Schistosoma mansoni: reduced efficacy of chemotherapy in infected T-cell-deprived mice

Praziquantel: An update on the mechanism of its action against schistosomiasis and new therapeutic perspectives

Praziquantel (PZQ) is the drug of choice for the treatment of all forms of schistosomiasis, although its mechanisms of action are not completely understood. PZQ acts largely on adult worms. This narrative literature review describes what is known about the mechanisms of action of PZQ against schistosomes from in vitro and in vivo studies and highlights the molecular targets in parasites and immune responses induced in definitive hosts by this drug. Moreover, new therapeutic uses of PZQ are discussed. Studies have demonstrated that in addition to impacting voltage-operated Ca2 + channels, PZQ may interact with other schistosome molecules, such as myosin regulatory light chain, glutathione S-transferase, and transient receptor potential channels. Following PZQ administration, increased T regulatory type 1 (Tr1) cell differentiation and decreased inflammation were observed, indicating that PZQ promotes immunoregulatory pathways. Although PZQ is widely used in mass drug administration schemes, the existence of resistant parasites has not been proven; however, it is a concern that should be constantly investigated in human populations. In addition, we discuss studies that evaluate health applications of PZQ (other than helminth infection), such as its effect in cancer therapy and its adjuvant action in vaccines against viruses.

Fifty years of the schistosome tegument: discoveries, controversies, and outstanding questions

The unique multilaminate appearance of the tegument surface of schistosomes was first described in 1973, in one of the earliest volumes of the International Journal for Parasitology. The present review, published almost 50 years later, traces the development of our knowledge of the tegument, starting with those earliest cytological advances, particularly the surface plasma membrane-membranocalyx complex, through an era of protein discovery to the modern age of protein characterization, aided by proteomics. More recently, analysis of single cell transcriptomes of schistosomes is providing insight into the organisation of the cell bodies that support the surface syncytium. Our understanding of the tegument, notably the nature of the proteins present within the plasma membrane and membranocalyx, has provided insights into how the schistosomes interact with their hosts but many aspects of how the tegument functions remain unanswered. Among the unresolved aspects are those concerned with maintenance and renewal of the surface membrane complex, and whether surface proteins and membrane components are recycled. Current controversies arising from investigations about whether the tegument is a source of extracellular vesicles during parasitism, and if it is covered with glycolytic enzymes, are evaluated in the light of cytological and proteomic knowledge of the layer.

Schistosoma mansoni alter transcription of immunomodulatory gene products following in vivo praziquantel exposure

Control of the neglected tropical disease schistosomiasis relies almost entirely on praziquantel (PZQ) monotherapy. How PZQ clears parasite infections remains poorly understood. Many studies have examined the effects of PZQ on worms cultured in vitro, observing outcomes such as muscle contraction. However, conditions worms are exposed to in vivo may vary considerably from in vitro experiments given the short half-life of PZQ and the importance of host immune system engagement for drug efficacy in animal models. Here, we investigated the effects of in vivo PZQ exposure on Schistosoma mansoni. Measurement of pro-apoptotic caspase activation revealed that worm death occurs only after parasites shift from the mesenteric vasculature to the liver, peaking 24 hours after drug treatment. This indicates that PZQ is not directly schistocidal, since PZQ’s half-life is ~2 hours in humans and ~30 minutes in mice, and focuses attention on parasite interactions with the host immune system following the shift of worms to the liver. RNA-Seq of worms harvested from mouse livers following sub-lethal PZQ treatment revealed drug-evoked changes in the expression of putative immunomodulatory and anticoagulant gene products. Several of these gene products localized to the schistosome esophagus and may be secreted into the host circulation. These include several Kunitz-type protease inhibitors, which are also found in the secretomes of other blood feeding animals. These transcriptional changes may reflect mechanisms of parasite immune-evasion in response to chemotherapy, given the role of complement-mediated attack and the host innate/humoral immune response in parasite elimination. One of these isoforms, SmKI-1, has been shown to exhibit immunomodulatory and anti-coagulant properties. These data provide insight into the effect of in vivo PZQ exposure on S. mansoni, and the transcriptional response of parasites to the stress of chemotherapy.

The disease schistosomiasis is caused by parasitic worms that live within the circulatory system. While this disease infects over 200 million people worldwide, treatment relies almost entirely on one drug, praziquantel, whose mechanism is poorly understood. In this study, we analyzed the effects of praziquantel treatment on the gene expression of parasites harvested from mice treated with praziquantel chemotherapy. Despite the rapid action of the drug on worms in vitro, we found that key outcomes in vivo (measurement of cell death and changes in gene expression) occurred relatively late (12+ hours after drug administration). We found that worms increased the expression of immunomodulatory gene products in response to praziquantel, including a Kunitz-type protease inhibitor that localized to the worm esophagus and may be secreted to the external host environment. These are an intriguing class of proteins, because they display anti-coagulant and immunomodulatory properties. Up-regulation of these gene products may reflect a parasite mechanism of immune-evasion in response to chemotherapy. This research provides insight into the mechanism of praziquantel by observing the effect of this drug on worms within the context of the host immune system.

Performance of an Ultra-Sensitive Assay Targeting the Circulating Anodic Antigen (CAA) for Detection of Schistosoma mansoni Infection in a Low Endemic Area in Brazil

Techniques with high sensitivity and specificity are required for an accurate diagnosis in low-transmission settings, where the conventional parasitological methods are insensitive. We determined the accuracy of an up-converting phosphor-lateral flow circulating anodic antigen (UCP-LF CAA) assay in urine and serum for Schistosoma mansoni diagnosis in low-prevalence settings in Ceará, Brazil, before and after praziquantel treatment. Clinical samples of a total of 258 individuals were investigated by UCP-LF CAA, point-of-care-circulating cathodic antigen (POC-CCA), soluble worm antigen preparation (SWAP)-ELISA and Kato-Katz (KK); a selection of 128 stools by real-time PCR technique. Three and 6-weeks after treatment, samples were collected and evaluated by detection Schistosoma circulating antigens (CAA and CCA). The UCP-LF CAA assays detected 80 positives (31%) with urine and 82 positives (31.8%) with serum. The urine POC-CCA and serum SWAP-ELISA assays detected 30 (11.6%) and 107 (40.7%) positives, respectively. The Kato-Katz technique revealed only 4 positive stool samples (1.6%). Among the 128 individuals with complete data records, 19 cases were identified by PCR (14.8%); Sensitivities and specificities of the UCP-LF CAA assays, determined versus a combined reference standard based on CCA/KK/PCR positivity, ranged from 60-68% to 68-77%, respectively. In addition only for comparative purposes, sensitivities of the different assays were determined vs. a comparative reference based on CAA/KK/PCR positivity, showing the highest sensitivity for the urine CAA assay (80%), followed by the serum CAA (70.9%), SWAP-ELISA (43.6%), PCR (34.5%), POC-CCA (29.1%), whilst triplicate Kato-Katz thick smears had a very low sensitivity (3.6%). CAA concentrations were higher in serum than in urine and were significantly correlated. There was a significant decrease in urine and serum CAA levels 3 and 6-weeks after treatment. The UCP-LF CAA assays revealed 33 and 28 S. mansoni-infected patients at the 3- and 6-week post-treatment follow-up, respectively. The UCP-LF CAA assays show high sensitivity for the diagnosis of S. mansoni in low-endemicity settings. It detects a considerably higher number of infections than microscopy, POC-CCA or PCR. Also it shows to be very useful for evaluating cure rates after treatment. Hence, the UCP-LF CAA assay is a robust and promising diagnostic approach in low-transmission settings.

Pharmacological and immunological effects of praziquantel against Schistosoma japonicum: a scoping review of experimental studies

BACKGROUND

Chemotherapy for schistosomiasis has been around for 100 years. During the past century, great efforts have been made to develop new antischistosomal drugs from antimonials to nonantimonials, and some of these have been used extensively in clinical treatment. With the exception of a few drugs, such as oxamniquine and metrifonate, most of the antischistosomals developed in the pre-praziquantel period have variable limitations with respect to safety and efficacy. Although oxamniquine and metrifonate have been used for schistosomiasis control, they are only effective against Schistosoma mansoni and S. haematobium, respectively. Currently, praziquantel is the only drug used for treatment of all five species of human schistosomes. In this review, the pharmacological and immunological effects of praziquantel against S. japonicum are summarized and discussed.

MAIN TEXT

From the end of the 1970s until the 2000s, scientists have conducted a series of experimental studies on the effects of praziquantel against S. japonicum. These have included examining its unique pharmacological action on schistosomes, the characteristics in susceptibility of the different developmental stages of schistosomes to the drug, the relationship between plasma concentration of the drug and efficacy, the impact of host factors on cidal action of the drug, prevention and early treatment of schistosomal infection, as well as praziquantel-resistant schistosomiasis.

CONCLUSION

The effects of praziquantel against S. japonicum, as elucidated by the experimental studies that are reviewed in this paper, may have some reference significance for the development of new antischistosomals.

Treatment of Schistosoma mansoni with miltefosine in vitro enhances serological recognition of defined worm surface antigens

Background

Miltefosine, an anti-cancer drug that has been successfully repositioned for treatment of Leishmania infections, has recently also shown promising effects against Schistosoma spp targeting all life cycle stages of the parasite. The current study examined the effect of treating Schistosoma mansoni adult worms with miltefosine on exposure of worm surface antigens in vitro.

Methodology/Principal findings

In an indirect immunofluorescence assay, rabbit anti-S.mansoni adult worm homogenate and anti-S. mansoni infection antisera gave strong immunofluorescence of the S. mansoni adult worm surface after treatment with miltefosine, the latter antiserum having previously been shown to synergistically enhance the schistosomicidal activity of praziquantel. Rabbit antibodies that recognised surface antigens exposed on miltefosine-treated worms were recovered by elution off the worm surface in low pH buffer and were used in a western immunoblotting assay to identify antigenic targets in a homogenate extract of adult worms (SmWH). Four proteins reacting with the antibodies in immunoblots were purified and proteomic analysis (MS/MS) combined with specific immunoblotting indicated they were the S. mansoni proteins: fructose-1,6 bisphosphate aldolase (SmFBPA), Sm22.6, alkaline phosphatase and malate dehydrogenase. These antibodies were also found to bind to the surface of 3-hour schistosomula and induce immune agglutination of the parasites, suggesting they may have a role in immune protection.

Conclusion/Significance

This study reveals a novel mode of action of miltefosine as an anti-schistosome agent. The immune-dependent hypothesis we investigated has previously been lent credence with praziquantel (PZQ), whereby treatment unmasks parasite surface antigens not normally exposed to the host during infection. Antigens involved in this molecular mechanism could have potential as intervention targets and antibodies against these antigens may act to increase the drug’s anti-parasite efficacy and be involved in the development of resistance to re-infection.

Schistosomiasis (Bilharzia) is a serious public health problem caused by a parasite of genus Schistosoma. There is an increasing concern about development of parasite resistance to the only drug available for treatment, praziquantel (PZQ). Miltefosine, a repurposed anti-cancer drug for treatment of Leishmania infection, was shown to have activity against Schistosoma in animal models at all the parasite’s life cycle stages. In this work, we examined the potential that miltefosine could act to expose parasite surface antigens that are normally hidden during natural infection as a way to avoid lethal effects of host immunity. We used two immunobinding techniques, immunofluorescence and western immunoblotting, and a protein identification technique, namely mass spectrometry, to identify proteins exposed on the worm surface following incubation with miltefosine. Four S. mansoni proteins were shown to be exposed by miltefosine treatment: fructose-bisphosphate aldolase (SmFBPA), Sm22.6, alkaline phosphatase and malate dehydrogenase. Antibodies specific for these antigens recognised and bound to the surface of early-stage schistosome larvae and antibodies specific for SmFBPA induced clumping of the larvae, suggesting a potential role in early parasite killing and protection against infection. These antibodies may be utilised to increase miltefosine’s anti-parasite efficacy and may be involved in resistance to re-infection.

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

Schistosomiasis, a major neglected tropical disease, affects more than 250 million people worldwide. Treatment of schistosomiasis has relied on the anthelmintic drug praziquantel (PZQ) for more than a generation. PZQ is the drug of choice for the treatment of schistosomiasis; it is effective against all major forms of schistosomiasis, although it is less active against juvenile than mature parasites. A pyrazino-isoquinoline derivative, PZQ is not considered to be toxic and generally causes few or transient, mild side effects. Increasingly, mass drug administration targeting populations in sub-Saharan Africa where schistosomiasis is endemic has led to the appearance of reduced efficacy of PZQ, which portends the selection of drug-resistant forms of these pathogens. The synthesis of improved derivatives of PZQ is attracting attention, e.g., in the (i) synthesis of drug analogues, (ii) rational design of pharmacophores, and (iii) discovery of new compounds from large-scale screening programs. This article reviews reports from the 1970s to the present on the metabolism and mechanism of action of PZQ and its derivatives against schistosomes.

Drug-induced exposure of Schistosoma mansoni antigens SmCD59a and SmKK7

Background

Schistosomiasis is a serious health problem especially in developing countries and affects more than 243 million people. Only few anthelmintic drugs are available up to now. A major obstacle for drug treatment is the different developmental stages and the varying host compartments during worm development. Anthelmintic drugs have been tested mainly on adult schistosomes or freshly transformed cercariae. Knowledge concerning the larval stages is lacking.

Methodology/Principal Findings

In this study, we used in vitro-grown schistosomula (aged between 2 to 14 days) to investigate drug effects of the three anthelmintics praziquantel, artemether, and oxamniquine. Further, we analyzed the antibody accessibility of two exemplary schistosome antigens SmCD59a and SmKK7, before and after drug treatment. Our results demonstrated that praziquantel applied at a concentration of 1 μM inhibited development of all life stages. Application of 10 μM praziquantel led to dramatic morphological changes of all schistosomula. Artemether at 1 and 10 μM had differential effects depending on whether it was applied to 2-day as compared to 7- and 14-day schistosomula. While 2-day schistosomula were not killed but inhibited from further development, severe morphological damage was seen in 7- and 14-day schistosomula. Oxamniquine (1 and 10 μM) led to severe morphological impairment in all life stages. Analyzing the accessibility of the antigens SmCD59a and SmKK7 before drug treatment showed no antibody binding on living intact schistosomula. However, when schistosomula were treated with anthelmintics, both antigens became exposed on the larvae. Oxamniquine turned out to be most effective in promoting antibody binding to all schistosomula stages.

Conclusion

This study has revealed marked differences in anthelmintic drug effects against larvae. Drug treatment increases surface antigen presentation and renders larvae accessible to antibody attack.

Schistosomiasis is one of the major parasitic diseases in developing countries and still causes 200,000 deaths per year. Mass drug administration programs with praziquantel, the drug of choice against schistosomiasis, are currently undertaken in Sub-Saharan Africa. Praziquantel, although efficient against adult worms, fails to cure early infection. The complex developmental stages of schistosomes and migration through varying host compartments with different local drug concentration are a challenge for drug treatment. After infecting their mammalian host, schistosomula traverse through skin and the vasculature of lung, liver and intestines. During their migration, they develop from larvae to paired adults in approximately 4 to 5 weeks. So far, drug effects have been analyzed on adult worms or freshly transformed schistosomula only. Information about the effects on the larval stages is lacking. We were able to transfer the larval development of the first three weeks into the culture dish. This tool can be used for the analysis of drug effects against schistosomula and for investigation of the accessibility, expression and localization of antigens. Rendering the parasite’s larvae vulnerable to the host’s immune system by increasing antigen presentation is an important aspect of drug activity. We demonstrate on in vitro-cultured Schistosoma mansoni larvae, that SmCD59a and SmKK7, as examples for hidden antigens, become accessible to antibodies following drug treatment.

Aryl hydantoin Ro 13-3978, a broad-spectrum antischistosomal

OBJECTIVES

Praziquantel is the only drug available for the treatment of schistosomiasis and the state of the exhausted drug discovery pipeline is alarming. We restarted investigations on the abandoned antischistosomal Ro 13-3978, an aryl hydantoin discovered in the early 1980s by Hoffmann La-Roche.

METHODS

Newly transformed schistosomula and adult Schistosoma mansoni were studied in the presence of Ro 13-3978 in vitro. The metabolic stability of Ro 13-3978 was determined in vitro using human and mouse liver S9 fractions. Dose-response relationship, stage specificity, hepatic shift and scanning electron microscopy studies were carried out in S. mansoni-infected mice. In addition, efficacy experiments were conducted in rodents infected with Echinostoma caproni and Fasciola hepatica as well as in S. mansoni-infected immunocompromised nude (Foxn1(nu)) mice.

RESULTS

Ro 13-3978 showed minor in vitro activity and no damage to the tegument was found. No cytotoxicity was detected for Ro 13-3978. Ro 13-3978 was metabolically stable. ED50 values of 138.9 and 14.6 mg/kg were calculated for the treatment of juvenile and adult S. mansoni infections, respectively, with a single oral dose of Ro 13-3978. SEM studies revealed severe damage to the worms 48 h post-treatment of infected mice. A single oral dose of Ro 13-3978 (100 mg/kg) administered to S. mansoni-infected (Foxn1(nu)) mice reduced the worm burden by 88%. Ro 13-3978 was not active against E. caproni and F. hepatica in vivo.

CONCLUSIONS

Ro 13-3978 has excellent antischistosomal properties in vivo. Structure-activity relationship studies with the aryl hydantoins have been launched in order to elucidate active pharmacophores, further investigate the mechanism of action and to identify a derivative with minimal antiandrogenic effects.

Preliminary evidence of transcriptional immunomodulation by praziquantel in bluefin tuna and Atlantic salmon in vitro cultures

Praziquantel (PZQ), long-used in veterinary and human medicine for the treatment of helminth parasites, is known to enhance humoral and cellular immune responsiveness in mammals but has unknown direct immunomodulatory capabilities in fish. In the present study, we examined the ability of PZQ to induce gene transcriptional changes in immune-competent primary tissue/organ cultures of two highly important yet evolutionarily discrete fish species--Southern bluefin tuna Thunnus maccoyii and Atlantic salmon Salmo salar. These cultures consisted of mixed blood cell population for both species, as well as intestinal explants from bluefin. Although expression profiles varied between species and tissue/organ type, PZQ induced both T-cell receptor (more than twofold) and IL-8 transcriptional expression (more than fourfold). Additionally, increased expression of other inflammatory cytokines including IL-1β was detected in blood cell cultures from both species, and a general pattern of heightened antiviral signaling was observed. Specifically, elevated transcription of Type I (IFNα) and Type II (IFNγ) interferon in Atlantic salmon blood cultures along with elevated expression of MHC class I in blood cultures of both species. These findings provide preliminary evidence for direct immunomodulation by PZQ in fish and insight into its potential capacity as an immune stimulant/adjuvant in the rapidly expanding aquaculture industry.

Schistosomiasis chemotherapy

After malaria, schistosomiasis (or bilharzia) is the second most prevalent disease in Africa, and is occurring in over 70 countries in tropical and subtropical regions. It is estimated that 600 million people are at risk of infection, 200 million people are infected, and at least 200,000 deaths per year are associated with the disease. All schistosome species are transmitted through contact with fresh water that is infested with free-swimming forms of the parasite, which is known as cercariae and produced by snails. When located in the blood vessels of the host, larval and adult schistosomes digest red cells to acquire amino acids for growth and development. Vaccine candidates have been unsuccessful up to now. Against such devastating parasitic disease, the antischistosomal arsenal is currently limited to a single drug, praziquantel, which has been used for more than 35 years. Because the question of the reduction of the activity of praziquantel was raised recently, it is thus urgent to create new and safe antischistosomal drugs that should be combined with praziquantel to develop efficient bitherapies.

Epidemiology and interactions of Human Immunodeficiency Virus - 1 and Schistosoma mansoni in sub-Saharan Africa

Human Immunodeficiency Virus-1/AIDS and Schistosoma mansoni are widespread in sub-Saharan Africa and co-infection occurs commonly. Since the early 1990s, it has been suggested that the two infections may interact and potentiate the effects of each other within co-infected human hosts. Indeed, S. mansoni infection has been suggested to be a risk factor for HIV transmission and progression in Africa. If so, it would follow that mass deworming could have beneficial effects on HIV-1 transmission dynamics. The epidemiology of HIV in African countries is changing, shifting from urban to rural areas where the prevalence of Schistosoma mansoni is high and public health services are deficient. On the other side, the consequent pathogenesis of HIV-1/S. mansoni co-infection remains unknown. Here we give an account of the epidemiology of HIV-1 and S. mansoni, discuss co-infection and possible biological causal relationships between the two infections, and the potential impact of praziquantel treatment on HIV-1 viral loads, CD4+ counts and CD4+/CD8+ ratio. Our review of the available literature indicates that there is evidence to support the hypothesis that S. mansoni infections can influence the replication of the HIV-1, cell-to-cell transmission, as well as increase HIV progression as measured by reduced CD4+ T lymphocytes counts. If so, then deworming of HIV positive individuals living in endemic areas may impact on HIV-1 viral loads and CD4+ T lymphocyte counts.

Use of praziquantel against schistosomiasis: a review of current status

Praziquantel therapy has become an important component of any programme directed towards schistosomiasis control. This disease being prevalent in many disadvantaged countries, where the means and resources are limited, the strategies for its control on a large scale are also beset with various other constraints. In this review, the potentials of praziquantel therapy in containing the intensities, prevalences and schistosomiasis-associated morbidities in endemic areas of different geographical and epidemiological settings are examined. By and large, regular community-based treatment produces a longer term favourable impact on infection levels and morbidity, but the impact on the disease transmission appears limited. Children constitute a high risk group in schistosomiasis. They are usually subjected to more rapid and intense reinfection, but they also appear more responsive to praziquantel therapy in preventing or reversing the effects of the disease. Modern techniques used in the assessment of impact of praziquantel treatment in schistosomiasis control are outlined.

Effect of levamisole on the immune response of patients with schistosomiasis after treatment with praziquantel

Successful therapy with praziquantel in schistosomiasis is dependent on a normal host immune system, i.e. the recognition of parasite antigen, to be effective in eradicating the parasite. Levamisole, a nonspecific immunomodulator, has been hypothesised to normalise deficient cell-mediated immunity. The aim of this study was to investigate the effect of levamisole on the immune response seen after presumed curative doses of praziquantel. After ethical approval, 29 male volunteers infected with Schistosoma haematobium were recruited and randomised to receive orally either (a) levamisole 5 mg/kg for 2 consecutive days, plus praziquantel 40 mg/kg as a single dose, (b) levamisole 5 mg/kg for 2 days, or (c) praziquantel 40 mg/kg as a single dose. Blood samples were collected on day 0 and again 3 months later for differential counts and specific IgG and IgE to whole-worm-antigen, as well as for the detection of eosinophil cationic protein (ECP). Levamisole treatment alone resulted in a significant drop in circulating eosinophil counts, i.e. a median (95% confidence interval) drop of 6.0 (1;7)%. Eosinophil counts did not change significantly after praziquantel therapy alone. ECP values were significantly reduced with levamisole alone and praziquantel alone, i.e. respective median (95% confidence interval) drops of 33.58 (18.94; 55.9) and 16.54 (3.6; 33.5) microg/L (p < 0.05). The group receiving combination therapy demonstrated significant increases in specific IgG values (p = 0.02) with no decline in ECP levels and eosinophil counts compared with baseline values. Levamisole alone had no effect on egg counts. In conclusion, levamisole inhibited circulating eosinophils and eosinophil activation when given alone, but caused immune stimulation when combined with praziquantel. The exact mechanism of action still needs to be determined.

Schistosomiasis: from drug deployment to drug development

PURPOSE OF REVIEW

Schistosomiasis is a chronic and morbid disease that affects hundreds of millions of the poorest individuals in (sub)tropical regions, particularly sub-Saharan Africa. Just one drug, praziquantel (PZQ), is available. As discussed, efforts to expand mass drug administration programs may accelerate the emergence of resistance. In addition, PZQ's peculiar pharmacological profile and undefined mechanism of action(s) complicate discriminating incomplete efficacy from true resistance. Accordingly, and in spite of the challenges associated with developing new antischistosomals as discussed herein, alternatives to PZQ should be identified. Various strategies to do this are highlighted here.

RECENT FINDINGS

The last 2 years have witnessed more engagement of the necessary infrastructure combined with the application of the latest strategies and technologies to facilitate antischistosomal drug discovery. Preclinical and clinical evaluation of new chemistries has benefited from various consortia and institutions that underwrite drug development for antiparasitics in general. Drug repositioning, target-based drug design, improved automation for compound screening, genomics and functional genomics are just some of the tools now being applied to identify possible new drugs and drug targets.

SUMMARY

The new momentum toward the discovery of alternatives to PZQ is encouraging but needs to be sustained by a stronger advocacy for drug development, in addition to drug deployment.

Chemotherapy of schistosomiasis: an update

No major changes have occurred during the past 20 years regarding the therapeutic tools available to the clinician for the treatment of schistosomiasis. If anything, the two drugs (oxamniquine and metrifonate) that are valuable alternatives to the drug of choice (praziquantel) have become more difficult to procure in some African countries. Here, Donato Cioli summarizes some of the most recent and interesting laboratory studies on potential antischistosomal compounds, and then reviews recent developments related to the mechanism of action of praziquantel and to the possible emergence of praziquantel-resistant schistosomes.

Activity of artemether and mefloquine against juvenile and adult Schistosoma mansoni in athymic and immunocompetent NMRI mice

Immune effector mechanisms can enhance the activity of antischistosomal drugs. We examined the in vivo effect of single oral doses of the antimalarials artemether (400 mg/kg) and mefloquine (200 mg/kg), recently described to have promising antischistosomal properties, against juvenile and adult Schistosoma mansoni in T cell-deficient and in comparably infected age- and sex-matched immunologically intact control mice. Artemether and mefloquine are equally effective in athymic and immunocompetent mice. Artemether treatment resulted in total and female worm burden reductions ranging between 71.1% and 85.3%, whereas mefloquine achieved total and female worm burden reductions of 80.4-97.8%. In conclusion, artemether and mefloquine act T-cell independently and no synergistic interaction with the immune response was involved.

Effect of single-dose oral mefloquine on the morphology of adult Schistosoma japonicum in mice

It has been recently documented that the antimalarial drug mefloquine shows in vivo activity against schistosomes. In the present study, we assessed the effect of mefloquine on the morphology of adult Schistosoma japonicum worms. Mice were infected with S. japonicum cercariae for 35 days and then treated with a single 400-mg/kg oral dose of mefloquine. Groups of mice were killed between 24 h and 14 days post-treatment and worms were recovered from the liver and mesenteric veins, fixed in 70% alcohol, stained with acid carmine, and examined under a light microscope. Worms obtained from nontreated mice served as controls. S. japonicum recovered from mice 24 h post-treatment had severely dilated guts and the entire worm body was swollen. Meanwhile, reproductive glands, including the testis, ovary, and vitelline gland, showed signs of degeneration. Damage further progressed, particularly among vitelline glands, which resulted in disturbance of ova formation and cessation of oviposition 3 days post-treatment. Three to 7 days after mefloquine administration, adherence of host leukocytes on the damaged tegument was observed. Our results confirm that mefloquine possesses antischistosomal properties, exhibiting a rapid onset of action and causing extensive morphologic damage to adult S. japonicum.

Antibody response in mice infected with Mesocestoides vogae (syn. Mesocestoides corti) tetrathyridia after treatment with praziquantel and liposomised glucan

The therapeutic effect of praziquantel (PZQ) involves synergy with the humoral immune response during helminth infections, which is modulated by parasitic antigens. During experimental murine infections with the larval stage of cestoda Mesocestoides vogae (syn. M. corti), dynamic changes in the IgG and IgM antibody serum levels to both soluble somatic and secretory larval antigens were investigated after administration of PZQ alone and after its co-administration with the immunomodulator (l-->3)-beta-D-glucan entrapped in liposomes (lip.glucan). During the 2 weeks of follow-up after termination of therapy, specific IgG and IgM serum levels to the somatic antigens (enzyme-linked immunosorbent assay test) significantly decreased, whereas concentrations of the antibodies to the secretory antigens moderately increased, both in comparison with the control. Moreover, the number of immunogenic larval antigens (analysed by Western blot) was higher after combined therapy in comparison with single drug administration, which correlated with the intensity of reduction of the larval counts in the liver and peritoneal cavity of mice. Our data showed that administration of PZQ alone and in combination with lip.glucan resulted in marked changes in the dynamics of IgG and IgM antibodies to the somatic larval antigens, which were probably induced by the newly exposed antigens. In this respect, glucan can enhance chemotherapeutic activity of PZQ against larval cestodes by means of stimulation of the macrophage/monocyte effector functions, which seemed to contribute to the more intense larval damage.

Interactions between schistosomiasis and infection with HIV-1

In many regions of the world, both schistosomiasis and HIV/AIDS are endemic, resulting in patients harbouring co-infections. Because interaction with host CD4(+) T cells is a characteristic of schistosome as well as HIV-1 infections, bi-directional disease effects may be sufficiently different from sequelae caused by either infectious agent alone to warrant alteration of public health approaches in areas of co-endemnicity. Studies published over the past decade provide useful insights into interactions between schistosomiasis and infection with HIV-1, and overall support the hypothesis that special emphasis on treatment of schistosomiasis in populations with elevated prevalence or risk of HIV-1 infection is justified.

Helminths and HIV infection: epidemiological observations on immunological hypotheses

Parasitic helminths have co-evolved with the mammalian immune system. Current hypotheses suggest that immunological stimulation in the presence of helminths is balanced by immuno-regulation and by the broad spectrum of mechanisms possessed by helminths for countering the host immune response. The degree to which this balance is perfected, and the mechanisms by which this is achieved, vary between helminth species; we suggest that this is reflected not only in the degree of pathology induced by helminths but also in a variety of relationships with HIV infection and HIV disease. Available epidemiological data regarding interactions between helminths and HIV are largely observational; results are variable and generally inconclusive. Well designed, controlled intervention studies are required to provide definitive information on the species-specific nature of these interactions and on the advantages, disadvantages and optimal timing of de-worming in relation to HIV infection.

Praziquantel for the treatment of schistosomiasis: its use for control in areas with endemic disease and prospects for drug resistance

Praziquantel became available for the treatment of schistosomiasis and other trematode-inflicted diseases in the 1970s. It was revolutionary because it could be administered orally and had very few unwanted side effects. As a result of marked reductions in the price of praziquantel, the rate at which it is used has accelerated greatly in recent years. For the foreseeable future it will be the mainstay of programs designed to control schistosome-induced morbidity, particularly in sub-Saharan Africa where schistosomiasis is heavily endemic. There is currently no evidence to suggest that any schistosomes have developed resistance to praziquantel as a result of its widespread use. Nevertheless, while resistance may not pose an obvious or immediate threat to the usefulness of praziquantel, complacency and a failure to monitor developments may have serious consequences in the longer term since it will be the only drug that is readily available for large-scale treatment of schistosomiasis.

Schistosomiasis and HIV in rural Zimbabwe: efficacy of treatment of schistosomiasis in individuals with HIV coinfection

BACKGROUND

There is evidence from experimental models that the praziquantel-induced clearance of schistosomiasis is dependent on the host's immune response. Consequently, human immunodeficiency virus (HIV)-related immunodeficiency may impair the effect of praziquantel treatment.

METHODS

In a prospective cohort study, schistosome-infected subjects who were or were not coinfected with HIV were treated with praziquantel and followed up 3, 6, and 12 months after treatment. Quantitative measures of intensity of schistosomiasis (egg counts and levels of circulating anodic antigen in serum) and immunodeficiency (CD4+ cell counts and viral loads) were collected.

RESULTS

Cure rates based on egg counts 3 months after treatment were satisfactory and were similar for HIV-positive individuals (cure rate, 86%) and HIV-negative individuals (cure rate, 85%); the magnitude of decrease in egg count was equal. Cure rates based on circulating anodic antigen levels were much lower than cure rates based on egg counts, with HIV-positive individuals experiencing significantly less clearance of schistosomiasis (cure rate, 31%) than HIV-negative individuals (cure rate, 52%), whereas the magnitude of decrease in circulating anodic antigen was also lower among HIV-positive individuals (P < .01).

CONCLUSION

The effect of praziquantel may be limited to affecting the fecundity of adult schistosomes in the immunocompromised host, thus reducing egg excretion while leaving schistosomes metabolically active, as shown by the fact that levels of antigen production are maintained. Special guidelines for treatment of schistosomiasis in HIV-coinfected individuals may need to be developed.

The immune dependence of chemotherapy

In this review, Mike Doenhoff and colleagues discuss the immune dependency of chemotherapy and the consequences for drug resistance. They also consider the implications for the control of infections that are relatively unresponsive to drugs, such as opportunistic infections in immunosuppressed patients.

Interactions between schistosomiasis and human immunodeficiency virus in Western Kenya

For the past ten years, we have been exploring the relationship between schistosomiasis and human immunodeficiency virus (HIV-1) and how coinfection with both agents may affect the pathology and progression of each infection. To date, given the systems we have examined, the effects of HIV-1 on schistosomiasis have been more profound than the effects of schistosomiasis on HIV-1 progression. Additional key questions with important public health implications remain unanswered, but hopefully not unanswerable.

Sex- and stage-related sensitivity of Schistosoma mansoni to in vivo and in vitro praziquantel treatment

The efficacy of praziquantel against a Puerto Rican strain of Schistosoma mansoni was assessed using both in vivo and in vitro approach. The drug effective dose (50%) in the infected mouse model was about 30 times higher when determined against 28-day-old infections than against 7-week-old parasites. Single-sex female infections were also largely refractory to treatment and single-sex male infections moderately refractory, in comparison with bisexual infections. The in vitro approach consisted of overnight exposure of parasite cultures to various drug concentrations, followed by several days of culture in drug-free medium. In vitro results confirmed in vivo data and allowed for the observation of schistosome morphological phenomena after praziquantel exposure. Early worm contraction was observed in all cases, even after exposure to sub-lethal concentrations of praziquantel or upon exposure of the largely refractory 28-day-old schistosomes. In these instances, however, worms resumed movements and normal shape upon drug removal and were able to survive. The inference of these observations on the clinical use of praziquantel and on its mechanism of action is discussed.

First Report ofSchistosoma mekongiInfection with Brain Involvement

We describe, to our knowledge, the first reported case of Schistosoma mekongi infection with brain involvement. S. mekongi is a distinct species most closely related to Schistosoma japonicum that is endemic in a defined area of the Mekong River in Laos and Cambodia and characteristically associated with hepatosplenic disease. The patient had an excellent response to praziquantel therapy but required repeated courses of corticosteroid therapy to suppress recrudescent neurological symptoms.

Efficacy and side effects of praziquantel treatment in a highly endemicSchistosoma mansoni focus at Lake Albert, Uganda

The aim of the study was to assess the efficacy and side effects following single and repeated (6 weeks apart) praziquantel treatment (40 mg/kg) in a Schistosoma mansoni-endemic focus with long-standing transmission at Lake Albert in Uganda between December 1996 and January 1997. The results were based on 482 individuals, randomly representing all age and both gender groups. The cure rate following the first and second treatments was 41.9% and 69.1%, respectively. The cure rate was higher in adults than in children, irrespective of intensity of infection. In addition, the cure rate declined markedly with increasing intensity of infection. The reduction in intensity of infection was marked, being 97.7% and 99.6% after the first and second treatments, respectively. A pre- and post-treatment symptom questionnaire revealed a broad range of side effects, including abdominal pain and diarrhoea. However, no serious or long-lasting complications affecting compliance were observed. The marked reductions in faecal egg excretion and the acceptable level of side effects point to a single praziquantel treatment (40mg/kg) as the strategy of choice in such a highly endemic S. mansoni focus.

Chemotherapeutic effects on larval stages of Schistosoma mansoni during infection and re-infection of mice

The sensitivity of the larval stages of Schistosoma mansoni to chemotherapy with praziquantel and oxamniquine was tested in mice during primary and secondary infections and after different intervals from cercarial exposure. Worm recovery by perfusion of the porto-mesenteric system, followed by counting and a morphometric study of the parasite, allowed the conclusion that the relative resistance of the larval stages of S. mansoni to schistosomicide drugs, demonstrated in primary infections, also persists when the host is already infected. This indicates that a therapeutic failure may result when an infected host is treated some time after being re-infected, because of the presence of migrating, drug-resistant, immature forms of the parasite.

Resistance of Schistosoma mansoni to praziquantel: is there a problem?

Evidence for resistance to praziquantel (PZQ) in Schistosoma mansoni has been sought in parasites taken from treated, but uncured human patients, and in a laboratory isolate of S. mansoni subjected to successive passages under drug pressure. Patients from villages in Egypt and Senegal have yielded isolates that can tolerate higher dosages of PZQ than other ostensible control isolates when passaged and subjected to drug treatment in mice. In vitro tests on these and the laboratory-selected isolate support the conclusion that a degree of resistance to PZQ can occur in S. mansoni, but the levels of drug resistance found so far are low. Preliminary studies have begun on these isolates to identify genetic, physiological and morphological characteristics associated with PZQ resistance and some of these may find use as markers for monitoring whether or not resistance is developing in endemic areas where the drug is used. More intensive application of PZQ can be expected in future, particularly in other parts of Africa, and vigilance will be needed to ensure that it continues to be useful as a drug for treatment of schistosomiasis. Further work is needed to elucidate the mode of action of PZQ and there is already a need for alternative drugs to treat PZQ-resistant schistosomiasis, such as already exists in northern Senegal.

HIV infection and tropical parasitic diseases - deleterious interactions in both directions?

HIV and parasitic infections interact and affect each other mutually. Whereas HIV infection may alter the natural history of parasitic diseases, impede rapid diagnosis or reduce the efficacy of antiparasitic treatment, parasitoses may facilitate the infection with HIV as well as the progression from asymptomatic infection to AIDS. We review data on known interactions for malaria, leishmaniasis, Human African Trypanosomiasis, Chagas' disease, onchocerciasis, lymphatic filariasis, schistosomiasis and intestinal helminthiases. The common immunopathogenetic basis for the deleterious effects parasitic diseases may have on the natural history of HIV infection seems to be a particular type of chronic immune activation and a preferential activation of the T helper (Th)2 type of help. Control of parasitic diseases should complement the tools currently used in combating the HIV pandemic.

Interpreting low praziquantel cure rates of Schistosoma mansoni infections in Senegal

Praziquantel is currently the drug of choice for the treatment of schistosomiasis. Selective treatment of Schistosoma mansoni infections in various endemic countries usually present cure rates of >70% when using the standard dose of 40 mg kg(-1) body weight of praziquantel. However, unusually low cure rates (18-38%) have been reported from Senegal, raising fears for emergence of resistance (or tolerance) to praziquantel. One major problem is the precise quantitative interpretation of cure rates, which allows an unequivocal distinction between drug failure and normal drug performance. This article reviews studies on praziquantel treatment of population by standardizing the data through an innovative meta-analysis and provides empirical evidence concerning the extent to which the reported low cure rates from Senegal are atypical.

Gastrointestinal complications of schistosomiasis

Schistosomiasis is an important disease in many parts of the world and has affected the course of human history many times over. The parasitic infection is acquired during contact with infected water. A chronic inflammatory response to schistosome eggs, mediated by both cellular and humoral mechanisms, is the root of the pathology seen in schistosomiasis. Hepatosplenic disease results in intrahepatic presinusoidal portal hypertension. The resultant esophageal and gastric varices are an important cause of morbidity and mortality. Standard treatment guidelines for managing varices can be applied to patients with schistosomiasis. Coinfection with viral hepatitis results in liver disease that progresses more rapidly and is more difficult to treat. Intestinal schistosomiasis may be confused with other disease states and can be an important cause of morbidity, especially in heavily infected patients. Diagnosis relies on demonstration of schistosome eggs in feces or tissue. Praziquantel is the treatment of choice. The development of a vaccine for schistosomiasis is an important goal in the attempt to control this disease.

Efficacy of praziquantel against Schistosoma mansoni with particular consideration for intensity of infection

Chemotherapy with praziquantel is the cornerstone of schistosomiasis control. In view of recent concern about tolerance or resistance to praziquantel, monitoring its efficacy in different epidemiological settings is required. We report a study among 253 schoolchildren in an area highly endemic for Schistosoma mansoni in western Côte d'Ivoire. After examining four consecutive stool specimens from each child, the first praziquantel treatment at 60 mg/kg divided into two doses was administered. Four weeks later, stool specimens were again screened over 4 consecutive days and revealed a cure rate of 71.6% and an egg reduction rate of 79.9%. There was a significant association between cure rate and intensity of infection prior to treatment with highest cure rates observed in light infections (P < 0.01). Praziquantel, at a single dose of 40 mg/kg, was again administered 35 days after the first treatment. The overall cure and egg reduction rates increased considerably. The association between cure rate and intensity of infection prior to the second treatment was significant but less pronounced. Twenty-two children remained S. mansoni positive after the two chemotherapy campaigns, and interestingly, many of these were only identified after repeated stool examinations. We argue that pre-patent infections may account for some of these 'treatment failures'. However, further studies in other endemic settings are needed, with parasitological diagnoses having a high sensitivity.

Interleukin 5 (IL-5) is not required for expression of a Th2 response or host resistance mechanisms during murine schistosomiasis mansoni but does play a role in development of IL-4-producing non-T, non-B cells

During schistosomiasis, interleukin-5 (IL-5)-dependent eosinophil responses have been implicated in immunopathology, resistance to superinfection, synergistic interactions with chemotherapeutic agents, and the inductive phase of the egg-induced Th2 response. We examined these issues in IL-5-deficient (IL-5(-/-)) mice. IL-5(-/-) and wild-type (WT) mice were indistinguishable in terms of susceptibility to primary infections and the ability to resist secondary infections. Moreover, hepatic pathology was similar in both strains apart from a relative lack of eosinophils and, during chronic infection, a significantly larger mast cell component in the granulomas of IL-5(-/-) mice. Splenocyte cytokine production in response to soluble egg antigen (SEA) or anti-CD3 revealed no significant differences except for heightened tumor necrosis factor alpha production by cells from chronically infected IL-5(-/-) mice compared to WT animals. In contrast, ionomycin-stimulated non-B, non-T (NBNT) cells from IL-5(-/-) mice produced significantly smaller IL-4 amounts than did NBNT cells from WT animals. This difference was not apparent following plate-bound anti-immunoglobulin E or SEA stimulation. The absence of IL-5 failed to affect the induction of Th2 responses in naive mice. Peritoneal exudate cells recovered from egg-injected IL-5(-/-) or WT mice produced equivalent levels of IL-4 following restimulation with SEA or anti-CD3.

Effect of Daucus carota var. boissieri extracts on immune response of Schistosoma mansoni infected mice

Isolation and structure elucidation was carried out of flavonoid constituents found in fractionated extracts of the seeds and green leaves of Daucus carota L. var. boissieri (Apiaceae). The flavonoids are mainly apigenin, luteolin, their glycosidic precursors and 2,4,5-trimethoxybenzaldehyde. Fatty acids, hydrocarbons and sterols were identified by GLC. The effect of various carrot extracts on the immune responses of Schistosoma mansoni infected mice was studied. The rate of reduction in worm infestation in mice injected with some fractions indicated a strong protection. Some extracts induced humoral immune response through raising the IgG level at 2, 4 and 6 weeks post-infection as compared with infected control. The phenotypic analysis of the cellular immune response in spleen and mesenteric lymph nodes was accomplished by direct immunofluorescence. The data showed that some extracts stimulated the blastogenesis of CD4(+)-T splenocytes and mesenteric lymph node cells.

Efficacy of an antipathology vaccine in murine schistosomiasis administered with and without chemotherapy

This study was undertaken to study the efficacy of praziquantel (PZQ) in potentially tolerized Schistosoma mansoni infected, egg-injected C57BL/6 mice, receiving multiple administrations of soluble egg antigen (SEA) intravenously (i.v.). Four animal groups were studied. Experimental group I received four injections of SEA (10 micrograms) intravenously on days -7, -5, -3 and -2 before infection and PZQ orally (500 mg/kg over two consecutive days 7 weeks post-infection. Three control groups received the following treatment: group II received the same tolerizing dose of SEA without PZQ, group III received PZQ in the same dose and at the same timing. Group IV received S. mansoni infection and egg injection 8 weeks post-infection and served as an infected, egg-injected control. Egg injection was conducted 8 weeks post-infection using viable S. mansoni eggs via the tail vein. Animals were killed 16 days post-egg injection, i.e. 10 weeks post-infection. After sacrifice, lungs and livers were removed for histopathological study and measurement of granuloma diameters. Spleens and serum were collected for the assay of lymphoproliferative response to SEA and antischistosomal immunoglobulins. The worm and egg burdens were also studied. Compared to infected, egg-injected untreated controls, repeated i.v. administrations of SEA down-regulated egg-injected (pulmonary) and egg-deposited (hepatic) granulomas and the lymphoproliferative response to SEA. Antischistosomal IgG level was increased. Susceptibility to S. mansoni infection was not found to be different from that in the infected, egg-injected controls. PZQ in the dose used caused complete eradication of worms, disappearance of immature egg stages, decrease in the number of mature eggs and an increase in the number of dead eggs. Hepatic granuloma diameter, lymphoproliferative response to SEA and IgG level were reduced. In mice receiving a combined regimen of multiple SEA administrations and PZQ with down-regulated granuloma and reduced lymphoproliferative response to SEA, the efficacy of PZQ was the same as in mice receiving PZQ alone. This was shown by comparable grades of worm and egg reduction. The histopathological examination of liver and lung sections in the different treated groups revealed moderate to small-sized hypocellular granulomas. Although no statistically significant difference was recorded between the mean granuloma diameters of the experimental group receiving both the tolerizing dose of SEA and PZQ compared to the group receiving the tolerizing dose of SEA without chemotherapy, this experimental group showed the least associated histopathological parenchymal changes. It appears from this work that combined SEA and PZQ provided many complementary goals; a reduction of egg-induced pathology, minimal parenchymal changes and the eradication of worms.

The immunopathology of human Schistosomiasis-III. Immunoglobulin isotype profiles and response to praziquantel

Immunoglobulin (Ig) isotype (IgG, IgG1, IgG2, IgG3, IgG4, IgM, IgD and IgE) levels were investigated, both pre- and post-treatment with praziquantel (PZQ), in 43 adults and children chronically infected with Schistosoma mansoni, by means of a two-site, isotype-specific immunoenzymometric assay. The patients were classified as responders (R) or non-responders (NR) on the basis of their circumoval precipitin test (COPT) results 12 months after treatment. In comparison with controls, pre-treatment R children showed significantly higher levels of IgG, IgG1, IgG4 (p < 0.001) and IgE (p < 0.01); and diminished IgG2 (p < 0.05), while NR children showed significantly elevated levels only of IgE (p < 0.05). Twelve months after therapy, R children maintained significantly lower levels of IgG2, but showed significantly decreased levels of IgG, IgG1, IgG4, and IgE, while the Ig isotype profile of NR children was unaltered. Adult R and NR showed similar isotype profiles before chemotherapy, with the exception of significantly elevated IgM levels in R. Twelve months after therapy, R adults showed significantly decreased levels of IgG, IgG1, and IgG4, while NR adults showed only diminished IgG4 levels. These results reveal different Ig isotype profiles in untreated adults and children chronically infected with S. mansoni. The results further show that the pre-treatment Ig isotype profile may be significantly modified after an effective R to chemotherapy, accounted for by down regulation of the IgG1 isotype in association with negative seroconversion of the COPT in R patients. The COPT reaction has been associated with the highly specific egg glycoprotein antigen omega 1, which shows a significant reduction in reactivity six months after treatment. IgG1 may thus play a main role in the response against the omega 1 antigen.

Schistosomiasis. Pathophysiology, diagnosis, and treatment

Globally, schistosomes infect 1 in 30 people. Tourists travel to endemic areas, whereas students, workers, and expatriates travel to nonendemic areas. Physicians around the world need to remain aware of this common parasitic infection. Pathology results from parasite eggs that lodge in the intestines and liver. Intestinal schistosomiasis is most often asymptomatic and presents with occult gastrointestinal bleeding. Hepatosplenic schistosomiasis develops insidiously because of cumulative fibrotic injury. Stigmata of liver failure are absent unless comorbid viral or alcoholic hepatitis is present. Patients with end-stage hepatosplenic schistosomiasis die from variceal hemorrhage. Diagnosis of schistosomiasis is confirmed by finding eggs in stool or biopsy specimens. Antischistosome antibodies may identify infected tourists returning from endemic areas. Circulating schistosome antigens distinguish current from past infections. Praziquantel is the schistosomicidal drug of choice. Most cases of hepatosplenic schistosomiasis resolve after effective treatment. Prophylactic propranolol may prevent hemorrhage in praziquantel-treated patients with high-grade varices. Sclerotherapy is also efficacious. When necessary, patients with hepatosplenic schistosomiasis tolerate decompressive surgery well.

Temporal differences in praziquantel- and oxamniquine-induced tegumental damage to adult Schistosoma mansoni: implications for drug-antibody synergy

A temporal study of the effects on the tegument of Schistosoma mansoni adult worm following in vivo praziquantel and oxamniquine treatment was performed. Drug-induced damage to the tegument, exposure of surface antigens and attachment of host antibody occurred rapidly, within 1 h, following praziquantel treatment. Oxamniquine-treated worms required 4-8 days for these effects to be apparent. The 2 drugs differed in the degree and sites of damage on the worm surface. The administration of 2 different polyspecific rabbit sera with drug significantly increased the efficacy of praziquantel when administered with the drug, but not when given 6-9 days after drug treatment. In contrast, only 1 serum was synergistic with oxamniquine when administered with drug and both sera were synergistic when given 6-9 days after drug treatment. The effect of immune killing of drug-treated worms is discussed.

Metabolism by Schistosoma mansoni of a new schistosomicide: 2-[(1-methylpropyl)amino]-1-octanethiosulphuric acid

In order to investigate the mode of action of a new class of schistosomicides, the N-alkylaminoalkanethiosulphuric acids, the [outer 25S] 2-[(1-methylpropyl)amino]-1-octanethiosulphuric acids was synthesized. Labelling studies of adult Schistosoma mansoni were performed in infected mice and in in vitro incubations. After a single oral dose of the drug to infected mice, 5 metabolites were detected by thin-layer chromatogrpahy in organic extracts of male and female adult schistosomes. In vitro studies showed that the same compounds were present in organic extracts obtained from adult male and female worms. One of these metabolites was identified by mass spectroscopy as being the dimeric disulphide derivative of the parent labelled thiosulphuric acid.

Efficacy of treatment of murine Schistosoma mansoni infections with praziquantel and oxamniquine correlates with infection intensity: role of host antibody

The reduction in worm burden obtained by treatment of Schistosoma mansoni with praziquantel and oxamniquine was greater in mice with heavy infections than in relatively lightly infected animals. The reduction in worm burden achieved by each drug correlated with the size of the pre-treatment worm burden (r2 = 0.82 and 0.81 for praziquantel and oxamniquine, respectively). Intensity of infection did not affect the degree of tegumental damage and drug-induced antigen exposure on worms recovered soon after treatment with praziquantel. However, praziquantel-treated worms from mice with heavy infections had significantly more murine antibody attached to the treated-worm surface than worms from praziquantel-treated lightly infected mice. Heavily infected mice had greater levels of circulating anti-worm antibodies than lighter infected mice. The correlation between infection intensity and cure rates achieved by praziquantel and oxamniquine may thus be a reflection of the higher titres of relevant antibody in heavily infected mice mediating death of drug-treated worms.

Active immunization of mice with Schistosoma mansoni worm membrane antigens enhances efficacy of praziquantel

The efficacy of praziquantel treatment was significantly enhanced (P < 0.01) in CBA/Ca mice that had been immunized prior to Schistosoma mansoni infection with a crude extract of worm membrane antigens. In Western immunoblots sera from the worm antigen-immunized animals had a polyspecific antibody response, with a 25-27 kDa antigen being reacted against with particular intensity. A molecule of similar size was also recognized by rabbit antisera raised against an antigen with esterase activity that has been previously identified as a sensitive target for drug-antibody synergy. The increase in efficacy of subcurative doses of praziquantel in immunized animals is attributed to drug-induced tegumental damage causing antigens to become exposed on the worm surface. Thus, specific antigens, including the 25-27 kDa antigen, become accessible to circulating schistosomicidal antibodies. The role of antibodies that can synergize with praziquantel to kill schistosome worms is discussed.