Schistosoma mansoni: dose-related tegumental surface changes after in vivo treatment with praziquantel

Myricetin Possesses Anthelmintic Activity and Attenuates Hepatic Fibrosis via Modulating TGFβ1 and Akt Signaling and Shifting Th1/Th2 Balance in Schistosoma japonicum-Infected Mice

Schistosomiasis is a zoonotic and debilitating parasitic disease caused by Schistosoma japonicum. Praziquantel remains the choice for treating schistosomiasis, but its efficacy could be hampered by emergence of resistance. In this study, using large-scale drug screening, we selected out myricetin, a natural flavonol compound, having a good anti-schistosome effect. We found that myricetin exhibited dose and time-dependent insecticidal effect on S. japonicum in vitro, with an LC₅₀ of 600 μM for 24 h, and inhibited female spawning. The drug mainly destroyed the body structure of the worms and induced apoptosis of the worm cells, which in turn led to death. In addition, oral administration of myricetin in mice infected with S. japonicum showed a deworming effect in vivo, as evidenced by a significant reduction in the liver egg load. H&E staining, quantitative RT-PCR, and Western blotting assays showed that myricetin significantly alleviated liver fibrosis in mice infected with S. japonicum. Myricetin also effectively inhibited the expression of TGFβ1, Smad2, phospho-Smad2, Smad3, phospho-Smad3, ERK, phospho-ERK, Akt, and phospho-Akt in the liver of infected mice, suggesting that myricetin attenuated liver fibrosis in mice via modulating TGFβ1 and Akt signaling. Flow cytometric analysis of Th subtypes (Th1/Th2/Th17/Treg) in the mouse spleen further revealed that myricetin significantly increased the percentage Th1 cells in infected mice and reduced the proportion of Th2 cells and Th17 cells. Immunology multiplex assay further showed that myricetin attenuated S. japonicum-induced rise in the plasma levels of IL-4, IL-5, IL-10, IL-13, and IL-17A in infected mice while increasing the plasma contents of IFN-γ, IL-12, and IL-7. In conclusion, our study provides the first direct evidence that myricin possesses potent anti-schistosome activities in vitro and in vivo, and offers new insights into the mechanisms of action by myricetin. The present findings suggest that myricetin could be further explored as a therapeutic agent for S. japonicum.

Quantifying the mechanics of locomotion of the schistosome pathogen with respect to changes in its physical environment

Schistosomiasis is a chronic and morbid disease of poverty affecting approximately 200 million people worldwide. Mature schistosome flatworms wander in the host's hepatic portal and mesenteric venous system where they encounter a range of blood flow conditions and geometrical confinement. However, the mechanisms that support schistosome locomotion and underlie the pathogen's adaptation to its physical environment are largely unknown. By combining microfabrication and traction force microscopy, we developed various in vitro assays to quantify the mechanics of locomotion of adult male Schistosoma mansoni in different physiologically relevant conditions. We show that in unconfined settings, the parasite undergoes two-anchor marching mediated by the coordinated action of its oral and ventral suckers. This mode of locomotion is maintained when the worm faces an external flow, to which it responds by adjusting the strength of its suckers. In geometrically confined conditions, S. mansoni switches to a different crawling modality by generating retrograde peristaltic waves along its body, a mechanism shared with terrestrial and marine worms. However, while the surface of most worms has backward-pointing bristles that rectify peristaltic waves and facilitate forward locomotion, S. mansoni has isotropically oriented tubercles. This requires tight coordination between muscle contraction and substrate friction but gives S. mansoni the ability to reverse its direction of locomotion without turning its body, which is likely advantageous to manoeuvre in narrow-bore vessels. We show that the parasite can also coordinate the action of its suckers with its peristaltic body contractions to increase crawling speed. Throughout this study, we report on a number of biomechanical parameters to quantify the motility of adult schistosomes (e.g. sucker grabbing strength, the rate of detachment under flow, peristaltic wave properties and traction stresses). The new series of in vitro assays make it possible to quantify key phenotypical aspects of S. mansoni motility that could guide the discovery of new drugs to treat schistosomiasis.

Morphological Characteristics of Schistosoma mansoni PZQ-Resistant and -Susceptible Strains Are Different in Presence of Praziquantel

Schistosomiasis is one of the most common human parasitic diseases whose socioeconomic impact is only surpassed by malaria. Praziquantel (PZQ) is the only drug commercially available for the treatment of all schistosome species causing disease in humans. However, there has been stronger evidences of PZQ-resistance on Schistosoma mansoni and thus it is very important to study the phenotypic characteristics associated with it. The aim of this study was to evaluate morphological alterations in S. mansoni PZQ-resistant adult worms and eggs, by comparing a PZQ- resistant strain obtained under PZQ drug pressure with a PZQ-susceptible strain. For this, scanning electronic microscopy was used to assess tegumental responsiveness of both strains under PZQ exposure, and optical microscopy allowed the monitoring of worms and eggs in the presence of the drug. Those assays showed that PZQ-susceptible worms exposed to the drug had more severe tegumental damages than the resistant one, which had only minor alterations. Moreover, contrary to what occurred in the susceptible strain, resistant worms were viable after PZQ exposure and gradually regaining full motility after removal of the drug. Eggs from resistant strain parasites are considerably smaller than those from susceptible strain. Our results suggest that there might be a difference in the tegument composition of the resistant strain and that worms are less responsive to PZQ. Changes observed in egg morphology might imply alterations in the biology of schistosomes associated to PZQ-resistance, which could impact on transmission and pathology of the disease. Moreover, we propose a hypothetical scenario where there is a different egg tropism of the S. mansoni resistant strain. This study is the first comparing two strains that only differ in their resistance characteristics, which makes it a relevant step in the search for resistance determinants.

In vitro and in vivo anti-schistosomal activity of the alkylphospholipid analog edelfosine

Background

Schistosomiasis is a parasitic disease caused by trematodes of the genus Schistosoma. Five species of Schistosoma are known to infect humans, out of which S. haematobium is the most prevalent, causing the chronic parasitic disease schistosomiasis that still represents a major problem of public health in many regions of the world and especially in tropical areas, leading to serious manifestations and mortality in developing countries. Since the 1970s, praziquantel (PZQ) is the drug of choice for the treatment of schistosomiasis, but concerns about relying on a single drug to treat millions of people, and the potential appearance of drug resistance, make identification of alternative schistosomiasis chemotherapies a high priority. Alkylphospholipid analogs (APLs), together with their prototypic molecule edelfosine (EDLF), are a family of synthetic antineoplastic compounds that show additional pharmacological actions, including antiparasitic activities against several protozoan parasites.

Methodology/Principal Findings

We found APLs ranked edelfosine> perifosine> erucylphosphocholine> miltefosine for their in vitro schistosomicidal activity against adult S. mansoni worms. Edelfosine accumulated mainly in the worm tegument, and led to tegumental alterations, membrane permeabilization, motility impairment, blockade of male-female pairing as well as induction of apoptosis-like processes in cells in the close vicinity to the tegument. Edelfosine oral treatment also showed in vivo schistosomicidal activity and decreased significantly the egg burden in the liver, a key event in schistosomiasis.

Conclusions/Significance

Our data show that edelfosine is the most potent APL in killing S. mansoni adult worms in vitro. Edelfosine schistosomicidal activity seems to depend on its action on the tegumental structure, leading to tegumental damage, membrane permeabilization and apoptosis-like cell death. Oral administration of edelfosine diminished worm and egg burdens in S. mansoni-infected CD1 mice. Here we report that edelfosine showed promising antischistosomal properties in vitro and in vivo.

Disposition of mefloquine and enpiroline is highly influenced by a chronic Schistosoma mansoni infection

Chronic Schistosoma mansoni infections lead to severe tissue destruction of the gut wall and liver and can influence drug disposition. This study aimed to investigate the impact of a chronic S. mansoni infection on the pharmacokinetic (PK) parameters of two promising antischistosomal lead candidates (mefloquine and enpiroline) in mice. Studies were conducted in two different mouse cohorts (S. mansoni-infected and uninfected mice) for both drugs. Plasma samples were collected at various time points after oral treatment (200 mg/kg of body weight) with study drugs. A high-performance liquid chromatography (HPLC) method was validated to analyze enpiroline and mefloquine in plasma. Livers and intestines were collected from infected animals to determine the onset of action, hepatic shift, and worm burden reduction. Following mefloquine administration, hepatic shifting and significant worm burden reductions (79.2%) were observed after 72 h. At 1 week posttreatment with enpiroline, the majority of worms had migrated to the liver and significant worm burden reductions were observed (93.1%). The HPLC method was selective, accurate (87.8 to 111.4%), and precise (<10%) for the analysis of both drugs in plasma samples. The PK profiles revealed increased values for half-life (t1/2) and area under the concentration-time curve (AUC) for both drugs in infected animals compared to the t1/2 and AUC values in uninfected animals. Considerable changes were observed for mefloquine, with a 5-fold increase of t1/2 (182.7 h versus 33.6 h) and 2-fold increase of AUC (1,116,517.8 ng · h/ml versus 522,409.1 ng · h/ml). S. mansoni infections in mice influence the PK profiles of enpiroline and mefloquine, leading to delayed clearance. Our data confirm that drug disposition should be carefully studied in schistosomiasis patients.

Ultrastructural study on the morphological changes to male worms of Schistosoma mansoni after in vitro exposure to allicin

INTRODUCTION

Garlic has a wide range of actions, including antibacterial, antiviral, antifungal, antiprotozoal and anthelmintic actions. This antiparasitic activity has been attributed to allicin, which is the main constituent of garlic. The present study aimed to investigate the in vitro activity of allicin on the tegument of adult Schistosoma mansoni worms using scanning electron microscopy.

METHODS

Swiss Webster mice were infected with S. mansoni cercariae (100 per mouse) and sacrificed 50 days later to acquire the adult worms. These worms were collected by perfusion and placed in RPMI medium 1,640 at 37°C before transferring to RPMI media containing 0 (control), 5, 10, 15 and 20mg/mL of allicin, where they were incubated for 2h. The worms were fixed in 2.5% glutaraldehyde solution, washed twice, post-fixed in osmium tetroxide, washed twice and then dehydrated with ascending grades of ethanol. The samples were air-dried, mounted on stubs, gold coated in an ion sputtering unit and viewed using a scanning electron microscope.

RESULTS

A concentration of 5mg/mL caused wrinkling in the tegument; a concentration of 10mg/mL resulted in changes to tubercles and loss or modification of spines. With 15 and 20mg/mL increasing damage to the tegument could be seen, such as vesicle formation and the presence of ulcers.

CONCLUSIONS

These findings demonstrate the effect of allicin on adult S. mansoni worms and indicate that most of the changes occur at concentrations greater than that normally indicated for treatment.

Schistosomiasis--an unusual cause of ureteral obstruction: a case history and perspective

A male, 32 years of age, presented with dysuria and abdominal pain, but no gross hematuria. He emigrated three years earlier from Somalia, East Africa, and was currently employed as a poultry processor in a rural Wisconsin community. The patient denied any trauma, sexual activity, or family history of significant illness. Abdominal and genitourinary exams were normal with negative tests for gonococcus and chlamydia. Urinalysis demonstrated microhematuria. A urogram and retrograde pyelogram revealed a mildly dilated right ureter down to the ureterovesical junction. Cystoscopy showed punctate white lesions on the bladder urothelium. Ureteroscopy was used to biopsy abnormal tissue in the distal ureter and bladder. Biopsy tissue demonstrated deposits of Schistosoma haematobium eggs. No ova were seen in collected urine specimens. The patient was successfully treated with praziquantel and will be monitored for sequelae of the disease. Schistosomiasis (Bilharziasis) can be expected to be seen with increasing frequency in the United States with the continuing influx of immigrants and refugees, as well as the return of travelers and soldiers from endemic areas. While no intermediate snail host exists for the transmission of Schistosoma sp. in the United States, the continued importation of exotic animals including snails from Africa, as well as the ability of schistosomes to shift host species warrants concern. Additionally, increasing disease associated with non-human bird schistosomes of the same genus seen in the midwestern United States is occurring throughout Europe. One should be aware that praziquantel may not always be available or effective in the treatment of schistosomiasis. It behooves the practicing clinician to remain updated on the status of this widespread zoonosis.

Sexual Biology of Schistosomes

Schistosomes are unusual, together with some of the didymozoidae, in that they are dioecious instead of being hermaphrodite. This gonochorism is accompanied with morphological, ecological, behavioural and molecular differences between the male and the female parasites all through their life cycle. This review is an overview of the sexual biology of schistosomes and aims to provide the most recent information that may help to build future control strategies against these parasites. It proposes a new view of the life cycle of schistosomes, taking into account the sexual status of each developmental stage. It presents the relevant information available on the genetic and phenotypic sexual dimorphisms of these parasites; it proposes a comparison between the host-male parasite and the host-female parasite interactions in both the molluscan intermediate and the mammalian definitive hosts; it exposes the male-female parasite interactions that exist in both the mollusc and the mammalian hosts at the parasite individual and populational levels. This review highlights the domains of research that are still unexplored but that would be of great interest for a better knowledge of the sexual way of life of the parasites which are still responsible for one of the most important human parasitic diseases in the world.

Ultrastructural alterations in adult Schistosoma mansoni caused by artemether

Progress has been made over the last decade with the development and clinical use of artemether as an agent against major human schistosome parasites. The tegument has been identified as a key target of artemether, implying detailed studies on ultrastructural damage induced by this compound. We performed a temporal examination, employing a transmission electron microscope to assess the pattern and extent of ultrastructural alterations in adult Schistosoma mansoni harboured in mice treated with a single dose of 400 mg/kg artemether. Eight hours post-treatment, damage to the tegument and subtegumental structures was seen. Tegumental alterations reached a peak 3 days after treatment and were characterized by swelling, fusion of distal cytoplasma, focal lysis of the tegumental matrix and vacuolisation. Tubercles and sensory organelles frequently degenerated or collapsed. Typical features of subtegumental alterations, including muscle fibres, syncytium and parenchyma tissues, were focal or extensive lysis, vacuolisation and degeneration of mitochondria. Severe alterations were also observed in gut epithelial cells and vitelline cells of female worms. Our findings of artemether-induced ultrastructural alterations in adult S. mansoni confirm previous results obtained with juvenile S. mansoni and S. japonicum of different ages.

Adverse effects of praziquantel treatment of Schistosoma japonicum infection: involvement of host anaphylactic reactions induced by parasite antigen release

The present study using a murine model heavily infected with Schistosoma japonicum aimed to elucidate the pathogenesis of adverse effects of praziquantel treatment of schistosome-infected subjects. Inbred BALB/c mice were infected with S. japonicum (Yamanashi strain) before being treated with a single dose of praziquantel at 4 or 8 weeks p.i. All the mice treated at 8 weeks p.i. exhibited signs typical of systemic anaphylaxis until half of them died shortly after praziquantel administration. At autopsy, these mice exhibited remarkable intestinal alterations characterised by increased mucosal permeability, mucosal oedema and petechial haemorrhage, which are changes typical of immediate intestinal anaphylaxis. In these mice treated at 8 weeks p.i., degranulation of intestinal mast cells was frequently observed, which was particularly remarkable around S. japonicum eggs hatched as an effect of praziquantel. Furthermore, the plasma histamine concentration just after praziquantel treatment was much higher in mice at 8 weeks p.i. than that in uninfected mice or in S. japonicum-infected mice without drug treatment. In contrast, none of these intestinal changes was observed in untreated or uninfected control mice, or in mice administered praziquantel at 4 weeks p.i., in which worm pairs had just reached sexual maturation and begun egg-laying. The finding by ELISA that serum IgM and IgA levels specific to S. japonicum eggs decreased immediately after praziquantel treatment, together with the results of immunohistochemistry, revealed the sudden release of parasite antigens from the eggs hatched by praziquantel treatment. The results of this study demonstrate that adverse effects of praziquantel treatment of schistosomiasis characterised by abdominal signs depend on anaphylactic reactions due to parasite antigens, especially antigens from eggs hatched as an effect of praziquantel.

Effects of free and liposomized praziquantel on worm burden and antibody response in mice infected with Mesocestoides corti tetrathyridia

The parasite burden in the liver and peritoneal cavity, and antibody levels directed to whole worm extract, have been monitored in serum from ICR-strain mice, infected orally with 55 tetrathyridia of Mesocestoides corti (Cestoda, Cyclophyllidea). The subcurative does (3x or 6x) of praziquantel (PZQ) (10 mg.kg-1 body weight) were administered to mice from day 14 post infection (p.i.) in two drug formulations: as PZQ suspended in Dorfman vehicle, or as PZQ incorporated in liposomes (lip.PZQ). The appearance of antibodies was time-dependent and correlated with the rate of reduction in numbers of tetrathyridia. PZQ in three and six doses caused the highest fall of parasite numbers in the liver on day 1 post therapy (p.t.). In the peritoneal cavity, a similar reduction in worm burden occurred but only after six doses of the drug. The worm count in the peritoneal cavity from groups of mice injected with lip.PZQ decreased most markedly on day 7 p.t., in the group treated with six doses of the drug. In the liver, the highest larvicidal effect, compared with the controls, was observed 6 days later (i.e. day 13 p.t.), following three doses of lip.PZQ. In all treated groups, two peak values of antitetrathyridial antibody levels were detected between days 1 and 13 p.t. (i.e. days 17 to 29 p.i.), after which there was a gradual but continuous increase in antibody tire.(ABSTRACT TRUNCATED AT 250 WORDS)

Fasciola hepatica: tegumental surface changes in adult and juvenile flukes following treatment in vitro with the sulphoxide metabolite of triclabendazole (Fasinex)

The effects of the novel benzimidazole, triclabendazole (Fasinex, Ciba-Geigy), in its active sulphoxide metabolite form (TCBZ-SX), on the tegumental surface of Fasciola hepatica has been examined in vitro. The tegument of adult flukes incubated in TCBZ-SX (50 micrograms/ml) appeared swollen and blebbed after only 6 h. In addition, progressive spine loss at the oral cone was evident following 12 h treatment. After 24 h, the tegumental syncytium and spines had completely sloughed away, leaving an exposed basal lamina and empty spine sockets. Juvenile flukes (3 weeks old) also demonstrated tegumental alterations after treatment with TCBZ-SX (20 micrograms/ml). The syncytium became extremely roughened and corrugated on both dorsal and ventral surfaces after only 3 h. Following 6- and 9-h incubations, there were many deep furrows, which were especially pronounced on the ventral surface, and by 18 h, the juvenile tegument was severely disrupted, especially on the ventral surface. In all cases, the effects were more marked than in the previous incubation periods. The results confirm the potent activity of triclabendazole against F. hepatica and suggest that the tegument of adult and juvenile flukes may be a target organ for this important fasciolicide.

Schistosoma mansoni: praziquantel-induced tegumental lesion exposes actin of surface spines and allows binding of actin depolymerizing factor, gelsolin

Praziquantel is widely used for treatment of schistosomiasis. Elimination of intravascular worms involves a combination of drug-induced changes at the worm surface and a host immune response against exposed parasite components. Loss of spines is a typical feature of schistosomes obtained from praziquantel-treated infected animals. The mechanism for this is unknown. We have considered the possibility that praziquantel treatment involves exposure of surface spines consisting of 'paracrystalline' actin and a subsequent host response against actin through mechanisms established in the host independently from schistosomal infection. Drug-induced exposure of actin was demonstrated by fluorescence microscopy using anti-actin antibodies and phallacidin, an actin-binding mushroom toxin. Actin spines remained intact at the schistosome surface after in vitro exposure, but spine morphology was lost after in vivo exposure to praziquantel. Disintegration of spines in vivo was associated with binding of host antibodies. In vitro spine destruction could be seen in the presence of normal human serum. The effect was linked to calcium-dependent binding of actin depolymerizing factor, gelsolin.

Immune-dependent chemotherapy of schistosomiasis

Host immune responses have been shown to enhance the efficacy of several schistosomicidal drugs. The evidence derives mainly from experiments on Schistosoma mansoni infections in the mouse with their immune status variously modulated; this review emphasises praziquantel (PZQ), which is now the main drug used for treatment of human schistosomiasis. Electron microscopy and indirect immunofluorescence indicate that PZQ disrupts the integrity of the surface membranes of S. mansoni, particularly those covering the dorsal tubercles of adult male worms, and this causes antigens which are the targets of antibody attack to be revealed. We review the evidence that two S. mansoni antigens in particular are implicated in the immune-dependent action of PZQ: a 200 kDa glycoprotein and a 27 kDa antigen with non-specific esterase activity. Consistent with the involvement of the latter antigen, increased non-specific esterase activity was demonstrated histochemically on the surface of intact PZQ-treated male worms, and we describe a chromogenic substrate assay for quantifying the amount of esterase activity that is exposed after drug treatment. The potential relevance of these observations for enhancing the efficacy of drugs currently used to treat human schistosomiasis, and for devising novel therapeutic strategies, is discussed.

Schistosoma mansoni: larval damage and role of effector cell(s) in the synergy between vaccine immunity and praziquantel treatment

A number of authors have demonstrated that the schistosomicidal compound, Praziquantel (Pzq), depends for its action upon the immune status of the host (Sabah et al. 1985; Brindley & Sher, 1987; Doenhoff et al. 1987). We have attempted to define the synergistic interaction between immuno- and chemotherapy further, using the murine irradiated vaccine model of schistosomiasis mansoni. In vaccinated mice, resistance operates in the skin but not the lungs; drug targeted towards lung-stage worms exacerbates lung-phase immunity, however, as depicted by the increased number and size of inflammatory reactions in the pulmonary tissues. Parasites are often found trapped within such foci. In the present investigation, light and ultrastructural studies have been utilized to examine the nature and extent of damage inflicted upon lung-stage larvae recovered from day 6 Pzq-treated vaccinated mice. Such studies have revealed that damage involves muscle disorganization, internal disruption and occasionally, loss of the tegument; in the latter case, cells are often seen attached to the denuded lung worms. To identify the crucial cellular effector cell(s) involved in the synergy between immuno- and chemotherapy, cell depletion studies have been performed in vivo. It would appear from these experiments that eosinophils or lymphocytes rather than neutrophils or macrophages are important effector cells in this synergy. Histological studies argue in favour of eosinophils being the key effector cells.

The effect of praziquantel on the ultrastructure of Schistosoma margrebowiei

The effect of various concentrations of praziquantel at different time intervals post-treatment on the ultrastructure of Schistosoma margrebowiei using scanning and transmission electron microscopy has been examined. The major changes involved blebbing of the entire surface tegument of both sexes (although more marked in males) together with vacuolation of the basal membrane accompanied by the development of membraneous whorls. These effects were progressively more marked with increased concentration and time of exposure resulting in severe erosion of the tubercles and collapse of the sensory organelles. Exposure of the underlying tegumental tissue resulted and paralysis and contraction of the suckers and neck region was apparent. Disruption of the subtegumental musculature and the appearance of vacuolation and membraneous whorl formation were seen. The gastrodermis was similarly affected and the S4 cells of the vitelline gland showed protein disruption of the vitelline droplets. Host cells were seen adhering to the surface of the worms following drug treatment and the synergism between PZQ and the action of the hosts immune system has been discussed.

Development and dynamics of regional specialization within the syncytial epidermis of the rat tapeworm, Hymenolepis diminuta

The epidermis of the tapeworm Hymenolepis diminuta is a highly organized syncytium, composed of an outer layer of continuous cytoplasm, or ectocytoplasm, and an inner layer of nucleated cell bodies, or perikarya. The perikarya are in direct cytoplasmic continuity with the ectocytoplasm via narrow plasmalemma-bound bridges called internuncial process. Although distinct structural and functional differences are apparent between ectocytoplasm and perikarya, all of the perikarya along the body of the cestode are morphologically similar, as are all regions of ectocytoplasm. However, immunocytochemically distinct subpopulations of perikarya and regionally defined areas of ectocytoplasm were identified along the tapeworm strobila by the use of monoclonal antibodies raised against a preparation of isolated tegument. The different types of perikarya and the regionally specialized areas of ectocytoplasm were organized in a topographically precise manner along the body of the parasite. Examination of labeling patterns after colchicine treatment suggests that different types of perikarya are specialized for biosynthesis of specific tegumental molecules and for turnover or recycling of tegumental material. Furthermore, it appears that a 52 kDa polypeptide synthesized by one population of perikarya is transported through the syncytium and ultimately resorbed by a different population of tegumental perikarya. These data suggest that the syncytial epidermis of parasitic platyhelminthes exhibits a more complex organization of function than previously appreciated.

Schistosoma mansoni: histological analysis of the synergistic interaction between vaccine immunity and praziquantel therapy in the lungs of mice

Naive CBA mice and mice vaccinated 4 weeks previously with gamma-irradiated cercariae of S. mansoni were challenged percutaneously with normal cercariae and then treated with 500 mg/kg body weight of Praziquantel (Pzq). The drug was administered intradermally on day 1 or intramuscularly on day 6, thus targeting against skin stage or lung stage challenge larvae respectively. The skin site of challenge and/or the lungs were removed at various time points to provide samples for histological examination. As reported elsewhere (Flisser, Delgado & McLaren 1989) the efficacy of Pzq was significantly enhanced in vaccinated mice and was influenced by the treatment regime. Histological analysis revealed that when Pzq was administered I/D on day 1 to vaccinated mice, the inflammatory response to challenge differed in extent but not nature from that seen in vaccinated but untreated cohorts. This correlates with worm recovery data showing no (this study), or only marginal synergy between drug treatment and immunity using this regimen of drug treatment (Flisser et al. 1989). Following the day 6 protocol of drug delivery, however, lungs from treated vaccinated mice exhibited many large inflammatory reactions containing trapped challenge larvae. In contrast, lungs from untreated vaccinated mice had only few foci which were small and rarely contained trapped larvae. These data again correlate well with worm recovery data showing that there is a highly significant synergy between vaccination and drug treatment administered at this time (Flisser et al. 1989; this study). It would seem, therefore, that Pzq exacerbates lung phase immunity in the NIMR vaccine mouse model where skin phase immunity predominates and pulmonary attrition is normally minimal. The results are discussed in the light of published data concerning the effector mechanisms thought to characterize skin and lung phase vaccine resistance in the murine model.

Immunocytochemistry of cytoskeletal proteins in adult Schistosoma mansoni

Antisera to vertebrate actin and actin-binding proteins were used to characterize the cytoskeleton of adult Schistosoma mansoni. Actin, alpha-actinin and tropomyosin immunoreactivities were detected in the cytoplasm of the apical tegument. Antiserum to alpha-actinin bound to the tegumental spines and this protein may be involved in cross-linking of spine actin filaments. Actin, alpha-actinin and tropomyosin antisera bound to the musculature. Strongest immunoreactivity was seen in the parenchyma. Antisera to actin, alpha-actinin, tropomyosin and spectrin bound to parenchyma cells including those of the tubercles, suggesting that these proteins are located in muscle cell bodies. The distribution of cytoskeletal proteins is discussed in relation to tegumental repair processes.

Immune dependence of schistosomicidal chemotherapy: an ultrastructural study of Schistosoma mansoni adult worms exposed to praziquantel and immune serum in vivo

This study examines the immune-dependence of praziquantel (PZQ) for the treatment of Schistosomiasis mansoni in mice. We have shown elsewhere from worm recovery data that the efficacy of PZQ is significantly enhanced when mice are treated concomitantly with antisera raised against antigens released from adult schistosomes, even though such antisera show no intrinsic helminthotoxic activity (Doenhoff et al. 1987, Doenhoff, Modha & Lambertucci 1988). Moreover, indirect immunofluorescence assays have shown that male worms exposed to the dual treatment regime in vivo bind antiserum to their dorsal surfaces in a pattern that seems to follow the outline of the dorsal tubercles. Scanning and transmission electron microscopy have now been used to further define the features of damage inflicted upon worms through exposure to antiserum alone, drug alone, or the two treatments in combination. Such investigations revealed that the antiserum induces a classical membrane repair process in worms of both sexes, but little other damage. PZQ causes the formation of spherical protuberances on the dorsal tubercles of male worms, while the dual treatment regime induces both kinds of damage in male schistosomes, but with much enhanced severity. The protuberances show evidence of explosion and some regions of the tegument become completely destroyed. Regions other than the dorsal surfaces of the male worms do not exhibit comparable trauma, and neither do the females. These data are discussed in relation to the known schistosomicidal activity of PZQ, the notion that male and female worms exhibit regional and sexual differences in susceptibility, documented evasive strategies of the parasite and the interdependence of immuno- and chemotherapy.

Effect of praziquantel treatment on lung-stage larvae of Schistosoma mansoni in vivo

Mice infected heavily with Schistosoma mansoni cercariae were treated 6 days later with Praziquantel and the parasites studied 1 h post-treatment. Immunofluorescence experiments showed that parasite surface antigens became available for labelling in larvae harvested from Praziquantel-treated mice, but not from untreated mice. Red blood cell antigens acquired from the host were localized on all lung worms studied. The distribution of each set of antigens, as revealed by fluorescence-labelling was, however, quite different. The lungs of heavily infected, drug-treated mice, exhibited severe haemorrhages which occurred in a dose-dependent manner. Fewer haemorrhages were found when heavily infected mice were treated simultaneously with Praziquantel and Aprotinin, a proteinase inhibitor. These results indicate that Praziquantel treatment in vivo induces the exposure of parasite antigens on lung-stage worms and may cause the release of parasite-derived enzymes which induce haemorrhages in the lung tissue of the host.

Evidence for an immune-dependent action of praziquantel on Schistosoma mansoni in mice

Effective schistosomicidal action of praziquantel against Schistosoma mansoni infections in mice appears to be dependent to some extent on appropriate immunological stimulation. Indirect evidence consistent with this hypothesis was obtained by demonstrating a positive relationship between drug efficacy and both the intensity and the age of the parasitic infection. More directly, it has previously been shown that praziquantel kills fewer S. mansoni worms in immunosuppressed T cell-deprived mice than in immunologically intact controls; and we show here that infections 5 weeks old, against which the drug alone is sub-optimally active, are more effectively killed by a combination of drug and a rabbit antiserum raised against adult worm antigens.

Therapeutical evaluation of different dose regimens of praziquantel in schistosomiasis mansoni, based on the quantitative oogram technique

A clinical trial involving 80 patients of both sexes, from ages 15 to 55, with chronic intestinal or hepatointestinal schistosomiasis mansoni, was carried out to evaluate the therapeutical efficacy of different dose regimens of praziquantel. The patients were randomly allocated into four groups with an equal number of cases and were then treated with one of the following dosages: 60 mg/kg for 1 day; 60 mg/kg daily for 2 days; 60 mg/kg daily for 3 days; and 30 mg/kg daily for 6 days. The assessment of parasitological cure was based on the quantitative oogram technique through rectal mucosa biopsies which were undertaken prior to, as well as, 1,2,4 and 6 months post-treatment. Concurrently, stool examinations according to the qualitative Hoffman, Pons & Janer (HPJ) and the quantitative Kato-Katz (K-K) methods were also performed. The best tolerability was observed with 30 mg/kg daily for 6 days whereas the highest incidence of side-effects (mainly dizziness and nausea) was found with 60 mg/kg daily for 3 days. No serious adverse drug reaction has occurred. The achieved cure rates were: 25% with 60 mg/kg for 1 day; 60% with 60 mg/kg daily for 2 days; 89.5% with 60 mg/kg daily for 3 days; and 90% with 30 mg/kg daily for 6 days. At the same time there has been a downfall of 64%, 73%, 87% and 84% respectively, in the median number of viable S. mansoni ova per gram of tissue. Thus, a very clear direct correlation between dose and effect could be seen. The corresponding cure rates according to stool examinations by HPJ were 39%, 80%, 100% and 95%; by K-K 89%, 100%, 100% and 100%. This discrepancy in results amongst the three parasitological methods is certainly due to their unequal accuracy. In fact, when the number of viable eggs per gram of tissue fell below 5,000 the difference in the percentage of false negative findings between HPJ (28%) and K-K (80%) became significative. When this number dropped to less than 2,000 the percentage of false negative results obtained with HPJ (49%) turned significant in relation to the oogram as well. In conclusion, it has been proven that praziquantel is a highly efficacious agent against S. mansoni infections. If administered at a total dose of 180 mg/kg divided into either 3 or 6 days, it yields a 90% cure rate. Possibly, one could reach 100% by increasing the total dose to 240 mg/kg. Furthermore, it was confirmed that the quantitative oogram technique is the most reliable parasitological method when evaluating the efficacy of new drugs in schistosomiasis mansoni.

Schistosoma mansoni: structural damage and tegumental repair after in vivo treatment with praziquantel

The long-term, in vivo effects of a single, subcurative dose (200 mg/kg body weight of mouse) of praziquantel on the structure of adult Schistosoma mansoni and on the process and speed of tegumental repair are described. In both male and female worms praziquantel caused often extensive damage to the tegument, in the form of surface blebbings, swellings and lesions, and vacuolization and disruption of the subtegumental tissues. Repair of the drug-induced tegumental damage occurred slowly with partial and, more rarely, complete repair only being seen after 65 days post-treatment (p.t.), although signs of damage were still observed, particularly in male worms, at 100 days p.t. In contrast, repair of damage to the subtegumental/parenchymal tissues including the tegumental perikarya occurred relatively quickly, with the majority of worms examined appearing normal by 8-12 days p.t. The possible role(s) of the host immune response in relation to the speed of tegumental repair in vivo is discussed.

Absorption, distribution and excretion of the anthelmintic praziquantel (Droncit) in rainbow trout (Salmo gairdneri R.)

Prazquantel is an anthelmintic active against trematodes and cestodes. The absorption, distribution and excretion of the drug was studied in serum, muscles, liver, bile fluid and kidneys of rainbow trout at two temperatures, 12 degrees C and 18 degrees C, after a single oral dose of 500 mg/kg body wt. A bioassay, using cercaria larvae of the trematode Diplostomum spathaceum as the test organism, was employed to measure the drug levels in tissues of the fish. The cercariae were very sensitive to praziquantel; their mobility was significantly reduced within 20 min in a 0.01 micrograms/ml solution. Praziquantel was readily absorbed from the gastrointestinal tract of the fish. Absorption was more rapid at 18 degrees C than at 12 degrees C. Only in the liver, however, did the peak values reach significantly higher levels at the higher temperature. The peak values in different tissues (10.2-31.8 micrograms/g) were reached 4-16 h after administration of the drug. The elimination of the drug from the tissues was less dependent on temperature than absorption. By 32 h p.a., 67%-96% of the maximum amounts had been eliminated from the tissues. Praziquantel was excreted partly with bile fluid and partly as water-soluble metabolites through the kidneys.

Fasciola hepatica: tegumental surface alterations following treatment in vitro with the deacetylated (amine) metabolite of diamphenethide

The effect of the deacetylated (amine) metabolite of diamphenethide (10 micrograms/ml) on the tegumental surface of Fasciola hepatica over a 24 h period in vitro has been determined by scanning electron microscopy. Blebbing begins around the oral sucker after 3 h and then passes backwards along the body, reaching the ventral sucker and midbody by 6 h, and finally the posterior end of the body (by 12 h). Initially, the blebs are small, the tegument surrounding the spines is swollen and the tegument generally has a smooth, swollen appearance. This submerges the spines below the body surface. At higher magnification the surface is seen to bear microvillous-like projections in addition to the blebs and surface pitting is deeper than normal. Later on, the blebs increase in size and burst, causing lesions and loss of spines. Lesions begin to appear on the oral cone and ventral sucker after 6 h, in the midbody by 12 h and on the dorsal surface of the posterior region after 24 h. By this time the damage is extensive: around the oral and ventral suckers, and over large areas of the oral cone and midbody region the tegument has been stripped off to expose the basal lamina beneath. The dorsal surface of the fluke is consistently more severely affected than the ventral surface.

Schistosoma mansoni: chemotherapy of infections of different ages

Mice were treated with potassium antimony tartrate, hycanthone, oxamniquine, niridazole, or praziquantel at different times after infection with Schistosoma mansoni. The rate of cure was assessed by perfusion of surviving worms approximately 4 weeks after treatment, and the percentage reduction in worm burden was estimated relative to the number of adult worms perfused from control mice, comparably infected but untreated. All six drugs were relatively inactive against S. mansoni between 3 and 4 weeks after infection when compared with treatment at 5 to 6 weeks. However, the drugs differed in the patterns of cure they achieved in the 2-week period after administration of cercariae and in the period around the onset of patency. Worms that had been subjected to amoscanate or hycanthone in the third week after infection showed evidence of this as adults in having a reduced fecundity. Factors such as worm or host physiology, or host immune status may have had roles in the outcome of chemotherapy at different stages of maturation of S. mansoni.

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

The effect of host immunosuppression on the efficacy of schistosomicidal chemotherapy has been tested in T-cell-deprived CBA mice infected with Schistosoma mansoni. The drugs hycanthone, oxamniquine, and praziquantel were found to kill fewer adult S. mansoni worms in deprived mice than in comparably infected strain-, age-, and sex-matched, immunologically intact controls. Inconsistent results were obtained with niridazole, and amoscanate was as effective in deprived mice as in controls. The possibility that hycanthone, oxamniquine, praziquantel, and previously studied antimony act synergistically with immune effector mechanisms in killing adult schistosomes is discussed.