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

Combined chemotherapy manifest less severe immunopathology effects in helminth-protozoa comorbidity

BACKGROUND

Co-infection with Leishmania major and Schistosoma mansoni may have significant consequences for disease progression, severity and subsequent transmission dynamics. Pentavalent antimonials and Praziquantel (PZQ) are used as first line of treatment for Leishmania and Schistosoma infections respectively. However, there is limited insight on how combined therapy with the standard drugs impacts the host in comorbidity. The study aimed to determine the efficacy of combined chemotherapy using Pentostam (P) and PZQ in murine model co-infected with L. major and S. mansoni.

METHODS

A 3 × 4 factorial design with three parasite infection groups (Lm, Sm, Lm + Sm to represent L. major, S. mansoni and L. major + S. mansoni respectively) and four treatment regimens [P, PZQ, P + PZQ, and PBS designating Pentostam (GlaxoSmithKline UK), Praziquantel (Biltricide^®, Bayer Ag. Leverkusen, Germany), Pentostam + Praziquantel and Phosphate buffered saline] as factors was applied.

RESULTS

Significant changes were observed in the serum Interferon gamma (IFN-γ), and Macrophage inflammatory protein-one alpha (MIP-1α) levels among various treatment groups between week 8 and week 10 (p < 0.05). There was increased IFN-γ in the L. major infected mice subjected to PZQ and PBS, and in L. major + S. mansoni infected BALB/c mice treated with P + PZQ. Subsequently, MIP-1α levels increased significantly in both the L. major infected mice under PZQ and PBS and in L. major + S. mansoni infected BALB/c mice undergoing concurrent chemotherapy with P + PZQ between 8 and 10 weeks (p < 0.05). In the comorbidity, simultaneous chemotherapy resulted in less severe histopathological effects in the liver.

CONCLUSION

It was evident, combined first line of treatment is a more effective strategy in managing co-infection of L. major and S. mansoni. The findings denote simultaneous chemotherapy compliments immunomodulation in the helminth-protozoa comorbidity hence, less severe pathological effects following the parasites infection. Recent cases of increased incidences of polyparasitism in vertebrates call for better ways to manage co-infections. The findings presented necessitate intrinsic biological interest on examining optimal combined chemotherapeutic agents strategies in helminth-protozoa concomitance and the related infections abatement trends vis-a-vis host-parasite relationships.

Adventure tourism and schistosomiasis: serology and clinical findings in a group of Danish students after white-water rafting in Uganda

Introduction

Diagnosis of schistosomiasis in travellers is a clinical challenge, since cases may present with no symptoms or a few non-specific symptoms. Here, we report on the laboratory and clinical findings in Danish travellers exposed to Schistosoma-infested water during white-water rafting on the Ugandan part of the upper Nile River in July 2009.

Case presentation

Forty travellers were offered screening for Schistosoma-specific antibodies. Serological tests were performed 6–65 weeks after exposure. A self-reporting questionnaire was used to collect information on travel activity and health history, fresh water exposure, and symptoms. Seropositive cases were referred to hospitals where clinical and biochemical data were collected. Schistosoma-specific antibodies were detected in 13/35 (37 %) exposed participants, with 4/13 (31 %) seroconverting later than 2 months following exposure. Four of thirteen (31 %) cases reported ≥3 symptoms compatible with schistosomiasis, with a mean onset of 41 days following exposure. No Schistosoma eggs were detected in stool or urine in any of the cases. Peripheral eosinophilia (>0.45×10⁹ cells l⁻¹) was seen in 4/13 cases, while IgE levels were normal in all cases.

Conclusion

Schistosomiasis in travellers is not necessarily associated with specific signs or symptoms, eosinophilia, raised IgE levels, or detection of eggs. The only prognostic factor for infection was exposure to freshwater in a Schistosoma-endemic area. Seroconversion may occur later than 2 months after exposure and therefore – in the absence of other diagnostic evidence – serology testing should be performed up to at least 2–3 months following exposure to be able to rule out schistosomiasis.

New approaches to measuring anthelminthic drug efficacy: parasitological responses of childhood schistosome infections to treatment with praziquantel

Background

By 2020, the global health community aims to control and eliminate human helminthiases, including schistosomiasis in selected African countries, principally by preventive chemotherapy (PCT) through mass drug administration (MDA) of anthelminthics. Quantitative monitoring of anthelminthic responses is crucial for promptly detecting changes in efficacy, potentially indicative of emerging drug resistance. Statistical models offer a powerful means to delineate and compare efficacy among individuals, among groups of individuals and among populations.

Methods

We illustrate a variety of statistical frameworks that offer different levels of inference by analysing data from nine previous studies on egg counts collected from African children before and after administration of praziquantel.

Results

We quantify responses to praziquantel as egg reduction rates (ERRs), using different frameworks to estimate ERRs among population strata, as average responses, and within strata, as individual responses. We compare our model-based average ERRs to corresponding model-free estimates, using as reference the World Health Organization (WHO) 90 % threshold of optimal efficacy. We estimate distributions of individual responses and summarize the variation among these responses as the fraction of ERRs falling below the WHO threshold.

Conclusions

Generic models for evaluating responses to anthelminthics deepen our understanding of variation among populations, sub-populations and individuals. We discuss the future application of statistical modelling approaches for monitoring and evaluation of PCT programmes targeting human helminthiases in the context of the WHO 2020 control and elimination goals.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1312-0) contains supplementary material, which is available to authorized users.

The contribution of mass drug administration to global health: past, present and future

Mass drug administration (MDA) is a means of delivering safe and inexpensive essential medicines based on the principles of preventive chemotherapy, where populations or sub-populations are offered treatment without individual diagnosis. High-coverage MDA in endemic areas aims to prevent and alleviate symptoms and morbidity on the one hand and can reduce transmission on the other, together improving global health. MDA is the recommended strategy of the World Health Organisation to control or eliminate several neglected tropical diseases (NTDs). More than 700 million people now receive these essential NTD medicines annually. The combined cost of integrated NTD MDA has been calculated to be in the order of $0.50 per person per year. Activities have recently been expanded due, in part, to the proposed attempt to eliminate certain NTDs in the coming two decades. More than 1.9 billion people need to receive MDA annually across several years if these targets are to be met. Such extensive coverage will require additional avenues of financial support, expanded monitoring and evaluation focusing on impact and drug efficacy, as well as new diagnostic tools and social science strategies to encourage adherence. MDA is a means to help reduce the burden of disease, and hence poverty, among the poorest sector of populations. It has already made significant improvements to global health and productivity and has the potential for further successes, particularly where incorporated into sanitation and education programmes. However logistical, financial and biological challenges remain.

Combination therapy using Pentostam and Praziquantel improves lesion healing and parasite resolution in BALB/c mice co-infected with Leishmania major and Schistosoma mansoni

Background

Most natural host populations are exposed to a diversity of parasite communities and co-infection of hosts by multiple parasites is commonplace across a diverse range of systems. Co-infection with Leishmania major and Schistosoma mansoni may have important consequences for disease development, severity and transmission dynamics. Pentavalent antimonials and Praziquantel (PZQ) have been relied upon as a first line of treatment for Leishmania and Schistosoma infections respectively. However, it is not clear how combined therapy with the standard drugs will affect the host and parasite burden in concomitance. The aim of the current study was to determine the efficacy of combined chemotherapy using Pentostam and PZQ in BALB/c mice co-infected with L. major and S. mansoni.

Methods

The study used BALB/c mice infected with L. major and S. mansoni. A 3 × 4 factorial design with three parasite infection groups (Lm, Sm, Lm + Sm designated as groups infected with L. major, S. mansoni and L. major + S. mansoni, respectively) and four treatment regimens [P, PZQ, P + PZQ and PBS designating Pentostam®(GlaxoSmithKline UK), Praziquantel (Biltricide®, Bayer Ag. Leverkusen, Germany), Pentostam + Praziquantel and Phosphate buffered saline] as factors was applied. In each treatment group, there were 10 mice. Lesion development was monitored for 10 weeks. The parasite load, body weight, weight of the spleen and liver were determined between week 8 and week 10.

Results

Chemotherapy using the first line of treatment for L. major and S. mansoni reduced the lesion size and parasite loads but did not affect the growth response, spleen and liver. In the co-infected BALB/c mice, the use of Pentostam or PZQ did not result in any appreciable disease management. However, treatment with P + PZQ resulted in significantly (p < 0.05) larger reduction of lesions, net increase in the body weight, no changes in the spleen and liver weight and reduced Leishman-Donovan Units (LDU) and worm counts than BALB/c mice treated with Pentostam or PZQ alone.

Conclusions

The present study demonstrated that the combined first line of treatment is a more effective strategy in managing co-infection of L. major and S. mansoni in BALB/c mice.

Regular treatments of praziquantel do not impact on the genetic make-up of Schistosoma mansoni in Northern Senegal

The Senegal River Basin (SRB) experienced a major epidemic of intestinal schistosomiasis in the early nineties, after the construction of a dam for irrigation purposes. Exceptionally low cure rates following praziquantel (PZQ) treatment at the onset of the epidemic raised concerns about PZQ resistant strains of Schistosoma mansoni, although they could also be attributed to the intense transmission at that time. A field study in the same region more than 15 years later found cure rates for S. mansoni still to be low, whereas Schistosomahaematobium responded well to treatment. We collected S. mansoni miracidia from children at base-line prior to treatment, six months after two PZQ treatments and two years after the start of the study when they had received a total of five PZQ treatments. In total, 434 miracidia from 12 children were successfully genotyped with at least six out of nine DNA microsatellite loci. We found no significant differences in the genetic diversity of, and genetic differentiation between parasite populations before and after repeated treatment, suggesting that PZQ treatment does not have an impact on the neutral evolution of the parasite. This is in stark contrast with a similar study in Tanzania where a significant decrease in genetic diversity was observed in S. mansoni miracidia after a single round of PZQ treatment. We argue that PZQ resistance might play a role in our study area, although rapid re-infection cannot be excluded. It is important to monitor this situation carefully and conduct larger field studies with short-term follow-up after treatment. Since PZQ is the only general schistosomicide available, the possibility of PZQ resistance is of great concern both for disease control and for curative use in clinical practice.

High rate of failure in treatment of imported schistosomiasis

BACKGROUND

There is an increasing number of imported cases of schistosomiasis in Europe, but there are only few studies on the efficacy of praziquantel for the treatment of schistosomiasis in non-endemic settings.

METHODS

Patients treated for schistosomiasis in 2003 to 2008 were offered reexamination with serology, eosinophil count, IgE, microscopy of 24 h urine samples and/or rectal biopsies >3 months after treatment. All patients had been treated with at least one dose of praziquantel 40 to 60 mg/kg >12 weeks after exposure and had not been reexposed to schistosomiasis after treatment.

RESULTS

Twenty-eight traveler (15 tourists and 13 expatriates) and two immigrants were reexamined after treatment. Viable ova were detected in six traveler (20%). Ova were found in 5/23 (22%) rectal biopsies and in 2/12 (17%) urine samples. Treatment failure was suspected in a symptomatic patient who 2 years after treatment had eightfold rise in antibody titer and elevated IgE but no detectable ova in urine or rectal biopsies. Additional 13 patients had one or more parameters, which could indicate persistent infection. There were no significant differences in eosinophil count, IgE or, change in antibody titer between patients with versus without detectable ova after treatment.

CONCLUSIONS

In traveler with a low parasite burden, assessment of treatment results can be difficult because of the low sensitivity of microscopy and persistence of antibodies for several years after treatment. We found a high rate of treatment failure among traveler, indicating that nonimmune patients may need more than the recommended single day of treatment for eradication of parasites. Until more sensitive and specific methods for detection of persistent, active infection are available, repeated treatment should be considered in patients with continuous symptoms or other indications of treatment failure even when viable ova cannot be detected by microscopy.

Further study on mefloquine concerning several aspects in experimental treatment of mice and hamsters infected with Schistosoma japonicum

Antischistosomal properties of mefloquine against Schistosoma japonicum have been further studied. A total of 260 mice were divided into four batches, and three batches of them were infected percutaneously with 40 S. japonicum cercariae. In the remaining batch, mice were infected with 20, 40, or 80 S. japonicum cercariae. Other 45 hamster, divided into two batches, were each infected two or three times with 50 S. japonicum cercariae at days 0 and 7 or 0, 14, and 21. The infected mice and hamsters were treated orally with single doses of mefloquine or praziquantel at various intervals post-infection, while infected but untreated mice and hamsters served as control. All treated animals were killed 4 weeks post-treatment for assessment of effect. In hamsters concurrently infected with 14- and 21-day-old or 14-, 21-, and 35-day-old schistosomes and treated orally with mefloquine at a single dose of 100 and 200 mg/kg, the total worm burdens were significantly lower than that of control (P < 0.05 or P < 0.01) with worm burden reductions of 45.4% and 89.9% as well as 82.5% and 90.6%, respectively. In the first batch of mice treated with mefloquine and four structurally related amino alcohol antimalarials 5 weeks post-infection at a single dose of 400 mg/kg, mefloquine, quinine, and quinidine possessed similar potential effect with total worm burden reductions of 80.9-90.3%, while halofantrine and lumefantrine showed moderate and poor effect with total worm burden reductions of 67.5% and 38.4%, respectively. In the second batch of mice infected with 20, 40, and 80 S. japonicum cercariae and treated orally with mefloquine at a single dose of 200 and 400 mg/kg 5 weeks post-infection, similar effects were seen in groups of mice with various infection intensity, the total worm burden reductions were 59.9-73.0% (200 mg/kg) and 85.0-89.1% (400 mg/kg). In the other two batches of mice infected with various stages of schistosomes and treated orally with mefloquine and praziquantel at a single dose of 200 or 400 mg/kg, potential and moderate effects of praziquantel against d0 worms (3-h-old) and adult worms (28- and 35-day-old) with total worm burden reductions of 83.6-95.6% and 42.4-69.3% were observed, but no effect against various stages of juvenile schistosome was seen. Under the two single doses used, mefloquine exhibited no effect against d0 worms, but showed moderate or potential effect against various stages of juvenile and adult schistosomes with total worm burden reductions of 56.3-89.1% (200 mg/kg) and 81.1-100% (400 mg/kg). The results indicate that mefloquine shows potential effect on hamsters concurrently infected with various stages of juvenile and adult S. japonicum; among the four structurally related amino alcohol antimalarials tested, quinine and its isomer quinidine exhibit potential effect against adult S. japonicum similar to that of mefloquine, while halofantrine and lumefantrine posses moderate and poor effect; no impact of infection intensity on the effect of mefloquine against schistosomes was observed in mice; under the same dose level, the effect of mefloquine against development stages of juvenile and adult S. japonicum is superior to that of praziquantel.

Schistosomiasis in Swedish travellers to sub-Saharan Africa: can we rely on serology?

In the absence of egg excretion, laboratory diagnosis of recently acquired schistosomiasis is dependent on serology. 42 of 83 Swedish adventure tourists to sub-Saharan Africa had serum anti-schistosome antibodies indicating recent infection. There is little doubt regarding the specificity and sensitivity of serology for the demonstration of infection, but there is a need for alternative serological methods which could be more widely used than the standard immunofluorescence assay (IFA) for antibodies against gut-derived antigens (anti-GAA). We present results suggesting that 40/42 anti-GAA positive cases also react with keyhole limpet haemocyanin (KLH), a readily available commercial antigen. High anti-GAA titres were seen for more than 2 y despite treatment with praziquantel. Thus we are faced with several questions. How likely is it that positive serology means treatment failure? What is the risk involved in chronic infection? What is the prospect for monitoring treatment outcome by serology? We conclude that there is a need for better information on the risk of becoming infected, for improved methods for testing and for monitoring the therapeutic effects in adventure tourists.

Evolutionary concepts in predicting and evaluating the impact of mass chemotherapy schistosomiasis control programmes on parasites and their hosts

Schistosomiasis is a parasitic disease of significant medical and veterinary importance in many regions of the world. Recent shifts in global health policy have led towards the implementation of mass chemotherapeutic control programmes at the national scale in previously 'neglected' countries such as those within sub-Saharan Africa. Evolutionary theory has an important role to play in the design, application and interpretation of such programmes. Whilst celebrating the rapid success achieved to date by such programmes, in terms of reduced infection prevalence, intensity and associated human morbidity, evolutionary change in response to drug selection pressure may be predicted under certain circumstances, particularly in terms of the development of potential drug resistance, evolutionary changes in parasite virulence, transmission and host use, and/or competitive interactions with co-infecting pathogens. Theoretical and empirical data gained to date serve to highlight the importance of careful monitoring and evaluation of parasites and their hosts whenever and wherever chemotherapy is applied and where parasite transmission remains.

Effect of adamantylamide dipeptide as adjuvant therapy to praziquantel in mice infected with different S. mansoni isolates

This work investigated the possible use of AdDP as adjuvant therapy to praziquantel (PZQ) in mice infected with PZQ-insusceptible Schistosoma mansoni isolate in a trial to increase the susceptibility of this isolate to the drug. Two batches of C57 BL/6 mice were infected with PZQ-susceptible and -insusceptible S. mansoni isolates, and each batch was divided into five groups. Seven weeks postinfection, the experimental group received AdDP (5 mg/kg) in addition to PZQ in reduced dose (3x100 mg/kg). Three of the remaining four groups were treated controls; they received AdDP, PZQ in reduced dose and in full dose (2x500 mg/kg), and the fourth group was infected untreated. In mice infected with PZQ-susceptible or -insusceptible S. mansoni isolate, praziquantel alone, and in addition to AdDP, reduced worm and egg loads and increased percentage dead eggs. Also, they improved the histopathological changes (reduction in granuloma diameter, percentage fibrotic area with increased percentage degenerated eggs). Inducible nitric oxide synthase (iNOS), nitric oxide (NO) in culture of peritoneal macrophages, and number of CD68-positive cells were decreased with improved alanine amino transaminase. In mice receiving combined therapy AdDP+PZQ, the antischistosomal efficacy and the reductions in the inflammatory granulomatous reactions, NO in cultured peritoneal macrophages, percentage fibrotic areas recorded, were comparable to that in mice receiving full dose of PZQ, with significantly higher reduction in CD68 cells denoting enhanced antischistosomal efficacy and healing of the inflammatory reactions in the liver.

Host population persistence in the face of introduced vector-borne diseases: Hawaii amakihi and avian malaria

The past quarter century has seen an unprecedented increase in the number of new and emerging infectious diseases throughout the world, with serious implications for human and wildlife populations. We examined host persistence in the face of introduced vector-borne diseases in Hawaii, where introduced avian malaria and introduced vectors have had a negative impact on most populations of Hawaiian forest birds for nearly a century. We studied birds, parasites, and vectors in nine study areas from 0 to 1,800 m on Mauna Loa Volcano, Hawaii from January to October, 2002. Contrary to predictions of prior work, we found that Hawaii amakihi (Hemignathus virens), a native species susceptible to malaria, comprised from 24.5% to 51.9% of the avian community at three low-elevation forests (55-270 m). Amakihi were more abundant at low elevations than at disease-free high elevations, and were resident and breeding there. Infection rates were 24-40% by microscopy and 55-83% by serology, with most infected individuals experiencing low-intensity, chronic infections. Mosquito trapping and diagnostics provided strong evidence for year-round local transmission. Moreover, we present evidence that Hawaii amakihi have increased in low elevation habitats on southeastern Hawaii Island over the past decade. The recent emergent phenomenon of recovering amakihi populations at low elevations, despite extremely high prevalence of avian malaria, suggests that ecological or evolutionary processes acting on hosts or parasites have allowed this species to recolonize low-elevation habitats. A better understanding of the mechanisms allowing coexistence of hosts and parasites may ultimately lead to tools for mitigating disease impacts on wildlife and human populations.

In vitro responses of praziquantel-resistant and -susceptible Schistosoma mansoni to praziquantel

The resistance status of five praziquantel-susceptible and five praziquantel-resistant isolates was confirmed by chemotherapy in CD(1) mice with 3 x 200mg/kg micronised praziquantel. Micronised praziquantel had higher efficacy than two other praziquantel formulations (prepared without milling). The five resistant isolates were less responsive to praziquantel than the five susceptible isolates (59-74% reduction in worm burden in resistant isolates compared with 92-100% in susceptible isolates). Observations were made on the in vitro responses of different stages of 10 isolates to praziquantel. There were different in vitro responses to praziquantel at the egg, miracidial, cercarial and adult stages of Schistosoma mansoni between praziquantel-resistant and praziquantel-susceptible isolates. There were differences in the response of resistant and susceptible isolates following exposure of freshly hatched miracidia to 10(-6)M praziquantel for 1 min and observing the percent change in shape. Using this test it should be possible to determine whether failed therapy in patients infected with S. mansoni is due to the presence of praziquantel-resistant worms. Similarly, by exposing freshly shed cercariae to 4 x 10(-7)M praziquantel and observing the percent of tail shedding over 80 min it should be possible to monitor for the presence of praziquantel-resistant worms in snails collected in the field.

Antibody responses to the fucosylated LacdiNAc glycan antigen in Schistosoma mansoni-infected mice and expression of the glycan among schistosomes

Infections of animals with parasitic worms, such as Schistosoma mansoni, induce humoral immune responses to carbohydrate antigens, raising the possibility that such antigens might be useful targets for the development of vaccines and new diagnostic approaches. Here we describe the identification of fucosylated LacdiNAc (LDNF) [GalNAc beta 1-4(Fuc alpha 1-3)GlcNAc-R] as a new carbohydrate antigen in S. mansoni that induces humoral immune responses in infected mice. The presence of antibodies was determined by ELISA using a neoglycoconjugate synthesized to express LDNF sequences. Sera from S. mansoni-infected, but not uninfected, mice contain IgM, IgG, IgA, and IgE antibodies to LDNF. The IgG antibodies are primarily of the IgG1 and IgG3 subclasses, with no detectable levels of the complement-fixing IgG2a and IgG2b isotypes. An IgM monoclonal antibody, designated SMLDNF1, was generated from the spleens of S. mansoni-infected mice, and the antibody exhibits specific recognition of LDNF sequences, but not other fucosylated glycans tested. Immunocytochemical analysis demonstrates that LDNF antigens are localized on the tegumental surface of adult S. mansoni. Western blot analysis indicates that LDNF sequences are expressed on numerous high-molecular-weight glycoproteins from the three major human schistosome species, as well as the bird schistosome Trichobilharzia ocellata. The identification of LDNF antigen on the tegumental glycoproteins of schistosomes and the ability to synthesize LDNF conjugates should aid in the development of glycan-based vaccines and immunodiagnostic tests for schistosomiasis and in determining the role(s) of the glycans in worm development and pathogenesis.

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.

Genotoxic activity of praziquantel

Praziquantel is a synthetic drug with a remarkable activity against parasites, particularly treamatodes and cestodes. Initial genotoxicity tests used a spectrum of endpoints including tests in bacteria, yeasts, mammalian cells and Drosophila and each one gave negative results. Effects on reproductive cells of mice were negative as well. However, host mediated studies in mice and humans were contradictory and a comutagenic effect with several mutagens and carcinogens was found. Later studies, including monitoring in humans and pigs have shown that Praziquantel induces a greater frequency of hyperploid lymphocytes as well as structural chromosomal aberrations, but not in all the individuals treated. In vitro studies have demonstrated that Praziquantel can induce micronuclei in syrian hamster embryonic (SHE) cells and in lymphocytes of some individuals. The same was found about structural chromosomal aberrations. Fetal death and fetal resorption were found when Praziquantel was administered in high doses to pregnant rats between the 6th and 10th day of gestation. Due to its efficiency as a parasiticide, Praziquantel is in use in Latin-American, Asiatic, African and East-European countries where infections by trematodes and cestodes are frequent. However, the extensive use of Praziquantel in multiple reinfections, in non-infected and non-diagnosed individuals for prevention, in higher doses or repeated doses for cysticercosis treatment and in individuals exposed to environmental mutagens, in conjunction with new findings about its metabolism and genotoxic properties, make it necessary to further evaluate the potential of this drug not only to be mutagenic per se, but to contribute in the development of neoplasm.

Schistosome resistance to praziquantel: Fact or artifact?

Praziquantel is the current drug of choice for human schistosomiasis. Recent reports from laboratory and field studies concerning reduced praziquantel efficacy against Schistosoma mansoni have generated some controversy. The prevailing question is whether the emergence of strains of schistosome resistant to praziquantel is a fact, or an artifact resulting from erroneous field or laboratory experimentation. In this article, Padraic Fallon, Liang-feng Tao, Magdi Ismail and James Bennett examine the available evidence for schistosome resistance to praziquantel. Contributory factors to the schistosomicidal activity of praziquantel, which may interfere with evaluation of drug efficacy or resistance, are also considered.

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.

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.