In vivo treatment with IL-17A attenuates hydatid cyst growth and liver fibrogenesis in an experimental model of echinococcosis

We aimed to assess the effect of exogenous Interleukin (IL)-17A in experimental model of echinococcosis. Swiss mice were inoculated intra-peritoneally with viable protoscoleces (PSCs). Then, IL-17A was administered at 100, 125 or 150 pg/mL two weeks after cystic echinococcosis (CE) induction. Cyst development and hepatic damage were macroscopically and histologically analyzed. We observed that in vivo IL-17A treatment at 100, 125, and 150 pg/mL, reduced metacestode growth by 72.3%, 93.8%, and 96.9%, respectively. Interestingly an amelioration of liver architecture was noted at 125 pg/mL without toxic effect. In this context, we showed less fibrosis reaction and reduced expression of iNOS, TNF-α, NF-κb and CD68 in hepatic parenchyma of treated mice by 125 pg/mL of IL-17A. Collectively, our results indicate an antihydatic effect and immunoprotective properties of IL-17A and suggest its potential therapeutic value against Echinococcus granulosus infection.

Ecology and Life Cycle Patterns of Echinococcus Species

The genus Echinococcus is composed of eight generally recognized species and one genotypic cluster (Echinococcus canadensis cluster) that may in future be resolved into one to three species. For each species, we review existing information on transmission routes and life cycles in different geographical contexts and - where available - include basic biological information of parasites and hosts (e.g., susceptibility of host species). While some Echinococcus spp. are transmitted in life cycles that involve predominantly domestic animals (e.g., dog - livestock cycles), others are wildlife parasites that do or do not interact with domestic transmission. In many cases, life cycle patterns of the same parasite species differ according to geography. Simple life cycles contrast with transmission patterns that are highly complex, involving multihost systems that may include both domestic and wild mammals. Wildlife transmission may be primary or secondary, i.e., resulting from spillovers from domestic animals. For most of the species and regions, existing information does not yet permit a conclusive description of transmission systems. Such data, however, would be highly relevant, e.g., for anticipation of geographical changes of the presence and frequency of these parasites in a warming world, or for initiating evidence-based control strategies.

Biology and Systematics of Echinococcus

The biology of Echinococcus, the causative agent of echinococcosis (hydatid disease) is reviewed with emphasis on the developmental biology of the adult and metacestode stages of the parasite. Major advances include determining the origin, structure and functional activities of the laminated layer and its relationship with the germinal layer; and the isolation, in vitro establishment and characterization of the multipotential germinal cells. Future challenges are to identify the mechanisms that provide Echinococcus with its unique developmental plasticity and the nature of activities at the parasite-host interface, particularly in the definitive host. The revised taxonomy of Echinococcus is presented and the solid nomenclature it provides will be essential in understanding the epidemiology of echinococcosis.

Report: Evaluation of the scolicidal effects of Nectaroscordum tripedale extract and its acute toxicity in mice model

Current scolicidal agents, which have been used for inactivation of protoscoleces during hydatid cyst surgery are associated with adverse side effects. This study aims to evaluate the in vitro scolicidal effects of Nectaroscordum tripedale L. leave extract against protoscoleces of hydatid cysts and its acute toxicity in mice model. Various concentrations of the extract (12.5-100 mg/mL) were used for 5 to 30 min. Viability of protoscoleces was confirmed using eosin exclusion test (0.1% eosin staining). In addition, the acute toxicity of N. tripedale extract was determined for 2 days in mice model. The results showed that the N. tripedale extract at the concentration of 100 mg/mL after 5 min of exposure killed 100% protoscoleces. Similarly, the mean of mortality rate of protoscoleces after 10 min of exposure to concentration of 50 mg/mL was 100%. The LD₅₀ values of intraperitoneal injection of the N. tripedale extract was 3.36 g/kg body wt. and the maximum nonfatal doses were 2.98 g/kg body wt. The results showed the potential of N. tripedale extract as a natural source for the production of new scolicidal agent for use in hydatid cyst surgery.

Validation of suitable reference genes for expression normalization in Echinococcus spp. larval stages

In recent years, a significant amount of sequence data (both genomic and transcriptomic) for Echinococcus spp. has been published, thereby facilitating the analysis of genes expressed during a specific stage or involved in parasite development. To perform a suitable gene expression quantification analysis, the use of validated reference genes is strongly recommended. Thus, the aim of this work was to identify suitable reference genes to allow reliable expression normalization for genes of interest in Echinococcus granulosus sensu stricto (s.s.) (G1) and Echinococcus ortleppi upon induction of the early pre-adult development. Untreated protoscoleces (PS) and pepsin-treated protoscoleces (PSP) from E. granulosus s.s. (G1) and E. ortleppi metacestode were used. The gene expression stability of eleven candidate reference genes (βTUB, NDUFV2, RPL13, TBP, CYP-1, RPII, EF-1α, βACT-1, GAPDH, ETIF4A-III and MAPK3) was assessed using geNorm, Normfinder, and RefFinder. Our qPCR data showed a good correlation with the recently published RNA-seq data. Regarding expression stability, EF-1α and TBP were the most stable genes for both species. Interestingly, βACT-1 (the most commonly used reference gene), and GAPDH and ETIF4A-III (previously identified as housekeeping genes) did not behave stably in our assay conditions. We propose the use of EF-1α as a reference gene for studies involving gene expression analysis in both PS and PSP experimental conditions for E. granulosus s.s. and E. ortleppi. To demonstrate its applicability, EF-1α was used as a normalizer gene in the relative quantification of transcripts from genes coding for antigen B subunits. The same EF-1α reference gene may be used in studies with other Echinococcus sensu lato species. This report validates suitable reference genes for species of class Cestoda, phylum Platyhelminthes, thus providing a foundation for further validation in other epidemiologically important cestode species, such as those from the Taenia genus.

Echinococcosis: historical landmarks and progress in research and control

Although hydatid cysts were recognised and described in ancient times, in both livestock and humans, it was not until the 17th Century that their biological nature began to be understood. The past 50 years have seen a veritable revolution in knowledge and technology applicable to the biology of the cestodes and the diseases they cause. The parasites that form hydatid cysts belong to the genus Echinococcus, which is now recognized as a complex of closely related cestode parasites adapted to a variety of host-assemblages linked by predator-prey relationships. Synanthropic transmission in dogs and domestic livestock greatly increases the possibilities of zoonotic transmission, and the highest prevalences of Echinococcus infection in humans therefore occur in populations engaged in livestock rearing in which domestic dogs have access to the viscera of the livestock that serve as intermediate hosts. The application of modern scientific technology over the last few decades has not only revealed the diversity of host-parasite relationships within the genus Echinococcus but also led to greatly improved technology for the diagnosis and treatment of the echinococcoses in humans and lower animals. Although control programmes have led to marked reductions in transmission in certain geographical and socio-political settings, transmission and the resultant diseases continue unabated throughout most of the parasites' world-wide distribution.

Hepatic hydatid cyst presenting as cutaneous abscess

Hydatidosis is a parasitic zoonotic echinococcal infection that affects both humans and other mammals. These diseases are common worldwide but particularly common in sheep and cattle farming regions. Anaphylaxis mediated by IgE is a serious complication of surgery or trauma which necessitates more aware of its clinical features, diagnosis and management. It is important to make a preoperative diagnosis based on the typical image findings, so that particular precaution can be taken not to rupture the lesion. A woman presented with a right upper quadrant cutaneous abscess. USG reveals multiple cystic lesions in the liver arranged in cartwheel appearance, CT disclosed a cystic lesions having daughter cysts, marginal calcifications, marginal enhancement and contiguous abdominal wall abscess, which led to a diagnosis of complicated hepatic hydatid cysts with abdominal wall abscess formation. FNAC showed scolices surrounded by chronic inflammatory cells. Abdominal wall abscess may be a presentation of hydatid liver disease.

[Application of in vitro cultivation technique for metacestodes in study of Echinococcus spp]

With the development of the in vitro cultivation of Echinococcus metacestodes, the technique is widely applied in research areas such as the pathogenic biological characteristics and the mechanism of infection and pathopoiesis of echinococcus, and development of novel therapeutic agents against echinococcosis. These will help futher understand the disease and its control. This paper reviews the application of the in vitro cultivation technique of Echinococcus spp.

[Development of a new hydrocarbon extract from the medicinal raw material of Circassian walnut (Juglans regia) and study of its antiparasitic activity]

The authors developed a technology for preparing a hydrocarbon extract from the medicinal raw material of Circassian walnut (Juglans regia), including its green fruits, green leaves, and fresh roots. To prepare the preparation, they obtained for the first time a new extragent called petroleum Russia that was found to contain more than hundred chemical compounds by chromatography mass spectrometry. The new agent was named irillen. Experiments on albino mice and albino rats established that the new agent was low toxic. The lethal doses of irillen were calculated: LD50 was 16377 +/- 457.5 mg/kg; LD16 = 12986.4 mg/kg; LD84 was 18976.6 mg/kg for albino mice; LD50 was 16998.0 +/- 535.4 mg/kg; LD16 = 12875.3 mg/ kg; LD84 = 18583.4 mg/kg for albino rats. The irillen prepared by the authors should be referred to as a low toxic and practically nontoxic agent (Toxicity Class IV and V). Irillen has a broad spectrum of antiparasitic activity. It is effective in treating toxocariasis in dogs, larval alveolar echinococcosis, ascaridiasis, and eimeriasis in chickens, and siphachiasis.

Production of experimental hydatid cyst in the eye, peritoneum and liver of BALB/c mice

As the main treatment for this infection is surgery, the surgery team personnel are at the risk of the protoscoleces released from the hydatid cysts (HC) of patients. The first goal of this study was to determine the probability of the production of ocular HC in mice due to the fluid of the aspirated protoscoleces from the sheep liver with HC. The second goal of this study was to produce HC in the peritoneum and liver, in order to gather more information for future studies on hepatic and peritoneal HC treatment procedures. For the first goal of this study, different concentrations of protoscoleces were prepared and injected into the eyes of 60 mice. After 20 weeks, 10 of the 60 mice of this group died. The remaining 50 mice were examined by a surgeon under the anesthesia. There weren't any symptoms of HC in the eyes and around it. For the second goal, 39 new mice were separated into three sub groups and 0.5 ml of protoscolex solution was injected intraperitoneally. After 20 weeks, they were anesthetized and their peritoneum, intestines and liver were examined. HC was seen in the peritoneum and liver of 6 mice.

Echinococcus, Giardia and Cryptosporidium: observational studies challenging accepted dogma

The development of in vitro culture systems that allow the maintenance, and support the development of Echinococcus, Giardia and Cryptosporidium in the laboratory have had a significant impact on their biology and taxonomy and the epidemiology of infections they cause. This short retrospective review demonstrates how radical shifts in our understanding have occurred as a result of being able to grow these organisms in culture, and how molecular tools have helped in the interpretation of such research that often reflects the observations of earlier workers.

Hydatidosis of slaughtered animals in Bahir Dar Abattoir, Northwestern Ethiopia

The study was conducted from May 2005 to December 2006 in Bahir Dar Abattoir to assess the current status of hydatidosis in cattle and sheep. Hydatid cyst count and characterization were conducted based on routine meat inspection. Of the total 420 cattle and 340 sheep slaughtered in Bahir Dar Abattoir 143 (34.05%) and 36 (10.6%) animals were found harboring hydatid cysts respectively. Thorough meat inspection in the abattoir revealed that 202 and 54 visceral organs were found harboring one or more hydatid cysts in cattle and sheep respectively. Differences in prevalence rates between the two species of animals were highly significant (P < 0.001). The infection of the lung, liver, kidney, spleen and heart were found to be 57.9% , 36.6% , 3% , 1.5% , 1% in cattle and 50%, 48.1% and 1.9% in sheep respectively. From the total of 864 in cattle and 138 in sheep hydatid cysts counted 315 (36.4%), 268 (31.0%), 65 (7.5%), 216 (25.0%) in cattle and 92 (66.7%), 20 (14.5%), 1 (0.7%), 25 (18.1%) in sheep were found to be small, medium, large and calcified cysts respectively and 484 (56.0%), 164 (18.9%), 216 (25%) in cattle and 35 (25.4%), 78 (56.5%), 25 (18.1%) in sheep were sterile, fertile and calcified cysts respectively. Viability rates of 62.2% in cattle and 78.2% in sheep were observed. The rate of cyst calcification was higher in the liver than in the lung while fertility rate was higher among the cysts of the lung for both cattle and sheep.

Prevention and control of cystic echinococcosis

Human cystic echinococcosis (hydatid disease) continues to be a substantial cause of morbidity and mortality in many parts of the world. Elimination is difficult to obtain and it is estimated that, using current control options, achieving such a goal will take around 20 years of sustained efforts. Since the introduction of current (and past) hydatid control campaigns, there have been clear technological improvements made in the diagnosis and treatment of human and animal cystic echinococcosis, the diagnosis of canine echinococcosis, and the genetic characterisation of strains and vaccination against Echinococcus granulosus in animals. Incorporation of these new measures could increase the efficiency of hydatid control programmes, potentially reducing the time required to achieve effective prevention of disease transmission to as little as 5-10 years.

Alveolar Echinococcus species from Vulpes corsac in Hulunbeier, Inner Mongolia, China, and differential development of the metacestodes in experimental rodents

Adults of alveolar Echinococcus species with different uterine structures were collected from Vulpes corsac in the Hulunbeier Pasture of Northeastern China in 2001. They were Echinococcus multilocularis Leuckart, 1863 (type No. 3, similar to E. m. multilocularis), with vaselike uterus; Echinococcus cf. sibiricensis Rausch et Schiller, 1954 (type No. 1), with pyriform uterus; and Echinococcus sp. (type No. 2) with spherical uterus at segment top. The metacestode development in rodents also differed among those 3 parasites. In the case of E. multilocularis (type No. 3), many germinal cells grew on the inner surface of early cysts, most of which metastasized into host tissue to form brood vesicles or from the germinal cell layer on the inner surface of the vesicle wall. Cells also had an appearance of proliferating by means of alveolar buds from alveolar tissue that developed outward to form new alveolar foci. In Echinococcus cf. sibiricensis (type No. 1), the formation of alveolar vesicles was due to the metastasizing of germinal tissue into host tissue; protoscoleces grew in the center of alveolar vesicles. In type No. 2 (Echinococcus sp.), the formation of the alveolar vesicle was by multiplication of germinal cell layers on the inner surface of alveolar cysts; protoscoleces grew from the germinal cell layer and mesh in the vesicles. On the basis of uterine structure and on differences in development of metacestodes in experimental rodents, we propose that the 3 types of Echinococcus represent 3 independent species: E. multilocularis, Echinococcus sibiricensis, and Echinococcus sp. (type No. 2-as yet under study).

Hydatid cysts: does every picture tell a story?

Ultrasound imaging is an effective aid to the detection of abdominal cystic echinococcosis. Recently, the images produced have provided more information than just a diagnosis. Different cyst morphologies have been classified into types, and such classifications can be considered to represent a natural history of cyst development. Understanding how cyst structures alter with time is crucial to evaluating the effectiveness of different treatment regimes and to understanding natural degeneration of cysts that can occur. However, the developmental events seen in ultrasound need to be matched more closely to immunological and cellular events if we are to have a fuller appreciation of disease progression and regression. At a community level, the relative proportions of cyst types could also provide epidemiological information on disease transmission.

Echinococcus shiquicus, a new species from the Qinghai–Tibet plateau region of China: Discovery and epidemiological implications

In Shiqu County of the Qinghai-Tibet plateau, many wild and domestic mammals are involved in the transmission cycles of Echinococcus spp. Echinococcus multilocularis and Echinococcus granulosus genotype G1 (sheep strain) are sympatrically distributed in the plateau. In 1995, we identified a unique strobilate stage of Echinococcus from the Tibetan fox, Vulpes ferrilata, but considered it to be a variant of E. multilocularis. Subsequent molecular genetic studies revealed that a hydatid cyst from the plateau pika, Ochotona curzoniae, had unique mitochondrial DNA sequences which are dissimilar to any published sequences of Echinococcus. The same sequences were subsequently found in adult worms from Tibetan foxes. Morphological, genetic and ecological features of the cestode led us to designate a new species Echinococcus shiquicus. E. shiquicus has been found at other areas surveyed on the plateau; however, no infections in humans caused by E. shiquicus have been yet identified.

The molecular mechanisms of larval cestode development: first steps into an unknown world

Several hundred million years ago, the free-living ancestors of all extant helminth parasites decided to colonize entirely new habitats, the bodies of other metazoan animals. As a consequence of the resulting adaptation processes, they evolved highly complex life-cycles in which many developmental transitions were initiated and controlled by host-derived signals. Understanding the molecular basis of the original developmental mechanisms, and the modifications that occurred during co-evolution with the host, is not only fundamental to our understanding of parasitism but also highly relevant for the design of anti-parasitic drugs and vaccines. In the past several years, molecular investigations on parasitic nematode and trematode development have made considerable progress and, supported by respective genome sequencing projects and emerging methods of genetic manipulation, will be a flourishing field in the years to come. We consider it time that corresponding studies are also pushed for the third large group of parasitic helminths, the cestodes. Here, we review the first experimental steps into that area, which have been undertaken recently. We report on cestode genomics, the identification of signaling factors associated with larval development, and the establishment as well as improvement of in vitro cultivation systems by which cestode life-cycles can be studied in the laboratory.

Methods for assessing the burden of parasitic zoonoses: echinococcosis and cysticercosis

Cysticercosis and echinococcosis cause illness and productivity losses in human and agricultural animal populations. Recent studies suggest that these diseases have large societal impacts on endemic areas. Estimates of burden provide essential, evidence-based data for conducting cost-benefit and cost-utility analyses that will secure political will, and financial and technical resources. To evaluate the burden, the monetary and non-monetary impacts of these zoonoses on human health, agriculture and society must be considered comprehensively. In this article, we review the framework used to assess the burden of cysticercosis and echinococcosis, and the data needed to estimate the extent of the problem for societies.

Immunobiology of cystic echinococcosis

The present report focuses on the ability of cystic echinoccocosis metacestode to survive for a long time, despite host immunity, by developing avoidance strategies. The tactics believed to come into play, ranging from intrinsic parasitic factors to host-related mechanisms, are briefly discussed and the importance of studies on experimental models is highlighted particularly in relation to furthering the theoretical understanding of the dynamic equilibrium between host and parasite, and to the feasibility of practical approaches in controlling the disease by artificial manipulation of the immunoregulatory mechanisms.

Characterization of excretory-secretory products from protoscoleces of Echinococcus granulosus and evaluation of their potential for immunodiagnosis of human cystic echinococcosis

This study describes, for the first time, the characterization of excretory-secretory antigens (ES-Ag) from Echinococcus granulosus protoscoleces, evaluating their usefulness in the immunodiagnosis of human cystic echinococcosis. ES-Ag were obtained from the first 50 h maintenance of protoscoleces in vitro. This preparation contained over 20 major protein components which could be distinguished by 1-dimensional SDS-PAGE with apparent masses between 9 and 300 kDa. The culture of of protoscoleces from liver produced a greater variety of excretory-secretory protein components than those from lung. Determination of enzymatic activities of secreted proteins revealed the presence of phosphatases, lipases and glucosidases, but no proteases. These findings were compared to those obtained from somatic extracts of protoscoleces and hydatid cyst fluid products. Immunochemical characterization was performed by immunoblotting with sera from individuals infected by cystic echinococcosis (n = 15), non-hydatidic parasitoses (n = 19), various liver diseases (n = 24), lung neoplasia (n = 16), and healthy donors (n = 18). Antigens with apparent masses of 89, 74, 47/50, 32, and 20 kDa showed specificity for immunodiagnosis of human hydatidosis. The 89 and 74 kDa components corresponded to antigens not yet described in E. granulosus, whereas proteins of 41-43 kDa and 91-95 kDa were recognized by the majority of the non-hydatid sera studied.

In vitro effects of nitazoxanide on Echinococcus granulosus protoscoleces and metacestodes

OBJECTIVES

Infection of humans and domestic ruminants with the larval stage (metacestode) of Echinococcus granulosus results in cystic echinococcosis (CE). The metacestode causes a space-occupying lesion in visceral organs, most commonly in the liver. Benzimidazole carbamate derivatives, such as mebendazole and albendazole, are currently used for chemotherapeutic treatment of CE. In human patients, benzimidazoles have to be applied in high doses for extended periods of time, and adverse side effects are frequently observed. In order to evaluate alternative treatment options, the in vitro efficacy of nitazoxanide, a broad-spectrum drug used against intestinal parasites and bacteria, was investigated.

METHODS

Freshly isolated E. granulosus protoscoleces were subjected to nitazoxanide treatment (1, 5 and 10 microg/mL), and the effects on parasite viability were monitored by Trypan Blue staining and scanning electron microscopy. Protoscolex cultures were maintained further, until metacestode development took place. Metacestodes were then subjected to nitazoxanide treatment (10 microg/mL), and corresponding effects were visualized by scanning and transmission electron microscopy.

RESULTS

Dose-dependent protoscolex death within a few days of nitazoxanide treatment was observed. Subsequent in vitro culture of drug-treated protoscoleces confirmed the non-viability of parasites, while further cultivation of non-treated protoscoleces for a period of at least 3 months resulted in stage conversion and the formation of small metacestodes 3-4 mm in diameter. Nitazoxanide had a deleterious effect on these metacestodes, which was comparable to that of albendazole.

CONCLUSIONS

Our study indicates a potential for nitazoxanide as an alternative treatment option against CE.

Echinococcus granulosus: oncosphere-specific transcription of genes encoding a host-protective antigen

A recombinant antigen vaccine has been developed which is effective in preventing the hydatid parasite, Echinococcus granulosus from infecting its animal intermediate hosts. The vaccine antigen, designated EG95, is expressed by a cDNA cloned from E. granulosus oncosphere mRNA. The gene encoding EG95 belongs to a small gene family where six of the members are transcribed in the oncosphere. Conditions were established which allowed specific RT-PCR amplification of mRNA for each gene family member and these conditions were applied to determine transcription patterns for each gene family member in gravid adult worms, oncospheres, and protoscoleces. The four eg95 gene family members which encode an identical EG95 protein, were transcribed only in the oncosphere. In contrast, two gene family members that encode variant EG95 proteins did not have transcription patterns confined to the oncosphere. These findings suggest a common biological role for four genes in the gene family and a separate role for the other, more variant gene family members.

Salvage treatment with amphotericin B in progressive human alveolar echinococcosis

Most patients with alveolar echinococcosis are diagnosed at a late stage when the disease has advanced to unresectable hepatic lesions. These patients require lifelong therapy with benzimidazoles, the only medical treatment currently available. To date, no treatment option remains for patients with benzimidazole intolerance or treatment failure. Amphotericin B was recently shown to exert antiparasitic activity in vitro. Here, we report the efficacy of amphotericin B in human alveolar echinococcosis. In three patients with extensive disease and without further treatment options, disease progression had been documented over several months. They were treated with amphotericin B intravenously at a dose of 0.5 mg/kg of body weight three times per week. Follow-up parameters were physical examination, laboratory parameters, and imaging techniques. Amphotericin B treatment effectively halted parasite growth in all three patients. The antiparasitic effect was most evident by spontaneous closure of cutaneous fistulae in two patients and by constant size of parasitic lesions during treatment, as assessed radiologically. Metabolic activity in parasitic areas was visualized by positron emission tomography and significantly decreased during treatment. However, progressive affection of the heart in one patient could not be stopped. All patients currently continue on amphotericin B and have been treated for 25, 17, and 14 months, respectively. We introduce amphotericin B as salvage treatment for alveolar echinococcosis patients with intolerance or resistance to benzimidazoles, as it effectively suppresses parasite growth. Amphotericin B is not parasitocidal; therefore long-term treatment has to be anticipated.

The Echinococcus granulosus antigen EgA31: localization during development and immunogenic properties

EgA31 is a fibrillar protein from Echinococcus granulosus that behaves as a potent antigen during infestation of dogs. The localization of this antigen during development of the parasite was investigated by immunohistochemistry in optical and electron microscopy. The protein is mostly abundant in the microtriches and subtegumental cells of the adult, whereas it is absent from protoscolex microtriches. Eggs, the periphery of calcareous corpuscles, and the germinal layer were other sites of accumulation. Immunogenicity of different domains of the protein was assessed during experimental infection of dogs. It was shown that the polypeptide encoded by the Pst I-Hind III fragment of the complete cDNA is the most antigenic during the infection. The uses of such polypeptide for infection diagnosis and as a candidate vaccine protein are discussed.

Transmission dynamics and control options for Echinococcus granulosus

Cystic echinococcosis, caused by the larval stage of Echinococcus granulosus, is a global public health problem. Whilst in a few localities, such as New Zealand, the parasite has been effectively controlled or even eradicated, in most endemic regions it remains a persistent problem. In some areas, such as the former Soviet Union, the disease incidence in humans has increased rapidly in recent years. It is important to have an understanding of the transmission dynamics, both between dogs and domestic livestock where the parasite maintains itself and from dogs to people. It is from this knowledge that effective control measures can be devised to reduce the prevalence of the parasite in animals and hence reduce the incidence of human disease. Mathematical models to describe the transmission of the parasite and the effects of different control strategies were first proposed over twenty years ago. Since then further information has been acquired, new technology has been developed and better computing technology has become available. In this review, we summarise these developments and put together a theoretical framework on the interpretation of surveillance information, how this affects transmission and how this information can be exploited to develop new intervention strategies for the control of the parasite. In particular, the parasite remains a persistent or re-emerging problem in countries of low economic output where resources for an intensive control programme, that has been successful in rich countries, are not available. By understanding of the transmission biology, including mathematical modelling, alternative and cost-effective means of control can be developed.

Transmission ecology of Echinococcus in wild-life in Australia and Africa

Following the introduction of E. granulosus into Australia with domestic animals during European settlement, the parasite quickly became established in the E. granulosus-naive native animals of the continent. The distribution of E. granulosus in wildlife in Australia is restricted by rainfall, but nevertheless the parasite is currently widespread and highly prevalent in many areas including numerous national parks and privately owned farms. The human population of Africa is rapidly increasing resulting in ever more pressure on wild-life populations and habitat. National parks, reserves and conservation areas now provide important tracts of preserved habitat for maintaining populations of wildlife that are also important in the maintenance of E. granulosus. In some parts of Africa, hydatid-infected humans provide a source of E. granulosus infection to wildlife definitive hosts. In many areas felids may also act as important definitive hosts for E. granulosus with the parasite being maintained in a prey/predator relationship between lions and a range of intermediate hosts. Populations of E. granulosus-infected wild-life both in Australia and Africa act as important reservoirs in perpetuating the transmission of E. granulosus to both domestic animals and humans. In Australia, E. granulosus-infected wild-life is infiltrating urban areas and currently represents a potentially important new public health problem.

Molecular epidemiology of cystic echinococcosis

Echinococcus granulosus exhibits substantial genetic diversity that has important implications for the design and development of vaccines, diagnostic reagents and drugs effective against this parasite. DNA approaches that have been used for accurate identification of these genetic variants are presented here as is a description of their application in molecular epidemiological surveys of cystic echinococcosis in different geographical settings and host assemblages. The recent publication of the complete sequences of the mitochondrial (mt) genomes of the horse and sheep strains of E. granulosus and of E. multilocularis, and the availability of mt DNA sequences for a number of other E. granulosus genotypes, has provided additional genetic information that can be used for more in depth strain characterization and taxonomic studies of these parasites. This very rich sequence information has provided a solid molecular basis, along with a range of different biological, epidemiological, biochemical and other molecular-genetic criteria, for revising the taxonomy of the genus Echinococcus. This has been a controversial issue for some time. Furthermore, the accumulating genetic data may allow insight to several other unresolved questions such as confirming the occurrence and precise nature of the E. granulosus G9 genotype and its reservoir in Poland, whether it is present elsewhere, why the camel strain (G6 genotype) appears to affect humans in certain geographical areas but not others, more precise delineation of the host and geographic ranges of the genotypes characterised to date, and whether additional genotypes of E. granulosus remain to be identified.

Echinococcus granulosus in Jordan: assessment of various antigenic preparations for use in the serodiagnosis of surgically confirmed cases using enzyme immuno assays and the indirect haemagglutination test

The Enzyme linked immunosorbent Assay (ELISA), indirect haemagglutination (IHA), and immunoblot techniques (IB) were used for the serodiagnosis of surgically confirmed cystic echinococcosis (CE) caused by the tapeworm Echinococcus granulosus. Antigens used for the detection of IgG or total antibodies included crude sheep hydatid fluid (CSHF), autoclaved antigen B (AAB), boiled antigen B (BAB), and homogenate protoscoleces antigen (HPA). The overall sensitivity of the ELISA and IHA tests used for the serodiagnosis of 57 surgically confirmed human cases was 91.2% and 68.4%, respectively. The sensitivity of both tests was comparable in groups whose sera were collected one week before surgery and up to one year after surgery at 95.8% and 87.5%, respectively. In contrast, the sensitivity of the ELISA was significantly higher than that of IHA for sera of patients collected after one year of surgery. There was a positive correlation (r = 0.61) between the titers of antibodies detected by the ELISA and IHA. Using the IB technique, antigen B fractions (8/12, 16, and 24 KDa) were detectable by sera of 68.4% using either CSHF or AAB, 49.1% using BAB and 22.8% using HPA as detecting antigens. The overall sensitivity of the three AgB fractions was identical or similar to that of the 8/12 KDa fraction alone, indicating that the detection of the latter fraction is sufficient for the serodiagnosis of CE infection in humans. In conclusion, the ELISA is the test of choice for the serodiagnosis of CE and the follow up of cases following surgery using CSHF as an antigen. The IB test is a confirmatory test when antigen B fractions of CSHF or AAB are detected.

Surgical treatment of hepatic hydatid cyst

Hydatid disease of the liver is caused by the tapeworm Echinococcus granulosus, and the highest incidence of human infestation occurs in sheep and cattle-raising areas. Although, still an uncommon occurrence, it is being seen with increasing frequency; hence, it is important that surgeons make themselves aware of the pathology and treatment of the disease. The liver is most commonly involved, although many other organs, including lungs and brain may also be affected. An echinococcal cyst of the liver was reported in a patient who is a resident in Northern Ireland but had originally lived and worked in mainland Britain. Details of the lifecycle, pathology, diagnostic techniques and surgical management of hydatid cysts are reviewed.

Molecular cloning, expression, and serological evaluation of an 8-kilodalton subunit of antigen B from Echinococcus multilocularis

Full-length cDNA and genomic DNA encoding an 8-kDa subunit of antigen B from Echinococcus multilocularis (designated EmAgB8/1) were isolated from an E. multilocularis metacestode cDNA library and a protoscolex genomic DNA library, respectively. The open reading frame of the cDNA clone encodes a polypeptide comprising 85 amino acids with a 20-amino-acid NH(2)-terminal signal sequence, which was confirmed following N-terminal sequencing of the native antigen. Reverse transcription-PCR analysis revealed that the clone encoding EmAgB8/1 is predominantly transcribed in larval E. multilocularis. The gene consists of two exons (encoding the signal sequence and mature protein) separated by a 91-bp intron. The mature form was expressed in Escherichia coli, and its antigenic reactivity was compared with that of a counterpart, an 8-kDa subunit of antigen B from Echinococcus granulosus (EgAgB8/1) by Western blotting and enzyme-linked immunosorbent assay (ELISA) with serum samples from patients confirmed to have cystic echinococcosis (CE) and alveolar echinococcosis (AE). Recombinant EmAgB8/1 showed positive reactions in Western blots with 81.3% (65 of 80) of serum samples from CE patients and 40.6% (26 of 64) of serum samples from AE patients, while recombinant EgAgB8/1 showed positive reactions with 86% (43 of 50) and 42% (19 of 45) of the serum samples from these CE and AE patients, respectively. By the ELISA, both EmAgB8/1 and EgAgB8/1 exhibited similar positive reactions with 88% (44 of 50) of serum samples from CE patients and 37.8% (17 of 45) serum samples from AE patients. Statistical analysis revealed that the sensitivity of EmAgB8/1 was comparable to that of EgAgB8/1 for the serodiagnosis of echinococcal diseases. There was no cross-reaction with sera from patients with cysticercosis, which often cross-react when native antigens are used for serodiagnosis.

Echinococcus granulosus coproantigens: chromatographic fractionation and characterization

Dogs infected with adult tapeworms of Echinococcus granulosus release antigens (coproantigens) in faeces which can be detected by a capture ELISA. Supernatants prepared from E. granulosus-infected dog faecal samples were fractionated by size-exclusion fast protein liquid chromatography (FPLC) on a Superose-6 column. Coproantigen ELISA and Western blotting were used to demonstrate the immunoreactivity of eluted fractions. Two main FPLC peaks of antigenic activity were detected and designated as fraction F1 and fraction F2 with approximate relative molecular weights > 670 kDa, and in the range of 146 to 440 kDa respectively. These two antigenic fractions (F1 and F2) fractionated from infected dog faeces were heat stable and largely protease-insensitive, but were highly sensitive to sodium periodate treatment, which strongly suggested the involvement of carbohydrates. Capture IgG antibodies against E. granulosus proglottis somatic extracts, detected a molecule with an approximate molecular weight of 155 kDa in fraction F2 after immunoblotting. The 155 kDa antigen could be completely ablated by sodium periodate treatment, but not after protease or lipase treatment. A surface tegument preparation of adult E. granulosus tapeworms contained large amounts of antigen that corresponded in size range and antigenicity to that observed in the FPLC fraction F2. There was also a peak of antigenic activity at > 670 kDa corresponding to fraction F1 from a culture derived excretory-secretory (E-S) adult tapeworm preparation. The involvement of carbohydrate moieties in coproantigen activity present in the FPLC fractions F1 and F2 from faecal supernatants of E. granulosus-infected dogs was confirmed by lectin-binding assays and exoglycosidase treatment, which showed that alpha-D-mannose and/or alpha-D-glucose, beta-galactose and N-acetyl-beta-glucosamine residues were the most important carbohydrate components in putative coproantigens present in both fractions. N-acetyl-beta-glucosamine and sialic acid residues were also contained in coproantigen molecules present in fraction F2. These results suggested that coproantigens detected in faeces of E. granulosus-infected dogs are large molecular weight molecules that may be derived from the carbohydrate-rich surface glycocalyx of adult worms, and are shed, released or secreted during the life-span of the tapeworm.

Effect of two formulations of benzimidazole carbamates on the viability of cysts of Echinococcus granulosus in vivo

Two different preparations, solution and suspension, of three benzimidazole carbamate drugs, mebendazole, albendazole and ricobendazole, were compared by analyzing their in vivo activity against Echinococcus granulosus cysts in a mouse model. Polyvinylpyrrolidone was used for the elaboration of drug solutions and these formulations manifested better results in terms of reduction of number of viable hydatid cysts in mice than the reference drug suspensions. The effect was more prominent on mebendazole-treated mice, at doses of 25-50 mg/kg. There was a correlation between ED50 and pharmacokinetical parameters of AUC0-infinity and Cmax, showing that a significant improvement on solubility affects the in vivo activity of these drugs.

Application of ultrasound in diagnosis, treatment, epidemiology, public health and control ofEchinococcus granulosusandE. multilocularis

The last 30 years have seen an impressive use of ultrasonography (US) in many fields of veterinary and clinical medicine and the technique is being increasingly applied to a wide variety of parasitic infections including the cestode zoonosesEchinococcus granulosusandE. multilocularis. US provides real-time results which are permanently recordable with a high resolution and diagnostic accuracy. These properties, coupled with the clinical value of the images obtained and the non-invasive nature of the test which is safe, require no special patient preparation time; it is easy to operate and this has resulted in the establishment of US as the diagnostic technique of choice for cystic (CE) and alveolar (AE) echinococcosis. The lack of ionizing radiation and side-effects mean that examination times are not restricted. The hand-held probes facilitate what amounts to a rapid, bloodless non-invasive laparotomy, enabling a search from an infinite number of angles for lesions producing information on their number, size and type of cysts, their location and clinical implications. Such clinical information has facilitated the development of treatment protocols for different cyst types. Less invasive surgical techniques, such as US guidance for PAIR (Puncture, Aspiration, Injection, Re-aspiration), PAIRD (PAIR plus Drainage) or PPDC (Percutaneous Puncture with Drainage and Curettage) are also possible. Longitudinal US studies have facilitated monitoring the effects of the outcome of treatment and chemotherapy. Portable ultrasound scanners which today weigh as little as a few pounds, powered by battery or generators have facilitated the use of the technique in mass community-based screening studies. The majority of these studies have been conducted in remote, low socio-economic areas where there were few, if any, hospitals, veterinary facilities, schools or trained personnel. The surveys led to the discovery of unexpectedly high prevalences of CE and AE in asymptomatic individuals of endemic areas and especially amongst transhumant or nomadic pastoralists living in various parts of the world. Screening for CE and AE is justified as an early diagnosis leads to a better prognosis following treatment. The application of US in field and clinical settings has led to a better understanding of the natural history of CE and AE and to the development of a WHO standardized classification of cyst types for CE. This classification can be used in helping define the treatment options for the different cysts found during the surveys, which in turn can also be used to calculate the public health cost of treating the disease in an endemic community. The case mix revealed can also influence the specificity (particularly proportions of cyst types CE4 and CE5 and cystic lesions – CL) of US as a diagnostic test in a particular setting. Community based US surveys have provided new insights into the public health importance of CE and AE in different endemic settings. By screening whole populations they disclose the true extent of the disease and reveal particular age and sex risk factors. Through the treatment and follow-up of all infected cases found during the mass screening surveys a drastic reduction in the public health impact of the disease in endemic communities can be achieved. Educational impacts of such surveys at the national, community and individual levels for both professional and lay people are beginning to be appreciated. The translation of the information gained into active control programmes remains to be realized. In areas where intermediate hosts, such as sheep and goats, are not slaughtered in large numbers mass US screening surveys to determine the prevalence of CE in livestock has proved possible. Longitudinal studies in such intermediate hosts would reveal changes in prevalence over time, which has been used as a marker for control success in other programmes. Mass US screening surveys in an ongoing control programme in Argentina has demonstrated the early impact of control in the human population and identified breakthroughs in that control programme. Mass US screening surveys must adhere to the highest ethical standards and the outcome of surveys should result in the application of appropriate WHO recommended treatment options for different cyst types. Follow-up strategies have to be in place prior to the implementation of such surveys for all infected individuals who do not require treatment and for all suspected, but not confirmed, cases found during the surveys. The use of US in community screening surveys has revealed the complexity of ethical issues (informed consent, confidentiality, follow-up, detection of lesions that are not the focus of the study etc) and also provided real solutions to providing the most ethical guidelines for the early detection and treatment of CE and AE.

Cystic echinococcosis in the Arctic and Sub-Arctic

The northern biotype ofEchinococcus granulosusoccurs throughout the holarctic zones of tundra and taiga, from eastern Fennoscandia to the Bering Strait in Eurasia and in North America from arctic Alaska approximately to the northern border of the United States. The cycle of the cestode is complex in taiga at lower latitudes, because of the greater diversity of potential hosts. In the Arctic and Subarctic, however, four patterns of predator/prey relationships may be discerned. Two natural cycles involve the wolf and wild reindeer and the wolf and elk (moose), respectively. Where deer of the two species coexist, both are prey of the wolf; the interactions of the wolf and elk are here described on the basis of long-term observations made on Isle Royale (in Lake Superior near the southern limit of taiga), where only the wolf and elk serve as hosts forE. granulosus. A synanthropic cycle involving herding-dogs and domesticated reindeer caused hyperendemicity of cystic echinococcosis in arctic Eurasia, mainly in northeastern Siberia. The 4th pattern, a semi-synanthropic cycle, formerly existed in Alaska, wherein sled-dogs of the indigenous hunters became infected by consuming the lungs of wild reindeer. The sequence of changes in life-style inherent in the process of acculturation affected the occurrence of cystic echinococcosis among nomadic Iñupiat in arctic Alaska. When those people became sedentary, the environs of their early villages soon became severely contaminated by faeces of dogs, and cases of cystic echinococcosis occurred. Compared to cystic echinococcosis caused byE. granulosusadapted to synanthropic hosts (dog and domestic ungulates), the infection produced by the northern biotype is relatively benign. Nearly all diagnosed cases of cystic echinococcosis (>300) in Alaska have occurred in indigenous people; only one fatality has been recorded (in a non-indigenous person). After sled-dogs were replaced by machines, cases have become rare in Alaska. A similar effect has been observed in Fennoscandia, in the Saami and domesticated reindeer. Recent records indicate that the prevalence of cystic echinococcosis is increasing in Russia, suggesting that dogs are used there in herding.

Molecular tools for studies on the transmission biology ofEchinococcus multilocularis

Two novel approaches for diagnosis of intestinalEchinococcus multilocularisinfection, the detection ofE. multilocularis-specific coproantigens in ELISA and of copro-DNA by PCR, have been successfully implemented. These methods have proven their value for thepost mortemand theintra vitamdiagnosis ofE. multilocularisin definitive hosts. They have also made novel approaches possible to study the transmission biology of the parasite as they allow detection of the infection in faecal samples collected in the environment. Coproantigen detection is the diagnostic method of choice as it is sensitive, fast and cheap. Studies on faecal samples collected in the field revealed that coproantigen detection did reflect the different prevalences in fox populations as assessed from foxes at necropsy and also the effect of deworming efforts in foxes as achieved by long-term distribution of praziquantel-containing baits. The use of PCR for routine diagnostic or large-scale purposes is hampered by the fact that DNA extraction from faecal material is a very laborious task. Therefore, PCR is rationally used for confirmatory purposes of copro-antigen-positive samples. As taeniid eggs cannot further be differentiated morphologically, PCR is the method of choice to identifyE. multilocularisinfections in faecal or environmental samples containing taeniid eggs. In intermediate rodent hosts, PCR is routinely used in epidemiological studies for identifyingE. multilocularisfrom liver lesions which are often very small, atypical or calcified.

Long-term in vitro cultivation of Echinococcus multilocularis metacestodes under axenic conditions

We report here on the development of an in vitro system for the long-term cultivation of Echinococcus multilocularis larvae under axenic conditions. In the absence of feeder cells from the host, long-term survival of the parasite depended strictly on low oxygen conditions and the presence of reducing agents in the medium. Host serum supported survival of the parasite but the growth of metacestode vesicles and differentiation towards the protoscolex stage only occurred in the presence of culture medium that was preconditioned by hepatoma cells or several other immortal cell lines. On the basis of this in vitro system, future analyses on the identification of host-derived growth factors for E. multilocularis will be greatly facilitated.

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.

Functional expression and characterization of Echinococcus granulosus thioredoxin peroxidase suggests a role in protection against oxidative damage

A full-length cDNA sequence coding for Echinococcus granulosus thioredoxin peroxidase (EgTPx) was isolated from a sheep strain protoscolex cDNA library by immunoscreening using a pool of sera from mice infected with oncospheres. EgTPx expressed as a fusion protein with glutathione S-transferase (GST) exhibited significant thiol-dependent peroxidase activity that protected plasmid DNA from damage by metal-catalyzed oxidation (MCO) in vitro. Furthermore, the suggested antioxidant role for EgTPx was reinforced in an in vivo assay, whereby its expression in BL21 bacterial cells markedly increased the tolerance and survival of the cells to high concentrations of H2O2 compared with controls. Immunolocalization studies revealed that EgTPx was specifically expressed in all tissues of the protoscolex and brood capsules. Higher intensity of labelling was detected in many, but not all, calcareous corpuscle cells in protoscoleces. The purified recombinant EgTPx protein was used to screen sera from heavily infected mice and patients with confirmed hydatid infection. Only a portion of the sera reacted positively with the EgTPx-GST fusion protein in Western blots, suggesting that EgTPx may form antibody-antigen complexes or that responses to the EgTPx antigen may be immunologically regulated. Recombinant EgTPx may prove useful for the screening of specific inhibitors that could serve as new drugs for treatment of hydatid disease. Moreover, given that TPx from different parasitic phyla were phylogenetically distant from host TPx molecules, the development of antiparasite TPx inhibitors that do not react with host TPx might be feasible.

Octenidine hydrochloride in hydatid disease

Hydatid disease is still endemic in many devoloping countries and continues to be an important cause of morbidity. The objective of this study was to determine the in vitro scolicidal effects of octenidine hydrochloride in different concentrations using different exposure times. After hydatid cyst liquid was left to precipitate for 1 h to obtain cystic sand, various concentrations of octenidine (undiluted, 1% and 0.1% diluted) were added to concentrated hydatid cyst sediments for 5, 10, 15, 20, 25, 30, 45, and 60 min, and scolicidal effects of octenidine were compared with 20% saline and control group for the same times. It was found that undiluted octenidine had a strong scolicidal effect at 15 min compared to saline at 20%. One percent octenidine had a scolicidal effect at 30 min. However, 0.1% octenidine did not have enough scolicidal effect in 1 h. It was concluded that undiluted and 1% diluted octenidine might be used for scolicidal purpose in the treatment of hydatid disease.

A model for the transmission of Echinococcus multilocularis in Hokkaido, Japan

A mathematical model for Echinococcus multilocularis transmission would be useful for estimating its prevalence and determining control strategies. We propose a mathematical model which quantitatively describes the transmission of E. multilocularis in Hokkaido, Japan. The model takes into account the influence of the dynamics of both the definitive and the intermediate host populations, which show large scale seasonal variation as they are wild animals. The simulations based on the model clarify the mechanism of seasonal transmission of E. multilocularis quantitatively, notwithstanding a lack of seasonal prevalence data. At present, human alveolar echinococcosis is prevalent throughout the mainland of Hokkaido. The risk of being infected in the human population has been investigated by analyzing the seasonal fluctuation in parasite egg dispersion in the environment. This is necessary for the planning of more suitable preventive measures against E. multilocularis.

Prevention of alveolar echinococcosis--ecosystem and risk management perspectives in Japan

We focused on the epidemiology of alveolar echinococcosis especially in Japan and discussed control measures to prevent an epidemic. No effective control measures against alveolar echinococcosis have been identified thus far because it is difficult to fully understand the ecology of the parasite and its hosts, i.e. the precise infection route to humans. In Hokkaido, Japan, infection rates among red foxes have recently risen even in low endemic districts. Infection seems to be spreading not only among wild foxes but also among domestic dogs. Despite only sporadic reports of human cases in Japan, we predict that the incidence of alveolar echinococcosis will increase in the near future if no effective preventive measures are put in place. An Echinococcus multilocularis epidemic would have the potential to affect the economy of Hokkaido, due to its impact on the agricultural and tourist industries. Well-designed epidemiological surveys are, therefore, urgently required prior to large outbreaks, based on understanding of the ecosystem around E. multilocularis.

Observations on the Development of Echinococcus multilocularis in Cats

The development of a European isolate of Echinococcus multilocularis was compared in cats and dogs at the end of the prepatent period. Echinococcus multilocularis established in all dogs and cats, but worm recovery was significantly greater from dogs than from cats. Overall, worms in cats were not as advanced as those in dogs in terms of development and maturation, but there was no evidence of retarded development or stunted forms. These results confirm that dogs are highly susceptible to E. multilocularis, whereas cats have lower and more variable recovery rates. However, because cats produce thick-shelled eggs of E. multilocularis after experimental and natural infections, they have to be regarded as potential sources of infection both for intermediate and accidental hosts, including humans. However, their general role in the epidemiology of the infection has yet to be determined.

Epidemiology of echinococcosis

BACKGROUND

Various species and infraspecific forms of the cestode genus Echinococcus are causative agents of human echinococcosis. Pathology, epidemiology and geographical occurrence vary widely between the different Echinococcus taxa. As a general rule, those forms of echinococcosis that are transmitted mainly by wild animals are rather rare, due to limited contact between humans and wildlife. This is the case with alveolar echinococcosis (AE) caused by Echinococcus multilocularis, the 'fox tapeworm' (except in regions where domestic dogs are heavily involved in the lifecycle), and for the South American endemic species E. oligarthrus and E. vogeli. On the other hand, most forms of cystic echinococcosis (CE) are transmitted in domestic lifecycles involving dogs and livestock and constitute an emerging public health problem, especially in regions with extensive livestock husbandry and non-supervised slaughter.

METHOD

This review focuses on two fields where a wealth of new information became available in recent years.

RESULTS AND CONCLUSIONS

New data demonstrate that ' E. granulosus', the causative agent of CE, is an assembly of several, rather diverse, species and genotypes that show fundamental differences, not only in their epidemiology, but also in their pathogenicity to humans. This fact may explain the unequal distribution of high-endemicity areas for human CE on regional scales, which previously, has been attributed to differences in human behaviour. In addition, new data suggest that E. multilocularis is expanding its geographical range in the northern hemisphere, and its transmission is intensifying, e.g. in central Europe. Moreover, the lifecycle (involving wild foxes and rodents) is rapidly becoming 'urbanised' due to the recent establishment of fox populations in cities and towns. This shift from sylvatic to synanthropic occurrence is likely to result in an increased pressure on the human population of infection from AE.

Controlling Echinococcus multilocularis-ecological implications of field trials

Two field trials to reduce the prevalence of Echinococcus multilocularis in foxes have been conducted in recent years. Although both trials reduced prevalence considerably, they failed to eradicate the parasite in the study region. Following the control trial in northern Germany, prevalence recovered unexpectedly and rapidly, reaching pre-control levels five quarters (15 months) after the end of control. To understand the internal dynamics of the parasite-host system's reaction to control, we developed a spatially explicit simulation model, Echi. The simulation model incorporates the information available concerning fox tapeworm population dynamics. Using epidemiological parameters to adjust pre-control prevalence, the model predicts the temporal evolution of the prevalence of E. multilocularis in controlled foxes without departing from the range of uncertainty of the field data. However, the model does not predict the rapid pre-control recovery observed in the field trial. The deviation of the model's prediction from field data indicates the involvement of processes not yet taken into account. We modified the model step by step to mimic processes with the potential to cause the rapid post-control recovery of the prevalence of E. multilocularis in foxes. Neither the longevity of tapeworm eggs nor the migratory behaviour of foxes showed any influence on the post-control reaction of the parasite-host system. However, landscape structures leading to a heterogeneous distribution of infected foxes have the potential to alter the system's reaction to control. If infected foxes are concentrated in multiple clusters in the landscape, the model prediction tallied with the range of uncertainty of the field data. Such spatial distribution of infected foxes may be caused by differential abiotic conditions influencing the survival of tapeworm eggs. The model was found to comply best with field data if the foxes acquire partial immunity by being exposed to the fox tapeworm. Both hypotheses explaining the rapid post-control recovery of the prevalence of E. multilocularis observed in the fox population were supported by field data. Both hypotheses have far-reaching consequences for future control trials. The spatial aggregation of infected foxes would enable control efforts to be concentrated on these highly infected areas. However, the acquisition of immunity acts as a buffer to control, necessitating intensified control measures.

[Baiting intervals and duration of control of the small fox tapeworm: a simulation study]

Field trials to control the small fox tapeworm Echinococcus multilocularis failed to reduce the prevalence of the parasite persistently. With the experience from this empirical work, a simulation model for the population dynamics of the small fox tapeworm was developed. This model is used to examine the effect of different control strategies. Sufficient control duration is able to eradicate the parasite in simulation experiments. Baiting intervals of 4 or 6 weeks were found to be more efficient than shorter or longer intervals. The strategy used in field trials showed no sustainable effect in any of the simulation experiments. The applicability of simulation models for the planning of control measures for wildlife diseases is discussed.

Effect of mouse strain variations and cortisone treatment on the establishment and growth of primary Echinococcus multilocularis hydatid cysts

The main purpose of this study was to determine the effects of cortisone on the number and size of primary Echinococcus multilocularis cysts developing in a moderately resistant strain of mice, i.e., C3H/HeJ. Computerized image analysis was used to measure the surface area occupied by hydatid cysts 10 wk after inoculation of the mice with E. multilocularis eggs. Our second objective was to compare the infectivity of primary E. multilocularis hydatid cysts in C57BL/6J-Ay/a (lethal yellow) mice with that in C57BL/6J-a/a (non-agouti black) mice. The data obtained show no difference between the C3H/HeJ and C57BL/6J-a/a strains of mice; yet, the image analysis method was able to detect a slight increase in the total cyst size within the Ay/a mutant of the C57BL/6J strain. Treatment of C3H/HeJ mice with cortisone drastically increased both the number of cysts and the average size of each cyst when the treatment occurred early in the infection.

Echinococcosis--an international public health challenge

This review aims to summarise some of the recent studies that have been undertaken on parasites of the genus Echinococcus and the diseases which they cause. Although the adult parasite, which inhabits the intestine of various carnivore species is not pathogenic, the larval or metacestode stages can be highly pathogenic, causing economic losses to livestock and various forms of echinococcosis in humans, some of which have a high fatality rate. There is growing evidence that there are at least 5 species of Echinococcus rather than the generally accepted 4 species. Within these species there are a number of genotypes or strains. This can have implications for surveillance and control. In some wealthy countries, cystic echinococcosis caused by Echinococcus granulosus has been successfully controlled or indeed eradicated. However, in most parts of the world it remains a serious threat to human health. In the former Soviet Union, the disease has rapidly increased in incidence after the end of communist administration. Human alveolar echinococcosis, caused by Echinococcus multilocularis, is more sporadic. However, in some Chinese communities there is a disturbingly high human prevalence and in Europe there has been an increase in the detection rate of E. multilocularis in animals in the last 10 years. Echinococcosis can present diagnostic challenges, particularly in the definitive host in areas of low endemicity. Much of the recent work relating to the use of coproantigen and PCR to overcome these difficulties is summarized. New ideas for controlling the parasite are becoming available and these include both the use of vaccination and the application of mathematical models to determine the most cost effective means of control. Effective measures that are affordable are vital if the parasite is to be controlled in poor countries.