The ribosomal transcription units of five echinostomes and their taxonomic implications for the suborder Echinostomata (Trematoda: Platyhelminthes)

Five newly obtained nuclear ribosomal transcription unit (rTU) sequences from Echinostomatidae and Echinochasmidae are presented. The inter- and intrafamilial relationships of these and other families in the suborder Echinostomata are also analyzed. The sequences obtained are the complete rTU of Artyfechinostomum malayanum (9,499 bp), the near-complete rTU of Hypoderaeum conoideum (8,076 bp), and the coding regions (from 5'-terminus of 18S to 3'-terminus of 28S rRNA gene) in Echinostoma revolutum (6,856 bp), Echinostoma miyagawai (6,854 bp), and Echinochasmus japonicus (7,150 bp). Except for the longer first internal transcribed spacer (ITS1) in Echinochasmus japonicus, all genes and spacers were almost identical in length. Comprehensive maximum-likelihood phylogenies were constructed using the PhyML software package. The datasets were either the concatenated 28S + 18S rDNA sequences (5.7-5.8 kb) from 60 complete rTUs of 19 families or complete 28S sequences only (about 3.8-3.9 kb) from 70 strains or species of 22 families. The phylogenetic trees confirmed Echinostomatoidea as monophyletic. Furthermore, a detailed phylogeny constructed from alignments of 169 28S D1-D3 rDNA sequences (1.1-1.3 kb) from 98 species of 50 genera of 10 families, including 154 echinostomatoid sequences (85 species/42 genera), clearly indicated known generic relationships within Echinostomatidae and Echinochasmidae and relationships of families within Echinostomata and several other suborders. Within Echinostomatidae, Echinostoma, Artyfechinostomum, and Hypoderaeum appeared as monophyletic, while Echinochasmus (Echinochasmidae) was polyphyletic. The Echinochasmidae are a sister group to the Psilostomidae. The datasets provided here will be useful for taxonomic reappraisal as well as studies of evolutionary and population genetics in the superfamily Echinostomatoidea, the sole superfamily in the suborder Echinostomata.

Diversity of trematode cercariae among naturally infected lymnaeid snails from Phayao, Thailand

Lymnaeids are aquatic snails playing an important role in the transmission of many parasitic trematode species of veterinary and medical importance. In this study, we assessed the presence of cercarial flukes in naturally infected lymnaeid snails from Phayao province, Thailand, and determined the species diversity of both the intermediate snail hosts and parasite larvae. A total of 3,185 lymnaeid snails were collected from paddy fields at 31 sites in eight districts of Phayao province between October 2021 and December 2022. Larval fluke infection was assessed using the cercarial shedding method. The collected snails as well as emerging cercariae were identified at the species level via morphological and molecular methods. The sequences of snail internal transcribed spacer region 2 (ITS2) and cercarial 28S ribosomal RNA gene (28S rDNA) and cytochrome C oxidase1 (Cox1) were determined by PCR amplification and sequencing. Three species of lymnaeid snails were detected in this study, including Radix (Lymnaea) rubiginosa (Michelin, 1831), Radix (Lymnaea) swinhoei (Adams, 1866) and Austropeplea viridis (Quoy & Gaimard, 1832), of which R. rubiginosa was the most abundant, followed by A. viridis and R. swinhoei. The overall rate of trematode cercarial infection in the lymnaeid snails was 2.8% (90/3,185); the cercarial infection rate in R. rubiginosa and A. viridis was 3.5% (60/1,735) and 3.1% (30/981), respectively. No larval fluke infection was observed in the studied R. swinhoei (0/469). Nine morphotypes of cercariae were detected at 15 sites from four districts. The emerging cercariae were molecularly identified as Clinostomum sp., Aporocotylidae sp., Apharyngostrigea sp., Trichobilharzia sp., Apatemon sp., Pegosomum sp., Petasiger sp., Echinostoma revolutum and Plagiorchis sp. These findings emphasize the occurrence and diversity of trematode cercariae among naturally infected lymnaeid snails in Phayao province and could contribute to broadening our understanding of the host-parasite relationships between trematodes and their first intermediate hosts as well as developing effective interventions to control trematode parasitic diseases.

Molecular epidemiological analyses reveal extensive connectivity between Echinostoma revolutum (sensu stricto) populations across Eurasia and species richness of zoonotic echinostomatids in England

Echinostoma revolutum (sensu stricto) is a widely distributed member of the Echinostomatidae, a cosmopolitan family of digenetic trematodes with complex life cycles involving a wide range of definitive hosts, particularly aquatic birds. Integrative taxonomic studies, notably those utilising nad1 barcoding, have been essential in discrimination of E. revolutum (s.s.) within the 'Echinostoma revolutum' species complex and investigation of its molecular diversity. No studies, however, have focussed on factors affecting population genetic structure and connectivity of E. revolutum (s.s.) in Eurasia. Here, we used morphology combined with nad1 and cox1 barcoding to determine the occurrence of E. revolutum (s.s.) and its lymnaeid hosts in England for the first time, in addition to other echinostomatid species Echinoparyphium aconiatum, Echinoparyphium recurvatum and Hypoderaeum conoideum. Analysis of genetic diversity in E. revolutum (s.s.) populations across Eurasia demonstrated haplotype sharing and gene flow, probably facilitated by migratory bird hosts. Neutrality and mismatch distribution analyses support possible recent demographic expansion of the Asian population of E. revolutum (s.s.) (nad1 sequences from Bangladesh and Thailand) and stability in European (nad1 sequences from this study, Iceland and continental Europe) and Eurasian (combined data sets from Europe and Asia) populations with evidence of sub-population structure and selection processes. This study provides new molecular evidence for a panmictic population of E. revolutum (s.s.) in Eurasia and phylogeographically expands the nad1 database for identification of echinostomatids.

Research Note: Genetic analysis, pathology, and vectors of echinostomiasis, a zoonotic helminth infection in chickens in Bangladesh

Echinostomes (Trematoda: Echinostomatidae) are food-borne zoonotic flatworms that affect birds, animals and humans, and has been classified as neglected tropical diseases (NTDs) by the World Health Organization (WHO), which cause severe enteritis in poultry and hamper production. Here, we confirmed the species of echinostomes affecting chickens in Bangladesh along with their genetic analyses, pathology and vectors. We isolated and identified adult worms from chickens, cercariae from fresh water snails and metacerariae (MC) from some wild fishes. We recovered Echinostoma revolutum (10.3%) and Hypoderaeum conoideum (6.0%) from chickens. Zoonotic E. revolutum was confirmed by amplifying nad1 gene and subsequent sequencing. Several mutations were detected in nad1 gene and our isolates belonged to the Euro-Asian clade. We observed thickening of mucosal layer, hyperplasia of goblet cells, infiltration of eosinophils, lymphocytes and must cells in the infected intestine. About 5.3% snails were infected and the highest percentage of infection was found in Lymnaea luteola (12.1%). Echinostome infection in snails was the highest in November (9.6%) and lowest in February (3.1%) in Bangladesh. MC of echinostomes were identified from blue panchax (Aplocheilus panchax) and tank goby (Glossogobius giuris). In conclusion, echinostomiasis is a notable big problem in indigenous chickens in Bangladesh and people, especially, villagers are at risk.

[Morphological and molecular identification of trematode isloates from laying ducks in Nanchang City]

OBJECTIVE

To identify the species of trematodes isolated from laying ducks in Nanchang City using morphological and molecular approaches.

METHODS

Trematodes were isolated from the hepatobiliary duct, gallbladder and large intestine of market-sold laying ducks in Nanchang City. Following morphological characterization, total DNA was extracted from all trematode specimens, and internal transcribed spacer region (ITS) and cytochrome C oxidase subunit 1 (Cox1) genes were amplified using PCR assay and sequenced. Sequence alignment was performed using the Blast software, and homology and phylogenetic analyses were done in the trematode isolates based on ITS and Cox1 gene sequences.

RESULTS

The morphological characteristics of two trematode isolates from the large intestine of laying ducks were similar to those of Echinostoma revolutum and E. miyagawai, and the morphological characteristics of eight trematode samples isolated from the hepatobiliary duct and gallbladder of laying ducks were similar to those of Amphimerus anatis. The ITS and Cox1 gene sequences of the two trematode isolates from the large intestine of laying ducks had 99.3% and 98.9%-99.4% homology with E. miyagawai, and the phylogenetic analysis showed that two trematode isolates had the closest genetic relationship with E. miyagawai based on ITS and Cox1 gene sequences. The ITS gene sequences of eight trematode isolates from the hepatobiliary duct and gallbladder of laying ducks shared 95.1%-95.5% with Opisthorchis sudarikovi and Clonorchis sinensis, while the Cox1 gene sequences of eight trematode isolates from the hepatobiliary duct and gallbladder of laying ducks shared 86.3%-86.4% and 85.5%-85.7% with O. viverrini and O. sudarikovi. ITS gene sequence-based phylogenetic analysis showed that the duck-derived trematode isolates had the closest genetic relationship with C. sinensis, and Cox1 gene sequence-based phylogenetic analysis showed that the duck-derived trematode isolates had the closest genetic relationship with Metorchis orientalis and O. viverrini.

CONCLUSIONS

The trematode isolates from the large intestine of laying ducts in Nanchang City may be E. miyagawai, and the trematode isolates from the hepatobiliary duct and gallbladder may be an unidentified trematode species of the family Opisthorchiidae.

Echinostoma chankensis nom. nov., other Echinostoma spp. and Isthmiophora hortensis in East Asia: morphology, molecular data and phylogeny within Echinostomatidae

Life cycles, and morphological and molecular data were obtained for Echinostoma chankensis nom. nov., Echinostoma cinetorchis, Echinostoma miyagawai and Isthmiophora hortensis from East Asia. It was established that, based on both life cycle and morphology data, one of the trematodes is identical to the worms designated as Euparyphium amurensis. Genetic data showed that this trematode belongs to Echinostoma. The complex data on biological, morphological and genetic characterizations establish that the distribution of the morphologically similar species, I. hortensis and Isthmiophora melis, in the Old World are limited by the East Asian and European regions, respectively. Data on mature worms of East Asian E. miyagawai revealed morphological and genetic identity with E. miyagawai from Europe. However, E. miyagawai from Europe differs from E. miyagawai from the type locality (East Asia) in terms of reaching maturity and the morphology of cercariae. These data indicate that the European worm, designated E. miyagawai, does not belong to this species. An analysis of the phylogenetic relationships of Echinostomatidae was conducted based on the 28S, ITS2 and nad1 markers. Analysis using the nad1 gene for the known representatives of Echinostomatidae is carried out for the first time, showing that nuclear markers are ineffective separate from mitochondrial ones.

Echinostoma mekongi: Discovery of Its Metacercarial Stage in Snails, Filopaludina martensi cambodjensis, in Pursat Province, Cambodia

Echinostoma mekongi was reported as a new species in 2020 based on specimens collected from humans in Kratie and Takeo Province, Cambodia. In the present study, its metacercarial stage has been discovered in Filopaludina martensi cambodjensis snails purchased from a local market nearby the Tonle Sap Lake, Pursat Province, Cambodia. The metacercariae were fed orally to an experimental hamster, and adult flukes were recovered at day 20 post-infection. They were morphologically examined using light and scanning electron microscopes and molecularly analyzed by sequencing of their mitochondrial cox1 and nad1 genes. A total of 115 metacercariae (1-8 per snail) were detected in 60 (60.0%) out of 100 Filopaludina snails examined. The metacercariae were round, 174 µm in average diameter (163-190 µm in range), having a thin cyst wall, a head collar armed with 37 collar spines, and characteristic excretory granules. The adult flukes were elongated, ventrally curved, 7.3 (6.4-8.2)×1.4 (1.1-1.7) mm in size, and equipped with 37 collar spines on the head collar (dorsal spines in 2 alternating rows), being consistent with E. mekongi. In phylogenetic analyses, the adult flukes showed 99.0-100% homology based on cox1 sequences and 98.9-99.7% homology based on nad1 sequences with E. mekongi. The results evidenced that F. martensi cambodjensis snails act as the second intermediate host of E. mekongi, and hamsters can be used as a suitable experimental definitive host. As local people favor to eat undercooked snails, these snails seem to be an important source of human infection with E. mekongi in Cambodia.

Taxonomy of Echinostoma revolutum and 37-Collar-Spined Echinostoma spp.: A Historical Review

Echinostoma flukes armed with 37 collar spines on their head collar are called as 37-collar-spined Echinostoma spp. (group) or 'Echinostoma revolutum group'. At least 56 nominal species have been described in this group. However, many of them were morphologically close to and difficult to distinguish from the other, thus synonymized with the others. However, some of the synonymies were disagreed by other researchers, and taxonomic debates have been continued. Fortunately, recent development of molecular techniques, in particular, sequencing of the mitochondrial (nad1 and cox1) and nuclear genes (ITS region; ITS1-5.8S-ITS2), has enabled us to obtain highly useful data on phylogenetic relationships of these 37-collar-spined Echinostoma spp. Thus, 16 different species are currently acknowledged to be valid worldwide, which include E. revolutum, E. bolschewense, E. caproni, E. cinetorchis, E. deserticum, E. lindoense, E. luisreyi, E. mekongi, E. miyagawai, E. nasincovae, E. novaezealandense, E. paraensei, E. paraulum, E. robustum, E. trivolvis, and Echinostoma sp. IG of Georgieva et al., 2013. The validity of the other 10 species is retained until further evaluation, including molecular analyses; E. acuticauda, E. barbosai, E. chloephagae, E. echinatum, E. jurini, E. nudicaudatum, E. parvocirrus, E. pinnicaudatum, E. ralli, and E. rodriguesi. In this review, the history of discovery and taxonomic debates on these 26 valid or validity-retained species are briefly reviewed.

The complete mitochondrial genome of Echinostoma miyagawai: Comparisons with closely related species and phylogenetic implications

Echinostoma miyagawai (Trematoda: Echinostomatidae) is a common parasite of poultry that also infects humans. Es. miyagawai belongs to the "37 collar-spined" or "revolutum" group, which is very difficult to identify and classify based only on morphological characters. Molecular techniques can resolve this problem. The present study, for the first time, determined, and presented the complete Es. miyagawai mitochondrial genome. A comparative analysis of closely related species, and a reconstruction of Echinostomatidae phylogeny among the trematodes, is also presented. The Es. miyagawai mitochondrial genome is 14,416 bp in size, and contains 12 protein-coding genes (cox1-3, nad1-6, nad4L, cytb, and atp6), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs), and one non-coding region (NCR). All Es. miyagawai genes are transcribed in the same direction, and gene arrangement in Es. miyagawai is identical to six other Echinostomatidae and Echinochasmidae species. The complete Es. miyagawai mitochondrial genome A + T content is 65.3%, and full-length, pair-wise nucleotide sequence identity between the six species within the two families range from 64.2-84.6%. The Es. miyagawai sequences is most similar to Echinostoma caproni. Sequence difference are 15.0-33.5% at the nucleotide level, and 8.6-44.2% at the amino acid level, among the six species, for the 12 protein-coding genes. ATG and TAG are the most common initiation and termination codons, respectively. Twenty of the Es. miyagawai transfer RNA genes transcribe products of the conventional cloverleaf structure, while two of the transfer RNA genes, namely trnS1^(AGC) and trnS2^(UGA), have unpaired D-arms. Phylogenetic analyses using our mitochondrial data indicate that Es. miyagawai is closely related to other Echinostomatidae species, except for Echinostoma hortense, which forms a distinct paraphyletic branch, and Echinochasmus japonicus, which is outside the clade containing all other Echinostomatidae species. These phylogenetic results support the elevation of subfamily Echinostomatidae. Our dataset also provides a significant resource of molecular markers to study the taxonomy, population genetics, and systematics of the echinostomatids.

Echinostoma revolutum: Development of a high performance DNA-specific primer to demonstrate the epidemiological situations of their intermediate hosts

Echinostomiasis caused by the Echinostoma group, in particular E. revolutum are a significant problem for both humans and other animals. This group has a large number of morphological similarities that are difficult and time-consuming to identify. The present study aimed to develop high-performance tools for the detection of the prevalence of E. revolutum and to reveal the prevalence of E. revolutum infections in intermediate snail hosts in Lopburi province, Thailand. The snail specimens were collected by stratified sampling method and examined to collect trematodes in the larval stage. The specific primer was manually designed and based on 18 s rDNA and verified the specificity and sensitivity for use as an identification tool to compare with classical method, constructed by epidemic mapping. The overall prevalence value of E. revolutum was found to be 16.26%. Tha Luang district had the highest prevalence (70.14%), followed by Chai Badan, Phatthana Nikhom, Tha Wung, Ban Mi, Khok Samrong, Nong Muang and Sa Bot at 42%, 25.14%, 2.52%, 1.73%, 2%, 1.33% and 0.40%, respectively. With regard to the specific primer, it can amplify both cercarial and metacercarial DNA (90 pg/μl.) and discriminated E. revolutum from its hosts, other trematodes and other echinostome larvae with no cross-reactions. Therefore, the developed specific primer can be used as a species-specific identification tool with a high degree of sensitivity and specificity. Consequently, this data is important for monitoring the outbreak of E. revolutum. It can be applied for initiating surveillance programs of snail-borne diseases in both medical and veterinary studies.

Molecular characterisation of four echinostomes (Digenea: Echinostomatidae) from birds in New Zealand, with descriptions of Echinostoma novaezealandense n. sp. and Echinoparyphium poulini n. sp

Morphological and molecular characterisation of echinostome specimens (Digenea: Echinostomatidae) recovered in one Anas platyrhynchos L. and one Cygnus atratus (Latham) (Anseriformes: Anatidae) from New Zealand revealed the presence of two known species, Echinostoma miyagawai Ishii, 1932 and Echinoparyphium ellisi (Johnston & Simpson, 1944) and two species new to science. Comparative morphological and phylogenetic analyses supported the distinct species status of Echinostoma novaezealandense n. sp. ex Branta canadensis (L.), A. platyrhynchos and C. atratus, and Echinoparyphium poulini n. sp. ex C. atratus. Echinostoma novaezealandense n. sp., a species of the "revolutum" species complex characterised by the possession of a head collar armed with 37 spines, keyed down to E. revolutum but was distinguished from the latter in having a much narrower body with almost parallel margins, longer oesophagus, wider cirrus-sac, larger seminal vesicle, much smaller ventral sucker, ovary, Mehlis' gland and testes, more anteriorly located ovary and testes, and distinctly smaller eggs (81-87 × 42-53 vs 106-136 × 55-70 µm). This new species appears similar to Echinostoma acuticauda Nicoll, 1914 described in Australia but differs in having a longer forebody, more posteriorly located ovary and testes, and much smaller eggs (81-87 × 42-53 vs 112-126 × 63-75 µm). Echinoparyphium poulini n. sp. is differentiated from the four species of Echinoparyphium possessing 37 collar spines considered valid as follows: from E. chinensis Ku, Li & Chu, 1964 in having a much smaller body, four (vs five) angle spines and simple seminal vesicle (vs bipartite); from E. schulzi Matevosyan, 1951 in having a less robust body at a comparable body length, much smaller ventral sucker, ovary and testes, and longer but narrower eggs (87-109 × 50-59 vs 70-85 × 60-84 µm); and from the two smaller forms, E. serratum Howell, 1968 and E. aconiatum Dietz, 1909, in a number of additional metrical features correlated with body size and especially in the possession of much larger collar spines. Partial fragments of the mitochondrial nad1 and 28S rRNA genes were amplified for representative isolates of the four species and analysed together with sequences for Echinostoma spp. and Echinoparyphium spp. available on GenBank. Phylogenetic analyses based on the mitochondrial nad1 gene revealed congruence between the molecular data and species identification/delineation based on morphology; this was corroborated by the 28S rDNA sequence data.

Genetic characterization and phylogenetic analysis of echinostomes

We conducted this study to identify species and determine the phylogenetic relationships using ribosomal DNA (rDNA) sequences [partial sequences of 28S rDNA and second internal transcribed spacer (IT52)] of echinostomes collected from free-grazing ducks in Phitsanulok Province, Thailand. Four adult echinostomes were morphologically identified as Echinostoma revolutum, 4 as Hypoderaeulm conoideurn and 2 unidentified. Sequences of other species/isolates of echinostomes retrieved from the GenBank database were employed to compare and construct the phylogenetic tree. Three major lineages were found, namely, genus Echinostoma, genus Echinoparyphiulm and genus Hypoderaeulm. One of the unidentified echinostome specimen was 99% identical to and clustered with genus Echinoparyphiurm, whereas the other was located in the "revolutum" roup, but was closely related to the geographical isolates from America rather than from Thailand. This study indicates that 28S rDNA and 1T52 regions are suitable molecular markers for genetic characterization and phylogenetic analysis of echinostomes.

Allozyme analysis of the temporal populations of Echinostoma revolutum collected from domestic ducks in Khon Kaen Province, Thailand

Four temporal populations of Echinostoma revolutum (ER1, ER2, ER3, ER4) were collected from domestic ducks in Khon Kaen Province, Thailand during February-October 2008. The ER1, ER2, ER3 and ER4 were collected in February, April, June and October, respectively. The 12 enzymes encoding 15 loci were examined. Two loci were found in each of 3 enzymes, namely glucose-6-phosphate dehydrogenase (G6PD), malic enzyme (ME) and peptidase valine-leucine (PEPA). Of these, three loci, namely, G6pd-1, Me-1 and PepA-2, were polymorphic. Genotypes were assigned for the specific allelic profiles detected at these three polymorphic loci. Twenty-eight genotypes were observed in the 4 temporal populations of E. revolutum. Three genotypes, Er22, Er23 and Er25, were found in all populations. The Er6 genotype occurred had the highest frequency of all the populations. These 28 genotypes were clustered into 3 groups with genetic differences of 2-12% among the loci. A cluster of genotypes (Er1, Er3, Er9 and Er12) showed the greatest genetic difference among the genotypes (12% difference). These results show intraspecific variation exists in E. revolutum populations in domestic ducks from Khon Kaen Province, Thailand.

Revealing the secret lives of cryptic species: Examining the phylogenetic relationships of echinostome parasites in North America

The recognition of cryptic parasite species has implications for evolutionary and population-based studies of wildlife and human disease. Echinostome trematodes are a widely distributed, species-rich group of internal parasites that infect a wide array of hosts and are agents of disease in amphibians, mammals, and birds. We utilize genetic markers to understand patterns of morphology, host use, and geographic distribution among several species groups. Parasites from >150 infected host snails (Lymnaea elodes, Helisoma trivolvis and Biomphalaria glabrata) were sequenced at two mitochondrial genes (ND1 and CO1) and one nuclear gene (ITS) to determine whether cryptic species were present at five sites in North and South America. Phylogenetic and network analysis demonstrated the presence of five cryptic Echinostoma lineages, one Hypoderaeum lineage, and three Echinoparyphium lineages. Cryptic life history patterns were observed in two species groups, Echinostoma revolutum and Echinostoma robustum, which utilized both lymnaied and planorbid snail species as first intermediate hosts. Molecular evidence confirms that two species, E. revolutum and E. robustum, have cosmopolitan distributions while other species, E. trivolvis and Echinoparyphium spp., may be more geographically limited. The intra and interspecific variation detected in our study provides a genetic basis for seven species groups of echinostomes which will help accurately identify agents of disease as well as reveal cryptic aspects of trematode biology.

Echinostoma caproni: Identification of enolase in excretory/secretory products, molecular cloning, and functional expression

In order to investigate molecules that could be involved in host-trematode relationships, we have analysed the excretory/secretory products (ESP) of Echinostoma caproni following a proteomic approach. Actin, Gluthathione S-transferase (GST) and enolase have been identified in the ESP. Enolase, observed to be one of the most abundant proteins, was further characterized. The molecular cloning and in vitro expression in Escherichia coli of E. caproni enolase allowed us to determine that the protein contains 431 amino acids and a theoretical MW of 46272 Da. E. caproni enolase shows high homology to other trematode enolases. The recombinant protein binds specifically to human plasminogen in vitro, as observed for the native protein, confirming its properties as a host-interacting molecule.

Excretory-secretory proteome of larval Schistosoma mansoni and Echinostoma caproni, two parasites of Biomphalaria glabrata

Schistosoma mansoni and Echinostoma caproni are two trematode species that use different strategies (mimicry and immunosuppression, respectively) to interfere with the snail innate immune system. Parasites excretory-secretory (ES) products have been shown to play a key role in these host-parasite immune interactions. However, they remain largely uncharacterized in larval trematodes. We developed a global proteomic approach to characterize the ES proteome of S. mansoni and E. caproni primary sporocysts. In ES products of both parasites, we found proteins involved in reactive oxygen species scavenging, glycolysis, signalling or calcium binding (superoxide dismutase Cu/Zn; glutathione S-transferase; aldo-keto-reductase; triose-phosphate isomerase; glyceraldehyde-3-phosphate dehydrogenase; aldolase, enolase, MICAL-like, calreticulin). According to their predicted functions, we propose a model in which these proteins (i) are involved in antioxidant activity, (ii) prevent hemocyte encapsulation process or (iii) favor invasion and migration of sporocysts in host tissues. These results suggest that S. mansoni and E. caproni sporocysts develope a strong immune protection during the first hours of infection giving them enough time to build up a long lasting immune evasion strategy relying on molecular mimicry or immunosuppression, respectively.

Identification and expression of gene transcripts generated during an anti-parasitic response in Biomphalaria glabrata

In order to gain further insights into the molecular basis of gastropod anti-parasite immune responses, we investigated transcripts of Biomphalaria glabrata regulated during hemocytic encapsulation. Using a snail strain that is resistant to the parasite Echinostoma caproni, we performed suppression subtractive hybridization (SSH) to construct cDNA libraries of transcripts more abundantly expressed in unexposed or parasite-exposed snails. After sequence analysis and quantitative PCR analysis of expression, we identified 10 candidates of particular interest. They belonged to various functional groups such as detoxification enzymes (GST, SOD), antimicrobial proteins (LBI/BPI), protease inhibitors (cystatins), calcium-binding proteins, or C-type lectins. In situ hybridization (ISH) analysis revealed that one overexpressed cystatin-like candidate is specifically expressed in hemocytes participating in parasite encapsulation or aggregating at the site of infection. Two other candidates (C-type lectin and a LBP/BPI) were expressed in the albumen gland, further supporting the role of this organ in immunity and/or host-parasite interaction.

Echinostoma paraensei: differential gene transcription in the sporocyst stage

The sporocyst stage of trematode development plays the crucial role of establishing a successful infection in the molluscan intermediate host. Due to the small size and presence of this stage within the tissues of the host, much of our current knowledge of sporocyst biology relies on cultured specimens. To gain insight into the transcriptional patterns of early sporocysts, suppression subtractive hybridization was employed to identify 69 unique expressed sequence tags likely to be upregulated in cultured sporocysts of Echinostoma paraensei, a trematode parasite of the planorbid snail, Biomphalaria glabrata. Upwards of 70% of the unique sequences were not identified by homology to known genes. However, one transcript may encode an inhibitor of nitric oxide synthase, indicating a possible role in protection against host defense mechanisms. An array containing the majority of the sequenced clones was probed with in vivo-derived cDNA, confirming for the first time in vivo expression of putative sporocyst genes. However, qPCR quantification demonstrated significant reductions in transcription rates in cultured versus in vivo sporocysts for three of six transcripts tested. Additionally, five of the six tested transcripts demonstrated significant variation in expression over the entire life cycle, with the significant upregulation occurring during early intramolluscan development or in the free-living stages immediately preceding snail penetration, confirming the efficacy of the SSH technique.

Description of a tandem repeated DNA sequence of Echinostoma caproni and methods for its detection in snail and plankton samples

Echinostome larval stages in the snail have a great potential as effective competitors for the control of schistosomes and adult worms can cause painful intestinal diseases in humans. Ecology and transmission of the larval stages of trematodes are poorly understood, especially because their identification in field-collected samples by microscopy is difficult. We cloned, sequenced and analysed a 192 bp tandem repreated DNA sequence of Echinostoma caproni (EcSau3A), an often discussed antagonist of Schistosoma mansoni in Biomphalaria snails. PCR primers against this sequence can detect less than 10 fg of E. caproni DNA, 2 miracidia in snails 1 day p.i., 1 metacercaria in 50 mg snail tissue and 1 cercaria in 50 mg plankton with high specificity. Methods described in this study can support the discovery of fundamental ecological principles on distribution, host specificity and epidemiology of E. caproni larvae under field conditions.

Phylogenetic relationships of Echinostoma Rudolphi, 1809 (Digenea: Echinostomatidae) and related genera re-assessed via DNA and morphological analyses

In order to investigate the relationships within the Echinostomatidae two data sets of gene sequences were analysed. The first consisted of all previously published ND1 sequences (20) together with 17 new sequences. The latter represented six species from the cosmopolitan genera Echinostoma, Echinoparyphium, Hypoderaeum and Isthmiophora. The second data-set of ITS sequences again included all previously published sequences (12) and three new sequences from species of Echinostoma, Echinoparyphium and Isthmiophora. All new isolates, as well as voucher material from five previously sequenced isolates, were identified on the basis of morphological characters. The phylogenetic trees inferred from the ND1 data set helped to clarify the generic affiliation of all isolates and confirmed the morphological identifications. The only exception was Echinoparyphium aconiatum, whose current position in the genus Echinoparyphium was not supported by the sequence data. Although the ITS data provided insufficient resolution for an unequivocal solution to the relationships within the genus Echinostoma, it supported the identification of Echinoparyphium ellisi and the distinct species status of three isolates of Echinostoma revolutum as predicted from the ND1 data.

Description of the adult worms of a new Brazilian isolate of Echinostoma paraensei (Platyhelminthes:Digenea) from its natural vertebrate host Nectomys squamipes by light and scanning electron microscopy and molecular analysis

Echinostoma paraensei Lie and Basch, 1967 (Echinostomatidae:Platyhelminthes), a 37 collar spine echinostome of the "revolutum group", has been used extensively as a model organism to study the interactions of digenetic trematodes with both their snail and vertebrate hosts. This worm was first isolated from the snail Biomphalaria glabrata from Belo Horizonte (BH isolate), Minas Gerais State, Brazil, by Lie and Basch [J Parasitol (1967) 53:1192-1199]. The natural definitive host for the BH isolate was never determined, and it has been maintained in the laboratory since 1967 in B. glabrata and hamsters. In this study, using light and scanning electron microscopy and molecular analysis, we describe an echinostome recently obtained from its natural vertebrate host, the wild rodent Nectomys squamipes (Rodentia: Sigmodontinae) from Sumidouro, Rio de Janeiro State, Brazil (RJ isolate). This echinostome was also compared to the laboratory-maintained BH isolate of E. paraensei. We observed that adult worms of both BH and RJ isolates could be differentiated from other echinostome species by the relatively small size of the dorsal collar spines relative to lateral and corner collar spines. SEM confirmed the similarity of this morphological character between the two isolates. As additional diagnostic features, the tegumentary spines are scale-like and the region between the genital pore and the acetabulum lacks scales. There is a folded protuberance with a pore just posterior to the genital pore. The tegument of the acetabulum is unspined and radially wrinkled, and there are numerous randomly distributed small, domed, ciliated papillae. The sequences of the internal transcribed spacers of the nuclear rDNA complex of the RJ and BH isolates are identical. Together these shared features provide strong evidence that both isolates are the same and can be referred to as E. paraensei. In conclusion, we have identified, for the first time, one of the natural definitive hosts for E. paraensei, the rodent N. squamipes, and have extended the known geographical distribution of this species to include Sumidouro in Rio de Janeiro State, Brazil.

Analysis of messages expressed by Echinostoma paraensei miracidia and sporocysts, obtained by random EST sequencing

A lambdaZAP Express cDNA library was constructed with mRNA obtained from immature miracidia within eggs, hatched miracidia, and sporocysts of Echinostoma paraensei. This cDNA library was amplified and 213 expressed sequence tag (EST) sequences (averaging 466 nucleotides in length) were obtained. The mean percentage of unresolved bases within the EST sequences was 0.4%, ranging from 0 to 4.6%. The 213 ESTs represent 151 unique messages. BLAST (version 2.0.8) analysis disclosed that 64 unique E. paraensei messages (42.4%) had significant similarities (BLAST score < or =e-5), at deduced amino acid or nucleotide levels, with known sequences in the nonredundant GenBank databases or the dbEST database (NCBI). The remainder, 57.6% of the unique EST-encoded messages, scored nonsignificant hits. Most of the E. paraensei messages that could be assigned a cellular role based on sequence similarities were involved in gene/protein expression. Several ESTs scored highest similarities with sequences obtained from trematode species. A total of 22,560 nucleotides present in open reading frames from ESTs that aligned with known sequences was used to determine codon usage for E. paraensei. Analysis of a subset of eight ESTs that contained full-length open reading frames did not reveal a bias in codon usage. Also, EST sequences were found to contain 3' untranslated regions with an average length of 69.9 +/- 88.4 nucleotides (n = 46). The EST sequences were submitted to GenBank/dbEST, adding to the 51 available Echinostoma-derived sequences, to provide reference information for both phylogenetic analysis and study of general trematode biology.

Intraspecific variation in the rDNA its loci of 37-collar-spined echinostomes from North America: implications for sequence-based diagnoses and phylogenetics

The recent finding of the 37-collar-spined Echinostoma revolutum in North America prompted rDNA nucleotide sequence comparisons between this worm and the sympatric Echinostoma trivolvis. Three isolates of E. revolutum from distinct sites and 2 isolates of E. trivolvis collected from a single site were used in this analysis. Sequence data were compared to those from previously sequenced members of the 37-collar-spine group. The 3 North American isolates of E. revolutum were found to be identical, but they differed from Eurasian isolates of E. revolutum at 9 of the 1,006 sites sequenced. Further, 1 of the E. trivolvis isolates studied herein was identical to the published sequence for this species, but 6 nucleotide changes were observed in the second E. trivolvis isolate. Restriction fragment length polymorphisms at this locus support the nucleotide differences found between the E. trivolvis isolates. The degree of intraspecific variation detected raises questions regarding the utility of the internal-transcribed spacer regions of the ribosomal DNA repeat for taxonomic diagnosis and in phylogenetic studies for poorly differentiated groups, such as the 37-collar-spined congeners.

Experimental evidence of hybrid breakdown between genetically distinct populations of Echinostoma caproni

In this paper we investigate whether the assortative mating between individuals of the same genetic entity (i.e. coming from the same geographical area) of Echinostoma caproni, reported in a previous paper, may be explained by a post-zygotic isolating mechanism. The fecundity of the adults of 2 parental genetic entities and of their hybrids (i.e. F1, F2, F3) was quantified through 3 successive generations. Whereas the number of eggs released by F1 hybrids is similar to that of the mid-parent, that of recombinant hybrids (F2-3 hybrids) is significantly lower than that of F1 and that of the mid-parent. Since these results seem to demonstrate hybrid breakdown, 2 important factors maintaining reproductive isolation, i.e. pre-mating reproductive isolation and low hybrid fecundity, may influence the evolution of E. caproni.

Mitochondrial ND1 gene sequences used to identify echinostome isolates from Australia and New Zealand

Echinostomes were collected in Australia and New Zealand as cercariae, metacercariae or adults. Using DNA sequences from the mitochondrial ND1 gene Echinostoma revolutum and Echinostoma paraensei were discovered in Australia. The presence of a further five, as yet unidentified, echinostome species was inferred in Northern Australia and a further isolate, closely allied to E. revolutum, occurs in New Zealand. ND1 sequences of species within the genus diverge from each other by 9.6-30.8%. Sequence divergence levels among strains within a single species are 0-3.6%. The phylogenetic tree produced from the Australasian isolates, in addition to species described previously, identifies the 37-collar-spine species as a well supported monophyletic group. The five unidentified Australian species cluster away from the 37-collar-spine group. These unidentified species appear to divide further into > 37-collar-spine and < 37-collar-spine clusters. Three strains of E. revolutum, collected as metacercariae from snails, were identified from two ponds located 6 km apart. Two of these strains may be cycling through a planorbid snail, Glyptophysa sp., as first intermediate host; however, this hypothesis could not be confirmed as specimens could not be obtained to match sequences between larvae and adults.

Relative merits of nuclear ribosomal internal transcribed spacers and mitochondrial CO1 and ND1 genes for distinguishing among Echinostoma species (Trematoda)

Cryptic species, belonging to the 37 collar-spine Echinostoma group, were distinguished using nuclear rDNA ITS (884 bases) and mtDNA CO1 (257 bases) and ND1 (530 bases) sequences. Sequences were obtained from five 37 collar-spine species, Echinostoma trivolvis, E. paraensei, E. caproni, E. revolutum and E. sp.I, a parthenogenetic isolate from Africa. Three geographic isolates of E. caproni were compared. Average sequence divergence among the 37 collar-spine species range from 2.2% in the rDNA ITS through 8% for the CO1 and 14% for the ND1. In addition, genes were sequenced from 2 non 37 collar-spine species, E. hortense and an undescribed Australian species, E. sp. (Aus). For each gene, distances of terminals from a predicted ancestral sequence were calculated. These indicated that ND1 is diverging significantly faster than the other 2 regions. In the CO1 gene most substitutions are synonymous and saturation has been reached for the majority of pairwise comparisons. The ND1 gene exhibits greater pairwise divergence but less evidence of saturation due to weaker conservation of first and second codon positions. The ITS has no amino acid coding constraints and displays no evidence of saturation. Although all 3 regions successfully distinguished the nominal species, ND1 appears to be the most informative region for investigating relationships within the 37 collar-spine group.

Mating behaviour of Echinostoma caproni and E. trivolvis in concurrent infections in hamsters

Young adults of Echinostoma caproni and E. trivolvis were recovered from hamsters. Some worms of each species were exposed to [3H]tyrosine for 1 h to label sperm, and these were transplanted singly to uninfected hamsters with various combinations of unexposed worms of either the opposite species or both species. Worms recovered 5 days later were serially sectioned, processed for autoradiography and observed for the location of radioactive sperm. Interspecies mating was detected when E. caproni was the sperm donor and E. trivolvis the recipient, but not the converse. The cross-insemination rate during interspecies mating was very low (13%) when compared to the normal rate of E. caproni intraspecies mating (52%). When single donor adults of either E. caproni or E. trivolvis had a choice of both recipient species, no interspecies mating took place, but both self- and cross-inseminated in a non-restrictive mating pattern typical of echinostome species. After transplantation, both species localized in their normal habitat within the hamster intestine. However, 25% of opposite species recoveries were found within 1 cm of each other, making interspecies mating a possibility.

Molecular characterization of Echinostoma caproni and E. paraensei by random amplification of polymorphic DNA (RAPD) analysis

Genomic DNA from Echinostoma caproni and Echinostoma paraensei was amplified by the polymerase chain reaction using primers (5'-TCGTAGCCAA and 5'-TCACGATGCA), originally found to differentiate species and strain of Schistosoma. The 2 putative species of Echinostoma produced distinct banding patterns clearly distinguishable from one another, thereby suggesting that RAPD (random amplification of polymorphic DNA) analysis may be useful for the identification of echinostome strains and species previously misunderstood or undescribed, and that primers developed for species within a given genus, e.g., Schistosoma, may have broader application in identifying other trematodes.

Nuclear rDNA ITS sequence variation in the trematode genus Echinostoma: an aid to establishing relationships within the 37-collar-spine group

The taxonomic history of members of the 37-collar-spine group within the genus. Echinostoma has been very confused. We obtained DNA sequence data from the nuclear rDNA ITS1, 5.8S and ITS2 of 7 nominal species belonging to this group, Echinostoma trivolvis (Cort, 1914), E. revolutum (Frölich, 1802), E. caproni Richard, 1964, E. liei Jeyarasasingam et al. 1972, E. paransei Lie & Basch, 1967, two African isolates, E. sp.I and E. sp.II, and of one 28-collar-spined echinostome, E. hortense (Asada, 1926). Five of the eight species were clearly distinguishable using ITS data. Sequences from the remaining three taxa, E. caproni, E. sp.II and E. liei were identical to one another and the group containing these taxa was distant from other 37-collar-spine species on a phylogenetic tree. E. trivolvis and E. paraensei form a second, but less distinct group within the 37-collar-spine group. The resolution obtained using DNA sequencing will assist in the current reclassification of the group. It also provides a model for future work on sibling species.

The genetic relationships between Echinostoma caproni, E. paraensei, and E. trivolvis as determined by electrophoresis

Adults of Echinostoma caproni, E. paraensei, and E. trivolvis were processed for starchgel electrophoresis. Ten enzyme systems representing 12 structural loci were examined using three different buffer systems. E. paraensei and E. caproni were found to be genetically inbred as indicated by the lack of heterozygosity in individual worms. All three taxa showed fixed differences indicating they are distinct species. Fixed differences were found between E. paraensei and E. caproni in six enzyme systems, between E. paraensei and E. trivolvis in five enzyme systems, and between E. trivolvis and E. caproni in five enzyme systems. Phenic relationships among the three species showed E. caproni was genetically more similar to E. trivolvis than to E. paraensei.

A comparison of Echinostoma trivolvis and E. caproni using random amplified polymorphic DNA analysis

The random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) technique was applied to two closely-related echinostome species, Echinostoma trivolvis and E. caproni, demonstrate interspecific polymorphisms of genomic DNA. Band patterns generated using five individual primers showed that these two echinostomes were genetically distinct, although they share genomic DNA to some extent.

A comparison of Echinostoma caproni and Echinostoma trivolvis (Trematoda: Echinostomatidae) adults using isoelectrofocusing

An isoenzymatic analysis using thin-layer agarose gel isoelectrofocusing on laboratory strains of Echinostoma trivolvis and Echinostoma caproni adults showed characteristic monomorphic phenotypes for phosphoglucomutase and glucose phosphate isomerase. The fixed allelic variation observed between these 2 taxa is consistent with their current classification as distinct species.

Esterases in natural populations of normal and Echinostoma revolutum-infected Helisoma trivolvis (Gastropoda)

Esterases of the digestive gland-gonad (DGG) complex of individual snails from a wild population of Helisoma trivolvis infected with the trematode Echinostoma revolutum were analyzed by vertical slab PAGE and compared to similar DGG homogenates of uninfected conspecifics from the same population. Our analysis indicated that: 1. Four classes of esterases, some atypical, could be resolved using diagnostic inhibitors. 2. Uninfected snails demonstrated polymorphism for two of these four esterase groups, including cholinesterases (CHE), in the 34 individual DGGs analyzed. 3. The rarer of the two ChE phenotypes in the uninfected sample (29.4%) was present in 100% of the 17 infected snails examined. However, no changes in esterase zymograms of infected DGGs due to the parasite were noted. 4. The possibility that the 'rare' ChE phenotype is somehow related to host susceptibility to Echinostoma revolutum is discussed in view of similar apparent linkages in other snail-trematode systems.

Isoenzyme analysis of Echinostoma liei: comparison and hybridization with other African species

Isoenzyme analysis was carried out on the laboratory strain of Echinostoma liei. The results were compared with those from a preliminary study on Echinostoma caproni, Echinostoma togoensis, and Echinostoma sp. (A. Voltz, J. Richard, B. Pesson, and J. Jourdane, 1986, Annales de Parasitologie Humaine et Comparée, 61, 617-623). Isoelectrofocusing showed characteristic phenotypes for phosphoglucomutase (PGM, EC 5.4.2.2) and glucosephosphate isomerase (GPI, EC 5.3.1.9). The four experimental strains were monomorphic. Their genotypes were defined. Isoenzyme analysis of F1-hybrids and their F2 descendants indicated the subunit structure of both isoenzymes and showed that they were encoded by independent genes. Finally, it also suggested that the four strains corresponded to variants of the same species.

A genetic comparison between natural and laboratory strains of Echinostoma (Trematoda) by isoenzymatic analysis

A comparative isoenzyme study between a natural population of Echinostoma caproni and 2 strains of E. caproni and E. togoensis, maintained for a long time in the laboratory led to the following conclusions. (1) The natural E. caproni population showed polymorphism of associated PGM and GPI genotypes. Some zymograms were identical to those of experimental strains. Allelic frequencies show that the natural population is panmictic according to the Hardy-Weinberg equilibrium. (2) The laboratory strains were monomorphic, and interbreeding produced double-heterozygous F1 progeny, identical to those of the natural population.