Effect of amphotericin B on the infection success of Schistosoma mansoni in Biomphalaria glabrata

In the present study, we examined the effect of amphotericin B on larval stages (miracidia and primary sporocyst) of the helminth Schistosoma mansoni, the causative agent of human schistosomiasis. Amphotericin B (AmB) is a polyene macrolide that disturbs the function of the cell membrane; it is widely used as prophylactic antimycotic agent in in vitro culture. We show for the first time that S. mansoni miracidia infectivity is considerably reduced after AmB treatment. Moreover we demonstrate that AmB does not affect the development, growth, viability, and behavior of miracidia and primary sporocysts. Our data indicate that AmB effects on S. mansoni sporocyst prevalence are linked to the oxidative properties of AmB. These may alter the capacity of sporocysts to respond to the oxidative stress generated by the snail immune defence system.     

Female biased sex-ratio in Schistosoma mansoni after exposure to an allopatric intermediate host strain of Biomphalaria glabrata

For parasites that require multiple hosts to complete their development, the interaction with the intermediate host may have an impact on parasite transmission and development in the definitive host. The human parasite Schistosoma mansoni needs two different hosts to complete its life cycle: the freshwater snail Biomphalaria glabrata (in South America) as intermediate host and a human or rodents as final host. To investigate the influence of the host environment on life history traits in the absence of selection, we performed experimental infections of two B. glabrata strains of different geographic origin with the same clonal population of S. mansoni. One B. glabrata strain is the sympatric host and the other one the allopatric host. We measured prevalence in the snail, the cercarial infectivity, sex-ratio, immunopathology in the final host and microsatellite frequencies of individual larvae in three successive generations.     

Bursts of transposition from non-long terminal repeat retrotransposon families of the RTE clade in Schistosoma mansoni

The genus Schistosoma is composed of blood flukes that infect vertebrates, from which three species are major causative agents of human schistosomiasis, a tropical disease that affects more than 200 million people. Current models of the recent evolution of Schistosoma indicate multiple events of migration and speciation from an Asian ancestral species. Transposable elements are important drivers of genome evolution and have been hypothesised to have an important role in speciation. In this work, we describe a comprehensive inventory of Schistosoma mansoni and Schistosoma japonicum retrotransposons, based on their recently published genomic data. We find a considerable difference in retrotransposon representation between the two species (22% and 13%, respectively). A large part of this difference can be attributed to higher representation of two previously described families of S. mansoni retrotransposons (SR2 and Perere-3/SR3), compared with the representation of their closest relative families in S. japonicum. A more detailed analysis suggests that these two S. mansoni families were the subject of recent bursts of transposition that were not paralleled by their S. japonicum counterparts. We hypothesise that these bursts could be a consequence of the evolutionary pressure resulting from migration of Schistosoma from Asia to Africa and their establishment in this new environment, helping both speciation and adaptation.     

The extracellular release of Schistosoma mansoni HMGB1 nuclear protein is mediated by acetylation

Schistosoma mansoni HMGB1 (SmHMGB1) was revealed to be a substrate for the parasite histone acetyltransferases SmGCN5 and SmCBP1. We found that full-length SmHMGB1, as well as its HMG-box B (but not HMG-box A) were acetylated in vitro by SmGCN5 and SmCBP1. However, SmCBP1 was able to acetylate both substrates more efficiently than SmGCN5. Interestingly, the removal of the C-terminal acidic tail of SmHMGB1 (SmHMGB1ΔC) resulted in increased acetylation of the protein. We showed by mammalian cell transfection assays that SmHMGB1 and SmHMGB1ΔC were transported from the nucleus to the cytoplasm after sodium butyrate (NaB) treatment. Importantly, after NaB treatment, SmHMGB1 was also present outside the cell. Together, our data suggest that acetylation of SmHMGB1 plays a role in cellular trafficking, culminating with its secretion to the extracellular milieu. The possible role of SmHMGB1 acetylation in the pathogenesis of schistosomiasis is discussed.     

Schistosoma mansoni: Effect of dietary zinc supplement on egg granuloma in Swiss mice treated with praziqantel

Schistosomiasis is one of the most important parasitic diseases in Egypt and chemotherapy is considered the most effective method of control. This study was conducted to assess the effectiveness of zinc administration against Schistosoma mansoni infection by evaluating the activities of arylesterase and paraoxonase (PON1) enzymes, and the degree of liver damage.One hundred and twenty albino mice were divided into two groups; one was an infected control and the other a treated group which was further subdivided into three according to the praziquantel and zinc supplementation given. Blood and liver samples, collected 10 weeks post-infection, were subjected to parasitological, histopathological, and enzyme assays, and immunological studies. The results showed that dietary zinc supplementation led to marked reduction in worm load, and egg deposition in the liver and intestine.Histopathological examination showed marked reduction in the number and diameter of hepatic granulomas in the treated groups. The activity of arylesterase and PON1 enzymes were partially restored in infected animals receiving zinc. IL-10 mRNA expression was higher in the treated groups than in the infection control group. In conclusion, zinc administration could be a promising adjuvant therapy for S. mansoni infection.     

Schistosoma mansoni: Developmental arrest of miracidia treated with histone deacetylase inhibitors

In the present study, we examined the effect of the histone deacetylase (HDAC) inhibitors trichostatin A (TSA), valproic acid (VA) and sodium-butyrate on the metamorphosis of larvae of the human blood-fluke Schistosoma mansoni from the free-swimming miracidia into the intramolluskal sporocyst. We show that HDAC inhibitors block transformation in concentration dependant manner. TSA reversibly blocks this developmental process: only 13 ± 11% of TSA treated miracidia transform into sporocysts in-vitro, compared to 92 ± 3% in the mock-treated control. Other enzyme inhibitors such as cycloheximide or hydroxyurea had no effect on metamorphosis. For treatment of up to 4 h, the effect of TSA was completely reversible. Our data indicates that HDAC activity is necessary for the transformation of S. mansoni miracidia during infection of the snail host.     

Human helminth co-infection: No evidence of common genetic control of hookworm and Schistosoma mansoni infection intensity in a Brazilian community

Strong statistical associations between soil-transmitted helminths and schistosomes are frequently observed in co-endemic human populations, although the underlying explanations remain poorly understood. This study investigates the contribution of host genetics and domestic environment to hookworm and Schistosoma mansoni infection intensity and evaluates the role of genetic and non-genetic factors in co-variation of infection intensity. Detailed genealogical information allowed assignment of 1303 individuals living in the Brazilian community of Americaninhas, Minas Gerais state, to 25 pedigrees (containing between two and 1159 members) residing in 303 households. The prevalence of co-infection with both hookworms and schistosomes was high (38.5%), with significant correlation between Necator americanus and S. mansoni faecal egg counts. Bivariate variance component analysis demonstrated a modest but significant species-specific heritability for intensity of N. americanus (h² = 0.196) and S. mansoni infection (h² = 0.230). However, after accounting for demographic, socio-economic and household risk factors, no evidence for common genetic control of intensity of hookworm and schistosome infection was observed. There was some evidence for residual clustering within households but the majority (63%) of the covariance between N. americanus and S. mansoni infection intensity remained specific to the individual and could not be explained by shared genes, shared environment or other shared demographic, socio-economic or environmental risk factors. Our results emphasize the importance of exposure to hookworm and schistosome infection in driving the association between levels of infection with these species in hosts resident in areas of high transmission and suggest that much of this common exposure occurs outside the home.     

Development of Schistosoma mansoni in the laboratory rat analyzed by light and confocal laser scanning microscopy

The kinetic of maturation (schistogram) of Schistosoma mansoni worms grown in laboratory rats was studied by light and confocal laser scanning microscopy. Infected rats with the BH strain were weekly euthanized 3-9 weeks pi. Recovered flukes stained with hydrochloric carmine were preserved as whole-mounts and analyzed by confocal and brightfield microscopy. Worms displayed varying degrees of maturation of the reproductive system at weeks 3-6. Male worms showed complete maturation of the reproductive system at week 6, while female worms completed their maturation at week 7. Males presented few tubercles in tegument in all weeks. Despite the presence of a developing embryo within the ootype, no uterine egg was found. The schistogram in rats follows a pattern similar to that observed in mice hosts.     

Plasmodium yoelii: Adverse outcome of non-lethal P. yoelii malaria during co-infection with Schistosoma mansoni in BALB/c mouse model

Plasmodium yoelii and Schistosoma mansoni co-infections were studied in female BALB/c mice aged 4-6 weeks to determine the effect of time and stage of concomitant infections on malaria disease outcome. Patent S. mansoni infection in BALB/c mice increased malaria peak parasitemia and caused death from an otherwise non-lethal, self-resolving P. yoelii malaria infection. Exacerbation of malaria parasitemia occurred during both pre-patent and patent S. mansoni infection resulting in a delay of 4-8 days in malaria parasite resolution in co-infected mice. Praziquantel administered to mice with patent schistosome infection protected from fatal outcome during co-infection. However, this treatment did not completely clear the worm infestation, nor did it reduce the peak malaria parasitemia reached, which was nonetheless resolved completely. Hepatosplenomegaly was more marked in schistosome and malaria co-infected mice compared to either infection separately. The results suggest a complex relationship between schistosome co-infection and malaria disease outcome in which the timing of malaria infection in relation to schistosome acquisition is critical to disease outcome and pathology.     

Binding of von Willebrand factor and plasma proteins to the eggshell of Schistosoma mansoni

Schistosoma mansoni eggs have to cross the endothelium and intestinal wall to leave the host and continue the life cycle. Mechanisms involved in this essential step are largely unknown. Here we describe direct binding to the S. mansoni eggshell of von Willebrand factor and other plasma proteins involved in haemostasis. Using deletion-mutants, we demonstrated that it is the A1 domain of von Willebrand factor that binds to the eggshell. Our results suggest that binding of plasma proteins to the eggshell promotes binding to the endothelium, initiating the passage of the egg through the blood-vessel wall to be excreted in the end.     

Developmental regulation of protein kinase A expression and activity in Schistosoma mansoni

cAMP-dependent protein kinases (PKAs) are the main transducers of cAMP signalling in eukaryotic cells. Recently we reported the identification and characterisation of a PKA catalytic subunit (SmPKA-C) in Schistosoma mansoni that is required for adult schistosome viability in vitro. To gain further insights into the role of SmPKA-C in biological processes during the schistosome life cycle, we undertook a quantitative analysis of SmPKA-C mRNA expression in different life cycle stages. Our data shows that SmPKA-C mRNA expression is developmentally regulated, with the highest levels of expression in cercariae and adult female worms. To evaluate the biological role of SmPKA-C in these developmental stages, cercariae and adult worms were treated with various concentrations of PKA inhibitors. Treatment of cercariae with H-89 or PKI 14-22 amide resulted in loss of viability suggesting that, as in adults, PKA is an essential enzyme activity in this infectious larval stage. In adult worms, in vitro exposure to sub-lethal concentrations of H-89 or PKI 14-22 amide resulted in inhibition of egg production in a dose-dependent manner. Furthermore, using a murine model of schistosome infection where S. mansoni fecundity is impaired, we show that reduced rates of egg production in vivo correlate with significant reductions in SmPKA-C mRNA expression and PKA activity. Finally, restoration of parasite egg production in vivo also resulted in normalisation of SmPKA-C mRNA expression and PKA activity. Taken together, our data suggest that PKA signalling is required for cercarial viability and may play a specific role in the reproductive activity of adult worms.     

Penetration and maturation of Schistosoma mansoni in suckling and adult Swiss Webster and DBA/2 mice

Murine schistosomosis is a widely used experimental model of the human disease. Different methods have been employed to infect mice with Schistosoma mansoni cercariae, such as subcutaneous or intraperitoneal injections, the tail immersion technique, and the use of a metal ring placed on the abdominal skin of anaesthetized animals. An alternative method of infection that requires no anaesthesia and no restraint is to place suckling mice (10 days old) on a Petri dish with a small volume of water containing cercariae. In this study, we compared the penetration and maturation of S. mansoni in mice infected by this alternative method with those noted in mice infected at an older age (45 days) by the tail immersion technique. Besides evaluating the effects of age and method of infection, we also compared the susceptibility of two strains of mice (Swiss Webster (SW) and DBA/2). Mice were exposed to 100 cercariae and worms (by portal-hepatic perfusion) as well as eggs were recovered in the liver and intestines on postinfection (PI) days 35, 55 and 90. Skin penetration was very efficient (about 100%) irrespective of the mouse strain, sex, age and method of infection. Worm and egg recoveries were higher in SW mice at any PI interval, but strain differences tended to be less pronounced on PI day 90. In both strains, recoveries of worms and eggs were clearly higher in mice infected at a younger age (10 days old). This study thus suggests that infection of free-moving suckling mice is a suitable alternative to other methods of infection with S. mansoni.     

Metabolic profiling of a Schistosoma mansoni infection in mouse tissues using magic angle spinning-nuclear magnetic resonance spectroscopy

In order to enhance our understanding of physiological and pathological consequences of a patent Schistosoma mansoni infection in the mouse, we examined the metabolic responses of different tissue samples recovered from the host animal using a metabolic profiling strategy. Ten female NMRI mice were infected with ∼80 S. mansoni cercariae each, and 10 uninfected age- and sex-matched animals served as controls. At day 74 post infection (p.i.), mice were killed and jejunum, ileum, colon, liver, spleen and kidney samples were removed. We employed ¹H magic angle spinning-nuclear magnetic resonance spectroscopy to generate tissue-specific metabolic profiles. The spectral data were analyzed using multivariate modelling methods including an orthogonal signal corrected-projection to latent structure analysis and hierarchical principal component analysis to assess the differences and/or similarities in metabolic responses between infected and non-infected control mice. Most tissues obtained from S. mansoni-infected mice were characterized by high levels of amino acids, such as leucine, isoleucine, lysine, glutamine and asparagine. High levels of membrane phospholipid metabolites, including glycerophosphoryl choline and phosphoryl choline were found in the ileum, colon, liver and spleen of infected mice. Additionally, low levels of energy-related metabolites, including lipids, glucose and glycogen were observed in ileum, spleen and liver samples of infected mice. Energy-related metabolites in the jejunum, liver and renal medulla were found to be positively correlated with S. mansoni worm burden upon dissection. These findings show that a patent S. mansoni infection causes clear disruption of metabolism in a range of tissues at a molecular level, which can be interpreted in relation to the previously reported signature in a biofluid (i.e. urine), giving further evidence of the global effect of the infection.     

In vivo effect of single oral dose of artemether against early juvenile stages of Schistosoma mansoni Egyptian strain

The current treatment and control of schistosomiasis, rely on a single drug, praziquantel, although, it has minor activity against juvenile stages of the parasite. Studies have shown that artemether (ART) exhibits effects against juveniles of Schistosoma mansoni Liberian and Puerto Rican strains, Schistosoma japonicum and Schistosoma haematobium. Aiming to assess the in vivo activity of single oral dose of ART against early juvenile stages of S. mansoni Egyptian strain, this study was established. Mice were treated with ART (400 mg/kg) at two time points evenly spaced over the period of larval development (7 and 21 days post-infection; pi), and a third treatment point (day 49 pi) was included to elucidate when susceptibility decreases. Administration of ART on day 7 pi reduced the total worm burden by 85.94%. The greatest reductions were seen when treatment was given on day 21 pi, with total and female worm burden reductions of 91.52% and 90.57%, respectively, and cessation of oviposition. Similar dose given on day 49 pi reduced total worm burden by 55.17% and female worm burden by 66.51%. Moreover, it induced significant reduction in the tissue egg load and significant alterations in the oogram pattern with decreased immature eggs and increased dead eggs. Antipathological activities were evident in significant reductions in granulomata count and diameter. In conclusion, ART exhibits major in vivo schistosomicidal effects against the early larval migratory stages of S. mansoni Egyptian strain, mainly the 21-day old schistosomula, hence preventing disease progression and morbidity.     

Imatinib has a fatal impact on morphology, pairing stability and survival of adult Schistosoma mansoni in vitro

Schistosomes cause bilharzia (schistosomiasis), one of the most prevalent parasitic diseases for human and animals worldwide. Praziquantel (PZQ) is the only widely used drug for treatment and control of this parasitemia. Since a vaccine is not yet available, and in light of emerging resistance against PZQ, the search for alternatives has high priority. Here we present that Imatinib, a compound used in human cancer therapy (Gleevec; STI-571), significantly affected schistosome morphology and physiology in vitro. Besides its negative effect on gonad development and pairing stability, Imatinib led to pathological alterations of the gastrodermis, which finally caused the death of the parasite.     

The effects of immune rhesus monkey serum on schistosomula of Schistosoma mansoni during cultivation in vitro

Clegg J. A. and Smithers S. R., 1972. The effect of immune rhesus monkey serum on schistosomula of Schistosoma mansoni during cultivation in vitro. International journal for Parasitology2: 79–98. The sera of rhesus monkeys hyperimmunized by 2–4 exposures to S. mansoni cercariae contain an antibody lethal to schistosomula cultivated in vitro. The antibody (IgG) is dependent on labile factors in fresh monkey serum. It can be absorbed by adult worms cultivated in vitro and it is not the antibody responsible for CHR or COP reactions. A titre of lethal antibody sufficient to kill all schistosomula in vitro is maintained for 2–3 months following challenge: it then falls to a moderate level which may be retained for several years. After inactivation, hyperimmune serum inhibits the growth of cultured schistosomula but does not kill them. Following a small primary infection rhesus serum develops a marked growth-inhibiting property and a low titre of lethal antibody at about 4 months, i.e. the time when resistance to reinfection can first be reliably demonstrated.