Phylogenetic systematics of the genus Echinococcus (Cestoda: Taeniidae)

Echinococcosis is a serious helminthic zoonosis in humans, livestock and wildlife. The pathogenic organisms are members of the genus Echinococcus (Cestoda: Taeniidae). Life cycles of Echinococcus spp. are consistently dependent on predator–prey association between two obligate mammalian hosts. Carnivores (canids and felids) serve as definitive hosts for adult tapeworms and their herbivore prey (ungulates, rodents and lagomorphs) as intermediate hosts for metacestode larvae. Humans are involved as an accidental host for metacestode infections. The metacestodes develop in various internal organs, particularly in liver and lungs. Each metacestode of Echinococcus spp. has an organotropism and a characteristic form known as an unilocular (cystic), alveolar or polycystic hydatid. Recent molecular phylogenetic studies have demonstrated that the type species, Echinococcus granulosus, causing cystic echinococcosis is a cryptic species complex. Therefore, the orthodox taxonomy of Echinococcus established from morphological criteria has been revised from the standpoint of phylogenetic systematics. Nine valid species including newly resurrected taxa are recognised as a result of the revision. This review summarises the recent advances in the phylogenetic systematics of Echinococcus, together with the historical backgrounds and molecular epidemiological aspects of each species. A new phylogenetic tree inferred from the mitochondrial genomes of all valid Echinococcus spp. is also presented. The taxonomic nomenclature for Echinococcus oligarthrus is shown to be incorrect and this name should be replaced with Echinococcus oligarthra.     

A phylogeny of members of the family Taeniidae based on the mitochondrial cox1 and nad1 gene data

The cestode family Taeniidae consists of 2 genera, Taenia and Echinococcus, which both have been the focus of intensive taxonomic and epidemiological studies because of their zoonotic importance. However, a comprehensive molecular phylogeny of this family has yet to be reconstructed. In this study, 54 isolates representing 9 Taenia species were characterized using DNA sequences in the mitochondrial cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1) genes. Phylogenetic relationships within the family Taeniidae were inferred by combining cox1 and nad1 sequence data of the present and previous studies. In the phylogenetic analysis, the genus Echinococcus was shown to be monophyletic, but Taenia proved to be paraphyletic due to the position of T. mustelae as a probable sister taxon of Echinococcus. This indicates that T. mustelae should form a genus of its own. Taenia ovis krabbei was placed distant from T. ovis ovis, as a sister taxon of T. multiceps, supporting its recognition as a distinct species, T. krabbei. High intraspecific sequence variation within both T. polyacantha and T. taeniaeformis suggests the existence of cryptic sister species.     

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.     

A PCR system for detection of species and genotypes of the Echinococcus granulosus-complex, with reference to the epidemiological situation in eastern Africa

We describe the development of a specific and sensitive PCR/semi-nested PCR system for the rapid diagnosis of Echinococcus granulosus genotype G1, E. granulosus genotype G6/7, and Echinococcus ortleppi (G5). Diagnosis of G1 and the group G5/6/7 is performed by a simple PCR, while discrimination between E. ortleppi (G5) and G6/7 involves a subsequent semi-nested PCR step. The target sequence for amplification is part of the mitochondrial 12S rRNA gene. Specificity of the PCRs was 100% when evaluated with isolates of 16 species of cestodes, including Echinococcus multilocularis, Echinococcus equinus, E. ortleppi and three strains of E. granulosus (G1, G6 and G7). Sensitivity threshold was 0.25pg of DNA. This new approach was compared with published protocols of restriction fragment length polymorphism-PCR and sequencing of mitochondrial cytochrome c oxidase subunit 1 and NADH dehydrogenase 1 genes using Echinococcus isolates of human, sheep, goat, camel, cattle and pig origin from Kenya and Sudan. Additionally, two internal DNA probes were developed, one hybridising only with G1, the other with G5, G6 and G7 amplification products. Preliminary epidemiological results obtained with this PCR approach include the detection of a camel strain (G6) infection for the first time in a human patient from eastern Africa, and the first reports of E. ortleppi (G5) in livestock from Kenya and the Sudan.     

The impact of globalisation on the distribution of Echinococcus multilocularis

In the past three decades, Echinococcus multilocularis, the cause of human alveolar echinococcosis, has been reported in several new countries both in definitive hosts (canids) as well as in people. Unless treated, infection with this cestode in people is fatal. In previously endemic countries throughout the Northern Hemisphere, geographic ranges and human and animal prevalence levels seem to be increasing. Anthropogenic influences, including increased globalisation of animals and animal products, and altered human/animal interfaces are thought to play a vital role in the global emergence of this pathogenic cestode. Molecular epidemiological techniques are a useful tool for detecting and tracing introductions, and differentiating these from range expansions.     

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.     

Taxonomy and systematics of pathogenic microorganisms

The modern state of the problem of the systematics of microorganisms is analyzed and the data on the taxonomy of bacteria belonging to the family Enterobacteriaceae are presented. The importance of studies on the taxonomy of microorganisms is emphasized. These studies play a vital role in the development of diagnostic preparations and techniques for the identification of infective agents, as well as in the realization of epidemiological surveillance. Much attention is given to the works of Soviet microbiologists, discussing such problems as the unification of the classification scheme of dysentery bacteria, the intraspecific taxonomy of Francisella tularensis, the systematic position of Allomonas and the antigenic scheme of Hafnia, included into Bergey's Determinative Bacteriology, edition IX (1984).     

Genomic fingerprinting of microorganisms: its use as a hybridization probe of phage M13 DNA

Hypervariable nucleotide sequences detected by hybridization with the phage M13 DNA probe were found in the chromosomal DNAs of certain pathogenic microbial species. DNA fingerprinting, based on hybridization of M13-probe with hypervariable chromosomal DNA sequences, opens new approaches to epidemiological analysis, epidemiological prognosis, taxonomy, and other theoretical and applied fields of bacteriology.     

Ecology and epidemiology of Echinococcus multilocularis in Europe

Human alveolar echinococcosis (AE), caused by the larval stage of Echinococcus multilocularis has a high mortality rate in untreated patients. The life-cycle of E. multilocularis in Europe predominantly involves foxes as definitive hosts. However, experimental studies demonstrated a comparable biotic potential of E. multilocularis in dogs and raccoon dogs but an insignificant potential in cats. AE occurs in central and eastern Europe at low incidence rates. Recent studies in foxes have shown that E. multilocularis has a wider geographic range (including Italy) than previously thought. In recent years, increases in fox populations have been observed in many European countries, especially in urban areas. As a result, the E. multilocularis cycle is now established in the urban environment. This presents an increased risk of infection for a large human population. Based on these facts and new epidemiological data, possible intervention strategies are presented.     

The zoonotic transmission of Giardia and Cryptosporidium

The molecular characterisation of Giardia and Cryptosporidium has given rise to a more epidemiological meaningful and robust taxonomy. Importantly, molecular tools are now available for 'typing' isolates of the parasites directly from clinical and environmental samples. As a consequence, information on zoonotic potential has been obtained although the frequency of zoonotic transmission is still poorly understood. Analysis of outbreaks and case-control studies, especially when coupled with genotyping data, is slowly providing information on the public health significance of zoonotic transmission. Such studies support the hypothesis that Cryptosporidium hominis is spread only between humans but that the major reservoir for Cryptosporidium parvum is domestic livestock, predominantly cattle, and that direct contact with infected cattle is a major transmission pathway along with indirect transmission through drinking water. The situation is less clearcut for Giardia duodenalis but the evidence does not, in general, support zoonotic transmission as a major risk for human infections. However, for both parasites there is a need for molecular epidemiological studies to be undertaken in well-defined foci of transmission in order to fully determine the frequency and importance of zoonotic transmission.     

The epidemiology of hydatidosis with special reference to the Mediterranean area.

In the Mediterranean area 2 subspecies of Echinococcus granulosus exist: E. g. equinus and E. g. granulosus. The latter is divided into sheep, cattle, pig and camel strains, the adult forms of which mainly occur in farm-dogs but sometimes in wild canidae. Some of these strains can infect man: namely, the sheep and the pig strain. The infectivity of the cattle strains for man is not certain. The epidemiological cycle is mainly a rural one, but it can become sylvatic or even urban. Thus, the epidemiological features of hydatidosis in the Mediterranean area are not basically different from the general epidemiology of the disease. But extensive rearing of sheep, combined with the carelessness and ignorance of people and with some particular habits, favours the maintenance of the infection.     

Past and present of cystic echinococcosis in Bolivia

Viable eggs of the canine intestinal tapeworm Echinococcus granulosus sensu lato (s.l.) infect various intermediate hosts causing cystic echinococcosis (CE). Furthermore, CE represents a serious zoonosis causing a significant global burden of disease. CE is highly endemic in South America, including Argentina, Brazil, Chile, Uruguay, and Peru. For Bolivia, no official data concerning the incidence in humans or the number of livestock and dogs infected are available. However, it is well known that CE occurs in Bolivia. We aim here to fill the gap in the current knowledge of the epidemiological situation of CE in Bolivia, providing a historical overview of documents published within the country, which have never been comprehensively reviewed. The very first documentation of E. granulosus infection in animals dates in 1910, while the first human case was reported in 1913. In total, 876 human CE cases have been reported in the scientific literature, with an apparent increase since the 1970s. In the absence of other epidemiological studies, the highest prevalence in human comes from Tupiza, Potosí Department, where 4.1% (51/1,268) of the population showed signs of CE at mass ultrasound screening in 2011. In the same report, 24% of dog faecal samples were positive for coproantigens of E. granulosus s.l. in ELISA. The highest prevalence in intermediate hosts reported at abattoir reached 37.5% in cattle from Potosí, followed by 26.9% in llamas from Oruro, 2.4% in pigs and 1.4% in sheep from La Paz. Finally, Echinococcus granulosus sensu stricto (s.s.), Echinococcus ortleppi (G5), and Echinococcus intermedius (G7) have been identified in Bolivia. Data reviewed here confirm that E. granulosus s.l. is circulating in Bolivia and that a proper prospective nationwide epidemiological study of CE is urgently needed to define transmission patterns as a basis for the planning and implementation of future control measurements.     

Arvicola terrestris an intermediate host of Echinococcus multilocularis in France: Epidemiological consequences

Houin R., Deniau M., Liance M. and Puel F. 1981. Arvicola terrestris, an intermediate host of Echinococcus multilocularis in France: epidemiological consequences. International Journal for Parasitology12: 593–600. Hydatid cysts characteristic of E. multilocularis were found in 5 out of 2010 A. terristris trapped in France in 1980. A comparison of the distribution of human cases and rodents led to the conclusion that A. terrestris is probably the reservoir of the parasite. Another argument in favour of the epidemiological importance of this vole is that the parasite grows slowly in this host which has a relatively long life. Moreover, no other rodents were found in France naturally infected by larval E. multilocularis. As populations of A. terrestris undergo important cyclical fluctuations, high transmission periods must occur. During the periods of peak population, prophylactic measures should be taken to protect the human population.     

Species concepts for trypanosomes: from morphological to molecular definitions?

The way species and subspecies names are applied in African trypanosomes of subgenera Trypanozoon and Nannomonas is reviewed in the light of data from molecular taxonomy. In subgenus Trypanozoon the taxonomic importance of pathogenicity, host range and distribution appear to have been inflated relative to actual levels of genetic divergence. The opposite is true for subgenus Nannomonas, where current taxonomic usage badly underrepresents genetic diversity. Data from molecular characterisation studies are revealing a growing number of genotypes, which may represent distinct taxa. Unfortunately few of these genotypes are yet supported by sufficient biological data to be recognized taxonomically. But we may be missing fundamental epidemiological information, because of our inability to distinguish these trypanosomes in host blood morphologically or in tsetse by their developmental cycle. Molecular taxonomy has led the way in identifying these new genotypes and now offers the key to elucidating the biology of these organisms.     

Alveolar echinococcosis in humans: the current situation in Central Europe and the need for countermeasures.

Alveolar echinococcosis (AE) in humans is caused by a larval stage (metacestode) of Echinococcus multilocularis, which exhibits a tumor-like growth, initially in the liver, with the potential to induce serious disease. At the end of the 1980s, E. multilocularis was known to occur in four countries of Central Europe, but has now been identified in ten countries. Red foxes are the principal definitive hosts of E. multilocularis and sources of human infection, but dogs and cats can also be infected. Growing populations of foxes and their increasing immigration to urban areas are new risk factors. Human AE is rare but its potential high fatality rate, considerable costs of treatment and the persisting infection risk should be reasons for health authorities in European countries to establish coordinated systems of surveillance and risk assessment in combination with measures to reduce morbidity and mortality of AE in the human population. Here, J. Eckert and P. Deplazes outline the current epidemiological situation in Central Europe, and discuss options for surveillance, prevention and control.     

Near-infrared spectroscopy (NIRS) for taxonomic entomology: A brief review

For over two decades, near-infrared spectroscopy (NIRS) has been applied to a wide spectrum of problems in the field of insect taxonomy. It provides a rapid, non-destructive and relatively cheap method of metabolomic profiling, which can often be used to discriminate closely related species in the same genus. Furthermore, very little training or entomological knowledge is required to operate the instrument. However, a taxonomist is still required to ensure accurate identification of samples used for NIRS model creation and validation. To date, most research has focused on species of economic or epidemiological importance, such as mosquitoes, flies or stored product pests. However, an increasing number of studies are applying NIRS for entomological research with a purely “academic” purpose. As research continues in this field, NIRS has the potential to become more widely accepted in entomology, allowing for the rapid metabolomic profiling of thousands of species.     

Animal echinococcosis in Italy: epidemiological update

Cystic Echinococcosis (CE) is one of the most widespread parasitoses in the Mediterranean Region (MR). This is due to various factors, the most important being the close association between man, sheep and dogs in areas where open farming is practised. Although this disease has been known for several years and many studies have been carried out, nowadays in Italy there are no complete epidemiological data on its diffusion and distribution. The available data show that CE is mainly diffused in those districts where the sheep-dog cycle can be perpetuated, such as central and southern Italy, and the islands. Furthermore, no data are available on biomolecular characterisation of the strains of Echinococcus granulosus in Italy, apart form those in Sardinia, where the G1 (sheep-dog) and G7 (pig-dog) strains were recently isolated. One of the reasons why CE is a problem with no easy solution is undoubtedly the difficulty of making a certain diagnosis in the dog, the principal definitive host of E. granulosus.     

The role of epidemiological cutoff values (ECVs/ECOFFs) in antifungal susceptibility testing and interpretation for uncommon yeasts and moulds

The role of antimicrobial susceptibility testing is to aid in selecting the best agent for the treatment of bacterial and fungal diseases. This has been best achieved by the setting of breakpoints by Clinical Laboratory Standards Institute (CLSI) for prevalent Candida spp. versus anidulafungin, caspofungin, micafungin, fluconazole, and voriconazole. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) also has set breakpoints for prevalent and common Candida and Aspergillus species versus amphotericin B, itraconazole, and posaconazole. Recently, another interpretive category, the epidemiological cut off value, could aid in the early identification of strains with acquired resistance mechanisms. CLSI has postulated that epidemiological cut off values may, with due caution, aid physicians in managing mycosis by species where breakpoints are not available. This review provides (1) the criteria and statistical approach to establishing and estimating epidemiological cut off values (ECVs), (2) the role of the epidemiological cut off value in establishing breakpoints, (3) the potential role of epidemiological cut off values in clinical practice, (4) and the wide range of CLSI-based epidemiological cut off values reported in the literature as well as EUCAST and Sensititre Yeast One-ECVs. Additionally, we provide MIC/MEC (minimal inhibitory concentrations/minimum effective concentrations) ranges/modes of each pooled distribution used for epidemiological cut off value calculation. We focus on the epidemiological cut off value, the new interpretive endpoint that will identify the non-wild type strains (defined as potentially harboring resistance mechanisms). However, we emphasize that epidemiological cut off values will not categorize a fungal isolate as susceptible or resistant as breakpoints do, because the former do not account for the pharmacology of the antifungal agent or the findings from clinical outcome studies.