How schistosomes profit from the stress responses they elicit in their hosts

Littorina snails and Microphallus trematodes: Diverse consequences of the trematode-induced metabolic shifts

The intricate relationships between parasites and hosts encompass a wide range of levels, from molecular interactions to population dynamics. Parasites influence not only the physiological processes in the host organism, but also the entire ecosystem, affecting mortality of individuals, the number of offspring through parasitic castration, and matter and energy cycles. Understanding the molecular mechanisms that govern host-parasite relationships and their impact on host physiology and environment remains challenging. In this study, we analyzed how infection with Microphallus trematodes affects the metabolome of two Littorina snail species inhabiting different intertidal zone shore levels. We applied non-targeted GC-MS-based metabolomics to analyze biochemical shifts induced by trematode infection in a host organism. We have identified changes in energy, amino acid, sugar, and lipid metabolism. In particular, we observed intensified amino acid catabolism and nitrogenous catabolites (glutamine, urea) production. These changes primarily correlated with infection and interspecies differences of the hosts rather than shore level. The changes detected in the host metabolism indicate that other aspects of life may have been affected, both within the host organism and at a supra-organismal level. Therefore, we explored changes in microbiota composition, deviations in the host molluscs behavior, and acetylcholinesterase activity (ACE, an enzyme involved in neuromuscular transmission) in relation to infection. Infected snails displayed changes in their microbiome composition. Decreased ACE activity in snails was associated with reduced mobility, but whether it is associated with trematode infection remains unclear. The authors suggest a connection between the identified biochemical changes and the deformation of the shell of molluscs, changes in their behavior, and the associated microbiome. The role of parasitic systems formed by microphallid trematodes and Littorina snails in the nitrogen cycle at the ecosystem level is also assumed.

Protective role of chlorogenic acid in preserving cytochrome-c stability against HFIP-induced molten globule state at physiological pH

Numerous neurodegenerative disorders are characterized by protein misfolding and aggregation. The mechanism of protein aggregation is intricate, and it is very challenging to study at cellular level. Inhibition of protein aggregation by interfering with its pathway is one of the ways to prevent neurodegenerative diseases. In the present work, we have evaluated the protective effect of a polyphenol compound chlorogenic acid (CGA) on the native and molten globule state of horse heart cytochrome c (cyt c). A molten globule state of this heme protein was achieved in the presence of fluorinated alcohol 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) at physiological pH, as studied by UV-Vis absorption, circular dichroism, intrinsic and ANS fluorescence. We found that at 50 % (v/v) HFIP, the native cyt c transformed into a molten globule state. The same techniques were also used to analyze the protective effect of CGA on the molten globule state of cyt c, and the results show that the CGA prevented the molten globular state and retained the protein close to the native state at 1:1 protein:CGA sub molar ratio. Molecular dynamics study also revealed that CGA retains the stability of cyt c in HFIP medium by preserving it in an intermediate state close to native conformation.

Impact of Schistosoma sp., Infection on Biological, Feeding, Physiological, Histological, and Genotoxicological Aspects of Biomphalaria alexandrina and Bulinus truncatus Snails

BACKGROUND

Trematode infections of the genus Schistosoma can induce physiological and behavioral changes in intermediate snail hosts. This is because the parasite consumes essential resources necessary for the host's survival, prompting hosts to adapt their behavior to maintain some level of fitness before parasite-induced mortality occurs.

METHODS

In this study, the reproductive and biochemical parameters of Biomphalaria alexandrina and Bulinus truncatus were examined during the cercareal shedding stage of infection with Schistosoma mansoni and Schistosoma haematobium, respectively, compared with controls.

RESULTS

The study revealed an infection rate of 34.7% for S. mansoni and 30.4% for S. haematobium. In B. alexandrina infected with S. mansoni, a survival rate of 65.2% was recorded, along with a mean prepatent period of 30.3 ± 1.41 days, a mean shedding duration of 14.2 ± 0.16 days, and a mean lifespan of 44.1 ± 0.24 days. Meanwhile, in B. truncatus infected with S. haematobium, a survival rate of 56.4% was observed, with a mean prepatent period of 44.3 ± 1.41 days, a mean shedding duration of 22.6 ± 2.7 days, and a mean lifespan of 66.9 ± 1.6 days. Feeding increased in both infected species of snails, while the net reproductive rate (Ro) of the infected snails decreased. Total antioxidant (TAO) and lipid peroxidation activity increased in the two infected snail species during shedding, while Glutathione-S-transferase levels decreased. Lipid peroxidase activity and nitrogen oxide levels significantly decreased in infected B. alexandrina and increased in infected Bulinus. Steroid hormone levels were elevated in infected Biomphalaria, whereas they were reduced in infected Bulinus. Comet assay parameters showed an increase in the two infected genera after infection compared to control snails, indicating genotoxic damage and histopathological damage was observed.

CONCLUSIONS

These findings demonstrate that infection with larva species diverse biochemical, hormonal, genotoxic, and histopathological changes in the tissues responsible for fecundity and reproduction in B. alexandrina and B. truncates comparing with controls.

Reproductive alterations of Biomphalaria glabrata (Say, 1818) infected with Angiostrongylus cantonensis (Chen, 1935) and exposed to Euphorbia milii var. hislopii latex

The natural phytochemical latex of Euphorbia milii var. hislopii is one of the most promising natural molluscicides for the control of Biomphalaria glabrata, and has been widely studied under laboratory conditions for selective control of schistosomiasis transmission. However, the effect of this product on B. glabrata infected by other helminths had not yet been investigated. The present study reports evaluation of the effect of E. milii var. hislopii latex on the survival and reproductive activity of B. glabrata infected by Angiostrongylus cantonensis. For this purpose, the following groups were formed: control (C), exposed (E), infected (I) and infected and exposed for different time intervals (1 day - I+E-1D, 7 days - I+E-7D, 14 days - I+E-14D, 21 days - I+E-21D and 28 days - I+E-28D). The experimental infection was performed with L1 larvae of A. cantonensis and exposure to 0.08 mg/L (LC50) of E. milii latex for a period of 24 hours. We analyzed the effects of E. milii latex on the survival of snails during four weeks, reproductive parameters and possible histophysiopathological changes in the gonad and albumen gland of the snails. Regarding survival, there was reduction of more than 50% in the groups exposed to latex (E and I + E) compared to the control group. As for the number of ovigerous masses, eggs, and average number of hatched snails, significant increases were observed in the I+E-1D group at the 4th week compared to the control group and the other weeks in the same group. Angiostrongylus cantonensis larvae were observed in the gonad and albumen gland from day 21 and 28 of infection in groups I and I+E, respectively, with granuloma-like formation. At these observation periods and in these groups, an increase in galactogen was observed in the albumen gland, which influenced egg laying, suggesting the existence of a fecundity compensation mechanism phenomenon. It was possible to conclude that both stressors - A. cantonensis infection and exposure to E. milii latex - directly influenced the survival and reproductive parameters of B. glabrata.

FMRF-NH2 -related neuropeptides in Biomphalaria spp., intermediate hosts for schistosomiasis: Precursor organization and immunohistochemical localization

Freshwater snails of the genus Biomphalaria serve as intermediate hosts for the digenetic trematode Schistosoma mansoni, the etiological agent for the most widespread form of intestinal schistosomiasis. As neuropeptide signaling in host snails can be altered by trematode infection, a neural transcriptomics approach was undertaken to identify peptide precursors in Biomphalaria glabrata, the major intermediate host for S. mansoni in the Western Hemisphere. Three transcripts that encode peptides belonging to the FMRF-NH2 -related peptide (FaRP) family were identified in B. glabrata. One transcript encoded a precursor polypeptide (Bgl-FaRP1; 292 amino acids) that included eight copies of the tetrapeptide FMRF-NH2 and single copies of FIRF-NH2 , FLRF-NH2 , and pQFYRI-NH2 . The second transcript encoded a precursor (Bgl-FaRP2; 347 amino acids) that comprised 14 copies of the heptapeptide GDPFLRF-NH2 and 1 copy of SKPYMRF-NH2 . The precursor encoded by the third transcript (Bgl-FaRP3; 287 amino acids) recapitulated Bgl-FaRP2 but lacked the full SKPYMRF-NH2 peptide. The three precursors shared a common signal peptide, suggesting a genomic organization described previously in gastropods. Immunohistochemical studies were performed on the nervous systems of B. glabrata and B. alexandrina, a major intermediate host for S. mansoni in Egypt. FMRF-NH2 -like immunoreactive (FMRF-NH2 -li) neurons were located in regions of the central nervous system associated with reproduction, feeding, and cardiorespiration. Antisera raised against non-FMRF-NH2 peptides present in the tetrapeptide and heptapeptide precursors labeled independent subsets of the FMRF-NH2 -li neurons. This study supports the participation of FMRF-NH2 -related neuropeptides in the regulation of vital physiological and behavioral systems that are altered by parasitism in Biomphalaria.

Identification and localization of a gonadotropin-releasing hormone-related neuropeptide in Biomphalaria, an intermediate host for schistosomiasis

Freshwater snails of the genus Biomphalaria serve as obligatory hosts for the digenetic trematode Schistosoma mansoni, the causative agent for the most widespread form of intestinal schistosomiasis. Within Biomphalaria, S. mansoni larvae multiply and transform into the cercariae form that can infect humans. Trematode development and proliferation is thought to be facilitated by modifications of host behavior and physiological processes, including a reduction of reproduction known as "parasitic castration." As neuropeptides participate in the control of reproduction across phylogeny, a neural transcriptomics approach was undertaken to identify peptides that could regulate Biomphalaria reproductive physiology. The present study identified a transcript in Biomphalaria alexandrina that encodes a peptide belonging to the gonadotropin-releasing hormone (GnRH) superfamily. The precursor and the predicted mature peptide, pQIHFTPDWGNN-NH₂ (designated Biom-GnRH), share features with peptides identified in other molluscan species, including panpulmonates, opisthobranchs, and cephalopods. An antibody generated against Biom-GnRH labeled neurons in the cerebral, pedal, and visceral ganglia of Biomphalaria glabrata. GnRH-like immunoreactive fiber systems projected to all central ganglia. In the periphery, immunoreactive material was detected in the ovotestis, oviduct, albumen gland, and nidamental gland. As these structures serve crucial roles in the production, transport, nourishment, and encapsulation of eggs, disruption of the GnRH system of Biomphalaria could contribute to reduced reproductive activity in infected snails.

Biochemical and apoptotic changes in the nervous and ovotestis tissues of Biomphalaria alexandrina following infection with Schistosoma mansoni

Infection with trematodes produces physiological and behavioural changes in intermediate snail hosts. One response to infection is parasitic castration, in which energy required for reproduction of the host is thought to be redirected to promote development and multiplication of the parasite. This study investigated some reproductive and biochemical parameters in the nervous (CNS) and ovotestis (OT) tissues of Biomphalaria alexandrina during the course of Schistosoma mansoni infection. Antioxidant and oxidative stress parameters including catalase (CAT), nitric oxide (NO) and lipid peroxidation (MDA) were measured. Levels of steroid hormones, including testosterone, progesterone and estradiol, were also assessed. Finally, flow cytometry was used to compare measures of apoptosis between control snails and those shedding cercariae by examining mitochondrial membrane potential with the stain 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimi-dazolylcarbocyanine iodide (JC-1) and poly(ADP-ribose) polymerase (PARP). Infection with S. mansoni caused a 47.7% reduction in the net reproductive rate (R_o) of B. alexandrina. CAT activity was increased in the CNS at 21 days post infection (dpi) but by 28 dpi it was reduced below control values. Also, CAT activity increased significantly in the OT at 14, 21 and 28 dpi. In CNS tissues, NO levels were reduced at 7 dpi, increased at 14 and 21 dpi, and reduced again at 28 dpi. The overall level of lipid peroxidation gradually increased during the course of infection to reach its highest levels at 28 dpi. Steroid hormone measurements showed that concentrations of testosterone and estradiol were reduced in the CNS tissues at 28 dpi, while those of progesterone were slightly increased in the CNS and OT tissues. The percentage of cells that positively stained with JC-1was significantly increased in CNS and OT tissues of infected snails while the percentage of cells positively stained with PARP was decreased compared to controls. Together, these findings indicate that infection initiates diverse biochemical and hormonal changes leading to loss of cells responsible for egg laying and reproduction in B. alexandrina.

Snail defence responses to parasite infection: The Lymnaea stagnalis-Trichobilharzia szidati model

Lymnaea stagnalis is a common freshwater gastropod. Importantly, the snail serves as the intermediate host for more than one hundred species of digenetic trematodes, including the avian schistosome Trichobilharzia szidati, a causative agent of cercarial dermatitis in humans. Infection of L. stagnalis by T. szidati initiates a dynamic confrontation between the host and the parasite that culminates in immunocompatibility ensuring survival and development of larvae. Unfortunately, the molecular mechanisms determining this immunocompatibility remain poorly characterised. By employing a variety of immune elicitors, including chemical compounds, PAMPs and bacteria, research in the last two decades has elucidated some of the molecular processes that regulate the snail internal defence response such as haemocyte signalling pathways. These discoveries provide a framework for future studies of molecular interactions between T. szidati and L. stagnalis to help elucidate factors and mechanisms enabling transmission of schistosome parasites. Moreover, support from recently available next generation sequence data and CRISPR-enabled functional genomics should further enable L. stagnalis as an important model for comparative immunology and contribute to a more comprehensive understanding of immune functions in gastropod molluscs.

Central nervous system transcriptome of Biomphalaria alexandrina, an intermediate host for schistosomiasis

Objective

Globally, more than 200 million people live at risk of the neglected tropical disease schistosomiasis (or snail fever). Larval schistosomes require the presence of specific snail species that act as intermediate hosts, supporting their multiplication and transformation into forms that can infect humans. This project was designed to generate a transcriptome from the central nervous system (CNS) of Biomphalaria alexandrina, the major intermediate host for Schistosoma mansoni in Egypt.

Results

A transcriptome was generated from five pooled central nervous systems dissected from uninfected specimens of B. alexandrina. Raw Illumina RNA-seq data (~ 20.3 million paired end reads of 150 base pairs length each) generated a transcriptome consisting of 144,213 transcript elements with an N50 contig size of 716 base pairs. Orthologs of 15,246 transcripts and homologs for an additional 16,810 transcripts were identified in the UniProtKB/Swiss-Prot database. The B. alexandrina CNS transcriptome provides a resource for future research exploring parasite-host interactions in a simpler nervous system. Moreover, increased understanding of the neural signaling mechanisms involved in the response of B. alexandrina to infection by S. mansoni larvae could lead to novel and highly specific strategies for the control of snail populations.

Electronic supplementary material

The online version of this article (10.1186/s13104-017-3018-6) contains supplementary material, which is available to authorized users.

Potential Vaccine Targets against Rabbit Coccidiosis by Immunoproteomic Analysis

The aim of this study was to identify antigens for a vaccine or drug target to control rabbit coccidiosis. A combination of 2-dimensional electrophoresis, immunoblotting, and mass spectrometric analysis were used to identify novel antigens from the sporozoites of Eimeria stiedae. Protein spots were recognized by the sera of New Zealand rabbits infected artificially with E. stiedae. The proteins were characterized by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF/TOF-MS) analysis in combination with bioinformatics. Approximately 868 protein spots were detected by silver-staining, and a total of 41 immunoreactive protein spots were recognized by anti-E. stiedae sera. Finally, 23 protein spots were successfully identified. The proteins such as heat shock protein 70 and aspartyl protease may have potential as immunodiagnostic or vaccine antigens. The immunoreactive proteins were found to possess a wide range of biological functions. This study is the first to report the proteins recognized by sera of infected rabbits with E. stiedae, which might be helpful in identifying potential targets for vaccine development to control rabbit coccidiosis.

Analysis of hemocytes in Lymnaea stagnalis: Characterization and effects of repeated hemolymph collections

The first part of the study was devoted to test the hypothesis according to which the hemolymph of Lymnaea stagnalis can be collected repeatedly - regardless the time-intervals - at an individual scale without impact on survival nor immunocapacity defined as the hemocyte density and viability. No significant effects on snail survival were observed when repeated hemolymph samplings were performed at frequencies ranging from 96 h up to 24 h. The frequency of hemolymph sampling had no significant effects on hemocyte density but the hemocyte viability was slightly increased for the 24 h frequency group. Hence, we recommend setting the frequency lower than 48 h after two consecutive samplings for further assessment of hemocyte density and viability. Furthermore, a slight "day" effect was observed on snail immunocapacity. These results support the idea that L. stagnalis is a promising gastropod model in environmental immunotoxicology. A time-course analysis of individual hemocytes parameters can be evaluated with a relative confidence in the non-detrimental effect of the sampling. Linear mixed-effect models allow taking the "day" effect into account and so the possible effect of an environmental factor (i.e. xenobiotic exposures) can be analyzed. Statistical inferences indicated that the inter-individual variability for these hemocyte endpoints were on the same order of magnitude than intra-individual variability. The second part of the study was devoted to provide greater insights into the structure/ultrastructure of hemocytes in L. stagnalis. Only one type of hemocyte has been observed. The hemocytes in their free-floating status showed ovoid or spherical shapes. Some hemocytes exerted filopodia and structures shaped like sailboats. Their ultrastructure showed signs of intense cellular activity. Two peculiar organelles were observed. One corresponds to a massive perinuclear structure of dense aspect. The other corresponds to a structure with fibrillary arrangements. These two structures deserve further investigation in order to understand their nature, function and importance in the snails' immunocompetence.

The nervous systems of Tylodelphys metacercariae (Digenea: Diplostomidae) from the catfish Clarias gariepinus (Clariidae) in freshwater habitats of Tanzania

The nervous systems of three Tylodelphys metacercariae (T. mashonense, Tylodelphys spp. 1 and 2) co-occurring in the cranial cavity of the catfish, Clarias gariepinus, were examined by the activity of acetylthiocholine iodide (AcThI), with the aim of better understanding the arrangement of sensillae on the body surface and the nerve trunks and commissures, for taxonomic purposes. Enzyme cytochemistry demonstrated a comparable orthogonal arrangement in the three metacercariae: the central nervous system (CNS) consisting of a pair of cerebral ganglia, from which anterior and posterior neuronal pathways arise and inter-link by cross-connectives and commissures. However, the number of transverse nerves was significantly different in the three diplostomid metacercariae: Tylodelphys sp. 1 (30), Tylodelphys sp. 2 (21) and T. mashonense (15). The observed difference in the nervous system of the three metacercariae clearly separates them into three species. These findings suggest that consistent differences in the transverse nerves of digenean metacercariae could enable the differentiation of metacercariae to the species level in the absence of molecular techniques. This, however, might require further testing on a larger number of species of digenean metacercariae.

Impact of the age of Biomphalaria alexandrina snails on Schistosoma mansoni transmission: modulation of the genetic outcome and the internal defence system of the snail

Of the approximately 34 identified Biomphalaria species,Biomphalaria alexandrina represents the intermediate host of Schistosoma mansoni in Egypt. Using parasitological and SOD1 enzyme assay, this study aimed to elucidate the impact of the age of B. alexandrina snails on their genetic variability and internal defence against S. mansoni infection. Susceptible and resistant snails were reared individually for self-reproduction; four subgroups of their progeny were used in experiment. The young susceptible subgroup showed the highest infection rate, the shortest pre-patent period, the highest total cercarial production, the highest mortality rate and the lowest SOD1 activity. Among the young and adult susceptible subgroups, 8% and 26% were found to be resistant, indicating the inheritance of resistance alleles from parents. The adult resistant subgroup, however, contained only resistant snails and showed the highest enzyme activity. The complex interaction between snail age, genetic background and internal defence resulted in great variability in compatibility patterns, with the highest significant difference between young susceptible and adult resistant snails. The results demonstrate that resistance alleles function to a greater degree in adults, with higher SOD1 activity and provide potential implications for Biomphalaria control. The identification of the most susceptible snail age enables determination of the best timing for applying molluscicides. Moreover, adult resistant snails could be beneficial in biological snail control.

Immunoproteomic analysis of Schistosoma japonicum schistosomulum proteins recognized by immunoglobulin G in the sera of susceptible and non-susceptible hosts

The aim of this study was to search for immunogenic schistosomula proteins in the hope of identifying novel intervention targets. Schistosomula proteins were analyzed by immunoproteomic which the probes were sera derived from BALB/c mice (susceptible hosts) and Microtus fortis (resistant hosts). A total of 116 immunoreactive proteins recognized by 10 days post-infected BALB/c mice, M. fortis sera, and uninfected M. fortis sera were selected for further analysis. Finally, 95 protein spots were identified by mass spectrometry (MS) analysis. Bioinformatics analysis showed that the differentially identified immunogenic proteins participated mainly in cytoskeleton organization, cell motility, energy metabolism, responses to stimuli, and protein folding. Many of these proteins were the tegument or excretory-secretory products of schistosomes reported in previous studies. Among of them, Schistosoma japonicum DnaJ (Hsp40) homologue (SjDnaJ) was successfully expressed and the purified recombinant product was evaluated by immunoprotective experiment. After immunization of BALB/c mice with recombinant SjDnaJ, it could induce 34.5% and 48.9% reductions in the numbers of worms and eggs in the liver. These results contribute to a better understanding of the molecular mechanisms underlying the host-parasite relationship and provide a major dataset to facilitate the further development of new vaccine candidates and/or diagnostic markers for schistosomiasis.

BIOLOGICAL SIGNIFICANCE

Schistosomiasis is caused by parasitic blood-dwelling flukes in tropical and subtropical areas, and it is one of the world's most prevalent tropical diseases. The lack of effective vaccine and reliable diagnostic methods make this disease difficult to control. In China, S. japonicum can infect more than 40 different susceptible mammals for this parasite. However, M. fortis is the only known mammal where the schistosome cannot develop and it exhibits no significant pathological effects. Many studies' results showed that native antibodies against S. japonicum are present in M. fortis that may have important anti-schistosomiasis roles during the infection process. The aim of this study was to search for immunogenic schistosomula proteins in the hope of identifying novel intervention targets. We present a comparative immunoproteomics analysis of the proteins recognized by susceptible and resistant host antibodies before and 10-days after infections. The results of this analysis will be helpful for identifying the key molecules required for the survival and development of schistosomes. At the same time, the study contributes to a better understanding of the molecular mechanisms underlying the host-parasite relationship associated with schistosomes and they also provide a major dataset to facilitate the further development of new diagnostic assays and/or vaccine candidates for schistosomiasis.

Isoforms of Hsp70-binding human LDL in adult Schistosoma mansoni worms

Schistosoma mansoni is one of the most common parasites infecting humans. They are well adapted to the host, and this parasite's longevity is a consequence of effective escape from the host immune system. In the blood circulation, lipoproteins not only help to conceal the worm from attack by host antibodies but also act as a source of lipids for S. mansoni. Previous SEM studies showed that the low-density lipoprotein (LDL) particles present on the surface of adult S. mansoni worms decreased in size when the incubation time increased. In this study, immunocytochemical and proteomic analyses were used to locate and identify S. mansoni binding proteins to human plasma LDL. Ultrathin sections of adult worms were cut transversely from the anterior, medial and posterior regions of the parasite. Immunocytochemical experiments revealed particles of gold in the tegument, muscle region and spine in male worms and around vitelline cells in females. Immunoblotting and 2D-electrophoresis using incubations with human serum, anti-LDL antibodies and anti-chicken IgG peroxidase conjugate were performed to identify LDL-binding proteins in S. mansoni. Analysis of the binding proteins using LC-MS identified two isoforms of the Hsp70 chaperone in S. mansoni. Hsp70 is involved in the interaction with apoB in the cytoplasm and its transport to the endoplasmic reticulum. However, further studies are needed to clarify the functional role of Hsp70 in S. mansoni, mainly related to the interaction with human LDL.

Avian schistosomes and outbreaks of cercarial dermatitis

Cercarial dermatitis (swimmer's itch) is a condition caused by infective larvae (cercariae) of a species-rich group of mammalian and avian schistosomes. Over the last decade, it has been reported in areas that previously had few or no cases of dermatitis and is thus considered an emerging disease. It is obvious that avian schistosomes are responsible for the majority of reported dermatitis outbreaks around the world, and thus they are the primary focus of this review. Although they infect humans, they do not mature and usually die in the skin. Experimental infections of avian schistosomes in mice show that in previously exposed hosts, there is a strong skin immune reaction that kills the schistosome. However, penetration of larvae into naive mice can result in temporary migration from the skin. This is of particular interest because the worms are able to migrate to different organs, for example, the lungs in the case of visceral schistosomes and the central nervous system in the case of nasal schistosomes. The risk of such migration and accompanying disorders needs to be clarified for humans and animals of interest (e.g., dogs). Herein we compiled the most comprehensive review of the diversity, immunology, and epidemiology of avian schistosomes causing cercarial dermatitis.

Proteomic profile of Bithynia siamensis goniomphalos snails upon infection with the carcinogenic liver fluke Opisthorchis viverrini

The snail Bithynia siamensis goniomphalos acts as the first intermediate host for the human liver fluke Opisthorchis viverrini, the major cause of cholangiocarcinoma (CCA) in Northeast Thailand. The undisputed link between CCA and O. viverrini infection has precipitated efforts to understand the molecular basis of host-parasite interactions with a view to ultimately developing new control strategies to combat this carcinogenic infection. To date most effort has focused on the interactions between the parasite and its human host, and little is known about the molecular relationships between the liver fluke and its snail intermediate host. In the present study we analyse the protein expression changes in different tissues of B. siamensis goniomphalos induced by infection with larval O. viverrini using iTRAQ labelling technology. We show that O. viverrini infection downregulates the expression of oxidoreductases and catalytic enzymes, while stress-related and motor proteins are upregulated. The present work could serve as a basis for future studies on the proteins implicated in the susceptibility/resistance of B. siamensis goniomphalos to O. viverrini, as well as studies on other pulmonate snail intermediate hosts of various parasitic flukes that infect humans.

BIOLOGICAL SIGNIFICANCE

Despite the importance and high prevalence of opisthorchiasis in some regions of Southeast Asia and the direct relationship between infection by Opisthorchis viverrini and the incidence of cholangiocarcinoma, little is known of the modifications induced by this parasite in its snail intermediate hosts. This time-course study provides the first in-depth quantitative proteomic analysis of experimentally infected Bithynia siamensis goniomphalos. We show how motor and stress-related proteins are upregulated in infected snails, while O. viverrini infection downregulates the expression of oxidoreductases and catalytic enzymes. This work serves as a basis for the development of new strategies, focused on the invertebrate intermediate hosts, to control parasite transmission.

Localization of tyrosine hydroxylase-like immunoreactivity in the nervous systems of Biomphalaria glabrata and Biomphalaria alexandrina, intermediate hosts for schistosomiasis

Planorbid snails of the genus Biomphalaria are major intermediate hosts for the digenetic trematode parasite Schistosoma mansoni. Evidence suggests that levels of the neurotransmitter dopamine (DA) are reduced during the course of S. mansoni multiplication and transformation within the snail. This investigation used immunohistochemical methods to localize tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamines, in the nervous system of Biomphalaria. The two species examined, Biomphalaria glabrata and Biomphalaria alexandrina, are the major intermediate hosts for S. mansoni in sub-Saharan Africa, where more than 90% of global cases of human intestinal schistosomiasis occur. TH-like immunoreactive (THli) neurons were distributed throughout the central nervous system (CNS) and labeled fibers were present in all commissures, connectives, and nerves. Some asymmetries were observed, including a large distinctive neuron (LPeD1) in the pedal ganglion described previously in several pulmonates. The majority of TH-like immunoreactive neurons were detected in the peripheral nervous system (PNS), especially in lip and foot regions of the anterior integument. Independent observations supporting the dopaminergic phenotype of THli neurons included 1) block of LPeD1 synaptic signaling by the D2/3 antagonist sulpiride, and 2) the similar localization of aqueous aldehyde (FaGlu)-induced fluorescence. The distribution of THli neurons indicates that, as in other gastropods, dopamine functions as a sensory neurotransmitter and in the regulation of feeding and reproductive behaviors in Biomphalaria. It is hypothesized that infection could stimulate transmitter release from dopaminergic sensory neurons and that dopaminergic signaling could contribute to modifications of both host and parasite behavior.

Impacts of an endoparasitic copepod, Ismaila belciki, on the reproduction, growth and survivorship of its nudibranch host, Janolus fuscus

Copepods from the genus Ismaila are large endoparasites that inhabit the main body cavity and/or cerata of opisthobranch molluscs. These parasites exhibit many life history characteristics typically found in parasitic castrators, yet the actual impact of infection on reproduction, growth or survivorship of the hosts are unknown. On the Oregon (USA) coast, Ismaila belciki can infect over 80% of their hermaphroditic hosts, Janolus fuscus. In laboratory mating experiments, we compared the reproductive output (egg mass weight, number of egg capsules, number of viable embryos) and the gonadal somatic index of infected versus uninfected J. fuscus. Infected J. fuscus could produce viable sperm and copulate. Mating with an infected individual did not limit a sea slug's reproductive output. However, infected J. fuscus had significantly lower reproductive output (by 34-54%), producing smaller egg masses with fewer capsules and viable embryos. Infected hosts had significantly lower gonadal somatic index than their uninfected counterparts, although there was no significant difference in gonadal somatic index between hosts with single and double infections. By collecting the egg sacs produced by the copepod parasite during experiments, we estimated that 25-34% of the host's reproductive output is usurped by the parasite and re-directed to the parasite's own reproduction. In the laboratory, infection did not alter growth in J. fuscus. However, infection significantly decreased survivorship in mature (but not immature) nudibranch hosts. These results suggest that I. belciki is not a true castrator, but it does reduce the reproductive output of its host and may therefore limit the natural population size of J. fuscus.

Diversity of the RFamide Peptide Family in Mollusks

Since the initial characterization of the cardioexcitatory peptide FMRFamide in the bivalve mollusk Macrocallista nimbosa, a great number of FMRFamide-like peptides (FLPs) have been identified in mollusks. FLPs were initially isolated and molecularly characterized in model mollusks using biochemical methods. The development of recombinant technologies and, more recently, of genomics has boosted knowledge on their diversity in various mollusk classes. Today, mollusk FLPs represent approximately 75 distinct RFamide peptides that appear to result from the expression of only five genes: the FMRFamide-related peptide gene, the LFRFamide gene, the luqin gene, the neuropeptide F gene, and the cholecystokinin/sulfakinin gene. FLPs display a complex spatiotemporal pattern of expression in the central and peripheral nervous system. Working as neurotransmitters, neuromodulators, or neurohormones, FLPs are involved in the control of a great variety of biological and physiological processes including cardiovascular regulation, osmoregulation, reproduction, digestion, and feeding behavior. From an evolutionary viewpoint, the major challenge will then logically concern the elucidation of the FLP repertoire of orphan mollusk classes and the way they are functionally related. In this respect, deciphering FLP signaling pathways by characterizing the specific receptors these peptides bind remains another exciting objective.

Proteomic analysis of schistosomiasis japonica vaccine candidate antigens recognized by UV-attenuated cercariae-immunized porcine serum IgG2

Many studies have showed that the radiation-attenuated cercariae (RAC) vaccine could induce the high protection of laboratory animals to resist the schistosoma infection by cellular and humoral mechanism. Here, we aimed to identify possible vaccine antigens by using specific IgG2 antibody from RAC-vaccinated pigs or vaccination and challenge pigs. The antigens from the schistosomal soluble worm antigen preparation (SWAP) recognized by the porcine IgG2 antibody were obtained using immunoprecipitation technique. These antigens were separated by 2-D electrophoresis, and 116 spots were successfully identified by MALDI-TOF MS from about 400 putative spots in gels. Among these spots, 113 spots could match to the Schistosoma japonicum. These identified proteins in four groups were classified by Gene Ontology (Go) database, and the mainly functions of these proteins were involved in binding, catalytic activity (thioredoxin peroxidase-2, et al.), signal transduction class (MAP Kinase, et al.), cell process (the heat shock 70-kDa protein 9B, et al.), and the intracellular component (tektin, et al.). Our methods suggested that it was possible to pull-down the interesting proteins recognized by specific antibodies. Our results may provide new clues for exploring the mechanism of high protection induced by RAC and shed some light on the research for anti-schistosomiasis japonica vaccine.

Parasites: evolution’s neurobiologists

For millions of years, parasites have altered the behaviour of their hosts. Parasites can affect host behaviour by: (1) interfering with the host’s normal immune–neural communication, (2) secreting substances that directly alter neuronal activity via non-genomic mechanisms and (3) inducing genomic- and/or proteomic-based changes in the brain of the host. Changes in host behaviour are often restricted to particular behaviours, with many other behaviours remaining unaffected. Neuroscientists can produce this degree of selectivity by targeting specific brain areas. Parasites, however, do not selectively attack discrete brain areas. Parasites typically induce a variety of effects in several parts of the brain. Parasitic manipulation of host behaviour evolved within the context of the manipulation of other host physiological systems (especially the immune system) that was required for a parasite’s survival. This starting point, coupled with the fortuitous nature of evolutionary innovation and evolutionary pressures to minimize the costs of parasitic manipulation, likely contributed to the complex and indirect nature of the mechanisms involved in host behavioural control. Because parasites and neuroscientists use different tactics to control behaviour, studying the methods used by parasites can provide novel insights into how nervous systems generate and regulate behaviour. Studying how parasites influence host behaviour will also help us integrate genomic, proteomic and neurophysiological perspectives on behaviour.

Proteomic analysis of schistosoma japonicum schistosomulum proteins that are differentially expressed among hosts differing in their susceptibility to the infection

Schistosomiasis is a tropical, parasitic disease affecting humans and several animal species. The aim of this study was to identify proteins involved in the growth and survival of the parasitic forms inside a host. Schistosomula of Schistosoma japonicum were isolated from three different hosts: the susceptible BALB/c mice; the Wistar rats, which have a considerably lower susceptibility; and the resistant reed vole, Microtus fortis. Soluble proteins of the schistosomula collected from the above three hosts 10 days postinfection were subjected to two-dimensional difference gel electrophoresis. Comparative proteomic analyses revealed that 39, 21, and 25 protein spots were significantly differentially expressed between schistosomula from mice and rats, mice and reed voles, or rats and reed voles, respectively (ANCOVA, p < 0.05). Further, the protein spots were identified by liquid chromatography-tandem MS. Bioinformatics analysis showed that the differentially expressed proteins were essentially those involved in the metabolism of proteins, ribonucleotides, or carbohydrates, or in stress response or cellular movement. This study represents the first attempt at profiling S. japonicum living in different states and provides a basis for a better understanding of the molecular mechanisms in the development and survival of S. japonicum in different host environments.

Experimental evidence of size/age-biased infection of Biomphalaria glabrata (Pulmonata: Planorbidae) by an incompatible parasite species: consequences for biological control

Because the digenetic trematode Plagiorchis elegans can elicit a rapid, severe and permanent suppression of the reproductive output in the snail Biomphalaria glabrata, it is considered as a potential biological control agent of human schistosomiasis. This assumption however is derived from laboratory experiments that are poor approximations of what occurs in a natural ecosystem. In order to recreate conditions that resemble those found in nature, we exposed B. glabrata as individual populations composed of a young, juvenile and adult snails to various concentrations of P. elegans eggs to assess the probability of encountering the parasite eggs by the different snail sizes/age groups. We demonstrated that within populations composed of different size/age classes, larger/older snails displayed the negative effects typical of exposure to P. elegans, whereas smaller individuals appeared relatively unaffected, particularly at lower levels of exposure. These findings coupled with the difficulty of producing large quantities of parasite eggs suggest that P. elegans has limited efficiency as a biological control agent of human schistosomiasis.

Molecular and functional characterization of a mortalin-like protein from Schistosoma japonicum (SjMLP/hsp70) as a member of the HSP70 family

Schistosomes are the causative agent of schistosomiasis. The 70-kDa heat-shock proteins (HSP70) are considered the predominant HSP family and play a key regulatory role in parasite development and pathogenesis. Based on the published sequences in Genbank/EMBL, an open-reading frame (ORF) encoding 653 amino acids (XP_002581385.1) and belonging to the Schistosoma HSP70 protein family with a molecular weight of 71.49 kDa was identified by bioinformatic analysis. Since the sequence shared 77% identity with the published full-length Homo sapiens HSP70 protein, it was named Schistosoma mortalin-like protein (MLP/Hsp70). Here, we report the molecular and functional characterization of the Schistosoma japonicum SjMLP/hsp70 as a member of the HSP70 family. The complete SjMLP/hsp70 coding sequence was amplified from a S. japonicum adult worm cDNA library by polymerase chain reaction (PCR) and subcloned into the pET28a expression vector. The purified recombinant protein, rSjMLP/hsp70, was identified as a member of 70-kDa HSP family by mass spectrometry and could be recognized by the S. japonicum-infected mouse serum. Reverse transcriptase polymerase chain reaction (RT-PCR) and western blotting analysis revealed that SjMLP/hsp70 was widely expressed in the eggs, cercariae, schistosomula, and adult worms of S. japonicum. A thermotolerance assay showed that rSjMLP/hsp70 could protect Escherichia coli cells from heat damage. This chaperone-like activity was demonstrated by full-length SjMLP/hsp70. The detection of specific antibody levels by indirect enzyme-linked immunosorbent assay and IFN-gamma secretion of splenocytes by ELISpot assay suggested that mice immunized with SjMLP/hsp70 were able to elicit Th1-type bias immune response. The challenge-protective experiment showed that DNA vaccine of SjGST combined with SjMLP/hsp70 could induce a 31.31% reduction of worm burden and 58.59% reduction of egg burden in intestinal tissue of immunized mice. Our results imply that SjMLP/hsp70 has a potential adjuvant function and might be a vaccine candidate for schistosomiaisis, which is the first report of the expression and preliminary characterization analysis of this molecule.

Time series analysis of the transcriptional responses of Biomphalaria glabrata throughout the course of intramolluscan development of Schistosoma mansoni and Echinostoma paraensei

Successful colonization of a compatible snail host by a digenetic trematode miracidium initiates a complex, proliferative development program requiring weeks to reach culmination in the form of production of cercariae which, once started, may persist for the remainder of the life span of the infected snail. How are such proliferative and invasive parasites able to circumvent host defenses and establish chronic infections? Using a microarray designed to monitor the internal defense and stress-related responses of the freshwater snail Biomphalaria glabrata, we have undertaken a time course study to monitor snail responses following exposure to two different trematode species to which the snail is susceptible: the medically important Schistosoma mansoni, exemplifying sporocyst production in its larval development, or Echinostoma paraensei, representing an emphasis on rediae production in its larval development. We sampled eight time points (0.5, 1, 2, 4, 8, 16 and 32 days p.i.) that cover the period required for cercariae to be produced. Following exposure to S. mansoni, there was a preponderance of up-regulated over down-regulated array features through 2 days p.i. but by 4 days p.i. and thereafter, this pattern was strongly reversed. For E. paraensei, there was a preponderance of down-regulated array features over up-regulated features at even 0.5 days p.i., a pattern that persists throughout the course of infection except for 1 day p.i., when up-regulated array features slightly outnumbered down-regulated features. Examination of particular array features revealed several that were up-regulated by both parasites early in the course of infection and one, fibrinogen related protein 4 (FREP 4), that remained significantly elevated throughout the course of infection with either parasite, effectively serving as a marker of infection. Many defense-related transcripts were persistently down-regulated, including several fibrinogen-containing lectins and homologs of molecules best known from vertebrate phagocytic cells. Our results are consistent with earlier studies suggesting that both parasites are able to interfere with host defense responses, including a tendency for E. paraensei to do so more rapidly and strongly than S. mansoni. They further suggest mechanisms for how trematodes are able to establish the chronic infections necessary for their continued success.

Biological invasion and parasitism: invaders do not suffer from physiological alterations of the acanthocephalanPomphorhynchus laevis

Biological invasions expose parasites to new invasive hosts in addition to their local hosts. However, local parasites are often less successful in infecting and exploiting their new hosts. This may have major consequences for the competitive ability of hosts, and finally on the fate of the parasite-host community. In Burgundy (Eastern France), the acanthocephalan parasite,Pomphorhynchus laevis, infects 2 amphipod species living in sympatry: the nativeGammarus pulexand the invasiveGammarus roeseli. WhileP. laevisaffects the behaviour and the immunity ofG. pulex,G. roeseliseems unaffected by the infection. In this study, we examined in detail the ability of the parasite to affect the immune system and resource storage of both gammarid species. We found that the infection was associated with a general decrease of the prophenoloxidase activity, haemocyte density, resistance to an artificial bacterial infection and level of sugar reserves inG. pulex, but not inG. roeseli. These results demonstrate a differential ability ofP. laevisto exploit its local and its invasive gammarid hosts. Potential mechanisms of these differential physiological alterations and their potential consequences on the coexistence of both gammarid species in sympatry are discussed.

Evolutionary drivers of parasite-induced changes in insect life-history traits from theory to underlying mechanisms

Many hosts are able to tolerate infection by altering life-history traits that are traded-off one against another. Here the reproductive fitness of insect hosts and vectors is reviewed in the context of theories concerning evolutionary mechanisms driving such alterations. These include the concepts that changes in host reproductive fitness are by-products of infection, parasite manipulations, host adaptations, mafia-like strategies or host compensatory responses. Two models are examined in depth, a tapeworm/beetle association, Hymenolepis diminuta/Tenebrio molitor and malaria infections in anopheline mosquitoes. Parasite-induced impairment of vitellogenesis ultimately leads to a decrease in female reproductive success in both cases, though by different means. Evidence is put forwards for both a manipulator molecule of parasite origin and for host-initiated regulation. These models are backed by other examples in which mechanisms underlying fecundity reduction or fecundity compensation are explored. It is concluded that evolutionary theories must be supported by empirical evidence gained from studying molecular, biochemical and physiological mechanisms underlying changes in host life-history traits, ideally using organisms that have evolved together and that are in their natural environment.

Schistosoma japonicum: proteomics analysis of differentially expressed proteins from ultraviolet-attenuated cercariae compared to normal cercariae

Schistosomiasis is considered the most important human helminthiasis in terms of morbidity and mortality. In this study, comparative soluble proteomic analysis of normal cercariae and ultraviolet-irradiated attenuated cercariae (UVAC) from Schistosoma japonicum were carried out in view of the high efficiency of irradiation-attenuated cercariae vaccine. The results revealed that some proteins showed significant differential expression in the parasite after treatment with ultraviolet light. Total 20 protein spots were identified by mass spectrometry, corresponded to five groups according to their functions in the main that were structural and motor proteins (actin, et al.), energy metabolism associated enzymes (glyceraldehydes-3-phosphage dehydrogenase, et al.), signaling transduction pathway-associated molecules (14-3-3 protein, et al.), heat shock protein families (HSP 70 family, et al.), and other functional proteins (20S proteasome). Furthermore, our results indicated that the differential expression of the proteins by ultraviolet irradiation may be, at least partially, acquired by regulating the mRNA levels of corresponding proteins. These results may provide new clues for further exploring the mechanism of protective immunity induced by UVAC and may shed some light on the development of vaccines against schistosomiasis.

Digenean trematode infections of native freshwater snails and invasive Potamopyrgus antipodarum in the Grand Teton National Park/John D. Rockefeller Memorial Parkway Area

Outside its native range, the invasive New Zealand mud snail (NZMS), Potamopyrgus antipodarum, is rarely reported to harbor parasites. To test this observation, 7 sites along the Snake River and Polecat Creek in the Grand Teton National Park/John D Rockefeller Memorial Parkway area (Wyoming) were surveyed for native aquatic snails, NZMS, and associated digenean trematodes, in July 2005. At 6 sites, native snails harbored patent digenean infections; within 2 hr, < or =10% of lymnaeid snails shed furcocercariae or xiphidiocercariae, and < or =42% of physid snails released furcocercariae or echinostome cercariae. Partial 18S rDNA sequences were recovered from several furcocercariae. Potamopyrgus antipodarum was present at, and collected from, 5 sites. Polymerase chain reaction assays targeting digenean rDNA sequences in DNA extracted from pools of 150 NZMS snails did not detect parasites. The examination of 960 NZMS by overnight shedding yielded 1 occurrence of (surface-encysted) metacercariae of an unclassified notocotylid (based on 18S and 28S rDNA sequences). The dissection of 150 ethanol-fixed NZMS (30/site) revealed 2 types of digenean metacercariae encysted in tissues of 5 snails from Polecat Creek. Thus, invasive NZMS may serve as first and second intermediate host for digenean parasites.

Manipulation of host behavior by parasitic insects and insect parasites

Parasites often alter the behavior of their hosts in ways that are ultimately beneficial to the parasite or its offspring. Although the alteration of host behavior by parasites is a widespread phenomenon, the underlying neuronal mechanisms are only beginning to be understood. Here, we focus on recent advances in the study of behavioral manipulation via modulation of the host central nervous system. We elaborate on a few case studies, in which recently published data provide explanations for the neuronal basis of parasite-induced alteration of host behavior. Among these, we describe how a worm may influence the nervous system of its cricket host and manipulate the cricket into committing suicide by jumping into water. We then focus on Ampulex compressa, which uses an Alien-like strategy for the sake of its offspring. Unlike most venomous hunters, this wasp injects venom directly into specific cerebral regions of its cockroach prey. As a result of the sting, the cockroach remains alive but immobile, but not paralyzed, and serves to nourish the developing wasp larva.

Life history cost of trematode infection in Helisoma anceps using mark-recapture in Charlie's Pond

Parasitism has the potential to affect key life history traits of an infected host. Perhaps the most studied interactions are in snail-trematode systems, where infection can result in altered growth rates, survival, and/or fecundity of the individual. Positive correlations between host size and parasite prevalence are often attributed to changes in growth rates or mortality, which have been observed in the laboratory. Extending lab-based conclusions to the natural setting is problematic, especially when environmental conditions differ between the laboratory and the field. The present study uses reproduction experiments and mark-recapture methods to directly measure key life history traits of the pulmonate snail Helisoma anceps in Charlie's Pond. Based on previous laboratory and field experiments on H. anceps, we predict a significant reduction in fecundity, but not growth rate or survival, of infected snails. Individual capture histories were analyzed with multistate models to obtain estimates of survival and infection probabilities throughout the year. Recaptured individuals were used to calculate specific growth rates. Trematode infection resulted in complete castration of the host. However, neither survival nor growth rates were found to differ between infected and uninfected individuals. The probability of infection exhibited seasonal variation, but it did not vary with size of the snail. These results suggest that the correlation between host size and trematode prevalence is not due to differential mortality or changes in growth rates. Instead, the infection accumulates in large snails via the growth of smaller, infected individuals.

Effect of Echinostoma friedi (Trematoda: Echinostomatidae) experimental infection on longevity, growth and fecundity of juvenile Radix peregra (Gastropoda: Lymnaeidae) and Biomphalaria glabrata (Gastropoda: Planorbidae) snails

The effect of Echinostoma friedi experimental infection on longevity, growth and fecundity of two susceptible first intermediate host snails, Radix peregra and Biomphalaria glabrata, was studied to contrast the level of compatibility. 120 R. peregra and 150 B. glabrata snails were used exposed to one, three or five miracidia and divided in three categories: INF (snails exposed and infected); ENI (exposed but not infected) and C (control or not miracidial-exposed snails). R. peregra INF snails' death process starts sooner, but in a prolonged extension, while B. glabrata INF snails have a much shorter life span. The infection and the miracidial exposure are able to reduce R. peregra normal development (stunting). B. glabrata INF snails' growth exceeds that of C snails (gigantism). E. friedi produces a total parasitic castration of R. peregra and B. glabrata INF snails. R. peregra would be considered as the required snail host, while B. glabrata only as an adequate snail host.

Comparative psychoneuroimmunology: evidence from the insects

Interactions between immune systems, nervous systems, and behavior are well established in vertebrates. A comparative examination of these interactions in other animals will help us understand their evolution and present adaptive functions. Insects show immune-behavioral interactions similar to those seen in vertebrates, suggesting that many of them may have a highly conserved function. Activation of an immune response in insects results in illness-induced anorexia, behavioral fever, changes in reproductive behavior, and decreased learning ability in a broad range of species. Flight-or-fight behaviors result in a decline in disease resistance. In insects, illness-induced anorexia may enhance immunity. Stress-induced immunosuppression is probably due to physiological conflicts between the immune response and those of other physiological processes. Because insects occupy a wide range of ecological niches, they will be useful in examining how some immune-behavioral interactions are sculpted by an animal's behavioral ecology.

Resistance to Schistosoma mansoni by transplantation of APO Biomphalaria tenagophila

Transplantation of the haematopoietic organ from Biomphalaria tenagophila (Taim strain, RS, Brazil), resistant to Schistosoma mansoni, to a highly susceptible strain (Cabo Frio, RJ, Brazil) of the same species, showed in the recipient snails resistance against the trematode, when a successful transplant occurred. The success of transplantation could be confirmed by a typical molecular marker of the Taim strain in haemocytes of the recipients (350 bp detected by PCR-RFLP). The recipient snails which did not present the donor marker in haemocytes (unsuccessful transplantation) were infected with the parasite. The use of an atoxic modelling clay for closing the hole in the transplantation site reduced significantly the mortality caused by bleeding after transplantation procedures.

Signal transduction in larval trematodes: putative systems associated with regulating larval motility and behaviour

The multi-host lifestyle of parasitic trematodes necessitates their ability to communicate with their external environment in order to invade and navigate within their hosts' internal environment. Through recent EST and genome sequencing efforts, it has become clear that members of the Trematoda possess many of the elaborate signal transduction systems that have been delineated in other invertebrate model systems like Drosophila melanogaster and Caenorhabditis elegans. Gene homologues representing several well-described signal receptor families including receptor tyrosine kinases, receptor serine tyrosine kinases, G protein-coupled receptors and elements of their downstream signalling systems have been identified in larval trematodes. A majority of this work has focused on the blood flukes, Schistosoma spp. and therefore represents a narrow sampling of the diverse digenean helminth taxon. Despite this fact and given the substantial evidence supporting the existence of such signalling systems, the question then becomes, how are these systems employed by larval trematodes to aid them in interpreting signals received from their immediate environment to initiate appropriate responses in cells and tissues comprising the developing parasite stages? High-throughput, genome-wide analysis tools now allow us to begin to functionally characterize genes differentially expressed throughout the development of trematode larvae. Investigation of the systems used by these parasites to receive and transduce external signals may facilitate the creation of technologies for achieving control of intramolluscan schistosome infections and also continue to yield valuable insights into the basic mechanisms regulating motility and behaviour in this important group of helminths.

Facultative virulence: a strategy to manipulate host behaviour?

Examples of behavioural manipulation by parasites are numerous, but the processes underlying these changes are not well characterized. From an evolutionary point of view, behavioural changes in infected hosts have often been interpreted as illustrations of the extended phenotype concept, in which genes in one organism (the parasite) have phenotypic effects on another organism (the host). Here, we approach the problem differently, suggesting that hosts, by cooperating with manipulative parasites rather than resisting them, might mitigate fitness costs associated with manipulation. By imposing extra fitness costs on their hosts in the absence of compliance, parasites theoretically have the potential to select for cooperative behaviour by their hosts. Although this 'mafia-like' strategy remains poorly documented, we believe that it has substantial potential to resolve issues specific to the evolution of behavioural alterations induced by parasites.

Parasitic suppression of feeding in the tobacco hornworm, Manduca sexta: parallels with feeding depression after an immune challenge

The parasitic wasp, Cotesia congregata, suppresses feeding in its host Manduca sexta. Feeding suppression in the host coincides with the emergence of the wasps through the host's cuticle. During wasp emergence, host hemocyte number declined, suggesting that the host mounts a wound/immune response against the exiting parasitoids and/or resulting tissue damage. Eliciting a different type of immune response by injecting heat-killed Serratia marcescens also resulted in a decline in feeding and a reduction in hemocyte number. Both the emerging wasps and the bacteria induced an increase in hemolymph octopamine concentration and a decrease in foregut peristalsis in M. sexta. The emerging parasitoids produced the largest changes. The source of the additional octopamine appeared to be the host in both cases. S. marcescens was found to contain no detectable amounts of octopamine. The parasitoids had insufficient octopamine to account for the amount found in host hemolymph and they did not secrete octopamine in vitro. One cause for the high concentration of octopamine in parasitized M. sexta was that octopamine was removed from the hemolymph approximately 23 times more slowly after the wasps emerged than prior to wasp emergence. The striking similarity between the effects of parasitoids and bacteria on M. sexta feeding, hemocyte number, hemolymph octopamine concentration, and foregut peristalsis supports the possibility that the immune/wound reaction induced by the emerging wasps could play a role in the suppression of host feeding. These results also support the hypothesis that M. sexta exhibit an immune-activated anorexia.

Molluscan and vertebrate immune responses to bird schistosomes

There is a growing understanding of risks posed by human contact with the cercariae of bird schistosomes. In general, there are no fundamental biological differences between human and bird schistosomes in terms of their interactions with snail and vertebrate hosts. The penetration of host surfaces is accompanied by the release of penetration gland products and the shedding of highly antigenic surface components (miracidial ciliated plates and cercarial glycocalyx) which trigger host immune reactions. New surface structures are formed during transformation: the tegument of mother sporocysts and the tegumental double membrane of schistosomula. These surfaces apparently serve as protection against the host immune response. Certain parasite excretory-secretory products may contribute to immunosuppression or, on the other hand, stimulation of host immune reactions. Discovery of new species and their life cycles, the characterization of host-parasite interactions (including at the molecular level), the determination of parasite pathogenicity towards the host, the development of tools for differential diagnosis and the application of protective measures are all topical research streams of the future. Regularly updated information on bird schistosomes and cercarial dermatitis can be found at http://www.schistosomes.cz (web pages of Schistosome Group Prague).

Carbohydrates that mimic schistosome surface coat components affect ERK and PKC signalling in Lymnaea stagnalis haemocytes

Molluscs are intermediate hosts for helminth parasites such as Schistosoma spp. that possess an immunogenic surface coat of high carbohydrate content, with fucose as the predominant saccharide. More than a decade ago, it was postulated that such components could block receptors on snail haemocytes thus preventing recognition of intra-molluscan schistosome stages. Although more recent studies have shown that carbohydrates can suppress processes such as phagocytosis by haemocytes, interference of the haemocyte cell signalling pathways that regulate immunity by saccharides has not yet been investigated. We have recently reported the presence of extracellular-signal regulated kinase and protein kinase C in Lymnaea stagnalis haemocytes. Here we show that extracellular-signal regulated kinase and protein kinase C activities are down-regulated when haemocytes are exposed to albumin-linked fucose and galactose in the absence of haemolymph. Moreover, we demonstrate that phagocytosis is reduced under these conditions. Interestingly, in the presence of haemolymph, only protein kinase C activity is down-regulated and only galactose suppresses phagocytosis, implying a role for serum factors in the preservation of haemocyte function following exposure. We therefore propose that the establishment of a compatible relationship between a schistosome and its snail host is at least in part due to down-regulation of cell signalling events in haemocytes.

Plasma bioactive LH and testosterone profiles in male New Zealand rabbits experimentally infected with Schistosoma mansoni

The effects of Schistosoma mansoni (S. mansoni) infection on plasma levels of bioactive luteinising hormone (LH) and testosterone in the New Zealand rabbit model were studied. S. mansoni infection significantly decreased the pulse frequency (P < 0.05), amplitude (P < 0.05), area under LH curve (P < 0.05) and mean plasma LH concentrations (P < 0.05) on days 42 and 70 post-infection, as compared to values for day 14 pre-infection. Areas under the response curves for plasma testosterone levels decreased significantly (P < 0.05) on days 42 and 70 post-infection in infected animals compared to day 14 pre-infection. In the praziquantel-treated group, the levels of LH and testosterone remained unchanged throughout the experimental period. The pulsatile secretion of LH was completely inhibited in S. mansoni-infected animals 70 days post-infection. These results suggest that the effects on reproductive gonadal hormones caused by S. mansoni in the rabbit model may partly be induced by alteration in pituitary synthesis or release of LH.

Morphological basis for coordination of growth and reproduction processes in the CNS of two terrestrial snails

The morphology of cells immunoreactive to an antibody against molluscan insulin-related peptide (MIP-IR) was studied in two species of terrestrial snail: Helix lucorum L. and Eobania vermiculata L. Immunocytochemical staining with this antibody to MIP revealed 100-130 cells in the postcerebrum, located in two clusters with common pathways in the dorsal body nerve and the cerebral artery nerve. About 75% of the MIP-IR cells were labeled by backfilling of the dorsal body nerve in Helix and Eobania; the corresponding figures for labeling by backfilling of the cerebral artery nerve were about 60% in Helix and 30% in Eobania. Upon intracellular staining of neurons of the dorsomedial postcerebrum, where most of the MIP-IR cells were located, it was found that they projected either in the dorsal body nerve or in the cerebral artery nerve or in both. The obtained data suggest that growth and reproduction processes (both functions were attributed to the insulin-related peptide-containing neurons) are regulated by the two, partially coinciding subsets of postcerebral MIP-IR neurons with different types of branching.

Granularin, a novel molluscan opsonin comprising a single vWF type C domain is up‐regulated during parasitation

Snails are intermediate hosts to schistosome parasites, some of which are the main cause of human schistosomiasis (bilharzia), and have been used as models for parasite-host interactions for a long time. Here, we have characterized a novel internal defense peptide of the snail Lymnaea stagnalis, of which the relative abundance in brain tissue increases upon infection with the avian schistosome Trichobilharzia ocellata. This protein, named granularin, is secreted by granular cells, which are numerous in the connective tissue surrounding the brain. The protein is unique because it comprises only a single Von Willebrand factor type C domain that is normally found in large transmembrane and secreted extracellular matrix proteins. The granularin gene is twice up-regulated during parasitation. Purified granularin stimulates phagocytosis of foreign particles by blood hemocytes. Together, our data indicate that granularin represents a novel protein that acts as an opsonin in the molluscan internal defense response.

A first infection of Galba truncatula with Fasciola hepatica modifies the prevalence of a subsequent infection and cercarial production in the F1 generation

Snails from two populations highly susceptible to Fasciola hepatica and their F1 generations were subjected to individual bimiracidial exposures to determine if changes noted in infection parameters were due to an effect imposed on the snail by the parasite, or to some other effect such as the food used for the snails. Apart from the higher survival of unexposed parents at day 30 post exposure (p.e.) and their higher shell heights at day 45 p.e., the differences between the survival rates of exposed parents, prevalences of infections, and shell sizes were not significant. In the F1 snails born to previously infected parents, the prevalences of F. hepatica infection and cercarial production were significantly lower than those noted for the F1 born to unexposed parents. The survival of these snails and their shell growth did not show any significant variation. The F1 snails born to previously exposed snails would have developed a partial resistance against F. hepatica and this process would probably be maximal in the first 2 weeks of larval development inside the snail.

Biology of the schistosome genus Trichobilharzia

Trichobilharzia is the largest genus within the family Schistosomatidae, covering over 40 species of avian parasites. To clarify the existing confusion in the systematics of the genus, we recommend combining knowledge of life cycles and developmental stages, snail/bird hosts, cytogenetical and molecular data together with morphological criteria for the characterization of particular species. The high specificity of Trichobilharzia for the intermediate host is a likely reflection of the ability to avoid the internal defence of specific snails. The spectrum of final hosts (birds) seems to be much wider. The infection of birds--trichobilharziasis--may lead to considerable tissue injuries, caused by eggs of the parasite or migration of immature/mature worms through the body. Most Trichobilharzia (visceral species) migrate through the viscera of the host, but nasal species display a neurotropic mode of migration. Due to a low specificity of penetrating cercariae, mammals (including humans) can be attacked. This leads to cercarial dermatitis, predominantly in sensitized hosts. Experimental infections indicate that Trichobilharzia never mature in an incompatible (mammalian) host. However, not all cercariae and schistosomula are necessarily trapped and eliminated in the skin, and parasites may migrate throughout the viscera and the nervous system of mammals. These findings suggest that the pathogenicity of Trichobilharzia may have been underestimated in the past and health risks associated with trichobilharziasis need to be studied further.