypes for both parents were determined with 205 arbitrary decamer primers by random amplified polymorphic DNA-PCR. Of the 205 primers, 144 were informative, and the relative allele frequencies between the pools for these primers were determined. Two primers, OPM-04 and OPZ-11, produced fragments in the resistant parent of one cross that were inherited in a dominant fashion in the resistant F2 and backcross-bulked segregant progeny. Subsequent typing of DNA samples of individual progeny snails showed that the 1.2-kb marker amplified by primer OPM-04 and the 1.0-kb marker produced by primer OPZ-11 segregated in the same dominant fashion with the resistant phenotype. Sequence analysis of the 1.2-kb marker showed that it corresponds to a repetitive sequence in the snail genome with no homology to existing DNA sequences in the public databases. Analysis of the 1. 0-kb marker showed that it also corresponds to a repetitive sequence in the B. glabrata genome that contains an imperfect ORF, with homology to retrovirus-related group-specific antigens (gag) polyprotein.     

Recombinant human interleukin-1-mediated killing of Schistosoma mansoni primary sporocysts in Biomphalaria glabrata

Previous work has indicated that injection of recombinant-human interleukin (rhIL)-1beta in Schistosoma mansoni-infected M-line Biomphalaria glabrata resulted in a significant reduction in the number of cercariae shed. The purpose of the present work was to determine if primary sporocysts were killed following rhIL-1beta injection in susceptible snails and, if so, to determine if killing was the direct result of hemocyte activity. Counting of primary sporocysts indicated a 50% reduction in the number surviving at 3 days PE in snails from 2 susceptible strains following injection. Histological analysis indicated that killing occurred with little-to-no observable hemocyte/parasite contact, whereas short-term culture of primary sporocysts with cell-free plasma (hemolymph) from injected snails rapidly initiated killing in vitro. Because levels of a snail IL-1-like molecule (SnaIL-1) drop significantly following schistosome exposure in M-line snails, because resistant snails maintain higher SnaIL-1 levels following infection, and because rhIL-1beta upregulates hemocyte cytotoxic mechanisms, these data support the contention that SnaIL-1 plays a role in determining resistance in B. glabrata. These data also indicate that schistosome death may be separated from parasite encapsulation by hemocytes and that an as yet unidentified humoral killing mechanism/factor may exist in B. glabrata. Lastly, these data further support the hypothesis that cytokine-like molecules are important, functionally conserved immunodefense mediators in both vertebrates and invertebrates.     

Host choice by larval parasites: a study of Biomphalaria glabrata snails and Schistosoma mansoni miracidia related to host size

Within snail/trematode associations the age/size of the host at infection has consequences with regard to miracidial infection success, further intramolluscan parasite development and reproduction, and the host response, mainly in terms of growth and reproductive effort. Taking into account these differences, we were interested in determining whether miracidia could discriminate and make a choice between snails of different sizes. Using the Schistosoma mansoni/Biomphalaria glabrata system, we compared data on the snail infection rate and the mother sporocyst abundance among three size classes of snails (juvenile, subadult, and adult) exposed separately or together to the parasite larvae. When exposed individually, juvenile snails (3-5 mm) had significantly higher prevalence and abundance values than did subadult snails, followed by adult snails. In contrast, when snails of the three size classes were exposed together in heterogeneous size groups the prevalence and abundance values were always significantly higher for subadult snails of the 7- to 9-mm class than for juvenile and adult snails. A host choice experiment confirmed that significantly more miracidia were attracted by subadult snails, suggesting that the parasite has been selected for specific locating and recognition mechanisms increasing the infection rate of subadult snails when the latter have been exposed in a heterogeneous size group. Selective forces that may be responsible for such a preferential infectivity of the parasite vis-à-vis particular host age/size class are discussed in relation to host resources and host responses.     

Observations on the miraxonal attraction exercised by sexually immature or adult Biomphalaria glabrata infected or not by Schistosoma mansoni

With CT imaging, the lumbar facet joints are well visualised and enlargement secondary to degeneration may be noted. We measured the cross-sectional area of the superior articular process of the L5 facet joint in 100 consecutive CT scans and in 71 patients, the L4 process was also measured. We found that the mean cross-sectional area was significantly larger at L5 than at L4. Patient age and sex had no significant effect on the size at either L4 or L5. A review of the radiological reports revealed that the 13 patients with degenerative facet joints and radiologically normal discs did not have significantly larger facet joints than the 35 patients with disc disease and radiologically normal facet joints. In conclusion, the term "facet joint hypertrophy" should not be used when osteoarthritic changes are noted on CT scan, because these joints are not significantly larger than normal facet joints.     

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

Standard photographic technique in plastic surgery is an important topic that has been stressed in the discipline over the past several years. Clinical photographs should always be taken with the same camera lens, lens setting, lighting, film, and patient position to ensure reproducibility and to enable valid pre- and postoperative comparisons. A 35-mm single lens reflex camera is highly recommended for this type of photography. Two lenses are suggested, one with a focal length range of 50 to 60 mm and one with a focal length range of 90 to 105 mm. Both should have macro capability. Two or more flash units are recommended, either camera-mounted or a studio system set-up in the office. Using the patient preparation method and technique outlined in the text, the Standards in Clinical Photography achieve consistency from patient to patient and also in the same patient in pre- and postoperative photographs. Henceforth, the information discussed in the article forms the basis for standard views, regardless of the image-capture medium.     

A light and electron microscope study on oogenesis in the freshwater pulmonate snail Biomphalaria glabrata

In the freshwater snail Biomphalaria glabrata the formation and composition of yolk granules and the role of the follicle cells were studied by histochemical and electron microscopical techniques. The rough endoplasmic reticulum and the Golgi apparatus appeared to be involved in yolk formation, which is a continuous process throughout oogenesis. From the very beginning of yolk formation two main types of yolk granules were distinguished morphologically. However, with histochemical and enzyme cytochemical methods no differences were observed between these types. The granules acquire lysosomal enzymes after oviposition, indicating that their main function is probably digestion of perivitelline fluid, which contains nutrients for the developing embryo. Yolk formation and the activity of the follicle cells were studied in successive stages of oogenesis by quantitative electron microscopy. The data strongly suggest that the follicle cells are involved in the formation of the follicular cavity and hence in the ovulation process.     

Schistosoma japonicum: in vitro cultivation of miracidium to daughter sporocyst using a Biomphalaria glabrata embryonic cell line

In vitro cultivation of Schistosoma japonicum miracidia to the mother sporocyst (MS) and then to the daughter sporocyst (DS) stage was achieved using the Biomphalaria glabrata embryonic (Bge) cell line as a coculture system. When comparing the effect of Bge cell and MS density on MS development, it was apparent that Bge cell density had a highly significant effect on both MS viability and growth. Viability and growth rate of MS cultured under high cell density conditions (350 cells/mm2) were almost 2 times greater than those of MS cultured under conditions of low cell density (60 cells/mm2). Growth under high cell density conditions corresponded to a 20 to 30 times increase in MS estimated volume within the first 9 weeks of cultivation. Emergence of fully formed motile DS was first observed after 11 weeks of cocultivation. A few DS lived for 14 weeks after emergence and attained a size of 770 +/- 100 microns in length and 48 +/- 13 microns in width. In contrast to what was observed in Bge cell/Schistosoma mansoni cocultures, Bge cells did not encapsulate S. japonicum MS. Our results show that, although the cellular interactions between Bge cells and schistosomes MS display some level of specificity, Bge cells apparently secrete soluble factors that permit excellent survival and can trigger advanced in vitro development of S. japonicum.     

The status of Schistosoma mansoni and snail hosts in Tigray and northern Wello regions, northern Ethiopia

A survey of Schistosoma mansoni infection and snail hosts was carried out in 1992 in six accessible schools and 11 water bodies respectively. Five to ten per cent of the students were randomly selected for stool examination by the Ritichie's method. In Adwa town, however, stools of 100 students out of the 199 selected were re-examined by Kato's method to assess intensity of infection. Results of stools examined by Ritichie's method showed that S. mansoni positive patients were present in four out of six (66.7%) schools, the prevalence for school ranging from 1% in Maychew to 61.8% in Adwa. In all the localities, there was significant male preponderance in the prevalence of infection (p < 0.05). Among those whose stools were examined by the Kato's method in Adwa town, both prevalence and geometric mean egg count per gram of faeces (EPG) were highest in the 10 to 14 years age group reaching 68% and 597 followed by 64% and 591 respectively in the 15 to 19 years of age. Of the S. mansoni positive students in Adwa, 86% excreted 200 or more EPG, 84% of those in the 10 to 14 years of age excreted as high as 1,600 EPG. Sexwise, no significant difference was observed in EPG (p > 0.05). Biomphalaria pfeifferi, the principal snail host of S. mansoni in Ethiopia, were collected from five out of the 11 waterbodies and were found shedding human schistosome cercariae in two of them, their infection rate reaching 0.7%. The ecological characteristics observed were found suitable for snail propagation.(ABSTRACT TRUNCATED AT 250 WORDS)     

The immunogenic effect of purified antigens of B. alexandrina against Schistosoma mansoni in experimental animals (I) as measured by worm load and viability of ova

Current stratigies for the control of schistosomiasis are based primarily on chemotherapy but successful vaccination against infection has been also demonstrated in several host parasite models. In this study, the immunogenic effect of two purified antigens (Fiv 20-29 000 daltons & Fv 20-24 000 daltons) extracted from non infected hepatopancreas of B. alexandrina as measured by worm load, state of copulation and viability of ova in tissues. The antigens were prepared using gel filtration chromatography and their molecular weights were estimated through sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Four dilutions from each antigen were prepared and injected in two groups (33 each) of Swiss albino mice at weekly intervals. A control group was injected with phosphate buffer saline (PBS) in the same manner. All mice were injected with 100 cercariae using immersion method. Sacrification was done regularly after 7 weeks of injection. On the basis of worm load, Fiv gave protection of 44% while Fv gave only 36%. The number of worms in copula was significantly reduced and they became delicate, fragile, stunted and malformed. Both antigens gave a significant reduction in total viable eggs in tissues.     

Prevalence and epidemiology of Schistosoma mansoni and S. haematobium infection in two areas of Egypt recently reclaimed from the desert

Projects are being carried out in many regions of Egypt to reclaim land from the desert for agriculture. This paper presents findings from a baseline epidemiologic study conducted in 1992 in two newly reclaimed areas near Ismailia, Egypt. In the first area, just east of the Suez Canal, 40.0% of the residents tested positive for Schistosoma mansoni and 1.7% tested positive for S. haematobium, while in the second area, 15 km southwest of Ismailia, 49.3% tested positive for S. mansoni and 3.3% tested positive for S. haematobium. The intensities of S. mansoni infection were moderately high, with a geometric mean egg count of 76 eggs/gram of feces among positive individuals in the first area, and 100 eggs/gram of feces in the second area. When compared with a previous study conducted in 1985, the prevalence of S. mansoni infection in the first area has increased from 21.7% to 42.1% among settlers in the last seven years, while that of S. haematobium has decreased from 7.8% to 1.7%. These trends may result from changes in irrigation practices or other alterations in the local environment. There is a risk of schistosomiasis becoming a major public health problem in reclaimed areas if adequate control measures are not taken.     

Predation of Biomphalaria glabrata during the development of Belostoma anurum (Hemiptera, Belostomatidae)

m-Nifedipine (m-Nif 20 mg.kg-1.d-1 ig for 9 wk) decreased left ventricular weight in the renovascular hypertensive rats (P < 0.01). Though not significantly affecting the density of dihydropyridines (DHP) receptor (Bmax), m-Nif administered whether for prevention (6 wk postclipping) or for regression (9 wk postclipping), markedly decreased the total number of DHP binding sites in hypertrophied left ventricle (LV). m-Nif also reduced the dissociation constant (Kd) of DHP binding sites in the membranes of LV and cerebral cortex from cardiac hypertrophied rats (P < 0.01). These effects of m-Nif were similar to those of nifedipine (Nif) in the same dosage. The results suggest that m-Nif can prevent and regress the LV hypertrophy resulted from renovascular hypertension and reduce the total number of DHP binding sites in the membranes of LV from cardiac hypertrophied rats.     

Leukocytes of Biomphalaria glabrata: morphology and behavior of granulocytic cells in vitro

Resistance to 6-thioguanine was induced by 5-bromodeoxyuridine (BUdR) in synchronous Chinese hamster cells. The yield of mutant colonies was not proportional to the amount of BUdR incorporated into DNA; thus mutants were not due to mispairing of BUdR with guanine during replication. Few mutants were induced until BUdR concentrations exceeded that of the intracellular thymidine triphosphate pool and mutant yield was depressed by addition of thymidine to the medium. These data suggest that BUdR exerts an allosteric effect on the DNA synthesizing system which renders it more error prone.     

Tegument changes of Schistosoma japonicum and Schistosoma mansoni in mice treated with artemether

AIM: To study the effect of artemether (Art) on the tegument of schistosomes. METHODS: Mice infected with S japonicum cercariae for 7 and 35 d, or with S mansoni cercariae for 49 d were treated intragastrically with Art 200-300 mg.kg-1.d-1 for 2 d. Schistosomes were collected in groups of 2 mice at various intervals after medication for scanning electron microscopic observation. RESULTS: The tegumental changes induced by Art appeared to be similar in S japonicum and S mansoni: swelling and fusion of tegumental surfaces, vesicle formation and collapse of discoid-like sensory structures. In S japonicum the emergence of tegumental alterations was earlier in 7-d-old schistosomulae than that in 35-d-old adult worms. CONCLUSION: Art injured the teguments of S japonicum and S mansoni.     

Synthesis and characterization of a protective peptide-based vaccine against Schistosoma mansoni

Two synthetic peptides, corresponding to the N-terminal sequence of the 45-kDa subunit of the protective 9B antigen of Schistosoma mansoni and differing in only one amino acid residue, were synthesized. These peptides were recognized by the protective monoclonal antibody 152-66-9B, as well as by sera of mice and humans infected with schistosomiasis. The peptides were coupled to a protein carrier and used for immunization. One of the peptides, 9B-peptide1, induced in mice significant protection against challenge infection, manifested in a 40 to 50% reduction in worm burden.     

Inactivation of Tritrichomonas foetus and Schistosoma mansoni purine phosphoribosyltransferases by arginine-specific reagents

The arginine-specific reagents phenylglyoxal and butane-2,3-dione irreversibly inactivate the Tritrichomonas foetus hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGXPRT) and Schistosoma mansoni hypoxanthine-guanine phosphoribosyltransferase (HGPRT). The inactivation of the tritrichomonal enzyme by phenylglyoxal follows time-dependent and concentration-dependent pseudo-first-order kinetics. Complete protection against inactivation is afforded by the addition of 25 microM GMP, whereas 5-phosphoribosyl-1-diphosphate (PRibPP) at 50-250 microM can only slow down the inactivation, without being protective. Digestion of [7-(14)C]phenylglyoxal-modified enzyme with trypsin and separation of the peptides by reverse-phase HPLC shows that only one radioactive peak is greatly diminished by incubation with 25 microM GMP or 1 mM PRibPP. Mass-spectral analysis identifies Arg155 as the target site of two molecules of phenylglyoxal that is protected by the substrates. This amino acid residue is positioned next to Tyr156, which is a highly conserved aromatic residue among all the purine phosphoribosyltransferases (PRT) and is always found stacked on top of the purine substrate. This may explain why phenylglyoxal labeling of Arg155 inactivates the enzyme and why GMP can protect Arg155 more effectively than PRibPP. Among the purine PRT in our possession, only schistosomal HGPRT, the only other enzyme that contains an arginine residue at the corresponding location (Arg187), was susceptible to phenylglyoxal and butane-2,3-dione. The presence of Lys185-Phe186 and Ser179-Trp180 at the corresponding locations in human HGPRT and Giardia lamblia GPRT, respectively, may explain their resistance to phenylglyoxal. Thus, Arg155 in T. foetus HGXPRT and Arg187 in S. mansoni HGPRT will be attractive targets for future studies.