Form and Function in the Digenea, with an Emphasis on Host-Parasite and Parasite-Bacteria Interactions.

This review covers the general aspects of the anatomy and physiology of the major body systems in digenetic trematodes, with an emphasis on new knowledge of the area acquired since the publication of the second edition of this book in 2019. In addition to reporting on key recent advances in the morphology and physiology of tegumentary, sensory, neuromuscular, digestive, excretory, and reproductive systems, and their roles in host-parasite interactions, this edition includes a section discussing the known and putative roles of bacteria in digenean biology and physiology. Furthermore, a brief discussion of current trends in the development of novel treatment and control strategies based on a better understanding of the trematode body systems and associated bacteria is provided.

The Human Blood Fluke, Schistosoma mansoni, Harbors Bacteria Throughout the Parasite's Life Cycle.

While symbiotic relationships between invertebrates and bacteria have been extensively described, studies of microbial communities inhabiting parasitic worms remain scarce. Exploring the microbiota associated with helminths responsible for major infectious diseases will inform on parasite biology, host-pathogen interactions, and disease pathophysiology. We investigated the presence of microorganisms inhabiting tissues of the human parasite Schistosoma mansoni. In situ hybridization using a pan-bacterial 16S rRNA gene probe revealed bacteria colonizing key developmental stages that were successfully removed after antibiotic treatment of live parasites. Understanding the composition and function of the S. mansoni-associated microbiota may lead to the development of novel microbiome-targeting control strategies.

Gastrointestinal worms and bacteria: From association to intervention.

A plethora of studies, both experimental and epidemiological, have indicated the occurrence of associations between infections by gastrointestinal (GI) helminths and the composition and function of the host gut microbiota. Given the worldwide risk and spread of anthelmintic resistance, particularly for GI parasites of livestock, a better understanding of the mechanisms underpinning the relationships between GI helminths and the gut microbiome, and between the latter and host health, may assist the development of novel microbiome-targeting and other bacteria-based strategies for parasite control. In this article, we review current and prospective methods to manipulate the host gut microbiome, and/or to exploit the immune stimulatory and modulatory properties of gut bacteria (and their products) to counteract the negative impact of GI worm infections; we also discuss the potential applications of these intervention strategies in programmes aimed to aid the fight against helminth diseases of humans and livestock.

The role of the host gut microbiome in the pathophysiology of schistosomiasis.

The pathophysiology of schistosomiasis is linked to the formation of fibrous granulomas around eggs that become trapped in host tissues, particularly the intestines and liver, during their migration to reach the lumen of the vertebrate gut. While the development of Schistosoma egg-induced granulomas is the result of finely regulated crosstalk between egg-secreted antigens and host immunity, evidence has started to emerge of the likely contribution of an additional player-the host gut microbiota-to pathological processes that culminate with the formation of these tissue lesions. Uncovering the role(s) of schistosome-mediated changes in gut microbiome composition and function in granuloma formation and, more broadly, in the pathophysiology of schistosomiasis, will shed light on the mechanisms underlying this three-way parasite-host-microbiome interplay. Such knowledge may, in turn, pave the way towards the discovery of novel therapeutic targets and control strategies.

Experimental infection with the hookworm, Necator americanus, is associated with stable gut microbial diversity in human volunteers with relapsing multiple sclerosis.

BACKGROUND: Helminth-associated changes in gut microbiota composition have been hypothesised to contribute to the immune-suppressive properties of parasitic worms. Multiple sclerosis is an immune-mediated autoimmune disease of the central nervous system whose pathophysiology has been linked to imbalances in gut microbial communities. RESULTS: In the present study, we investigated, for the first time, qualitative and quantitative changes in the faecal bacterial composition of human volunteers with remitting multiple sclerosis (RMS) prior to and following experimental infection with the human hookworm, Necator americanus (N+), and following anthelmintic treatment, and compared the findings with data obtained from a cohort of RMS patients subjected to placebo treatment (PBO). Bacterial 16S rRNA high-throughput sequencing data revealed significantly decreased alpha diversity in the faecal microbiota of PBO compared to N+ subjects over the course of the trial; additionally, we observed significant differences in the abundances of several bacterial taxa with putative immune-modulatory functions between study cohorts. Parabacteroides were significantly expanded in the faecal microbiota of N+ individuals for which no clinical and/or radiological relapses were recorded at the end of the trial. CONCLUSIONS: Overall, our data lend support to the hypothesis of a contributory role of parasite-associated alterations in gut microbial composition to the immune-modulatory properties of hookworm parasites.

Exclusive dependence of IL-10Rα signalling on intestinal microbiota homeostasis and control of whipworm infection.

The whipworm Trichuris trichiura is a soil-transmitted helminth that dwells in the epithelium of the caecum and proximal colon of their hosts causing the human disease, trichuriasis. Trichuriasis is characterized by colitis attributed to the inflammatory response elicited by the parasite while tunnelling through intestinal epithelial cells (IECs). The IL-10 family of receptors, comprising combinations of subunits IL-10Rα, IL-10Rß, IL-22Rα and IL-28Rα, modulates intestinal inflammatory responses. Here we carefully dissected the role of these subunits in the resistance of mice to infection with T. muris, a mouse model of the human whipworm T. trichiura. Our findings demonstrate that whilst IL-22Rα and IL-28Rα are dispensable in the host response to whipworms, IL-10 signalling through IL-10Rα and IL-10Rß is essential to control caecal pathology, worm expulsion and survival during T. muris infections. We show that deficiency of IL-10, IL-10Rα and IL-10Rß results in dysbiosis of the caecal microbiota characterised by expanded populations of opportunistic bacteria of the families Enterococcaceae and Enterobacteriaceae. Moreover, breakdown of the epithelial barrier after whipworm infection in IL-10, IL-10Rα and IL-10Rß-deficient mice, allows the translocation of these opportunistic pathogens or their excretory products to the liver causing organ failure and lethal disease. Importantly, bone marrow chimera experiments indicate that signalling through IL-10Rα and IL-10Rß in haematopoietic cells, but not IECs, is crucial to control worm expulsion and immunopathology. These findings are supported by worm expulsion upon infection of conditional mutant mice for the IL-10Rα on IECs. Our findings emphasize the pivotal and complex role of systemic IL-10Rα signalling on immune cells in promoting microbiota homeostasis and maintaining the intestinal epithelial barrier, thus preventing immunopathology during whipworm infections.

Virulence and in vitro antifungal susceptibility of Candida albicans and Candida catenulata from laying hens.

In spite of evidence that domestic and wild birds may act as carriers of human pathogenic fungi, data on the role of laying hens as reservoirs of drug resistant and virulent yeasts is lacking. Here, we assess several virulence factors (phospholipase and haemolysin activity) and the antifungal susceptibility profiles of 84 Candida albicans and 17 Candida catenulata strains isolated from cloacae (group A), faeces (group B) and eggs (group C) of laying hens. Of these strains, 95% C. albicans and 23% C. catenulata strains displayed phospholipase and haemolytic activities. For C. albicans, the highest values of phospholipase (Pz = 0.62) and haemolytic activities (Hz = 0.49) were recorded among the strains from group C whilst for C. catenulata (Pz = 0.54; Hz = 0.49) among those from group A. High minimum inhibitory concentration (MIC) values for azoles and amphotericin B (AmB) were recorded irrespective of their sources in all C. albicans strains. A total of 22 C. albicans strains were multidrug resistant, displaying resistance to fluconazole, itraconazole (ITZ), voriconazole (VOR) and posaconazole (POS). All C. catenulata strains from group C were resistant to ITZ, POS, micafungin and anidulafungin and susceptible to AmB. In this study, C. albicans and C. catenulata isolated from the cloacae, faeces and eggs of laying hens produced phospholipase and haemolysin and might be multidrug resistant. In the environment (faeces) or in eggs, C. albicans and C. catenulata strains might acquire pathogenic virulence traits and/or show multidrug resistance profiles. Based on these results, breeding and handling of laying hens and/or eggs may have implications for human and animal health.

The best type of inoculum for testing the antifungal drug susceptibility of Microsporum canis: In vivo and in vitro results.

BACKGROUND: Data correlating in vitro drug susceptibility of Microsporum canis with clinical outcomes of its infections are lacking as well as the most suitable inoculum and incubation time in broth microdilution assays. OBJECTIVES AND METHODS: Microsporum canis strains were collected from animal hosts that tested positive (Group I; n = 13) and negative (Group II; n = 14) to this pathogen following itraconazole (ITC) therapy. In vitro ITC susceptibility was assessed according to the Clinical Laboratory Standards Institute (CLSI M38-A2) methodology using conidia, hypha-conidia and arthroconidia at 3 and 7 days of incubation in order to assess the most suitable inoculum and incubation time. Successively, ketoconazole (KTC), voriconazole (VRC), terbinafine (TRB), posaconazole (PSZ), fluconazole (FLC) and griseofulvin (GRI) susceptibilities were assessed using the chosen inoculum. RESULTS: The MIC values of ITC after three-day incubation were equal than those recorded after 7-day incubation. Itraconazole MICs were ≤1 µg/mL for strains from Group II and >1 µg/mL for those of Group II only when conidia were used. All strains showed high susceptibility to VRC, POS, TEB and low susceptibility to ITC, KTC, GRI and FLC regardless of the source and incubation time. CONCLUSIONS AND CLINICAL IMPORTANCE: Results suggest that correlation between the in vitro results and clinical outcome was observed only by incubating conidia for 3 days at 30 ± 2°C. These conditions might be most suitable to assess in vitro susceptibility of M. canis and assist in determining the occurrence of drug resistance and cross-resistance phenomena.

Helminths and microbes within the vertebrate gut - not all studies are created equal.

The multifaceted interactions occurring between gastrointestinal (GI) parasitic helminths and the host gut microbiota are emerging as a key area of study within the broader research domain of host-pathogen relationships. Over the past few years, a wealth of investigations has demonstrated that GI helminths interact with the host gut flora, and that such interactions result in modifications of the host immune and metabolic statuses. Nevertheless, whilst selected changes in gut microbial composition are consistently observed in response to GI helminth infections across several host-parasite systems, research in this area to date is largely characterised by inconsistent findings. These discrepancies are particularly evident when data from studies of GI helminth-microbiota interactions conducted in humans from parasite-endemic regions are compared. In this review, we provide an overview of the main sources of variance that affect investigations on helminth-gut microbiota interactions in humans, and propose a series of methodological approaches that, whilst accounting for the inevitable constraints of fieldwork, are aimed at minimising confounding factors and draw biologically meaningful interpretations from highly variable datasets.

Ascaris suum draft genome.

Parasitic diseases have a devastating, long-term impact on human health, welfare and food production worldwide. More than two billion people are infected with geohelminths, including the roundworms Ascaris (common roundworm), Necator and Ancylostoma (hookworms), and Trichuris (whipworm), mainly in developing or impoverished nations of Asia, Africa and Latin America. In humans, the diseases caused by these parasites result in about 135,000 deaths annually, with a global burden comparable with that of malaria or tuberculosis in disability-adjusted life years. Ascaris alone infects around 1.2 billion people and, in children, causes nutritional deficiency, impaired physical and cognitive development and, in severe cases, death. Ascaris also causes major production losses in pigs owing to reduced growth, failure to thrive and mortality. The Ascaris-swine model makes it possible to study the parasite, its relationship with the host, and ascariasis at the molecular level. To enable such molecular studies, we report the 273 megabase draft genome of Ascaris suum and compare it with other nematode genomes. This genome has low repeat content (4.4%) and encodes about 18,500 protein-coding genes. Notably, the A. suum secretome (about 750 molecules) is rich in peptidases linked to the penetration and degradation of host tissues, and an assemblage of molecules likely to modulate or evade host immune responses. This genome provides a comprehensive resource to the scientific community and underpins the development of new and urgently needed interventions (drugs, vaccines and diagnostic tests) against ascariasis and other nematodiases.

Filarial infection caused by Onchocerca boehmi (Supperer, 1953) in a horse from Italy.

Equids can be infected by a range of skin-dwelling filarial nematodes, including four species of the genus Onchocerca. Current literature on equine onchocercosis is fragmentary and often limited to isolated case reports. The present study aimed to describe a clinical case of equine onchocercosis caused by Onchocerca boehmi (Supperer, 1953) (syn. Elaeophora boehmi) in an 8-year-old gelding Belgian show jumper from northern Italy. The horse was presented with a firm and painless mass on the proximal third of the right metacarpal region. Ultrasound examination showed a peritendinous enlargement around the palmaro-lateral area of the tendons, characterized by an elongated hypoechoic and well-defined structure, embedding a coiled hyperechoic line. The metacarpal nodule was resected and histologically examined. Fragments of a parasitic nematode were detected, isolated and examined. The morphological analysis allowed identifying the nematode as O. boehmi. In addition, total genomic DNA was extracted from individual fragments using a commercial kit for the nematode identification and a comparative sequence analysis of the nematode cytochrome oxidase subunit 1 (cox1) sequence with data available in the GenBankTM database revealed the closest identity (i.e. 91 %) with that of Onchocerca lupi. Thus far, O. boehmi has only been reported in Austria and Iran, and information about its life-cycle and vectors is lacking. The systematic position of this species within the genus Onchocerca, not in Elaeophora where it was originally described, is in concordance with the morphological and molecular analysis. In this article, we describe the first autochthonous case of equine onchocercosis in Italy caused by O. boehmi and discuss novel parasitological, clinical, and pathological data on these pathogens of horses.

Secreted proteomes of different developmental stages of the gastrointestinal nematode Nippostrongylus brasiliensis.

Hookworms infect more than 700 million people worldwide and cause more morbidity than most other human parasitic infections. Nippostrongylus brasiliensis (the rat hookworm) has been used as an experimental model for human hookworm because of its similar life cycle and ease of maintenance in laboratory rodents. Adult N. brasiliensis, like the human hookworm, lives in the intestine of the host and releases excretory/secretory products (ESP), which represent the major host-parasite interface. We performed a comparative proteomic analysis of infective larval (L3) and adult worm stages of N. brasiliensis to gain insights into the molecular bases of host-parasite relationships and determine whether N. brasiliensis could indeed serve as an appropriate model for studying human hookworm infections. Proteomic data were matched to a transcriptomic database assembled from 245,874,892 Illumina reads from different developmental stages (eggs, L3, L4, and adult) of N. brasiliensis yielding∼18,426 unigenes with 39,063 possible isoform transcripts. From this analysis, 313 proteins were identified from ESPs by LC-MS/MS-52 in the L3 and 261 in the adult worm. Most of the proteins identified in the study were stage-specific (only 13 proteins were shared by both stages); in particular, two families of proteins-astacin metalloproteases and CAP-domain containing SCP/TAPS-were highly represented in both L3 and adult ESP. These protein families are present in most nematode groups, and where studied, appear to play roles in larval migration and evasion of the host's immune response. Phylogenetic analyses of defined protein families and global gene similarity analyses showed that N. brasiliensis has a greater degree of conservation with human hookworm than other model nematodes examined. These findings validate the use of N. brasiliensis as a suitable parasite for the study of human hookworm infections in a tractable animal model.

Probing of a human proteome microarray with a recombinant pathogen protein reveals a novel mechanism by which hookworms suppress B-cell receptor signaling.

Na-ASP-2 is an efficacious hookworm vaccine antigen. However, despite elucidation of its crystal structure and studies addressing its immunobiology, the function of Na-ASP-2 has remained elusive. We probed a 9000-protein human proteome microarray with Na-ASP-2 and showed binding to CD79A, a component of the B-cell antigen receptor complex. Na-ASP-2 bound to human B lymphocytes ex vivo and downregulated the transcription of approximately 1000 B-cell messenger RNAs (mRNAs), while only approximately 100 mRNAs were upregulated, compared with control-treated cells. The expression of a range of molecules was affected by Na-ASP-2, including factors involved in leukocyte transendothelial migration pathways and the B-cell signaling receptor pathway. Of note was the downregulated transcription of lyn and pi3k, molecules that are known to interact with CD79A and control B-cell receptor signaling processes. Together, these results highlight a previously unknown interaction between a hookworm-secreted protein and B cells, which has implications for helminth-driven immunomodulation and vaccine development. Further, the novel use of human protein microarrays to identify host-pathogen interactions, coupled with ex vivo binding studies and subsequent analyses of global gene expression in human host cells, demonstrates a new pipeline by which to explore the molecular basis of infectious diseases.

Carcinogenic Liver Fluke Secretes Extracellular Vesicles That Promote Cholangiocytes to Adopt a Tumorigenic Phenotype.

BACKGROUND: Throughout Asia, there is an unprecedented link between cholangiocarcinoma and infection with the liver fluke Opisthorchis viverrini. Multiple processes, including chronic inflammation and secretion of parasite proteins into the biliary epithelium, drive infection toward cancer. Until now, the mechanism and effects of parasite protein entry into cholangiocytes was unknown. METHODS: Various microscopy techniques were used to identify O. viverrini extracellular vesicles (EVs) and their internalization by human cholangiocytes. Using mass spectrometry we characterized the EV proteome and associated changes in cholangiocytes after EV uptake, and we detected EV proteins in bile of infected hamsters and humans. Cholangiocyte proliferation and interleukin 6 (IL-6) secretion was measured to assess the impact of EV internalization. RESULTS: EVs were identified in fluke culture medium and bile specimens from infected hosts. EVs internalized by cholangiocytes drove cell proliferation and IL-6 secretion and induced changes in protein expression associated with endocytosis, wound repair, and cancer. Antibodies to an O. viverrini tetraspanin blocked EV uptake and IL-6 secretion by cholangiocytes. CONCLUSIONS: This is the first time that EVs from a multicellular pathogen have been identified in host tissues. Our findings imply a role for O. viverrini EVs in pathogenesis and highlight an approach to vaccine development for this infectious cancer.

Impact of experimental hookworm infection on the human gut microbiota.

The interactions between gastrointestinal parasitic helminths and commensal bacteria are likely to play a pivotal role in the establishment of host-parasite cross-talk, ultimately shaping the development of the intestinal immune system. However, little information is available on the impact of infections by gastrointestinal helminths on the bacterial communities inhabiting the human gut. We used 16S rRNA gene amplification and pyrosequencing to characterize, for the first time to our knowledge, the differences in composition and relative abundance of fecal microbial communities in human subjects prior to and following experimental infection with the blood-feeding intestinal hookworm, Necator americanus. Our data show that, although hookworm infection leads to a minor increase in microbial species richness, no detectable effect is observed on community structure, diversity or relative abundance of individual bacterial species.

A deep exploration of the transcriptome and "excretory/secretory" proteome of adult Fascioloides magna.

Parasitic liver flukes of the family Fasciolidae are responsible for major socioeconomic losses worldwide. However, at present, knowledge of the fundamental molecular biology of these organisms is scant. Here, we characterize, for the first time, the transcriptome and secreted proteome of the adult stage of the "giant liver fluke," Fascioloides magna, using Illumina sequencing technology and one-dimensional SDS-PAGE and OFFGEL protein electrophoresis, respectively. A total of ∼54,000,000 reads were generated and assembled into ∼39,000 contiguous sequences (contigs); ∼20,000 peptides were predicted and classified based on homology searches, protein motifs, gene ontology, and biological pathway mapping. From the predicted proteome, 48.1% of proteins could be assigned to 384 biological pathway terms, including "spliceosome," "RNA transport," and "endocytosis." Putative proteins involved in amino acid degradation were most abundant. Of the 835 secreted proteins predicted from the transcriptome of F. magna, 80 were identified in the excretory/secretory products from this parasite. Highly represented were antioxidant proteins, followed by peptidases (particularly cathepsins) and proteins involved in carbohydrate metabolism. The integration of transcriptomic and proteomic datasets generated herein sets the scene for future studies aimed at exploring the potential role(s) that molecules might play at the host-parasite interface and for establishing novel strategies for the treatment or control of parasitic fluke infections.

A preliminary investigation of serological tools for the detection of Onchocerca lupi infection in dogs.

Onchocerca lupi is a neglected filarioid causing nodular lesions associated with acute or chronic ocular disease in dogs. Despite the recent appraisal of its zoonotic potential, human cases are increasingly reported in the Old and New Worlds. Therefore, the development of accurate tools for the rapid diagnosis of O. lupi infections in dogs is becoming a priority. In this study, we conducted a preliminary investigation aimed at evaluating the usefulness of a commercially available ELISA test for the detection of O. lupi antigens in canine sera. The potential use of this tool for larger epidemiological studies of canine onchocerciasis is discussed.

Assessing the microbiota of the snail intermediate host of trematodes, Galba truncatula.

BACKGROUND: The microbiome is known to play key roles in health and disease, including host susceptibility to parasite infections. The freshwater snail Galba truncatula is the intermediate host for many trematode species, including the liver and rumen flukes Fasciola hepatica and Calicophoron daubneyi, respectively. The snail-parasite system has previously been investigated. However, the specific interaction between the snail-associated microbiota and intra-snail developmental stages of trematodes has yet to be explored. METHODS: Galba truncatula snails were collected from farms in Northern Ireland and trematode infection was diagnosed using PCR. High-throughput sequencing analysis of the bacterial 16S ribosomal DNA V3-V4 hypervariable regions was subsequently applied to characterise the microbiota of both uninfected and infected snails. RESULTS: We first showed that the snail harboured microbiota that was distinct for its environment. The microbiota of infected snails was found to differ significantly from that of uninfected snails. In particular, the bacterial genera Mycoplasma and Methylotenera were significantly more abundant in infected snails, while genera Sphingomonas and Nocardioides were predominantly associated with uninfected snails. CONCLUSION: These findings pave the way to future studies on the functional roles of bacteria in host-parasite relationships.

Development of an indirect ELISA for the serodiagnosis of canine infection by Onchocerca lupi.

Onchocerca lupi is a zoonotic filarioid parasite of dogs and cats with widespread distribution. A specific non-invasive diagnostic assay for the detection of O. lupi infections remains unavailable. This study aimed to assess the accuracy, specificity, and sensitivity of an ELISA test designed using nine peptides from two O. lupi proteins. Sera (n = 54) collected from O. lupi infected dogs from endemic areas (Portugal and USA), alongside sera from dogs positive for Dirofilaria immitis, D. repens, Cercopithifilaria bainae, and Acanthocheilonema reconditum (n = 53) from a non-endemic area for O. lupi, as well as from helminth-free dogs (n = 60), were tested. The checkerboard titration method was applied for the optimization of peptide concentrations and conjugate anti-dog dilutions. Sensitivity, specificity, and optimal cut-off values were calculated using ROC curve analysis. All peptides reacted against sera of O. lupi, with no correlation between optic density (OD) values and microfilariae (mfs) loads. Sensitivity and specificity values ranging from 85.45 to 100%, and 88.89% to 100%, respectively, were recorded for all peptides examined, with 100% specificity and sensitivity observed for peptides 40_3, 40_5, 130_3, 120_3 and 40_1, 130_5, respectively. The maximum cut-off value was observed for peptides 40_5 (0.765) and 40_3 (0.708). Testing of sera from dogs positive for other filarioids resulted in lower OD values (up to 1.565) for peptides 40_3 and 40_5 when compared with O. lupi (up to 2.929). The availability of this assay will be of value in epidemiological studies of canine O. lupi infection in both endemic and non-endemic areas, and in assessing the risk for zoonotic transmission.