The Echinococcus canadensis (G7) genome: a key knowledge of parasitic platyhelminth human diseases.

BACKGROUND: The parasite Echinococcus canadensis (G7) (phylum Platyhelminthes, class Cestoda) is one of the causative agents of echinococcosis. Echinococcosis is a worldwide chronic zoonosis affecting humans as well as domestic and wild mammals, which has been reported as a prioritized neglected disease by the World Health Organisation. No genomic data, comparative genomic analyses or efficient therapeutic and diagnostic tools are available for this severe disease. The information presented in this study will help to understand the peculiar biological characters and to design species-specific control tools. RESULTS: We sequenced, assembled and annotated the 115-Mb genome of E. canadensis (G7). Comparative genomic analyses using whole genome data of three Echinococcus species not only confirmed the status of E. canadensis (G7) as a separate species but also demonstrated a high nucleotide sequences divergence in relation to E. granulosus (G1). The E. canadensis (G7) genome contains 11,449 genes with a core set of 881 orthologs shared among five cestode species. Comparative genomics revealed that there are more single nucleotide polymorphisms (SNPs) between E. canadensis (G7) and E. granulosus (G1) than between E. canadensis (G7) and E. multilocularis. This result was unexpected since E. canadensis (G7) and E. granulosus (G1) were considered to belong to the species complex E. granulosus sensu lato. We described SNPs in known drug targets and metabolism genes in the E. canadensis (G7) genome. Regarding gene regulation, we analysed three particular features: CpG island distribution along the three Echinococcus genomes, DNA methylation system and small RNA pathway. The results suggest the occurrence of yet unknown gene regulation mechanisms in Echinococcus. CONCLUSIONS: This is the first work that addresses Echinococcus comparative genomics. The resources presented here will promote the study of mechanisms of parasite development as well as new tools for drug discovery. The availability of a high-quality genome assembly is critical for fully exploring the biology of a pathogenic organism. The E. canadensis (G7) genome presented in this study provides a unique opportunity to address the genetic diversity among the genus Echinococcus and its particular developmental features. At present, there is no unequivocal taxonomic classification of Echinococcus species; however, the genome-wide SNPs analysis performed here revealed the phylogenetic distance among these three Echinococcus species. Additional cestode genomes need to be sequenced to be able to resolve their phylogeny.

[Advances in research on the MAPK signal transduction pathway of Echinococcus].

Mitogen-activated protein kinase (MAPK) is an important signaling transduction molecules, which can enter the nucleus and activate target gene when it was stimulated and become phosphorylation. MAPK signaling pathway is closely associated with various diseases. Recent studies have indicated that MAPK signaling transduction pathway is also involved in the growth and development of Echinococcus. This review summarizes the progress on the relationship between MAPK signal pathway and Echinococcus.

[Transformation of the fungus Paecilomyces variotii and the causes of host cell lysis at the boundary with a fungal mycelium-containing Echinococcus capsule].

Experiments were carried out on animal species. The experiments used 30-day chicks, 80 rats, and 70 rabbits. Three hundred and twenty-nine patients with echinococcus complicated by paecilomycosis were meticulously examined. The fungi of the genus Paecilomyces undergo two transformation directions: the saprotrophic mycelial form of the fungus Paecilomyces variotii transforms to the tissue parasitic one as a globular form of spherules that transforms to the mycelial form in larval Echinococcus infection because the cyst capsule is a favorable environment for growth of fungal mycelia. The growth and aggressiveness of larval Echinococcus in the human lung are associated with the fact that fungal mycelial fibrous tunic contains Paecilomyces that have been first used to isolate active hyaluronidase that lyses host cells. Pulmonary echinococcosis complicated by the tissue form of paecilomycosis can be complicated by the mycelial form of the fungus of the genus Paecilomyces, by afflicting the nails and skin of patients, which requires particular treatment after surgery for hydatid disease. The chicks that had been brooded in an incubator and grown under special conditions to rule out fungal infection were first contaminated with the fungal mycelium labeled with methionine, sodium sulfate, sodium phosphate, or iodine. Each chick received 0.5 g of the labeled fungal mycelium. Regardless of the contamination mode, all the chicks from 3 groups were infected with Paecilomyces; the spherules exhibited labeled isotopes. Thus, it has been first conclusively proven that the diagnosis of paecilomycosis based on the blood detection of fungal globular spherules is valid and easy-to-use in any health care facility.

Characterization of a new type of neuronal 5-HT G- protein coupled receptor in the cestode nervous system.

Cestodes are platyhelminth parasites with a wide range of hosts that cause neglected diseases. Neurotransmitter signaling is of critical importance for these parasites which lack circulatory, respiratory and digestive systems. For example, serotonin (5-HT) and serotonergic G-protein coupled receptors (5-HT GPCRs) play major roles in cestode motility, development and reproduction. In previous work, we deorphanized a group of 5-HT7 type GPCRs from cestodes. However, little is known about another type of 5-HT GPCR, the 5-HT1 clade, which has been studied in several invertebrate phyla but not in platyhelminthes. Three putative 5-HT GPCRs from Echinococcus canadensis, Mesocestoides vogae (syn. M. corti) and Hymenolepis microstoma were cloned, sequenced and bioinformatically analyzed. Evidence grouped these new sequences within the 5-HT1 clade of GPCRs but differences in highly conserved GPCR motifs were observed. Transcriptomic analysis, heterologous expression and immunolocalization studies were performed to characterize the E. canadensis receptor, called Eca-5-HT1a. Functional heterologous expression studies showed that Eca-5-HT1a is highly specific for serotonin. 5-Methoxytryptamine and α-methylserotonin, both known 5-HT GPCR agonists, give stimulatory responses whereas methysergide, a known 5-HT GPCR ligand, give an antagonist response in Eca-5-HT1a. Mutants obtained by the substitution of key predicted residues resulted in severe impairment of receptor activity, confirming that indeed, these residues have important roles in receptor function. Immunolocalization studies on the protoscolex stage from E. canadensis, showed that Eca-5-HT1a is localized in branched fibers which correspond to the nervous system of the parasite. The patterns of immunoreactive fibers for Eca-5-HT1a and for serotonin were intimately intertwined but not identical, suggesting that they are two separate groups of fibers. These data provide the first functional, pharmacological and localization report of a serotonergic receptor that putatively belongs to the 5-HT1 type of GPCRs in cestodes. The serotonergic GPCR characterized here may represent a new target for antiparasitic intervention.

Identification of universal diagnostic peptide candidates for neglected tropical diseases caused by cestodes through the integration of multi-genome-wide analyses and immunoinformatic predictions.

Neglected tropical diseases caused by helminth infections currently affect millions of people worldwide. Among them, there are three tapeworm species of outstanding importance: Echinococcus granulosus, E. multilocularis, and Taenia solium, which are responsible for cystic echinococcosis, alveolar echinococcosis, and cysticercosis, respectively. Despite several attempts, there is still a need for an effective and low-cost serological diagnostic test that can be used in endemic countries. In the present work, we described an innovative bioinformatic workflow for a rational prediction of putative peptide candidates for one-step serological diagnosis of any of these infections. First, we predicted the theoretical secretome shared by the three tapeworms starting from their full reported proteomes. Then, through immunoinformatics, we identified proteins within the shared secretome displaying high antigenicity scores and bearing T cell epitopes able to bind most human MHC-II alleles. Secondly, in such proteins, we identified linear B cell epitopes without post-translational modifications, and mapped them on 3D modelled structures to visualize their antibody accessibilities. As a result, we finally suggested two antigenic peptides shared between the secretomes of the three parasite species, which could be further tested for their immunodiagnostic potential.

Intraprostatic hydatid cyst: an unusual presentation.

A case of intraprostatic cyst is reported. The patient presented with a completely evacuated hydatid cyst of the prostate. The intraprostatic cystic cavity that was communicating with the urethra developed urinary stones. The patient had transurethral resection of the prostate, the stones in the cyst were pushed into the bladder and fragmented using a ballistic lithotripter. Pathological examination concluded to a prostatic hydatid cyst that had evacuated through the urethra and was complicated by stone formation within the residual cavity. Postoperative course was uneventful and follow-up did not show evidence of recurrence. This is the first case of hydatid cyst of the prostate to present as an intraprostatic stone pouch.

Genomic structure and expression of a gene coding for a new fatty acid binding protein from Echinococcus granulosus.

This work describes a new gene coding for a fatty acid binding protein (FABP) in the parasite Echinococcus granulosus, named EgFABP2. The complete gene structure, including the promoter sequence, is reported. The genomic coding domain organisation of the previously reported E. granulosus FABP gene (EgFABP1) has been also determined. The corresponding polypeptide chains share 76% of identical residues and an overall 96% of similarity. The two EgFABPs present the highest amino acid homologies with the mammalian FABP subfamily containing heart-FABPs (H-FABPs). The coding sequences of both genes are interrupted by a single intron located in the position of the third intron reported for vertebrate FABP genes. Both genes are expressed in the protoscolex stage of the parasite. The promoter region of EgFABP2 presents several consensus putative cis-acting elements found in other members of the family, suggesting interesting possible mechanisms involved in the host-parasite adaptation.

Binding properties of Echinococcus granulosus fatty acid binding protein.

EgFABP1 is a developmentally regulated intracellular fatty acid binding protein characterized in the larval stage of parasitic platyhelminth Echinococcus granulosus. It is structurally related to the heart group of fatty acid binding proteins (H-FABPs). Binding properties and ligand affinity of recombinant EgFABP1 were determined by fluorescence spectroscopy using cis- and trans-parinaric acid. Two binding sites for cis- and trans-parinaric acid were found (K(d(1)) 24+/-4 nM, K(d(2)) 510+/-60 nM for cis-parinaric acid and K(d(1)) 32+/-4 nM, K(d(2)) 364+/-75 nM for trans-parinaric). A putative third site for both fatty acids is discussed. Binding preferences were determined using displacement assays. Arachidonic and oleic acids presented the highest displacement percentages for EgFABP1. The Echinococcus FABP is the unique member of the H-FABP group able to bind two long chain fatty acid molecules with high affinity. Structure-function relationships and putative roles for EgFABP1 in E. granulosus metabolism are discussed.

The crystal structure of Echinococcus granulosus fatty-acid-binding protein 1.

We describe the 1.6 A crystal structure of the fatty-acid-binding protein EgFABP1 from the parasitic platyhelminth Echinococcus granulosus. E. granulosus causes hydatid disease, which is a major zoonosis. EgFABP1 has been implicated in the acquisition, storage, and transport of lipids, and may be important to the organism since it is incapable of synthesising most of its lipids de novo. Moreover, EgFABP1 is a promising candidate for a vaccine against hydatid disease. The crystal structure reveals that EgFABP1 has the expected 10-stranded beta-barrel fold typical of the family of intracellular lipid-binding proteins, and that it is structurally most similar to P2 myelin protein. We describe the comparison of the crystal structure of EgFABP1 with these proteins and with an older homology model for EgFABP1. The electron density reveals the presence of a bound ligand inside the cavity, which we have interpreted as palmitic acid. The carboxylate group of the fatty acid interacts with the protein's P2 motif, consisting of a conserved triad R em leader R-x-Y. The hydrophobic tail of the ligand assumes a fairly flat, U-shaped conformation and has relatively few interactions with the protein.We discuss some of the structural implications of the crystal structure of EgFABP1 for related platyhelminthic FABPs.

microRNA profiling in the zoonotic parasite Echinococcus canadensis using a high-throughput approach.

BACKGROUND: microRNAs (miRNAs), a class of small non-coding RNAs, are key regulators of gene expression at post-transcriptional level and play essential roles in fundamental biological processes such as development and metabolism. The particular developmental and metabolic characteristics of cestode parasites highlight the importance of studying miRNA gene regulation in these organisms. Here, we perform a comprehensive analysis of miRNAs in the parasitic cestode Echinococcus canadensis G7, one of the causative agents of the neglected zoonotic disease cystic echinococcosis. METHODS: Small RNA libraries from protoscoleces and cyst walls of E. canadensis G7 and protoscoleces of E. granulosus sensu stricto G1 were sequenced using Illumina technology. For miRNA prediction, miRDeep2 core algorithm was used. The output list of candidate precursors was manually curated to generate a high confidence set of miRNAs. Differential expression analysis of miRNAs between stages or species was estimated with DESeq. Expression levels of selected miRNAs were validated using poly-A RT-qPCR. RESULTS: In this study we used a high-throughput approach and found transcriptional evidence of 37 miRNAs thus expanding the miRNA repertoire of E. canadensis G7. Differential expression analysis showed highly regulated miRNAs between life cycle stages, suggesting a role in maintaining the features of each developmental stage or in the regulation of developmental timing. In this work we characterize conserved and novel Echinococcus miRNAs which represent 30 unique miRNA families. Here we confirmed the remarkable loss of conserved miRNA families in E. canadensis, reflecting their low morphological complexity and high adaptation to parasitism. CONCLUSIONS: We performed the first in-depth study profiling of small RNAs in the zoonotic parasite E. canadensis G7. We found that miRNAs are the preponderant small RNA silencing molecules, suggesting that these small RNAs could be an essential mechanism of gene regulation in this species. We also identified both parasite specific and divergent miRNAs which are potential biomarkers of infection. This study will provide valuable information for better understanding of the complex biology of this parasite and could help to find new potential targets for therapy and/or diagnosis.

Chromatin from two classes of platyhelminthes display both protist H1 and higher eukaryote core histones.

Histones from the parasitic platyhelminthes, Echinococcus granulosus and Fasciola hepatica, were systematically characterized. Core histones H2A, H2B, H3 and H4, which were identified on the basis of amino acid sequencing and mass spectrometry data, showed conserved electrophoretic patterns. Histones H1, identified on the basis of physicochemical properties, amino acid composition and amino acid sequencing, showed divergence, both in their number and electrophoretic mobilities, between the two species and among other organisms. According to these data, core histones but not H1 histones, would be stabilized during evolution at the level of platyhelminthes.

Cestode parasites: application of in vivo and in vitro models for studies on the host-parasite relationship.

Cestode worms, commonly also known as 'flat' worms or tapeworms, are an important class of endoparasitic organisms. In order to complete their life cycle, they infect intermediate and definitive hosts in succession, through oral ingestion of eggs or larvae, respectively. Serious disease in humans or other mammalian hosts is mostly caused by the larval stages. Echinococcus spp. and Taenia spp. have been extensively investigated in the laboratory due to the fact that they represent important veterinary medical challenges and also cause grave diseases in humans. In contrast, Hymenolepis spp. and Mesocestoides spp. infections are relatively rare in humans, but these parasites have been extensively studied because their life cycle stages can be easily cultured in vitro, and can also be conveniently maintained in laboratory animal hosts. Thus they are more easily experimentally accessible, and represent important models for investigating the various aspects of cestode biology. This review will focus on in vitro and in vivo models which have been developed for studies on the host-parasite relationship during infection with Echinococcus, Taenia, Hymenolepis, Mesocestoides and Spirometra, and will cover the use of these models to investigate the morphology and ultrastructure of respective genera, the immunological relationship with the host and the development of vaccination approaches, as well as applications of these models for studies on parasite metabolism, physiology and gene expression. In addition, the use of these models in the development of chemotherapeutic measures against cestode infections is reviewed.

Membrane permeability of secondary hydatid cysts of Echinococcus granulosus. Determination of the water diffusional and osmotic permeability coefficients through a syncytial membrane.

Diffusional (Pw) and osmotic (Pf) water permeability coefficients were determined for the syncytial epithelium of larval Echinococcus granulosus. Pw was calculated from simultaneous influx measurements of tritiated water and n-[14C]butanol through the hydatid cyst wall. The total diffusional water permeability coefficient, P'w, was found to be 2.2 X 10(-4) cm s-1; which is similar to that previously reported by Rotunno et al. (1974, J. Parasitol. 60, 13-620). Nevertheless, when P'f is corrected for the unstirred water layer effects, a Pw value of 6.2 X 10(-4) cm s-1 is obtained. Thus, the unstirred water layer effects have a very important contribution to P'w. Total steady state osmotic permeability coefficient, P'f, was bound to be about 15 X 10(-4) cm s-1 and it is scarcely affected by those mechanisms that tend to distort the evaluation of Pf. The experimentally determined osmotic coefficient differs from the corrected Pf by only 6%. The Pf/Pw ratio was found to be 2.4. The present study clearly confirms that syncytial membranes can be highly permeable to water, in spite of the fact that they lack tight junctions. Thus, water permeability through epithelial syncytium must be exclusively controlled by the permeability of the apical and/or basocellular membranes.

A gene family from Echinococcus granulosus differentially expressed in mature adult worms.

Differences in mRNA expression between immature adult worms (IAW) and mature adult worms (MAW) of Echinococcus granulosus were determined using polymerase chain reaction-based differential display (DDRT-PCR). Twenty-eight putative differential cDNA fragments were isolated, cloned and sequenced. mRNAs from IAW and MAW were probed with the labelled fragments. Six cDNA fragments (coded as egM12, egM13, egM22, egM26, egM30 and egM34) were putatively determined to be specific to MAW by Northern hybridisation. The stage-specificity of egM12, egM13 and egM34 was confirmed by RT-PCR. RNAs of IAW, MAW, protoscoleces and oncospheres, probed with egM13 and egM30, showed that the mRNAs were expressed exclusively in MAW, which implied involvement in the regulation of egg development. Using the labelled fragments to screen a cDNA library of MAW, 99 clones were identified and analysed. An alignment of selected clones showed that the MAW-specific mRNAs belonged to a family. Examination of the deduced amino acid sequence of three of the corresponding cDNAs (egM4, egM9 and egM123) indicated they were cysteine-rich and contained a 24 amino acid repeat sequence, repeated four to six times. The repeat regions were predominantly alpha helical in nature with interspersed turns, forming alternating zones of positive and negative charge. The functional significance of each of the cDNAs identified is unclear as none had significant sequence similarity to genes of known function. However, polypeptides encoded by egM4 and egM123 were recognised by antibodies in a serum pool from dogs experimentally infected with E. granulosus, suggesting they could prove of value in serodiagnosis of definitive hosts.

Cloning and expression of a cDNA encoding a nonintegrin laminin-binding protein from Echinococcus granulosus with localization of the laminin-binding domain.

We have isolated a cDNA from the hydatid tapeworm, Echinococcus granulosus, encoding a protein that binds laminin. This is the first report of a helminth parasite laminin-binding protein and the first description of a cDNA encoding a laminin-binding protein from a parasite. The cDNA clone (egmo3) was isolated from an E. granulosus protoscolex cDNA expression library, and identified on the basis of sequence homology to the nonintegrin mammalian metastasis-associated 67-kDa laminin receptor (67-LR). The amino acid sequence predicted from the cDNA sequence is 268 residues long with a calculated molecular mass of 29.9 kDa. Southern blot analysis suggested that many copies of the gene may occur in the E. granulosus genome. A Northern blot revealed that the gene is expressed as a single transcript of approximately 1 kb consistent with the size of the cDNA insert. Antibodies raised to the purified protein interacted with a 30 kDa protein in whole E. granulosus protoscoleces. A Western blot of the purified and refolded recombinant protein specifically bound 125I-labelled laminin, as did a synthetic peptide derived from the inferred amino acid sequence of egmo3 which is similar in homology to peptide G, the active ligand-binding site of 67-LR. We also isolated the 3' end of the cDNA encoding the homologous protein from the closely related species, E. multilocularis. The polypeptide encoded by egmo3 also shares substantial identity with the acidic class of ribosomal proteins which are involved in protein synthesis. As such, the egmo3 protein may be multifunctional in E. granulosus, acting as a laminin-binding molecule but also playing a role in cell division and growth.

A developmentally regulated gene of Echinococcus granulosus codes for a 15.5-kilodalton polypeptide related to fatty acid binding proteins.

A stage-specific expressed gene has been isolated from a cDNA expression library of Echinococcus granulosus protoscolices. The isolated clone contains the complete coding sequence. The corresponding protein (EgDf1) has a molecular weight of 15.5 kDa and is expressed at the tegumental level in the protoscolices, being undetectable in the germinal layer of the metacestode. This protein shares an important homology with a family of low-molecular weight proteins involved in the binding of hydrophobic ligands. This family includes a protein of Schistosoma mansoni (Sm 14) that has immunoprotective activity in rodents. Histochemical and metabolic data already reported for E. granulosus suggest that EgDf1 could be a molecular marker for early events in the process of protoscolex differentiation.

Full-length-enriched cDNA libraries from Echinococcus granulosus contain separate populations of oligo-capped and trans-spliced transcripts and a high level of predicted signal peptide sequences.

The tissue-dwelling larval stages of the cestode Echinococcus granulosus are intimately associated with the host, implying that a range of molecular mediators may be secreted by the parasite into the host environment. These mediators are being sought through a transcriptome-based analysis, using recombinant cDNA libraries. Conventional cDNA libraries of E. granulosus contain high levels of mitochondrial transcripts, as well as host (bovine) genomic DNA. In particular, 60% of a conventional protoscolex stage cDNA library corresponds to the large subunit (LSU) of mitochondrial rRNA. We attribute the presence of LSU rRNA copies to its polyadenylation in E. granulosus. To circumvent this problem, we adapted the 5' Rapid Amplification of cDNA Ends (RNA-ligase mediated RACE) technique that excludes all polynucleotides missing the 7-methyl-guanosine (7MG) cap specific to the 5' end of full-length mRNA. By ligating a specific oligonucleotide (oligo-cap) to 7MG-bearing mRNA, three cDNA libraries were made by PCR from oligo-cap and oligo-dT primers. Analysis of these libraries showed that mitochondrial RNA contaminants had been excluded. Moreover, no bovine genomic sequences were detected. In parallel, we constructed three cDNA libraries using the newly described trans-spliced leader (SL) from Echinococcus. Although these represent a smaller subset of parasite genes, mitochondrial and genomic contributions were again excluded. In both cases, a majority of cDNAs (61-92%) were judged to contain the initiation ATG codon, and 11-27% of inserts included potential N-terminal signal sequences. The 5' UTR tracts of most oligo-capped cDNAs were <100 nt, although approximately 8% were longer than this. Among the trans-spliced cDNAs, 43% potentially utilise the AUG donated by the SL, and in only 6% was the SL separated from an endogenous putative start site by >60 nt. Sequence analysis of randomly selected clones shows virtually no overlap between the oligo-capped and SL libraries, indicating that trans-spliced E. granulosus mRNAs appear to be insensitive to the enzymatic treatments used to 'oligo-cap' unspliced mRNAs. The oligo-capped and SL strategies represent efficient and complementary pathways to isolate full-length cDNA clones from this cestode parasite and, possibly, from related parasitic flatworms.

In vitro quantitative assessment of Echinococcus multilocularis metacestode viability after in vivo and in vitro maintenance.

The aim of this study was to apply the enzymatic MTT (3,5 dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide--formazan colorimetry for quantifying the viability of Echinococcus multilocularis whole cysts, after maintenance in vivo or in vitro. The enzymatic activities of young cysts freshly removed from rodents were linearly correlated with the parasite cyst weight. A comparative evaluation of the MTT assay and the in vitro viability assessments showed that the number of animals used for drug-screening purposes would be reduced by 35.8%. In this way, the use of different parasite samples removed from the same host is required, because of their different ages and their subsequent different abilities to reduce MTT. Cysts removed from mice exhibited higher colorimetric values than those removed from jirds. Thus, small entire cysts obtained from mice were maintained in the CMRL 1066 culture medium. Their enzymatic activities were evaluated at different times. The results indicate that, in such conditions, the optimal period of time for testing the effect of drugs against the metacestodes is limited to the 10 days following their transfer from mouse to culture flasks. The MTT assay encourages further studies to improve the viability of the whole cysts in vitro, using other standardizable culture conditions.

Primary pelvic hydatid cyst: an unusual cause of sciatica and foot drop.

STUDY DESIGN: A case report of primary pelvic hydatid cyst causing sciatica and foot drop. OBJECTIVE: To document the occurrence of primary pelvic hydatid cyst as one of the hidden causes of lower limb weakness and foot drop, and to recommend inclusion of the pelvic cavity when assessing sciatica and foot drop. SUMMARY OF BACKGROUND DATA: It is common to see foot drop caused by peripheral lesions around the knee or disc herniation in the lumbar spine, but if these sites were excluded, the pelvic cavity must be examined for hidden disease that may explain the cause of foot drop and sciatica. METHODS: The authors involved in the care and management of this patient were interviewed and all medical records, radiologic investigations, and related literature were reviewed. RESULTS: After exclusion of spinal and peripheral causes of foot drop, computed tomography of the pelvis showed a well-localized cystic swelling in the right side of the pelvis over the lumbosacral plexus roots. Surgical excision of the cyst resulted in partial recovery of the foot drop at 3 years of follow-up. CONCLUSION: Primary pelvic hydatid cyst rarely causes pressure on the lumbosacral plexus. This was a case of hydatid cyst in the pelvis causing sciatica and foot drop, and it indicates the pelvis as a hidden source of sciatica and foot drop. After surgical excision followed by 4 months' mebendazole therapy, there was no evidence of recurrence on long-term follow-up.

Purine metabolism in Echinococcus multilocularis.

The activities of the enzymes in Echinococcus multilocularis metacestodes involved in purine salvage were studied by HPLC. As in most parasites, this cestode relies entirely on salvage of preformed bases and nucleosides for its purine requirement. Therefore, these enzymes may be targets for drugs in the chemotherapeutic treatment of diseases caused by this parasite. The animals used in this study were gerbils (Meriones unguiculatus). Enzyme activities from sera and hepatic tissue in control and infected animals were similar with the exception of adenine phosphoribosyltransferase which showed an activity 4-fold greater in the serum from control than in serum from infected animals. In the parasite, adenine and hypoxanthine-guanine phosphoribosyltransferases and adenosine deaminase had the highest activities. Therefore, in E. multilocularis metacestodes, this pathway seems to be important for the parasite's metabolism.