Host Use Research Articles

Insect-Borne Plant Pathogens and Their Vectors: Ecology, Evolution, and Complex Interactions.

The transmission of insect-borne plant pathogens, including viruses, bacteria, phytoplasmas, and fungi depends upon the abundance and behavior of their vectors. These pathogens should therefore be selected to influence their vectors to enhance their transmission, either indirectly, through the infected host plant, or directly, after acquisition of the pathogen by the vector. Accumulating evidence provides partial support for the occurrence of vector manipulation by plant pathogens, especially for plant viruses, for which a theoretical framework can explain patterns in the specific effects on vector behavior and performance depending on their modes of transmission. The variability in effects of pathogens on their vectors, however, suggests inconsistency in the occurrence of vector manipulation but also may reflect incomplete information about these systems. For example, manipulation can occur through combinations of specific effects, including direct and indirect effects on performance and behavior, and dynamics in those effects with disease progression or pathogen acquisition that together constitute syndromes that promote pathogen spread. Deciphering the prevalence and forms of vector manipulation by plant pathogens remains a compelling field of inquiry, but gaps and opportunities to advance it remain. A proposed research agenda includes examining vector manipulation syndromes comprehensively within pathosystems, expanding the taxonomic and genetic breadth of the systems studied, evaluating dynamic effects that occur during disease progression, incorporating the influence of biotic and abiotic environmental factors, evaluating the effectiveness of putative manipulation syndromes under field conditions, deciphering chemical and molecular mechanisms whereby pathogens can influence vectors, expanding the use of evolutionary and epidemiological models, and seeking opportunities to exploit these effects to improve management of insect-borne, economically important plant pathogens. We expect this field to remain vibrant and productive in its own right and as part of a wider inquiry concerning host and vector manipulation by plant and animal pathogens and parasites.

Lessons in Mind Control: Trends in Research on the Molecular Mechanisms behind Parasite-Host Behavioral Manipulation

Scientific and public interest in host manipulation by parasites has surged over the past few decades, resulting in an exponential growth of cases where potential behavioural manipulation has been identified. However, these studies dwarf the number of genuine attempts to elucidate the mechanistic processes behind this behavioural manipulation. Ultimately, this imbalance has slowed progress in the study of the mechanisms underlying host manipulation. As it stands, research suggests that the mechanisms of host manipulation fall into three categories: immunological, genomic/proteomic and neuropharmacological, and forth potential category: symbioant-mediated manipulation. After exploration of the literature pertaining to these four pathways, four major trends become evident. First and foremost, there is a severe disconnect between the observed molecular and behavioural shifts in a parasitized host. Indeed, very rarely a study demonstrates that molecular changes observed in a host are the result of active manipulation by the resident parasite, or that these molecular changes directly result in behavioural manipulation that increases the parasite’s fitness. Secondly, parasites may often employ multiple pathways in unison to achieve control over their hosts. Despite this, current scientific approaches usually focus on each manipulation pathway in isolation rather than integrating them. Thirdly, the relative amount of host-parasite systems yet to be investigated in terms of molecular manipulation is staggering. Finally, as a result of the aforementioned trends, guiding mechanisms or principles for the multiple types of behavioural manipulation are yet to be found. Researchers should look to identify the manipulative factors required to generate the molecular changes seen in hosts, while also considering the ‘multi-pronged’ approach parasites are taking to manipulate behaviour. Assessing gene expression and its products during transitional periods in parasites may be a key methodological approach for tackling these recent trends in the host manipulation literature.

Fatal attraction of non‐vector impairs fitness of manipulating plant virus

Abstract Host manipulation refers to the expression of a host phenotype that is partly under the genetic control of a parasite. This phenomenon can enhance parasite transmission rates and is responsible for biological marvels such as “Zombie‐ants” and the “fatal attraction” of Toxoplasma‐infected rodents to their feline predators. Such host manipulation has evolved in all major phylogenetic lineages of parasites and is assumed to enhance the fitness of the parasite. However, the capacity to manipulate is not ubiquitous; that is, many clades of parasites comprise manipulating and non‐manipulating species. This pattern leads to the prediction of costs that select against the evolution of manipulation, but this has been difficult to show empirically. In the present study, we used a tripartitate system consisting of chili (Capsicum annuum) plants infected with Pepper golden mosaic virus and colonized by non‐vector whiteflies (Trialeurodes vaporariorum), to study the effects on viral load when a non‐vector herbivore feeds on the infected plants. We observed that virus‐infected plants emitted odours that attracted adult whiteflies, contained three times more amino acids in the phloem than mock‐inoculated controls and supported higher whitefly reproduction as compared to controls. However, viral load decreased almost 100‐fold in whitefly‐carrying plants, which was associated with a depletion of phloem amino acids. Synthesis. We show that a plant virus can suffer from a reduced within‐host reproduction rate when virus‐induced alterations of the plant cause a “fatal attraction” of a non‐vector insect that exploits the altered plant phenotype at its own benefits. The resulting fitness costs might represent a force that can select against the evolution of host manipulation by parasites.

Parasite-altered feeding behavior in insects: integrating functional and mechanistic research frontiers.

Research on parasite-altered feeding behavior in insects is contributing to an emerging literature that considers possible adaptive consequences of altered feeding behavior for the host or the parasite. Several recent ecoimmunological studies show that insects can adaptively alter their foraging behavior in response to parasitism. Another body of recent work shows that infection by parasites can change the behavior of insect hosts to benefit the parasite; manipulations of host feeding behavior may be part of this phenomenon. Here, we address both the functional and the underlying physiological frontiers of parasite-altered feeding behavior in order to spur research that better integrates the two. Functional categories of parasite-altered behavior that are adaptive for the host include prophylaxis, therapy and compensation, while host manipulation is adaptive for the parasite. To better understand and distinguish prophylaxis, therapy and compensation, further study of physiological feedbacks affecting host sensory systems is especially needed. For host manipulation in particular, research on mechanisms by which parasites control host feedbacks will be important to integrate with functional approaches. We see this integration as critical to advancing the field of parasite-altered feeding behavior, which may be common in insects and consequential for human and environmental health.

Large-Scale Identification of Wolbachia pipientis Effectors

Wolbachia pipientis is an intracellular symbiont of arthropods well known for the reproductive manipulations induced in the host and, more recently, for the ability of Wolbachia to block virus replication in insect vectors. Since Wolbachia cannot yet be genetically manipulated, and due to the constraints imposed when working with an intracellular symbiont, little is known about mechanisms used by Wolbachia for host interaction. Here we employed a bioinformatics pipeline and identified 163 candidate effectors, potentially secreted by Wolbachia into the host cell. A total of 84 of these candidates were then subjected to a screen of growth defects induced in yeast upon heterologous expression which identified 14 top candidates likely secreted by Wolbachia. These predicted secreted effectors may function in concert as we find that their native expression is correlated and is highly upregulated at specific time points during Drosophila development. In addition, the evolutionary histories of some of these predicted effectors are also correlated, suggesting they may function together, or in the same pathway, during host infection. Similarly, most of these predicted effectors are limited to one or two Wolbachia strains—perhaps reflecting shared evolutionary history and strain specific functions in host manipulation. Identification of these Wolbachia candidate effectors is the first step in dissecting the mechanisms of symbiont–host interaction in this important system.

Positive density-dependent growth supports costs sharing hypothesis and population density sensing in a manipulative parasite.

Parasites manipulate their hosts' phenotype to increase their own fitness. Like any evolutionary adaptation, parasitic manipulations should be costly. Though it is difficult to measure costs of the manipulation directly, they can be evaluated using an indirect approach. For instance, theory suggests that as the parasite infrapopulation grows, the investment of individual parasites in host manipulation decreases, because of cost sharing. Another assumption is that in environments where manipulation does not pay off for the parasite, it can decrease its investment in the manipulation to save resources. We experimentally infected rainbow trout Oncorhynchus mykiss with the immature larvae of the trematode Diplostomum pseudospathaceum, to test these assumptions. Immature D. pseudospathaceum metacercariae are known for their ability to manipulate the behaviour of their host enhancing its anti-predator defenses to avoid concomitant predation. We found that the growth rate of individual parasites in rainbow trout increased with the infrapopulation size (positive density-dependence) suggesting cost sharing. Moreover, parasites adjusted their growth to the intensity of infection within the eye lens where they were localized suggesting population density sensing. Results of this study support the hypothesis that macroparasites can adjust their growth rate and manipulation investment according to cost sharing level and infrapopulation size.

Gametocytemia and Attractiveness of Plasmodium falciparum-Infected Kenyan Children to Anopheles gambiae Mosquitoes.

It has been suggested that Plasmodia manipulate their vertebrate hosts to enhance parasite transmission. Using a dual-choice olfactometer, we investigated the attraction of Anopheles gambiae to 50 Kenyan children (aged 5-12 years) who were naturally infected with Plasmodium falciparum or noninfected controls. Microscopic gametocyte carriers attracted almost 2 times more mosquitoes than children who were parasite free, harbored asexual stages, or had gametocytes at submicroscopic densities. By using highly sensitive stage-specific molecular methods to detect P. falciparum, we show that gametocytes-and not their noninfectious asexual progenitors-induce increased attractiveness of humans to mosquitoes. Our findings therefore support the parasite host manipulation hypothesis.

Changes in diet associated with cancer: An evolutionary perspective.

Changes in diet are frequently correlated with the occurrence and progression of malignant tumors (i.e., cancer) in both humans and other animals, but an integrated conceptual framework to interpret these changes still needs to be developed. Our aim is to provide a new perspective on dietary changes in tumor‐bearing individuals by adapting concepts from parasitology. Dietary changes may occur alongside tumor progression for several reasons: (i) as a pathological side effect with no adaptive value, (ii) as the result of self‐medication by the host to eradicate the tumor and/or to slow down its progression, (iii) as a result of host manipulation by the tumor that benefits its progression, and finally (iv) as a host tolerance strategy, to alleviate and repair damages caused by tumor progression. Surprisingly, this tolerance strategy can be beneficial for the host even if diet changes are beneficial to tumor progression, provided that cancer‐induced death occurs sufficiently late (i.e., when natural selection is weak). We argue that more data and a unifying evolutionary framework, especially during the early stages of tumorigenesis, are needed to understand the links between changes in diet and tumor progression. We argue that a focus on dietary changes accompanying tumor progression can offer novel preventive and therapeutic strategies against cancer.

VIRUS-INDUCED MANIPULATION PARADIGMS AND ALTERATIONS IN HOST PLANTS AND THEIR VECTORS

This review focuses on virus-plant pathosystems, manipulation paradigms and alterations induced by viruses in their hosts and vectors. After forming a suitable cell environment viruses elude the defense mechanism of cell, having a transformative interaction with hosts and vectors urge the scientists to work on different molecular alterations and manipulations induced by viruses in their hosts and vectors. Different manipulation paradigms are regulated by viruses, that start after acquisition of viruses by corresponding vectors in adaptive manipulation and behavioral manipulation manners, which are generally known as “Host Manipulation Hypothesis” (HMH). Because of these mediated alterations, secondary chemistry of vector’s behavior can be affected. In the same way, plants are also extensively influenced by viruses which cause dramatic fluctuations in; genotype, phenotype, metabolism, systemic and hormones of the plants. The combination of viral proteins and host proteins evidenced efficacious viral infection. After viral infection defense system of plants is activated in the way of Induced Systemic Resistance (ISR) that is (1) Rapid/ Extreme resistance (2) Slower host response or (hypersensitive response, HR) also known as programmed death of plant cells. Proteome-level alterations have been reported in phloem sap at the time of virus infection but this phenomenon needs to be investigated. Viruses have also been reported for making alterations in primary phytohormones of plants; Salicylic acid (SA), Abscisic acid (ABA), Jasmonic acid (JA), Ethylene (ET) actively involved in defense mechanism of the plant

Proximate mechanism of behavioral manipulation of an orb-weaver spider host by a parasitoid wasp.

Some ichneumonid wasps induce modifications in the web building behavior of their spider hosts to produce resistant “cocoon” webs. These structures hold and protect the wasp’s cocoon during pupa development. The mechanism responsible for host manipulation probably involves the inoculation of psychotropic chemicals by the parasitoid larva during a specific developmental period. Recent studies indicate that some spiders build cocoon webs similar to those normally built immediately before ecdysis, suggesting that this substance might be a molting hormone or a precursor chemical of this hormone. Here, we report that Cyclosa spider species exhibiting modified behavior presented higher 20-OH-ecdysone levels than parasitized spiders acting normally or unparasitized individuals. We suggest that the lack of control that spiders have when constructing modified webs can be triggered by anachronic activation of ecdysis.

Unravelling the Function of a Bacterial Effector from a Non-cultivable Plant Pathogen Using a Yeast Two-hybrid Screen.

Unravelling the molecular mechanisms of disease manifestations is important to understand pathologies and symptom development in plant science. Bacteria have evolved different strategies to manipulate their host metabolism for their own benefit. This bacterial manipulation is often coupled with severe symptom development or the death of the affected plants. Determining the specific bacterial molecules responsible for the host manipulation has become an important field in microbiological research. After the identification of these bacterial molecules, called "effectors," it is important to elucidate their function. A straightforward approach to determine the function of an effector is to identify its proteinaceous binding partner in its natural host via a yeast two-hybrid (Y2H) screen. Normally the host harbors numerous potential binding partners that cannot be predicted sufficiently by any in silico algorithm. It is thus the best choice to perform a screen with the hypothetical effector against a whole library of expressed host proteins. It is especially challenging if the causative agent is uncultivable like phytoplasma. This protocol provides step-by-step instructions for DNA purification from a phytoplasma-infected woody host plant, the amplification of the potential effector, and the subsequent identification of the plant's molecular interaction partner with a Y2H screen. Even though Y2H screens are commonly used, there is a trend to outsource this technique to biotech companies that offer the Y2H service at a cost. This protocol provides instructions on how to perform a Y2H in any decently equipped molecular biology laboratory using standard lab techniques.

Unravelling the Function of a Bacterial Effector from a Non-cultivable Plant Pathogen Using a Yeast Two-hybrid Screen

Unravelling the molecular mechanisms of disease manifestations is important to understand pathologies and symptom development in plant science. Bacteria have evolved different strategies to manipulate their host metabolism for their own benefit. This bacterial manipulation is often coupled with severe symptom development or the death of the affected plants. Determining the specific bacterial molecules responsible for the host manipulation has become an important field in microbiological research. After the identification of these bacterial molecules, called "effectors," it is important to elucidate their function. A straightforward approach to determine the function of an effector is to identify its proteinaceous binding partner in its natural host via a yeast two-hybrid (Y2H) screen. Normally the host harbors numerous potential binding partners that cannot be predicted sufficiently by any in silico algorithm. It is thus the best choice to perform a screen with the hypothetical effector against a whole library of expressed host proteins. It is especially challenging if the causative agent is uncultivable like phytoplasma. This protocol provides step-by-step instructions for DNA purification from a phytoplasma-infected woody host plant, the amplification of the potential effector, and the subsequent identification of the plant's molecular interaction partner with a Y2H screen. Even though Y2H screens are commonly used, there is a trend to outsource this technique to biotech companies that offer the Y2H service at a cost. This protocol provides instructions on how to perform a Y2H in any decently equipped molecular biology laboratory using standard lab techniques.

Murine Cytomegalovirus Deubiquitinase Regulates Viral Chemokine Levels To Control Inflammation and Pathogenesis.

ABSTRACTMaintaining control over inflammatory processes represents a paradox for viral pathogens. Although many viruses induce host inflammatory responses to facilitate infection, control is necessary to avoid overactivation. One way is through the manipulation of proinflammatory chemokine levels, both host and viral. Murine cytomegalovirus (MCMV), a model betaherpesvirus, encodes a viral C-C chemokine, MCK2, which promotes host inflammatory responses and incorporates into virions to facilitate viral dissemination. Here, we show that the activity of M48, the conserved MCMV deubiquitinating enzyme (DUB), regulates MCK2 levels during infection. Inactivation of M48 DUB activity results in viral attenuation and exacerbates virally induced, MCK2-dependent inflammatory responses. M48 DUB activity also influences MCK2 incorporation into virions. Importantly, attenuation of DUB-mutant virus acute replication in vitro and in vivo is largely ameliorated by targeted deletion of MCK2. Thus, uncontrolled MCK2 levels appear to mediate DUB-mutant virus attenuation in specific tissues or cell types. This demonstrates that MCMV M48 DUB activity plays a previously unappreciated role in controlling MCK2 levels, thereby managing MCK2-dependent processes. These findings reveal a novel intrinsic control mechanism of virally induced inflammation and support the identification of betaherpesvirus DUBs as possible new targets for antiviral therapies.

Virus Innexins induce alterations in insect cell and tissue function

Polydnaviruses are dsDNA viruses that induce immune and developmental alterations in their caterpillar hosts. Characterization of polydnavirus gene families and family members is necessary to understand mechanisms of pathology and evolution of these viruses, and may aid to elucidate the role of host homologues if present. For example, the polydnavirus vinnexin gene family encodes homologues of insect gap junction genes (innexins) that are expressed in host immune cells (hemocytes). While the roles of Innexin proteins and gap junctions in insect immunity are largely unclear, we previously demonstrated that Vinnexins form functional gap junctions and alter the junctional characteristics of a host Innexin when co-expressed in paired Xenopus oocytes. Here, we test the effect of ectopic vinnexin expression on host cell physiology using both a lepidopteran cell culture model and a dipteran whole organism model. Vinnexin expression in the cell culture system resulted in gene-specific alterations in cell morphology and a slight, but non-statistically significant, reduction in gap junction activity as measured by dye transfer, while ectopic expression of a lepidopteran innexin2 gene led to morphological alterations and increase in gap junction activity. Global ectopic expression in the model dipteran, Drosophila melanogaster, of one vinnexin (vinnexinG) or D. melanogaster innexin2 (Dm-inx2) resulted in embryonic lethality, while expression of the other vinnexin genes had no effect. Furthermore, ectopic expression of vinnexinG, but not other vinnexin genes or Dm-inx2, in D. melanogaster larval gut resulted in developmental arrest in the pupal stage. These data indicate the vinnexins likely have gene-specific roles in host manipulation. They also support the use of Drosophila in further analysis of the role of Vinnexins and other polydnavirus genes in modifying host physiological processes. Finally, our findings suggest the vinnexin genes may be useful to perturb and characterize the physiological functions of insect Innexins.

病原細菌による宿主粘膜感染の分子機構の解明

蛋白質の翻訳後修飾の一つであるユビキチン修飾経路はヒトの高次生命現象や疾患に深く関わることが古くより知られている。近年、病原細菌やウイルスの感染症においても、これらの病原体が宿主細胞のユビキチン修飾経路を制御する分子を有し、感染成立に必要な細胞応答を引き起こしていることが明らかになってきた。病原細菌が宿主細胞に分泌する分子（病原因子）の中には、（1）ユビキチン化関連の酵素活性を持つ分子、（2）宿主細胞内でユビキチン修飾を受ける分子、（3）宿主のユビキチン分解経路をハイシャックする分子が同定されている。これらの病原因子の機能が構造生物学的な手法を含めた解析手法により解明され、病原細菌の新たな感染戦略として理解されつつある。本稿では、腸管病原細菌の感染を中心に、宿主のユビキチン修飾経路を利用する病原因子及びその作用機序について概説する。

Potential Host Manipulation by the Aphid Parasitoid Aphidius avenae to Enhance Cold Tolerance.

During parasitoid development, the immature parasitoid is confined to the host species. As a result, any potential to modify the physiology or behaviour of the host could play an important role in parasitoid fitness. The potential for host manipulation by the aphid parasitoid Aphidius avenae to increase cold thermotolerance was investigated using the aphid host species Metopolophium dirhodum and Sitobion avenae. Aphids were parasitized at L3/L4 instar stage (5 d old) and allowed to develop into pre-reproductive adults (10 d old) containing a 5 d old parasitoid larva. A control group was created of non-parasitized pre-reproductive adults (10 d old). The inherent physiological thermotolerance (LT50) and potential behavioural thermoregulation (behaviour in a declining temperature regime) of parasitized and non-parasitized aphids were investigated. Results revealed no effect of parasitism on the physiological thermotolerance of S. avenae and M. dirhodum. Significant differences in the behaviour of parasitized and non-parasitized aphids were observed, in addition to differences between host species, and such behaviours are discussed in view of the potential for host manipulation.

Puppet Master: Possible Influence of the ParasiteToxoplasma Gondiion Managers and Employees

The article reviews recent literature on the effects of host manipulation by the parasite Toxoplasma gondii (prevalent in about a third of the world’s population) on perception, cognition, and behavior of humans, and on the changes in their physical appearance and personality characteristics. I argue that the mind-affecting parasite paradigm offers many research opportunities for management sciences, especially for organizational psychology and neuroscience. The article summarizes the parasite’s physiological mechanisms of affecting the host; highlights important behavioral effects of the infection in humans; and speculates on the possible impacts on skills and careers of employees and managers, organizational dynamics, intercultural management, and gender work roles. The conclusion shows limitations of the presented speculations and possible directions for future research on Toxoplasma’s effect on organizational dynamics.

Immunity, Sex and Parasites: Does Sex of Sand-Field Cricket (Gryllus firmus) Affect Immune Response to Eugregarine Parasites?

There is controversy about the effects gut-dwelling eugregarine parasites have on their invertebrate hosts. If crickets (Gryllus firmus) apportion resources to reproduction differently in males vs. females, then resources used to mount immune responses to parasites may also differ – especially if the parasites are pathogenic. I investigated the possible differences in immune response between male and female crickets and attempted to determine whether these differences are related to intensity of parasitic infection. To do this, pieces of nylon filament were implanted into the hemocoel of crickets which tested the immune response where hemocytes surround the filament (encapsulation). These responses were compared to intensity of parasitic infection. No statistically significant relationship between sex and melanisation, or sex and parasite load were found. I found that the duration of melanization was negatively correlated to parasite abundance and that there was a positive correlation between body size and parasite number. This result suggests the existence of a relationship between the parasite and host that could be conflicting with sexual selection theory, such as host manipulation by the parasite.

Zombie ant heads are oriented relative to solar cues

Abstract Parasite manipulation of host behavior is a compelling example of an extended phenotype. Some parasitic Ophiocordyceps species manipulate their ant victims to behave like zombies, causing them to walk abnormally, have convulsions that make them fall down, and climb vegetation to bite the veins or margins on the underside of plant leaves. Manipulation of the ants' behavior supports the fungus's growth and reproductive success. This study reports that Ophiocordyceps pseudolloydii can naturally infect Dolichoderus thoracicus ants in a broad-leaved forest in central Taiwan. The infected ants behaved as zombies but did not display ‘death grip’ behavior. Instead, the entire ant was covered in a dense matrix of fungal hyphae, securing the abdominal segments and the mandibles, but not the legs, to the leaf. Furthermore, the direction of the canopy opening and the orientation of the ants' heads were correlated, suggesting that a direct solar cue orients the dying ant. By detailed survey records from three squares with different canopy geometries within the graveyard areas, our data indicate that sunlight plays an important role in manipulation of ant hosts. These findings provide further indications of how the parasites have evolved to manipulate the host's behavior to increase fitness of the fungus.

Release of extracellular vesicles containing small RNAs from the eggs of Schistosoma japonicum.

Background Schistosoma japonicum is a parasitic flatworm that causes human schistosomiasis. Secreted extracellular vesicles (EVs) play a key role in pathogen-host interfaces. Previous studies have shown that S. japonicum adult worms can release microRNA (miRNA)-containing EVs, which can transfer their cargo to mammalian cells and regulate gene expression in recipient cells. Tissue-trapped eggs are generally considered the major contributor to the severe pathology of schistosomiasis; however, the interactions between the host and parasite in this critical stage remain largely unknown.MethodsThe culture medium for S. japonicum eggs in vitro was used to isolate EVs. Transmission electron microscopy (TEM) analysis was used to confirm that vesicles produced by the eggs were EVs based on size and morphology. Total RNA extracted from EVs was analyzed by Solexa technology to determine the miRNA profile. The in vitro internalization of the EVs by mammalian cells was analyzed by confocal microscopy. The presence of EVs associated miRNAs in the primary hepatocytes of infected mice was determined by quantitative real-time PCR (qRT-PCR).ResultsEVs were isolated from the culture medium of in vitro cultivated S. japonicum eggs. TEM analysis confirmed that nanosized vesicles were present in the culture medium. RNA-seq analysis showed that the egg-derived EVs contained small non-coding RNA (sncRNA) populations including miRNAs, suggesting a potential role in host manipulation. This study further showed that Hepa1-6, a murine liver cell line, internalized the purified EVs and their cargo miRNAs that were detectable in the primary hepatocytes of mice infected with S. japonicum.Conclusions Schistosoma japonicum eggs can release miRNA-containing EVs, and the EVs can transfer their cargo to recipient cells in vitro. These results demonstrate the regulatory potential of S. japonicum egg EVs at the parasite-host interface.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1845-2) contains supplementary material, which is available to authorized users.