Schistosoma mansoni granulomas in the skeletal striated muscles in the murine model of neuroschistosomiasis: histological findings

Schistosomiasis mansoni presents many clinical manifestations during migration of schistosomes in their hosts, including diarrhea, hepatomegaly, splenomegaly, liver abscesses, skinlesions, brain tumors and myeloradiculopathy. No lesions have been reported in skeletal striated muscles due to schistosomiasis mansoni in the literature. This short communication reports the histopathological findings on skeletal musculature in a murine model of neuroeschistosomiasis mansoni. Lesions were found in the tongue, masseter muscle, buccinator muscle, digastric muscle and temporalis muscle. Worm recovery was carried out to confirm the infection. We describe here, for the first time in the literature, injuries in the skeletal musculature due to Schistosoma mansoni nfection.

Characterisation of ocular involvement in an experimental model of neuroschistosomiasis mansoni

The Global Burden of Disease Study 2010 listed schistosomiasis among the leading 100 causes of death in Brazil, responsible for 3.6% of the estimated total of deaths globally. Eye and adnexa are very rarely affected by schistosomiasis mansoni, with limited documentation of ocular pathology in this setting. This short communication reports ocular histolopathological findings in a murine model of neuroschistosomiasis mansoni. Lesions were found in the bulbar conjunctiva, lacrimal gland, choroid and corneoscleral limbus.

Suitability of commercially available POC-CCA tests for schistosomiasis: Considerations for efficiency, reproducibility and decision making criteria for field application in areas of low endemicity

BACKGROUND

Point of care tests would be valuable for field diagnosis. However, high sensitivity will likely be required in low endemicity sets where individuals with low schistosome burden are hard to diagnose.

METHODS

Commercially available POC tests (POC-CCA® and Urine CCA (Schisto) ECO Teste®) were evaluated to evidence their potential in low endemicity areas. Individuals with 0-76 eggs per gram of feces were selected, and comparison was performed between Kato-Katz, Saline Gradient and POC-CCA® after urine concentration (POC FLT) methods.

RESULTS

Both POC-CCA had poor performances, showing low identification of less than half of positive individuals and several undiagnosed cases, revealing an accuracy of 0.44 and 0.46, and a Kappa Index of 0.308 and 0, respectively. Positivity rates of POC-CCA tests were below the one found for a single Kato-Katz slide. POC FLT had a Kappa Index of 0.617, an accuracy of 0.81, 67% of reproducibility, and was shown to have the same sensitivity of 21 Kato-Katz slides when two tests were performed.

CONCLUSIONS

POC-CCA® and POC Eco presented exactly the same inadequacy in low endemicity areas. POC FLT significantly improved the performance of POC-CCA®. More accurate methods must be evaluated in low endemicity areas.

Innovative methodology for point-of-care circulating cathodic antigen with rapid urine concentration for use in the field for detecting low Schistosoma mansoni infection and for control of cure with high accuracy

Background

Prior to eliminating schistosomiasis, efforts must address accurate and fast individual diagnosis. Diagnosis is still inaccurate by parasitological and point-of-care circulating cathodic antigen (POC-CCA) in areas of low endemicity.

Methods

Our group has optimized POC-CCA with a 30 min urine concentration step with no need for specialized technicians or equipment and with high accuracy. We evaluated this new method, called POC-CCA filter (FLT), in two Brazilian endemic areas with distinct profiles.

Results

At baseline, POC-CCA had a poor performance with several false results and undefined trace readings, revealing a prevalence rate of 10% against a rate of 23% for POC-CCA FLT, which was similar to the parasitological rates. Accuracy increased from as low as 0.36 to 0.96 after urine concentration in one area. POC-CCA properly diagnosed only half of the cases at three post-treatment time points, while POC-CCA FLT was able to diagnose 96, 83 and 100%, respectively.

Conclusions

The improvement of conventional POC methodology by a fast and simple urine concentration step provided not only an increase in its accuracy before and after praziquantel treatment, but also preserved its applicability in low-prevalence endemic areas, allowing the definition of trace readings as negative cases.

In vitro evaluation of the schistosomicidal potential of Eremanthus erythropappus (DC) McLeisch (Asteraceae) extracts

Eremanthus erythropappus (DC) McLeisch, a plant popularly known as Candeia (Asteraceae), has high therapeutic potential. In this study, the in vitro schistosomicidal potentials of the ethanolic, dichloromethane and hexane extract of branches were evaluated. Couples of worms obtained from the infected mice were cultured in RPMI supplemented with foetal bovine serum and antibiotics. Four pairs of adult worms were exposed to increasing concentrations of each extract and examined by light microscope. The extracts at 100 and 200 µg mL(-1) had schistosomicidal activity, as demonstrated by the analysis of several aspects such as tegument darkening, absence of motility, incapacity of adhesion in culture plate and absence of egg in culture medium. At 50 and 75 µg mL(-1), the dichloromethane and hexane extracts were highly effective. The results suggest that these extracts could be useful in the development of new schistosomicidal drugs.

Schistosoma mansoni: a method for inducing resistance to praziquantel using infected Biomphalaria glabrata snails

To elucidate the mechanisms of antischistosoma resistance, drug-resistant Schistosoma mansoni laboratory isolates are essential. We developed a new method for inducing resistance to praziquantel (PZQ) using successive drug treatments of Biomphalaria glabrata snails infected with S. mansoni. Infected B. glabrata were treated three times with 100 mg/kg PZQ for five consecutive days with a one-week interval between them. After the treatment, the cercariae (LE-PZQ) produced from these snails and the LE strains (susceptible) were used to infect mice. Forty-five days after infection, mice were treated with 200, 400 or 800 mg/kg PZQ. Thirty days post-treatment, we observed that the mean number of worms recovered by perfusion was significantly higher in the group of mice infected with the LE-PZQ isolate treated with 200 and 400 mg/kg in comparison to the LE strain with the same treatment. Moreover, there was a significant difference between the ED50 (effective dose required to kill 50% of the worms) of the LE-PZQ isolate (362 mg/kg) and the LE strain (68 mg/kg). In the in vitro assays, the worms of the LE-PZQ isolate were also less susceptible to PZQ. Thus, the use of infected snails as an experimental model for development of resistance to S. mansoni is effective, fast, simple and cheap.

Phylogenetic analysis of Biomphalaria tenagophila (Orbigny, 1835) (Mollusca: Gastropoda)

Mitochondrial DNA of Biomphalaria tenagophila, a mollusc intermediate host of Schistosoma mansoni in Brazil, was sequenced and characterised. The genome size found for B. tenagophila was 13,722 bp and contained 13 messenger RNAs, 22 transfer RNAs (tRNA) and two ribosomal RNAs (rRNA). In addition to sequencing, the mitochondrial DNA (mtDNA) genome organization of B. tenagophila was analysed based on its content and localization of both coding and non-coding regions, regions of gene overlap and tRNA nucleotide sequences. Sequences of protein, rRNA 12S and rRNA 16S nucleotides as well as gene organization were compared between B. tenagophila and Biomphalaria glabrata, as the latter is the most important S. mansoni intermediate host in Brazil. Differences between such species were observed regarding rRNA composition. The complete sequence of the B. tenagophila mitochondrial genome was deposited in GenBank (accession EF433576). Furthermore, phylogenetic relationships were estimated among 28 mollusc species, which had their complete mitochondrial genome deposited in GenBank, using the neighbour-joining method, maximum parsimony and maximum likelihood bootstrap. B. tenagophila was positioned at a branch close to B. glabrata and Pulmonata molluscs, collectively comprising a paraphyletic group, contrary to Opistobranchia, which was positioned at a single branch and constituted a monophyletic group.

Ageing down-modulates liver inflammatory immune responses to schistosome infection in mice

Ageing is associated with several alterations in the immune system. Our aim in this study was to compare the development of immunity to Schistosoma mansoni infection in young versus aged C57Bl/6 mice using the liver as the main organ to evaluate pathological alterations and immune responses. In the acute phase, young mice had large liver granulomas with fibrosis and inflammatory cells. Chronic phase in young animals was associated with immunomodulation of granulomas that became reduced in size and cellular infiltrate. On the other hand, aged animals presented granulomas of smaller sizes already in the acute phase. Chronic infection in these mice was followed by no alteration in any of the inflammatory parameters in the liver. In concert with this finding, there was an increase in activated CD4+ T, CD19+ B and NK liver cells in young mice after infection whereas old mice had already higher frequencies of activated B, NK and CD4+ T liver cells and infection does not change these frequencies. After infection, liver production of inflammatory and regulatory cytokines such as IFN-gamma, IL-4 and IL-10 increased in young but not in old mice that had high levels of IL-4 and IL-10 regardless of their infection status. Our data suggest that the unspecific activation status of the immune system in aged mice impairs inflammatory as well as regulatory immune responses to S. mansoni infection in the liver, where major pathological alterations and immunity are at stage. This poor immune reactivity may have a beneficial impact on disease development.

Further evaluation of an updated PCR assay for the detection of Schistosoma mansoni DNA in human stool samples

A previously reported sensitive PCR assay for the detection of Schistosoma mansoni DNA was updated and evaluated. Changes in the DNA extraction method, including the use of a worldwide available commercial kit and the inclusion of additional quality control measures, increased the robustness of the test, as confirmed by the analysis of 67 faecal samples from an endemic area in Brazil. The PCR assay is at hand as a proven, reliable diagnostic test for the control of schistosomiasis in specific settings.

Use of a saline gradient for the diagnosis of schistosomiasis

The development of novel methods for parasitological diagnosis that are both highly sensitive and low in cost has been strongly recommended by the World Health Organization. In this study, a new technique for diagnosis of schistosomiasis mansoni is proposed based on the differential sedimentation of eggs when subjected to a slow continuous flux of 3% saline solution through a porous plaque. This influx suspends low-density faecal material, effectively cleaning the sample. The remaining sediment covering the porous plaque surface is then transferred to a glass slide and examined under a bright field microscope. Twelve Kato-Katz slides were used for comparison in the present study. Our results suggest that the saline gradient method detects a significantly higher number of eggs than the 12 Kato-Katz slides (p < 0.0001). We also found microscopic inspection to be quicker and easier with our newly described method. After cleaning the sample, the obtained sediment can also be conserved in a 10% formaldehyde solution and examined for at least 45 days later without statistically significant egg count differences.

The embryonic development of Schistosoma mansoni eggs: proposal for a new staging system

Schistosomiasis is a water-borne parasitic illness caused by neoophoran trematodes of the genus Schistosoma. Using classical histological techniques and whole-mount preparations, the present work describes the embryonic development of Schistosoma mansoni eggs in the murine host and compares it with eggs maintained under in vitro conditions. Two pre-embryonic stages occur inside the female worm: the prezygotic stage is characterized by the release of mature oocytes from the female ovary until its fertilization. The zygotic stage encompasses the migration of the zygote through the ootype, where the eggshell is formed, to the uterus. Fully formed eggs are laid still undeveloped, without having suffered any cleavage. In the outside environment, eight embryonic stages can be defined: stage 1 refers to early cleavages and the beginning of yolk fusion. Stage 2 represents late cleavage, with the formation of a stereoblastula and the onset of outer envelope differentiation. Stage 3 is defined by the elongation of the embryonic primordium and the onset of inner envelope formation. At stage 4, the first organ primordia arise. During stages 5 to 7, tissue and organ differentiation occurs (neural mass, epidermis, terebratorium, musculature, and miracidial glands). Stage 7 is characterized by the nuclear condensation of neurons of the central neural mass. Stage 8 refers to the fully formed larva, presenting muscular contraction, cilia, and flame-cell beating. This staging system was compared to a previous classification and could underlie further studies on egg histoproteomics (morphological localizome). The differentiation of embryonic structures and their probable roles in granulomatogenesis are discussed herein.

Participation of cell-free haemolymph of Biomphalaria tenagophila in the defence mechanism against Schistosoma mansoni sporocysts

Biomphalaria tenagophila of Taim strain is able to completely destroy Schistosoma mansoni sporocyst few hours after parasite penetration, although the mechanism is still not well known. In this experimental work we show that passive transference of cell-free haemolymph, especially from B. tenagophila Taim, resulted in higher resistance of B. tenagophila Cabo Frio to S. mansoni infection. This effect was demonstrated in vivo, by the reduction in the infection rate, and the significantly lower production of sporocysts and cercariae of the parasite in snails treated with Taim cell-free haemolymph compared to CBSS-inoculated snails. The protective effect of Taim cell-free haemolymph was also observed during the in vitro interaction between haemocytes and sporocysts. In this system, addition of B. tenagophila cell-free haemolymph, especially from Taim strain, was responsible for significant increase in sporocyst mortality compared to B. glabrata cell-free haemolymph or culture medium. Moreover, the combination of Taim cell-free haemolymph and Cabo Frio haemocytes increased significantly the mortality of sporocysts. The results show that Taim cell-free haemolymph would act direct and indirectly on destruction of S. mansoni sporocysts. The results also suggest that cell-free haemolymph indirectly increases parasite recognition by the circulating granulocytes and it is species specific.

The effects of drugs, ions, and poly-l-lysine on the excretory system of Schistosoma mansoni

We have been able to label the excretory system of cercariae and all forms of schistosomula, immature and adult worms with the highly fluorescent dye resorufin. We have shown that the accumulation of the resorufin into the excretory tubules and collecting ducts of the male adult worm depends on the presence of extracellular calcium and phosphate ions. In the adult male worms, praziquantel (PZQ) prevents this accumulation in RPMI medium and disperses resorufin from tubules which have been prelabelled. Female worms and all other developmental stages are much less affected either by the presence of calcium and phosphate ions, or the disruption caused by PZQ. The male can inhibit the excretory system in paired female. Fluorescent PZQ localises in the posterior gut (intestine) region of the male adult worm, but not in the excretory system, except for the anionic carboxy fluorescein derivative of PZQ, which may be excreted by this route. All stages of the parasite can recover from damage by PZQ treatment in vitro. The excretory system is highly sensitive to damage to the surface membrane and may be involved in vesicle movement and damage repair processes. In vivo the adult parasite does not recover from PZQ treatment, but what is inhibiting recovery is unknown, but likely to be related to immune effector molecules.

Differential lectin labelling of circulating hemocytes from Biomphalaria glabrata and Biomphalaria tenagophila resistant or susceptible to Schistosoma mansoni infection

Lectins/carbohydrate binding can be involved in the Schistosoma mansoni recognition and activation of the Biomphalaria hemocytes. Therefore, expression of lectin ligands on Biomphalaria hemocytes would be associated with snail resistance against S. mansoni infection. To test this hypothesis, circulating hemocytes were isolated from B. glabrata BH (snail strain highy susceptible to S. mansoni), B. tenagophila Cabo Frio (moderate susceptibility), and B. tenagophila Taim (completely resistant strains), labelled with FITC conjugated lectins (ConA, PNA, SBA, and WGA) and analyzed under fluorescence microscopy. The results demonstrated that although lectin-labelled hemocytes were detected in hemolymph of all snail species tested, circulating hemocytes from both strains of B. tenagophila showed a larger number of lectin-labelled cells than B. glabrata. Moreover, most of circulating hemocytes of B. tenagophila were intensively labelled by lectins PNA-FITC and WGA-FITC, while in B. glabrata small hemocytes were labeled mainly by ConA. Upon S. mansoni infection, lectin-labelled hemocytes almost disappeared from the hemolymph of Taim and accumulated in B. glabrata BH. The role of lectins/carbohydrate binding in resistance of B. tengophila infection to S. mansoni is still not fully understood, but the data suggest that there may be a correlation to its presence with susceptibility or resistance to the parasite.

A new miracidia hatching device for diagnosing schistosomiasis

It is still imperative to develop a parasitological technique highly sensitive for diagnosing schistosomiasis in epidemiological and individual surveys. A simple and cheap hatching device with a collecting container was manufactured and tested under experimental conditions. Twelve Kato-Katz slides were performed as golden standard for comparison. Quantitative results can be carried out by counting miracidia in a plate and parasite load can be calculated (miracidia/gram of feces). Statistically significant values were higher in the hatching test. More sensitive results, with statistical significance, were achieved using 1.5 g of feces (which corresponds to 36 Kato-Katz slides) than by using the Kato-Katz method. Advantages of this technique and its limitations are presented.

Evaluation of the effect of oxamniquine, praziquantel and a combination of both drugs on the intramolluscan phase of Schistosoma mansoni

The activity of oxamniquine (OXA), praziquantel (PZQ), and a combination of both drugs was evaluated at the intramolluscan phase of Schistosoma mansoni. Biomphalaria glabrata snails infected with S. mansoni were treated with 500 mg/kg OXA, 1000 mg/kg PZQ or with 250 mg/kg OXA and 500 mg/kg PZQ, in association, at the pre-patent and patent phases of infection. The results showed that either treatments with OXA or PZQ, alone, at the pre-patent period, delayed the parasite's development, increasing the pre-patent period by approximately 10 days. At the same pre-patent period, treatment with a combination of OXA/PZQ delayed the parasite's development even more, extending the pre-patent period up to 56 days. At the patent period, treatment with OXA and PZQ, alone, interrupted cercarial shedding. When the snails were treated with 1000 mg/kg PZQ, the cercarial production was re-established 15 days after treatment, but in lower numbers than those obtained before treatment, whereas the snails treated with 500 mg/kg OXA were able to shed cercariae in similar quantities to those observed before treatment. The association 250 mg/kg OXA+500 mg/kg PZQ, at the patent period, not only discontinued cercarial shedding, but also led to the "cure" of the snails, showing a synergistic effect of this combination of drugs. These results suggest that this model will be useful for selection of resistant parasites, as well as for screening new antischistosomal drugs.

Cross-immunoreactivity between anti-potato apyrase antibodies and mammalian ATP diphosphohydrolases: potential use of the vegetal protein in experimental schistosomiasis

We have previously showed that Schistosoma mansoni ATP-diphosphohydrolase and Solanum tuberosum potato apyrase share epitopes and the vegetable protein has immunostimulatory properties. Here, it was verified the in situ cross-immunoreactivity between mice NTPDases and anti-potato apyrase antibodies produced in rabbits, using confocal microscopy. Liver samples were taken from Swiss Webster mouse 8 weeks after infection with S. mansoni cercariae, and anti-potato apyrase and TRITC-conjugated anti-rabbit IgG antibody were tested on cryostat sections. The results showed that S. mansoni egg ATP diphosphohydrolase isoforms, developed by anti-potato apyrase, are expressed in miracidial and egg structures, and not in granulomatous cells and hepatic structures (hepatocytes, bile ducts, and blood vessels). Therefore, purified potato apyrase when inoculated in rabbit generates polyclonal sera containing anti-apyrase antibodies that are capable of recognizing specifically S. mansoni ATP diphosphohydrolase epitopes, but not proteins from mammalian tissues, suggesting that autoantibodies are not induced during potato apyrase immunization. A phylogenetic tree obtained for the NTPDase family showed that potato apyrase had lower homology with mammalian NTPDases 1-4, 7, and 8. Further analysis of potato apyrase epitopes could implement their potential use in schistosomiasis experimental models.

Activity of praziquantel on in vitro transformed Schistosoma mansoni sporocysts

Praziquantel (PZQ) is effective against all the evolutive phases of Schistosoma mansoni. Infected Biomphalaria glabrata snails have their cercarial shedding interrupted when exposed to PZQ. Using primary in vitro transformed sporocysts, labeled with the probe Hoechst 33258 (indicator of membrane integrity), and lectin of Glycine max (specific for carbohydrate of N-acetylgalactosamine membrane), we evaluated the presence of lysosomes at this evolutive phase of S. mansoni, as well as the influence of PZQ on these acidic organelles and on the tegument of the sporocyst. Although the sporocyst remained alive, it was observed that there was a marked contraction of its musculature, and there occurred a change in the parasite's structure. Also, the acidic vesicles found in the sporocysts showed a larger delimited area after contact of the parasites with PZQ. Damages to the tegument was also observed, as show a well-marked labeling either with Hoechst 33258 or with lectin of Glycine max after contact of sporocysts with the drug. These results could partially explain the interruption/reduction mechanism of cercarial shedding in snails exposed to PZQ.

Primary culture of the region of the amebocyte-producing organ of the snail Biomphalaria glabrata, the intermediate host of Schistosoma mansoni

Biomphalaria glabrata snails are major hosts for the digenetic trematoda Schistosoma mansoni, the causative agent of human schistosomiasis. The success or failure of the infection will be dependent on the mobilization of the molluskan internal defense system, where a major role will be played by circulating hemocytes produced by the APO (amebocyte-producing organ) of the snail. In this report, the primary culture of the APO region of B. glabrata was obtained for the first time, as well as a control culture of the ovotestis. Three different cell populations migrated easily from the explants in culture, with no need of any dispersion agent. The cells grew in suspension at an incubation temperature of 15 degrees C and the cultures were maintained viable for up to two weeks. Two of these cell populations obtained resembled cell types known to be present in the hemolymph of Biomphalaria. The availability of APO cells in culture may contribute to a better understanding of the internal defense in mollusks, in general, as well as the specific response of B. glabrata to S. mansoni infection.

Effect of Angiostrongylus vasorum infection on Biomphalaria tenagophila susceptibility to Schistosoma mansoni

Concomitant infection with different parasites may be a helpful laboratorial strategy leading to the better understanding of the mechanisms used by the internal defense system (IDS) of Gastropoda to deal with helminth infection, such as Schistosoma mansoni. This work reports the effect of co-infection of Angiostrongylus vasorum and S. mansoni in hemocyte activity and in the outcome of infection. The simultaneous infection resulted in an increase of snail susceptibility to S. mansoni. In contrast, snails infected with both parasites, 15 days apart, did not show differences in the susceptibility compared to a single parasite infection. The increased susceptibility was measured by the significantly higher number of migrating sporocysts, higher percentage of snails shedding cercariae, higher number of cercariae shed and higher mortality in the experimental group that were simultaneously infected with A. vasorum and S. mansoni, when compared to snails infected only with S. mansoni. Snails simultaneously infected with A. vasorum and S. mansoni showed lower hemocyte activation during the first few days of infection, compared to activation induced only by A. vasorum infection. Between 5 and 15 days post-infection (dpi), granulocyte number and nitric oxide (NO) contents of simultaneously infected snails were lower than the S. mansoni-infected snails. Based on the results, we suggest that differences in the level of hemocyte response could explain the increased S. mansoni susceptibility observed in snails simultaneously infected with both parasites. However, when S. mansoni infection occurred after A. vasorum larvae are completely encapsulated, the response against S. mansoni was not altered, and therefore there were no differences in the susceptibility level.

Resistance to Schistosoma mansoni by transplantation of APO Biomphalaria tenagophila

Transplantation of the haematopoietic organ from Biomphalaria tenagophila (Taim strain, RS, Brazil), resistant to Schistosoma mansoni, to a highly susceptible strain (Cabo Frio, RJ, Brazil) of the same species, showed in the recipient snails resistance against the trematode, when a successful transplant occurred. The success of transplantation could be confirmed by a typical molecular marker of the Taim strain in haemocytes of the recipients (350 bp detected by PCR-RFLP). The recipient snails which did not present the donor marker in haemocytes (unsuccessful transplantation) were infected with the parasite. The use of an atoxic modelling clay for closing the hole in the transplantation site reduced significantly the mortality caused by bleeding after transplantation procedures.

Responses of the surface membrane and excretory system of Schistosoma mansoni to damage and to treatment with praziquantel and other biomolecules

Damage to the surface membrane of adult Schistosoma mansoni, and the activity of the excretory system, as shown by resorufin fluorescence, was observed following treatment with praziquantel and incubation with other molecules. Praziquantel treatment induced damage to the surface membrane as measured by the use of a variety of fluorescent compounds. The excretory system of the male worm was inhibited immediately after praziquantel treatment, but fully recovered after culture for 2 h following removal of praziquantel. The excretory system of the female, observed to be minimally active in untreated worm pairs, was often greatly activated in paired females, as shown by intense resorufin labelling, after praziquantel treatment, and this continued during recovery of the male excretory system. In experiments with normal worm pairs, the female could be activated by inhibiting the metabolic rate of the pair by a cooling procedure. The effects on the excretory system of changes in culture conditions (such as changes in pH, concentrations of bacterial lipopolysaccharide, cytokines, reactive oxygen species, compounds which remove cholesterol, such as beta-methyl cyclodextrin, and damaging basic poly-L-lysine) were also assessed. It is concluded that the extensive excretory system of the adult worm is responsive to drug treatment and to certain changes in environmental conditions. Its activity seems to be strongly linked to the integrity of the surface membrane.

Biomphalaria tenagophila/Schistosoma mansoni interaction: premises for a new approach to biological control of schistosomiasis

Biomphalaria tenagophila is very important for schistosomiasis transmission in Brazil. However its mechanisms of interaction with Schistosoma mansoni are still scantly studied. Since this snail displays strains highly susceptible or completely resistant to the parasite infection, the knowledge of that would be a useful tool to understand the mechanism of snail resistance. Particularly, the Taim strain consistently shows absolute resistance against the trematode, and this resistance is a dominant character. A multidisciplinary research group was created aiming at studying B. tenagophila/S. mansoni interaction. The possibility for applying the knowledge acquired to obtain a biological model for the control of S. mansoni transmission in endemic areas is discussed.

ATP diphosphohydrolase fromSchistosoma mansoniegg: characterization and immunocytochemical localization of a new antigen

The fact that theSchistosoma mansoniegg has two ATP diphosphohydrolase (EC 3.6.1.5) isoforms with different net charges and an identical molecular weight of 63000, identified by non-denaturing polyacrylamide gel electrophoresis and immunological cross-reactivity with potato apyrase antibodies, is shown. In soluble egg antigen (SEA), only the isoform with the lower net negative charge was detected and seemed to be the predominant species in this preparation. By confocal fluorescence microscopy, using anti-potato apyrase antibodies, theS. mansoniegg ATP diphosphohydrolase was detected on the external surface of miracidium and in von Lichtenberg's envelope. Intense fluorescence was also seen in the outer side of the egg-shell, entrapped by the surface microspines, suggesting that a soluble isoform is secreted. ATP diphosphohydrolase antigenicity was tested using the vegetable protein as antigen. The purified potato apyrase was recognized in Western blots by antibodies present in sera from experimentallyS. mansoni-infected mice. In addition, high levels of IgG anti-ATP diphosphohydrolase antibodies were detected by ELISA in the same sera. This work represents the first demonstration of antigenic properties ofS. mansoniATP diphosphohydrolase and immunological cross-reactivity between potato apyrase and sera from infected individuals.

The use and misuse of the "impact factor" as a parameter for evaluation of scientific publication quality: a proposal to rationalize its application

We present a critical analysis of the generalized use of the "impact factor". By means of the Kruskal-Wallis test, it was shown that it is not possible to compare distinct disciplines using the impact factor without adjustments. After assigning the median journal the value of one (1.000), the impact factor value for each journal was calculated by the rule of three. The adjusted values were homogeneous, thus permitting comparison among distinct disciplines.

Silica treatment increases the susceptibility of the Cabo Frio strain of Biomphalaria tenagophila to Schistosoma mansoni infection but does not alter the natural resistance of the Taim strain

The present work demonstrates that silica treatment represents a suitable in vivo method to evaluate the role of host phagocytic hemocytes in the mechanisms of resistance to parasitic infection. Silica inoculation into Biomphalaria tenagophila snail induced a significant reduction in the circulating hemolymph granulocytes in both strains tested (Taim and Cabo Frio). The granulocyte reduction was accompanied by a significant increase in the number of circulating dead cells. In B. tenagophila Cabo Frio, silica treatment enhanced snail susceptibility to Schistosoma mansoni, shortening the intramolluskan phase of the parasite and increasing the number of sporocysts and cercariae produced. In B. tenagophila Taim, the same treatment did not abrogate natural resistance to S. mansoni reported for this snail strain. These in vivo results demonstrate that macrophage-like granulocytes are involved in the mechanism of S. mansoni sporocyst destruction in Cabo Frio snails and suggest that another, different mechanism may be responsible to the natural resistance of B. tenagophila Taim.

On the increase of portal pressure during the acute and chronic phases of murine schistosomiasis mansoni and its reversibility after treatment with oxamniquine

The purpose of the present study was to evaluate the effect of treatment with oxamniquine on the portal pressure of mice infected with Schistosoma mansoni. The animals were infected with 30 cercariae and portal pressure was measured with a polygraph at 70 (acute phase) and 160 (chronic phase) days after infection. On days 70 and 160 two other groups of infected mice were treated with 400 mg/kg of oxamniquine and portal pressure was measured 90 days later (160 and 250 days after infection). A group of uninfected mice was used as control. The measured portal pressures, in mmHg, were: matched uninfected control mice 8.7+/-2.1 and acute phase group, measured at day 70, 13.4+/-3.5. Matched uninfected control 7.5+/-0.6 and chronic phase group, measured at day 160 post-infection, 11.6+/-1.5. Matched uninfected mice 6.9+/-0.9 and chronic phase group, measured at day 250, 10.4+/-1.8. Oxamniquine-treated at day 70 and measured at day 160 7.9+/-0.4; oxamniquine-treated at day 160 and measured at day 250, 7.6+/-1.7. The infection of mice with 30 cercariae of S. mansoni induced portal hypertension, both during the acute and chronic phases and treatment with oxamniquine caused portal pressure to return to normal levels.

Efficacy of oxamniquine and praziquantel in the treatment of Schistosoma mansoni infection: a controlled trial

OBJECTIVE

To evaluate the therapeutic efficacy of oxamniquine and praziquantel, the two most clinically important schistosomicide drugs, and to compare the accuracy of faecal examination with the accuracy of oogram in testing for Schistosoma mansoni infection.

METHODS

In a triple-masked and randomized controlled trial, 106 patients infected with S. mansoni were randomly allocated to one of three statistically homogeneous groups. One group was given 60 mg/kg praziquantel per day for three consecutive days, another was given two daily doses of 10 mg/kg oxamniquine, and the placebo group received starch. Faecal examinations (days 15, 30, 60, 90, 120, 150, and 180 after treatment) and biopsy of rectal mucosa by quantitative oogram (days 30, 60, 120, and 180) were used for the initial diagnosis and for evaluating the degree of cure. The chi2 test and the Kruskal-Wallis test were used to compare variables in the three groups. Survival analysis (Kaplan-Meier) and the log-rank test were used to evaluate the efficacy of the treatments.

FINDINGS

The sensitivity of stool examinations ranged from 88.9% to 94.4% when patients presented with >5000 S. mansoni eggs per gram of tissue (oogram); when the number of eggs dropped to <1000 eggs per gram, sensitivity was reduced (range, 22.7-34.0%). When cure was evaluated by stool examination, oxamniquine and praziquantel had cure rates of 90.3% and 100%, respectively. However, when the oogram was used as an indicator of sensitivity, the oxamniquine cure rate dropped dramatically (to 42.4%), whereas the rate for praziquantel remained high, at 96.1%.

CONCLUSIONS

Praziquantel was significantly more effective than oxamniquine in treating S. mansoni infection. The oogram was markedly more sensitive than stool examinations in detecting S. mansoni eggs and should be recommended for use in clinical trials with schistosomicides.

A new method for fixing Biomphalaria glabrata for histologic studies, using shell perforation

A new technique for fixation of Biomphalaria glabrata for histologic studies is described. It consists in performing several external holes in the shell, before placing the entire snail into the fixative. It is a very practical and quick procedure that showed excellent results when compared to the usual techniques.