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There is a great need to understand the impact of complex communities on the free-living parasite stages that are part of them. This task becomes more complex as nonnative species emerge, changing existing relationships and shaping new interactions in the community. A relevant question would be: Can the coexistence of nontarget snails with the target hosts contribute to trematodasis control? We used field and experimental approaches to investigate nonnative competitor-induced parasite dilution. During a three-year field study, we investigated digenean infection in Lymnaea stagnalis from eight Polish lakes inhabited or uninhabited by Potamopyrgus antipodarum. Additionally, we verified the presence of digenean infections in the populations of P. antipodarum. Moreover, we conducted an experimental infection of L. stagnalis with miracidia of Trichobilharzia szidati under increasing densities of P. antipodarum and aimed to infect P. antipodarum with them separately. The prevalence of avian schistosomes in lymnaeid snails was significantly higher in uninhabited lakes than in lakes inhabited by P. antipodarum. Our study indicates that waters with a higher density of invaders have a lower prevalence of avian schistosomes in lymnaeid hosts. The results of experimental studies confirmed that the presence of high densities of P. antipodarum reduces the probability of target host infection. Both field and experimental studies rule out the role of P. antipodarum as a source of avian schistosome cercariae. Here, a nonnative species was tested as a diluter, which in practice may be harmful to the local environment. This work is not a call for the introduction of nonnative species; it is intended to be a stimulus for researchers to continue searching for natural enemies of parasites because, as our results show, they exist. Finding natural enemies to the most dangerous species of human and animal parasites that will pose no threat to the local environment could be groundbreaking.

Schistosome invasive stages, cercariae, leave intermediate snail hosts, penetrate the skin of definitive hosts, and transform to schistosomula migrating to final localization. During invasion, cercariae employ histolytic and other bioactive products of specialized holocrine secretory cells – postacetabular (PA) and circumacetabular (CA) penetration glands. Although several studies attempted to characterize protein composition of the in vitro induced gland secretions in Schistosoma mansoni and Schistosoma japonicum, the results were inconsistent and dependent on the method of sample collection and processing. Products of both gland types mixed during their secretion did not allow localization of identified proteins to a particular gland. Here we compared proteomes of separately isolated cercarial gland cells of the avian schistosome Trichobilharzia szidati employing laser-assisted microdissection and shotgun LC-MS/MS, thus obtaining the largest dataset so far concerning the representation and localization of cercarial penetration gland proteins. We optimized the methods of sample processing with cercarial bodies (heads) first. Alizarin-pre-stained, chemically non-fixed samples provided optimal results of MS analyses, and enabled distinguishing PA and CA glands for microdissection. Using 7.5 × 106 μm3 sample volume per gland replicate, we identified 3347 peptides assigned to 792 proteins, from which 461 occurred in at least 2 of 3 replicates in either gland type (PA = 455, 40 exclusives; CA = 421, 6 exclusives; 60 proteins differed significantly in their abundance between the glands). Peptidases of 5 catalytic types accounted for ca. 8 % and 6 % of reliably identified proteins in PA and CA glands, respectively. Invadolysin, nardilysin, cathepsins B2 and L3, and elastase 2b orthologs were the major gland endopeptidases. Two cystatins and a serpin were highly abundant peptidase inhibitors in the glands. CA glands were rich in venom allergen-like proteins. The assembled total cercarial body proteome included 1631 identified proteins and revealed additional interesting factors possibly related to tissue invasion.HighlightsProteomes of two penetration gland types in schistosome cercariae greatly differPostacetabular glands possess 40 unique proteins and are abundant in hydrolasesCircumacetabular glands posses 6 unique proteins and are rich in VAL proteinsPeptidases make up 8 % of postacetabular and 6 % of circumacetabular gland proteinsCercarial elastase is unique to circumacetabular glands of Trichobilharzia szidatiNote: Supplementary data associated with this article All supplementary data files can be accessed from the following link: http://www.helminthology.cz/supplementary_files.html

In the present study, we analyzed the morphology of three genetic types of the bird-infecting acanthocephalan Polymorphus cf. minutus (PspT1, PspT2, PspT3), mainly based on the cystacanth-stage obtained from amphipods (Gammarus fossarum, Gammarus pulex, Gammarus roeselii, Echinogammarus spp.). Males and females were pooled as there was no considerable difference between the sexes concerning the hook measurements. Additionally, we conducted a laboratory infection of one domestic duck for each Polymorphus type, to compare their performance and localization in this host species, and to obtain adult specimens for morphological comparison. The recovery rate from the ducks 4 weeks after infection was 16% for PspT1, 23.8% for PspT2, and 25% for PspT3. The adult worms were gravid, and the females contained mature eggs. Hook size did not differ considerably between cystacanths and adults of the respective type. The three Polymorphus types could be distinguished based on the cystacanth stage by a linear discriminant analysis that included hook measurements, proboscis length, proboscis width, and number of longitudinal hook rows and hooks per row. Furthermore, PspT3 was more different from PspT1 and PspT2 than the latter types from each other. Mainly the number of longitudinal hook rows differed in PspT3 from the existing descriptions of P. minutus (mainly 14 vs. mainly 16 rows). Potentially, PspT3 could be a non-indigenous parasite that was introduced with G. roeselii and that adapted to use the indigenous G. pulex as a host, while PspT2 might have been introduced to central Europe together with Echinogammarus spp.

Trichobilharzia species are parasitic flatworms (called schistosomes or flukes) that cause important diseases in birds and humans, but very little is known about their molecular biology. Here, using a transcriptomics-bioinformatics-based approach, we explored molecular aspects pertaining to the nutritional requirements of Trichobilharzia szidati (‘visceral fluke’) and T. regenti (‘neurotropic fluke’) in their avian host. We studied the larvae of each species before they enter (cercariae) and as they migrate (schistosomules) through distinct tissues in their avian (duck) host. Cercariae of both species were enriched for pathways or molecules associated predominantly with carbohydrate metabolism, oxidative phosphorylation and translation of proteins linked to ribosome biogenesis, exosome production and/or lipid biogenesis. Schistosomules of both species were enriched for pathways or molecules associated with processes including signal transduction, cell turnover and motility, DNA replication and repair, molecular transport and/or catabolism. Comparative informatic analyses identified molecular repertoires (within, e.g., peptidases and secretory proteins) in schistosomules that can broadly degrade macromolecules in both T. szidati and T. regenti, and others that are tailored to each species to selectively acquire nutrients from particular tissues through which it migrates. Thus, this study provides molecular evidence for distinct modes of nutrient acquisition between the visceral and neurotropic flukes of birds.

No effective method has yet been developed to prevent the threat posed by the emerging disease—cercarial dermatitis (swimmer’s itch), caused by infective cercariae of bird schistosomes (Digenea: Schistosomatidae). In our previous studies, the New Zealand mud snail—Potamopyrgus antipodarum (Gray, 1853; Gastropoda, Tateidae)—was used as a barrier between the miracidia of Trichobilharzia regenti and the target snails Radix balthica. Since the presence of non-indigenous snails reduced the parasite prevalence under laboratory conditions, we posed three new research questions: (1) Do bird schistosomes show totally perfect efficacy for chemotactic swimming behavior? (2) Do the larvae respond to substances emitted by incompatible snail species? (3) Do the excretory-secretory products of incompatible snail species interfere with the search for a compatible snail host? The experiments were carried out in choice-chambers for the miracidia of T. regenti and T. szidati. The arms of the chambers, depending on the variant, were filled with water conditioned by P. antipodarum, water conditioned by lymnaeid hosts, and dechlorinated tap water. Miracidia of both bird schistosome species chose more frequently the water conditioned by snails—including the water conditioned by the incompatible lymnaeid host and the alien species, P. antipodarum. However, species-specific differences were noticed in the behavior of miracidia. T. regenti remained more often inside the base arm rather than in the arm filled with water conditioned by P. antipodarum or the control arm. T. szidati, however, usually left the base arm and moved to the arm filled with water conditioned by P. antipodarum. In conclusion, the non-host snail excretory-secretory products may interfere with the snail host-finding behavior of bird schistosome miracidia and therefore they may reduce the risk of swimmer’s itch.

Migration of parasitic worms through the host tissues, which may occasionally result in fatal damage to the internal organs, represents one of the major risks associated with helminthoses. In order to track the parasites, traditionally used 2D imaging techniques such as histology or squash preparation do not always provide sufficient data to describe worm location/behavior in the host. On the other hand, 3D imaging methods are widely used in cell biology, medical radiology, osteology or cancer research, but their use in parasitological research is currently occasional. Thus, we aimed at the evaluation of suitability of selected 3D methods to monitor migration of the neuropathogenic avian schistosome Trichobilharzia regenti in extracted spinal cord of experimental vertebrate hosts. All investigated methods, two of them based on tracking of fluorescently stained larvae with or without previous chemical clearing of tissue and one based on X-ray micro-CT, exhibit certain limits for in vivo observation. Nevertheless, our study shows that the tested methods as ultramicroscopy (used for the first time in parasitology) and micro-CT represent promising tool for precise analyzing of parasite larvae in the CNS. Synthesis of these 3D imaging techniques can provide more comprehensive look at the course of infection, host immune response and pathology caused by migrating parasites within entire tissue samples, which would not be possible with traditional approaches.

Trichobilharzia species are parasitic flatworms (called schistosomes or flukes) that cause important diseases in birds and humans, but very little is known about their molecular biology. Here, using a transcriptomics-bioinformatics-based approach, we explored molecular aspects pertaining to the nutritional requirements of Trichobilharzia szidati (‘visceral fluke’) and T. regenti (‘neurotropic fluke’) in their avian host. We studied the larvae of each species before they enter (cercariae) and as they migrate (schistosomules) through distinct tissues in their avian (duck) host. Cercariae of both species were enriched for pathways or molecules associated predominantly with carbohydrate metabolism, oxidative phosphorylation and translation of proteins linked to ribosome biogenesis, exosome production and/or lipid biogenesis. Schistosomules of both species were enriched for pathways or molecules associated with processes including signal transduction, cell turnover and motility, DNA replication and repair, molecular transport and/or catabolism. Comparative informatic analyses identified molecular repertoires (within, e.g., peptidases and secretory proteins) in schistosomules that can broadly degrade macromolecules in both T. szidati and T. regenti, and others that are tailored to each species to selectively acquire nutrients from particular tissues through which it migrates. Thus, this study provides molecular evidence for distinct modes of nutrient acquisition between the visceral and neurotropic flukes of birds.

Swimmer’s itch is a re-emerging human disease caused by bird schistosome cercariae, which can infect bathing or working people in water bodies. Even if cercariae fail after penetrating the human skin, they can cause dangerous symptoms in atypical mammal hosts. One of the natural methods to reduce the presence of cercariae in the environment could lie in the introduction of non–host snail species to the ecosystem, which is known as the “dilution” or “decoy” effect. The caenogastropodPotamopyrgus antipodarum—an alien in Europe—could be a good candidate against swimmer’s itch because of its apparent resistance to invasion by European bird schistosome species and its high population density. As a pilot study on this topic, we have carried out a laboratory experiment on howP. antipodaruminfluences the infestation of the intermediate hostRadix balthica(a native lymnaeid) by the bird schistosomeTrichobilharzia regenti. We found that the co–exposure of 200P. antipodarumindividuals per oneR. balthicato theT. regentimiracidia under experimental conditions makes the infestation ineffective. Our results show that a non–host snail population has the potential to interfere with the transmission of a trematode via suitable snail hosts.

Like several other bird schistosomes, neurotropic schistosome of Trichobilharzia regenti can invade also mammals, including humans. Repeated infections cause cercarial dermatitis, a skin inflammatory reaction leading to parasite elimination in non-specific mammalian hosts. However, in experimentally primo-infected mice, the worms escape from the skin and migrate to the central nervous system. In order to evade host immune reactions, schistosomes undergo cercaria/schistosomulum transformation accompanied with changes of surface antigens. The present study is focused on localization of the main antigens of T. regenti; cercariae, schistosomula developed under different conditions and adults were compared. Antigens were localized by immunofluorescence and ultrastructural immunocytochemistry using sera of mice repeatedly infected with T. regenti. Detected antibody targets were located in glycocalyx and penetration glands of cercariae and in tegument of cercariae, schistosomula and adults. Shedding of cercarial glycocalyx significantly reduced surface reactivity; further decrease was reported during ongoing development of schistosomula. Spherical bodies, probably transported from subtegumental cell bodies to worm surface, were identified as the most reactive tegumental structures. Based on similar results for schistosomula developed in specific, non-specific hosts and in vitro, it seems that the ability of T. regenti to decrease the surface immunoreactivity during ontogenesis is independent on the host type.

Trichobilharzia regenti (Schistosomatidae, Digenea), a parasite of birds, exhibits a unique strategy among schistosomes, having affinity to the nervous system of vertebrate hosts. Migration of parasitic stages within hosts and/or swimming of non-parasitic larvae in water environment depend on the action of body wall muscles which were studied with confocal and electron microscopy. In all stages, body wall musculature is comprised of differently organized circular and longitudinal muscles. During the development, an extensive change of musculature characteristics and/or formation of new muscle structures were recorded; cercariae, schistosomula and adult worms produce additional underlying diagonal muscle fibers and inner plexus of radial musculature. Substantial changes of the outer environment during penetration of a host (osmotic values of water vs. host tissues) are accompanied by surface transformation of miracidia/mother sporocysts and cercariae/schistosomula. Contrary to that, changes of body musculature in these stages are characterized only by growth and re-organization of existing structures, and never by formation of new components of body musculature. Future studies in this field may contribute to a better knowledge of morphology and function of trematode muscles, including those of schistosomes that are important pathogens of humans and animals.

The invasive larvae (cercariae) of schistosomes penetrate the skin of their definitive hosts. During the invasion, they undergo dramatic ultrastructural and physiological transitions. These changes result in the development of the subsequent stage, schistosomulum, which migrates through host tissues in close contact with host's immune system. One of the striking changes in the transforming cercariae is the shedding of their thick tegumental glycocalyx, which represents an immunoattractive structure; therefore its removal helps cercariae to avoid immune attack. A set of commercial fluorescently labeled lectin probes, their saccharide inhibitors and monoclonal antibodies against the trisaccharide Lewis-X antigen (LeX, CD15) were used to characterize changes in the surface saccharide composition of the neuropathogenic avian schistosome Trichobilharzia regenti during the transformation of cercariae to schistosomula, both in vitro and in vivo. The effect of various lectins on glycocalyx shedding was evaluated microscopically. The involvement of peptidases and their inhibitors on the shedding of glycocalyx was investigated using T. regenti recombinant cathepsin B2 and a set of peptidase inhibitors. The surface glycocalyx of T. regenti cercariae was rich in fucose and mannose/glucose residues. After the transformation of cercariae in vitro or in vivo within their specific duck host, reduction and vanishing of these epitopes was observed, and galactose/N-acetylgalactosamine emerged. The presence of LeX was not observed on the cercariae, but the antigen was gradually expressed from the anterior part of the body in the developing schistosomula. Some lectins which bind to the cercarial surface also induced secretion from the acetabular penetration glands. Seven lectins induced the shedding of glycocalyx by cercariae, among which five bound strongly to cercarial surface; the effect could be blocked by saccharide inhibitors. Mannose-binding protein, part of the lectin pathway of the complement system, also bound to cercariae and schistosomula, but had little effect on glycocalyx shedding. Our study did not confirm the involvement of proteolysis in glycocalyx shedding.

Trematodes of the order Diplostomida are well known as serious pathogens of man, and both farm and wild animals; members of the genus Schistosoma (Schistosomatidae) are responsible for human schistosomosis affecting more than 200 million people in tropical and subtropical countries, infections of mammals and birds by animal schistosomes are of great veterinary importance. The order Diplostomida is also rich in species parasitizing other major taxa of vertebrates. The Aporocotylidae are pathogenic in fish, Spirorchiidae in reptiles. All these flukes have two-host life cycles, with asexually reproducing larvae usually in molluscs and occasionally in annelids, and adults usually live in the blood vessels of their vertebrate hosts. Pathology is frequently associated with inflammatory reactions to eggs trapped in various tissues/organs. On the other hand, the representatives of Diplostomidae and Strigeidae have three- or four-host life cycles in which vertebrates often serve not only as definitive, but also as intermediate or paratenic hosts. Pathology is usually associated with migration of metacercariae and mesocercariae within the host tissues. The impact of these trematode infections on both farm and wild animals may be significant.

Notocotylus attenuatus (Digenea: Notocotylidae) is a monostome fluke parasitizing the intestinal caeca of waterfowl that uses an injection apparatus to infect its intermediate snail host. Morphology of the invading larva (a sporocyst), and the intramolluscan larval development of this fluke have not been characterized extensively. In this study, experimental infections of Lymnaea stagnalis using N. attenuatus eggs resulted in the development of sporocysts containing one germ ball or mother redia between 12 and 21 days post exposure (p.e.) within the hepatopancreas. Independent mother rediae and developing daughter rediae were present between day 25 and day 42 p.e. Cercariae, within the body of rediae, were detected 42 days p.e. The development of daughter rediae and cercariae started posteriorly in the body of parent redia and these larvae migrated anteriorly during development towards the birth pore. A cercaria was also observed emerging from the birth pore and released cercariae maturated further within the snail hepatopancreas prior to leaving the snail. The intramolluscan development was completed 45 days p.e. when the first fully formed cercariae were shed into the outer environment. These data detail the fascinating post-embryonic development of N. attenuatus and highlight the intricate nature of larval transitions within its snail host.

Background Cercariae of schistosomes employ bioactive molecules for penetration into their hosts. These are released from specialized unicellular glands upon stimuli from host skin. The glands were previously well-described in the human pathogen Schistosoma mansoni. As bird schistosomes can also penetrate human skin and cause cercarial dermatitis, our aim was to characterize the architecture and ultrastructure of glands in the neurotropic bird schistosome Trichobilharzia regenti and compare it with S. mansoni. In the context of different histolytic enzymes used by these two species, we focused also on the estimations of gland volumes and pH in T. regenti. Results The architecture and 3-D models of two types of acetabular penetration glands, their ducts and of the head gland are shown here. We characterized secretory vesicles in all three gland types by means of TEM and confirmed accuracy of the models obtained by confocal microscopy. The results of two independent approaches showed that the glands occupy ca. one third of cercarial body volume (postacetabular glands ca. 15%, circumacetabular 12% and head gland 6%). The inner environment within the two types of acetabular glands differed significantly as evidenced by dissimilar ability to bind fluorescent markers and by pH value which was higher in circumacetabular (7.44) than in postacetabular (7.08) glands. Conclusions As far as we know, this is the first presentation of a 3-D model of cercarial glands and the first exact estimation of the volumes of the three gland types in schistosomes. Our comparisons between T. regenti and S. mansoni implied that the architecture and ultrastructure of the glands is most likely conserved within the family. Only minor variations were found between the two species. It seems that the differences in molecular composition have no effect on general appearance of the secretory cells in TEM. Fluorescent markers employed in this study, distinguishing between secretory vesicles and gland types, can be useful in further studies of mechanisms used by cercariae for host invasion. Results of the first attempts to estimate pH within schistosome glands may help further understanding of regulation of enzymatic activities present within the glands.

Cercariae of bird schistosomes (Trichobilharzia szidati and Trichobilharzia regenti) were mechanically stimulated to transform to schistosomula and kept in different cultivation media supplemented with duck red blood cells and/or homogenized nervous tissue. The development under in vitro conditions was compared with that in vivo, using the following characters: emptying of penetration glands, surface changes, food uptake, and growth of early schistosomula. The results show that the cultivation medium routinely used for human schistosomes is also suitable for mass production of early schistosomula of bird schistosomes, including the unique nasal species—T. regenti. The changes observed resemble those present in worms developing in vivo; therefore, the in vitro produced early schistosomula might be used for further studies of host–parasite interactions.

Hepatozoon ayorgbor n. sp. is described from specimens of Python regius imported from Ghana. Gametocytes were found in the peripheral blood of 43 of 55 snakes examined. Localization of gametocytes was mainly inside the erythrocytes; free gametocytes were found in 15 (34.9%) positive specimens. Infections of laboratory-reared Culex quinquefasciatus feeding on infected snakes, as well as experimental infection of juvenile Python regius by ingestion of infected mosquitoes, were performed to complete the life cycle. Similarly, transmission to different snake species (Boa constrictor and Lamprophis fuliginosus) and lizards (Lepidodactylus lugubris) was performed to assess the host specificity. Isolates were compared with Hepatozoon species from sub-Saharan reptiles and described as a new species based on the morphology, phylogenetic analysis, and a complete life cycle.

Two experimental trials were performed to elucidate the role of rodents in the life cycle of Hepatozoon species using snakes as intermediate hosts. In one trial, two ball pythons, Python regius Shaw, 1802 were force fed livers of laboratory mice previously inoculated with sporocysts of Hepatozoon ayorgbor Sloboda, Kamler, Bulantová, Votýpka et Modrý, 2007. Transmission was successful in these experimentally infected snakes as evidenced by the appearance of intraerythrocytic gamonts, which persisted until the end of trial, 12 months after inoculation. Developmental stages of haemogregarines were not observed in histological sections from mice. In another experimental trial, a presence of haemogregarine DNA in mice inoculated with H. ayorgbor was demonstrated by PCR in the liver, lungs and spleen.