Praziquantel for Schistosomiasis: Single-Drug Metabolism Revisited, Mode of Action, and Resistance

Identification of annotated bioactive molecules that impair motility of the blood fluke Schistosoma mansoni

Neglected tropical diseases are of growing worldwide concern and schistosomiasis, caused by parasitic flatworms, continues to be a major threat with more than 200 million people requiring preventive treatment. As praziquantel (PZQ) remains the treatment of choice, an urgent need for alternative treatments motivates research to identify new lead compounds that would complement PZQ by filling the therapeutic gaps associated with this treatment. Because impairing parasite neurotransmission remains a core strategy for control of parasitic helminths, we screened a library of 708 compounds with validated biological activity in humans on the blood fluke Schistosoma mansoni, measuring their effect on the motility on schistosomulae and adult worms. The primary phenotypic screen performed on schistosomulae identified 70 compounds that induced changes in viability and/or motility. Screening different concentrations and incubation times identified molecules with fast onset of activity on both life stages at low concentration (1 μM). To complement this study, similar assays were performed with chemical analogs of the cholinomimetic drug arecoline and the calcilytic molecule NPS-2143, two compounds that rapidly inhibited schistosome motility; 17 arecoline and 302 NPS-2143 analogs were tested to enlarge the pool of schistosomicidal molecules. Finally, validated hit compounds were tested on three functionally-validated neuroregulatory S. mansoni G-protein coupled receptors (GPCRs): Sm5HTR (serotonin-sensitive), SmGPR2 (histamine) and SmD2 (dopamine), revealing NPS-2143 and analogs as potent inhibitors of dopamine/epinine responses on both human and S. mansoni GPCRs. This study highlights the potential for repurposing known human therapeutic agents for potential schistosomicidal effects and expands the list of hits for further progression.

Three monthly doses of 60 mg/kg praziquantel for Schistosoma haematobium infection is a safe and effective treatment regimen

Background

Praziquantel (PZQ) is the standard treatment for Schistosomiasis in sub-Saharan Africa. However, there is evidence suggesting praziquantel treatment failure in Schistosome infections with associated potential renal impairment. The objective of this study was to determine the effect of three monthly doses of 60 mg/kg/day PZQ on schistosome egg count, liver and renal function during the treatment of urinary schistosomiasis in Ghana.

Methods

A nested case-control study was designed from a cohort screened for schistosomiasis; 28 schistosomiasis positive cases by microscopy matched with 53 healthy controls by age and gender. The study population was urban dwellers from the Asokwa sub-metropolitan area, Kumasi in Ghana. Participants were within the age range of 6 to 30 years. We assessed Schistosoma haematobium egg counts in urine and its associated impact on liver and renal function at baseline, treatment and post-treatment phases using serum.

Results

Of the 28 cases and 53 controls, 78.6% and 81.1% were males respectively. Globulin levels before treatment was higher in cases [36.7 (32.8, 40.1) vrs 30.5 (22.4, 33.8), p = 0.005] at pre-treatment but not at post-treatment [35.8 (31.2, 39.1) vrs 37.4 (29.7, 43.0), p = 0.767]. Estimated cure rate was 42.9, 46.4 and 96.4% after first, second and third dose respectively. Schistosome egg counts dropped significantly (p = 0.001) from before second dose to post-treatment. Similarly, levels of alanine aminotransferase (p = 0.001), aspartate aminotransferase (p = 0.028) and gamma glutamyl transferase (p = 0.001) significantly declined towards post-treatment. Estimated glomerular filtration rate significantly improved from before second dose to post-treatment using both the Chronic Kidney Disease Epidemiology Program (p = 0.001) and 4-variable Modification of Diet in Renal Disease (p = 0.002) equations.

Conclusion

Treatment of urinary Schistosoma hematobium infections with a repeated high monthly dose of 60 mg/kg of praziquantel for 3 months is safe and effective.

Antiparasitic activity of piplartine (piperlongumine) in a mouse model of schistosomiasis

Schistosomiasis is one of the most important parasitic infections in terms of its negative effects on public health and economics. Since praziquantel is currently the only drug available to treat schistosomiasis, there is an urgent need to identify new anthelmintic agents. Piplartine, also known as piperlongumine, is a biologically active alkaloid/amide from peppers that can be detected in high amounts in the roots of Piper tuberculatum. Previously, it has been shown to have in vitro schistosomicidal effects. However, its anthelmintic activity in an animal host has not been reported. In the present work, in vivo antischistosomal properties of isolated piplartine were evaluated in a mouse model of schistosomiasis infected with either adult (patent infection) or juvenile (pre-patent infection) stages of Schistosoma mansoni. A single dose of piplartine (100, 200 or 400 mg/kg) or daily doses for five consecutive days (100 mg/kg/day) administered orally to mice infected with schistosomes resulted in a reduction in worm burden and egg production. Treatment with the highest piplartine dose (400 mg/kg) caused a significant reduction in a total worm burden of 60.4% (P < 0.001) in mice harbouring adult parasites. S. mansoni egg production, a process responsible for pathology in schistosomiasis, was also significantly inhibited by piplartine. Studies using scanning electron microscopy revealed substantial tegumental alterations in parasites recovered from mice. Since piplartine has well-characterized mechanisms of toxicity, is easily available, and is cost-effective, our results indicate that this bioactive molecule derived from medicinal plants could be a potential lead compound for novel antischistosomal agents.

Co-administration of silymarin elevates the therapeutic effect of praziquantel through modulation of specific antibody profiles, Th1/Th2/Tregs cytokines and down-regulation of fibrogenesis in mice with Mesocestoides vogae (Cestoda) infection

Silymarin (SIL) represents a natural mixture of polyphenols showing an array of health benefits. The present study, carried out on a model cestode infection induced by Mesocestoides vogae tetrathyridia in the ICR strain of mice, was aimed at investigating the impact of SIL as adjunct therapy on the activity of praziquantel (PZQ) in relation to parasite burden, immunity and liver fibrosis within 20 days post-therapy. In comparison with PZQ alone, co-administration of SIL and PZQ stimulated production of total IgG antibodies to somatic and excretory-secretory antigens of metacestodes and modified the expression patterns of immunogenic molecules in both antigenic preparations. The combined therapy resulted in the elevation of IFN-γ and a decline of TNF-α and TGF-β1 in serum as compared to untreated group; however, SIL attenuated significantly the effect of PZQ on IL-4 and stimulated PZQ-suppressed phagocytosis of peritoneal macrophages. In the liver, SIL boosted the effect of PZQ on gene expression of the same cytokines in a similar way as was found in serum, except for down-regulation of PZQ-stimulated TNF-α. Compared to PZQ therapy, the infiltration of mast cells into liver after SIL co-administration was nearly abolished and correlated with suppressed activities of genes for collagen I, collagen III and α-SMA. In conclusion, co-administration of SIL modified the effects of PZQ therapy on antigenic stimulation of the immune system and modulated Th1/Th2/Tregs cytokines. In liver this was accompanied by reduced fibrosis, which correlated with significantly higher reduction of total numbers of tetrathyridia after combined therapy as compared with PZQ treatment.

Drug resistance in liver flukes

Liver flukes include Fasciola hepatica, Fasciola gigantica, Clonorchis sinensis, Opisthorchis spp., Fascioloides magna, Gigantocotyle explanatum and Dicrocoelium spp. The two main species, F. hepatica and F. gigantica, are major parasites of livestock and infections result in huge economic losses. As with C. sinensis, Opisthorchis spp. and Dicrocoelium spp., they affect millions of people worldwide, causing severe health problems. Collectively, the group is referred to as the Food-Borne Trematodes and their true significance is now being more widely recognised. However, reports of resistance to triclabendazole (TCBZ), the most widely used anti-Fasciola drug, and to other current drugs are increasing. This is a worrying scenario. In this review, progress in understanding the mechanism(s) of resistance to TCBZ is discussed, focusing on tubulin mutations, altered drug uptake and changes in drug metabolism. There is much interest in the development of new drugs and drug combinations, the re-purposing of non-flukicidal drugs, and the development of new drug formulations and delivery systems; all this work will be reviewed. Sound farm management practices also need to be put in place, with effective treatment programmes, so that drugs can be used wisely and their efficacy conserved as much as is possible. This depends on reliable advice being given by veterinarians and other advisors. Accurate diagnosis and identification of drug-resistant fluke populations is central to effective control: to determine the actual extent of the problem and to determine how well or otherwise a treatment has worked; for research on establishing the mechanism of resistance (and identifying molecular markers of resistance); for informing treatment options; and for testing the efficacy of new drug candidates. Several diagnostic methods are available, but there are no recommended guidelines or standardised protocols in place and this is an issue that needs to be addressed.

Schistosoma mansoni glyceraldehyde-3-phosphate dehydrogenase enhances formation of the blood-clot lysis protein plasmin

Schistosomes are intravascular blood flukes that cause the parasitic disease schistosomiasis. In agreement with Schistosoma mansoni (Sm) proteomic analysis, we show here that the normally intracellular glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is also found at the parasite surface; live worms from all intravascular life stages display GAPDH activity. Suppressing GAPDH gene expression using RNA interference significantly lowers this live worm surface activity. Medium in which the worms are cultured overnight displays essentially no activity, showing that the enzyme is not shed or excreted but remains associated with the worm surface. Immunolocalization experiments confirm that the enzyme is highly expressed in the parasite tegument (skin). Surface activity in schistosomula amounts to ∼8% of that displayed by equivalent parasite lysates. To address the functional role of SmGAPDH, we purified the protein following its expression in Escherichiacoli strain DS113. The recombinant protein displays optimal enzymatic activity at pH 9.2, shows robust activity at the temperature of the parasite's hosts, and has a Michaelis-Menten constant for glyceraldehyde-3-phosphate (GAP) of 1.4 mM±0.24. We show that recombinant SmGAPDH binds plasminogen (PLMG) and promotes PLMG conversion to its active form (plasmin) in a dose response in the presence of tissue plasminogen activator. Since plasmin is a key mediator of thrombolysis, our results support the hypothesis that SmGAPDH, a host-interactive tegumental protein that can enhance PLMG activation, could help degrade blood clots around the worms in the vascular microenvironment and thus promote parasite survival in vivoThis article has an associated First Person interview with the first author of the paper.

Identification of anisomycin, prodigiosin and obatoclax as compounds with broad-spectrum anti-parasitic activity

Parasitic infections are a major source of human suffering, mortality, and economic loss, but drug development for these diseases has been stymied by the significant expense involved in bringing a drug though clinical trials and to market. Identification of single compounds active against multiple parasitic pathogens could improve the economic incentives for drug development as well as simplifying treatment regimens. We recently performed a screen of repurposed compounds against the protozoan parasite Entamoeba histolytica, causative agent of amebic dysentery, and identified four compounds (anisomycin, prodigiosin, obatoclax and nithiamide) with low micromolar potency and drug-like properties. Here, we extend our investigation of these drugs. We assayed the speed of killing of E. histolytica trophozoites and found that all four have more rapid action than the current drug of choice, metronidazole. We further established a multi-institute collaboration to determine whether these compounds may have efficacy against other parasites and opportunistic pathogens. We found that anisomycin, prodigiosin and obatoclax all have broad-spectrum antiparasitic activity in vitro, including activity against schistosomes, T. brucei, and apicomplexan parasites. In several cases, the drugs were found to have significant improvements over existing drugs. For instance, both obatoclax and prodigiosin were more efficacious at inhibiting the juvenile form of Schistosoma than the current standard of care, praziquantel. Additionally, low micromolar potencies were observed against pathogenic free-living amebae (Naegleria fowleri, Balamuthia mandrillaris and Acanthamoeba castellanii), which cause CNS infection and for which there are currently no reliable treatments. These results, combined with the previous human use of three of these drugs (obatoclax, anisomycin and nithiamide), support the idea that these compounds could serve as the basis for the development of broad-spectrum anti-parasitic drugs.

Harnessing the gut microbiome in the fight against anthelminthic drug resistance

Intestinal helminth parasites present major challenges to the welfare of humans and threaten the global food supply. While the discovery of anthelminthic drugs empowered our ability to offset these harms to society, the alarming rise of anthelminthic drug resistance mitigates contemporary efforts to treat and control intestinal helminthic infections. Fortunately, emerging research points to potential opportunities to combat anthelminthic drug resistance by harnessing the gut microbiome as a resource for discovering novel therapeutics and informing responsible drug administration. In this review, we highlight research that demonstrates this potential and provide rationale to support increased investment in efforts to uncover and translationally utilize knowledge about how the gut microbiome mediates intestinal helminthic infection and its outcomes.

Current and Novel Therapies Against Helminthic Infections: The Potential of Antioxidants Combined with Drugs

Infections caused by Schistosoma haematobium and Opisthorchisviverrini are classified as Group 1 biological carcinogen and it has been postulated that parasites produce oxysterol and estrogen-like metabolites that might be considered as initiators of infection-associated carcinogenesis. Chemotherapy for these helminthic infections relies on a single drug, praziquantel, (PZQ) that mainly targets the parasite. Additionally, PZQ has some major drawbacks as inefficacy against juvenile form and alone it is not capable to counteract pathologies associated to infections or prevent carcinogenesis. There is an urgent need to develop novel therapeutic approaches that not only target the parasite but also improve the pathologies associated to infection, and ultimately, counteract or/and prevent the carcinogenesis processes. Repurposing the drug in combination of compounds with different modes of action is a promising strategy to find novel therapeutics approaches against these helminthic infections and its pathologies. Here, we emphasized that using antioxidants either alone or combined with anthelmintic drugs could ameliorate tissue damage, infection-associated complications, moreover, could prevent the development of cancer associated to infections. Hence, antioxidants represent a potential adjuvant approach during treatment to reduce morbidity and mortality. Despite the success of some strategies, there is a long way to go to implement novel therapies for schistosomiasis.

Vesical schistosomiasis and squamous cell carcinoma associated with schistosoma haematobium: A re-emerging neglected tropical disease in Tehran, Iran

Hematobium species of this parasite tends to bladder and mesenteric arteries and it causes lesions in the bladder wall, urethra, and renal tubes. A 25-year-old man living in Tehran (a non-endemic and very rare area for schistosoma) suffers from symptoms such as hematuria with suprapubic pain, dysuria, fever, nausea and vomiting. Urine analysis showed a lot of red blood cells, after using cystoscopy of the area and receiving a bladder biopsy, a definitive diagnosis of schistosomiasis was made and after determining the extent of damage to the urinary tract, appropriate treatment with surgery and praziquantel (40 mg/kg) were prescribed.

Molecular basis for hycanthone drug action in schistosome parasites

Hycanthone (HYC) is a retired drug formerly used to treat schistosomiasis caused by infection from Schistosoma mansoni and S. haematobium. Resistance to HYC was first observed in S. mansoni laboratory strains and in patients in the 1970s and the use of this drug was subsequently discontinued with the substitution of praziquantel (PZQ) as the single antischistosomal drug in the worldwide formulary. In endemic regions, multiple organizations have partnered with the World Health Organization to deliver PZQ for morbidity control and prevention. While the monotherapy reduces the disease burden, additional drugs are needed to use in combination with PZQ to stay ahead of potential drug resistance. HYC will not be reintroduced into the schistosomiasis drug formulary as a combination drug because it was shown to have adverse properties including mutagenic, teratogenic and carcinogenic activities. Oxamniquine (OXA) was used to treat S. mansoni infection in Brazil during the brief period of HYC use, until the 1990s. Its antischistosomal efficacy has been shown to work through the same mechanism as HYC and it does not possess the undesirable properties linked to HYC. OXA demonstrates cross-resistance in Schistosoma strains with HYC resistance and both are prodrugs requiring metabolic activation in the worm to toxic sulfated forms. The target activating enzyme has been identified as a sulfotransferase enzyme and is currently used as the basis for a structure-guided drug design program. Here, we characterize the sulfotransferases from S. mansoni and S. haematobium in complexes with HYC to compare and contrast with OXA-bound sulfotransferase crystal structures. Although HYC is discontinued for antischistosomal treatment, it can serve as a resource for design of derivative compounds without contraindication.

The Schistosoma mansoni tegumental allergen protein, SmTAL1: Binding to an IQ-motif from a voltage-gated ion channel and effects of praziquantel

SmTAL1 is a calcium binding protein from the parasitic worm, Schistosoma mansoni. Structurally it is comprised of two domains - an N-terminal EF-hand domain and a C-terminal dynein light chain (DLC)-like domain. The protein has previously been shown to interact with the anti-schistosomal drug, praziquantel (PZQ). Here, we demonstrated that both EF-hands in the N-terminal domain are functional calcium ion binding sites. The second EF-hand appears to be more important in dictating affinity and mediating the conformational changes which occur on calcium ion binding. There is positive cooperativity between the four calcium ion binding sites in the dimeric form of SmTAL1. Both the EF-hand domain and the DLC-domain dimerise independently suggesting that both play a role in forming the SmTAL1 dimer. SmTAL1 binds non-cooperatively to PZQ and cooperatively to an IQ-motif from SmCa_v1B, a voltage-gated calcium channel. PZQ tends to strengthen this interaction, although the relationship is complex. These data suggest the hypothesis that SmTAL1 regulates at least one voltage-gated calcium channel and PZQ interferes with this process. This may be important in the molecular mechanism of this drug. It also suggests that compounds which bind SmTAL1, such as six from the Medicines for Malaria Box identified in this work, may represent possible leads for the discovery of novel antagonists.

Development of Biarylalkyl Carboxylic Acid Amides with Improved Anti-schistosomal Activity

The parasitic disease schistosomiasis is the cause of more than 200 000 human deaths per year. Although the disease is treatable, there is one major shortcoming: praziquantel has been the only drug used to combat these parasites since 1977. The risk of the emergence of resistant schistosomes is known to be increasing, as a reduced sensitivity of these parasites toward praziquantel has been observed. We developed a new class of substances, which are derived from inhibitors of human aldose reductase, and which showed promising activity against Schistosoma mansoni couples in vitro. Further optimisation of the compounds led to an increase in anti‐schistosomal activity with observed phenotypes such as reduced egg production, vitality, and motility as well as tegumental damage and gut dilatation. Here, we performed structure–activity relationship studies on the carboxylic acid moiety of biarylalkyl carboxylic acids. Out of 82 carboxylic acid amides, we identified 10 compounds that are active against S. mansoni at 25 μm. The best five compounds showed an anti‐schistosomal activity up to 10 μm and induced severe phenotypes. Cytotoxicity tests in human cell lines showed that two derivatives had no cytotoxicity at 50 or 100 μm. These compounds are promising candidates for further optimisation toward the new anti‐schistosomal agents.

Enhanced dissolution and oral bioavailability of praziquantel by emulsification with human serum albumin followed by spray drying

The goal of this study was to enhance the oral bioavailability of praziquantel through its conjugation with human serum albumin (HSA). Praziquantel-HSA particles were produced by spray drying an emulsion of an aqueous solution of HSA and a solution of praziquantel in oil. The particles were agglomerates of multiple smooth corrugated particles containing amorphous praziquantel nearly equivalent to the theoretical doses. The solubility of praziquantel in an aqueous medium was enhanced in both the produced particles and the physical mixture. In addition, the dissolution rate in an aqueous medium was enhanced in the case of particles, but not in a physical mixture. Thus, the inclusion of HSA by emulsification followed by spray drying appeared to contribute to the enhanced dissolution rate. In a pharmacokinetic study, the maximum plasma concentration (C_max) and the area under the concentration-time curve (AUC) for the produced particles (HSA/praziquantel = 1/1 w/w) were approximately two times higher than the corresponding values for raw praziquantel. This increased oral bioavailability of the particles was considered to be due to the enhanced dissolution rate. This process for producing praziquantel-HSA particles could be useful in terms of improving the oral bioavailability of the other hydrophobic drugs.

Enhancement of the therapeutic efficacy of praziquantel in murine Schistosomiasis mansoni using silica nanocarrier

The main objective of this work is preparation of mesoporous silica nanoparticles loaded with praziquantel (PZQ-Si) in order to enhance the therapeutic efficacy of praziquantel (PZQ). Mice were experimentally infected with Schistosoma mansoni and treated 6 weeks post-infection with PZQ in different doses via either oral or intraperitoneal (IP) routes. PZQ in the same doses orally administered to S. mansoni-infected mice was used as a drug control, and infected and non-infected non-treated mice served as positive and negative controls, respectively. PZQ-Si exhibited good physicochemical attributes in terms of small uniform size (105 nm), spherical shape, and PZQ entrapment efficiency (83%). A maximum antischistosomal effect was achieved using orally administered PZQ-Si as reflected by total worm burden, tissue egg count, oogram pattern, and hepatic granuloma count and diameter. The biomarkers related to liver oxidative stress status and immunomodulatory effect (serum TNF-α and IL-10) were significantly improved. Data obtained implied that IP route was less efficacious for the delivery of PZQ-Si. Encapsulation of PZQ permits the reduction of the used therapeutic dose of PZQ. Hepatic DNA fragmentation, measured by comet assay, was significantly improved in infected mice treated with maximum dose of PZQ-Si as compared to positive or PZQ control groups. The results indicate that mesoporous silica NP is a promising safe nanocarrier for PZQ potentiating its antischistosomal, antioxidant, immunomodulatory, and anti-inflammatory action in animal model infected with S. mansoni. From a practical standpoint, PZQ-Si using a lower dose of PZQ could be suggested for effective PZQ antischistosomal mass chemotherapy.

Inhibition of the Formation In Vitro of Putatively Carcinogenic Metabolites Derived from S. haematobium and O. viverrini by Combination of Drugs with Antioxidants

Infections caused by Schistosoma haematobium and Opisthorchis viverrini are classified as carcinogenic. Although carcinogenesis might be a multifactorial process, it has been postulated that these helminth produce/excrete oxysterols and estrogen-like metabolites that might act as initiators of their infection-associated carcinogenesis. Current treatment and control of these infections rely on a single drug, praziquantel, that mainly targets the parasites and not the pathologies related to the infection including cancer. Thus, there is a need to search for novel therapeutic alternatives that might include combinations of drugs and drug repurposing. Based on these concepts, we propose a novel therapeutic strategy that combines drugs with molecule antioxidants. We evaluate the efficacy of a novel therapeutic strategy to prevent the formation of putative carcinogenic metabolites precursors and DNA adducts. Firstly, we used a methodology previously established to synthesize metabolites precursors and DNA adducts in the presence of CYP450. Then, we evaluated the inhibition of their formation induced by drugs and antioxidants alone or in combination. Drugs and resveratrol alone did not show a significant inhibitory effect while N-acetylcysteine inhibited the formation of most metabolite precursors and DNA adducts. Moreover, the combinations of classical drugs with antioxidants were more effective rather than compounds alone. This strategy might be a valuable tool to prevent the initiation of helminth infection-associated carcinogenesis.

The contribution of domestic animals to the transmission of schistosomiasis japonica in the Lindu Subdistrict of the Central Sulawesi Province, Indonesia

Background and Aim:

Schistosomiasis is endemic in Indonesia and is found in three remote areas in Central Sulawesi Province. Non-human mammals serve as reservoir hosts, meaning the disease is zoonotic. The previous schistosomiasis studies in animals from the Lindu Subdistrict did not determine which domestic animal species can serve as the primary source of transmission. No animals have been treated in Indonesia to control the disease; therefore, the parasite’s life cycle is not blocked entirely. This study aimed to determine the prevalence and identify the risk factors associated with, Schistosoma japonicum infection in animals, and identify animals’ relative contributions to S. japonicum transmission in the Lindu Subdistrict.

Materials and Methods:

A cross-sectional survey of S. japonicum infected animals was conducted in five villages of the Lindu Subdistrict. Fecal samples were collected from 134 selected animals (13 cattle, 26 buffaloes, 28 horses, 59 pigs, and 8 dogs). S. japonicum infection and infection intensity were determined using the Danish Bilharziasis Laboratory method. Environmental contamination with schistosome eggs was measured. The data were analyzed using a Chi-square test.

Results:

The overall prevalence of schistosomiasis was 32.9%, with the prevalence of infection in each species of animal at 61.5% in cattle, 42.3% in buffaloes, 25.0% in horses, 35.6% in pigs, and 12.5% in dogs. Free-range pigs were 8.667 times more likely to have S. japonicum infection than pigs kept in cages. Buffaloes, cattle, and horses were the primary sources of S. japonicum egg contamination, with relative transmission indices of 59.15%, 22.80%, and 10.61%, respectively.

Conclusion:

Bovines and horses are the main contributors to schistosomiasis transmission in the Lindu Subdistrict. In conjunction with other schistosomiasis control programs, the government should treat infected animals living within endemic areas where there are high infection rates of S. japonicum.

Differential impact of mass and targeted praziquantel delivery on schistosomiasis control in school-aged children: A systematic review and meta-analysis

Background

Schistosomiasis is a widespread public health concern in the poorest regions of the world. The principal control strategy is regular praziquantel administration to school-aged children in endemic areas. With calls for the elimination of schistosomiasis as a public health problem, expanding praziquantel delivery to all community members has been advocated. This systematic review and meta-analysis compares the impact of community-wide and child-targeted praziquantel distribution on schistosomiasis prevalence and intensity in school-aged children.

Methodology/Principal findings

We searched MEDLINE, Embase and Web of Science to identify papers that reported schistosome prevalence before and after praziquantel administration, either to children only or to all community members. Extracted data included Schistosoma species, drug administration strategy, number of treatment rounds, follow-up interval and prevalence and intensity before and after treatment. We used inverse variance weighted generalised linear models to examine the impact of mass versus targeted drug administration on prevalence reduction, and weighted boxplots to examine the impact on infection intensity reduction. This study is registered with PROSPERO, number CRD42018095377.

In total, 34 articles were eligible for systematic review and 28 for meta-analysis. Schistosoma mansoni was reported in 20 studies; Schistosoma haematobium in 19 studies, and Schistosoma japonicum in two studies. Results of generalised linear models showed no detectable difference between mass and targeted treatment strategies on prevalence reduction in school-aged children for S. mansoni (odds ratio 0.47, 95%CI 0.13–1.68, p = 0.227) and S. haematobium (0.41, 95%CI 0.06–3.03, p = 0.358). Box plots also showed no apparent differences in intensity reduction between the two treatment strategies.

Conclusions/Significance

The results of this meta-analysis do not support the hypothesis that community-wide treatment is more effective than targeted treatment at reducing schistosomiasis infections in children. This may be due to the relatively small number of included studies, insufficient treatment coverage, persistent infection hotspots and unmeasured confounders. Further field-based studies comparing mass and targeted treatment are required.

Schistosomiasis is a neglected tropical disease, caused by parasitic worms, that affects more than 143 million people worldwide. Chronic infections can lead to significant morbidity including kidney damage, anaemia, malnutrition, infertility and growth impairment. School-aged children between six and 15 years are often targeted for regular treatment with praziquantel in large-scale drug delivery programs, because they suffer a disproportionate burden of morbidity. On the other hand, a mass drug delivery strategy that treats all members of the community has been suggested in a move towards elimination of schistosomiasis as a public health problem. In this systematic review, we assess the impact of community-wide versus children-only praziquantel distribution in reducing schistosomiasis infections in school-aged children. We did not detect a difference between mass and targeted treatment strategies, possibly due to factors including insufficient treatment coverage and persistent sources of reinfection. Addressing these factors may assist in optimising control programs.

Promethazine exhibits antiparasitic properties in vitro and reduces worm burden, egg production, hepato-, and splenomegaly in a schistosomiasis animal model

The treatment and control of schistosomiasis, a neglected disease that affects more than 200 million people worldwide, rely on the use of a single drug, praziquantel. A vaccine has yet to be developed and since new drug design and development is a lengthy and costly process, drug repurposing is a promising strategy. In this study, the efficacy of promethazine, a first-generation antihistamine, was evaluated against Schistosoma mansoni ex vivo and in a murine model of schistosomiasis. In vitro assays demonstrated that promethazine affected parasite motility, viability, and it induced severe tegumental damage in schistosomes. The LC₅₀ of the drug was 5.84 μM. Similar to promethazine, schistosomes incubated with atropine, a classical anticholinergic drug, displayed reduced motor activity. In an animal model, promethazine treatment was introduced at an oral dose of 100 mg/kg for five successive days at different intervals from the time of infection, for the evaluation of the stage-specific susceptibility (pre-patent and patent infections). Various parasitological criteria indicated the in vivo antischistosomal effects of promethazine: there were significant reductions in worm burden, egg production, and hepato- and splenomegaly. The highest worm burden reduction was achieved with promethazine in patent infections (> 90%). Taken together, considering the importance of the repositioning of drugs in infectious diseases, especially those related to poverty, our data revealed the possibility of promethazine repositioning as an antischistosomal agent.

Praziquantel Resistance in the Zoonotic Cestode Dipylidium caninum

Dipylidium caninum is a cosmopolitan cestode infecting dogs, cats, and humans. Praziquantel is a highly effective cestocidal drug and resistance in adult cestodes has not been reported. From 2016 to 2018, a population of dogs with cestode infections that could not be eliminated despite multiple treatments with praziquantel or epsiprantel was identified. Cases of D. caninum were clinically resistant to praziquantel and could not be resolved despite increasing the dose, frequency, and duration of treatment. Resistant isolates were identified and characterized by sequencing the 28S, 12S, and voltage-gated calcium channel beta subunit genes. Cases were only resolved following treatment with nitroscanate or a compounded pyrantel/praziquantel/oxantel product. Clinicians should be aware of this alarming development as treatment options for cestodes are limited in both human and veterinary medicine.

Ultrasound Evolution of Pediatric Urinary Schistosomiasis after Treatment with Praziquantel in a Highly Endemic Area

Urinary schistosomiasis causes damage to the urological system. Ultrasound is a method that detects the burden of secondary disease, individually and in epidemiological studies. In this study, the Schistosoma haematobium-associated urinary tract pathology is analyzed before and after treatment in a short period of time. Seventy children who had previously participated in an epidemiological study on schistosomiasis in the city of Cubal, Angola, and had also performed urinary ultrasound between August 2013 and February 2014 were cited 6-8 months later to assess the possible reinfection and repeat new urinary ultrasound, analyzing changes at the level of urinary pathology. The presence of hematuria and proteinuria was also analyzed. Of the 70 children analyzed, 29 (41.4%) were girls, with an average age of 10.4 years (standard deviation 2.3). Fifty-three (75.7%) had an improvement in their bladder and/or kidney scores, whereas 12 (17.1%) had no change and five (7.1%) had progression of the disease. None of the parameters analyzed completely disappeared. After one single course of treatment with praziquantel, all the analyzed parameters showed regression. Improvement was greater in the urinary bladder than in the upper urinary tract, though these lesions also reversed; the reversion of all parameters was greater among children older than 10 years old than the younger ones. Proteinuria was the parameter with a smaller reduction. Ultrasound should be a usual tool for diagnosis and follow-up in urinary schistosomiasis, particularly in children; more accurate recommendations about follow-up in the case of children whose lesions do not reverse should be established.

Antischistosomal Properties of Sclareol and Its Heck-Coupled Derivatives: Design, Synthesis, Biological Evaluation, and Untargeted Metabolomics

Sclareol, a plant-derived diterpenoid widely used as a fragrance and flavoring substance, is well-known for its promising antimicrobial and anticancer properties. However, its activity on helminth parasites has not been previously reported. Here, we show that sclareol is active against larval (IC₅₀ ≈ 13 μM), juvenile (IC₅₀ = 5.0 μM), and adult (IC₅₀ = 19.3 μM) stages of Schistosoma mansoni, a parasitic trematode responsible for the neglected tropical disease schistosomiasis. Microwave-assisted synthesis of Heck-coupled derivatives improved activity, with the substituents choice guided by the Matsy decision tree. The most active derivative 12 showed improved potency and selectivity on larval (IC₅₀ ≈ 2.2 μM, selectivity index (SI) ≈ 22 in comparison to HepG2 cells), juvenile (IC₅₀ = 1.7 μM, SI = 28.8), and adult schistosomes (IC₅₀ = 9.4 μM, SI = 5.2). Scanning electron microscopy studies revealed that compound 12 induced blebbing of the adult worm surface at sublethal concentration (12.5 μM); moreover, the compound inhibited egg production at the lowest concentration tested (3.13 μM). The observed phenotype and data obtained by untargeted metabolomics suggested that compound 12 affects membrane lipid homeostasis by interfering with arachidonic acid metabolism. The same methodology applied to praziquantel (PZQ)-treated worms revealed sugar metabolism alterations that could be ascribed to the previously reported action of PZQ on serotonin signaling and/or effects on glycolysis. Importantly, our data suggest that compound 12 and PZQ exert different antischistosomal activities. More studies will be necessary to confirm the generated hypothesis and to progress the development of more potent antischistosomal sclareol derivatives.

The antioxidants resveratrol and N-acetylcysteine enhance anthelmintic activity of praziquantel and artesunate against Schistosoma mansoni

Background

Treatment of schistosomiasis has relied on the anthelmintic drug praziquantel (PZQ) for more than a generation. Despite its celebrated performance for treatment and control of schistosomiasis and other platyhelminth infections, praziquantel has some shortcomings and the inability of this drug to counteract disease sequelae prompts the need for novel therapeutic strategies.

Methods

Using a host-parasite model involving Biomphalaria glabrata and Schistosoma mansoni we established mechanical transformation of S. mansoni cercariae into newly transformed schistosomula (NTS) and characterized optimal culture conditions. Thereafter, we investigated the antischistosomal activity and ability of the antioxidants N-acetylcysteine (NAC) and resveratrol (RESV) to augment the performance of praziquantel and/or artesunate (AS) against larval stages of the parasite. Drug effects were evaluated by using an automated microscopical system to study live and fixed parasites and by transmission electron microscopy (TEM).

Results

Transformation rates of cercariae to schistosomula reached ~ 70% when the manipulation process was optimized. Several culture media were tested, with M199 supplemented with HEPES found to be suitable for S. mansoni NTS. Among the antioxidants studied, RESV alone or combined with anthelminthic drugs achieved better results rather N-acetylcysteine (NAC). TEM observations demonstrated that the combination of AS + RESV induced severe, extensive alterations to the tegument and subtegument of NTS when compared to the constituent compounds alone. Two anthelmintic–antioxidant combinations, praziquantel-resveratrol [combination index (CI) = 0.74] and artesunate-resveratrol (CI = 0.34) displayed moderate and strong synergy, respectively.

Conclusions

The use of viability markers including staining with propidium iodide increased the accuracy of drug screening assays against S. mansoni NTS. The synergies observed might be the consequence of increased action by RESV on targets of AS and PZQ and/or they may act through concomitantly on discrete targets to enhance overall antischistosomal action. Combinations of active agents, preferably with discrete modes of action including activity against developmental stages and/or the potential to ameliorate infection-associated pathology, might be pursued in order to identify novel therapeutic interventions.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3566-9) contains supplementary material, which is available to authorized users.

Identification of a new panel of reference genes to study pairing-dependent gene expression in Schistosoma mansoni

Facilitated by the Schistosoma mansoni genome project, multiple transcriptomic studies were performed over the last decade to elucidate gene expression patterns among different developmental stages of the complex schistosome life cycle. While these analyses enable the identification of candidate genes with key functions in schistosome biology, a diverse molecular tool set is needed that allows comprehensive functional characterization at the single gene level. This includes the availability of reliable reference genes to confirm changes in the transcription of genes of interest over different biological samples and experimental conditions. In particular, the investigation of one key aspect of schistosome biology, the pairing-dependent gene expression in females and males, requires knowledge on reference genes that are expressed independently of both pairing and of in vitro culture effects. Therefore, the present study focused on the identification of quantitative reverse transcription (qRT)-PCR reference genes suitable for the investigation of pairing-dependent gene expression in the S. mansoni male. The "pipeline" we present here is based on qRT-PCR analyses of high biological replication combined with three different statistical analysis tools, BestKeeper, geNorm, and NormFinder. Our approach resulted in a statistically robust ranking of 15 selected reference genes with respect to their transcription stability between pairing-unexperienced and -experienced males. We further tested the top seven candidate genes for their transcription stability during invitro culture of adult S. mansoni. Of these, the two most suitable reference genes were used to investigate the influence of the pairing contact on the transcription of genes of interest, comprising a tyrosine decarboxylase gene Smtdc1, an ebony ortholog Smebony, and the follistatin ortholog Smfst in S. mansoni males. Performing pairing, separation and re-pairing experiments with adult S. mansoni in vitro, our results indicate for the first time that pairing can act as a molecular on/off-switch of specific genes to strictly control their expression in schistosome males.

In vitro and in vivo activities of DW-3-15, a commercial praziquantel derivative, against Schistosoma japonicum

Background

Schistosomiasis is a debilitating neglected tropical disease that affects approximately 190 million people around the world. Praziquantel (PZQ) is the only drug available for use against all Schistosoma species. Although PZQ has a high efficacy, recognized concerns have prompted the development of new, alternative drugs for repeated use in endemic areas where PZQ efficacy against strains of Schistosoma is reduced. A hybrid drug containing different pharmacophores within a single molecule is a promising strategy. Our earlier in vivo studies showed the significant antiparasitic activity of a praziquantel derivative, DW-3-15, against Schistosoma japonicum. In the present study, DW-3-15 was synthesized in large amounts by a pharmaceutical company and its schistosomicidal efficacy and stability were further confirmed. Parameters such as parasite viability, pairing and oviposition were evaluated in vitro. An in vivo study was conducted to assess the effect of commercial DW-3-15 on worm burden, egg production and diameter of granulomas. Additionally, to gain insight into the mechanism of action for DW-3-15, morphological changes in the tegument of S. japonicum were also examined.

Results

The in vitro study showed the antiparasitic activity of DW-3-15 against S. japonicum, with significant reductions in viability of adult and juvenile worms, worm pairings and egg output. Compared to PZQ, DW-3-15 induced similar ultrastructural changes and evident destruction of the tegument surface in male worms. In vivo, the oral administration of DW-3-15 at a dose of 400 mg/kg per day for five consecutive days in mice significantly reduced the total worm burden and number of eggs in the liver. Histological analysis of the livers showed a marked reduction in the average diameter of the egg granuloma.

Conclusions

Our findings suggest that DW-3-15, a PZQ derivative with the prospect of commercial production, can be developed as a potential promising schistosomicide.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3442-7) contains supplementary material, which is available to authorized users.

The Impact of Intensive Versus Standard Anthelminthic Treatment on Allergy-related Outcomes, Helminth Infection Intensity, and Helminth-related Morbidity in Lake Victoria Fishing Communities, Uganda: Results From the LaVIISWA Cluster-randomized Trial

BACKGROUND

The prevalence of allergy-related diseases is increasing in low-income countries. Parasitic helminths, common in these settings, may be protective. We hypothesized that intensive, community-wide, anthelminthic mass drug administration (MDA) would increase allergy-related diseases, while reducing helminth-related morbidity.

METHODS

In an open, cluster-randomized trial (ISRCTN47196031), we randomized 26 high-schistosomiasis-transmission fishing villages in Lake Victoria, Uganda, in a 1:1 ratio to receive community-wide intensive (quarterly single-dose praziquantel plus albendazole daily for 3 days) or standard (annual praziquantel plus 6 monthly single-dose albendazole) MDA. Primary outcomes were recent wheezing, skin prick test positivity (SPT), and allergen-specific immunoglobulin E (asIgE) after 3 years of intervention. Secondary outcomes included helminths, haemoglobin, and hepatosplenomegaly.

RESULTS

The outcome survey comprised 3350 individuals. Intensive MDA had no effect on wheezing (risk ratio [RR] 1.11, 95% confidence interval [CI] 0.64-1.93), SPT (RR 1.10, 95% CI 0.85-1.42), or asIgE (RR 0.96, 95% CI 0.82-1.12). Intensive MDA reduced Schistosoma mansoni infection intensity: the prevalence from Kato Katz examinations of single stool samples from each patient was 23% versus 39% (RR 0.70, 95% CI 0.55-0.88), but the urine circulating cathodic antigen test remained positive in 85% participants in both trial arms. Hookworm prevalence was 8% versus 11% (RR 0.55, 95% CI 0.31-1.00). There were no differences in anemia or hepatospenomegaly between trial arms.

CONCLUSIONS

Despite reductions in S. mansoni intensity and hookworm prevalence, intensive MDA had no effect on atopy, allergy-related diseases, or helminth-related pathology. This could be due to sustained low-intensity infections; thus, a causal link between helminths and allergy outcomes cannot be discounted. Intensive community-based MDA has a limited impact in high-schistosomiasis-transmission fishing communities, in the absence of other interventions.

CLINICAL TRIALS REGISTRATION

ISRCTN47196031.

Phenotypic screening of nonsteroidal anti-inflammatory drugs identified mefenamic acid as a drug for the treatment of schistosomiasis

Background

Treatment and control of schistosomiasis, one of the most insidious and serious parasitic diseases, depend almost entirely on a single drug, praziquantel. Since the funding for drug development for poverty-associated diseases is very limited, drug repurposing is a promising strategy. In this study, 73 nonsteroidal anti-inflammatory drugs (NSAIDs) commonly used in medical and veterinary fields were evaluated for their anti-schistosomal properties.

Methods

The efficacy of NSAIDs was first tested against adult Schistosoma mansoni ex vivo using phenotypic screening strategy, effective drugs were further tested in a murine model of schistosomiasis. The disease parameters measured were worm and egg burden, hepato- and splenomegaly.

Findings

From 73 NSAIDs, five (mefenamic acid, tolfenamic acid, meclofenamic acid, celecoxib, and diclofenac) were identified to effectively kill schistosomes. These results were further supported by scanning electron microscopy analysis. In addition, the octanol-water partition coefficient, both for neutral and ionized species, revealed to be a critical property for the ex vivo activity profile. Compounds were then tested in vivo using both patent and a prepatent S. mansoni infection in a mouse model. The most effective NSAID was mefenamic acid, which highly reduced worm burden, egg production, and hepato- and splenomegaly.

Interpretation

The treatment regimen used in this study is within the range for which mefenamic acid has been used in clinical practice, thus, it is demonstrated the capacity of mefenamic acid to act as a potent anti-schistosomal agent suitable for clinical repurposing in the treatment of schistosomiasis.

Schistosoma and Other Relevant Helminth Infections in HIV-Positive Individuals-an Overview

For many years, researchers have postulated that helminthic infections may increase susceptibility to HIV, and that immune activation may have contributed to the extensive spread of HIV in sub-Saharan Africa. In the meantime, immunological studies have provided some evidence in support of this hypothesis, while cross-sectional clinical studies were able to further support the assumed association between HIV infection and selected helminthic co-infections. However, as many of the helminthic infections relevant to HIV-infected patients belong to the group of “neglected tropical diseases”, as defined by the World Health Organization, a certain lack of attention has inhibited progress in fully scaling up treatment and prevention efforts. In addition, despite the fact that the challenges of co-infections have preoccupied clinicians for over two decades, relevant research questions remain unanswered. The following review aims to provide a concise overview of associations between HIV and selected helminthic co-infections concerning aspects of HIV acquisition and transmission, clinical and immunological findings in co-infected individuals, as well as treatment and prevention efforts.

Usnic acid potassium salt from Cladonia substellata (Lichen): Synthesis, cytotoxicity and in vitro anthelmintic activity and ultrastructural analysis against adult worms of Schistosoma mansoni

We report for the first time the in vitro effect of Potassium Salt, derived from Usnic Acid (PS-UA), isolated from the lichen Cladonia substellata Vanio, on couples of Schistosoma mansoni. As schistosomicide parameters, we evaluated mortality, motility, cell viability of the worms and tegument changes by scanning electron microscopy (SEM). Exposure to a concentration of 100 μM caused 75% mortality after 3 h. After 6 h, changes in motility in concentrations of 50 and 25 μM are evidenced. After 12 h and 24h, the concentrations of 50 and 100 μM caused 6.25% and 87.5% and 50% and 100% mortality, respectively. PS-UA reduced the cell viability of the worms by 27.36% and 52.82% at concentrations 50 and 100 μM, respectively. Through SEM we observed progressive dose-and time-dependent, alterations such as swelling, blisters, dorsoventral contraction, erosion until disintegration of the tubercles in the tegument of male and female. PS-UA did not alter the viability of human peripheral blood mononuclear cells and showed high selectivity indices (IC₅₀ > 200 μM). Our results indicate that PS-UA represents a possible candidate for a new anthelmintic drug in the control of schistosomiasis.

WIPO Re:Search: Catalyzing Public-Private Partnerships to Accelerate Tropical Disease Drug Discovery and Development

Tropical diseases, including malaria and a group of infections termed neglected tropical diseases (NTDs), pose enormous threats to human health and wellbeing globally. In concert with efforts to broaden access to current treatments, it is also critical to expand research and development (R&D) of new drugs that address therapeutic gaps and concerns associated with existing medications, including emergence of resistance. Limited commercial incentives, particularly compared to products for diseases prevalent in high-income countries, have hindered many pharmaceutical companies from contributing their immense product development know-how and resources to tropical disease R&D. In this article we present WIPO Re:Search, an international initiative co-led by BIO Ventures for Global Health (BVGH) and the World Intellectual Property Organization (WIPO), as an innovative and impactful public-private partnership model that promotes cross-sector intellectual property sharing and R&D to accelerate tropical disease drug discovery and development. Importantly, WIPO Re:Search also drives progress toward the United Nations Sustainable Development Goals (SDGs). Through case studies, we illustrate how WIPO Re:Search empowers high-quality tropical disease drug discovery researchers from academic/non-profit organizations and small companies (including scientists in low- and middle-income countries) to leapfrog their R&D programs by accessing pharmaceutical industry resources that may not otherwise be available to them.

Schistosomicidal and prophylactic activities of phthalimido-thiazoles derivatives on schistosomula and adult worms

Schistosomiasis is a major public health problem worldwide, especially in poor communities. Praziquantel is currently the only drug available to treat schistosomiasis and it shows low efficacy against schistosomula and juveniles stages of Schistosoma mansoni, allowing lower cure rate in areas with high endemicity. There is an urgent need to identify new antischistosomal drugs. Previous works identified phthalimido-thiazoles as privileged structures acting as schistossomicidal agent. In this way, a phthalimido-thiosemicarbazide intermediate and eight phthalimido-thiazoles derivatives were evaluated concerning the in vitro antischistosomal activity compounds in adult phase of Schistosoma mansoni and examined alterations on the tegumental surface. The results revealed that compounds 2f, 2 l and 2 m caused significant mortality in adult worms at concentrations range of 20 μg/mL to 100 μg/mL. These compounds were also selected in view to verify the activity against the schistosomula. Compound 2 m promoted 100% of mortality of larval forms until doses of 2.5 μg/mL within 48 h. In addition, when compound 2 m was administered orally at dose of 200 mg/kg for 5 consecutive days to the infected mouse with adult schistosomes, a reduction in the parasite burden was observed. Furthermore, scanning electron microscopy revealed that compound 2 m kill the parasite by tegumental damage and bubbles generation.

Alterations of the Mice Gut Microbiome via Schistosoma japonicum Ova-Induced Granuloma

Schistosomiasis, also called bilharziasis, is a neglected tropical disease induced by Schistosoma spp. that causes hundreds of millions of infections. Although Schistosoma ova-induced granulomas commonly cause inflammation, hyperplasia, ulceration, micro abscess formation, and polyposis, the role of the egg granuloma on the gut microbiome remains unclear. To explore the role, gut microbial communities in mice infected with Schistosoma japonicum were surveyed. Female C57BL/6 and BALB/c mice were exposed to cercariae of S. japonicum for 45 and 65 days and then sacrificed. Intestinal contents and feces were collected, DNA was extracted, and high-throughput 16S rRNA gene-based pyrosequencing was used to provide a comparative analysis of gut microbial diversity. The intestinal mucosal tissues were also examined. Histopathologic analysis demonstrated that the basic structure of the colonic mucosa was damaged by ova-induced granuloma. Regarding the gut microbiome, 2,578,303 good-quality sequences were studied and assigned to 25,278 Operational Taxonomic Units (OTUs) at a threshold of 97% similarity. The average number of OTUs for C57BL/6 and BALB/c were 545 and 530, respectively. At the phylum level, intestinal microbial communities were dominated by Firmicutes, Bacteroidetes, Proteobacteria, and Verrucomicrobia. Infection with S. japonicum modified bacterial richness in the fecal associated microbiota. Exposure significantly modified bacterial community composition among different groups. At the phylogenetic levels, LEfSe analysis revealed that several bacterial taxa were significantly associated with the S. japonicum-infected mice. The present results suggest that egg granulomas in the intestine influence differentiation of the gut microbial community under pathophysiological conditions. This result suggests that intestinal microbiome-based strategies should be considered for early diagnosis, clinical treatment, and prognosis evaluation of schistosomiasis.

Asian Schistosomiasis: Current Status and Prospects for Control Leading to Elimination

Schistosomiasis is an infectious disease caused by helminth parasites of the genus Schistosoma. Worldwide, an estimated 250 million people are infected with these parasites with the majority of cases occurring in sub-Saharan Africa. Within Asia, three species of Schistosoma cause disease. Schistosoma japonicum is the most prevalent, followed by S. mekongi and S. malayensis. All three species are zoonotic, which causes concern for their control, as successful elimination not only requires management of the human definitive host, but also the animal reservoir hosts. With regard to Asian schistosomiasis, most of the published research has focused on S. japonicum with comparatively little attention paid to S. mekongi and even less focus on S. malayensis. In this review, we examine the three Asian schistosomes and their current status in their endemic countries: Cambodia, Lao People's Democratic Republic, Myanmar, and Thailand (S. mekongi); Malaysia (S. malayensis); and Indonesia, People's Republic of China, and the Philippines (S. japonicum). Prospects for control that could potentially lead to elimination are highlighted as these can inform researchers and disease control managers in other schistosomiasis-endemic areas, particularly in Africa and the Americas.

In Vitro and In Vivo Studies of Spironolactone as an Antischistosomal Drug Capable of Clinical Repurposing

Schistosomiasis is a parasitic flatworm disease that infects over 200 million people worldwide, especially in poor communities. Treatment and control of the disease rely on just one drug, praziquantel. Since funding for drug development for poverty-associated diseases is very limited, drug repurposing is a promising strategy. In this study, from a screening of 13 marketed diuretics, we identified that spironolactone, a potassium-sparing diuretic, had potent antischistosomal effects on Schistosoma mansoni in vitro and in vivo in a murine model of schistosomiasis. In vitro, spironolactone at low concentrations (<10 µM) is able to alter worm motor activity and the morphology of adult schistosomes, leading to parasitic death. In vivo, oral treatment with spironolactone at a single dose (400 mg/kg) or daily for five consecutive days (100 mg/kg/day) in mice harboring either patent or prepatent infections significantly reduced worm burden, egg production, and hepato- and splenomegaly (P < 0.05 to P < 0.001). Taken together, with the safety profile of spironolactone, supported by its potential to affect schistosomes, these results indicate that spironolactone could be a potential treatment for schistosomiasis and make it promising for repurposing.

The impact of cinnarizine and griseofulvin on juvenile and adult stages of Schistosoma mansoni

Schistosomiasis affects millions globally. There is no vaccine, and treatment depends entirely on praziquantel (PZQ). Field isolates exhibit reduced susceptibility to PZQ, and resistance has been experimentally induced, suggesting that reliance on a single treatment is particularly dangerous. The present study investigated the value of cinnarizine and griseofulvin against Schistosoma mansoni through their in vitro effects on adult worms and oviposition as well as in vivo evaluation in early and late infection, compared to PZQ, in a preliminary experimental model. In vitro, both cinnarizine and griseofulvin showed uncoupling, sluggish worm movement and complete absence of ova at 100 μg/ml. In early infection, cinnarizine showed a significant reduction in the number of porto-mesenteric couples compared to the griseofulvin and control groups, a finding similar to PZQ. Remarkably, cinnarizine significantly exceeded PZQ and griseofulvin in reducing the total worm burden. In late infection, cinnarizine and griseofulvin showed results similar to PZQ by significantly reducing the numbers of hepatic and porto-mesenteric couples and total worm burden compared to controls. Cinnarizine performed better than griseofulvin by reducing hepatic and intestinal ovum counts, and it led to complete disappearance of the first two immature stages. The current work suggests the possibility of using cinnarizine and griseofulvin, mainly in late S. mansoni infection, especially cinnarizine, which showed similar results to PZQ and surpassed it in early infection. Further studies are required to elucidate their exact mechanisms of action and particularly their synergistic effect with PZQ.

14-3-3 protein and ubiquitin C acting as SjIAP interaction partners facilitate tegumental integrity in Schistosoma japonicum

Schistosomiasis, caused by trematodes of the genus Schistosoma, remains an important public health issue. Adult schistosomes can survive in the definitive host for several decades, although they are subject to the host immune response. Consequently, understanding the mechanism underlying worm survival in the definitive hosts could aid in developing novel strategies against schistosomiasis. We previously found that an inhibitor of apoptosis in Schistosoma japonicum (SjIAP) could negatively regulate apoptosis by inhibiting caspase activity, which plays a critical role in maintaining tegument integrity. The current study aimed to further analyze the mechanism related to SjIAP governing worm tegument integrity; therefore, we used a yeast two-hybrid screen and identified a series of putative interacting partners of SjIAP, including 14-3-3 (Sj14-3-3) and ubiquitin C (SjUBC). Quantitative real time PCR (qRT-PCR) analysis indicated that transcript profiles of Sj14-3-3 and SjUBC increased together with worm development in definitive hosts, which corresponds to those of SjIAP in S. japonicum. Immunohistochemical analysis showed Sj14-3-3 and SjUBC were located in the tegument of adult parasites while they were also ubiquitously distributed in the bodies of worms. Silencing of Sj14-3-3/SjUBC expression led to increased caspase activity and induced worm death. Inhibition of Sj14-3-3 or SjUBC resulted in significant morphological alterations in the schistosome tegument. Overall, our findings indicated that Sj14-3-3 and SjUBC interacting with SjIAP may belong to another strategy of S. japonicum to maintain the tegument integrity.

Combination Anthelmintic/Antioxidant Activity Against Schistosoma Mansoni

Schistosomiasis is a major neglected tropical disease. Treatment for schistosomiasis with praziquantel (PZQ), which is effective against the parasite, by itself is not capable to counteract infection-associated disease lesions including hepatic fibrosis. There is a pressing need for novel therapies. Due to their biological properties, antioxidant biomolecules might be useful in treating and reverting associated pathological sequelae. Here, we investigated a novel therapy approach based on a combination of anthelmintic drugs with antioxidant biomolecules. We used a host-parasite model involving Bioamphalaria glabrata and newly transformed schistosomula (NTS) of Schistosoma mansoni. For in vitro drug screening assays, was selected several antioxidants and evaluated not only antischistosomal activity but also ability to enhance activity of the anthelmintic drugs praziquantel (PZQ) and artesunate (AS). The morphological alterations induced by compounds alone/combined were assessed on daily basis using an inverted and automated microscope to quantify NTS viability by a fluorometric-based method. The findings indicated that not only do some antioxidants improve antischistosomal activity of the two anthelmintics, but they exhibit activity per se, leading to high mortality of NTS post-exposure. The combination index (CI) of PZQ + Mel (CI = 0.80), PZQ + Resv (CI = 0.74), AS + Resv (CI = 0.34), AS + NAC (CI = 0.89), VDT + Flav (CI = 1.03) and VDT + Resv (CI = 1.06) reveal that they display moderate to strong synergism. The combination of compounds with discrete mechanisms of action might provide a valuable adjunct to contribution for treatment of schistosomiasis-associated disease.

A novel cell-free method to culture Schistosoma mansoni from cercariae to juvenile worm stages for in vitro drug testing

Background

The arsenal in anthelminthic treatment against schistosomiasis is limited and relies almost exclusively on a single drug, praziquantel (PZQ). Thus, resistance to PZQ could constitute a major threat. Even though PZQ is potent in killing adult worms, its activity against earlier stages is limited. Current in vitro drug screening strategies depend on newly transformed schistosomula (NTS) for initial hit identification, thereby limiting sensitivity to new compounds predominantly active in later developmental stages. Therefore, the aim of this study was to establish a highly standardized, straightforward and reliable culture method to generate and maintain advanced larval stages in vitro. We present here how this method can be a valuable tool to test drug efficacy at each intermediate larval stage, reducing the reliance on animal use (3Rs).

Methodology/Principal findings

Cercariae were mechanically transformed into skin-stage (SkS) schistosomula and successfully cultured for up to four weeks with no loss in viability in a commercially available medium. Under these serum- and cell-free conditions, development halted at the lung-stage (LuS). However, the addition of human serum (HSe) propelled further development into liver stage (LiS) worms within eight weeks. Skin and lung stages, as well as LiS, were submitted to 96-well drug screening assays using known anti-schistosomal compounds such as PZQ, oxamniquine (OXM), mefloquine (MFQ) and artemether (ART). Our findings showed stage-dependent differences in larval susceptibility to these compounds.

Conclusion

With this robust and highly standardized in vitro assay, important developmental stages of S. mansoni up to LiS worms can be generated and maintained over prolonged periods of time. The phenotype of LiS worms, when exposed to reference drugs, was comparable to most previously published works for ex vivo harvested adult worms. Therefore, this in vitro assay can help reduce reliance on animal experiments in search for new anti-schistosomal drugs.

Schistosomiasis remains a major health threat, predominantly in developing countries. Even though there has been some progress in search of new drugs, praziquantel remains the only available drug. Probably the most important advance in the search for new drugs was in vitro transformation of cercariae and their subsequent culture. However, hit identification in compound screenings is exclusively tested in skin stage parasites and is only confirmed for more mature worms in a subsequent step. This is in part due to the lack of an easy culture system for advance-stage parasites. We present here a reliable and highly standardized way to generate LiS worms in vitro in a cell-free culture system. The inclusion of in vitro drug tests on advanced-stage parasites in initial hit identification will help to identify compounds that might otherwise be overlooked. Furthermore, the ability to continuously observe the parasite’s development in vitro will provide an important platform for a better understanding of its maturation in the human host. Taken together, this opens up new avenues to investigate the influence of specific cell types or host proteins on the development of Schistosoma mansoni and provides an additional tool to reduce animal use in future drug discovery efforts (3Rs).

PZQ Therapy: How Close are we in the Development of Effective Alternative Anti-schistosomal Drugs?

Today schistosomiasis, caused mainly by the three major schistosome species (S. mansoni, S. haematobium and S. japonicum), has for many decades and still continues to be on a rapid and swift rise globally, claiming thousands of lives every year and leaving 800 million people at the risk of infection. Due to the high prevalence of this disease and the steady increase in the infection rates, praziquantel (PZQ) remains the only effective drug against this acute disease although it has no effect on the juvenile schistosome parasite. However, no significant approaches have been made in recent years in the discovery of new or alternative drugs and unfortunately, resistance to this drug has been reported in some parts of the world. Therefore, it is imperative to develop a new drug for this debilitating disease. In this review, a brief history of past, present, and new promising anti-schistosomal drugs is presented.