Echinococcus granulosus protoscolex formation in natural infections

Echinococcus granulosus is a parasitic platyhelminth that is responsible for cystic hydatid disease. From the inner, germinal layer of hydatid cysts protoscoleces are generated, which are are the infective forms to the dog. Systematic studies on the cell biology of E. granulosus protoscolex formation in natural infections are scarce and incomplete. In the present report we describe seven steps in the development of protoscoleces. Cellular buds formed by a clustering of cells emerge from the germinal layer of hydatid cysts. The buds elongate and the cells at their bases seem to diminish in number. Very early on a furrow appears in the elongated buds, delimiting anterior (scolex) and caudal (body) regions. Hooks are the first fully-differentiated structures formed at the apical region of the nascent scolex. In a more advanced stage, the scolex shows circular projections and depressions that develop into suckers. A cone can later be seen at the center of the hooks, the body is expanded and a structured neck is evident between the scolex and the body. During protoscolex development this parasitic form remains attached to the germinative layer through a stalk. When fully differentiated, the stalk is cut off and the infective protoscolex is now free in the hydatid fluid.

Cytokine response and outcome of infection depends on the infective dose of parasites in experimental infection by Echinococcus granulosus

We here analysed whether the cytokine responses in early and late experimental infection with Echinococcus granulosus depend on the dose of parasites to which the host is exposed. To this purpose Balb/c mice were inoculated intraperitoneally (i.p.) with either 500 or 2000 protoscoleces. Splenocytes of mice were obtained at days 3, 7, 14 and 21 and also on week 37 post-infection and cultured in vitro with protoscolex antigens. Type-1 and type-2 cytokines were analysed in supernatants by ELISA. Results showed that the inoculation of 500 protoscoleces induced an early type-0 and a late type-2 cytokine response, whereas the inoculation of 2000 protoscoleces induced an early type-2 and a late type-0 cytokine response. Parasite growth was lower in the group inoculated with the low infective dose. These results indicate that the cytokine response during the infection by the helminth E. granulosus depends on the dose of parasites to which the host has been exposed.

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.

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

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

Performance characteristics and quality control of community based ultrasound surveys for cystic and alveolar echinococcosis

The probability of disease given the results of a test, is called the predictive value of the test. The predictive value of a test is not a property of the test itself but will vary according to the prevalence of the disease in the studied population. The positive predictive value (PPV) is the probability that the subject tested has the disease given that a positive result is obtained. The negative predictive value (NPV) is the probability that the subject tested is normal given that a negative result is obtained. As the prevalence of a disease in a population approaches zero so does the PPV and most of the positive cases will be 'false positives'. Conversely the NPV will be very high at low prevalences and there will be few 'false negative' results. The sensitivity and specificity of a test are properties of the test and do not vary with prevalence. The higher the sensitivity and specificity of a particular test the greater the predictive values will be at any given prevalence of the disease. Ultrasound (US) is increasingly used for detecting lesions due to cystic and alveolar echinococcosis (CE and AE) and portable US scanners facilitate community based mass screening surveys in remote rural communities. Screening is justified with AE and CE in endemic areas as diagnosis at an early stage can lead to a better prognosis following treatment. The sensitivity and specificity of US has been reported to be between 88-98% and 95-100% respectively for CE and the sensitivity is a little higher for AE. Both species have pathognomonic signs on US and the technique is considered to be the 'gold standard' although it is still an imperfect test. Clinical, laboratory and epidemiological data also play an important role in the diagnosis of CE and AE. US results where possible, should be evaluated in relation to these findings. Suspected CE and AE images, may benefit from the use of other imaging techniques such as magnetic resonance imaging, computerised tomography and in the case of AE angiography or cholangiography. Immunological tests or molecular biological techniques also provide a useful back up, especially for AE. As sensitivity and specificity are properties of the US diagnostic test they should not vary if the case mix reported in different studies remains the same. The use of the WHO standardised US classifications for CE and AE should be used so that the properties of the test are standardised. Quality control of field based studies will depend on geographical variations in the case mix and the relative proportions of cyst types without pathognomonic signs. The latter will have the most bearing on variations in specificity, as would the use of different classifications. Inter- and intra-observer variability and differences in prevalence will affect the performance of US in different endemic settings. Community based surveys must adhere to the highest ethical standards and the outcome of surveys should result in appropriate treatment and follow-up strategies for all infected individuals and suspected cases found during the surveys.

Predictive values and quality control of techniques for the diagnosis of Echinococcus multilocularis in definitive hosts

By the end of the 1980s the only reliable technique for diagnosing the intestinal Echinococcus multilocularis infection of definitive hosts was parasite detection at necropsy. Currently, several techniques for the post mortem and in vivo diagnosis are available, including classical and modern methods. The sedimentation and counting technique (SCT) is used for the exact determination of the worm burden in the intestine after necropsy. The SCT has high sensitivity and specificity values (both close to 100%) and can be regarded as 'gold standard'. The principle of the intestinal scraping technique (IST) is the stereomicroscopic examination of at least 15 intestinal thick smears. This technique has a sensitivity of 78% and a specificity approximating 100%. In recent years, the IST has been successfully used in large post mortem surveys of foxes for E. multilocularis. The newer techniques for detecting coproantigens by ELISA (CA-ELISA) exhibit rather high sensitivities between 84 and 95%, combined with very high specificities of >96%, the latter regarding non-Echinococcus cestodes and other parasites. However, cross-reactivity may occur with E. granulosus. Copro-DNA detection by PCR is also highly sensitive (89-94%) and specific (100%). With the SCT, IST and Copro-PCR one person can only examine about 10-20 animals per day, whereas the CA-ELISA allows the examination of 200 samples. Therefore, the latter test is suited for mass-screening of definitive host populations. Both the CA-ELISA and the Copro-PCR allow the examination of materials from dead and living animals, including faecal samples collected in the field. Quite often diagnostic techniques have been used without adequate quality control and proper definition of their performance characteristics, including diagnostic sensitivity, specificity, predictive values and some other parameters. Examples are presented with the aim to demonstrate the need and the value of calculating the predictive values for assays used to diagnose the E. multilocularis infection in individual animals and in definitive host populations.

National prevalence of larval echinococcosis in sheep in slaughtering plants Ovis aries as an indicator in control programmes in Uruguay

Diagnostic surveys carried out on ovine larval echinococcosis in slaughtering plants at a national level in 1998 made it possible to meet several objectives, i.e. to estimate the existing levels of prevalence, to evaluate the effectiveness of the control actions applied by the Programme against Hydatidosis and to contribute to the improvement of the health information systems for epidemiological surveillance. The work included sheep (Ovis aries), both lambs (2-4 teeth) and adults (6-8 teeth). A random sample was performed among sheep from the plants that slaughter the majority of animals in the country. The sample included 22 animals per herd, and it involved removing their offal (liver, lungs and heart) and processing serial sections at the laboratory. The histopathological studies were performed on the lesions that could not be adequately identified at gross examination, and those that were so small that had to be submitted for confirmation of the diagnosis. Of the 2035 animals that were examined, 1019 were lambs (2-4 teeth) and 1016 were adults (6-8 teeth). The prevalence of larval echinococcosis was 7.7% in lambs and 18.0% in adults. The overall prevalence in the liver was 8.5 and 8.0% in the lungs. As to the characteristics of the morphologic structures of the larvae, in younger animals 29% of the lesions were calcified, and 71.0% were hyaline, while in older animals the proportions were 34.4% calcified versus 65.6% hyaline. Other conditions found in the liver parenchyma included: white stain (0.8%), caseous lymphadenitis (3.0%), abscess (0.4%), larvae of Taenia hydatigena (5.1%), Fasciola hepatica (3.9%). And 1.7% of the animals presented larvae of Taenia ovis in the cardiac muscle. Previous surveys carried out in 1994 using the same methodology showed a prevalence of 15.2% in 2-4 teethed animals and 33.9% in 6-8 teethed animals, thus confirming that rates have decreased by 49.6 and 47.0%, respectively. The data obtained reflect the reduction of areas contaminated with eggs of Echinococcus granulosus, which would cause a loss in immunity against this parasite after a certain time. Prevalence of larvae T. hydatigena and T. ovis could change if more sites were considered, a fact that was confirmed in studies carried out in our country. The species O. aries must be used as an indicator in the control programmes, especially in the category of 2-4 teethed lambs. The fact they are not as frequent in our market must be considered; in 1998 they accounted for only 3.0% of the total numbers of animals.

Pro-inflammatory (IL-1beta, IL-18) cytokines and IL-8 chemokine release by PBMC in response to Echinococcus multilocularis metacestode vesicles

In humans infected with Echinococcus multilocularis, larval metacestodes will develop, proliferate and progressively infiltrate the surrounding host tissues by exogenous budding of parasitic microvesicles or cell lines which detach from the original tumour and thus become transported through blood or lymph vessels into other organs. Cellular effector mechanisms constitute the most effective means to restrict parasite persistence and proliferation, and here we demonstrate that E. multilocularis vesicle antigens will induce pro-inflammatory, regulatory and chemokine release by PBMC from patients. The pro-inflammatory cytokines IL-1beta and IL-18 were reduced in echinococcosis patients, regulatory IL-10 was similar, but parasite vesicle-induced IL-8 was dominant and clearly elevated in patients. Such selective and opposite dynamics of inflammatory cytokines and chemokine release may prevent overwhelming and pathogenic inflammation, and constitute an appropriate response for attraction of effector cells into the periparasitic tissues with the capacity to limit E. multilocularis metacestode proliferation and dissemination.

Effect of amphotericin B on larval growth of Echinococcus multilocularis

Alveolar echinococcosis is caused by the parasitic cestode Echinococcus multilocularis. Benzimidazoles, namely, mebendazole and albendazole, are the only drugs available for the treatment of inoperable alveolar echinococcosis. At present, no therapeutic alternative is available for patients with progressive disease under treatment or for patients who are unable to tolerate the side effects of the benzimidazoles. In addition, benzimidazoles are only parasitostatic for E. multilocularis. Thus, new therapeutic options are of paramount importance. In the present study we examined the in vitro effect of amphotericin B on E. multilocularis larvae. E. multilocularis metacestodes grown in the peritoneal cavities of Mongolian gerbils were transferred into a culture system. Vesicles budded from the tissue blocks and increased in number and size during the first 5 weeks. After 6 weeks drugs were added and deleterious effects on the vesicles were observed macroscopically and microscopically. By use of this in vitro tissue culture model we demonstrated that amphotericin B effectively inhibits the growth of E. multilocularis metacestodes. This destructive effect was significantly more rapid with amphotericin B than with the benzimidazoles. Cyclic treatment was effective in suppressing parasite growth. However, amphotericin B appears to be parasitostatic for E. multilocularis larvae, and regrowth occurs even after extended periods. In summary, amphotericin B constitutes the first promising alternative for the treatment of alveolar echinococcosis in cases of intolerance or resistance to benzimidazoles. It holds promise as an effective treatment option for otherwise fatal courses of disease.

Public health education/importance and experience from the field. Educational impact of community-based ultrasound screening surveys

The public health educational impact of community-based ultrasound (US) surveys for cystic echinococcosis (CE) can form an important part of the development about the awareness of the importance of the disease in an endemic area. In addition to identifying asymptomatic carriers and thereby facilitating early diagnosis and treatment, such surveys can be used to impart important educational messages at the individual, household, community, regional and national levels. US surveys are usually appealing to rural communities where such services are not available but where the technique is generally appreciated by its application in a wide field of medical applications. The qualities of the test (painless, non-invasive and gives instant recordable results) are also attractive to participants during such surveys and the majority of the population in a selected study area choose to be screened. Two such surveys were carried out amongst the Berber people of the mid-Atlas mountains in central Morocco in May 2000 and 2001. Over 11,000 people were screened in the two 10-day surveys. Informed consent had been obtained through community meetings and with the chiefs of villages prior to the surveys being conducted. Individuals who volunteered to be screened entered the study and as far as is known there were no refusals. The concept of voluntary participation, the explanation of the life cycle and clinical manifestations of the disease and its prevention are all-important educational messages. The occurrence of CE is almost always known in an endemic community but is usually very poorly understood leading in many cases to a fear of the disease, especially amongst families with an infected individual who has previously undergone surgery. During the US survey considerable attention was paid to provide educational input before, during and after the survey. Information was provided at the start of the survey to local leaders, doctors, veterinarians and school teachers on the aims of the study and to obtain informed consent. At the start of the study everyone was individually schooled about the route of transmission of the parasite and how this may be best prevented. The knowledge level of those screened was assessed by showing hydatid cysts, either freshly obtained from the abattoir of from photographs. Animal cysts were recognised by almost everyone but its transmission and link to human disease was invariably unknown. Patients found to be infected with CE were always confidentially counselled and followed up for treatment, if required. Treatment options were explained to the individual or to parents in the case of a child. Local physicians participated in discussions on the WHO guidelines for the treatment of CE and all cases were fully discussed providing an educational element for the local doctors. The 1% US prevalence found sent an important message to the local politicians and the perceived importance of the disease had an impact at the leadership level. Local leaders made calls for a control programme. The long term educational impact remains to be evaluated as does the role such surveys play in the future collaboration of communities with the implementation of a control programme.

Latex agglutination test (LAT) for antigen detection in the cystic fluid for the diagnosis of cystic echinococcosis

Latex agglutination test (LAT) was standardized and evaluated to detect hydatid antigen in fluid samples aspirated from 6 surgically proved human cases of cystic echinococcosis (CE), 4 suspected human cases of CE (2 cases of cysts in the liver which were not confirmed surgically and 2 cases of pelvic cysts later confirmed as abscesses) and 7 cases of hydatid cysts of liver in cattle. Echinococcus granulosus scolices and hook lets were seen in aspirated fluid by microscopy and the characteristic germinal layer of the cyst wall was demonstrated by histopathology in 6 human hydatid cysts operated and removed by surgery. In case of cattle hydatid liver cysts no scolices or hook lets were seen in aspirated fluid as they were sterile cysts but characteristic laminated layer of the cyst wall was demonstrated by histopathology of these cysts. The LAT could detect antigen in fluid samples collected from all 6 human cases of surgically proved CE and 7 cases of hydatid cyst liver in cattle, thus showing sensitivity of 100%. The LAT could detect antigen in fluid samples collected from 2 suspected cases of CE liver in humans, which were not operated. The LAT was found to be specific. No cross reactivity was observed. The results of the study showed that LAT could be employed as a simple and rapid diagnostic procedure, as an alternate to microscopy, to confirm the hydatid etiology of a suspected cyst.

Hydatid cyst of the liver-criteria for the selection of appropriate treatment

The appropriate treatment of hydatid cysts of the liver is determined by several factors, namely the patient, the cyst, the therapeutic resources and the physician. Characteristics of cysts, can be described by ultrasonography (US). Based on US images, we can classify hydatid cysts, according the evolutionary phase of the larval parasite and to choose the most appropriate therapeutic approach. US is also important to evaluate the efficacy of the treatment. Concerning the therapeutic methods, surgery had long been the only treatment available for the hydatid cyst of the liver. Beginning the 1970s benzimidazoles, Mebendazole and Albendazole, have been used for the treatment of the hydatid disease and in the early 1980s, with the development of diagnostic US, the deliberate puncture of abdominal cysts, particularly those in the liver, was evaluated this lead to puncture/aspiration, followed by injection of a scolicide which became a therapeutic method known as puncture, aspiration, injection and re-aspiration (PAIR). So, according to the cyst's characteristics based on US evaluation we can establish a therapeutic strategy: cysts type 1 and 3 may be treated by chemotherapy. Alternative treatment should be PAIR but only if the cysts cannot be treated with benzimidazoles. If there are contraindications for PAIR and chemotherapy the treatment should be surgical. Type 2 hydatid cysts can be treated by PAIR following initial treatment with benzimidazoles. If PAIR is not feasible or there is no evidence of degenerative changes after chemotherapy, surgery is indicated. Type 4 cysts are usually inactive and, in these cases, treatment is not indicated. If there is evidence that the cysts contents are still viable PAIR may be indicate. If PAIR is not possible, surgery is the method of choice. Cysts type 5 do not require treatment.

[Cystic echinococcosis (CE) in the Poznan region in the years 1990-2000]

The results of multidisciplinary studies on cystic echinococcosis (CE) in Poznan region, Poland carried out in 1990-2000, in co-operation with CDC, Atlanta GA, USA, are summarised as follows. The distinct focality of Echinococcus granulosus (Eg) infections has been demonstrated on some private farms rearing pigs (refs 12, 13). A reduction in Eg prevalence rates in pigs has been achieved, from 13.0% in 1989 down to 0.5% in 1998. This was an effect of various factors, including free treatment of all dogs in the Eg foci, i.e. farms, supplying infected pigs (ref. 13). The experimental studies confirmed, that pig's strain of Eg has some distinct characteristics, in comparison with the other Eg strains (ref. 8). It also had a separate genotype, classified as G7 (G9) (refs 9, 10). It has been demonstrated, that pig's strain was the only one found in 16 patients with CE, hospitalised in the Clinic of Parasitic and Tropical Diseases in Poznan, Poland (refs 9, 10) The same genotype in pigs was found in Slovakia and Ukraine (ref. 10). In clinical research the fine needle aspiration biopsy (FNAB) has been introduced in the doubtful cases and confirmed to be a safe and useful diagnostic technique (ref. 11). The FNAB material was examined for Eg protoscolices as well as for the presence of antigen 5 (ref. 24). Studies with intradermal Multiest suggested, that development of Eg cysts depend much on immune system, especially a switch between Th1 and Th2 (ref. 19). It has been observed that FNAB may have a beneficial effect on treatment of CE with albendazole, which can be reduced to 1 month only in the patients treated after FNAB (refs 11, 25, 26). The studies carried out were a basis for one habilitation (ref. 11) and 3 MD dissertations (13, 19, 23).

Echinococcosis: disease, detection and transmission

Echinococcosis is one of the world's most geographically widespread parasitic zoonoses, with transmission occurring in tropical, temperate and arctic biomes. Most human infections are due to Echinococcus granulosus transmitted between domestic dogs and livestock, but this cosmopolitan species also cycles between wild carnivores (principally canids) and wild ungulates. The other species with significant zoonotic potential is E. multilocularis that occurs naturally in fox definitive hosts and small mammal intermediate hosts. These two species cause human cystic or alveolar echinococcosis respectively, which may be considered serious public health problems in several regions including developed countries. This review provides an introductory overview to the Supplement and summarises the biology and epidemiology of these two related cestodes with an emphasis on applied aspects relating to detection, diagnosis and surveillance in animal and human populations, and includes aspects of transmission ecology, and also considers aspects of community epidemiology and potential for control.

Epidemiology of alveolar echinococcosis with particular reference to China and Europe

Human alveolar echinococcosis (AE), caused by the metacestode of the fox tapeworm Echinococcus multilocularis, is the most pathogenic zoonosis in temperate and arctic regions of the northern hemisphere. Prospective collection of human cases in some areas and mass screenings using ultrasound imaging and confirmation with serological techniques have markedly improved our knowledge of the epidemiology of the disease in humans during the past two decades. Transmission occurs when eggs of the tapeworm, excreted by the final hosts (usually foxes but also dogs, wolves and cats), are ingested accidentally by humans or during normal feeding by a variety of rodents and small lagomorphs. However, the species of host animals differ according to regional changes in mammalian fauna. This review mostly focuses on epidemiology of alveolar echinococcosis in those parts of the world where new and more accurate epidemiological data are now available, i.e. China and Europe, as well as on new epidemiological trends that can be suspected from recent case reports and/or from recent changes in animal epidemiology of E. multilocularis infection. The People's Republic of China (PRC) is a newly recognized focus on AE in Asia. Human AE cases were firstly recognized in Xinjiang Uygur Autonomous Region and Qinghai Provinces at the end of 1950s and infected animals were first reported from Ningxia in central China and northeast of Inner Mongolia in the 1980s. E. multilocularis (and human cases of AE) appears to occur in three areas: (1) Northeastern China (northeast focus): including Inner Mongolia Autonomous region and Heliongjiang Province (2) Central China (central focus): including Gansu Province, Ningxia Hui Autonomous Region, Sichuan Province, Qinghai Province and Tibet Autonomous Region and (3) Northwestern China: including Xinjiang Uygur Autonomous Region, bordered with Mongolia, Russia, Kazakhstan and Kyrgyzstan. The highest prevalence of the disease, up to 15 per cent of the population in some villages, is reached in China. In Europe, data from the European Echinococcosis Registry (EurEchinoReg: 1982-2000) show 53 autochthonous cases of AE in Austria, 3 in Belgium, 235 in France, 126 in Germany, 1 in Greece, and 112 in Switzerland, and 15 'imported' cases, especially from central Asia; 14 cases were collected in Poland, a country not previously considered endemic for AE. Improved diagnostic technology, as well as a real increase in the infection rate and an extension to new areas, can explain that more than 500 cases have been reported for these 2 decades while less than 900 cases were published for the previous 7 decades. New epidemiological trends are related to an unprecedented increase in the fox population in Europe, to the unexpected development of urban foxes in Japan and in Europe, and to changes in the environmental situation in many countries worldwide due to climatic or anthropic factors which might influence the host-predator relationship in the animal reservoir and/or the behavioural characteristics of the populations in the endemic areas.

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.

Short report: Echinococcus granulosus from Xinjiang, PR China: cDNAS encoding the EG95 vaccine antigen are expressed in different life cycle stages and are conserved in the oncosphere

The EG95-based vaccine protects sheep from infection with the dog tapeworm Echinococcus granulosus. The EG95 encoding gene is a member of a multigene family, several members of which are expressed in the oncosphere, believed to be the target of immunity induced by the vaccine. E. granulosus exhibits extensive intraspecific (strain) variation, and variability of the eg95 gene in different isolates of E. granulosus may directly impact the effectiveness of the EG95-based vaccine. We analyzed the eg95 gene from E. granulosus collected in Xinjiang, in northwest China, where hydatid disease is hyperendemic. The gene is expressed in oncospheres, protoscoleces, and immature and mature adult worms, and the eg95 gene family was shown to comprise two basic sequence types. Very limited sequence variation was evident in the EG95 protein from oncospheres. This high degree of sequence conservation predicts that the vaccine will continue to be effective in China and elsewhere.

Perspective on control options for Echinococcus multilocularis with particular reference to Japan

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

Multi-scale spatial analysis of human alveolar echinococcosis risk in China

Risk factors for the transmission of Echinococcus multilocularis to humans operate at a range of spatial scales. Over a large area, such as China, regional scale risk is correlated with variation in climatic conditions because of its effect on the spatial distribution of landscapes that can support E. multilocularis transmission in wildlife hosts and the probability of egg survival. At a local scale of a few kilometres, or tens of kilometres, transmission risk is related to the spatial proximity of human populations and landscapes with active transmission. At the patch scale, when considering individual villages or households, human behavioural factors are important and for individuals genetic and immunological factors play a role. Satellite remote sensing can provide landscape information at a range of spatial scales and provide a spatial framework within which to examine transmission patterns. This paper reviews the application of remotely sensed data and spatial data analysis to develop a better understanding of disease transmission and shows how such data have been used to examine human alveolar echinococcosis infection patterns, at a range of spatial scales, in an endemic area in central China.

Morphological variability and degenerative evolution of human hepatic hydatid cysts

The findings are presented of a macro and microscopic investigation of 89 hydatid hepatic cysts removed intact from 59 patients by total pericystectomy. Detailed analysis revealed significant morphostructural variability and cysts grouped into 10 types were characterized, providing useful clinical indications. Only 30 cysts resulted fertile (33.7%), probably due to mean age of sample; 7 of these were "classic" cysts, 1 "septated" and 22 "multivesicular" packed with daughter cysts (DC), of varying turgidity or collapsed. Among the remaining 59 sterile cysts, 52 were degenerated and classified as "hyperlaminated" cysts due to the presence of large convoluted sheets of laminar tissue (SLT) surrounded by varying amounts of caseous (40 specimens), granular (6) or gelatinous (6) matrix. Moreover, "multivesicular", "acephalocyst", "caseous" and "serous" cysts were also recovered among the sterile specimens. Some "multivesicular" cysts (14) appeared as "transitional forms" towards the various types of "hyperlaminated" cysts containing all different forms of DC and large SLT intermingled with a variously degenerated matrix. The comprehensive study allows to hypothesize the train of events leading, over the years, to the gradual transformation and degeneration of the larval form Echinococcus granulosus in the human liver.

Characterization of the immune response induced by a carbohydrate enriched fraction from Echinococcus granulosus protoscoleces in patients with cystic hydatid disease

The serological and cellular immune response against a carbohydrate-enriched fraction of Echinococcus granulosus (E4+) was studied in a group of patients with cystic hydatid disease (CHD). The profile of IgG subclass against E4+ and the native non-enriched extract (protoscolex somatic antigen, PSA) were compared. A relatively higher ratio of IgG2:IgG4 was induced by E4+ than by PSA (12.4 vs 3.6 respectively). Serological data were associated with clinical parameters dealing with the outcome of disease. The expression of IgG1 and IgG4 subclasses against both of the antigens was associated with the progression of the disease. Interestingly, anti-PSA IgG4 was the only variable that was specifically associated with the stage of cysts (P < 0.04). Similar levels of IL-13 were evoked by peripheral blood mononuclear cells from patients with CHD when incubated with either of the antigens, while higher levels of IL-10 were obtained in supernatants from cells stimulated with E4+ (P < 0.029) than from those stimulated by PSA. Considerable amounts of IL-10 (median 60 pg/ml) were obtained in the supernatants of cells from healthy individuals incubated with E4+. Our results suggest a putative role for E4+ in immunoregulation during the course of infection with E. granulosus in humans.

Culture of Echinococcus multilocularis metacestodes: an alternative to animal use

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

[Comparative observation on experimental infection with Echinococcus multilocularis in Cricetulus Migratorius and Meriones meridianus]

AIM

To search for an animal model with higher susceptibility to Echinococcus multilocularis and shorter experimental period.

METHODS

Cricetulus migratorius, Meriones meridianus and NIH mice were experimentally infected with protoscolices of E. multilocularis and were autopsed at different times after their infection. The development of E. multilocularis in these three species of rodents was observed and compared.

RESULTS

The average wet cyst weight and the ratio of cyst weight to body weight on the 91st day after infection were 15.0 +/- 2.1 g and 32.3% for C. migratorius, 3.3 +/- 1.1 g and 6.9% for M. meridianus, 0.6 +/- 0.6 g and 2.4% for NIH mice; and the corresponding figures on the 188th day after infection were 11.8 +/- 2.7 g and 21.7% for C. migratorius, 8.1 +/- 5.1 g and 15.4% for M. meridianus and 8.4 +/- 8.3 g and 26.7% for NIH mice, respectively. On the 91st day, matured protoscolices were found in C. migratorius and M. meridianus, whereas NIH mice had matured protoscolices on the 188th day after infection.

CONCLUSION

C. migratorius has higher sensitivity to E. multilocularis infection than the other two species of animals as manifested by high infection rate, well-developed vesicles and rapid growth speed. C. migratorius proved to be an ideal experimental animal for E. multilocularis.

Fertility assessment of hydatid cyst by proton MR spectroscopy

BACKGROUND

Hydatid cysts, the larvae of the parasite Echinococcus granulosus, may lodge in any organ of intermediate hosts, namely, man and sheep. Complete cyst removal is the treatment of choice; however, spillage of fertile cysts during surgery leads to disease recurrence that may be prevented by preoperative detection of the fertility status of the cyst. With this perspective, ex vivo proton (1H) MR spectroscopy of hydatid fluid of human and sheep origin was performed to differentiate fertile from sterile cysts on the basis of their metabolite pattern.

PATIENTS AND MATERIALS

Cysts of sheep and human origin were used as source of hydatid fluid. A fraction of this fluid was tested for cyst fertility and the rest was used for ex vivo1H spectroscopy. Histopathology of the cyst wall was done as a gold standard for this study.

RESULTS

Of 10 sheep samples, 7 were fertile and 3 were sterile, while among 6 human samples, 5 were fertile and 1 was sterile. Spectroscopic and histopathological results corroborated each other. The fluid from microbiologically proven fertile cysts contained malate and fumarate along with other resonances and the histopathology of the fertile cyst wall demonstrated germinal lining and protoscoleces.

CONCLUSIONS

The ex vivo spectroscopic differentiation of fertile and sterile cysts may be a stepping-stone for their in vivo separation in future and thus help in framing strategies for percutaneous/surgical management.