Leucine aminopeptidase and hatching of Schistosoma mansoni eggs

Leucine aminopeptidase (LAP) activity has been measured in extracts of eggs, miracidia, cercariae and adult worms of Schistosoma mansoni. Activity measured at pH 7.2 using L-leu-7-amino-4-trifluoro-methylcoumarin as substrate is 6- to 17-fold greater in eggs than in other life stages. LAP activity is also high in soluble egg antigen preparations and in hatching fluid. The release of LAP from eggs parallels hatching, and inhibitors of LAP also inhibit hatching. The possible role of LAP in the hatching process of S. mansoni eggs is discussed.     

Schistosoma mansoni: factors affecting hatching of eggs

The effect of light, oxygen tension, reducing conditions and thermal shock on egg hatching in Schistosoma mansoni were examined. Hatching was found to be unaffected by light or dark conditions or aerobic or anaerobic conditions. Cold shock from 15 to 120 sec was also ineffective in stimulating hatching. The reducing agents ascorbic acid and cysteine inhibited egg hatching. However, the oxidized forms of these compounds inhibited hatching as well, indicating that the reducing conditions they provided were not responsible for the inhibition.     

Effect of chemotherapy on the Schistosoma mansoni eggs

Praziquantel administered to mice with Schistosoma mansoni infection (50 cercarias/8 weeks) was observed to cause death of adult worms and disintegration of the eggs trapped within granulomas, sometimes with calcification, after the 4th day of treatment. Combined administration of oxamniquine/hycanthone to animals similarly infected, although quite effective in killing adult worms, did not interfere with the eggs in the tissue. The miracidium eclosion test was positive up to the 15th day after the curative treatment of these animals. Since praziquantel treatment causes a rapid destruction of eggs, possible serological and pathogenic effects are expected that may enable a faster reabsorption of granulomas by the host tissues than that produced by other equally effective drugs.     

Seeding experiments demonstrate poor performance of the hatching test for detecting small numbers of Schistosoma mansoni eggs in feces

Parasitological methods for the evaluation of schistosomiasis tend to be limited when parasitic burdens are low, which is a major characteristic of low intensity transmission areas. While the hatching test (HT) method has been considered to be “very sensitive”, reports of its capacity to detect low numbers of eggs remain scarce in the published literature. Our main hypothesis is that HT has limitations and cannot be recommended for diagnosing light infections or as a control of cure. Hence, this study aims to describe the performance of HT in detail, with respect to seeding experiments for egg numbers in the range of 4 to 24 eggs per gram (epg) of feces. Different numbers of eggs of Schistosoma mansoni were seeded in normal human feces. The first set of experiments evaluated the amount of feces (higher than 0.5 g prevented hatching), the proximity of the light source (50 cm was preferred), and the observation time required for the detection of miracidia (more than 3 h did not add to sensitivity). HT was subsequently performed with 12, 10, 8, 6, 4, and 2 eggs in 0.5 g of feces. The final set of experiments was performed to analyze the initial filtration step, in which surgical gauze versus a 500 μm nylon mesh was compared and demonstrated losses of eggs that occurred with washing and gauze (better with nylon) sieving steps. The proposed method was found to produce 100% positivity for up to 12 epg, with a sharp decrease to 33% for 8 epg and less. In conclusion, HT is not recommended for diagnosing intestinal schistosomiasis in populations with light infections, considering the complexity of the procedure and its lack of effectiveness with fecal amounts higher than 0.5 g even at optimized conditions.     

Eosinophil-mediated destruction of Schistosoma mansoni eggs III. lymphokine involvement in the induction of eosinophil functional abilities

Granulomas isolated from the livers of CBA/J mice infected for 8 weeks with Schistosoma mansoni produced a chemotactic activity for eosinophils, in a manner which correlated with the production of the lymphokine eosinophil stimulation promoter (ESP). ESP and chemotactic activities were also produced when eosinophilrich peritoneal exudative cells from S. mansoni-infected mice were cultured with S. mansoni eggs. These S. mansoni-related eosinophils destroyed approximately 20% of the eggs whereas eosinophils from normal (uninfected) mice did not have this ability. However, normal cells exposed to ESP-containing fluids in the co-cultivation system actively participated in egg destruction. Eosinophil-rich peritoneal exudative cells obtained from Trichinella spiralis-infected mice were incapable of destroying S. mansoni eggs during the normal 24 hr co-cultivation period, but did achieve destruction if the incubation period was extended to 48 hr. Marginal levels of chemotactic activity for eosinophils were detected in the co-cultivation fluids from T. spiralis-related cells and S. mansoni eggs, although these fluids did not contain demonstrable levels of ESP. Together, these data indicate that ESP/chemotactic factor-containing culture fluids can induce in normal, unreactive eosinophils the functional ability to destroy S. mansoni eggs in vitro. This may account for the ability of T. spiralis-related eosinophils to do so upon extended incubation.     

Structural characterization of glycosphingolipids from the eggs of Schistosoma mansoni and Schistosoma japonicum

The granulomatous pathology in human intestinal schistosomiasisis induced primarily by the egg antigens of schistosome, a parasitictrematode. Glycolipids and glycoproteins were extracted fromthe eggs of the two major species which infect human, Schistosomamansoni and Schistosoma japonicum, for structural characterizationbased on highly sensitive mass spectrometric analysis coupledwith chemical derivatization. Here, we demonstrate that a seriesof uniquely multifucosylated glycosphingolipids constitute themajor egg glycolipids of S.mansoni but not of S.japonicum. TheS.mansoni glycosphingolipids were found to be extended by varyingnumbers of an unusual repeating unit,     

Possible implications of CpG avoidance in the flatworm Schistosoma mansoni

We report the analysis of the biases of CpG, TpG, and CpA of all the DNA sequences data from the Trematode Schistosoma mansoni. Our results show CpG avoidance whereas TpG and CpA frequencies are over the expected values. These characteristics are similar to the biases displayed by methylated genomes, but in platyhelminths 5mC has not been detected by biochemical methods. The possible implications of this CpG shortage are discussed.     

Possible mechanisms of the decoy effect in Schistosoma mansoni transmission

Combes C. and Moné H. 1987. Possible mechanisms of the decoy effect in Schistosoma mansoni transmission. International Journal for Parasitology17: 971–975. Three main possible mechanisms of the decoy effect have been showed in Schistosoma mansoni transmission: (1) miracidia penetrated into the non-target molluscs and then degenerated; (2) miracidia were exhausted by trying to penetrate the nontarget molluscs, excitation of miracidia was more specific than the penetration behaviour; (3) the defense mechanisms of the target mollusc Biomphalaria glabrata were stimulated by the miracidia that have been in contact with non target molluscs. The authors concluded in classifying the molluscs in three types of ranges: interference range, penetration range, and developmental range.     

Isolation of a polysaccharide antigen from Schistosoma mansoni eggs.

A polysaccharide antigen was isolated from Schistosoma mansoni egg homogenates by the phenol procedure. The crude preparation (CPEA) contained at least two antigens. The more purified antigen (PEA) was isolated by sequential enzymatic treatment of CPEA with DNase, RNase, Pronase, and alpha-amylase. PEA was resistant to boiling, freezing and thawing, mild acid and alkali, and chloroform, but was destroyed with periodate. It gave a positive reaction with anthrone reagent. PEA was eluted in the wash fraction from a DEAE cellulose collumn and in the void volume of a Sephacryl 200 column. After immunoelectrophoresis and polyacrylamide electrophoresis there was little or no migration. Amino acid analysis failed to reveal ninhydrin-positive material in the a hydrolyzate of PEA. These resluts suggested that PEA is a neutral polysaccharide with a m.w. of more than 200,000 and contains no amino acids or hexosamine. Antibodies against PEA were detected in sera obtained from mice infected with S. mansoni. PEA is different from previously described antigens derived from schistosome eggs.     

Schistosoma mansoni: utilization of exogenous metabolites by eggs in vitro

Schistosoma mansoni eggs were isolated from the livers of mice infected for 8 wk and were purified by a series of settling and sieving procedures. Aliquots of eggs were suspended in saline with added Eagle's minimal essential medium supplemented with NaHCO₃, glutamine, penicillin, and streptomycin to which a variety of radioisotope labelled metabolites were added. The uptake and utilization of tritiated thymidine demonstrated a high rate of DNA synthesis, particularly in the more immature eggs studied. RNA synthesis as shown with tritiated uridine was also significant. Large amounts of ¹⁴C-labelled isoleucine and arginine were incorporated into protein. Little glycolytic activity was demonstrated on prolonged incubation with ¹⁴C-labelled glucose. A high rate of catabolism of amino acids to CO₂ was observed, as was a very high rate of acetate metabolism. Degradation of radiolabelled glutamate after incubation of eggs with ¹⁴C acetate revealed labelling consistent with metabolism via the Krebs cycle. Thus, Schistosoma mansoni eggs utilize a wide variety of exogenous metabolites. They show active DNA and RNA metabolism, incorporation of amino acids into protein, and intermediary metabolism characterized by a low rate of glycolysis and an active Krebs cycle.     

Ultraviolet disinfection of Schistosoma mansoni cercariae in water

BackgroundSchistosomiasis is a parasitic disease that is transmitted by skin contact with waterborne schistosome cercariae. Mass drug administration with praziquantel is an effective control method, but it cannot prevent reinfection if contact with cercariae infested water continues. Providing safe water for contact activities such as laundry and bathing can help to reduce transmission. In this study we examine the direct effect of UV light on Schistosoma mansoni cercariae using ultraviolet light-emitting diodes (UV LEDs) and a low-pressure (LP) mercury arc discharge lamp.MethodologyS. mansoni cercariae were exposed to UV light at four peak wavelengths: 255 nm, 265 nm, 285 nm (UV LEDs), and 253.7 nm (LP lamp) using bench scale collimated beam apparatus. The UV fluence ranged from 0–300 mJ/cm² at each wavelength. Cercariae were studied under a stereo-microscope at 0, 60, and 180 minutes post-exposure and the viability of cercariae was determined by assessing their motility and morphology.ConclusionVery high UV fluences were required to kill S. mansoni cercariae, when compared to most other waterborne pathogens. At 265 nm a fluence of 247 mJ/cm² (95% confidence interval (CI): 234–261 mJ/cm²) was required to achieve a 1-log₁₀ reduction at 0 minutes post-exposure. Cercariae were visibly damaged at lower fluences, and the log reduction increased with time post-exposure at all wavelengths. Fluences of 127 mJ/cm² (95% CI: 111–146 mJ/cm²) and 99 mJ/cm² (95% CI: 85–113 mJ/cm²) were required to achieve a 1-log₁₀ reduction at 60 and 180 minutes post-exposure at 265 nm. At 0 minutes post-exposure 285 nm was slightly less effective, but there was no statistical difference between 265 nm and 285 nm after 60 minutes. The least effective wavelengths were 255 nm and 253.7 nm. Due to the high fluences required, UV disinfection is unlikely to be an energy- or cost-efficient water treatment method against schistosome cercariae when compared to other methods such as chlorination, unless it can be demonstrated that UV-damaged cercariae are non-infective using alternative assay methods or there are improvements in UV LED technology.