Parasitic Flatworms Research Articles

Isolation and molecular identification of liver fluke cercariae in freshwater snails of Chaharmahal and Bakhtiari province, Iran

ABSTRACT Liver flukes are parasitic flatworms that can infect humans and other mammals. In this study, freshwater snails from Chaharmahal and Bakhtiari province in Iran were investigated for the presence of liver fluke larvae. The snails were collected from various rivers and analysed using standard morphological and molecular techniques. Additionally, molecular identification of the collected snails was conducted through polymerase chain reaction (PCR) and sequencing of the COI gene. The freshwater snails were identified as Physella acuta (Draparnaud, 1805), Galba truncatula (O.F. Müller, 1774), Radix euphratica (Mousson, 1874), Radix auricularia (Linnaeus, 1758) and Planorbis planorbis (Linnaeus, 1758). The presence of larval stages of Fasciola spp. in individual snails was examined using stereomicroscopy and a crushing method. Morphological and molecular identification based on the ITS-1 marker for identifying Fasciola spp. revealed that 10.9% (59 out of 549) of R. auricularia and 5.8% (37 out of 630) of P. acuta were infected. A blastn analysis of the collected samples revealed that all isolates belonged to F. hepatica, indicating a potential risk of liver fluke infection in the study area. These findings emphasise the importance of regular surveillance and control measures to prevent the spread of these parasites.

A compartmental model for Schistosoma japonicum transmission dynamics in the Philippines

Schistosomiasis is a chronic and debilitating neglected tropical disease (NTD), second only to malaria as one of the most devastating parasitic diseases. Caused by a parasitic flatworm of the genus Schistosoma, infection occurs when skin comes in contact with contaminated freshwater that contains schistosome-hosting snails. The disease continues to be endemic in many regions of the Philippines, where it poses a significant public health challenge due to a lack of healthcare resources. In the Philippines, additional mammalian reservoirs for the S. japonicum parasite, especially bovines such as carabaos, also facilitate the spread of schistosomiasis. We extend existing compartment models to include human, snail, bovine, and free-living Schistosoma for a comprehensive look at the transmission dynamics of the disease. Sensitivity analysis of model parameters shows that the carabaos themselves can sustain the endemicity of schistosomiasis. Thus, we consider the control method of farming mechanization to avoid contaminated freshwater sources. We find that a reduction of contaminated water contacts by at least 77% will break the transmission cycle and eliminate the disease. However, reducing the contact by about 70% will still result in decrease of human schistosomiasis prevalence to under 1% in 15 years or less. Achieving such high reduction of contact rates could be a daunting task, especially in rural areas. Still, the potential to eliminate or at least reduce the schistosomiasis prevalence should be considered an additional benefit of mechanization efforts in the Philippines.

Diversity and Phylogeny of Gyrodactylus spp. (Monogenea: Gyrodactylidae) across the Strait of Gibraltar: Parasite Speciation and Historical Biogeography of West Mediterranean Cyprinid Hosts

Knowledge on the diversity of parasitic flatworms of Western Mediterranean cyprinids is extremely scarce. In the present study, we parasitologically investigated 12 cyprinid species across the Strait of Gibraltar inhabiting watersheds in northwest Africa (Morocco) and Iberia (Portugal and Spain). Taxonomically relevant features of the attachment organ and sequences of the 18S rDNA and ITS regions were used for species delineation and to investigate their phylogenetic relatedness. Among the Gyrodactylus collected from Morocco and Spain, we identified specimens with an unusual T-shaped dorsal bar observed herein for the first time. In contrast, the membranous patch-like structure surrounding the twisted inner roots of hamuli and the median ridge of the ventral bar have been generally observed in Eurasian relatives. Our analyses suggest vicariant speciation of Gyrodactylus across the Strait of Gibraltar. We describe herein G. gibraltarensis sp. nov. from Iberian Luciobarbus graellsii; G. moroccensis sp. nov. from northwest African cyprinids, i.e., L. maghrebensis, L. rabatensis, L. rifensis, L. yahyaouii, and L. zayanensis; and finally, G. pseudomoroccensis sp. nov. from Moroccan L. ksibi, all possessing a new haptoral configuration. The genetic divergence and conservative morphologies in populations of G. moroccensis sp. nov. from five cyprinid species support its ongoing speciation in Northwest Africa. The West Mediterranean lineage was revealed to be monophyletic, with Eurasian species forming a sister group. Morphologically, West Mediterranean Gyrodactylus also appeared to be of Middle Eastern origin. Gyrodactylus spp. possessing an unusual T-shaped dorsal bar have most likely speciated, allowing for the appearance of a haptoral morphology that is restricted to the region across the Strait of Gibraltar. To conclude, viviparous Gyrodactylus reflect parasite speciation across the Strait of Gibraltar and the historical biogeography of cyprinids in the West Mediterranean.

Praziquantel activates a native cation current in Schistosoma mansoni

IntroductionPraziquantel (PZQ), an anthelmintic drug discovered in the 1970s, is still used to treat schistosomiasis and various other infections caused by parasitic flatworms. PZQ causes a triad of phenotypic effects on schistosome worms – rapid depolarization, muscle contraction, and damage throughout the worm tegument. The molecular target mediating these effects has been intimated as a Ca2+-permeable ion channel, but native currents evoked by PZQ have not been reported in any schistosome cell type. The properties of the endogenous PZQ activated conductance therefore remain unknown. MethodsHere, invasive electrophysiology was used to probe for responses to PZQ from different locales in a living schistosome worm.Results and discussionNo direct response was seen in tegument-derived vesicles, or from the sub-tegumental muscle layer despite the presence of voltage-operated currents. However, PZQ rapidly triggered a sustained, non-selective cation current in recordings from neuronal tissue, targeting both the anterior ganglion and the main longitudinal nerve cord. The biophysical signature of this PZQ-evoked current resolved at single channel resolution matched that of a transient receptor potential ion channel named TRPMPZQ, recently proposed as the molecular target of PZQ. The endogenous PZQ-evoked current was also inhibited by a validated TRPMPZQ antagonist. PZQ therefore is a neuroactive anthelmintic, causing a sustained depolarization through ion channels with the characteristics of TRPMPZQ.

Trends in Paragonimiasis Global Research: Bibliometric Analysis of a Neglected Food-Borne Parasite.

Paragonimus is a genus of parasitic flatworms known as lung flukes that cause the parasitic disease paragonimiasis in humans and other mammals. We aimed to use bibliometric analysis to identify the global characteristics and temporal trends of published literature about paragonimiasis. Using the Web of Science database, we identified all original articles on paragonimiasis 1997 to 2022. After collecting the bibliographic and citation data, keywords, citation networks, and co-citations pertaining to paragonimiasis was carried out using the VOSviewer program. The study identified 563 paragonimiasis articles published in 250 journals. Publications in paragonimiasis research have been cited 6190 times and 2803 times without self-citations. The years with the most publications were 2013, 2016, and 2021. The minimal threshold for analysis was met by 19 of the 52 countries investigated. The study included 19 items, yielding 170 links between countries. The total strength of these links was discovered to be 104772. The journal with the most publications in this category was Parasitology Research (n=31). The most frequently used terms in paragonimiasis study were "paragonimiasis", "Paragonimus westermanii", and "lung-fluke." The study concluded by providing an overview of the paragonimiasis research field, including current trends, development, and researcher collaboration. By addressing gaps in this bibliometric analysis and increasing collaboration, stake-holders could strengthen their strategies to effectively combat paragonimiasis and improve public health outcomes.

Species identity and phylogeny of Paramphistomoidea Fischoeder, 1901 occurring in cattle and sheep in North Cameroon.

Paramphistomidae and Gastrothylacidae are parasitic flatworms occurring in wild and domestic ruminants in different parts of the world especially in Asia and Africa. In Central Africa, few studies have been done using molecular techniques to resolve taxonomical groupings and understand the epizootiology of these parasites. In this study, we molecularly characterized two hundred adult flukes collected from the fore stomachs of cattle and sheep in the Adamawa region of the northern Cameroon. PCR and sequencing of the nuclear ITS-2 of the ribosomal DNA gene and a portion of the mitochondrial cox-1 locus revealed the presence of at least nine species belonging to the genera of Cotylophoron, Calicophorn, Orthocoelium and Carmyerius. In Zebu cattle, we identified Ca. microbothrium, Ca. clavula, Ca. phillerouxi, Co. cotylophorum, Co. fuelleborni, O. scoliocoelium, Car. gregarius, Car. graberi and Car. mancupatus and one yet unknown Paramphistomoidea sp, whereas in sheep, only Ca. microbothrium was found. The present study also strongly suggests cross-hybridization between the two Cotylophoron species coexisting in cattle. These results have implications for the diagnosis and control of rumen flukes in the region and point to the need for accurate species identification to understand parasite distribution and population genetics.

Polymorphic parasitic larvae cooperate to build swimming colonies luring hosts

Parasites have evolved a variety of astonishing strategies to survive within their hosts, yet the most challenging event in their personal chronicles is the passage from one host to another. It becomes even more complex when a parasite needs to pass through the external environment. Therefore, the free-living stages of parasites present a wide range of adaptations for transmission. Parasitic flatworms from the group Digenea (flukes) have free-living larvae, cercariae, which are remarkably diverse in structure and behavior.1,2 One of the cercariae transmission strategies is to attain a prey-like appearance for the host.3 This can be done through the formation of a swimming aggregate of several cercariae adjoined together by their tails.4 Through the use of live observations and light, electron, and confocal microscopy, we described such a supposedly prey-mimetic colony comprising cercariae of two distinct morphotypes. They are functionally specialized: larger morphotype (sailors) enable motility, and smaller morphotype (passengers) presumably facilitate infection. The analysis of local read alignments between the two samples reveals that both cercaria types have identical 18S, 28S, and 5.8S rRNA genes. Further phylogenetic analysis of these ribosomal sequences indicates that our specimen belongs to the digenean family Acanthocolpidae, likely genus Pleorchis. This discovery provides a unique example and a novel insight into how morphologically and functionally heterogeneous individuals of the same species cooperate to build colonial organisms for the purpose of infection. This strategy bears resemblance to the cooperating castes of the same species found among insects.5.

The evolution of endoparasitism and complex life cycles in parasitic platyhelminths

Within flatworms, the vast majority of parasitism is innate to Neodermata, the most derived and diversified group of the phylum Platyhelminthes.1,2 The four major lineages of Neodermata maintain various combinations of life strategies.3 They include both externally (ecto-) and internally feeding (endo-) parasites. Some lineages complete their life cycles directly by infecting a single host, whereas others succeed only through serial infections of multiple hosts of various vertebrate and invertebrate groups. Food sources and modes of digestion add further combinatorial layers to the often incompletely understood mosaic of neodermatan life histories. Their evolutionary trajectories have remained molecularly unresolved because of conflicting evolutionary inferences and a lack of genomic data.4 Here, we generated transcriptomes for nine early branching neodermatan representatives and performed detailed phylogenomic analyses to address these critical gaps. Polyopisthocotylea, mostly hematophagous ectoparasites, form a group with the mostly hematophagous but endoparasitic trematodes (Trematoda), rather than sharing a common ancestor with Monopisthocotylea, ectoparasitic epithelial feeders. Phylogenetic placement of the highly specialized endoparasitic Cestoda alters depending on the model. Regardless of this uncertainty, this study brings an unconventional perspective on the evolution of platyhelminth parasitism, rejecting a common origin for the endoparasitic lifestyle intrinsic to cestodes and trematodes. Instead, our data indicate that complex life cycles and invasion of vertebrates' gut lumen, the hallmark features of these parasites, evolved independently within Neodermata. We propose the demise of the traditionally recognized class Monogenea and the promotion of its two subclasses to the class level as Monopisthocotyla new class and Polyopisthocotyla new class.

Host-bacteriome transplants of the schistosome snail host Biomphalaria glabrata reflect species-specific associations.

Microbial symbionts can affect host phenotypes and, thereby, ecosystem functioning. The microbiome is increasingly being recognized as an important player in the tripartite interaction between parasitic flatworms, snail intermediate hosts, and the snail microbiome. In order to better understand these interactions, transplant experiments are needed, which rely on the development of a reliable and reproducible protocol to obtain microbiome-disturbed snails. Here, we report on the first successful snail bacteriome transplants, which indicate that Biomphalaria glabrata can accrue novel bacterial assemblies depending on the available environmental bacteria obtained from donor snails. Moreover, the phylogenetic relatedness of the donor host significantly affected recipients' survival probability, corroborating the phylosymbiosis pattern in freshwater snails. The transplant technique described here, complemented by field-based studies, could facilitate future research endeavors to investigate the role of specific bacteria or bacterial communities in parasitic flatworm resistance of B. glabrata and might ultimately pave the way for microbiome-mediated control of snail-borne diseases.

Praziquantel inhibits Caenorhabditis elegans development and species-wide differences might be cct-8-dependent.

Anthelmintic drugs are used to treat parasitic roundworm and flatworm infections in humans and other animals. Caenorhabditis elegans is an established model to investigate anthelmintics used to treat roundworms. In this study, we use C. elegans to examine the mode of action and the mechanisms of resistance against the flatworm anthelmintic drug praziquantel (PZQ), used to treat trematode and cestode infections. We found that PZQ inhibited development and that this developmental delay varies by genetic background. Interestingly, both enantiomers of PZQ are equally effective against C. elegans, but the right-handed PZQ (R-PZQ) is most effective against schistosome infections. We conducted a genome-wide association mapping with 74 wild C. elegans strains to identify a region on chromosome IV that is correlated with differential PZQ susceptibility. Five candidate genes in this region: cct-8, znf-782, Y104H12D.4, Y104H12D.2, and cox-18, might underlie this variation. The gene cct-8, a subunit of the protein folding complex TRiC, has variation that causes a putative protein coding change (G226V), which is correlated with reduced developmental delay. Gene expression analysis suggests that this variant correlates with slightly increased expression of both cct-8 and hsp-70. Acute exposure to PZQ caused increased expression of hsp-70, indicating that altered TRiC function might be involved in PZQ responses. To test if this variant affects development upon exposure to PZQ, we used CRISPR-Cas9 genome editing to introduce the V226 allele into the N2 genetic background (G226) and the G226 allele into the JU775 genetic background (V226). These experiments revealed that this variant was not sufficient to explain the effects of PZQ on development. Nevertheless, this study shows that C. elegans can be used to study PZQ mode of action and resistance mechanisms. Additionally, we show that the TRiC complex requires further evaluation for PZQ responses in C. elegans.

Solution structure of the N-terminal extension domain of a Schistosoma japonicum asparaginyl-tRNA synthetase

Several secreted proteins from helminths (parasitic worms) have been shown to have immunomodulatory activities. Asparaginyl-tRNA synthetases are abundantly secreted in the filarial nematode Brugia malayi (BmAsnRS) and the parasitic flatworm Schistosoma japonicum (SjAsnRS), indicating a possible immune function. The suggestion is supported by BmAsnRS alleviating disease symptoms in a T-cell transfer mouse model of colitis. This immunomodulatory function is potentially related to an N-terminal extension domain present in eukaryotic AsnRS proteins but few structure/function studies have been done on this domain. Here we have determined the three-dimensional solution structure of the N-terminal extension domain of SjAsnRS. A protein containing the 114 N-terminal amino acids of SjAsnRS was recombinantly expressed with isotopic labelling to allow structure determination using 3D NMR spectroscopy, and analysis of dynamics using NMR relaxation experiments. Structural comparisons of the N-terminal extension domain of SjAsnRS with filarial and human homologues highlight a high degree of variability in the β-hairpin region of these eukaryotic N-AsnRS proteins, but similarities in the disorder of the C-terminal regions. Limitations in PrDOS-based intrinsically disordered region (IDR) model predictions were also evident in this comparison. Empirical structural data such as that presented in our study for N-SjAsnRS will enhance the prediction of sequence-homology based structure modelling and prediction of IDRs in the future. Communicated by Ramaswamy H. Sarma

Amino acid usage and protein expression levels in the flatworm Schistosoma mansoni

Schistosoma mansoni is a parasitic flatworm that causes a human disease called schistosomiasis, or bilharzia. At the genomic level, S. mansoni is AT-rich, but has some compositional heterogeneity. Indeed, some regions of its genome are GC-rich, mainly in the regions located near the extreme ends of the chromosomes. Recently, we showed that, despite the strong bias towards A/T ending codons, highly expressed genes tend to use GC-rich codons. Here, we address the following question: are highly expressed sequences biased in their amino acid frequencies? Our analyses show that these sequences in S. mansoni, as in species ranging from bacteria to human, are strongly biased in nucleotide composition. Highly expressed genes tend to use GC-rich codons (in the first and second codon positions), which code the energetically cheapest amino acids. Therefore, we conclude that amino acid usage, at least in highly expressed genes, is strongly shaped by natural selection to avoid energetically expensive residues. Whether this is an adaptation to the parasitic way of life of S. mansoni, is unclear since the same pattern occurs in free-living species.

Schistosoma mansoni infection alters the host pre-vaccination environment resulting in blunted Hepatitis B vaccination immune responses.

Schistosomiasis is a disease caused by parasitic flatworms of the Schistosoma spp., and is increasingly recognized to alter the immune system, and the potential to respond to vaccines. The impact of endemic infections on protective immunity is critical to inform vaccination strategies globally. We assessed the influence of Schistosoma mansoni worm burden on multiple host vaccine-related immune parameters in a Ugandan fishing cohort (n = 75) given three doses of a Hepatitis B (HepB) vaccine at baseline and multiple timepoints post-vaccination. We observed distinct differences in immune responses in instances of higher worm burden, compared to low worm burden or non-infected. Concentrations of pre-vaccination serum schistosome-specific circulating anodic antigen (CAA), linked to worm burden, showed a significant bimodal distribution associated with HepB titers, which was lower in individuals with higher CAA values at month 7 post-vaccination (M7). Comparative chemokine/cytokine responses revealed significant upregulation of CCL19, CXCL9 and CCL17 known to be involved in T cell activation and recruitment, in higher CAA individuals, and CCL17 correlated negatively with HepB titers at month 12 post-vaccination. We show that HepB-specific CD4+ T cell memory responses correlated positively with HepB titers at M7. We further established that those participants with high CAA had significantly lower frequencies of circulating T follicular helper (cTfh) subpopulations pre- and post-vaccination, but higher regulatory T cells (Tregs) post-vaccination, suggesting changes in the immune microenvironment in high CAA could favor Treg recruitment and activation. Additionally, we found that changes in the levels of innate-related cytokines/chemokines CXCL10, IL-1β, and CCL26, involved in driving T helper responses, were associated with increasing CAA concentration. This study provides further insight on pre-vaccination host responses to Schistosoma worm burden which will support our understanding of vaccine responses altered by pathogenic host immune mechanisms and memory function and explain abrogated vaccine responses in communities with endemic infections.

Dimerization, host-parasite communication and expression studies of an Echinococcus granulosus 2DBD nuclear receptor.

Nuclear receptors (NRs) are ligand-modulated transcription factors that regulate various biological processes, such as metabolism, development and reproduction. Although NRs with two DNA-binding domains (2DBD) were identified in Schistosoma mansoni (Platyhelminth, Trematoda) more than fifteen years ago, these proteins have been poorly studied. 2DBD-NRs could become attractive therapeutic targets to combat parasitic diseases such as cystic echinococcosis since this type of protein is absent in vertebrate hosts. Cystic echinococcosis is a worldwide zoonosis caused by the larval stage of the parasitic platyhelminth Echinococcus granulosus (Cestoda) that generates an important public health problem and a significant economic loss. Recently, our research group identified four 2DBD-NRs in E. granulosus, named Eg2DBDα, Eg2DBDα.1 (an isoform of Eg2DBDα), Eg2DBDβ, and Eg2DBDγ. This work demonstrated that Eg2DBDα.1 forms homodimers through the E and F regions, whereas its interaction with EgRXRβa could not be detected. In addition, the stimulation of Eg2DBDα.1 homodimerization by intermediate host serum was shown, suggesting that at least one lipophilic molecule from bovine serum could bind to Eg2DBDα.1. Finally, Eg2DBDs expression studies in the protoscolex larval stage were performed, indicating that Eg2dbdγ is not expressed, whereas Eg2dbdα has the highest expression level followed by Eg2dbdβ and Eg2dbdα.1 in decreased order. Overall, these findings provide new insights into the mechanism of action of Eg2DBDα.1 and its potential role in host-parasite communication.

Infection prevalence, intensity, and gill coverage by the parasitic flatworm, Bdelloura candida, in the American horseshoe crab (Limulus polyphemus)

Infection prevalence, intensity, and gill coverage by the parasitic flatworm, Bdelloura candida, in the American horseshoe crab (Limulus polyphemus)

Investigating Evolutionary Pressures on Protein Sequence: Applications to Drug Resistance in Flatworm Parasites

Abstract: The aim of This report is that it focuses on a particular flatworm called S mansoni and the disease it causes in humans and cattle, called schistosomiasis. This disease causes a million deaths annually across the globe. The drug for this disease is praziquantel, which is quite effective. Though lately, S mansoni is showing resistance towards this drug. In particular, The aim of this project is to find the regions showing evolutionary pressure in its protein structure and, hence, know how the protein structure mutates. The methods used in this project, amongst others, are SNAP, rasmol, clustal omega mainly. They are supported by using fundamentals from PDB, Biomart, blast. These methods are very helpful to biologists or people with less programming experience. This report will explore each method in detail before using them, and the steps needed to properly execute them are discussed as well. Along with the methods, this will use raw data in the form of protein sequence/ FASTA sequence from biomart. For the results, 12 different types of flatworms are chosen but narrowed down to 3-4, which closely resemble the structure of S mansoni. These flatworms are combined into a multiple sequence alignment. They are later compared using SNAP tool. Using the data from SNAP, the dn/ds ratio for each codon number is computed and the type of selection is determined. {dn/ds ratio and selection type are defined in further sections} For discussion and conclusion, the selection type, if positive, shows evolutionary pressure and the protein structure mutates and discusses its inference. It is shown visually through RASMOL tool. This tool helps in locating the binding sites where mutation takes place, so, focusing on those will help future researchers in finding a universal vaccine for this and some other viruses as well. The main finding of this experiment is the detection of regions of positive selection in the protein structure of the flatworm, using dn/ds. Also, the amino acid residues are explored as well. As with every experiment, this report covers the limitations of the process and the future works being carried on. The referencing style is APA Harvard, and the appendix section covers all the raw data used.

In memory of Dr. Norman O. Dronen, Jr. (9 October 1945-9 December 2022): Associate Editor for Parasitic Platyhelminthes (Zootaxa).

In memory of Dr. Norman O. Dronen, Jr. (9 October 1945-9 December 2022): Associate Editor for Parasitic Platyhelminthes (Zootaxa).

Human Water Contact Behaviour and Schistosoma haematobium Infection among Almajiri School Children in Kurfi Local Government Area of Katsina State, Nigeria

Urinary schistosomiasis is caused by a parasitic flatworm (Schistosoma haematobium) commonly called blood fluke which infects humans and causes public health problems. The study was conducted to determine the current status of human water contact behaviour and Schistosoma haematobium infection among Almajiri school children in Kurfi local area of Katsina State, Nigeria. Questionnaires were administered to 367 randomly selected Almajiris to assess the risk factors and to identify the relationship between human water contact and the infection of urinary schistosomiasis. Parasitological analysis was also used to determine the prevalence and intensity of infection among the Almajiri. Out of 367 sampled tested 161 were positive. The prevalence is significantly higher in Kofar Yamma Almajiri School with 51(47.66%) when compared to other schools and there is no significant relationship between human water contact and the infection in the study area due to the absence of intermediate host snail found in the study area.

A Diverse Virome Is Identified in Parasitic Flatworms of Domestic Animals in Xinjiang, China.

Parasitic flatworms infect diverse vertebrates and are major threats to animal and even human health; however, little is known about the virome of these lower life forms. Using viral metagenomic sequencing, we characterized the virome of the parasitic flatworms collected from major domestic animals, including Dicrocoelium lanceatum and Taenia hydatigena, Echinococcus granulosus sensu stricto and Echinococcus multilocularis. Seven and three different viruses were discovered from D. lanceatum and T. hydatigena, respectively, and no viral sequences were found in adult tapeworms and protoscoleces of E. granulosus sensu stricto and E. multilocularis. Two out of the five parasitic flatworm species carry viruses, showing a host specificity of these viruses. These viruses belong to the Parvoviridae, Circoviridae, unclassified circular, Rep-encoding single-stranded (CRESS) DNA virus, Rhabdoviridae, Endornaviridae, and unclassified RNA viruses. The presence of multiple highly divergent RNA viruses, especially those that cluster with viruses found in marine animals, implies a deep evolutionary history of parasite-associated viruses. In addition, we found viruses with high identity to common pathogens in dogs, including canine circovirus and canine parvovirus 2. The presence of these viruses in the parasites implies that they may infect parasitic flatworms but does not completely exclude the possibility of contamination from host intestinal contents. Furthermore, we demonstrated that certain viruses, such as CRESS DNA virus may integrate into the genome of their host. Our results expand the knowledge of viral diversity in parasites of important domestic animals, highlighting the need for further investigations of their prevalence among other parasites of key animals. IMPORTANCE Characterizing the virome of parasites is important for unveiling the viral diversity, evolution, and ecology and will help to understand the "Russian doll" pattern among viruses, parasites, and host animals. Our data indicate that diverse viruses are present in specific parasitic flatworms, including viruses that may have an ancient evolutionary history and viruses currently circulating in parasite-infected host animals. These data also raise the question of whether parasitic flatworms acquire and/or carry some viruses that may have transmission potential to animals. In addition, through the study of virus-parasite-host interactions, including the influence of viral infection on the life cycle of the parasite, as well as its fitness and pathogenicity to the host, we could find new strategies to prevent and control parasitic diseases.

Diversity of trematodes from the amphibian anomaly P hotspot: Role of planorbid snails.

Trematode infection of the second intermediate hosts can lead to changes in their fitness and, as a result, a change in the invasion rate of animal communities. It is especially pronounced during the invasion of parasite species that reduce activity due to the manipulation of hosts through the changes of their morphology and physiology. One of these cases is an anomaly P syndrome hotspot found in some populations of water frogs and toads in Europe caused by the trematode Strigea robusta metacercariae. The occurrence of pathogen and their participation in ecosystems are intrigues questions in the anomaly P phenomenon, as well as the role of planorbid snails that serve as the first intermediate hosts for many trematode species. Herein, we focused on trematodes spectra from planorbid snails and amphibians from the anomaly P hosts with the aim to undetected interactions between the pathways of parasites. Emerging cercariae of 6802 planorbid snails of dominant species (Planorbarius corneus, Planorbis planorbis, and Anisus spp.) were detected by both morphological and molecular methods in seven waterbodies in Privolzhskaya Lesostep Nature Reserve (Russia). A total of 95 sequences of 18 species were received, and 48 sequences were unique and did not present in any genetic databases. The 18 species of trematodes from snails and 14 species of trematodes from amphibian hosts (Pelophylax ridibundus; Ranidae; Anura) were detected. Three species (Echinostoma nasincovae, Tylodelphys circibuteonis and Australapatemon burti) was new for the trematode fauna of the Middle Volga River region and Russia as a whole. Eleven species of parasitic flatworms have amphibians in their life cycles and nine species used amphibians as metacercariae hosts: Echinostoma nasincovae, E. miyagawai, Echinoparyphium recurvatum, Tylodelphys circibuteonis, Neodiplostomum spathula, Paralepoderma cloacicola, Macrodera longicollis, Strigea robusta, and Strigea strigis. The occurrence of trematode species from planorbid mollusks and frogs were compared.