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

New morphological and molecular data for Xystretrum solidum (Gorgoderidae, Gorgoderinae) from Sphoeroides testudineus (Tetraodontiformes, Tetraodontidae) in Mexican waters

Adults of trematodes in the genus Xystretrum Linton, 1910 (Gorgoderidae, Gorgoderinae) are parasites found exclusively in the urinary bladders of tetraodontiform fishes. However, limited and unclear morphological data were used to describe the type species, X. solidum Linton, 1910. Here, we present the first detailed morphological information for a member of Xystretrum. Morphological characters were described using light and scanning electron microscopy (SEM) of Xystretrum specimens from Sphoeroides testudineus (Linnaeus) (Tetraodontiformes, Tetraodontidae), collected at six localities off the northern Yucatan Peninsula coast of the Gulf of Mexico. We also compared sequence fragments of the 28S (region D1–D3) ribosomal DNA and mitochondrial Cytochrome c oxidase subunit 1 (COI) gene with those available for other gorgoderine taxa. We assigned these Xystretrum specimens to X. solidum, despite the incompleteness of published descriptions. The data provide a foundation for future work to validate the identities of X. solidum, X. papillosum Linton, 1910 and X. pulchrum (Travassos, 1920) with new collections from the type localities and hosts. Comparisons of 28S and COI regions described here also provide an opportunity to evaluate the monophyletic status of Xystretrum.

Morphological and Molecular Identification of Paramphistomum epiclitum from Buffaloes in Pakistan

INTRODUCTION

Little is known about the genetic and morphological characters of Paramphistomum epiclitum. For the first time in Pakistan, adult flukes were morphologically characterized and the sequence variation in the nuclear ribosomal DNA (rDNA) region, including the first internal transcribed spacers (ITS1) and the 5.8S gene of the Paramphistomum epiclitum were studied.

METHODS

Adult amphistomes were examined by light microscopy and sequences of ITS1 and 5.88S rDNA genes were obtained.

RESULTS

Twenty adult flukes were measured, 13.17 ± 1.19 mm in length and 5.28 ± 1.34 mm in width. Seventeen adult flukes were sequenced and high sequence variability was observed in 5' end of ITS1 region. The 5.8S and 3' end of ITS1 sequences had 100% identity among the samples. A comparative analysis revealed that different types and numbers of repeats were found within each ITS1 region. The 3' end of ITS1 region from P. epiclitum showed 98% homology with P. cervi from China and formed a subclade with genetic distance of 0.1663. The 5.8S gene showed 100% identity within Paramphistomidae family and formed a sub-clade with P. epiclitum, P. leydeni, P. cervi and Cotylophoron cotylophorum species isolated from China, India and Uruguay.

CONCLUSION

This work provides new information on morphological identity and genetics of P. epiclitum from Pakistan.

Antagonism between parasites within snail hosts impacts the transmission of human schistosomiasis

Human disease agents exist within complex environments that have underappreciated effects on transmission, especially for parasites with multi-host life cycles. We examined the impact of multiple host and parasite species on transmission of the human parasite Schistosoma mansoni in Kenya. We show S. mansoni is impacted by cattle and wild vertebrates because of their role in supporting trematode parasites, the larvae of which have antagonistic interactions with S. mansoni in their shared Biomphalaria vector snails. We discovered the abundant cattle trematode, Calicophoron sukari, fails to develop in Biomphalaria pfeifferi unless S. mansoni larvae are present in the same snail. Further development of S. mansoni is subsequently prevented by C. sukari’s presence. Modeling indicated that removal of C. sukari would increase S. mansoni-infected snails by two-fold. Predictable exploitation of aquatic habitats by humans and their cattle enable C. sukari to exploit S. mansoni, thereby limiting transmission of this human pathogen.

Mini-FLOTAC as an alternative, non-invasive diagnostic tool for Schistosoma mansoni and other trematode infections in wildlife reservoirs

BACKGROUND

Schistosomiasis and food-borne trematodiases are not only of major public health concern, but can also have profound implications for livestock production and wildlife conservation. The zoonotic, multi-host nature of many digenean trematodes is a significant challenge for disease control programmes in endemic areas. However, our understanding of the epidemiological role that animal reservoirs, particularly wild hosts, may play in the transmission of zoonotic trematodiases suffers a dearth of information, with few, if any, standardised, reliable diagnostic tests available. We combined qualitative and quantitative data derived from post-mortem examinations, coprological analyses using the Mini-FLOTAC technique, and molecular tools to assess parasite community composition and the validity of non-invasive methods to detect trematode infections in 89 wild Hubert's multimammate mice (Mastomys huberti) from northern Senegal.

RESULTS

Parasites isolated at post-mortem examination were identified as Plagiorchis sp., Anchitrema sp., Echinostoma caproni, Schistosoma mansoni, and a hybrid between Schistosoma haematobium and Schistosoma bovis. The reports of E. caproni and Anchitrema sp. represent the first molecularly confirmed identifications for these trematodes in definitive hosts of sub-Saharan Africa. Comparison of prevalence estimates derived from parasitological analysis at post-mortem examination and Mini-FLOTAC analysis showed non-significant differences indicating comparable results between the two techniques (P = 1.00 for S. mansoni; P = 0.85 for E. caproni; P = 0.83 for Plagiorchis sp.). A Bayesian model, applied to estimate the sensitivities of the two tests for the diagnosis of Schistosoma infections, indicated similar median posterior probabilities of 83.1% for Mini-FLOTAC technique and 82.9% for post-mortem examination (95% Bayesian credible intervals of 64.0-94.6% and 63.7-94.7%, respectively).

CONCLUSIONS

Our results showed that the Mini-FLOTAC could be applied as an alternative diagnostic technique for the detection of the zoonotic S. mansoni and other trematodes in rodent reservoirs. The implementation of non-invasive diagnostics in wildlife would offer numerous advantages over lethal sampling methodologies, with potential impact on control strategies of zoonotic helminthiases in endemic areas of sub-Saharan Africa and on fostering a framework of animal use reduction in scientific practice.

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.

Molecular identification and histological aspects of Renicola sloanei (Digenea: Renicolidae) in Puffinus puffinus (Procellariiformes): a first record

Abstract Renicolids are parasites that inhabit the renal tubules and ureters of molluscivorous and piscivorous birds. Puffinus puffinus is a migratory seabird that was identified as the definitive host of Renicola spp. Studies focusing on the renicolid species and the resulting renal lesions are valuable for their association with causes of stranding in seabirds. The aim of this study was to identify the renicolid trematodes and evaluate the histological findings in two P. puffinus stranded on the coast of Paraná state, Brazil. The parasites were evaluated by histologic, ultrastructural and molecular assays, while tissue changes were analyzed by histologic methods. The morphological and morphometrical characteristics of the parasites, along with polymerase chain reaction and sequencing assays (ribosomal and mitochondrial regions), identified the species as Renicola sloanei. The results also suggest that this helminth can be the adult form of Cercaria pythionike. The dilation of collecting ducts was the main histological finding in the kidneys. In conclusion, R. sloanei was identified, and for the first time, P. puffinus was described as a host of this digenean inducing mild renal changes.

The diverse echinostomes from East Africa: With a focus on species that use Biomphalaria and Bulinus as intermediate hosts

Echinostomes are a diverse group of digenetic trematodes that are globally distributed. The diversity of echinostomes in Africa remains largely unknown, particularly in analyses using molecular markers. Therefore, we were interested in the composition and host usage patterns of African echinostomes, especially those that also use schistosome transmitting snails as intermediate hosts. We collected adults and larval stages of echinostomes from 19 different localities in East Africa (1 locality in Uganda and 18 in Kenya). In this study we provide locality information, host use, museum vouchers, and genetic data for two loci (28S and nad1) from 98 samples of echinostomes from East Africa. Combining morphological features, host use information, and phylogenetic analyses we found 17 clades of echinostomes in East Africa. Four clades were found to use more than one genus of freshwater snails as their first intermediate hosts. We also determined at least partial life cycles (2 of the 3) of four clades using molecular markers. Of the 17 clades, 13 use Biomphalaria or Bulinus as a first intermediate host. The overlap in host usage creates opportunities for competition, including against human schistosomes. Thus, our study can be used as a foundation for future studies to ascertain the interactions between schistosomes and echinostomes in their respective intermediate hosts.

Is species identification of Echinostoma revolutum using mitochondrial DNA barcoding feasible with high-resolution melting analysis?

The taxonomic evaluation of Echinostoma species is controversial. Echinostoma species are recognized as complex, leading to problems associated with accurate identification of these species. The aim of this study was to test the feasibility of using DNA barcoding of cytochrome c oxidase subunit I (COI) and NADH dehydrogenase subunit 1 (ND1) conjugated with high-resolution melting (HRM) analysis to identify Echinostoma revolutum. HRM using COI and ND1 was unable to differentiate between species in the "revolutum complex" but did distinguish between two isolates of 37-collar-spined echinostome species, including E. revolutum (Asian lineage) and Echinostoma sp. A from different genera, e.g., Hypoderaeum conoideum, Haplorchoides mehrai, Fasciola gigantica, and Thapariella anastomusa, based on the T_m values derived from HRM analysis. Through phylogenetic analysis, a new clade of the cryptic species known as Echinostoma sp. A was identified. In addition, we found that the E. revolutum clade of ND1 phylogeny obtained from the Thailand strain was from a different lineage than the Eurasian lineage. These findings reveal the complexity of the clade, which is composed of 37-collar-spined echinostome species found in Southeast Asia. Taken together, the systematic aspects of the complex revolutum group are in need of extensive investigation by integrating morphological, biological, and molecular features in order to clarify them, particularly in Southeast Asia.

Molecular phylogeny provides new insights on the taxonomy and composition of Lyperosomum Looss, 1899 (Digenea, Dicrocoeliidae) and related genera

Lyperosomum Looss, 1899 is one of the largest genera of the Dicrocoeliidae and is one of the best examples of the systematic complexity and taxonomic instability within this family. We present the molecular analyses based on novel sequences of nuclear and mitochondrial genes obtained from 56 isolates of adult flukes and larval stages of dicrocoeliids belonging to Lyperosomum, Skrjabinus, Zonorchis as well as previously available sequence data. According to obtained results we propose to return Zonorchis clathratus and Z. petiolatus into Lyperosomum, and to recognize L. alagesi as a synonym of L. petiolatum. Our study shows that L. petiolatum commonly occurs in Europe in corvids as well as in several species of migratory songbirds, e.g. Sylvia atricapilla. At the same time, the Turdidae appear to host a distinct species of Lyperosomum. The phylogenetic analysis has clearly demonstrated the paraphylepic nature of Lyperosomum and indicated the need of its thorough revision preferably using specimens from type hosts and type territories of nominal species. In addition, inclusion of numerous not yet sequenced dicrocoeliid genera into future phylogenetic studies is necessary to clarify the interrelationships of taxa within the family and stabilize its system.

Characterization of Echinostoma revolutum and Echinostoma robustum from ducks in Bangladesh based on morphology, nuclear ribosomal ITS2 and mitochondrial nad1 sequences

Precise discrimination of Echinostoma species within the 'revolutum' group is quite difficult because of their morphological similarities. The objective of this study was to precisely characterize the echinostomes of ducks from Bangladesh based on both morphological and molecular characteristics. Two Echinostoma species were identified: E. revolutum and E. robustum. In the phylogenetic trees (ITS2 and nad1), E. revolutum and E. robustum belonged to their respective Eurasian clade, which is distinct from the American clade. These results suggest that both species have two distinct and geographically separated lineages, Eurasian and American. Our molecular and morphological data combined with previously published data supports the synonymy of E. robustum, E. miyagawai, and E. friedi previously based on either molecular or morphological evidence. This study thus improves our understanding of species diversity of the 'revolutum' group, particularly in Asia.

Clinostomum poteae n. sp. (Digenea: Clinostomidae), in the trachea of a double-crested cormorant Phalacrocorax auritus Lesson, 1831 and molecular data linking the life-cycle stages of Clinostomum album Rosser, Alberson, Woodyard, Cunningham, Pote & Griffin, 2017 in Mississippi, USA

Clinostomum spp. (Digenea: Clinostomidae) are a group of trematodes commonly found in the buccal cavity and oesophagus of a variety of piscivorous birds. The metacercariae, colloquially known as "yellow grubs," have been reported from a diverse group of freshwater fishes worldwide. In the catfish farming region of the southeastern USA, piscivorous birds present a continuous challenge for aquaculturists in the form of fish depredation and the introduction of trematodes into these static, earthen pond systems. Clinostomum spp. are commonly encountered in farm-raised catfish. While generally considered pests of minimal importance, heavy infections can result in unmarketable fillets. Of the piscivorous birds that frequent catfish aquaculture operations in the southeastern US, the double-crested cormorant (Phalacrocorax auritus Lesson) is one of the most damaging, although reports of Clinostomum spp. from P. auritus are limited. In this study, adult trematodes morphologically consistent with Clinostomum sp. were found in the trachea of a double-crested cormorant captured in Lowndes Co., Mississippi, USA. These specimens differed from other recognised Clinostomum spp. in several key morphological characters. Moreover, sequence data of mitochondrial cytochrome c oxidase subunit 1 gene (cox1), nicotinamide adenine dinucleotide dehydrogenase subunit 1 gene (nad1) and ribosomal internal transcribed spacer (ITS) regions did not match any known Clinostomum sp. for which sequence data are available. While genetically similar to C. marginatum and C. album Rosser, Alberson, Woodyard, Cunningham, Pote & Griffin, 2017 reported from the great egret Ardea alba L. in Mississippi, these adult clinostomids were larger in size and limited to the trachea, whereas both C. marginatum Rudolphi, 1819 and C. album are found in the oral cavity and esophagus. Given these distinct morphological and molecular characters we propose a new member of the genus, known hereafter as Clinostomum poteae n. sp. Additionally, larval stages in the life-cycle of C. album are morphologically and molecularly identified for the first time from ramshorn snails Planorbella trivolvis Say and fathead minnows Pimephales promelas Rafinesque.

Alligator wrestling: morphological, molecular, and phylogenetic data on Odhneriotrema incommodum (Leidy, 1856) (Digenea: Clinostomidae) from Alligator mississippiensis Daudin, 1801 in Mississippi, USA

Based on specimens collected from harvested American alligator Alligator mississippiensis Daudin, 1801 in Mississippi, USA, novel molecular data for both nuclear ribosomal genes (18S, ITS1-5.8S, ITS2, and 28S) and mitochondrial genes (cytochrome c oxidase subunit 1 and nicotinamide adenine dinucleotide dehydrogenase subunit 1) are provided for Odhneriotrema incommodum (Leidy, 1856), a trematode of the family Clinostomidae Lühe, 1901 infecting A. mississippiensis and the Florida spotted gar Lepisosteus platyrhincus DeKay, 1842. This represents the first sequencing data available for the genus Odhneriotrema and the subfamily Nephrocephalinae Travassos, 1928. Additionally, the results of phylogenetic analyses, additional morphometric data, a photomicrograph, and a line drawing supporting the present identification of O. incommodum are provided. These data will aid in elucidating the life cycle of O. incommodum through molecular identification of larval stages as well as understanding the evolutionary history of Clinostomidae and its subfamilies. Implications for the currently accepted organization of the Clinostomidae are discussed.

Evidence of Diversity, Site, and Host Specificity of Sea Turtle Blood Flukes (Digenea: Schistosomatoidea: "Spirorchiidae"): A Molecular Prospecting Study

Neospirorchis (Digenea: "Spirorchiidae") are blood flukes of sea turtles. Trematodes tentatively identified as Neospirorchis sp. infect various sites within sea turtles inhabiting waters of the southeastern United States, but efforts to obtain specimens adequate for morphologic study has proven difficult. Two genetic targets, the internal transcribed spacer region of the ribosomal RNA gene and the partial mitochondrial cytochrome c oxidase subunit I gene, were used to investigate potential diversity among parasite specimens collected from stranded sea turtles. Sequence data were obtained from 215 trematode and egg specimens collected from 92 individual free-ranging cheloniid sea turtles comprising 4 host species. Molecular analysis yielded more than 20 different genotypes. We were able to assign 1 genotype to 1 of the 2 recognized species, Neospirorchis pricei Manter and Larson, 1950 . In many examples, genotypes exhibited host and site specificity. Our findings indicate considerable diversity of parasites resembling Neospirorchis with evidence of a number of uncharacterized blood flukes that require additional study.

Molecular and morphological characterization of Isthmiophora melis (Schrank, 1788) Luhe, 1909 (Digenea: Echinostomatidae) from American mink (Neovison vison) and European polecat (Mustela putorius) in Lithuania

The specimens collected from American mink (Neovison vison) and European polecat (Mustela putorius) in Lithuania were morphologically identified as Isthmiophora melis (Schrank, 1788) Lühe, 1909 and were molecularly characterized through sequencing of partial 18S rDNA, 28S rDNA, ITS1- 5.8S-ITS2 region, and ND1. Relations of I. melis to other species of the genus Isthmiophora Lühe 1909 were discussed. According to ITS1 and ND1 sequences the closest species to I. melis is Isthmiophora hortensis (Asada, 1926).

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.

Long-Distance Travellers: Phylogeography of a Generalist Parasite, Pholeter gastrophilus, from Cetaceans

We studied the phylogeography and historical demography of the most generalist digenean from cetaceans, Pholeter gastrophilus, exploring the effects of isolation by distance, ecological barriers and hosts’ dispersal ability on the population structure of this parasite. The ITS2 rDNA, and the mitochondrial COI and ND1 from 68 individual parasites were analysed. Worms were collected from seven oceanic and coastal cetacean species from the south western Atlantic (SWA), central eastern Atlantic, north eastern Atlantic (NEA), and Mediterranean Sea. Pholeter gastrophilus was considered a single lineage because reciprocal monophyly was not detected in the ML cladogram of all individuals, and sequence variability was <1% for mtDNA and 0% for ITS2. These results rule out a recent suggestion that P. gastrophilus would actually be a cryptic-species complex. The genetic cohesion of P. gastrophilus could rely on the extensive exploitation of wide-ranging and highly mobile cetaceans, with a putative secondary role, if any, of intermediate hosts. Unique haplotypes were detected in SWA and NEA, and an AMOVA revealed significant population structure associated to the genetic variation in these regions. The Equator possibly acts as a significant geographical barrier for cetacean movements, possibly limiting gene flow between northern and southern populations of P. gastrophilus. A partial Mantel tests revealed that the significant isolation of NEA populations resulted from geographic clustering. Apparently, the limited mobility of cetaceans used by P. gastrophilus as definitive hosts in this region, coupled with oceanographic barriers and a patchy distribution of potential intermediate hosts could contribute to significant ecological isolation of P. gastrophilus in NEA. Rather unexpectedly, no genetic differentiation was found in the Mediterranean samples of this parasite. Historical demographic analyses suggested a recent population expansion of P. gastrophilus in the Atlantic Ocean, perhaps linked to initial association and subsequent spreading in cetaceans.

Molecular Phylogenetic Analysis of Infidum similis, Including Morphological Data and Estimation of its Genome Size

:   Infidum similis Travassos, 1916 (Dicrocoeliidae: Leipertrematinae) was found in the gall bladder of Leptophis diplotropis Günther, 1872 from El Podrido, Acapulco, Guerrero, Mexico. A phylogenetic analysis based on partial sequences of the 28S ribosomal RNA using maximum likelihood (ML) and Bayesian inference (BI) analyses was carried out to assess its phylogenetic position within suborder Xiphidiata, alongside members of the superfamilies Gorgoderoidea and Plagiorchoidea. The phylogenetic trees showed that the genus is most-closely related to the Plagiorchoidea rather than to the Gorgoderoidea, in keeping with previous taxonomic designations. Phylogenies obtained from ML and BI analysis of the 28S rDNA gene revealed a well supported clade in which Choledocystus hepaticus (Lutz, 1928) Sullivan, 1977 is sister to I. similis. On the other hand, a tree obtained using a partial sequence of the cytochrome c oxidase subunit 1 (cox1) mtDNA gene (ML and BI analysis), with species supposed to be closely related to I. similis according to 28S, does not support this relatedness. Based on the independence of Infidum from the subfamily Leipertrematinae Yamaguti, 1958 , our results clearly demonstrated that the genus corresponds to a different family and with species closely related to C. hepaticus within Plagiorchoidea. New data are presented about the tegumental surface of I. similis by scanning electron microscopy as well as the estimation of its haploid genome size using Feulgen Image Analysis Densitometry of sperm nuclei as part of the characterization of this species. This is the first genome size estimated for a member of Plagiorchiida, and these data will provide a new source of knowledge on helminth diversity and evolutionary studies. This constitutes the first host record, and new geographical distribution, for this species in Mexico.

Digenean trematode cysts within the heads of threatened Galaxiella species (Teleostei : Galaxiidae) from south-eastern Australia

The dwarf galaxias (Galaxiella pusilla) and little galaxias (Galaxiella toourtkoourt) are both threatened freshwater fish from south-eastern Australia. Occasionally populations have been found with enlarged heads associated with the accumulation of ‘white balls’, but the cause of these deformities has not previously been investigated. In this study, histopathology and molecular techniques were employed to identify cysts extracted from the heads of Galaxiella species across six populations. Histopathology and DNA sequences from both mitochondrial (cytochrome c oxidase subunit I) and nuclear (ribosomal internal transcribed spacer 1) regions identified the cysts as metacercariae of Apatemon gracilis (Rudolphi, 1819), a cosmopolitan digenean trematode species. Heavy infestations of trematode metacercariae within Galaxiella populations are of concern due to the potential to cause increased mortality associated with altered behaviour of the fish host that increases the likelihood of predation. Direct mortality from infestations is also possible, but not quantified in this study.

Life-history trade-offs in a generalist digenean from cetaceans: the role of host specificity and environmental factors

Background

Adults and larvae of generalist parasites are exposed to diverse hosts and local environmental conditions throughout their life cycles, thus local adaptation is expected to occur through phenotypic plasticity and/or natural selection. We investigated how the combined effect of cryptic host specificity and local selective pressures could shape reproductive traits of a putative generalist parasite in the oceanic realm.

Methods

The LSU rDNA, ITS2 and the mt-COI of individuals of the digenean Pholeter gastrophilus (Kossack, 1910) Odhner, 1914 (Heterophyidae Leiper, 1909) from oceanic striped dolphins, Stenella coeruleoalba Meyen, and coastal bottlenose dolphins, Tursiops truncatus Montagu, in the western Mediterranean were used to elucidate whether worms were conspecific. Infection parameters were compared between both dolphin species. General Linear Mixed Models were used to analyse the influence of host species on four reproductive traits of P. gastrophilus: body size, maturity stage (non-gravid/gravid), egg size, and number of eggs in utero. AIC values were used to rank competing models, and p-values to assess the effect of specific predictors.

Results

Evidence indicated that worms collected from both dolphin species were conspecific. All worms collected were gravid and infection parameters did not differ between dolphin species. However, body size and egg size of individuals of P. gastrophilus were significantly larger in striped dolphins. The number of eggs in utero did not significantly differ between dolphin species but, for a given body size, worms in bottlenose dolphins harboured more eggs. A trade-off between egg size and egg number was found in worms from both dolphin species, with a higher slope in striped dolphins.

Conclusions

Apparently, striped dolphin is a more suitable host for P. gastrophilus, but reproductive investment seems to be adapted to the habitat where the life-cycle develops. Worms from striped dolphins likely face the problem of finding intermediate hosts in the oceanic realm and apparently invest into offspring size to enhance the early survival of larvae and the potential to multiply asexually within the first intermediate host. The small-sized worms from bottlenose dolphins would be adapted to reproduce early because of higher adult mortality, generating smaller and numerous eggs in a coastal habitat where chances of transmission are presumably higher.

Molecular characterization and classification of Trypanosoma spp. Venezuelan isolates based on microsatellite markers and kinetoplast maxicircle genes

BACKGROUND

Livestock trypanosomoses, caused by three species of the Trypanozoon subgenus, Trypanosoma brucei brucei, T. evansi and T. equiperdum is widely distributed throughout the world and constitutes an important limitation for the production of animal protein. T. evansi and T. equiperdum are morphologically indistinguishable parasites that evolved from a common ancestor but acquired important biological differences, including host range, mode of transmission, distribution, clinical symptoms and pathogenicity. At a molecular level, T. evansi is characterized by the complete loss of the maxicircles of the kinetoplastic DNA, while T. equiperdum has retained maxicircle fragments similar to those present in T. brucei. T. evansi causes the disease known as Surra, Derrengadera or "mal de cadeiras", while T. equiperdum is the etiological agent of dourine or "mal du coit", characterized by venereal transmission and white patches in the genitalia.

METHODS

Nine Venezuelan Trypanosoma spp. isolates, from horse, donkey or capybara were genotyped and classified using microsatellite analyses and maxicircle genes. The variables from the microsatellite data and the Procyclin PE repeats matrices were combined using the Hill-Smith method and compared to a group of T. evansi, T. equiperdum and T. brucei reference strains from South America, Asia and Africa using Coinertia analysis. Four maxicircle genes (cytb, cox1, a6 and nd8) were amplified by PCRfrom TeAp-N/D1 and TeGu-N/D1, the two Venezuelan isolates that grouped with the T. equiperdum STIB841/OVI strain. These maxicircle sequences were analyzed by nucleotide BLAST and aligned toorthologous genes from the Trypanozoon subgenus by MUSCLE tools. Phylogenetic trees were constructed using Maximum Parsimony (MP) and Maximum Likelihood (ML) with the MEGA5.1® software.

RESULTS

We characterized microsatellite markers and Procyclin PE repeats of nine Venezuelan Trypanosoma spp. isolates with various degrees of virulence in a mouse model, and compared them to a panel of T. evansi and T. equiperdum reference strains. Coinertia analysis of the combined repeats and previously reported T. brucei brucei microsatellite genotypes revealed three distinct groups. Seven of the Venezuelan isolates grouped with globally distributed T. evansi strains, while TeAp-N/D1 and TeGu-N/D1 strains clustered in a separate group with the T. equiperdum STIB841/OVI strain isolated in South Africa. A third group included T. brucei brucei, two strains previously classified as T. evansi (GX and TC) and one as T. equiperdum (BoTat-1.1). Four maxicircle genes, Cytochrome b, Cythocrome Oxidase subunit 1, ATP synthase subunit 6 and NADH dehydrogenase subunit 8, were identified in the two Venezuelan strains clustering with the T. equiperdum STIB841/OVI strain. Phylogenetic analysis of the cox1 gene sequences further separated these two Venezuelan T. equiperdum strains: TeAp-N/D1 grouped with T. equiperdum strain STIB818 and T. brucei brucei, and TeGu-N/D1 with the T. equiperdum STIB841/OVI strain.

CONCLUSION

Based on the Coinertia analysis and maxicircle gene sequence phylogeny, TeAp-N/D1 and TeGu-N/D1 constitute the first confirmed T. equiperdum strains described from Latin America.

Host-dependent morphology of Isthmiophora melis (Schrank, 1788) Luhe, 1909 (Digenea, Echinostomatinae)--morphological variation vs. molecular stability

Background

Echinostomes are cosmopolitan digenean parasites which infect many different warm-blooded hosts. Their classification is extremely confused; the host spectrum is wide, and morphological similarities often result in misidentification. During our long-term studies on the helminth fauna of rodents and carnivores we have collected 27 collar-spined echinostomes which differ in morphology to an extent that suggests the presence of more than one species. Here, we describe this material, and the extent of host-related variation in this parasite.

Methods

Specimens of Isthmiophora isolated from four host species (badger, American mink, hedgehog, striped field mouse) were subject to morphological and molecular examination; the data were statistically analysed.

Results

Our results show that genetically all the Isthmiophora specimens obtained from all the examined hosts are conspecific and represent I. melis. On the other hand, the individuals isolated from Apodemus agrarius are morphologically distinct and, based on this criterion alone, should be described as a new species.

Conclusions

The morphological traits of Isthmiophora melis are much variable and host-dependent; without molecular analysis they would suggest a necessity to describe a new species or even genus. Such a high level of intraspecific variability may be affected by the host’s longevity.

Molecular Phylogeny of Nematodes (Oxyurida: Travassosinematidae) from Orthoptera (Gryllotalpidae) Inferred by Mitochondrial Cytochrome C Oxidase Subunit 1 Gene

In this study, we sequenced mt Cox 1 gene sequences of five nematode spp. that were infective to arthropod, Gryllotalpa africana. The nematode belongs to Thelastomatoidea, a group of pinworms that parasitizes only invertebrates. Currently, in India spp. of this group are distinguished mainly on the basis of morphological characters that present possible confusions. Therefore, we identified the species through morphological and genetic analysis. We selected mt Cox 1 gene region to show their phylogenetic position with closely related spp. and confirmed their molecular validation. The present findings are important to confirm the phylogenetic position and relationship among five nematode spp. and avoid misidentification regarding their validation, as it is more necessary in that case when many species harbours the same host.

Mitochondrial DNA sequences of 37 collar-spined echinostomes (Digenea: Echinostomatidae) in Thailand and Lao PDR reveals presence of two species: Echinostoma revolutum and E. miyagawai

The "37 collar-spined" or "revolutum" group of echinostomes is recognized as a species complex. The identification of members of this complex by morphological taxonomic characters is difficult and confusing, and hence, molecular analyses are a useful alternative method for molecular systematic studies. The current study examined the genetic diversity of those 37 collar-spined echinostomes which are recognized morphologically as Echinostoma revolutum in Thailand and Lao PDR using the cytochrome c oxidase subunit 1 (CO1) and the NADH dehydrogenase subunit 1 (ND1) sequences. On the basis of molecular investigations, at least two species of 37 collar-spined echinostomes exist in Southeast Asia, namely E. revolutum and Echinostoma miyagawai. The specimens examined in this study, coming from ducks in Thailand and Lao PDR, were compared to isolates from America, Europe and Australia for which DNA sequences are available in public databases. Haplotype analysis detected 6 and 26 haplotypes when comparing the CO1 sequences of E. revolutum and E. miyagawai, respectively, from different geographical isolates from Thailand and Lao PDR. The phylogenetic trees, ND1 haplotype network and genetic differentiation (ɸST) analyses showed that E. revolutum were genetically different on a continental scale, i.e. Eurasian and American lineages.

Morphological and ITS2 Molecular Characterization of Ribeiroia Cercariae (Digenea: Psilostomidae) from Biomphalaria spp. (Gastropoda: Planorbidae) in Northern Argentina

Species of Ribeiroia use planorbid snails as intermediate host. Since there is little information about these digenean parasites in South America, we aimed to assess whether Ribeiroia cercariae from 3 north Argentina locations belonged to the same species and differed from Ribeiroia cercariae described elsewhere. Specimens were obtained from Biomphalaria tenagophila and Biomphalaria orbignyi (Salta Province), and Biomphalaria occidentalis (Corrientes Province). Morphological traits of cercariae were analyzed, as well as their sequence of the ribosomal internal transcribed spacer 2 (ITS2). The ITS2 region consisted of 426 nucleotides identical in all samples, suggesting that all specimens belong to the same species in spite of their morphological differences and first intermediate host species. Comparison of the ITS2 region with GenBank database records showed that specimens from Argentina were different from Ribeiroia ondatrae (0.9% divergence), Ribeiroia marini (0.7% divergence), and Cercaria lileta (0.2% divergence). In summary, morphological, ecological, and ITS2 molecular data suggest that specimens from Argentina belong to a different species.

Taxonomy and phylogeny of Trichuris globulosa Von Linstow, 1901 from camels. A review of Trichuris species parasitizing herbivorous

At the present work, we carried out a morph-biometrical and molecular study of Trichuris species isolated from Camelus dromedarius from Iran and from Ovis aries from South Africa comparatively with other species of Trichuris from different herbivorous hosts and geographical regions. The population from camels from Iran was identified as Trichuris globulosa. Two different morphometrically populations of Trichuris sp. from sheep from South Africa were identified: Trichuris ovis and Trichuris skrjabini. Ribosomal data did not reveal significate differences in the ITS2 sequences between T. ovis and T. globulosa to assess a specific determination. The mitochondrial data suggest that T. globulosa constitute a different genetic lineage to T. ovis. Cytochrome c-oxidase and cytochrome b partial gene sequences corroborated the existence of a different genetic lineage of T. ovis from sheep of South Africa that would be closely related to the populations of T. globulosa from camels from Iran. The cytochrome c-oxidase and cytochrome b partial gene sequences of T. globulosa have been reported for the first time.

Biomphalaria straminea (Mollusca: Planorbidae) as an intermediate host of Drepanocephalus spp. (Trematoda: Echinostomatidae) in Brazil: a morphological and molecular study

Species of trematodes belonging to the genus Drepanocephalus are intestinal parasites of piscivorous birds, primarily cormorants (Phalachrocorax spp.), and are widely reported in the Americas. During a 4-year malacological study conducted on an urban lake in Brazil, 27-collar-spined echinostome cercariae were found in 1665/15,459 (10.7 %) specimens of Biomphalaria straminea collected. The cercariae were identified as Drepanocephalus spp. by sequencing the 18S (SSU) rDNA, ITS1/5.8S rDNA/ITS2 (ITS), 28S (LSU) rDNA region, cytochrome oxidase subunit 1 (CO1), and nicotinamide adenine dinucleotide dehydrogenase subunit 1 (ND1) markers. In experimental life cycle studies, metacercariae developed in laboratory-reared guppies (Poecilia reticulata); however, attempts to infect birds and rodents were unsuccessful. Two closely related morphotypes of cercariae were characterized. One species, identified by molecular markers as a genetic variant of Drepanocephalus auritus (99.9 % similarity at SSU, ITS, LSU; 97.2 % at CO1; 95.8 % at ND1), differs slightly from an archived North American isolate of this species also sequenced as part of this study. A second species, putatively identified as Drepanocephalus sp., has smaller cercariae and demonstrates significant differences from D. auritus at the CO1 (11.0 %) and ND1 (13.6 %) markers. Aspects related to the morphological taxonomic identification of 27-collar-spined echinostome metacercariae are briefly discussed. This is the first report of the involvement of molluscs of the genus Biomphalaria in the transmission of Drepanocephalus and the first report of D. auritus in South America.

Morphological characterisation and identification of four species of Cardicola Short, 1953 (Trematoda: Aporocotylidae) infecting the Atlantic bluefin tuna Thunnus thynnus (L.) in the Mediterranean Sea

Blood flukes of the genus Cardicola Short, 1953 are considered the most potentially pathogenic parasites in bluefin tuna cultures. Morphological study and genetic analyses of the ribosomal internal transcribed spacer ITS-2 and the mitochondrial cytochrome c oxidase 1 (cox1) gene fragments revealed the occurrence of four aporocotylid species (C. forsteri Cribb, Daintith & Munday, 2000, C. orientalis Ogawa, Tanaka, Sugihara & Takami, 2010, C. opisthorchis Ogawa, Ishimaru, Shirakashi, Takami & Grabner, 2011 and Cardicola sp.) in 421 Thunnus thynnus (L.) from the Western Mediterranean (274 fished from the wild and 147 from sea-cages). Cardicola opisthorchis was the most abundant species, with higher prevalence in the cage-reared fish than in those fished in the wild (21 vs 6%, p < 0.05). Adults of three species were recovered: C. forsteri from both gills and heart, C. opisthorchis from heart and C. orientalis from gills. The secondary gill lamellae were profusely infected by eggs of C. orientalis. A fourth species was found in four tunas, based on the molecular analyses of eggs apparently indistinguishable in size and shape from the eggs of C. orientalis. The findings provided evidence that infections with Cardicola spp. differed in relation to locality, host origin (wild vs cage-reared) and site of infection. It is necessary to estimate the possible different pathogenic effects of each species of Cardicola in order to take appropriate control measures.

Phylogenetic relationships of some species of the family Echinostomatidae Odner, 1910 (Trematoda), inferred from nuclear rDNA sequences and karyological analysis

The family Echinostomatidae Looss, 1899 exhibits a substantial taxonomic diversity, morphological criteria adopted by different authors have resulted in its subdivision into an impressive number of subfamilies. The status of the subfamily Echinochasminae Odhner, 1910 was changed in various classifications. Genetic characteristics and phylogenetic analysis of four Echinostomatidae species - Echinochasmus sp., Echinochasmuscoaxatus Dietz, 1909, Stephanoprorapseudoechinata (Olsson, 1876) and Echinoparyphiummordwilkoi Skrjabin, 1915 were obtained to understand well enough the homogeneity of the Echinochasminae and phylogenetic relationships within the Echinostomatidae. Chromosome set and nuclear rDNA (ITS2 and 28S) sequences of parthenites of Echinochasmus sp. were studied. The karyotype of this species (2n=20, one pair of large bi-armed chromosomes and others are smaller-sized, mainly one-armed, chromosomes) differed from that previously described for two other representatives of the Echinochasminae, Echinochasmusbeleocephalus (von Linstow, 1893), 2n=14, and Episthmiumbursicola (Creplin, 1937), 2n=18. In phylogenetic trees based on ITS2 and 28S datasets, a well-supported subclade with Echinochasmus sp. and Stephanoprorapseudoechinata clustered with one well-supported clade together with Echinochasmusjaponicus Tanabe, 1926 (data only for 28S) and Echinochasmuscoaxatus. These results supported close phylogenetic relationships between Echinochasmus Dietz, 1909 and Stephanoprora Odhner, 1902. Phylogenetic analysis revealed a clear separation of related species of Echinostomatoidea restricted to prosobranch snails as first intermediate hosts, from other species of Echinostomatidae and Psilostomidae, developing in Lymnaeoidea snails as first intermediate hosts. According to the data based on rDNA phylogeny, it was supposed that evolution of parasitic flukes linked with first intermediate hosts. Digeneans parasitizing prosobranch snails showed higher dynamic of karyotype evolution provided by different chromosomal rearrangements including Robertsonian translocations and pericentric inversions than more stable karyotype of digenean worms parasitizing lymnaeoid pulmonate snails.

Chronic pathology and longevity of Drepanocephalus spathans infections in juvenile Channel Catfish

Drepanocephalus spathans (Digenea: Echinostomatidae) is a common parasite of the double-crested cormorant Phalacrocorax auritus. The cercariae of D. spathans have been shown infective to juvenile Channel Catfish Ictalurus punctatus. The developing metacercariae concentrate in the cranial regions, often occluding blood vessels at the base of the branchial arch, occasionally resulting in death. The purpose of this study was to determine how long metacercariae of D. spathans persist in experimentally challenged Channel Catfish. Two separate infectivity trials were conducted. In both trials, metacercariae persisted at least 49 d postinfection, although prevalence and intensity of infection decreased over time. In the first trial, juvenile catfish (1-3 g) were exposed over three consecutive days to 100, 100, and 80 cercariae/fish/d, respectively. Fish were sampled 7 d after the final exposure, and metacercariae were observed in 83.3% (five of six) of challenged fish. At 21 d postexposure, metacercariae were present in only 50% of exposed fish (three of six). No metacercaria were observed in fish sampled at 35 d, however, metacercariae were present in one of six (16.7%) fish sampled 49 and 70 d postexposure, respectively. A second challenge consisted of a 24-h pooled exposure of 500 cercariae per fish. Again, metacercariae were present in most (six of seven; 85.7%) fish at 7 d postexposure. At 21 d postexposure, metacercariae were only evident in one of seven (14.3%) sampled fish. No metacercariae were present in any fish at 35 d postchallenge, yet one of seven (14.3%) fish was positive at 49 d postchallenge. The second study was terminated at 63 d postchallenge, as all fish sampled (n = 14) were negative for metacercariae. These data suggest that cercariae of D. spathans are infective to juvenile Channel Catfish, although the infection appears short lived as metacercariae rarely persisted longer than 2 months.

Echinostoma 'revolutum' (Digenea: Echinostomatidae) species complex revisited: species delimitation based on novel molecular and morphological data gathered in Europe

BACKGROUND

The systematics of echinostomes within the so-called 'revolutum' group of the genus Echinostoma, which encompasses the type-species E. revolutum and a number of morphologically similar species, has long been controversial. Recent molecular studies indicate the existence of more species than previously considered valid, thus stressing the need for wider taxon sampling from natural host populations. This is especially true for Europe where morphological evidence indicates higher species diversity than previously thought, but where molecular data are virtually lacking. This gap in our knowledge was addressed in the present study through an integration of morphological and molecular approaches in the investigation of a dataset with larger taxonomic and geographical coverage.

METHODS

More than 20,000 freshwater snails belonging to 16 species were collected during 1998-2012 from various localities in eight countries in Europe. Snail screening provided representative larval isolates for five species of the 'revolutum' group, identified by their morphology. Adult isolates for four species recovered from natural and experimental infections were also identified. Partial fragments of the mitochondrial nad1 and 28S rRNA genes were amplified for 74 and 16 isolates, respectively; these were analysed together with the sequences of Echinostoma spp. available on GenBank.

RESULTS

Delineation of the European Echinostoma spp. was carried out based on molecular, morphological and ecological data. The large-scale screening revealed infections with five Echinostoma spp., including one new species: E. revolutum (sensu stricto), E. miyagawai, E. paraulum, E. bolschewense and Echinostoma n. sp. The newly-generated nad1 sequences from Europe fall into six distinct, well-supported, reciprocally monophyletic lineages corresponding to the species identifications based on morphology; this was corroborated by the 28S rDNA sequences. The analyses of the total nad1 dataset provided evidence for 12 monophyletic groups and five singletons, which represent seven described/named species and ten cryptic species-level lineages of Echinostoma.

CONCLUSION

We conclude that nad1 should be the first choice for large-scale barcode-based identification of the species of the 'revolutum' group. Our study provides a comprehensive reference library for precisely identified isolates of the European species and highlights the importance of an integrative approach for species identification linking molecular, morphological and biological data.

Molecular and morphological differentiation of two similar species of Accacoeliidae (Digenea): Accacladocoelium macrocotyle and A. nigroflavum from sunfish, Mola mola

In a study of 106 sunfish, Mola mola (L.), from Mediterranean waters, 2,731 worms, belonging to 2 congeneric species of accacoeliids, Accacladocoelium macrocotyle (Diesing, 1858) Robinson, 1934 and Accacladocoelium nigroflavum (Rudolphi, 1819) Robinson, 1934 , were collected from the digestive system. It is often difficult to differentiate between these 2 species as they are sympatric and very similar; in fact, according to previous descriptions, the extent of the vitellarium is the only interspecific difference, described as extending posteriorly to the ovary in A. macrocotyle and as anterior to the anterior testis in A. nigroflavum. However, this diagnostic trait is not always valid; moreover, it is often indistinguishable because it is masked by the uterine eggs. Here, the morphology of new specimens of both species has been studied in detail and combined with molecular analysis. This study shows that the extension of the vitellarium is very similar in both species, but the degree of ramification differs. Furthermore, although the morphological differences are very slight, both species seemed genetically different: intraspecific differences ranged between 0.8 and 1.5% in internal transcribed spacer (ITS)-2 rRNA gene (ITS2) and between 0.5 and 1.6% in cytochrome c oxidase subunit 1 (COI) and interspecific differences ranged between 2 and 3.2% in ITS2 and between 9.6 and 10.6% in COI. In addition, we observed previously undescribed morphological differences, which help to differentiate these 2 species: the oral sucker is relatively smaller in A. nigroflavum than in A. macrocotyle and the ovary is usually relatively longer in A. nigroflavum than in A. macrocotyle.

Phylogenetic relationships of 3 Korean Neodiplostomum species (Digenea: Neodiplostomidae) based on partial CO1 gene

The phylogenetic relationships of the 3 Neodiplostomum spp. (Digenea: Neodiplostomidae) occurring in Korea (N. seoulense, N. leei, and N. boryongense) were analyzed using the partial mitochondrial cytochrome c oxidase subunit 1 (CO1) gene. The adult flukes were recovered from Sprague-Dawley rats (N. seoulense) and newborn chicks (N. leei and N. boryongense) experimentally infected with the neodiplostomula from the grass snake, Rhabdophis tigrinus tigrinus. The genomic DNA was amplified using specific primers, and the sequence of CO1 was obtained. According to the results, the pairwise similarity was 96.1% between N. boryongense and N. seoulense, but was 95.0% between N. boryongense and N. leei and 94.2% between N. leei and N. seoulense. The results demonstrated a closer phylogenetic relationship between N. seoulense and N. boryongense. This high relationship of N. seoulense and N. boryongense may be related to their similar morphologic features including the limited distribution of vitellaria and the presence of a genital cone. N. leei is distinct on the other hand with an extensive distribution of vitellaria and the absence of a genital cone.

Molecular analysis of echinostome metacercariae from their second intermediate host found in a localised geographic region reveals genetic heterogeneity and possible cryptic speciation

Echinostome metacercariae are the infective stage for humans and animals. The identification of echinostomes has been based until recently on morphology but molecular techniques using sequences of ribosomal RNA and mitochondrial DNA have indicated major clades within the group. In this study we have used the ITS2 region of ribosomal RNA and the ND1 region of mitochondrial DNA to identify metacercariae from snails collected from eight well-separated sites from an area of 4000 km² in Lamphun Province, Thailand. The derived sequences have been compared to those collected from elsewhere and have been deposited in the nucleotide databases. There were two aims of this study; firstly, to determine the species of echinostome present in an endemic area, and secondly, to assess the intra-specific genetic diversity, as this may be informative with regard to the potential for the development of anthelmintic resistance and with regard to the spread of infection by the definitive hosts. Our results indicate that the most prevalent species are most closely related to E. revolutum, E. trivolvis, E. robustum, E. malayanum and Euparyphium albuferensis. Some sites harbour several species and within a site there could be considerable intra-species genetic diversity. There is no significant geographical structuring within this area. Although the molecular techniques used in this study allowed the assignment of the samples to clades within defined species, however, within these groupings there were significant differences indicating that cryptic speciation may have occurred. The degree of genetic diversity present would suggest the use of targeted regimes designed to minimise the selection of anthelmintic resistance. The apparent lack of geographic structuring is consistent with the transmission of the parasites by the avian hosts.

Infections by food-borne trematodes are estimated to infect over 40 million people worldwide, although infections by echinostomes make up only a portion of these cases, usually in regions where their prevalence is high. In South East Asia and in the far east of Asia, human infection is associated with cultural and dietary factors and the prevalence of infection may reach 50% in parts of Thailand, Cambodia, and Laos. Treatment is generally dependent on the use of praziquantel or benzimidazole drugs but with the occurrence of anthelmintic resistance to these compounds it would be desirable to have an understanding of the diversity present in the echinostome populations within a given locality. This study deals with the systematics of echinostomes and informs various aspects of the epidemiology of echinostomiasis which may aid the development of future control strategies.

Phylogeography and molecular diversity analysis of Jatropha curcas L. and the dispersal route revealed by RAPD, AFLP and nrDNA-ITS analysis

Jatropha curcas L. (Euphorbiaceae) has acquired a great importance as a renewable source of energy with a number of environmental benefits. Very few attempts were made to understand the extent of genetic diversity and its distribution. This study was aimed to study the diversity and deduce the phylogeography of Jatropha curcas L. which is said to be the most primitive species of the genus Jatropha. Here we studied the intraspecific genetic diversity of the species distributed in different parts of the globe. The study also focused to understand the molecular diversity at reported probable center of origin (Mexico), and to reveal the dispersal route to other regions based on random amplified polymorphic DNA, amplified fragment length polymorphism and nrDNA-ITS sequences data. The overall genetic diversity of J. curcas found in the present study was narrow. The highest genetic diversity was observed in the germplasm collected from Mexico and supports the earlier hypothesis based on morphological data and natural distribution, it is the center for origin of the species. Least genetic diversity found in the Indian germplasm and clustering results revealed that the species was introduced simultaneously by two distinct germplasm and subsequently distributed in different parts of India. The present molecular data further revealed that J. curcas might have spread from the center of the origin to Cape Verde, than to Spain, Portuguese to other neighboring countries and simultaneously to Africa. The molecular evidence supports the Burkill et al. (A dictionary of the economic products of the Malay Peninsula, Governments of Malaysia and Singapore by the Ministry of Agriculture and Co-operatives. Kuala Lumpur, Malaysia, 1966) view of Portuguese might have introduced the species to India. The clustering pattern suggests that the distribution was interfered by human activity.

Parasite predators exhibit a rapid numerical response to increased parasite abundance and reduce transmission to hosts

Predators of parasites have recently gained attention as important parts of food webs and ecosystems. In aquatic systems, many taxa consume free-living stages of parasites, and can thus reduce parasite transmission to hosts. However, the importance of the functional and numerical responses of parasite predators to disease dynamics is not well understood. We collected host–parasite–predator cooccurrence data from the field, and then experimentally manipulated predator abundance, parasite abundance, and the presence of alternative prey to determine the consequences for parasite transmission. The parasite predator of interest was a ubiquitous symbiotic oligochaete of mollusks, Chaetogaster limnaei limnaei, which inhabits host shells and consumes larval trematode parasites. Predators exhibited a rapid numerical response, where predator populations increased or decreased by as much as 60% in just 5 days, depending on the parasite:predator ratio. Furthermore, snail infection decreased substantially with increasing parasite predator densities, where the highest predator densities reduced infection by up to 89%. Predators of parasites can play an important role in regulating parasite transmission, even when infection risk is high, and especially when predators can rapidly respond numerically to resource pulses. We suggest that these types of interactions might have cascading effects on entire disease systems, and emphasize the importance of considering disease dynamics at the community level.

Molecular characterization and phylogeny of whipworm nematodes inferred from DNA sequences of cox1 mtDNA and 18S rDNA

A molecular phylogenetic hypothesis is presented for the genus Trichuris based on sequence data from the mitochondrial cytochrome c oxidase 1 (cox1) and ribosomal 18S genes. The taxa consisted of different described species and several host-associated isolates (undescribed taxa) of Trichuris collected from hosts from Spain. Sequence data from mitochondrial cox1 (partial gene) and nuclear 18S near-complete gene were analyzed by maximum likelihood and Bayesian inference methods, as separate and combined datasets, to evaluate phylogenetic relationships among taxa. Phylogenetic results based on 18S ribosomal DNA (rDNA) were robust for relationships among species; cox1 sequences delimited species and revealed phylogeographic variation, but most relationships among Trichuris species were poorly resolved by mitochondrial sequences. The phylogenetic hypotheses for both genes strongly supported monophyly of Trichuris, and distinct genetic lineages corresponding to described species or nematodes associated with certain hosts were recognized based on cox1 sequences. Phylogenetic reconstructions based on concatenated sequences of the two loci, cox1 (mitochondrial DNA (mtDNA)) and 18S rDNA, were congruent with the overall topology inferred from 18S and previously published results based on internal transcribed spacer sequences. Our results demonstrate that the 18S rDNA and cox1 mtDNA genes provide resolution at different levels, but together resolve relationships among geographic populations and species in the genus Trichuris.

Development of primers for the mitochondrial cytochrome c oxidase I gene in digenetic trematodes (Platyhelminthes) illustrates the challenge of barcoding parasitic helminths

The phylum Platyhelminthes is a diverse group of flatworms that includes parasites with serious impacts on human health, animal husbandry, aquaculture and wildlife management. Here we present degenerate primers for the barcode region of the mitochondrial cytochrome c oxidase I (COI) gene in flatworms. Although amplicons were obtained from a wide taxonomic range in the Cestoda and Trematoda, COI fragments from many taxa in these classes did not amplify. Primers specific to trematodes in the family Diplostomidae were also developed. Amplification success was much higher with diplostomid-specific primers and sequences were obtained from 504 of 585 specimens of Diplostomum and Tylodelphys. Sequences from the barcode region resolved all specimens to the species level, with mean divergence between congeners of 19% (3.9-25%). Because many of our specimens were small, we initially amplified part of the nuclear small subunit ribosomal (r) RNA gene to evaluate the quality and quantity of DNA in our specimens. Short sequences (~380 nt) of this gene were recovered from most specimens and can be used to distinguish specimens at the family level and often the generic level. We suggest that rRNA genes could be used to screen samples of completely unknown taxonomy, after which specific COI primers could be used to obtain species-level identifications.

Metacercariae of Clinostomum complanatum (Trematoda: Digenea) in European newts Triturus carnifex and Lissotriton vulgaris (Caudata: Salamandridae)

Adults of Clinostomum spp. are digenetic trematodes found in fish-eating birds, reptiles and occasionally mammals, including humans. Freshwater snails serve as first intermediate hosts and many fish species and amphibians as second intermediate hosts. To date, amphibian hosts of Clinostomum metacercariae include members of urodele and anuran families in North America, but no data are available on infections of European amphibians, including newts. In this study, we characterize infections of Clinostomum complanatum metacercariae in four smooth (Lissotriton vulgaris) and 18 Italian crested newts (Triturus carnifex) from an artificial pond located in a protected area in Tuscany, Italy. Parasites were surgically removed from the infected newts and identified both morphologically and using sequences of a mitochondrial gene, cytochrome c oxidase I, and the ribosomal markers, internal transcribed spacers. This is the first record of C. complanatum in European newts and, more generally, in amphibians in Europe.

New cryptic species of the 'revolutum' group of Echinostoma (Digenea: Echinostomatidae) revealed by molecular and morphological data

BACKGROUND

The digenean species of Echinostoma (Echinostomatidae) with 37 collar spines that comprise the so-called 'revolutum' species complex, qualify as cryptic due to the interspecific homogeneity of characters used to differentiate species. Only five species were considered valid in the most recent revision of the group but recent molecular studies have demonstrated a higher diversity within the group. In a study of the digeneans parasitising molluscs in central and northern Europe we found that Radix auricularia, R. peregra and Stagnicola palustris were infected with larval stages of two cryptic species of the 'revolutum' complex, one resembling E. revolutum and one undescribed species, Echinostoma sp. IG. This paper provides morphological and molecular evidence for their delimitation.

METHODS

Totals of 2,030 R. auricularia, 357 R. peregra and 577 S. palustris were collected in seven reservoirs of the River Ruhr catchment area in Germany and a total of 573 R. peregra was collected in five lakes in Iceland. Cercariae were examined and identified live and fixed in molecular grade ethanol for DNA isolation and in hot/cold 4% formaldehyde solution for obtaining measurements from fixed materials. Partial fragments of the mitochondrial gene nicotinamide adenine dinucleotide dehydrogenase subunit 1 (nad1) were amplified for 14 isolates.

RESULTS

Detailed examination of cercarial morphology allowed us to differentiate the cercariae of the two Echinostoma spp. of the 'revolutum' species complex. A total of 14 partial nad1 sequences was generated and aligned with selected published sequences for eight species of the 'revolutum' species complex. Both NJ and BI analyses resulted in consensus trees with similar topologies in which the isolates from Europe formed strongly supported reciprocally monophyletic lineages. The analyses also provided evidence that North American isolates identified as E. revolutum represent another cryptic species of the 'revolutum' species complex.

CONCLUSION

Our findings highlight the need for further analyses of patterns of interspecific variation based on molecular and morphological evidence to enhance the re-evaluation of the species and advance our understanding of the relationships within the 'revolutum' group of Echinostoma.