Microdiversity of Echinococcus granulosus sensu stricto in Australia

Global distribution and definitive host range of Echinococcus species and genotypes: A systematic review

Echinococcus species (spp.) are regarded as neglected cestodes causing several potential zoonoses of global public health. This systematic review critically appraises the worldwide distribution of Echinococcus spp. and genotypes (Echinococcus spp.: recognized species in the genus; genotypes: variants identified within E. granulosus sensu lato.) in definitive hosts. We analyzed 82 studies from major databases, comprising 24 individual host species, including canids, felids, and a hyenid species. Canids, particularly dogs, were the most studied group among the host species, with E. granulosus sensu stricto (G1-G3) being the most frequently reported. E. granulosus s.s. was distributed across five major continents, while other Echinococcus spp. and genotypes exhibited an uneven continental distribution. The highest overlap of species existed among Asia, Europe, and Africa. Among the reported host species, 4.2 % were endangered (e.g. Lycaon pictus), 12.5 % species were vulnerable (e.g. Panthera leo, Panthera pardus, and Acinonyx jubatus), and 4.2 % were near threatened (e.g. Speothos venaticus). Overall, our review highlights the significance of canids, particularly dogs, as the core focus of scientific investigations, with E. granulosus s.s. being the most widely distributed species across five major continents, emphasizing the urgent need for continued research and public health efforts.

Echinococcus species in wildlife

Transmission of Echinococcus spp. in life cycles that involve mainly wildlife is well recognized for those species with small mammals as intermediate hosts (e. g. E. multilocularis), as well as for E. felidis and the 'northern' genotypes of E. canadensis (G8 and G10). In contrast, the remaining taxa of E. granulosus sensu lato are best known for their domestic life cycles, and the numerous wild mammal species (mainly ungulates) that have been recorded with cystic echinococcosis in the past were mainly considered a result of spill-over from the dog-livestock transmission system. This view was challenged with the advent of molecular characterization, allowing discrimination of the metacestodes, although the contribution of wild mammals to various Echinococcus life cycles has remained uncertain for scarcity of wildlife studies. Numerous records of cysts in wild ungulates date back to the 20th century, but cannot with certainty be allocated to the Echinococcus species and genotypes that are recognized today. This means that our current knowledge is largely restricted to studies of the past two decades that kept adding gradually to our concepts of transmission in various geographic regions. In particular, new insights were gathered in the past years on E. granulosus s.l. in wildlife of sub-Saharan Africa, but also on transmission patterns of E. multilocularis in previously neglected regions, e. g. North America. Here, an update is provided on the current state of knowledge on wild mammals as hosts for all Echinococcus species, listing >150 species of wild hosts with references, as well as estimates on their epidemiological impact and our current gaps of knowledge.

Introductory Chapter: Changes in Eco-System Change Echinococci - “One Health Concept” against Echinococci

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Survey and Molecular Characterization of Echinococcus granulosus sensu stricto from Livestock and Humans in the Altai Region of Xinjiang, China

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.

Food-borne zoonotic echinococcosis: A review with special focus on epidemiology

Echinococcosis is a neglected, WHO-listed cyclozoonotic parasitic disease that is caused by a number of species belonging to the genus Echinococcus. This disease is widespread across the globe, resulting in heavy economic losses for farmers and cystic disease in aberrant human hosts. This review paper briefly discussed taxonomy, a brief history, the magnitude of economic losses, host spectrum and life cycle, risk factors, and clinical manifestations. Furthermore, the copro- and sero-ELISA-based prevalence of echinococcosis on different continents was summarized. Finally, the authors analyzed the frequency and use of molecular epidemiology in the taxonomy of Echinococcus species based on molecular markers. This review will serve as a quick reference to Echinococcus.

Genetic diversity of Echinococcus granulosus sensu lato in China: Epidemiological studies and systematic review

Cystic echinococcosis (CE) is a neglected tropical zoonosis caused by Echinococcus granulosus sensu lato (s.l.) and remains a major public health concern globally. Here, CE isolates (n = 3310) with clearly defined genotypes and geographical origins in China were retrieved through our epidemiological survey (2016-2020) and systematic review (1992-2020). Existing known genotypes of Echinococcus granulosus sensu lato (E. granulosus s.l.) except for G4 have been found in China, particularly on the Tibetan Plateau, where their genetic diversity is unique to that part of the world. According to the systematic review, genetic compositions of E. granulosus s.l. in China were as follows: E. granulosus (G1, G3), 98.3%; Echinococcus ortleppi (G5), 0.1%; Echinococcus intermedius (G6, G7), 1.4%; and Echinococcus canadensis (G8, G10), 0.2%. Specifically, G1 was responsible for 97.7% of infections and characterized by the broadest host ranges and geographic distributions. Our epidemiological results showed a relatively stable genetic composition of E. granulosus s.l. in sheep and yaks from three CE hyperendemic provinces (Xinjiang, Sichuan, Qinghai). A higher proportion of fertile cysts were found in sheep (287/406, 70.7%) than in yaks (28/184, 15.2%). During the past 29 years, 51 cox1 haplotypes of E. granulosus s.l. were endemic in China. The ancestral haplotype (Hap_2) remained the most common haplotype, 12 relatively common haplotypes were endemic and nine newly reported haplotypes were found during the survey. Overall, our results demonstrate that the compulsory immunization of sheep and the pilot EG95 vaccination campaign in yaks are well matched with the current genotypic situation. In addition to yaks, we advocate for more surveillance of CE isolates from pigs, cattle, goats and camels, since their roles in the transmission and reservation of E. granulosus s.l. have been largely ignored in China.

Occurrence and genetic characterization of Echinococcus granulosus sensu lato from domestic animals in Central Iran

Background

The species complex of Echinococcus granulosus sensu lato (s.l.) causes cystic echinococcosis distributed worldwide. There is no genotype information from hydatid cysts in the intermediate hosts in Central Iran. Therefore, in this study, we analyzed the hydatid cysts in livestock slaughtered in an abattoir in this region. Six hundred fifty-seven hydatid cysts were isolated from 97 animals, including sheep, cattle, camels, and goats slaughtered in Yazd abattoir from September 2018 to January 2020. The demographic data was collected as well as cyst location, fertility, and viability. Out of 657 samples, 164 samples were genotyped. Then, phylogenetic analysis was performed using MEGAX. Statistical analyses were done using SPSS version 16.0 by chi-square with a significant difference of less than 0.05.

Results

Out of 164 samples, the G1-G3 complex genotype had the most frequency in samples, with 135 cases recognized. The G6/G7 was observed in 19 isolates and G5 was reported in nine samples. One sample was detected as Taenia hydatigena.

Conclusions

This study showed that G1-G3 and G6/G7 genotypes were presented in all animals, but G5 was reported only in cattle, goats, and camels. It is the first molecular identification of cystic echinococcosis in Central Iran. Hence, reporting G5 in livestock in this area should be considered due to transmission to humans.

Genotypes of Echinococcus Species from Cattle in Tanzania

Cystic echinococcosis is a zoonotic parasitic disease caused by Echinococcus species. Tanzania is one of the endemic countries with cystic echinococcosis. This study focussed on identifying genotypes of Echinococcus spp. in Tanzania. We collected 7 cysts from cattle in Mwanza municipal (n=4) and Loliondo district (n=3). The cysts from Mwanza were all E. ortleppi and fertile. In contrast, the cysts from Loliondo were all E. granulosus sensu stricto and sterile. Two from the 4 cysts were a new haplotype of E. ortleppi (G5). These results can improve the preventive and control programs for humans and livestock in Tanzania. To our knowledge, this study is considered the first to identify the genotype and haplotype of Echinococcus spp. in Tanzania.

Three species of Echinococcus granulosus sensu lato infect camels on the Arabian Peninsula

We report on the genetic identity of 36 Echinococcus cysts that were collected during a recent slaughterhouse survey of 810 locally bred camels (dromedaries) in the Eastern Province of the Kingdom of Saudi Arabia. Analysis of a partial nad1 gene sequence showed that the majority (n = 29) belonged to E. granulosus sensu stricto, four to E. canadensis G6/7, and three to E. ortleppi. Eight of the 29 E. granulosus s.s. cysts contained protoscoleces; all other cysts were calcified and non-viable. This is the first report of the presence E. ortleppi from the Arabian Peninsula, a parasite that is typically transmitted via cattle. The results indicate widespread infection of camels with CE in eastern Saudi Arabia and an active role of camels in the lifecycles of at least E. granulosus s.s.. Complete cox1 haplotype analysis of 21 E. granulosus s.s. isolates shows that the majority of variants circulating in eastern Saudi Arabia is distinct from but closely related to haplotypes from neighboring countries in the Middle East, which indicates the presence of this parasite in KSA for a longer period of time. All isolates of E. granulosus s.s. in this study belonged to the G1 cluster, although the G3 genotype has previously also been reported from the Middle East.

Occurrence of Echinococcusgranulosussensulato and Other Taeniids in Bhutan

The present research shows the results of a national study documenting the occurrence and genetic diversity of Echinococcus and Taenia species across Bhutan. Environmental dog faecal samples (n = 953) were collected from 2016 to 2018 in all 20 Bhutanese districts, mainly in urbanised areas. Cystic echinococcosis cysts were isolated from 13 humans and one mithun (Bos frontalis). Isolation of taeniid eggs from faeces was performed by sieving/flotation technique, followed by DNA isolation, PCR and sequence analyses for species identification (gene target: small subunit of ribosomal RNA). Genetic diversity of E. granulosuss.s. was based on the sequence (1609 bp) of the cox1 gene. A total of 67 out of 953 (7%) dog faecal samples were positive for at least one taeniid species. From the 670 free-roaming dog faecal samples, 40 (5.9%) were positive for taeniid DNA, 22 (3.2%) of them were identified as E. granulosuss.s. and four (0.5%) as E. ortleppi (G5). From the 283 faecal samples originating from yak-grazing areas, 27 (9.5%) were taeniid positive, including eight (2.8%) infected with E. granulosuss.s. and four (1.4%) with E. ortleppi. E. granulosuss.s. was identified in all isolates from human and the cyst from mithun. A haplotype network (cox1 gene) from E. granulosuss.s, including isolates from 12 dogs, two human and one mithun, revealed eight different haplotypes. The most common cox1 haplotype was the globally distributed Eg01, followed by Eg40 and Eg37 (previously described in China). Five new cox1 haplotypes (EgBhu1–5) originated from human, dogs, and a mithun were identified. The study indicated the contamination of urban areas and pastures with Echinococcus eggs in seven districts in Bhutan. The molecular characterisation of E. granulosuss.l. revealed different E. granulosuss.s. haplotypes as well as E. ortleppi. The transmission of T. multiceps was documented only in the western part of the country. Considering the zoonotic feature of E. granulosus s.s. and E. ortleppi and the economic impact of coenurosis caused by T. multiceps (also known as gid) in Bhutan, the findings of this study represent a significant contribution towards an epidemiological baseline for the establishment of a national control programme.

Molecular survey on cattle and sheep hydatidosis and first detection of Echinococcus canadensis (G6/G7) in sheep in Turkey

Larval stage of genus Echinococcus is the causing agent for the zoonotic infection which is life threatening known as Echinococcosis. The purpose of this study was the identification, molecular analysis and characterization of Echinococcus spp. in sheep and cattle. The sampling was done from slaughterhouse of Elazig, Turkey. A total of 85 isolates (sheep, n = 19 and cattle, n = 66) have been collected after slaughtering. Following the gDNA isolation and PCR products of mt-CO1 gene (446 bp) of all the samples were sequenced. Out of 85 isolates, 84 were recognized as Echinococcus granulosus sensu stricto and one sheep isolate was found as Echinococcus canadensis (G6/G7 ) which is identified for the first time in Turkey. However, single nucleotide polymorphism has been observed not only in samples of different animals but also in samples collected from the same cattle. Six liver and three lung hydatid cysts have been detected in cattle. Although no nucleotide differences have been observed in the liver samples, there was single nucleotide polymorphism (C→T) in 40th nucleotide of two lung cysts. As a result of haplotype analysis, 16 haplotypes of E. granulosus s.s. were detected in 66 cattle isolates whereas 7 haplotypes of E. granulosus s.s. were identified in 19 sheep samples.

Echinococcus granulosus sensu stricto, Echinococcus ortleppi; and E. intermedius (G7) are present in Bolivia

Cystic echinococcosis (CE) is a zoonotic disease caused by a complex of species known as Echinococcus granulosus sensu lato. CE is endemic in Argentina, Chile, Peru, Uruguay and the South part of Brazil. In contrast, little is known regarding the presence of CE in Bolivia. In this study, 35 cysts isolated from livestock (mostly from the Department of La Paz) and 3 from humans (La Paz, Oruro and Potosi) were genetically characterized analysing the sequence of the cox1 gene (1609 bp). In total, 30 cysts (from La Paz, Cochabamba and Beni) were characterized as E. granulosus sensu stricto (3 fertile and 4 non-fertile cysts from sheep, 8 fertile and 12 non-fertile cysts from cattle and 3 fertile cysts from humans). A detailed analysis of the cox1 haplotypes of E. granulosus s.s. is included. Echinococcus ortleppi (G5) was found in 5 fertile cysts from cattle (from La Paz and Cochabamba). Echinococcus intermedius (G7) was identified in 3 fertile cysts from pigs (from Santa Cruz). Additionally, E. granulosus s.s. was detected in 4 dog faecal samples, while E. ortleppi was present in other two dog faecal samples. The implications of these preliminary results in the future implementation of control measures are discussed.

Multiple haplotypes of Echinococcus granulosus sensu stricto in single naturally infected intermediate hosts

Cystic echinococcosis is a disease that affects both humans and animals, caused by cryptic species complex belonging to the platyhelminth Echinococcus granulosus sensu lato (s.l.). This disease is distributed worldwide, with E. granulosus sensu stricto (s.s.) being the most widespread of the species. High genetic variability has been demonstrated within E. granulosus s.s. studying single cyst per infected animal identifying a number of different haplotypes. However, few studies have addressed the genetic diversity of this parasite within a single intermediate host with multiple Echinococcus cysts. To date, it remains unknown if specific haplotypes of E. granulosus s.s. produce differences in biological features of the cyst. Here, we use the full length of the mitochondrial gene cox1 to determine E. granulosus s.s. haplotypes in samples from both cattle and sheep which harboured more than one cyst in different areas in Chile, where this parasite is endemic. We found 16 different haplotypes in 66 echinococcal cysts from 10 animals, and both cattle and sheep can harbour up to five different haplotypes of E. granulosus s.s. in the same animal. Regarding cyst fertility, five animals had both fertile and infertile Echinococcus cysts in both single and multiple haplotype infections. There was no association between haplotype and cyst fertility, size, or adventitial layer characteristics. Sampling and sequencing every Echinococcus cyst found in the intermediate host reveals a high molecular variability. We speculate that multiple haplotype infections could also suggest that intermediate hosts come from hyperendemic areas.

Long-read sequencing reveals a 4.4 kb tandem repeat region in the mitogenome of Echinococcus granulosus (sensu stricto) genotype G1

Background

Echinococcus tapeworms cause a severe helminthic zoonosis called echinococcosis. The genus comprises various species and genotypes, of which E. granulosus (sensu stricto) represents a significant global public health and socioeconomic burden. Mitochondrial (mt) genomes have provided useful genetic markers to explore the nature and extent of genetic diversity within Echinococcus and have underpinned phylogenetic and population structure analyses of this genus. Our recent work indicated a sequence gap (> 1 kb) in the mt genomes of E. granulosus genotype G1, which could not be determined by PCR-based Sanger sequencing. The aim of the present study was to define the complete mt genome, irrespective of structural complexities, using a long-read sequencing method.

Methods

We extracted high molecular weight genomic DNA from protoscoleces from a single cyst of E. granulosus genotype G1 from a sheep from Australia using a conventional method and sequenced it using PacBio Sequel (long-read) technology, complemented by BGISEQ-500 short-read sequencing. Sequence data obtained were assembled using a recently-developed workflow.

Results

We assembled a complete mt genome sequence of 17,675 bp, which is > 4 kb larger than the complete mt genomes known for E. granulosus genotype G1. This assembly includes a previously-elusive tandem repeat region, which is 4417 bp long and consists of ten near-identical 441–445 bp repeat units, each harbouring a 184 bp non-coding region and adjacent regions. We also identified a short non-coding region of 183 bp, which includes an inverted repeat.

Conclusions

We report what we consider to be the first complete mt genome of E. granulosus genotype G1 and characterise all repeat regions in this genome. The numbers, sizes, sequences and functions of tandem repeat regions remain to be studied in different isolates of genotype G1 and in other genotypes and species. The discovery of such ‘new’ repeat elements in the mt genome of genotype G1 by PacBio sequencing raises a question about the completeness of some published genomes of taeniid cestodes assembled from conventional or short-read sequence datasets. This study shows that long-read sequencing readily overcomes the challenges of assembling repeat elements to achieve improved genomes.

Molecular characterization of human echinococcosis in Sichuan, Western China

Cystic echinococcosis (CE) and alveolar echinococcosis (AE) are highly co-endemic in Sichuan, a part of Qinghai-Tibet Plateau where is a typical Tibetan nomadic community living area. In order to better understand the Echinococcus spp. of human being infected origins in this area, 140 lesions were collected from echinococcosis patients who were received operations during the period of 2014-2016 in different geographic districts in this region. Partial DNA sequences of the mitochondrial cox1 gene were analyzed. The genetic characterization of the isolates from 3 different places including Ganzi, Aba and Liangshan were assessed. Of all the 140 samples, the great majority was identified as Echinococcus granulosus sensu stricto (n = 108). Echinococcus multilocularis was confirmed to be another important pathogen of the human infections (n = 31). Additionally, one Echinococcus canadensis (G6/7) isolate from Ganzi was confirmed. Comparing the clinical diagnosis with the sequencing results, 6.4% (9/140) of the cases were misdiagnosed between AE and CE, and another 8.6% (12/140) were unclassified to sub-type in echinococcosis. Higher rates of misdiagnosis and unclassified diagnosis were found in AE cases (12.9%, 4/31 and 16.1%, 5/31 respectively) compared to CE (4.6%, 5/109 and 6.4%, 7/109 respectively). In E.granulosus s.s., a total of 34 haplotypes were detected, and 4 haplotypes were inferred from E.multilocularis. The haplotype networks of the 2 species exhibited a similar star-shaped feature with a dominant haplotype in the center. Geographically specific haplotypes were observed in Ganzi and Aba respectively. This study provides insight into the current species causing human echinococcosis in the Tibetan districts of Sichuan. E.granulosus s.s. and E.multilocularis are confirmed to be the main causative agents, and the existence of E.canadensis (G6/7) is also observed in the region. Molecular diagnosis was proven to be essential for the confirmation of human echinococcosis in the area.

Frequency and genetic diversity of Echinococcus granulosus sensu stricto in sheep and cattle from the steppe region of Djelfa, Algeria

Cystic echinococcosis (CE) of humans and animals is caused by various species of Echinococcus granulosus sensu lato. Of these, E. granulosus sensu stricto has the widest geographical distribution and is the most important agent of human cystic echinococcosis. Previous molecular studies showed that E. granulosus s.s. isolates from the Middle East and western Asia exhibit higher intraspecific diversity than those from other parts of the world, which led to hypotheses on the origin of the species in that region. However, various high-endemicity regions have not been sufficiently covered by such studies, including northern Africa as a well-known focus of this parasite. Here, we report data on the mitochondrial cox1 gene (1609bp) sequence diversity of E. granulosus s.s. from Algerian livestock. An abattoir survey of 1278 animals from the Algerian steppe region (Djelfa) resulted in CE prevalence of 13.9% in cattle (n = 266), 5.7% in sheep (n = 975), and 0% in goats (n = 37). All of 125 molecularly examined cyst isolates belonged to E. granulosus s.s. In total, 73 haplotypes were found, only five of which have been previously reported (from the Middle East and Australia). One haplotype sequence (EgAlg01X) was found to contain an insertion of three bases at the end of the gene. To the best of our knowledge, this has not been reported before for Echinococcus spp. Diversity values of our panel of Algerian samples were in the range of those that have been previously reported from the Middle East and far higher than those from elsewhere. This, together with the low number of shared haplotypes, indicates a more complex biogeographical history of this parasite than hitherto assumed.

Global phylogeography and genetic diversity of the zoonotic tapeworm Echinococcus granulosus sensu stricto genotype G1

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.

Genetic diversity and phylogeography of the elusive, but epidemiologically important Echinococcus granulosus sensu stricto genotype G3

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.

Two haplotype clusters of Echinococcus granulosus sensu stricto in northern Iraq (Kurdistan region) support the hypothesis of a parasite cradle in the Middle East

Human cystic echinococcosis (CE) caused by Echinococcus granulosus s.s. is a major public health problem in Iraqi Kurdistan with a reported surgical incidence of 6.3 per 100,000 Arbil inhabitants. A total of 125 Echinococcus isolates retrieved from sheep, goats and cattle were used in this study. Our aim was to determine species/genotypes infecting livestock in Iraqi Kurdistan and examine intraspecific variation and population structure of Echinococcus granulosus s.s. in this region and relate it to that of other regions worldwide. Using nucleotide sequences of the mitochondrial cytochrome c oxidase subunit 1 (cox 1) we identified E. granulosus s.s. as the cause of hydatidosis in all examined animals. The haplotype network displayed a double-clustered topology with two main E. granulosus s.s. haplotypes, (KU05) and (KU33). The 'founder' haplotype (KU05) confirmed the presence of a common lineage of non-genetically differentiated populations as inferred by the low non-significant fixation index values. Overall diversity and neutrality indices indicated demographic expansion. We used E. granulosus s.s. nucleotide sequences from GenBank to draw haplotype networks for the Middle East (Iran, Jordan and Turkey), Europe (Albania, Greece, Italy, Romania and Spain), China, Mongolia, Russia, South America (Argentina, Brazil, Chile and Mexico) and Tunisia. Networks with two haplotype clusters like that reported here for Iraqi Kurdistan were seen for the Middle East, Europe, Mongolia, Russia and Tunisia using both 827bp and 1609bp cox1 nucleotide sequences, whereas a star-like network was observed for China and South America. We hypothesize that the double clustering seen at what is generally assumed to be the cradle of domestication may have emerged independently and dispersed from the Middle East to other regions and that haplotype (KU33) may be the main haplotype within a second cluster in the Middle East from where it has spread into Europe, Mongolia, Russia and North Africa. Further studies using metacestodes of human origin are required to investigate the biological importance of E. granulosus s.s. haplotypes/clusters and their association, if any with clinical manifestations of CE infection.

Ecology and Life Cycle Patterns of Echinococcus Species

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

Phylogenetic Pattern, Evolutionary Processes and Species Delimitation in the Genus Echinococcus

An accurate and stable alpha taxonomy requires a clear conception of what constitutes a species and agreed criteria for delimiting different species. An evolutionary or general lineage concept defines a species as a single lineage of organisms with a common evolutionary trajectory, distinguishable from other such lineages. Delimiting evolutionary species is a two-step process. In the first step, phylogenetic reconstruction identifies putative species as groups of organisms that are monophyletic (share a common ancestor) and exclusive (more closely related to each other than to organisms outside the group). The second step is to assess whether members of the group possess genetic exchangeability (where cohesion is maintained by gene flow among populations) or ecological exchangeability (where cohesion is maintained because populations occupy the same ecological niche). Recent taxonomic reviews have recognized nine species within the genus Echinococcus. Phylogenetic reconstructions of the relationships between these putative species using mtDNA and nuclear gene sequences show that for the most part these nine species are monophyletic, although there are important incongruences that need to be resolved. Applying the criteria of genetic and ecological exchangeability suggests that seven of the currently recognized species represent evolutionarily distinct lineages. The species status of Echinococcus canadensis and Echinococcus ortleppi could not be confirmed. Coalescent-based analyses represent a promising approach to species delimitation in these closely related taxa. It seems likely, from a comparison of sister species groups, that speciation in the genus has been driven by geographic isolation, but biogeographic scenarios are largely speculative and require further testing.

A novel zoonotic genotype related to Echinococcus granulosus sensu stricto from southern Ethiopia

Complete mitochondrial and two nuclear gene sequences of a novel genotype (GOmo) related to Echinococcus granulosus sensu stricto are described from a metacestode isolate retrieved from a human patient in southwestern Ethiopia. Phylogenetically, the genotype is positioned within the E. granulosus sensu stricto/Echinococcus felidis cluster, but cannot easily be allocated to either species. Based on different mitochondrial DNA markers, it is closest to the haplotype cluster that currently defines the species E. granulosus sensu stricto (which includes variants showing the widely cited G1, G2 and G3 sequences), but is clearly not part of this cluster. Pairwise distances between GOmo and E. granulosus sensu stricto are in the range of those between the most distant members of the Echinococcus canadensis complex (G6-10) that were recently proposed as separate species. At this stage, we prefer to list GOmo informally as a genotype rather than giving it any taxonomic rank because our knowledge rests on a single isolate from a dead-end host (human), and its lifecycle is unknown. According to data on molecularly characterised Echinococcus isolates from this region, GOmo has never been found in the usual livestock species that carry cystic echinococcosis and the possibility of a wildlife source of this newly recognised zoonotic agent cannot be excluded. The discovery of GOmo adds complexity to the already diverse array of cystic echinococcosis agents in sub-Saharan Africa and challenges hypotheses on the biogeographical origin of the E. granulosus sensu stricto clade.