Concept: Fasciola hepatica
The study of host-parasite interactions has increased considerably in the last decades, with many studies focusing on the identification of parasite molecules (i.e. surface or excretory/secretory proteins (ESP)) as potential targets for new specific treatments and/or diagnostic tools. In parallel, in the last few years there have been significant advances in the field of extracellular vesicles research. Among these vesicles, exosomes of endocytic origin, with a characteristic size ranging from 30-100 nm, carry several atypical secreted proteins in different organisms, including parasitic protozoa. Here, we present experimental evidence for the existence of exosome-like vesicles in parasitic helminths, specifically the trematodes Echinostoma caproni and Fasciola hepatica. These microvesicles are actively released by the parasites and are taken up by host cells. Trematode extracellular vesicles contain most of the proteins previously identified as components of ESP, as confirmed by proteomic, immunogold labeling and electron microscopy studies. In addition to parasitic proteins, we also identify host proteins in these structures. The existence of extracellular vesicles explains the secretion of atypical proteins in trematodes, and the demonstration of their uptake by host cells suggests an important role for these structures in host-parasite communication, as described for other infectious agents.
The aim of this study was to compare three different techniques for the early diagnosis of the infection by Fasciola hepatica in experimentally and naturally infected sheep. The experimental group consisted of 7 sheep infected with 200 metacercariae; faecal samples were taken weekly until 12 week post-infection (wpi). Under natural conditions, 45 individual faecal samples and 2 pools of faeces were collected from three different flocks with a history of F. hepatica infection. The results obtained by a coprological method were compared with a commercial immunoassay and with two PCR assays in faecal samples. Faecal eggs were detected by 9wpi in experimental infection. On the other hand, only 24 out of 45 sheep were positive in naturally infected flocks. By means of a sandwich-ELISA kit, the infection was first detected by 4wpi in the 57.1% experimentally infected sheep and this percentage reached 100% by 8wpi. All naturally infected animals were positive with this method. Regarding PCR, a specific 423bp fragment of mitochondrial DNA was amplified in faecal samples. The F. hepatica infection was detected from 3wpi with a standard PCR, and from 2wpi with a nested-PCR. Only 37 sheep out of 45 were positive by the standard PCR although the infection was diagnosed in all animals by the nested-PCR. In conclusion, the sensitivity of the nested-PCR described in our study is higher than the detection of eggs in faeces as well as the commercial immunoassay. Moreover, no cross reactions were described with gastrointestinal nematodes.
Fasciolosis is a parasitic infection by the liver fluke Fasciola hepatica, which costs the global agricultural community over US $2 billion per year. Its prevalence is rising due to factors such as climate change and drug resistance. ATP-dependent membrane transporters are considered good potential drug targets as they are essential for cellular processes and are in an exposed, accessible position in the cell. Immunolocalisation studies demonstrated that a plasma membrane calcium ATPase (PMCA) was localised to the parenchymal tissue in F. hepatica. The coding sequence for a F. hepatica PMCA (FhPMCA) has been obtained. This sequence encodes a 1,163 amino acid protein which contains motifs which are commonly conserved in PMCAs. Molecular modelling predicted that the protein has 10 transmembrane segments which include a potential calcium ion binding site and phosphorylation motif. FhPMCA interacts with the calmodulin-like protein FhCaM1, but not the related proteins FhCaM2 or FhCaM3, in a calcium-ion dependent manner. This interaction occurs through a region in the C-terminal region of FhPMCA which most likely adopts an α-helical conformation. When FhPMCA was heterologously expressed in a budding yeast strain deleted for its PMCA (Pmc1p), it restored viability. Microsomes prepared from these yeast cells had calcium ion stimulated ATPase activity which was inhibited by the known PMCA inhibitors, bisphenol and eosin. The potential of FhPMCA as a new drug target is discussed.
Fasciola jacksoni (Cobbold, 1869) is a highly prevalent (18-62 %) species colonizing the liver (less frequently the lungs, kidneys, pericardia, and intestines) of Elephas maximus indicus and Elephas maximus maximus in the Indomalayan region, causing cirrhosis, hemorrhages, and connective tissue proliferation. The phylogenetic relationships of Fasciola jacksoni in relation to representative species of the superfamily Echinostomatoidea was assessed using four independent DNA regions. The analysis involved conserved (28S rDNA) and highly variable (ITS1, ITS2, and ND1) loci utilizing both mitochondrial (ND1) and nuclear (28S rDNA, ITS1, and ITS2) DNA. Although the analyses confirmed the monophyletic origin of the Fasciolidae family, all four analyzed regions suggested high similarity of Fasciola jacksoni to Fascioloides magna, member of a hitherto monotypic genus, parasitizing a variety of wild and domestic ruminants through the Holarctic. Supporting evidence stems also from the morphological similarities, host spectrum overlaps, and similarities in disease onset and progression. Fasciola jacksoni was reclassified to its genus in the nineteenth century by Cobbold based on the shared possession of dendriform system of gastric canals. However, Fascioloides magna (discovered later) shares this feature as well. Conversely, Fascioloides magna and Fasciola hepatica possess long median intestinal branches, whereas relatively shorter median intestinal branches are characteristic for Fasciola hepatica and Fasciola gigantica only. Both, Fascioloides magna and Fasciola hepatica, are also similar in their possession of small, but distinctive cephalic cone, while the larger one is typical for Fasciola hepatica and Fasciola gigantica. Reflecting the combined data, reclassification of Fasciola jacksoni as Fascioloides jacksoni comb. nov. is suggested.
The plant-derived, diterpenoid 7-keto-sempervirol was recently reported to display moderate activity against larval stages of Schistosoma mansoni (IC50 = 19.1 μM) and Fasciola hepatica (IC50 = 17.7 μM), two related parasitic blood and liver flukes responsible for the neglected tropical diseases schistosomiasis and fascioliasis, respectively. Here, we aimed to increase the potency of 7-keto-sempervirol by total synthesis of 30 structural analogues. Subsequent screening of these new diterpenoids against juvenile and adult lifecycle stages of both parasites as well as the human HepG2 liver cell line and the bovine MDBK kidney cell line revealed structure-activity relationship trends. The most active analogue, 7d, displayed improved dual anthelmintic activity over 7-keto-sempervirol (IC50 ≈ 6 μM for larval blood flukes; IC50 ≈ 3 μM for juvenile liver flukes) and moderate selectivity (SI ≈ 4-5 for blood flukes, 8-13 for liver flukes compared to HepG2 and MDBK cells, respectively). Phenotypic studies using scanning electron microscopy revealed substantial tegumental alterations in both helminth species, supporting the hypothesis that the parasite surface is one of the main targets of this family of molecules. Further modifications of 7d could lead to greater potency and selectivity metrics resulting in a new class of broad-spectrum anthelmintic.
Fascioliasis is a pathogenic disease transmitted by lymnaeid snails and recently emerging in humans, in part due to effects of climate changes, anthropogenic environment modifications, import/export and movements of livestock. South America is the continent presenting more human fascioliasis hyperendemic areas and the highest prevalences and intensities known. These scenarios appear mainly linked to altitude areas in Andean countries, whereas lowland areas of non-Andean countries, such as Uruguay, only show sporadic human cases or outbreaks. A study including DNA marker sequencing of fasciolids and lymnaeids, an experimental study of the life cycle in Uruguay, and a review of human fascioliasis in Uruguay, are performed.
Food borne trematodes (FBTs) are an assemblage of platyhelminth parasites transmitted through the food chain, four of which are recognized as neglected tropical diseases (NTDs). Fascioliasis stands out among the other NTDs due to its broad and significant impact on both human and animal health, as Fasciola sp., are also considered major pathogens of domestic ruminants. Here we present a reference genome sequence of the common liver fluke, Fasciola hepatica isolated from sheep, complementing previously reported isolate from cattle. A total of 14,642 genes were predicted from the 1.14 GB genome of the liver fluke. Comparative genomics indicated that F. hepatica Oregon and related food-borne trematodes are metabolically less constrained than schistosomes and cestodes, taking advantage of the richer milieus offered by the hepatobiliary organs. Protease families differentially expanded between diverse trematodes may facilitate migration and survival within the heterogeneous environments and niches within the mammalian host. Surprisingly, the sequencing of Oregon and Uruguay F. hepatica isolates led to the first discovery of an endobacteria in this species. Two contigs from the F. hepatica Oregon assembly were joined to complete the 859,205 bp genome of a novel Neorickettsia endobacterium (nFh) closely related to the etiological agents of human Sennetsu and Potomac horse fevers. Immunohistochemical studies targeting a Neorickettsia surface protein found nFh in specific organs and tissues of the adult trematode including the female reproductive tract, eggs, the Mehlis' gland, seminal vesicle, and oral suckers, suggesting putative routes for fluke-to-fluke and fluke-to-host transmission. The genomes of F. hepatica and nFh will serve as a resource for further exploration of the biology of F. hepatica, and specifically its newly discovered trans-kingdom interaction with nFh and the impact of both species on disease in cattle and humans.
The liver fluke Fasciola gigantica is a trematode parasite of ruminants and humans that occurs naturally in Africa and Asia. Cases of human fascioliasis, attributable at least in part to F. gigantica, are significantly increasing in the last decades. The introduced snail species Galba truncatula was already identified to be an important intermediate host for this parasite and the efficient invader Pseudosuccinea columella is another suspect in this case. Therefore, we investigated snails collected in irrigation canals in Fayoum governorate in Egypt for prevalence of trematodes with focus on P. columella and its role for the transmission of F. gigantica. Species were identified morphologically and by partial sequencing of the cytochrome oxidase subunit I gene (COI). Among all 689 snails found at the 21 sampling sites, P. columella was the most abundant snail with 296 individuals (42.96%) and it was also the most dominant species at 10 sites. It was not found at 8 sites. Molecular detection by PCR and sequencing of the ITS1-5.8S-ITS2 region of the ribosomal DNA (rDNA) revealed infections with F. gigantica (3.38%), Echinostoma caproni (2.36%) and another echinostome (7.09%) that could not be identified further according to its sequence. No dependency of snail size and trematode infection was found. Both high abundance of P. columella in the Fayoum irrigation system and common infection with F. gigantica might be a case of parasite spill-back (increased prevalence in local final hosts due to highly susceptible introduced intermediate host species) from the introduced P. columella to the human population, explaining at least partly the observed increase of reported fascioliasis-cases in Egypt. Eichhornia crassipes, the invasive water hyacinth, which covers huge areas of the irrigation canals, offers safe refuges for the amphibious P. columella during molluscicide application. As a consequence, this snail dominates snail communities and efficiently transmits F. gigantica.
Two platyhelminths of biomedical and commercial significance are Schistosoma mansoni (blood fluke) and Fasciola hepatica (liver fluke). These related trematodes are responsible for the chronic neglected tropical diseases schistosomiasis and fascioliasis, respectively. As no vaccine is currently available for anti-flukicidal immunoprophylaxis, current treatment is mediated by mono-chemical chemotherapy in the form of mass drug administration (MDA) (praziquantel for schistosomiasis) or drenching (triclabendazole for fascioliasis) programmes. This overreliance on single chemotherapeutic classes has dramatically limited the number of novel chemical entities entering anthelmintic drug discovery pipelines, raising significant concerns for the future of sustainable blood and liver fluke control.
Fasciola hepatica is a parasitic trematode of global importance in livestock. Control strategies reliant on anthelmintics are unsustainable due to the emergence of drug resistance. Vaccines are under development, but efficacy is variable. Evidence from experimental infection suggest vaccine efficacy may be affected by parasite-induced immunomodulation. Little is known about the immune response to F. hepatica following natural exposure. Hence we analysed the immune responses over time in calves naturally exposed to F. hepatica infection.Cohorts of replacement dairy heifer calves (n=42) with no prior exposure to F. hepatica, on three commercial dairy farms, were sampled over the course of a grazing season. Exposure was determined through F. hepatica-specific serum antibody ELISA and fluke egg counts. Concurrent changes in peripheral blood leukocyte sub-populations, lymphocyte proliferation and cytokine responses were measured. Relationships between fluke infection and immune responses were analysed using multivariable linear mixed effect models.All calves from one farm showed evidence of exposure, whilst cohorts from the remaining two farms remained negative over the grazing season. A type-2 immune response was associated with exposure, with increased interleukin (IL)-4 production, IL-5 transcription and eosinophilia. Suppression of parasite-specific PBMC proliferation was evident; while decreased mitogen stimulated IFN-γ production suggested immunomodulation, which was not restricted to parasite-specific responses. Our findings show that the global immune response is modulated towards a non-proliferative type-2 state following natural challenge with F. hepatica This has implications for vaccination programmes in terms of the timing of administration of vaccination programmes, and for host susceptibility to co-infecting pathogens.