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Molecular phylogeny based on six nuclear genes suggests that Echinococcus granulosus sensu lato genotypes G6/G7 and G8/G10 can be regarded as two distinct species
Parasitology
Abstract and Figures
Tapeworms of the species complex of Echinococcus granulosus sensu lato ( s. l. ) are the cause of a severe zoonotic disease – cystic echinococcosis, which is listed among the most severe parasitic diseases in humans and is prioritized by the World Health Organization. A stable taxonomy of E. granulosus s. l. is essential to the medical and veterinary communities for accurate and effective communication of the role of different species in this complex on human and animal health. E. granulosus s. l . displays high genetic diversity and has been divided into different species and genotypes. Despite several decades of research, the taxonomy of E. granulosus s. l . has remained controversial, especially the species status of genotypes G6–G10. Here the Bayesian phylogeny based on six nuclear loci (7387 bp in total) demonstrated, with very high support, the clustering of G6/G7 and G8/G10 into two separate clades. According to the evolutionary species concept, G6/G7 and G8/G10 can be regarded as two distinct species. Species differentiation can be attributed to the association with distinct host species, largely separate geographical distribution and low level of cross-fertilization. These factors have limited the gene flow between genotypic groups G6/G7 and G8/G10, resulting in the formation of distinct species. We discuss ecological and epidemiological differences that support the validity of these species.
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... consists of 5 distinct species: E. granulosus sensu stricto (s.s.), Echinococcus equinus, Echinococcus ortleppi, Echinococcus felidis and Echinococcus canadensis. The latter species is the most diverse, holding distinct genotypes (G6, G7, G8 and G10), and there is debate whether E. canadensis should be split into 2 or even 3 species (Lymbery et al., 2015;Yanagida et al., 2017;Laurimäe et al., 2018a). The various genotypes, formerly named 'strains', differ with respect to life cycle, geography and genetics. ...
... While all variants of G6 and G7 are genetically close (and are often referred to as the G6/7 cluster) (Addy et al., 2017), the relationship of G8 and G10 with each other and with G6/7 is differently resolved depending on whether nuclear or mitochondrial DNA is considered. Analysis of the mitochondrial genome suggests a closer affinity of G10 to G6/7, while some nuclear marker genes support a clade with G8 and G10 (Yanagida et al., 2017;Laurimäe et al., 2018a). ...
... In contrast to G6/7, whose genetic structure is well known, only very few specimens of G8 and G10 have ever been characterized and showed little intra-strain variability. However, the great majority came from the European region, and the study of the nuclear genome was performed exclusively with sample material from Europe (Laurimäe et al., 2018a). The northeastern part of Asia is particularly data-deficient, although this is the only known region where all genotypes of E. canadensis have been recorded, leading to speculation on the geographic origin of the species Ito et al., 2014;Zhang et al., 2014;Yang et al., 2015;Wu et al., 2018;Hua et al., 2019). ...
Echinococcus canadensis consists of 4 genotypes: G6, G7, G8 and G10. While the first 2 predominantly infect domestic animals, the latter are sylvatic in nature involving mainly wolves and cervids as hosts and can be found in the northern temperate to Arctic latitudes. This circumstance makes the acquisition of sample material difficult, and little information is known about their genetic structure. The majority of specimens analysed to date have been from the European region, comparatively few from northeast Asia and Alaska. In the current study, Echinococcus spp. from wolves and intermediate hosts from the Republic of Sakha in eastern Russia were examined. Echinococcus canadensis G10 was identified in 15 wolves and 4 cervid intermediate hosts. Complete mitochondrial cytochrome c oxidase subunit 1 ( cox1 ) sequences were obtained from 42 worm and cyst specimens from Sakha and, for comparison, from an additional 13 G10 cysts from Finland. For comparative analyses of the genetic diversity of G10 of European and Asian origin, all available cox1 sequences from GenBank were included, increasing the number of sequences to 99. The diversity found in northeast Asia was by far higher than in Europe, suggesting that the geographic origin of E. canadensis (at least of G10) might be northeast Asia.
... Formerly, CE was known to be caused by a single polymorphic species, Echinococcus granulosus. Data based on morphology, intraspecific genetic diversity, host specificity, life cycle, developmental patterns and other biological parameters have led to division of Echinococcus granulosus sensu lato into a cryptic species complex with five major taxa in which taxonomic uncertainties still exist (Thompson, 2017;Laurimäe et al. 2018). Current nomenclature of this group includes most commonly distributed and highly zoonotic E. granulosus sensu stricto (G1 and G3 genotypes; Kinkar et al., 2017), while other species in the complex include E. equinus (G4 genotype), E. ortleppi (G5 genotype), E. ...
... intermedius and E. canadensis cluster ( genotypes G6-G8 and G10 genotypes) and E. felidis (lion strain) (Romig et al. 2015;Lymbery, 2017). The taxonomy of the genotypes G6/G7 and G8/G10 is still unresolved (Laurimäe et al. 2018). ...
... DNA sequences were subjected to multiple alignment along with E. granulosus s.l. reference sequences from the GenBank database (Kinkar et al., 2018a, b;Laurimäe et al. 2018) for the determination of species and genotypes. The sequences were submitted in NCBI GenBank database under the accession numbers: MZ271962-MZ271971 and MZ848399. ...
Cystic echinococcosis (CE), caused by Echinococcus granulosus sensu lato, is a neglected tropical disease known mainly for its zoonotic nature. CE is endemic to Pakistan, however, the disease is not given due consideration and millions of people remain at health risk. This study was undertaken to assess the species and genotypes of E. granulosus sensu lato in sheep, buffaloes and cattle, brought to slaughterhouses of two major cities (Multan and Bahawalpur) of south Punjab, Pakistan. A total of 26 hydatid cyst specimens were characterized through complete cox1 mitochondrial gene (1609 bp) sequencing. Species and genotypes of E. granulosus sensu lato discovered in the southern Punjab consisted of E. granulosus sensu stricto (n =21), E. ortleppi (n=4) and E. canadensis G6 genotype (n=1). Of E. granulosus s.s. isolates, the genotype G3 was predominantly involved in causing infections to the livestock of this region. Since all of these species are zoonotic, wide and effective surveillance studies are required to ascertain the risks to human population in Pakistan. Additionally, a global overview on cox1 phylogenetic structure of E. ortleppi was carried out. Despite the widespread occurrence, the species is mostly limited to the southern hemisphere. The highest burden has been reported in the South America (62.15%) and Africa (28.44%) and by far the most common host is cattle, accounting for >90% of cases.
... The mtDNA data show G10 to be more closely related to G6/G7 than to G8 (e.g. Nakao et al., 2006;Moks et al., 2008;Knapp et al., 2011), while evidence from nuclear genes has indicated that the cervid G8 and G10 form one clade, and G6/G7 another (Saarma et al., 2009;Laurimäe et al., 2018a). As such, some have suggested that G8/G10 should be regarded as one species (E. ...
... canadensis) together with G6/G7 (e.g. Nakao et al., 2006), while others have proposed three (Lymbery et al., 2015) or two species (Thompson, 2008;Saarma et al., 2009;Laurimäe et al., 2018a). Until the taxonomic dispute has been resolved, the authors have herein elected to refer to genotypes G6-G8 and G10 as genotypes of the E. canadensis cluster or whenever E. canadensis is mentioned, genotypes are also specified (Vuitton et al., 2020). ...
Echinococcus granulosus sensu lato is a group of tapeworm species known to cause cystic echinococcosis. Within this group, the Echinococcus canadensis cluster includes genotypes G8 and G10 that have a predominantly sylvatic life cycle – transmission occurs between wild cervids and wolves. Relatively few studies have explored the genetic variation of the elusive G8 and G10, and their extent of genetic variation is yet to be investigated at the complete mitochondrial (mt) genome level. The aim was to explore the genetic variation of these 2 genotypes in Europe using complete mtDNA sequences and provide a high-quality reference dataset for future studies. Sequences of complete mt genomes were produced for 29 samples of genotype G8 and G10 from wolves, moose, reindeer and roe deer, originating from Finland, Sweden, Russia, Poland, Latvia and Estonia. Genetic variation was explored based on phylogenetic network analysis, revealing marked differences between G8 and G10 (over 400 mutations), and more detailed patterns of variability within the 2 genotypes than previously observed. Understanding the mt genetic composition of a species provides a baseline for future studies aiming to understand whether this mt distinctiveness is mirrored in the nuclear genome and whether it has any impact on any phenotypic traits or parasite transmission.
... Further molecular studies on Echinococcus canadensis revealed that E. canadensis (G6/G7) and E. canadensis (G8/ G10) are sister species but are still different species (Nakao et al., 2013c;Laurimäe et al., 2018). It was also confirmed in later studies that the G1 and G3 strains of E. granulosus s. s. differ from each other (Kinkar et al., 2018b). ...
... This should be considered in the context of new taxonomic proposals offered for the E. granulosus s.l. complex, especially involving E. canadensis G6/G7, G8, and G10 (Lymbery et al. 2015a(Lymbery et al. , 2015bNakao et al. 2015;Laurimäe et al. 2018b), and principally E. canadensis G6, which is more frequent than E. canadensis G7 in South America, with previously reported human infections (Cucher et al. 2016). ...
Echinococcus granulosus sensu lato (s.l.) is a species complex with the potential to cause cystic echinococcosis (CE). Contact with the feces of domestic dogs (Canis familiaris) fed with raw viscera of intermediate livestock hosts is a risk factor for this infection in the southern region of Brazil. Although the region has been considered endemic to CE for many years, molecular data regarding the species of the complex causing CE in humans are scarce. This study aimed to perform a molecular analysis of the biological fluid from a human liver cyst to investigate the species responsible for CE. Genetic material obtained from the hydatid fluid of a hepatic cyst from a human with CE was subjected to PCR to amplify mitochondrial and nuclear DNA sequences. The phylogenetic analysis confirmed the human infection by Echinococcus canadensis G7 in the state of Paraná, Brazil. This is the first molecular record of E. canadensis G7 infecting a human in Brazil, and it is important to reiterate the risk of human CE caused by this species in South America, as reported by a previous study in Patagonia, Argentina. From the epidemiological point of view, this finding is of great relevance for the southern region of Brazil, since this parasite has previously only been detected in pigs in the state of Rio Grande do Sul, neighboring Paraná. The finding points to the importance of this identification in the molecular epidemiology of E. granulosus s.l., especially in South America.
... Some studies have suggested that the genetic differences taken together with biological, ecological and distribution range factors would warrant defining G6/ G7 as a separate species (proposed name: E. intermedius) from the cervid G8/G10 (E. canadensis), while others have suggested the 4 genotypes belong to 1 species E. canadensis (G6-G8, G10) (Lymbery et al., 2015;Nakao et al., 2015;Laurimäe et al., 2018aLaurimäe et al., , 2018b. Until a clear consensus is reached, for the purposes of this study, the genotypes G6 and G7 are referenced as E. granulosus s.l. ...
There are no scientific data available on the occurrence of the Echinococcus granulosus sensu lato ( s.l. ) cluster in definitive hosts (domestic dogs), intermediate hosts (domestic livestock) nor humans in Cape Verde. In this pilot study, environmental dog fecal samples ( n = 369) were collected around food markets, official slaughterhouses, as well as home and small business slaughter spots in 8 of the 9 inhabited islands from the Cape Verde archipelago, between June 2021 and March 2022. Additionally, during the same period, 40 cysts and tissue lesions were opportunistically collected from 5 islands, from locally slaughtered cattle ( n = 7), goats ( n = 2), sheep ( n = 1) and pigs ( n = 26). Genetic characterization by a multiplex polymerase chain reaction assay targeting the 12S rRNA gene confirmed the presence of E. granulosus s.l. in fecal and tissue material. In total, 17 cyst samples from Santiago ( n = 9), Sal ( n = 7) and São Vicente ( n = 1) and 8 G6/G7-positive dog fecal samples from Santiago ( n = 4) and Sal ( n = 4) were identified as E. granulosus s.l. G7 by sequence analysis ( nad 2, nad 5 and nad 1 genes). This study discloses the transmission of E. granulosus s.l. G7, in pig, cattle and dog in Cape Verde.
... These include the species E. granulosus sensu stricto (s.s.; genotypes G1 and G3; Kinkar et al., 2017), E. equinus (G4), E. felidis, E. ortleppi (G5) and the E. canadensis cluster (G6-G8, G10) for which the number and name(s) of species are under dispute (e.g. Moks et al., 2008;Thompson, 2008;Saarma et al., 2009;Knapp et al., 2011;Nakao et al., 2015;Romig et al., 2017;Laurimäe et al., 2018a;Vuitton et al., 2020). The life cycle of these tapeworms involves canids as definitive hosts, harbouring the adult worm, and various herbi-and omnivores that act as intermediate hosts. ...
Cystic echinococcosis (CE) is considered the most severe parasitic disease that ever affected the human population in Iceland. Before the start of eradication campaign in the 1860s, Iceland was a country with very high prevalence of human CE, with approximately every fifth person infected. Eradication of CE from Iceland by 1979 was a huge success story and served as a leading example for other countries on how to combat such a severe One Health problem. However, there is no genetic information on Echinococcus parasites before eradication. Here, we reveal the genetic identity for one of the last Echinococcus isolates in Iceland, obtained from a sheep 46 years ago (1977). We sequenced a large portion of the mitochondrial genome (8141 bp) and identified the isolate as Echinococcus granulosus sensu stricto genotype G1. As G1 is known to be highly infective genotype to humans, it may partly explain why such a large proportion of human population in Iceland was infected at a time . The study demonstrates that decades-old samples hold significant potential to uncover genetic identities of parasites in the past.
... Some of these genotypes were considered distinct species, like E. granulosus sensu stricto (s. s; genotype G1 and G3), E. equinus (G4), E. ortleppi (G5), and E. canadensis (G6-G8, and G10), or E. intermedius (G6, G7) and E. canadensis (G8, G10) (Kinkar et al. 2017;Laurimae et al. 2018). The parasite completes its life cycle using dogs and wild canines as the definitive host and various domestic and wild ungulates as intermediate hosts. ...
The present study assessed the antioxidants and oxidative stress markers in the liver of buffalo naturally infected with cystic echinococcosis. Infected and non-infected livers were collected from the abattoir, and processed to determine the markers of oxidative stress and antioxidants. In addition, samples were also analyzed for liver tissue injury markers. A significantly higher level of glutathione-s-transferase (GST) and glutathione peroxidase (GPx) were observed in the infected liver compared to a healthy liver. On the other hand, the levels of glutathione reductase (GR) and thioredoxin reductase (TR) were significantly reduced in the infected liver compared to a healthy liver. Reduced glutathione (GSH), a key non-enzymatic antioxidant, was also decreased in the infected than in the non-infected liver. The cystic echinococcosis is accompanied by the enhanced production of ROS with subsequent elevation of lipid peroxidation and protein oxidation, as evident from increased malondialdehyde (MDA) and protein carbonyl (PC), respectively. Enhanced MDA disrupts the cell membrane leading to the release of liver injury markers AST, ALT, ACP, and ALP, which suggest liver damage. This could result from the mechanical pressure and the space-occupying affect of cystic echinococcosis cysts. In summary, our findings suggest that alteration in the level of antioxidants and oxidative stress markers may potentially serve as evidence for the oxidative stress in the liver of infected buffalo.
... The constraints of using short gene sequences to assess Echinococcus spp. (28). ...
Taenia hydatigenia refers as cestoda in carnivorous species, whereas Cysticercus tenicollis is a common larval stage found in herbivorous animals, ruminants and swine. An investigation into molecular identification of C. tenicollis from slaughtered sheep and goats was carried out by creating Cysticercus species-specific and Cysticercus specific primers in Basrah governorate, southern Iraq. Study the molecular characterization of C. tenicollis and C. ovis from sheep and goats, by designing primer to Cysticercus spp. and specific primers to detect C. tenicollis and C. ovis. a total of 23 sheep (7 males, 16 females) and 23 goats (19 males, 4 females) were inspected. This investigation took place in Basrah province from November 2020 to November 2021, and the animal isolates were gathered throughout that time. The primers were developed as universal for the identification of Cysticercus species; they can amplify a portion of (ND1) and (COX1) genes of C. tenicollis and C. ovis, respectively. In general, Each cyst was identified as belonging to the genus T. hydatigenia by its unique mt-CO1 sequence, which yielded 267 bp product. This strain of T. hydatigenia is 100% identical to the Iraqi strain first isolated from Southern Iraq and entered into the Gene Bank under the designation "Iraqi strain," as shown by multiple sequence alignment of the nucleotide with previously published references (OK3556791, OK356792, OK356793, and OK356794).
... According to "International consensus on terminology to be used in the field of echinococcoses" published in the journal Parasite in 2020, the new classification was E. granulosus s.s. (G1 and G3) [10,11], E. equinus (G4), E. ortleppi (G5) [11,12], E. canadesis (G6/7 and G8/10) [13][14][15][16], and E. felidis (lion strain). The G2 genotype is not a separate strain or even a monophyletic cluster but belongs to the G3 genotype [17], while the G9 genotype is no longer recognized as a distinct strain, as it is probably a microvariant of the G7 genotype [10]. ...
Cystic echinococcosis (CE), caused by the metacestode Echinococcus granulosus sensu stricto (s.s.), is an important zoonotic parasite, endemic in the Altai region of China. It is a serious human health risk and causes livestock losses. To evaluate the prevalence, genetic variation, and population structure of CE, 2898 sheep and 703 cattle were examined from October 2019 to mid-February 2020 in the Altai region (Altai, Habahe, Fuhai, and Buerjin). Sheep had an infection rate of 4.52% (131/2898) and cattle had an infection rate of 4.84% (34/703). In total, 180 cyst isolates were obtained, including 131 sheep, 34 cattle, and 15 from CE human patients. The cysts were investigated using mitochondrial cytochrome C oxidase subunit 1 (cox1). Polymerase Chain Reaction (PCR) results showed that, among the two genotypes of E. granulosus s.s., there were 22 different haplotypes (Haps). Phylogenetic analysis and parsimony network indicated that seventeen (77.27%) Haps belonged to the sheep strain (G1 genotype) and five Haps (22.73%) belonged to the buffalo strain (G3 genotype). Hap3 was the most common haplotype (65.00%, 112/180), which belongs to the G1 genotype. Hap18–Hap22 were found in human samples, indicating that sheep and cattle reservoirs of human CE. Molecular diversity indices revealed the high levels of haplotype diversity and relatively low levels of nucleotide diversity. Tajima’s D and Fu’s Fs tests displayed that the Altai population had a significant deviation from neutrality. Based on pairwise fixation index (Fst) values, a low level of genetic differentiation was found between the populations of E. granulosus s.s. isolated from different regions. The present survey findings represent an epidemiological survey of CE in the Altai region where there were two genotypes simultaneously and will provide more information on the genetic structure of E. granulosus s.s. within this region.
Echinococcus granulosus sensu stricto (s.s.) is the major cause of human cystic echinococcosis worldwide and is listed among the most severe parasitic diseases of humans. To date, numerous studies have investigated the genetic diversity and population structure of E. granulosus s.s. in various geographic regions. However, there has been no global study. Recently, using mitochondrial DNA, it was shown that E. granulosus s.s. G1 and G3 are distinct genotypes, but a larger dataset is required to confirm the distinction of these genotypes. The objectives of this study were to: (i) investigate the distinction of genotypes G1 and G3 using a large global dataset; and (ii) analyse the genetic diversity and phylogeography of genotype G1 on a global scale using near-complete mitogenome sequences. For this study, 222 globally distributed E. granulosus s.s. samples were used, of which 212 belonged to genotype G1 and 10 to G3. Using a total sequence length of 11,682 bp, we inferred phylogenetic networks for three datasets: E. granulosus s.s. (n = 222), G1 (n = 212) and human G1 samples (n = 41). In addition, the Bayesian phylogenetic and phylogeographic analyses were performed. The latter yielded several strongly supported diffusion routes of genotype G1 originating from Turkey, Tunisia and Argentina. We conclude that: (i) using a considerably larger dataset than employed previously, E. granulosus s.s. G1 and G3 are indeed distinct mitochondrial genotypes; (ii) the genetic diversity of E. granulosus s.s. G1 is high globally, with lower values in South America; and (iii) the complex phylogeographic patterns emerging from the phylogenetic and geographic analyses suggest that the current distribution of genotype G1 has been shaped by intensive animal trade.
The specific status of Echinococcus canadensis has long been controversial, mainly because it consists of the mitochondrial lineages G6, G7, G8 and G10 with different host affinity: G6 (camel strain) and G7 (pig strain) with domestic cycles and G8 (cervid strain) and G10 (Fennoscandian cervid strain) with sylvatic or semi-domestic cycles. There is an argument whether the mitochondrial lineages should be recognised as separate species which correspond to the biological or epidemiological aggregation. In the present study, the specific status of E. canadensis was investigated using mitochondrial DNA (mtDNA) and single copy nuclear DNA (nDNA) markers. Nucleotide sequences of complete mitochondrial cytochrome c oxidase subunit 1 (cox1) and partial nuclear phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold) were determined for 48 isolates of E. canadensis collected from different hosts in a wide range of regions. The mitochondrial phylogeny of cox1 showed that all the isolates were clearly divided into three clades corresponding to G6/G7, G8 and G10. Five and three alleles were confirmed at pepck and pold loci, respectively. These alleles were generally divided into two groups corresponding to G6/G7 or G8 and G10. However, allele sharing was confirmed among individuals belonging to different lineages. The allele sharing occurred primarily in regions where different mtDNA lineages were found in sympatry. The resultant nuclear mitochondrial discordance suggests the genetic exchangeability among E. canadensis isolates belonging to different lineages. An apparently mosaic parasite fauna that reflects faunal mixing due to natural and anthropogenic disturbance, including introductions and invasion, precludes us from designating each of G6/G7, G8 and G10 into a different species.
The grey wolf (Canis lupus) is an iconic large carnivore that has increasingly been recognized as an apex predator with intrinsic value and a keystone species. However, wolves have also long represented a primary source of human–carnivore conflict, which has led to long-term persecution of wolves, resulting in a significant decrease in their numbers, genetic diversity and gene flow between populations. For more effective protection and management of wolf populations in Europe, robust scientific evidence is crucial. This review serves as an analytical summary of the main findings from wolf population genetic studies in Europe, covering major studies from the ‘pre-genomic era’ and the first insights of the ‘genomics era’. We analyse, summarize and discuss findings derived from analyses of three compartments of the mammalian genome with different inheritance modes: maternal (mitochondrial DNA), paternal (Y chromosome) and biparental [autosomal microsatellites and single nucleotide polymorphisms (SNPs)]. To describe large-scale trends and patterns of genetic variation in European wolf populations, we conducted a meta-analysis based on the results of previous microsatellite studies and also included new data, covering all 19 European countries for which wolf genetic information is available: Norway, Sweden, Finland, Estonia, Latvia, Lithuania, Poland, Czech Republic, Slovakia, Germany, Belarus, Russia, Italy, Croatia, Bulgaria, Bosnia and Herzegovina, Greece, Spain and Portugal. We compared different indices of genetic diversity in wolf populations and found a significant spatial trend in heterozygosity across Europe from south-west (lowest genetic diversity) to north-east (highest). The range of spatial autocorrelation calculated on the basis of three characteristics of genetic diversity was 650−850 km, suggesting that the genetic diversity of a given wolf population can be influenced by populations up to 850 km away. As an important outcome of this synthesis, we discuss the most pressing issues threatening wolf populations in Europe, highlight important gaps in current knowledge, suggest solutions to overcome these limitations, and provide recommendations for science-based wolf conservation and management at regional and Europe-wide scales.
Cystic echinococcosis (CE) is a severe parasitic disease caused by the species complex Echinococcus granulosus sensu lato. Human infections are most commonly associated with E. granulosus sensu stricto (s.s.), comprising genotypes G1 and G3. The objective of the current study was to provide first insight into the genetic diversity and phylogeography of genotype G3. Despite the epidemiological importance of the genotype, it has remained poorly explored due to the ambiguity in the definition of the genotype. However, it was recently demonstrated that long sequences of mitochondrial DNA (mtDNA) provide a reliable method to discriminate G1 and G3 from each other. Therefore, we sequenced near-complete mtDNA of 39 G3 samples, covering most of the known distribution range and host spectra of the genotype. The phylogenetic network revealed high genetic variation within E. granulosus s.s. G3 and while G3 is significantly less prevalent worldwide than G1, the genetic diversity of both of the genotypes is equally high. We also present the results of the Bayesian phylogeographic analysis, which yielded several well-supported diffusion routes of genotype G3 originating from Turkey and Iran, suggesting the Middle East as the origin of the genotype.
Among the genotype/species causing cystic echinococcosis (CE), the taxonomic status of Echinococcus canadensis is only partially resolved. Within E. canadensis, four genotypes (G6, G7, G8 and G10) have been described based on short mitochondrial sequences, of which G6 and G7 (the ‘camel’ and the ‘pig’ strain, respectively) are closely related and variously regarded as microvariants of a single strain G6/7. Globally, this G6/7 cluster is the second most important agent of human CE and is the predominant Echinococcus taxon in large parts of sub-Saharan Africa. To add data on the internal structure and the geographical distribution of this cluster, we analysed diversity and population structure of 296 isolates of E. canadensis from sub-Saharan Africa, the Middle East and Europe using the complete mitochondrial cytochrome c oxidase subunit 1 (cox1) (1,608 bp) and NADH dehydrogenase subunit 1 (nad1) (894 bp) gene sequences. Polymorphism of the mtDNA loci gave 51 (cox1), 33 (nad1) and 73 (cox1-nad1 concatenated) haplotypes. African and Middle Eastern isolates mainly grouped in a star-like structure around a predominant haplotype, while the European isolates produced more diversified networks. Although the cox1 diagnostic sequence for G6 is frequent in the African/Middle Eastern sub-cluster, and that for G7 is common in the European isolates, numerous intermediate variants prevent a clear distinction into ‘G6’ or ‘G7’, and the entire taxon is best treated as a common haplotype cluster G6/7. In contrast, wildlife isolates from the northern hemisphere showed that the G6/7 cluster is clearly distinct from both G8 and G10, and isolates of the latter genotypes were remarkably distant from each other. It is clear from the present study based on mitochondrial data that G6/7 is a coherent genotypic entity within E. canadensis that retains substantial intraspecific variance, and sub-populations share common ancestral polymorphisms and haplotypes. This study provides the basis for wider biogeographic comparison and population genetics studies of this taxon.
Human cystic echinococcosis (CE) has been eliminated or significantly reduced as a public health problem in several previously highly endemic regions. This has been achieved by the long-term application of prevention and control measures primarily targeted to deworming dogs, health education, meat inspection, and effective surveillance in livestock and human populations. Human CE, however, remains a serious neglected zoonotic disease in many resource-poor pastoral regions. The incidence of human alveolar echinococcosis (AE) has increased in continental Europe and is a major public health problem in parts of Eurasia. Better understanding of wildlife ecology for fox and small mammal hosts has enabled targeted anthelmintic baiting of fox populations and development of spatially explicit models to predict population dynamics for key intermediate host species and human AE risk in endemic landscapes. Challenges that remain for echinococcosis control include effective intervention in resource-poor communities, better availability of surveillance tools, optimal application of livestock vaccination, and management and ecology of dog and wildlife host populations.
Cystic echinococcosis, a zoonotic disease caused by Echinococcus granulosus sensu lato (s. l.), is a significant global public health concern. Echinococcus granulosus s. l. is currently divided into numerous genotypes (G1–G8 and G10) of which G1–G3 are the most frequently implicated genotypes in human infections. Although it has been suggested that G1–G3 could be regarded as a distinct species E. granulosus sensu stricto (s. s.), the evidence to support this is inconclusive. Most importantly, data from nuclear DNA that provide means to investigate the exchange of genetic material between G1–G3 is lacking as none of the published nuclear DNA studies have explicitly included G2 or G3. Moreover, the commonly used relatively short mtDNA sequences, including the complete cox1 gene, have not allowed unequivocal differentiation of genotypes G1–G3. Therefore, significantly longer mtDNA sequences are required to distinguish these genotypes with confidence. The main aim of this study was to evaluate the phylogenetic relations and taxonomy of genotypes G1–G3 using sequences of nearly complete mitogenomes (11,443 bp) and three nuclear loci (2984 bp). A total of 23 G1–G3 samples were analysed, originating from 5 intermediate host species in 10 countries. The mtDNA data demonstrate that genotypes G1 and G3 are distinct mitochondrial genotypes (separated by 37 mutations), whereas G2 is not a separate genotype or even a monophyletic cluster, but belongs to G3. Nuclear data revealed no genetic separation of G1–G3, suggesting that these genotypes form a single species due to ongoing gene flow. We conclude that: (a) in the taxonomic sense, genotypes G1 and G3 can be treated as a single species E. granulosus s. s.; (b) genotypes G1 and G3 should be regarded as distinct genotypes only in the context of mitochondrial data; (c) we recommend excluding G2 from the genotype list.
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.
Human cystic echinococcosis (CE) has been eliminated or significantly reduced as a public health problem in several previously highly endemic regions. This has been achieved by the long-term application of prevention and control measures primarily targeted to deworming dogs, health education, meat inspection, and effective surveillance in livestock and human populations. Human CE, however, remains a serious neglected zoonotic disease in many resource-poor pastoral regions. The incidence of human alveolar echinococcosis (AE) has increased in continental Europe and is a major public health problem in parts of Eurasia. Better understanding of wildlife ecology for fox and small mammal hosts has enabled targeted anthelmintic baiting of fox populations and development of spatially explicit models to predict population dynamics for key intermediate host species and human AE risk in endemic landscapes. Challenges that remain for echinococcosis control include effective intervention in resource-poor communities, better availability of surveillance tools, optimal application of livestock vaccination, and management and ecology of dog and wildlife host populations.
Echinococcus granulosus is a taeniid cestode and the etiological agent of an infectious zoonotic disease known as cystic echinococcosis (CE) or hydatid disease. CE is a serious public health concern in many parts of the world, including the Americas, where it is highly endemic in many regions. Echinococcus granulosus displays high intraspecific genetic variability and is divided into multiple genotypes (G1–G8, G10) with differences in their biology and etiology. Of these, genotype G1 is responsible for the majority of human and livestock infections and has the broadest host spectrum. However, despite the high significance to the public and livestock health, the data on genetic variability and regional genetic differences of genotype G1 in America are scarce. The aim of this study was to evaluate the genetic variability and phylogeography of G1 in several countries in America by sequencing a large portion of the mitochondrial genome. We analysed 8279 bp of mtDNA for 52 E. granulosus G1 samples from sheep, cattle and pigs collected in Argentina, Brazil, Chile and Mexico, covering majority of countries in the Americas where G1 has been reported. The phylogenetic network revealed 29 haplotypes and a high haplotype diversity (Hd = 0.903). The absence of phylogeographic segregation between different regions in America suggests the importance of animal transportation in shaping the genetic structure of E. granulosus G1. In addition, our study revealed many highly divergent haplotypes, indicating a long and complex evolutionary history of E. granulosus G1 in the Americas.