Echinococcus multilocularis metacestodes: immunological and immunocytochemical analysis of the relationships between alkaline phosphatase and the Em2 antigen

Laboratory Diagnosis of Echinococcus spp. in Human Patients and Infected Animals

Among the species composing the genus Echinococcus, four species are of human clinical interest. The most prevalent species are Echinococcus granulosus and Echinococcus multilocularis, followed by Echinococcus vogeli and Echinococcus oligarthrus. The first two species cause cystic echinococcosis (CE) and alveolar echinococcosis (AE) respectively. Both diseases have a complex clinical management, in which laboratory diagnosis could be an adjunctive to the imaging techniques. To date, several approaches have been described for the laboratory diagnosis and followup of CE and AE, including antibody, antigen and cytokine detection. All of these approaches are far from being optimal as adjunctive diagnosis particularly for CE, since they do not reach enough sensitivity and/or specificity. A combination of several methods (e.g., antibody and antigen detection) or of several (recombinant) antigens could improve the performance of the adjunctive laboratory methods, although the complexity of echinococcosis and heterogeneity of clinical cases make necessary a deep understanding of the host-parasite relationships and the parasite phenotype at different developmental stages to reach the best diagnostic tool and to make it accepted in clinical practice. Standardization approaches and a deep understanding of the performance of each of the available antigens in the diagnosis of echinococcosis for the different clinical pictures are also needed. The detection of the parasite in definitive hosts is also reviewed in this chapter. Finally, the different methods for the detection of parasite DNA in different analytes and matrices are also reviewed.

Immunoregulation in larval Echinococcus multilocularis infection

Alveolar echinococcosis (AE) is a clinically very severe zoonotic helminthic disease, characterized by a chronic progressive hepatic damage caused by the continuous proliferation of the larval stage (metacestode) of Echinococcus multilocularis. The proliferative potential of the parasite metacestode tissue is dependent on the nature/function of the periparasitic immune-mediated processes of the host. Immune tolerance and/or down-regulation of immunity are a marked characteristic increasingly observed when disease develops towards its chronic (late) stage of infection. In this context, explorative studies have clearly shown that T regulatory (Treg) cells play an important role in modulating and orchestrating inflammatory/immune reactions in AE, yielding a largely Th2-biased response, and finally allowing thus long-term parasite survival, proliferation and maturation. AE is fatal if not treated appropriately, but the current benzimidazole chemotherapy is far from optimal, and novel options for control are needed. Future research should focus on the elucidation of the crucial immunological events that lead to anergy in AE, and focus on providing a scientific basis for the development of novel and more effective immunotherapeutical options to support cure AE by abrogating anergy, anticipating also that a combination of immuno- and chemotherapy could provide a synergistic therapeutical effect.

An Echinococcus multilocularis Antigen B3 Proteoform That Shows Specific Antibody Responses to Active-Stage Alveolar Echinococcosis

Alveolar echinococcosis (AE), caused by the Echinococcus multilocularis metacestode, represents one of the most frequently fatal zoonoses. Early diagnosis significantly reduces morbidity and mortality associated with AE. Diagnosis of AE largely depends on a combination of imaging and serological tests due to its minimal clinical manifestations. Several antigens derived from the whole worm and protoscolex have been targeted for AE serodiagnosis, while the antigenic properties of E. multilocularis hydatid fluid (EmHF) are unclear. We observed two AE-specific 6- and 8-kDa antigen proteoforms through an immunoproteome array of the EmHF. We identified these proteins as representing an E. multilocularis antigen B3 (EmAgB3) isoform, and the proteins were shown to be encoded by the same gene. We cloned the gene and expressed the recombinant EmAgB3 protein (rEmAgB3) in Escherichia coli. rEmAgB3 exhibited sensitivity of 90.9% (80/88 cases) and specificity of 98.5% (597/606 samples) by immunoblotting. The positive and negative predictive values were 89.9% and 98.6%, respectively. The protein did not show antibody responses to 33 AE sera collected during posttreatment follow-up monitoring. Mouse sera experimentally infected with AE protoscoleces began to demonstrate specific antibody responses to native and recombinant EmAgB3 6 months after infection. At that stage, fully mature metacestode vesicles that harbored the brood capsule, primary cell, and protoscolex were observed within an AE mass(es). The response declined along with worm degeneration. Our results demonstrate that the immune responses to this EmAgB3 isoform were highly correlated with worm viability accompanied with AE progression. rEmAgB3 is a promising biomarker for serological assessment of AE patients.

Strategies of Echinococcus species responses to immune attacks: implications for therapeutic tool development

Echinococcus species have been studied as a model to investigate parasite-host interactions. Echinococcus spp. can actively communicate dynamically with a host to facilitate infection, growth and proliferation partially via secretion of molecules, especially in terms of harmonization of host immune attacks. This review systematically outlines our current knowledge of how the Echinococcus species have evolved to adapt to their host's microenvironment. This understanding of parasite-host interplay has implications in profound appreciation of parasite plasticity and is informative in designing novel and effective tools including vaccines and drugs for the treatment of echinococcosis and other diseases.

Echinococcus multilocularis and its intermediate host: a model of parasite-host interplay

Host-parasite interactions in the E. multilocularis-intermediate host model depend on a subtle balance between cellular immunity, which is responsible for host's resistance towards the metacestode, the larval stage of the parasite, and tolerance induction and maintenance. The pathological features of alveolar echinococcosis. the disease caused by E. multilocularis, are related both to parasitic growth and to host's immune response, leading to fibrosis and necrosis, The disease spectrum is clearly dependent on the genetic background of the host as well as on acquired disturbances of Th1-related immunity. The laminated layer of the metacestode, and especially its carbohydrate components, plays a major role in tolerance induction. Th2-type and anti-inflammatory cytokines, IL-10 and TGF-β, as well as nitric oxide, are involved in the maintenance of tolerance and partial inhibition of cytotoxic mechanisms. Results of studies in the experimental mouse model and in patients suggest that immune modulation with cytokines, such as interferon-α, or with specific antigens could be used in the future to treat patients with alveolar echinococcosis and/or to prevent this very severe parasitic disease.

Echinococcus metacestodes as laboratory models for the screening of drugs against cestodes and trematodes

Among the cestodes, Echinococcus granulosus, Echinococcus multilocularis and Taenia solium represent the most dangerous parasites. Their larval stages cause the diseases cystic echinococcosis (CE), alveolar echinococcosis (AE) and cysticercosis, respectively, which exhibit considerable medical and veterinary health concerns with a profound economic impact. Others caused by other cestodes, such as species of the genera Mesocestoides and Hymenolepis, are relatively rare in humans. In this review, we will focus on E. granulosus and E. multilocularis metacestode laboratory models and will review the use of these models in the search for novel drugs that could be employed for chemotherapeutic treatment of echinococcosis. Clearly, improved therapeutic drugs are needed for the treatment of AE and CE, and this can only be achieved through the development of medium-to-high throughput screening approaches. The most recent achievements in the in vitro culture and genetic manipulation of E. multilocularis cells and metacestodes, and the accessability of the E. multilocularis genome and EST sequence information, have rendered the E. multilocularis model uniquely suited for studies on drug-efficacy and drug target identification. This could lead to the development of novel compounds for the use in chemotherapy against echinococcosis, and possibly against diseases caused by other cestodes, and potentially also trematodes.

Echinococcus multilocularis metacestode metabolites contain a cysteine protease that digests eotaxin, a CC pro-inflammatory chemokine

In many helminthic infections, eotaxin, a CC-chemokine, triggers the mobilization of eosinophils, thus, contributing to an elevated blood and periparasitic eosinophil level. Following an experimental intraperitoneal infection of C57BL6 mice with Echinococcus multilocularis metacestodes, however, we observed the absence of eosinophils in the peritoneal cavity and a low number of such cells in the blood of infected animals. Therefore, we carried out an explorative study to address the question why eosinophilia did not occur especially in the peritoneal cavity of such secondarily AE-infected mice. In an in vitro assay, we showed that metacestode antigens (in vitro generated vesicle fluid and E/S products) were able to proteolytically digest eotaxin. This effect was confirmed with semiquantitative Western blotting, which demonstrated a decreasing intensity of remaining eotaxin signals. Proteolysis of eotaxin was, thus, dose-dependent and proportional to the time of incubation with the metacestode antigens. Using appropriate inhibitors, the respective protease was identified as a cysteine protease, which required the presence of Ca(++) as co-enzyme. A chromatographic fractionation procedure by successive separation of VF molecules using a superpose column and subsequently a MonoQ column mounted on an FPLC system allowed to yield a fraction, referred to us as fraction 6; containing the enriched cysteine protease, this fraction will be used for further molecular studies. Eotaxin inactivation by VF and E/S products may contribute to explain the absence of eosinophils within the peritoneal cavity of AE-secondary infected mice. Absent eosinophils, thus, may be a part of a series of events that maintain a low level of inflammation displayed within the peritoneal cavity of experimentally infected mice.

Echinococcus multilocularis: the parasite-host interplay

Alveolar echinococcosis (AE) is a severe chronic helminthic disease caused by the intrahepatic tumor-like growth of the metacestode of Echinococcus multilocularis. Metacestodes are fluid-filled, asexually proliferating vesicles, which are entirely covered by the laminated layer, an acellular carbohydrate-rich surface structure that protects the parasite from immunological and physiological reactions on part of the host. The E. multilocularis metacestode has acquired specific means of manipulating and using the immunological host response to its own advantage. These include the expression of distinct immunoregulatory parasite molecules that manipulate and interfere in the functional activity of macrophages and T cells. Recent research findings have led to a better understanding of the protein- and glycoprotein composition of the laminated layer and the E/S fraction of the metacestode, including Em2- and Em492-antigens, two metacestode antigen fractions that exhibit immunosuppressive or -modulatory properties. Understanding of the events taking place at the host-parasite interface is the key for development of novel immuno-therapeutical and/or chemotherapeutical tools.

The immunodiagnosis of Echinococcus multilocularis infection

Alveolar echinococcosis (AE) is a severe zoonotic disease caused by the metacestode stage of Echinococcus multilocularis. The infection can have fatal consequences in humans if treatment is not provided, so early diagnosis is fundamental for initiating treatment and reducing morbidity and mortality. In addition, detection of the parasite in the definitive host plays a central role in epidemiological studies and surveillance programmes for control of AE. This review presents an overview of the present situation regarding the immunodiagnosis of E. multilocularis infection. Special attention is given to the description of the native, partially purified and recombinant antigens available currently for immunodiagnostic purposes. Recent advances in the primary serodiagnosis and follow-up of AE patients are highlighted, including the detection of specific cytokine profiles. Progress in the immunodiagnosis of intestinal E. multilocularis infection in definitive hosts, particularly the detection of excretory-secretory and integument products of the worm in faeces (copro-antigens) by ELISA, is also discussed.

Perspective on control options forEchinococcus multiloculariswith particular reference to Japan

Following a brief introduction of recent advances in molecular and immunological technology for detection of persons and animals infected withEchinococcus multilocularisand an overview of the current situation of alveolar echinococcosis (AE) in Japan, perspectives on control options are discussed with reference to different epidemiological situations. AE is considered the most serious parasitic zoonosis in temperate and arctic regions of the northern hemisphere. The number of human cases differs drastically among regions. While high numbers of patients are apparently associated with highE. multilocularisprevalence in domestic dogs, e.g. in parts of Alaska and western China, the number of cases is moderate or low in areas where the parasite is mainly transmitted by wild canid species (e.g. in central Europe or temperate North America). However, the severity of the disease, the absence of curative treatment for most cases, the high cost of long-term chemotherapy and the anxiety caused for the population in highly endemic areas call for the development of preventive strategies even in regions where human AE is rare. Furthermore, in view of (1) drastically increasing numbers and infection rates of foxes involved in transmission ofE. multilocularis, and (2) increasingly close contact between humans and foxes e.g. in Europe and Japan, there is considerable concern that AE incidences may in future increase in these regions. Control options depend on a variety of factors including the species of canid principally responsible for transmission and the socio-economic situation in the region. Where domestic dogs (stray or owned) are the principal hosts forE. multilocularis, control options can include those applicable toE. granulosus, i.e. reduction of the number of stray dogs, registration and regular preventive chemotherapy of owned dogs, and information campaigns for the population promoting low-risk behaviour for man and dogs. WhereE. multilocularisis mainly transmitted by wild canids, the situation is far more difficult with preventive strategies still being in trial stage. Integrated control measures could include prevention information campaigns, restricting access of pet animals (dogs and cats) to rodents, chemotherapy of foxes on local or regional scales, and strategies to minimize contacts between people and foxes.

Isolation and characterization of a secretory component of Echinococcus multilocularis metacestodes potentially involved in modulating the host-parasite interface

Echinococcus multilocularis metacestodes are fluid-filled, vesicle-like organisms, which are characterized by continuous asexual proliferation via external budding of daughter vesicles, predominantly in the livers of infected individuals. Tumor-like growth eventually leads to the disease alveolar echinococcosis (AE). We employed the monoclonal antibody (MAb) E492/G1, previously shown to be directed against a carbohydrate-rich, immunomodulatory fraction of Echinococcus granulosus, to characterize potentially related components in E. multilocularis. Immunofluorescence studies demonstrated that MAb E492/G1-reactive epitopes were found predominantly on the laminated layer and in the periphery of developing brood capsules. The respective molecules were continuously released into the exterior medium and were also found in the parasite vesicle fluid. The MAb E492/G1-reactive fraction in E. multilocularis, named Em492 antigen, was isolated by immunoaffinity chromatography. Em492 antigen had a protein/carbohydrate ratio of 0.25, reacted with a series of lectins, and is related to the laminated layer-associated Em2(G11) antigen. The epitope recognized by MAb E492/G1 was sensitive to sodium periodate but was not affected by protease treatment. Anti-Em492 immunoglobulin G1 (IgG1) and IgG2 and, at lower levels, IgG3 were found in sera of mice suffering from experimentally induced secondary, but not primary, AE. However, with regard to cellular immunity, a suppressive effect on concanavalin A- or crude parasite extract-induced splenocyte proliferation in these mice was observed upon addition of Em492 antigen, but trypan blue exclusion tests and transmission electron microscopy failed to reveal any cytotoxic effect in Em492 antigen-treated spleen cells. This indicated that Em492 antigen could be modulating the periparasitic cellular environment during E. multilocularis infection through as yet unidentified mechanisms and could be one of the factors contributing to immunosuppressive events that occur at the host-parasite interface.

In vitro culture of Echinococcus multilocularis and Echinococcus vogeli metacestodes: studies on the host-parasite interface

The larval stage of Echinococcus multilocularis causes alveolar echinococcosis (AE) in various mammalians including humans, while Echinococcus vogeli larvae cause a related disease which is also occasionally found in man. Traditionally, Echinococcus metacestodes have been maintained in the laboratory by serial transplantation passages into susceptible animals such as mice or gerbils, enabling the parasite to proliferate asexually. These experimental animal models have been used extensively to investigate host-parasite interactions and to study immunological events occurring at the host-parasite interface. However, with the use of laboratory animals it has always been difficult to investigate in more detail those factors modulating metacestode differentiation, and investigations on gene expression and respective regulation have been hampered by the complexity of the host-parasite interplay. There has been a need for an in vitro culture model which would enable researchers to dissect specific parasite compartments involved in the host-parasite relationship in more detail. This review summarises the studies leading to the development and application of a suitable in vitro culture model for the maintenance and proliferation of E. multilocularis and E. vogeli metacestodes, including the formation of protoscoleces, in a chemically defined medium devoid of host influence. These culture models have been used to study the basic parameters of metacestode in vitro proliferation and differentiation, and for the dissection of the ultrastructure and composition of the acellular laminated layer, the structure of which is predominantly involved in the physical interaction between the parasite and host immune and non-immune cells and tissues. For E. multilocularis, in vitro cultured parasites have been more extensively employed to study the localisation of several antigens, and to generate defined antigens for immunological studies. Although in vitro culture will not completely eliminate the need of animal experimentation, a wider application of this technique could significantly reduce the use of animals, and thus the costs and time required for respective experimental investigations.

Serologic and molecular diagnosis of zoonotic larval cestode infections

Neurocysticercosis, cystic echinococcosis and alveolar echinococcosis are the three major zoonotic larval cestodiases worldwide and threatening human life. Early therapeutic treatment based on early differential diagnosis at the early stage of infection and epidemiological surveillance with the expectation for control and prevention are the keys for improvement of quality of human life. Recent advances in (1). differential serodiagnosis of these three diseases, (2). molecular identification of human taeniid species and (3). polymorphism of mitochodrial DNA highly informative for future molecular epidemiology are reviewed in this article.

Culture of Echinococcus multilocularis metacestodes: an alternative to animal use

This article reviews the use of an in vitro culture model for the maintenance and proliferation of Echinococcus multilocularis metacestodes and the formation of protoscoleces. This model has been used to identify and characterize parasite molecules involved in host-parasite interactions, and is a suitable tool to perform in vitro drug-screening assays. The development of a simple and easy-to-handle assay to determine the effects of drugs on parasite viability, without the need for time-consuming animal experimentation, has opened the way for larger-scale in vitro drug screening.

A major Echinococcus multilocularis antigen is a mucin-type glycoprotein

The metacestode of Echinococcus multilocularis is surrounded by a carbohydrate-rich laminated layer, which plays a key role in the establishment of the infection in the mammalian host. A major component of the laminated layer is an antigen referred to as Em2(G11). This highly species-specific antigen has been used for serodiagnoses of alveolar echinococcosis and is suggested to contain carbohydrates as major constituents. The results of this work have shown that immunoaffinity-purified Em2(G11) subjected to size-exclusion chromatography eluted mainly in the void volume, indicating a high molecular weight structure of this antigen. Amino acid analysis revealed a large proportion of threonine and proline residues in Em2(G11). The carbohydrate moiety of the antigen was found to be composed of galactose, N-acetylgalactosamine, and N-acetylglucosamine with a ratio of 2.4:1.0:0.5 as determined by gas-chromatography/mass spectrometry. An isotope tag was introduced to the beta-eliminated glycans, and an integrated mass spectrometric O-glycan profiling and sequencing approach was employed to obtain detailed sequence and linkage information of the unseparated glycoform pool. Novel glycoforms containing mucin-type core Gal1-3GalNAc and branched core structures attached to both serine and threonine residues are described. The data presented reveal that the Em2(G11) antigen is a mucin-type glycosylated protein.

Echinococcus multilocularis alkaline phosphatase as a marker for metacestode damage induced by in vitro drug treatment with albendazole sulfoxide and albendazole sulfone

Alveolar echinococcosis (AE) is caused by the metacestode stage of the fox tapeworm Echinococcus multilocularis. The disease affects the human liver and occasionally other organs and is fatal if treatment is unsuccessful. The present chemotherapy of AE is based on the administration of benzimidazole carbamate derivatives, such as mebendazole and albendazole. Albendazole treatment has been found to be ineffective in some cases, parasitostatic rather than parasiticidal, and the recurrence rate is rather high. Therefore, chemotherapy usually involves the lifelong uptake of massive doses of albendazole and new treatment options are urgently needed. In order to avoid costly and time-consuming animal experimentation, a first step in searching for novel parasiticidal compounds could be the in vitro drug screening of novel compounds by employing metacestode cultivation. However, presently used techniques (e.g., transmission electron microscopy) for determination of parasite viability involve costly equipment and time-consuming preparation of rather large amounts of parasite material. We therefore searched for a parasite marker which can be easily traced and the presence or absence of which is indicative of parasite viability. In this study we show that the increase of E. multilocularis alkaline phosphatase activity in culture supernatants during in vitro drug treatment with albendazole derivatives correlates with the progressive degeneration and destruction of the metacestode tissue. The inexpensive and rapid assay presented here will serve as an ideal tool for performing first-round in vitro tests on the efficacy of a large number of antiparasitic compounds.

Molecular tools for the diagnosis of cystic and alveolar echinococcosis

In the past years, the diagnostic tools applied to identify alveolar (AE) and cystic echinococcosis (CE) in human patients have not only increased in number but also substantially improved in quality. The identification and characterization of species-specific parasite proteins/antigens allowed to generate subsequently recombinant or synthetic polypeptide antigens, as well as corresponding monoclonal antibodies. Some of these new tools have already demonstrated operating characteristics superior to conventional tests used for the immunodiagnosis of CE and AE, and thus may be suggested for routine laboratory application. Powerful molecular techniques, such as the polymerase chain reaction (PCR), have been developed and adapted to advance laboratory diagnosis of AE and CE. Detecting minute amounts of parasite DNA and mRNA, not only to identify but also to characterize the biological status of parasite material, thus becomes a complementary method to synergize immunodiagnostic techniques. This review focuses on recent developments of molecular tools, discussing their potential use as a primary or a supporting diagnostic element. We also outline some future developments to be undertaken in the field of molecular diagnosis, linked to clinical and laboratory problems.

Efficacies of albendazole sulfoxide and albendazole sulfone against In vitro-cultivated Echinococcus multilocularis metacestodes

The metacestode stage of Echinococcus multilocularis is the causative agent of alveolar echinococcosis (AE), a parasitic disease affecting the liver, with occasional metastasis into other organs. Benzimidazole carbamate derivatives such as mebendazole and albendazole are currently used for chemotherapeutic treatment of AE. Albendazole is poorly resorbed and is metabolically converted to its main metabolite albendazole sulfoxide, which is believed to be the active component, and further to albendazole sulfone. Chemotherapy with albendazole has been shown to have a parasitostatic rather than a parasitocidal effect; it is not effective in all cases, and the recurrence rate is rather high once chemotherapy is stopped. Thus, development of new means of chemotherapy of AE is needed. This could include modifications of benzimidazoles and elucidiation of the respective biological pathways. In this study we performed in vitro drug treatment of E. multilocularis metacestodes with albendazole sulfoxide and albendazole sulfone. High-performance liquid chromatography analysis of vesicle fluids showed that the drugs were taken up rapidly by the parasite. Transmission electron microscopic investigation of parasite tissues and nuclear magnetic resonance spectroscopy of vesicle fluids demonstrated that albendazole sulfoxide and albendazole sulfone had similar effects with respect to parasite ultrastructure and changes in metabolites in vesicle fluids. This study shows that the in vitro cultivation model presented here provides an ideal first-round test system for screening of antiparasite drugs.