Towards a taxonomic revision of the genus Echinococcus

Echinococcus remains a significant public health problem worldwide and, in several regions, the aetiological agents of cystic hydatid disease/echinococcosis are extending their range. The taxonomy of Echinococcus has been a controversial issue for decades, but the outcome of recent molecular epidemiological studies has served to reinforce proposals made ten years ago to revise the taxonomy of Echinococcus. A formal nomenclature is essential for effective communication, and provides the stability that underpins epidemiological investigations. It will also serve to recognize the contribution of early taxonomists.     

Emergence/re-emergence of Echinococcus spp.--a global update

This review provides an update of the biological aspects of the genus Echinococcus and focuses on newly recognized endemic areas. Infection with the intermediate cystic stage of all species of Echinococcus causes disease and incapacity in animals and humans, and in the most serious cases, death of the host. Transmission of Echinococcus to new continents has occurred during European colonisation and the parasite has often taken advantage of Echinococcus-naive wildlife populations in these new environments, incorporating them into its transmission pattern. Echinococcus granulosus consists of a complex of 10 strains. Host specificities of these strains have important implications for transmission and control. As a result of human behaviour and/or political instability in a number of countries Echinococcus is re-emerging as an important public health issue. The importance of wildlife reservoirs in perpetuating transmission and as a source of infection for domestic animals and humans is addressed. The review also refers to the transmission pattern of a recently described new species, Echinococcus shiquicus, from China.     

泡状棘球蚴病病原生物学研究进展

泡状棘球蚴病(alveolar echinoeoeeosis,AE)是一种重要的人兽共患寄生虫病。本文综述了其病原泡状棘球蚴的地理分布、宿主类别、传播情况及其发育生物学方面的研究情况,指出研究病原生物学的现实意义和今后仍需努力的方向。     

Recent advances in the immunology and diagnosis of echinococcosis

Echinococcosis is a cosmopolitan zoonosis caused by adult or larval stages of cestodes belonging to the genus Echinococcus (family Taeniidae). The two major species of medical and public health importance are Echinococcus granulosus and Echinococcus multilocularis, which cause cystic echinococcosis and alveolar echinococcosis, respectively. Both cystic echinococcosis and alveolar echinococcosis are serious diseases, the latter especially so, with a high fatality rate and poor prognosis if managed inappropriately. This review highlights recent advances in immunity to infection and vaccination against both parasites in their intermediate and definitive hosts and procedures for diagnosis of cystic echinococcosis and alveolar echinococcosis, including the value of immunodiagnostic and DNA approaches. There is discussion also of progress in genomics and related technologies that is providing valuable insights on the functional biology of the Echinococcus organisms. These studies will underpin future research that will reveal a better understanding of the Echinococcus-host interplay, and suggest new avenues for the identification of additional targets for diagnosis, vaccination and chemotherapy.     

The diagnosis of Echinococcus granulosus in dogs

The problem of diagnosing Echinococcus granulosus in dogs has still only been partially resolved, even after the advent of biotechnology. The eggs of taeniid Cestoda are extremely similar, and thus identification by microscopic examination of the faeces is risky and non-specific. For this reason, Echinococcus granulosus was traditionally diagnosed in dogs ante mortem after an arecoline hydrobromate purge. The faeces were examined macro and microscopically to establish if the adult tapeworm or its proglottids were present. Although this method is 100% specific, it is bio-hazardous and time-consuming, requires trained personnel, and its sensitivity varies. In the 1990s copro-antigens were discovered and characterised. These are released by the adult worm in the faeces. This made it possible to use enzyme-linked immune-adsorbent assay (ELISA) for in vitam diagnosis of Echinococcus granulosus. In recent years several PCR protocols have been published on the identification of Echinococcus granulosus DNA from eggs or from adult parasites and new ways of diagnosing this cestode have been developed.     

Echinococcus multilocularis in a European beaver from Switzerland

Infection with the larval stage of the cestode parasite Echinococcus multilocularis was diagnosed in a European beaver (Castor fiber) in central Switzerland. The animal was hit, run over by a car, and died of trauma. It was in normal body condition and no signs of disease were seen. At necropsy, multiple cystic structures up to 1 cm in diameter were found in the liver adjacent to the hilus. Within the parasite vesicles, multiple protoscolices were visible. The species was determined to be Echinococcus multilocularis by upon polymerase chain reaction and direct immunofluorescence with MAbG11-FITC. This is the first report of Echinococcus multilocularis in European beaver.     

Phylogenetic relationships within Echinococcus and Taenia tapeworms (Cestoda: Taeniidae): an inference from nuclear protein-coding genes

The family Taeniidae of tapeworms is composed of two genera, Echinococcus and Taenia, which obligately parasitize mammals including humans. Inferring phylogeny via molecular markers is the only way to trace back their evolutionary histories. However, molecular dating approaches are lacking so far. Here we established new markers from nuclear protein-coding genes for RNA polymerase II second largest subunit (rpb2), phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold). Bayesian inference and maximum likelihood analyses of the concatenated gene sequences allowed us to reconstruct phylogenetic trees for taeniid parasites. The tree topologies clearly demonstrated that Taenia is paraphyletic and that the clade of Echinococcus oligarthrus and Echinococcusvogeli is sister to all other members of Echinococcus. Both species are endemic in Central and South America, and their definitive hosts originated from carnivores that immigrated from North America after the formation of the Panamanian land bridge about 3 million years ago (Ma). A time-calibrated phylogeny was estimated by a Bayesian relaxed-clock method based on the assumption that the most recent common ancestor of E. oligarthrus and E. vogeli existed during the late Pliocene (3.0 Ma). The results suggest that a clade of Taenia including human-pathogenic species diversified primarily in the late Miocene (11.2 Ma), whereas Echinococcus started to diversify later, in the end of the Miocene (5.8 Ma). Close genetic relationships among the members of Echinococcus imply that the genus is a young group in which speciation and global radiation occurred rapidly.     

Immunological features and efficacy of the recombinant subunit vaccine LTB-EMY162 against Echinococcus multilocularis metacestode

Applied Microbiology and Biotechnology - Alveolar echinococcosis is a zoonotic disease caused by the infection of the larval stage Echinococcus multilocularis with worldwide distribution especially...     

Immunology and molecular biology of Echinococcus infections

Echinococcus spp. are the etiological agents of hydatid disease in man and other intermediate hosts. Many questions regarding the factors which determine susceptibility/resistance to hydatid disease, and the factors which influence the viability and fertility of hydatid cysts, remain to be answered. Recent research into the effects of hydatid infection on the immune system of the host has provided some insights into the host-parasite relationships. Immunochemical and recombinant DNA techniques are being applied to improve diagnosis of hydatidosis in man and E. granulosus infection in dogs, and also in the development of vaccines against infection with taeniid cestode larvae. The successes which have been achieved in these areas are likely to provide valuable tools for the control of cystic hydatidosis in man. These recent studies in the areas of immunobiology, serological diagnosis and vaccination are reviewed.     

Understanding the laminated layer of larval Echinococcus II: immunology

The laminated layer (LL) is the massive carbohydrate-rich structure that protects Echinococcus larvae, which cause cystic echinococcosis (hydatid disease) and alveolar echinococcosis. Increased understanding of the biochemistry of the LL is allowing a more informed analysis of its immunology. The LL not only protects the parasite against host attack but also shapes the overall immune response against it. Because of its dense glycosylation, it probably contains few T-cell epitopes, being important instead in T-cell independent antibody responses. Crucially, it is decoded in non-inflammatory fashion by innate immunity, surely contributing to the strong immune-regulation observed in Echinococcus infections. Defining the active LL molecular motifs and corresponding host innate receptors is a feasible and promising goal in the field of helminth-derived immune-regulatory molecules.     

Echinococcus: biology and strain variation

Biology and strain variation in the causative agent of hydatid disease is reviewed with emphasis on developmental and genetic aspects. In vitro cultivation experiments have made a significant contribution to current knowledge of the developmental plasticity of Echinococcus. However, the mechanisms which regulate and determine developmental strategies in the parasite, as well as the characteristics, source and cytodifferentiation of germinal cells, are not understood. The nature, significance and origin of strain variation in Echinococcus are examined. Before we can fully appreciate the phenotypic consequences of genetic differentiation between populations, we need to know something about the genetic and environmental components of variation in traits such as development rate, host preference, host specificity, virulence and drug resistance. There is an urgent need for research on the developmental pathways by which genetic differences within and between strains of E. granulosus are translated to phenotypic differences in these traits.     

Release and survival of Echinococcus eggs in different environments in Turkana, and their possible impact on the incidence of hydatidosis in man and livestock

In Turkana, Kenya, a prevalence of hydatidosis of nearly 10% has been recorded among the pastoralists yet their livestock have a much lower prevalence of the disease. The present study investigated the release from dogs and subsequent survival of Echinococcus eggs in Turkana huts, water-holes and in the semi-arid environment. The results were compared with the survival of eggs of Taenia hydatigena and T. saginata. The study was repeated under the cooler and moister conditions found in Maasailand where livestock have a greater incidence of hydatid disease than in Turkana but where the incidence in man is ten times lower. The average number of Echinococcus eggs per proglottid is 823. Nine percent of these remain in proglottids 15 minutes after release from a dog and the released eggs lose their viability in less than two, 48 and 300 hours in the sun, huts and water in Turkana respectively: the major influencing factor being temperature. The greater survival of eggs in the houses, coupled with the fact that dogs congregate for most of the day in the small houses facilitating a close man:dog contact, provide ideal conditions for the transmission of the parasite to man. The hostile environmental conditions and lack of contact between dogs and livestock contributes to the lower infection rate in livestock. Conversely in Maasailand, Echinococcus eggs survive in the environment for longer than three weeks and in addition, dogs are used for herding. This partly explains the higher infection rate among Maasai livestock but the low human infection rate remains arcane and requires further study.(ABSTRACT TRUNCATED AT 250 WORDS)     

The occurrence of Echinococcus spp. in golden jackal (Canis aureus) in southwestern Hungary: Should we need to rethink its expansion?

Alveolar echinococcosis and cystic echinococcosis are severe zoonotic diseases caused by Echinococcus multilocularis and Echinococcus granulosus s.l. in Europe. To present knowledge, in the European continent, the most important definitive hosts of these parasites belong to the Canidae family. The golden jackal as an opportunistic mesopredator frequently preys on rodents including arvicolids and other easily available food resources, such as viscera and other carrion. By these reasons, the golden jackal can promote the maintenance of both Echinococcus multilocularis and Echinococcus granulosus s.l. Our investigation was conducted in the southwestern part of Hungary where one of the densest golden jackal populations exists. We examined altogether 173 golden jackal small intestines to determine the presence of Echinococcus multilocularis and Echinococcus granulosus s.l. After the molecular diagnostic procedure, we found 27 Echinococcus multilocularis-positive (prevalence: 15.6%; mean intensity: 664 worms) and three Echinococcus granulosus s.l. infected hosts (prevalence: 1.7%; mean intensity: 554.3 worms). We suggest the invasion of the golden jackal in Europe can enhance the spread of both Echinococcus multilocularis and Echinococcus granulosus s.l. This novel epidemiological situation can influence the geographical distribution of these helminths and the characteristics of their endemic in different host species, as well as in humans.     

Echinococcus granulosus: Diagnosis of human hydatid disease by the indirect haemoagglutination reaction with antigens from hydatid fluid and scoleces

Tassi Carmelo, Dottorini Silvio, Scalise Giorgio and Geranio Nadia. 1981. Echinococcus granulosus: diagnosis of human hydatid disease by the Indirect Haemoagglutination reaction with antigens from hydatid fluid and scoleces. International Journal for Parasitology11: 85–88. Various antigenic fractions were prepared from sheep hydatid fluid and scoleces of Echinococcus granulosus by ammonium sulphate salting out. Sheep red blood cells were sensitized with all antigenic preparations and tested, by Indirect Haemoagglutination reaction, against 63 sera from humans with hydatid disease and 163 controls. The greatest sensitivity was obtained with the ‘0·8 M fraction’ and ‘Band 7’ from hydatid fluid. The specificity was excellent for all antigens examined.     

Immunomodulatory mechanisms during Echinococcus granulosus infection

The pathologic events that ensue after humans ingest the eggs of Echinococcus granulosus and continue while cystic echinococcosis develops, provide an excellent example illustrating the evasive strategies helminth parasites use to develop, progress and cause chronic disease. The hydatid cyst secretes and exposes numerous immunomodulatory molecules to the host’s immune system. By characterizing these molecules we can understand the mechanisms that E. granulosus uses for increasing the efficiency and persistency of infection in the host. These molecules modulate both the innate and adaptive arms of the immune response and appear to target cellular and humoral responses. In this review, we discuss recent advances in the immunobiology of host-E. granulosus interactions that provide intriguing insights into the complex interplay between host and parasite that ultimately facilitates parasite survival.     

Hydatid cyst of the uterine cervix

I report and discuss a very rare case of primary involvement of the uterine cervix by hydatid cyst a parasitic disease caused by Echinococcus granulosus, whose first and most important site is the liver. The case was misdiagnosed as an ovarian cyst until the time of operation. And this is to alert the gynaecologist to the possibility of hydatid cyst when a septated mass is found in the pelvis.     

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).     

Comment on the status of Echinococcus granulosus in the UK

Echinococcus granulosus is composed of a complex of strains, the status of which has caused controversy and doubt. All have different characteristics which have arisen from animal husbandry practices, resulting in isolation and restriction of gene flow, and/or from the reproductive characteristics of the organisms. Whatever the mechanism for strain variation, Don McManus, Alan Lymbery and Andrew Thompson have no doubts that distinct variants occur in spite of a recent publication that suggests there is only one form of E. granulosus in the UK.     

宠物与肝包虫病

棘球绦虫寄生于犬科动物的小肠内,其幼虫棘球蚴寄生在动物和人的肝脏,该病严重危害人类和动物健康,对公共卫生造成了严重威胁。本文对包虫病的类型、危害、流行情况以及防治进行综述,希望有助于社会对该病正确的认识、深入的研究和对疾病的防治工作。     

The origin of a new focus of infection with Echinococcus granulosus in tasmania

Hydatid cysts were discovered in cattle on King Island, north of Tasmania, where Echinococcus granulosus was thought to have been eradicated. Using enzyme electrophoresis, isolates from King Island were compared genetically with isolates from Tasmania and the mainland of Australia. The genetic distinctness of the King Island isolates make it unlikely that they originated from a recent introduction from either Tasmania or mainland Australia. Alternative possibilities, that the infection resulted from a recent introduction from another source or from previously undetected persistence of E. granulosus on King Island, could not be distinguished from available data.