A library of 426 FDA-approved drugs was screened for in vitro activity against E. multilocularis metacestodes employing the phosphoglucose isomerase (PGI) assay. Initial screening at 20 µM revealed that 7 drugs induced considerable metacestode damage, and further dose-response studies revealed that bortezomib (BTZ), a proteasome inhibitor developed for the chemotherapy of myeloma, displayed high anti-metacestodal activity with an EC50 of 0.6 µM. BTZ treatment of E. multilocularis metacestodes led to an accumulation of ubiquinated proteins and unequivocally parasite death. In-gel zymography assays using E. multilocularis extracts demonstrated BTZ-mediated inhibition of protease activity in a band of approximately 23 kDa, the same size at which the proteasome subunit beta 5 of E. multilocularis could be detected by Western blot. Balb/c mice experimentally infected with E. multilocularis metacestodes were used to assess BTZ treatment, starting at 6 weeks post-infection by intraperitoneal injection of BTZ. This treatment led to reduced parasite weight, but to a degree that was not statistically significant, and it induced adverse effects such as diarrhea and neurological symptoms. In conclusion, the proteasome was identified as a drug target in E. multilocularis metacestodes that can be efficiently inhibited by BTZ in vitro. However, translation of these findings into in vivo efficacy requires further adjustments of treatment regimens using BTZ, or possibly other proteasome inhibitors.
Tapeworms (cestodes) are a class of important human pathogens, causing very severe diseases in man such as alveolar echinococcosis (Echinococcus multilocularis), cystic echinococcosis (E. granulosus) and neurocysticercosis (Taenia solium). Current treatments are mainly based on benzimidazoles that show some limited activity against cestode larvae, but often do not kill them. These compounds have to be taken for extended periods of time, and can cause adverse side-effects. Cestode infections cause neglected diseases and the pharmaceutical industry is generally not interested in investments for developing novel bioactive compounds. In this study we focus on a panel of FDA-approved drugs and assessed them in E. multilocularis, which causes the most deadly of all helminth infections. One compound, the anti-cancer drug bortezomib, exhibits considerable in vitro activity against E. multilocularis metacestodes, and we provide evidence that it acts on the proteasome. In experimentally infected mice bortezomib activity was lower than the currently used albendazole and induced adverse effects. Bortezomib is therefore not a useful drug for treatment of Echinococcus larvae, but our results demonstrate that in future studies the cestode proteasome should gain more attention as a drug target.
The metacestode (larval) stage of the tapeworm Echinococcus multilocularis causes alveolar echinococcosis (AE), a very severe and in many cases incurable disease. To date, benzimidazoles such as albendazole and mebendazole are the only approved chemotherapeutical treatment options. Benzimidazoles inhibit metacestode proliferation, but do not act parasiticidal. Thus, benzimidazoles have to be taken a lifelong, can cause adverse side effects such as hepatotoxicity, and are ineffective in some patients. We here describe a newly developed screening cascade for the evaluation of the in vitro efficacy of new compounds that includes assessment of parasiticidal activity. The Malaria Box from Medicines for Malaria Venture (MMV), comprised of 400 commercially available chemicals that show in vitro activity against Plasmodium falciparum, was repurposed. Primary screening was carried out at 10 μM by employing the previously described PGI assay, and resulted in the identification of 24 compounds that caused physical damage in metacestodes. Seven out of these 24 drugs were also active at 1 μM. Dose-response assays revealed that only 2 compounds, namely MMV665807 and MMV665794, exhibited an EC50 value below 5 μM. Assessments using human foreskin fibroblasts and Reuber rat hepatoma cells showed that the salicylanilide MMV665807 was less toxic for these two mammalian cell lines than for metacestodes. The parasiticidal activity of MMV665807 was then confirmed using isolated germinal layer cell cultures as well as metacestode vesicles by employing viability assays, and its effect on metacestodes was morphologically evaluated by electron microscopy. However, both oral and intraperitoneal application of MMV665807 to mice experimentally infected with E. multilocularis metacestodes did not result in any reduction of the parasite load.
The fox tapeworm Echinococcus multilocularis causes a deadly disease in humans that is characterized by cancer-like parasite growth in the liver of patients. Hence E. multilocularis is ideally removed by radical resection. However, as this is not always possible, patients are treated by chemotherapy to stop further parasite growth. To date, the drugs in use cannot kill the parasite E. multilocularis and they also induce side-effects, therefore new options for treatment are needed. We here screened a library of 400 compounds with proven activity against Plasmodium falciparum, the cause of malaria, for their effects against E. multilocularis in vitro. We developed and refined an in vitro screening cascade and developed an assay that can identify compounds with parasiticidal effects against E. multilocularis cells. We here show that MMV665807 acts parasiticidal as demonstrated by in vitro viability tests and by electron microscopy. In the mouse infection model the drug was not active, but work will focus on the evaluation of derivatives with improved bioavailability and pharmacokinetic properties to achieve parasiticidal activity not only in vitro, but also in vivo.
When humans serve as inadvertent intermediate hosts for Echinococcus multilocularis, disease (alveolar echinococcosis [AE]) may result from the expanding parasite metacestode in visceral organs, mostly in the liver. Benzimidazole carbamate derivatives such as mebendazole and albendazole are used for chemotherapeutic treatment of AE. However, these treatments are, in most cases, parasitistatic rather than parasiticidal. As treatment is discontinued, a recurrence of parasite growth has been observed in many AE patients with nonradical resections. The only curative treatment for AE is radical surgical resection of the parasite tissue and support by chemotherapy. As there is a need for new treatment options for AE, the in vitro efficacy of nitazoxanide (NTZ), a broad-spectrum drug used against intestinal parasites and bacteria, was investigated. We showed that in vitro treatment of E. multilocularis metacestodes with NTZ induced high levels of alkaline phosphatase activity in the medium. Concurrently, distinct morphological and ultrastructural alterations were detected. Most significantly, two distinct types of alterations were observed as soon as after 3 h of NTZ treatment. At first, the drug induced a peripheral output of membranous vesicles from the tegumental membrane into the laminated layer. Simultaneously, germinal layer-associated undifferentiated cells produced large vacuoles filled with lipid-like and often electron-dense membranous segments. Other alterations were observed at later time points, including vacuolization of the germinal layer, accumulation of lipid droplets, and lastly, loss of microtriches and separation of the laminated and germinal layers. The pattern of damage induced by NTZ was different from the alterations earlier observed in albendazole sulfoxide-treated vesicles. The nonviability of NTZ-treated metacestodes was confirmed through bioassay, i.e., inoculation of treated and untreated parasites into mice. These experiments demonstrate the in vitro parasiticidal effect of NTZ on E. multilocularis metacestodes.
Alveolar echinococcosis, caused by Echinococcus multilocularis larvae, is a chronic disease associated with considerable modulation of the host immune response. Dendritic cells (DC) are key effectors in shaping the immune response and among the first cells encountered by the parasite during an infection. Although it is assumed that E.multilocularis, by excretory/secretory (E/S)-products, specifically affects DC to deviate immune responses, little information is available on the molecular nature of respective E/S-products and their mode of action.
We established cultivation systems for exposing DC to live material from early (oncosphere), chronic (metacestode) and late (protoscolex) infectious stages. When co-incubated with Echinococcus primary cells, representing the invading oncosphere, or metacestode vesicles, a significant proportion of DC underwent apoptosis and the surviving DC failed to mature. In contrast, DC exposed to protoscoleces upregulated maturation markers and did not undergo apoptosis. After pre-incubation with primary cells and metacestode vesicles, DC showed a strongly impaired ability to be activated by the TLR ligand LPS, which was not observed in DC pre-treated with protoscolex E/S-products. While none of the larvae induced the secretion of pro-inflammatory IL-12p70, the production of immunosuppressive IL-10 was elevated in response to primary cell E/S-products. Finally, upon incubation with DC and naïve T-cells, E/S-products from metacestode vesicles led to a significant expansion of Foxp3+ T cells in vitro.
This is the first report on the induction of apoptosis in DC by cestode E/S-products. Our data indicate that the early infective stage of E. multilocularis is a strong inducer of tolerance in DC, which is most probably important for generating an immunosuppressive environment at an infection phase in which the parasite is highly vulnerable to host attacks. The induction of CD4+CD25+Foxp3+ T cells through metacestode E/S-products suggests that these cells fulfill an important role for parasite persistence during chronic echinococcosis.
Parasitic helminths are inducers of chronic diseases and have evolved mechanisms to suppress the host immune response. Mostly from studies on roundworms, a picture is currently emerging that helminths secrete factors (E/S-products) that directly act on sentinels of the immune system, dendritic cells, in order to achieve an expansion of immunosuppressive, regulatory T cells (T-reg). Parasitic helminths are currently also intensely studied as therapeutic agents against autoimmune diseases and allergies, which is directly linked to their immunosuppressive activities. The immunomodulatory products of parasitic helminths are therefore of high interest for understanding immunopathology during infections and for the treatment of allergies. The present work was conducted on larvae of the tapeworm E. multilocularis, which grow like a tumor into surrounding host tissue and thus cause the lethal disease alveolar echinococcosis. The authors found that E/S-products from early infective larvae are strong inducers of tolerogenic DC in vitro and show that E/S-products of larvae of the chronic stage lead to an in vitro expansion of Foxp3+ T cells, suggesting that both the expansion of these T cells and poorly responsive DC are important for the establishment and persistence of E. multilocularis larvae within the host.
Alveolar echinococcosis (AE) is a disease predominantly affecting the liver, with metacestodes (larvae) of the tapeworm Echinococcus multilocularis proliferating and exhibiting tumor-like infiltrative growth. For many years, chemotherapeutical treatment against alveolar echinococcosis has relied on the benzimidazoles albendazole and mebendazole, which require long treatment durations and exhibit parasitostatic rather than parasiticidal efficacy. Although benzimidazoles have been and still are beneficial for the patients, there is clearly a demand for alternative and more efficient treatment options. Aromatic dications, more precisely a small panel of di-N-aryl-diguanidino compounds, were screened for efficacy against E. multilocularis metacestodes in vitro. Only those with a thiophene core group were active against metacestodes, while furans were not. The most active compound, DB1127, was further investigated in terms of in vivo efficacy in mice experimentally infected with E. multilocularis metacestodes. This diguanidino compound was effective against AE when administered intraperitoneally but not when applied orally. Thus, thiophene-diguanidino derivatives with improved bioavailability when administered orally could lead to treatment options against AE.
Echinococcosis is an infectious disease of humans caused by the larval (metacestode) stage of the cestode species Echinococcus granulosus (cystic echinococcosis or hydatid disease) or Echinococcus multilocularis (alveolar echinococcosis or alveolar hydatid disease). Clinical manifestations depend primarily on localization and size of hepatic lesions and may include hepatomegaly, obstructive jaundice, or cholangitis. Prognostically, alveolar echinococcosis is considered similar to liver malignancies, including a lethality rate of 90% for untreated cases. Diagnosis is based on imaging techniques coupled with immunodiagnostic procedures. Antibody detection tests for E. multilocularis have markedly improved with the use of affinity-purified Em2 antigen and recombinant antigen II/3-10 in enzyme immunoassays. Antigens of corresponding quality for E. granulosus are still unavailable. The detection of circulating antigens and immune complexes in the sera of patients with cystic echinococcosis, the demonstration of in vitro lymphocyte proliferation in response to stimulation with Echinococcus antigens, and the discrimination of serum immunoglobulin isotype activity to various Echinococcus antigens in both cystic and alveolar echinococcosis have been suggested for diagnostic purposes as well as for monitoring patients after treatment. New diagnostic molecular tools include DNA probes for Southern hybridization tests and polymerase chain reaction for the amplification of E. multilocularis and E. granulosus species-specific DNA fragments.
Cystic echinococcosis is a worldwide distributed helminth zoonosis caused by the larval stage of Echinococcus granulosus. Human secondary cystic echinococcosis is caused by dissemination of protoscoleces after accidental rupture of fertile cysts and is due to protoscoleces ability to develop into new metacestodes. In the experimental model of secondary cystic echinococcosis mice react against protoscoleces producing inefficient immune responses, allowing parasites to develop into cysts. Although the chronic phase of infection has been analyzed in depth, early immune responses at the site of infection establishment, e.g., peritoneal cavity, have not been well studied. Because during early stages of infection parasites are thought to be more susceptible to immune attack, this work focused on the study of cellular and molecular events triggered early in the peritoneal cavity of infected mice.
Data obtained showed disparate behaviors among subpopulations within the peritoneal lymphoid compartment. Regarding B cells, there is an active molecular process of plasma cell differentiation accompanied by significant local production of specific IgM and IgG2b antibodies. In addition, peritoneal NK cells showed a rapid increase with a significant percentage of activated cells. Peritoneal T cells showed a substantial increase, with predominance in CD4+ T lymphocytes. There was also a local increase in Treg cells. Finally, cytokine response showed local biphasic kinetics: an early predominant induction of Th1-type cytokines (IFN-γ, IL-2 and IL-15), followed by a shift toward a Th2-type profile (IL-4, IL-5, IL-6, IL-10 and IL-13).
Results reported here open new ways to investigate the involvement of immune effectors players in E. granulosus establishment, and also in the sequential promotion of Th1- toward Th2-type responses in experimental secondary cystic echinococcosis. These data would be relevant for designing rational therapies based on stimulation of effective responses and blockade of evasion mechanisms.
Cystic echinococcosis is a zoonotic disease caused by the larval stage of the cestode Echinococcus granulosus and shows a cosmopolitan distribution with a worldwide prevalence of roughly 6 million infected people. Human cystic echinococcosis can develop in two types of infection. Primary infection occurs by ingestion of oncospheres, while secondary infection is caused by dissemination of protoscoleces after accidental rupture of fertile cysts. Murine experimental secondary infection in Balb/c mice is the current model to study E. granulosus-host interaction. Secondary infection can be divided into two stages: an early stage in which protoscoleces develop into hydatid cysts (infection establishment) and a later stage in which already differentiated cysts grow and eventually become fertile cysts (chronic infection). During infection establishment parasites are more susceptible to immune attack, thus our study focused on the immunological phenomena triggered early in the peritoneal cavity of experimentally infected mice. Our results suggest that early and local Th2-type responses are permissive for infection establishment.
Cystic echinococcosis (CE), a zoonotic parasitic infection caused by the metacestode (larvae) stage of dog tapeworm Echinococcus granulosus and recognized as a major economic and public health concern in the world. This study aimed to investigate the in vitro scolicidal effect of methanolic extract of Berberis vulgaris L. roots and its main compound, berberine against protoscoleces of hydatid cysts.
For this purpose, protoscoleces were aseptically aspirated from sheep livers having hydatid cysts. Various concentrations of the methanolic extract (0.25-2 mg/ml) and berberine (0.062- 0.5 mg/ml) were used for 5 to 30 min. Viability of protoscoleces was confirmed by eosin exclusive test.
In the present study, all of the various concentrations of the B. vulgaris methanolic extract (0.25, 0.5, 1 and 2 mg/ml) and berberine (0.062, 0.125, 0.25 and 0.5 mg/ml) revealed significant (P<0.05) scolicidal effects against protoscoleces of E. granulosus in a dose-dependent manner. Both berberine and methanolic extract exhibited 100% inhibition against protoscoleces of E. granulosus at the concentration of 2.0 and 0.5 mg/ml after 10 min incubation, respectively.
According to the results, both B. vulgaris methanolic extract and berberine alone demonstrated high scolicidal activities against protoscoleces of hydatid cysts in low concentration and short exposure time on in vitro model. However, in vivo efficacy of B. vulgaris and berberine also requires to be evaluated using an animal model with hydatid infection.
Hydatid cyst; European barberry; Scolicidal; Echinococcus granulosus
Epidemiological studies have demonstrated that most humans infected with Echinococcus spp. exhibit resistance to disease. When infection leads to disease, the parasite is partially controlled by host immunity: in case of immunocompetence, the normal alveolar echinococcosis (AE) or cystic echinococcosis (CE) situation, the metacestode grows slowly, and first clinical signs appear years after infection; in case of impaired immunity (AIDS; other immunodeficiencies), uncontrolled proliferation of the metacestode leads to rapidly progressing disease. Assessing Echinococcus multilocularis viability in vivo following therapeutic interventions in AE patients may be of tremendous benefit when compared with the invasive procedures used to perform biopsies. Current options are F18-fluorodeoxyglucose-positron emission tomography (FDG-PET), which visualizes periparasitic inflammation due to the metabolic activity of the metacestode, and measurement of antibodies against recEm18, a viability-associated protein, that rapidly regresses upon metacestode inactivation. For Echinococcus granulosus, similar prognosis-associated follow-up parameters are still lacking but a few candidates may be listed. Other possible markers include functional and diffusion-weighted Magnetic Resonance Imaging (MRI), and measurement of products from the parasite (circulating antigens or DNA), and from the host (inflammation markers, cytokines, or chemokines). Even though some of them have been promising in pilot studies, none has been properly validated in an appropriate number of patients until now to be recommended for further use in clinical settings. There is therefore still a need to develop reliable tools for improved viability assessment to provide the sufficient information needed to reliably withdraw anti-parasite benzimidazole chemotherapy, and a basis for the development of new alternative therapeutic tools.
Echinococcus multilocularis; Alveolar echinococcosis; Surgery; Medication; Follow-up; Em18; Em2; FDG-PET
Alveolar echinococcosis (AE) is a life-threatening disease caused by larvae of the fox-tapeworm Echinococcus multilocularis. Crucial to AE pathology is continuous infiltrative growth of the parasite's metacestode stage, which is driven by a population of somatic stem cells, called germinative cells. Current anti-AE chemotherapy using benzimidazoles is ineffective in eliminating the germinative cell population, thus leading to remission of parasite growth upon therapy discontinuation.
We herein describe the characterization of EmPlk1, encoded by the gene emplk1, which displays significant homologies to members of the Plk1 sub-family of Polo-like kinases that regulate mitosis in eukaryotic cells. We demonstrate germinative cell-specific expression of emplk1 by RT-PCR, transcriptomics, and in situ hybridization. We also show that EmPlk1 can induce germinal vesicle breakdown when heterologously expressed in Xenopus oocytes, indicating that it is an active kinase. This activity was significantly suppressed in presence of BI 2536, a Plk1 inhibitor that has been tested in clinical trials against cancer. Addition of BI 2536 at concentrations as low as 20 nM significantly blocked the formation of metacestode vesicles from cultivated Echinococcus germinative cells. Furthermore, low concentrations of BI 2536 eliminated the germinative cell population from mature metacestode vesicles in vitro, yielding parasite tissue that was no longer capable of proliferation.
We conclude that BI 2536 effectively inactivates E. multilocularis germinative cells in parasite larvae in vitro by direct inhibition of EmPlk1, thus inducing mitotic arrest and germinative cell killing. Since germinative cells are decisive for parasite proliferation and metastasis formation within the host, BI 2536 and related compounds are very promising compounds to complement benzimidazoles in AE chemotherapy.
The lethal disease AE is characterized by continuous and infiltrative growth of the metacestode larva of the tapeworm E. multilocularis within host organs. This cancer-like progression is exclusively driven by a population of parasite stem cells (germinative cells) that have to be eliminated for an effective cure of the disease. Current treatment options, using benzimidazoles, are parasitostatic only, and thus obviously not effective in germinative cell killing. We herein describe a novel, druggable parasite enzyme, EmPlk1, that specifically regulates germinative cell proliferation. We show that a compound, BI 2536, originally designed to inhibit the human ortholog of EmPlk1, can also inhibit the parasite protein at low doses. Furthermore, low doses of BI 2536 eliminated germinative cells from Echinococcus larvae in vitro and prevented parasite growth and development. We propose that BI 2536 and related compounds are promising drugs to complement current benzimidazole treatment for achieving parasite killing.
Infections of Echinococcus granulosus sensu stricto (s.s), E. multilocularis and E. shiquicus are commonly found co-endemic on the Qinghai-Tibet plateau, China, and an efficient tool is needed to facilitate the detection of infected hosts and for species identification.
A single-tube multiplex PCR assay was established to differentiate the Echinococcus species responsible for infections in intermediate and definitive hosts. Primers specific for E. granulosus, E. multilocularis and E. shiquicus were designed based on sequences of the mitochondrial NADH dehydrogenase subunit 1 (nad1), NADH dehydrogenase subunit 5 (nad5) and cytochrome c oxidase subunit 1 (cox1) genes, respectively. This multiplex PCR accurately detected Echinococcus DNA without generating nonspecific reaction products. PCR products were of the expected sizes of 219 (nad1), 584 (nad5) and 471 (cox1) bp. Furthermore, the multiplex PCR enabled diagnosis of multiple infections using DNA of protoscoleces and copro-DNA extracted from fecal samples of canine hosts. Specificity of the multiplex PCR was 100% when evaluated using DNA isolated from other cestodes. Sensitivity thresholds were determined for DNA from protoscoleces and from worm eggs, and were calculated as 20 pg of DNA for E. granulosus and E. shiquicus, 10 pg of DNA for E. multilocularis, 2 eggs for E. granulosus, and 1 egg for E. multilocularis. Positive results with copro-DNA could be obtained at day 17 and day 26 after experimental infection of dogs with larval E. multilocularis and E. granulosus, respectively.
The multiplex PCR developed in this study is an efficient tool for discriminating E. granulosus, E. multilocularis and E. shiquicus from each other and from other taeniid cestodes. It can be used for the detection of canids infected with E. granulosus s.s. and E. multilocularis using feces collected from these definitive hosts. It can also be used for the identification of the Echinococcus metacestode larva in intermediate hosts, a stage that often cannot be identified to species on visual inspection.
The canid adapted intestinal tapeworms, Echinococcus granulosus, E. multilocularis and E. shuiqucus are well known to be endemic in Northwestern China. The first two species can cause fatal disease in humans. Although E. shiquicus has not been reported to infect humans, all three species can be transmitted by dogs. The very close relationship between dogs and humans can readily lead to human infection. To aid the surveillance and management of echinococcosis, effective diagnostic approaches are urgently needed. We developed a single tube multiplex PCR assay for the accurate identification and discrimination of the three Echinococcus species for use in both clinical diagnosis and epidemiological studies.
Cystic echinococcosis is a zoonotic infection caused by the larval stage of the cestode Echinococcus granulosus. Chemotherapy currently employs benzimidazoles; however, 40% of cases do not respond favorably. With regard to these difficulties, novel therapeutic tools are needed to optimize treatment in humans. The aim of this work was to explore the in vitro and in vivo effects of tamoxifen (TAM) against E. granulosus. In addition, possible mechanisms for the susceptibility of TAM are discussed in relation to calcium homeostasis, P-glycoprotein inhibition, and antagonist effects on a putative steroid receptor. After 24 h of treatment, TAM, at a low micromolar concentration range (10 to 50 μM), inhibited the survival of E. granulosus protoscoleces and metacestodes. Moreover, we demonstrated the chemotherapeutic and chemopreventive pharmacological effects of the drug. At a dose rate of 20 mg/kg of body weight, TAM induced protection against the infection in mice. In the clinical efficacy studies, a reduction in cyst weight was observed after the administration of 20 mg/kg in mice with cysts developed during 3 or 6 months, compared to that of those collected from control mice. Since the collateral effects of high TAM doses have been largely documented in clinical trials, the use of low doses of this drug as a short-term therapy may be a novel alternative approach for human cystic echinococcosis treatment.
The search for novel therapeutic options to cure alveolar echinococcosis (AE), due to the metacestode of Echinococcus multilocularis, is ongoing, and these developments could also have a profound impact on the treatment of cystic echinococcosis (CE), caused by the closely related Echinococcus granulosus s.l. Several options are being explored. A viable strategy for the identification of novel chemotherapeutically valuable compounds includes whole-organism drug screening, employing large-scale in vitro metacestode cultures and, upon identification of promising compounds, verification of drug efficacy in small laboratory animals. Clearly, the current focus is targeted towards broad-spectrum anti-parasitic or anti-cancer drugs and compound classes that are already marketed, or that are in development for other applications. The availability of comprehensive Echinococcus genome information and gene expression data, as well as significant progress on the molecular level, has now opened the door for a more targeted drug discovery approach, which allows exploitation of defined pathways and enzymes that are essential for the parasite. In addition, current in vitro and in vivo models that are used to assess drug efficacy should be optimized and complemented by methods that give more detailed information on the host-parasite interactions that occur during drug treatments. The key to success is to identify, target and exploit those parasite molecules that orchestrate activities essential to parasite survival.
Alveolar echinococcosis (AE); Echinococcus multilocularis chemotherapy; In vitro culture; Drugs; Host-parasite interaction
Echinococcus granulosus is characterized by high intra-specific variability (genotypes G1–G10) and according to the new molecular phylogeny of the genus Echinococcus, the E. granulosus complex has been divided into E. granulosus sensu stricto (G1–G3), E. equinus (G4), E. ortleppi (G5), and E. canadensis (G6–G10). The molecular characterization of E. granulosus isolates is fundamental to understand the spatio-temporal epidemiology of this complex in many endemic areas with the simultaneous occurrence of different Echinococcus species and genotypes. To simplify the genotyping of the E. granulosus complex we developed a single-tube multiplex PCR (mPCR) allowing three levels of discrimination: (i) Echinococcus genus, (ii) E. granulosus complex in common, and (iii) the specific genotype within the E. granulosus complex. The methodology was established with known DNA samples of the different strains/genotypes, confirmed on 42 already genotyped samples (Spain: 22 and Bulgaria: 20) and then successfully applied on 153 unknown samples (Tunisia: 114, Algeria: 26 and Argentina: 13). The sensitivity threshold of the mPCR was found to be 5 ng Echinoccoccus DNA in a mixture of up to 1 µg of foreign DNA and the specificity was 100% when template DNA from closely related members of the genus Taenia was used. Additionally to DNA samples, the mPCR can be carried out directly on boiled hydatid fluid or on alkaline-lysed frozen or fixed protoscoleces, thus avoiding classical DNA extractions. However, when using Echinococcus eggs obtained from fecal samples of infected dogs, the sensitivity of the mPCR was low (<40%). Thus, except for copro analysis, the mPCR described here has a high potential for a worldwide application in large-scale molecular epidemiological studies on the Echinococcus genus.
The dog tapeworm Echinococcus granulosus (E. granulosus) is a cosmopolitan parasite. The adult worms reside in the small intestine of their definitive hosts (dogs). Infective eggs are shed with the feces into the environment and are orally ingested by intermediate hosts where they develop into the metacestode (larval) stage, causing cystic echinococcosis (CE) in humans and livestock. Ten intraspecific genotypes of E. granulosus (G1 to G10) have been reported from different intermediate host species. Based on the recently established molecular phylogeny, E. granulosus is now considered a complex consisting of four species: E. granulosus sensu stricto (G1/G2/G3), E. equinus (G4), E. ortleppi (G5) and E. canadensis (G6–G10). Simple and highly discriminative molecular epidemiological approaches are needed to explore dynamics, life cycle patterns, and the pathogenicity of the members of this complex. We here introduce a one-step multiplex PCR (mPCR) protocol for the genotyping and discrimination of the different members of the E. granulosus complex, allowing three levels of discrimination: (i) Echinococcus genus, (ii) E. granulosus complex, and (iii) genetic variants within the E. granulosus complex. The relatively complicated task of E. granulosus complex speciation and genotyping is clearly simplified by mPCR, and this technique therefore represents a useful tool for routine practice.
Human cystic echinococcosis (CE) is highly endemic in the Tibetan regions of Sichuan where most families keep guard dogs and where there are considerable numbers of ownerless/stray dogs. Strong Buddhist beliefs do not allow for elimination of stray dogs, and many strays are actually fed and adopted by households or monasteries. On account of the high altitude (3900–5000 m), pasturage is the major agricultural activity in this area. The harsh mountainous climate often leads to many grazing animals dying on the pasture at the end of a hard winter. The skin and some meat are taken, and the rest of the animal is left for scavenging birds and animals. The poor sanitation and hygiene, the Buddhist doctrine of allowing old livestock to die naturally, plus the unrestricted disposal of animal viscera post-slaughter may be responsible for the high prevalence of human CE in this setting.
Methods and Findings
As part of a large collaborative control program for CE in Ganzi County, situated in the west of Sichuan Province, surveillance for Echinococcus infection in domestic dogs using a coproantigen method and necropsy of unwanted dogs was carried out prior to (in 2000) and after (in 2005) dog anthelminthic treatment (5 mg/kg oral praziquantal at 6 month intervals) to determine the efficacy of the treatment for control. The prevalence of E. granulosus only in dogs by necropsy was 27% and 22%, and prevalence of both Echinococcus spp. by necropsy was 63% and 38%; prevalence of both Echinococcus spp. by coproantigen analysis was 50% and 17%. Necropsy of sheep/goats (age <1 to 12 years) (prevalence of E. granulosus in 1–6-year-old animals was 38% and in 10–12-year-old animals was 70%) and yaks (age 4 years) (prevalence of E. granulosus was 38%) was undertaken to determine the baseline transmission pressure. Protoscoleces were only found in very old sheep/goats and yaks. Necropsy of dogs in the Datangma district indicated that there was no apparent significant change in the overall prevalence of E. granulosus in unwanted dogs after 5 years of 6-month praziquantel treatment. However, this was likely due to the number of dogs available for necropsy being too small to reflect the real situation prevailing. There was a highly significant decrease in Echinococcus prevalence after the 5-year treatment program shown by coproantigen-ELISA. This indicated a decreasing but continuing risk for re-infection of domestic and stray dogs. Genotyping of E. granulosus samples obtained from necropsied sheep/goats and yaks and from locally infected humans at surgery was carried out to determine the strain of parasite responsible for human infection. DNA genotyping indicated that only the sheep strain (G1) of E. granulosus was present in the study area.
Considerable re-infection rates of E. granulosus among dogs indicated a high infection pressure from infected livestock in this region, most likely from older animals dying on the pasture. A combination of livestock vaccination with the Eg95 vaccine, which is effective against the sheep strain of E. granulosus, and dog anthelmintic treatment, thus targeting two critical points of the parasite life-cycle, would avoid the conflicts of religion or local culture and could achieve the goal of hydatid control in the long term.
Human cystic echinococcosis (CE) is highly endemic in Tibetan regions of Sichuan. As part of a control program for CE in Datangma district, Ganzi County, necropsy of strays and coproantigen-ELISA of all dogs was carried out prior to and post-drug treatment to determine the efficacy of the treatment for control. Examination of sheep/goats and yaks was undertaken to determine the baseline transmission pressure to dogs. The necropsy results indicated no apparent significant change in the overall prevalence of E. granulosus in unwanted dogs after 5 years of 6-month treatment. In contrast, there was a highly significant decrease in Echinococcus prevalence in domestic/stray dogs after the 5-year treatment program shown by coproantigen-ELISA. This indicated a decreasing but continuing risk for re-infection of dogs resulting from high infection pressure from the numerous infected domestic animals. DNA genotyping indicated the presence only of the sheep strain (G1) of E. granulosus in the study area. A combination of livestock vaccination with the highly effective Eg95 vaccine and dog drug treatment, targeting two critical points of the parasite life-cycle, would avoid the conflicts of religion or local culture and achieve the goal of hydatid control in the long term in the area.
Alveolar echinococcosis (AE) is caused by the metacestode stage of the fox tapeworm Echinococcus multilocularis and causes severe disease in the human liver, and occasionally in other organs, that is fatal when treatment is unsuccessful. The present chemotherapy against AE is based on mebendazole and albendazole. Albendazole treatment has been found to be ineffective in some instances, is parasitostatic rather than parasiticidal, and usually involves the lifelong uptake of large doses of drugs. Thus, new treatment options are urgently needed. In this study we investigated the in vitro and in vivo efficacy of mefloquine against E. multilocularis metacestodes. Treatment using mefloquine (20 μM) against in vitro cultures of metacestodes resulted in rapid and complete detachment of large parts of the germinal layer from the inner surface of the laminated layer within a few hours. The in vitro activity of mefloquine was dependent on the dosage. In vitro culture of metacestodes in the presence of 24 μM mefloquine for a period of 10 days was parasiticidal, as determined by murine bioassays, while treatment with 12 μM was not. Oral application of mefloquine (25 mg/kg of body weight administered twice a week for a period of 8 weeks) in E. multilocularis-infected mice was ineffective in achieving any reduction of parasite weight, whereas treatment with albendazole (200 mg/kg/day) was highly effective. However, when the same mefloquine dosage was applied intraperitoneally, the reduction in parasite weight was similar to the reduction seen with oral albendazole application. Combined application of both drugs did not increase the treatment efficacy. In conclusion, mefloquine represents an interesting drug candidate for the treatment of AE, and these results should be followed up in appropriate in vivo studies.
The life-threatening diseases alveolar and cystic echinococcoses are caused by larvae of the tapeworms Echinococcus multilocularis and E. granulosus, respectively. In both cases, intermediate hosts, such as humans, are infected by oral uptake of oncosphere larvae, followed by asexual multiplication and almost unrestricted growth of the metacestode within host organs. Besides surgery, echinococcosis treatment relies on benzimidazole-based chemotherapy, directed against parasite beta-tubulin. However, since beta-tubulins are highly similar between cestodes and humans, benzimidazoles can only be applied at parasitostatic doses and are associated with adverse side effects. Mostly aiming at identifying alternative drug targets, the nuclear genome sequences of E. multilocularis and E. granulosus have recently been characterized, revealing a large number of druggable targets that are expressed by the metacestode. Furthermore, recent cell biological investigations have demonstrated that E. multilocularis employs pluripotent stem cells, called germinative cells, which are the only parasite cells capable of proliferation and which give rise to all differentiated cells. Hence, the germinative cells are the crucial cell type mediating proliferation of E. multilocularis, and most likely also E. granulosus, within host organs and should also be responsible for parasite recurrence upon discontinuation of chemotherapy. Interestingly, recent investigations have also indicated that germinative cells might be less sensitive to chemotherapy because they express a beta-tubulin isoform with limited affinity to benzimidazoles. In this article, we briefly review the recent findings concerning Echinococcus genomics and stem cell research and propose that future research into anti-echinococcosis drugs should also focus on the parasite’s stem cell population.
Genome; Chemotherapy; Beta-tubulin; Benzimidazole; Stem cells; Germinative cells
The growth potential of the tumor-like Echinococcus multilocularis metacestode (causing alveolar echinococcosis, AE) is directly linked to the nature/function of the periparasitic host immune-mediated processes. We previously showed that Fibrinogen-like-protein 2 (FGL2), a novel CD4+CD25+ Treg effector molecule, was over-expressed in the liver of mice experimentally infected with E. multilocularis. However, little is known about its contribution to the control of this chronic helminth infection.
Key parameters for infection outcome in E. multilocularis-infected fgl2-/- (AE-fgl2-/-) and wild type (AE-WT) mice at 1 and 4 month(s) post-infection were (i) parasite load (i. e. wet weight of parasitic metacestode tissue), and (ii) parasite cell proliferation as assessed by determining E. multilocularis 14-3-3 gene expression levels. Serum FGL2 levels were measured by ELISA. Spleen cells cultured with ConA for 48h or with E. multilocularis Vesicle Fluid (VF) for 96h were analyzed ex-vivo and in-vitro. In addition, spleen cells from non-infected WT mice were cultured with rFGL2/anti-FGL2 or rIL-17A/anti-IL-17A for further functional studies. For Treg-immune-suppression-assays, purified CD4+CD25+ Treg suspensions were incubated with CD4+ effector T cells in the presence of ConA and irradiated spleen cells as APCs. Flow cytometry and qRT-PCR were used to assess Treg, Th17-, Th1-, Th2-type immune responses and maturation of dendritic cells. We showed that AE-fgl2-/- mice exhibited (as compared to AE-WT-animals) (a) a significantly lower parasite load with reduced proliferation activity, (b) an increased T cell proliferative response to ConA, (c) reduced Treg numbers and function, and (d) a persistent capacity of Th1 polarization and DC maturation.
FGL2 appears as one of the key players in immune regulatory processes favoring metacestode survival by promoting Treg cell activity and IL-17A production that contributes to FGL2-regulation. Prospectively, targeting FGL2 could be an option to develop an immunotherapy against AE and other chronic parasitic diseases.
In larval E. multilocularis infection causing alveolar echinococcosis (AE) in humans as well as mice, immune tolerance and/or down-regulation of protective immunity is a marked characteristic of this chronic disease. Our study provides a comprehensive evidence for a major involvement of the recently identified CD4+ CD25+ Regulatory T Cell Effector Molecule FGL2 to the outcome of AE. Our major findings are as follows: 1) FGL2 is mostly secreted by Tregs and partly contributes to their functions; 2) FGL2 can down-regulate the maturation of DCs, suppress Th1 and Th17 immune responses, and support Th2 and Treg immune responses, and finally 3) IL-17A contributes to FGL2 secretion. Based on the present findings in mice, we will investigate FGL2 as a potential marker of progression of AE in human patients, or as a potential immunotherapeutical target. Early prediction of parasite regression (currently not yet possible) would allow clinicians to plan for withdrawing benzimidazole treatment, which is currently administered for life. Then, FGL2 should be investigated as a target for an anticipated immunomodulatory treatment of patients with progressive AE, especially of those who are non- or low-responders to benzimidazole treatment, or who suffer from side-effects due to chemotherapy.
Echinococcus granulosus is usually transmitted between canid definitive hosts and ungulate intermediate hosts.
Lesions found in the livers of ground squirrels, Spermophilus dauricus/alashanicus, trapped in Ningxia Hui Autonomous Region, an area in China co-endemic for both E. granulosus and E. multilocularis, were subjected to molecular genotyping for Echinococcus spp. DNA. One of the lesions was shown to be caused by E. granulosus and subsequently by histology to contain viable protoscoleces.
This is the first report of a natural infection of the ground squirrel with E. granulosus. This does not provide definitive proof of a cycle involving ground squirrels and dogs or foxes, but it is clear that there is active E. granulosus transmission occurring in this area, despite a recent past decline in the dog population in southern Ningxia.
Echinococcus granulosus and E. multilocularis are important zoonotic pathogens that cause serious disease in humans. E. granulosus can be transmitted through sylvatic cycles, involving wild carnivores and ungulates; or via domestic cycles, usually involving dogs and farm livestock. E. multilocularis is primarily maintained in a sylvatic life-cycle between foxes and rodents. As part of extensive investigations that we undertook to update available epidemiological data and to monitor the transmission patterns of both E. granulosus and E. mulilocularis in Ningxia Hui Autonomous Region (NHAR) in northwest China, we captured small mammals on the southern slopes of Yueliang Mountain, Xiji, an area co-endemic for human alveolar echinococcosis and cystic echinococcosis. Of 500 trapped small mammals (mainly ground squirrels; Spermophilus dauricus/alashanicus), macroscopic cyst-like lesions (size range 1–10 mm) were found on the liver surface of approximately 10% animals. One of the lesions was shown by DNA analysis to be caused by E. granulosus and by histology to contain viable protoscoleces. This is the first report of a natural infection of the ground squirrel with E. granulosus. We have no definitive proof of a cycle involving ground squirrels and dogs/foxes but it is evident that there is active E. granulosus transmission occurring in this area.
Alveolar echinococcosis, caused by the larval (metacestode) stage of the tapeworm Echinococcus multilocularis, is a lethal parasitosis of the liver prevalent in the Northern Hemisphere. For chemotherapy the benzimidazole derivatives mebendazole and albendazole were introduced, and their use has resulted in a significant improvement in the survival rates. However, data from experiments with animals and clinical observations indicate that these drugs elicit only parasitostatic activity and in most cases are not able to completely eliminate the parasitic metacestode tissue. In the present study, we applied a culture system for the in vitro growth and proliferation of E. multilocularis metacestodes to analyze the parasitostatic and parasitocidal potential of mebendazole. Here, we demonstrate for the first time that at concentrations of >0.1 μM, i.e., at concentrations used for therapy of human alveolar echinococcosis, this antihelminth drug is parasitocidal in vitro. Viability assessment was performed by infection experiments with Meriones unguiculatus and mebendazole-treated metacestode tissue and by reverse transcription-PCR for the detection of E. multilocularis mRNA. The E. multilocularis in vitro model proved to be a valuable tool for the analysis of the potential of antihelminth drugs.
Metformin (Met) is a biguanide anti-hyperglycemic agent, which also exerts antiproliferative effects on cancer cells. This drug inhibits the complex I of the mitochondrial electron transport chain inducing a fall in the cell energy charge and leading 5'-AMP-activated protein kinase (AMPK) activation. AMPK is a highly conserved heterotrimeric complex that coordinates metabolic and growth pathways in order to maintain energy homeostasis and cell survival, mainly under nutritional stress conditions, in a Liver Kinase B1 (LKB1)-dependent manner. This work describes for the first time, the in vitro anti-echinococcal effect of Met on Echinococcus granulosus larval stages, as well as the molecular characterization of AMPK (Eg-AMPK) in this parasite of clinical importance. The drug exerted a dose-dependent effect on the viability of both larval stages. Based on this, we proceeded with the identification of the genes encoding for the different subunits of Eg-AMPK. We cloned one gene coding for the catalytic subunit (Eg-ampkɑ) and two genes coding for the regulatory subunits (Eg-ampkβ and Eg-ampkγ), all of them constitutively transcribed in E. granulosus protoscoleces and metacestodes. Their deduced amino acid sequences show all the conserved functional domains, including key amino acids involved in catalytic activity and protein-protein interactions. In protoscoleces, the drug induced the activation of AMPK (Eg-AMPKɑ-P176), possibly as a consequence of cellular energy charge depletion evidenced by assays with the fluorescent indicator JC-1. Met also led to carbohydrate starvation, it increased glucogenolysis and homolactic fermentation, and decreased transcription of intermediary metabolism genes. By in toto immunolocalization assays, we detected Eg-AMPKɑ-P176 expression, both in the nucleus and the cytoplasm of cells as in the larval tegument, the posterior bladder and the calcareous corpuscles of control and Met-treated protoscoleces. Interestingly, expression of Eg-AMPKɑ was observed in the developmental structures during the de-differentiation process from protoscoleces to microcysts. Therefore, the Eg-AMPK expression during the asexual development of E. granulosus, as well as the in vitro synergic therapeutic effects observed in presence of Met plus albendazole sulfoxide (ABZSO), suggest the importance of carrying out chemoprophylactic and clinical efficacy studies combining Met with conventional anti-echinococcal agents to test the potential use of this drug in hydatidosis therapy.
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.
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.
Alveolar echinococcosis (AE) is caused by the metacestode stage of Echinococcus multilocularis. Differential diagnosis with cystic echinococcosis (CE) caused by E. granulosus and AE is challenging. We aimed at improving diagnosis of AE on paraffin sections of infected human tissue by immunohistochemical testing of a specific antibody.
We have analysed 96 paraffin archived specimens, including 6 cutting needle biopsies and 3 fine needle aspirates, from patients with suspected AE or CE with the monoclonal antibody (mAb) Em2G11 specific for the Em2 antigen of E. multilocularis metacestodes. In human tissue, staining with mAb Em2G11 is highly specific for E. multilocularis metacestodes while no staining is detected in CE lesions. In addition, the antibody detects small particles of E. multilocularis (spems) of less than 1 µm outside the main lesion in necrotic tissue, liver sinusoids and lymphatic tissue most probably caused by shedding of parasitic material. The conventional histological diagnosis based on haematoxylin and eosin and PAS stainings were in accordance with the immunohistological diagnosis using mAb Em2G11 in 90 of 96 samples. In 6 samples conventional subtype diagnosis of echinococcosis had to be adjusted when revised by immunohistology with mAb Em2G11.
Immunohistochemistry with the mAb Em2G11 is a new, highly specific and sensitive diagnostic tool for AE. The staining of small particles of E. multilocularis (spems) outside the main lesion including immunocompetent tissue, such as lymph nodes, suggests a systemic effect on the host.
Echinococcosis is a life-threatening disease in humans that is caused by the larval stages of the tapeworms Echinococcus multilocularis and Echinococcus granulosus. The eggs of the parasites are released with faeces of canids, and humans are aberrantly infected. In humans, the larval stages of the parasites cause tumour-like lesions mainly in the liver and the lungs. Precise diagnosis of the parasite responsible for human disease is of utmost importance since therapy regimens largely differ between cystic and alveolar echinococcosis. Diagnosis is based on serology, imaging and histology, the latter being the gold standard. However, conventional histology cannot always clearly identify the causative parasite because both parasites can cause human tissue to present similar features. Therefore, we have developed the monoclonal antibody Em2G11 and an immunohistological technique that allows a cheap and fast clear-cut diagnosis of E. multilocularis even on aspirates and small archived bioptic tissue samples. Furthermore, this technique disclosed an unknown feature of human alveolar echinococosis we called "small particles of E. multilocularis" (spems). We argue that these small particles represent micro-fragments of E. multilocularis and thus point to a new form of host-parasite interaction.
The metacestode larva of Echinococcus multilocularis (Cestoda: Taeniidae) develops in the liver of intermediate hosts (typically rodents, or accidentally in humans) as a labyrinth of interconnected cysts that infiltrate the host tissue, causing the disease alveolar echinococcosis. Within the cysts, protoscoleces (the infective stage for the definitive canid host) arise by asexual multiplication. These consist of a scolex similar to that of the adult, invaginated within a small posterior body. Despite the importance of alveolar echinococcosis for human health, relatively little is known about the basic biology, anatomy and development of E. multilocularis larvae, particularly with regard to their nervous system.
We describe the existence of a subtegumental nerve net in the metacestode cysts, which is immunoreactive for acetylated tubulin-α and contains small populations of nerve cells that are labeled by antibodies raised against several invertebrate neuropeptides. However, no evidence was found for the existence of cholinergic or serotoninergic elements in the cyst wall. Muscle fibers occur without any specific arrangement in the subtegumental layer, and accumulate during the invaginations of the cyst wall that form brood capsules, where protoscoleces develop. The nervous system of the protoscolex develops independently of that of the metacestode cyst, with an antero-posterior developmental gradient. The combination of antibodies against several nervous system markers resulted in a detailed description of the protoscolex nervous system, which is remarkably complex and already similar to that of the adult worm.
We provide evidence for the first time of the existence of a nervous system in the metacestode cyst wall, which is remarkable given the lack of motility of this larval stage, and the lack of serotoninergic and cholinergic elements. We propose that it could function as a neuroendocrine system, derived from the nervous system present in the bladder tissue of other taeniids. The detailed description of the development and anatomy of the protoscolex neuromuscular system is a necessary first step toward the understanding of the developmental mechanisms operating in these peculiar larval stages.
Echinococcus; Metacestode; Protoscolex; Nervous system; Neuropeptide; Serotonin; Acetylated tubulin