Fasciola hepatica and Fasciola gigantica: comparison of cellular response to experimental infection in sheep

Fasciolosis: pathogenesis, host-parasite interactions, and implication in vaccine development

Fasciola hepatica is distributed worldwide, causing substantial economic losses in the animal husbandry industry. Human fasciolosis is an emerging zoonosis in Andean America, Asia, and Africa. The control of the disease, both in humans and animals, is based on using anthelmintic drugs, which has resulted in increased resistance to the most effective anthelmintics, such as triclabendazole, in many countries. This, together with the concerns about drug residues in food and the environment, has increased the interest in preventive measures such as a vaccine to help control the disease in endemic areas. Despite important efforts over the past two decades and the work carried out with numerous vaccine candidates, none of them has demonstrated consistent and reproducible protection in target species. This is at least in part due to the high immunomodulation capacity of the parasite, making ineffective the host response in susceptible species such as ruminants. It is widely accepted that a deeper knowledge of the host-parasite interactions is needed for a more rational design of vaccine candidates. In recent years, the use of emerging technologies has notably increased the amount of data about these interactions. In the present study, current knowledge of host-parasite interactions and their implication in Fasciola hepatica vaccine development is reviewed.

Proteomic analysis of exosome-like vesicles from Fasciola gigantica adult worm provides support for new vaccine targets against fascioliasis

BACKGROUND

Extracellular vesicles (EVs) released by helminths play an important role in parasite-host communication. However, little is known about the characteristics and contents of the EVs of Fasciola gigantica, a parasitic flatworm that causes tropical fascioliasis. A better understanding of EVs released by F. gigantica will help elucidate the mechanism of F. gigantica-host interaction and facilitate the search for new vaccine candidates for the control and treatment of fascioliasis.

METHODS

Two different populations of EVs (15k EVs and 100k EVs) were purified from adult F. gigantica culture media by ultracentrifugation. The morphology and size of the purified EVs were determined by transmission electron microscopy (TEM) and by the Zetasizer Nano ZSP high performance particle characterization system. With the aim of identifying diagnostic markers or potential vaccine candidates, proteins within the isolated 100k EVs were analyzed using mass spectrometry-based proteomics (LC-MS/MS). Mice were then vaccinated with excretory/secretory products (ESPs; depleted of EVs), 15k EVs, 100k EVs and recombinant F. gigantica heat shock protein 70 (rFg-HSP70) combined with alum adjuvant followed by challenge infection with F. gigantica metacercariae. Fluke recovery and antibody levels were used as measures of vaccine protection.

RESULTS

TEM analysis and nanoparticle tracking analysis indicated the successful isolation of two subpopulations of EVs (15k EVs and 100k EVs) from adult F. gigantica culture supernatants using differential centrifugation. A total of 755 proteins were identified in the 100k EVs. Exosome biogenesis or vesicle trafficking proteins, ESCRT (endosomal sorting complex required for transport) pathway proteins and exosome markers, heat shock proteins and 14-3-3 proteins were identified in the 100k EVs. These results indicate that the isolated 100k EVs were exosome-like vesicles. The functions of the identified proteins may be associated with immune regulation, immune evasion and virulence. Mice immunized with F. gigantica ESPs, 15k EVs, 100k EVs and rFg-HSP70 exhibited a reduction in fluke burden of 67.90%, 60.38%, 37.73% and 56.6%, respectively, compared with the adjuvant control group. The vaccination of mice with F. gigantica 100k EVs, 15k EVs, ESP and rFg-HSP70 induced significant production of specific immunoglobulins in sera, namely IgG, IgG1 and IgG2a.

CONCLUSION

The results of this study suggest that proteins within the exosome-like vesicles of F. gigantica have immunomodulatory, immune evasion and virulence functions. This knowledge may lead to new strategies for immunotherapy, vaccination and the diagnosis of fascioliasis.

Proteomic analysis of Fasciola gigantica excretory and secretory products (FgESPs) co-immunoprecipitated using a time course of infected buffalo sera

Introduction

Widespread Fasciola gigantica infection in buffaloes has caused great economic losses in buffalo farming. Studies on F. gigantica excretory and secretory products (FgESP) have highlighted their importance in F. gigantica parasitism and their potential in vaccine development. Identifying FgESP components involved in F. gigantica-buffalo interactions during different periods is important for developing effective strategies against fasciolosis.

Methods

Buffaloes were assigned to non-infection (n = 3, as control group) and infection (n = 3) groups. The infection group was orally administrated 250 metacercariae. Sera were collected at 3, 10, and 16 weeks post-infection (wpi) for the non-infection group and at 0 (pre-infection), 1, 3, 6, 8, 10, 13, and 16 wpi for the infection group. FgESP components interacting with sera from the non-infection and infection groups assay were pulled down by co-IP and identified using LC-MS/MS. Interacting FgESP components in infection group were subjected to Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathway and gene ontology (GO) functional annotation to infer their potential functions.

Results and discussion

Proteins of FgESP components identified in the non-infection group at 3, 10, and 16 wpi accounted for 80.5%, 84.3%, and 82.1% of all proteins identified in these three time points, respectively, indicating surroundings did not affect buffalo immune response during maintenance. Four hundred and ninety proteins were identified in the infection group, of which 87 were consistently identified at 7 time points. Following GO analysis showed that most of these 87 proteins were in biological processes, while KEGG analysis showed they mainly functioned in metabolism and cellular processing, some of which were thought to functions throughout the infection process. The numbers of specific interactors identified for each week were 1 (n = 12), 3 (n = 5), 6 (n = 8), 8 (n = 15), 10 (n = 23), 13 (n = 22), and 16 (n = 14) wpi, some of which were thought to functions in specific infection process. This study screened the antigenic targets in FgESP during a dense time course over a long period. These findings may enhance the understanding of molecular F. gigantica-buffalo interactions and help identify new potential vaccine and drug target candidates.

Liver function markers and haematological dynamics during acute and chronic phases of experimental Fasciola hepatica infection in cattle treated with triclabendazole

Fasciola hepatica, a worldwide-distributed liver fluke, is one of the causative agents of fasciolosis, a zoonotic disease that affects livestock and humans. In livestock, fasciolosis causes huge economic losses worldwide, reducing animal fertility, milk production, weight gain and condemnation of livers. In spite of the availability of drugs, such as triclabendazole (TCZ), for the treatment of fasciolosis, they do not necessarily prevent liver damage or parasite reinfection and can eventually increase parasite resistance. The aim of this research was to relate the hepatic function, haematological parameters, leukocyte counts in circulation and parasite egg shedding during F. hepatica acute and chronic phases of infection in cattle as well as to determine how these parameters change with TCZ-treatment of chronically infected cattle. Our results show that increased levels of serum aspartate aminotransferase (AST) and gamma glutamyltransferase (GGT) were detected in early stages of the experimental infection. Moreover, high circulating eosinophil count and plateletcrit levels were correlated with fluke number in livers from infected cattle. On the other hand, although TCZ-treatment in the chronic phase of infection reduced parasite burden and damage in the liver, it was not able to completely avoid them. In conclusion, our work sheds light into the physiopathological mechanisms induced during fluke infection in cattle, revealing the complexity of the host response to the infection, together with the effects of TCZ-treatment in chronically infected animals.

Synergistic action of Viteselen with anti-Fasciola drug as a tool for improving fertility and hemato-biochemical biomarkers in Fasciola infected sheep

Fasciolosis causes public health problems and economic losses all over the world. The present study aimed to evaluate the synergistic action between Viteselen (anti-oxidant) and specific anti-Fasciola drug [Triclalbendazole (TCBZ)] for improving the body condition of F. gigantica naturally infected sheep with reference to some hematological and biochemical biomarkers in their sera. Animals were divided into five groups include G-1 as control non-infected animals, G-2 to G-5 are Fasciola naturally infected animals. G-2 are non-treated animals, G-3 treated with TCBZ, animals in G-4 were injected by Viteselen and those in G-5 were treated by both TCBZ and Viteselen. The results revealed a significant decrease in mean eggs in feces and F. gigantica circulating antigens (FCAg) in sera of TCBZ treated sheep after the 1st week post treatment. Complete disappearance of eggs from feces of drug treated groups was recorded at 21st d.p.t. While the value of FCAg decreased to negative at 14th d.p.t. The highest significant improvement (p < 0.05) in the estimated hematological parameters (RBCs, Hb and TLC), liver enzymes (AST and ALT), oxidative stress and anti-oxidant markers (TAC, MDA, SOD and GSH) and reproductive hormones (Progesterone and Estradiol) was recorded in animals in G-5 followed by G-3. While non-significant improvement was recorded in animals in G-4 in comparison with those in the control group. This improvement increased with increasing the time post treatment. In conclusion; using of Viteselen in association with specific anti-parasitic drug improved the general health parameters and reproductive performance of the investigated sheep.

Characterization of the Pathology, Biochemistry, and Immune Response in Kunming (KM) Mice Following Fasciola gigantica Infection

As a putative model of Fasciola gigantica infection, detailed data in Kunming (KM) mice infected with F. gigantica are lacking. In this study, KM mice were orally infected with 15 metacercaria for 8 weeks. Macroscopic and microscopic changes, serum biochemistry, cytokine responses, and changes in parasite-specific immunoglobulin G (IgG) antibody levels were monitored at 1, 3, 5, 7, and 8 weeks post-infection (wpi), respectively. The serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) increased after infection, while that of albumin (ALB) decreased, which was positively correlated with the degree of liver damage. Between 5 and 7 wpi, the mice showed symptoms of anemia and weight loss, possibly caused by the decrease of alkaline phosphatase (ALP). Moreover, the changing tendencies of the levels of globulin (GLB) and parasite-specific IgG antibody were similar, suggesting a potential correlation between GLB production and adaptive immune response in the host. Coordinated variations in interferon gamma (IFN-γ) and interleukin 4 (IL-4) indicated a mixed T helper 1 (Th1)/Th2 cellular immune response. Furthermore, the serum IgG antibody increased after infection and peaked at 5 wpi, and it was positively correlated with the average parasite burdens. The worms collected from mice were approximately 1 cm in length at 8 wpi, their digestive and reproductive systems were well developed, and no eggs were found in the uterus. To the best of our knowledge, this is the first report describing detailed histological, biochemical, and immunological indices in KM mice infected with F. gigantica, which provides basic information on KM mice against infection with F. gigantica.

Pathogenicity and virulence of the liver flukes Fasciola hepatica and Fasciola Gigantica that cause the zoonosis Fasciolosis

Fasciolosis caused by the liver flukes Fasciola hepatica and Fasciola gigantica is one of the most important neglected parasitic diseases of humans and animals. The ability of the parasites to infect and multiply in their intermediate snail hosts, and their adaptation to a wide variety of mammalian definitive hosts contribute to their high transmissibility and distribution. Within the mammalian host, the trauma caused by the immature flukes burrowing through the liver parenchyma is associated with most of the pathogenesis. Similarly, the feeding activity and the physical presence of large flukes in the bile ducts can lead to anemia, inflammation, obstruction and cholangitis. The high frequency of non-synonymous polymorphisms found in Fasciola spp. genes allows for adaptation and invasion of a broad range of hosts. This is also facilitated by parasite’s excretory-secretory (ES) molecules that mediate physiological changes that allows their establishment within the host. ES contains cathepsin peptidases that aid parasite invasion by degrading collagen and fibronectin. In the bile ducts, cathepsin-L is critical to hemoglobin digestion during feeding activities. Other molecules (peroxiredoxin, cathepsin-L and Kunitz-type inhibitor) stimulate a strong immune response polarized toward a Treg/Th2 phenotype that favors fluke’s survival. Helminth defense molecule, fatty acid binding proteins, Fasciola-specific glycans and miRNAs modulate host pro-inflammatory responses, while antioxidant scavenger enzymes work in an orchestrated way to deter host oxidant-mediated damage. Combining these strategies Fasciola spp. survive for decades within their mammalian host, where they reproduce and spread to become one of the most widespread zoonotic worm parasites in the world.

Antigen-specific response of CD4+ T cells and hepatic lymph node cells to Fasciola hepatica-derived molecules at the early and late stage of the infection in sheep

The immunomodulatory capacity of F. hepatica antigens is probably one of the main reasons for the development of a driven non-protective Th2 immune response. In this study, we analysed the cellular response of hepatic lymph node cells and CD4⁺ T cells in terms of proliferative response, efficiency of antigen presentation and cytokine production, to F. hepatica-derived molecules, at early and late stages of the infection. Thirty-one sheep were allocated into five groups and were slaughtered at 16 dpi and 23 wpi. In order to analyse antigen-specific response, the following F. hepatica recombinant molecules were used: rFhCL1, rFhCL2, rFhCL3, rFhCB1, rFhCB2, rFhCB3, rFhStf-1, rFhStf-2, rFhStf-3 and rFhKT1. A cell proliferation assay using hepatic lymph node cells and an antigen presentation cell assay using CD4⁺ T cells were performed. At 16 dpi, all molecules but rFhStf-2 and rFhKT1 elicited a significant cell proliferative response on hepatic lymph node cells of infected animals. At both early and late stage of the infection, antigen presentation of rFhCB3 and rFhCL2 resulted in higher stimulation index of CD4⁺ T cells which was IL-2 mediated, although no statistically significant when compared to uninfected animals. Significant cytokine production (IL-4, IL-10 and IFN-γ) was conditioned by the antigen-specific cell stimulation. No CD4⁺ T cell exhaustion was detected in infected sheep at the chronic stage of the infection. This study addressed antigen-specific response to F. hepatica-derived molecules that are involved in key aspects of the parasite survival within the host.

Current Status for Controlling the Overlooked Caprine Fasciolosis

The disease fasciolosis is caused by the liver flukes Fasciola hepatica and F. gigantica, which infect a wide range of mammals and production livestock, including goats. These flatworm parasites are globally distributed and predicted to cost the livestock industry a now conservative USD 3 billion per year in treatment and lowered on-farm productivity. Infection poses a risk to animal welfare and results in lowered fertility rates and reduced production yields of meat, milk and wool. This zoonotic disease is estimated to infect over 600 million animals and up to 2.4 million humans. Current and future control is threatened with the global emergence of flukes resistant to anthelmintics. Drug resistance calls for immediate on-farm parasite management to ensure treatments are effective and re-infection rates are kept low, while a sustainable long-term control method, such as a vaccine, is being developed. Despite the recent expansion of the goat industry, particularly in developing countries, there are limited studies on goat-focused vaccine control studies and the effectiveness of drug treatments. There is a requirement to collate caprine-specific fasciolosis knowledge. This review will present the current status of liver fluke caprine infections and potential control methods for application in goat farming.

Towards the comprehension of fasciolosis (re-)emergence: an integrative overview

The increasing distribution and prevalence of fasciolosis in both human and livestock are concerning. Here, we examine the various types of factors influencing fasciolosis transmission and burden and the interrelations that may exist between them. We present the arsenal of molecules, 'adjusting' capabilities and parasitic strategies of Fasciola to infect. Such features define the high adaptability of Fasciola species for parasitism that facilitate their transmission. We discuss current environmental perturbations (increase of livestock and land use, climate change, introduction of alien species and biodiversity loss) in relation to fasciolosis dynamics. As Fasciola infection is directly and ultimately linked to livestock management, living conditions and cultural habits, which are also changing under the pressure of globalization and climate change, the social component of transmission is also discussed. Lastly, we examine the implication of increasing scientific and political awareness in highlighting the current circulation of fasciolosis and boosting epidemiological surveys and novel diagnostic techniques. From a joint perspective, it becomes clear that factors weight differently at each place and moment, depending on the biological, environmental, social and political interrelating contexts. Therefore, the analyses of a disease as complex as fasciolosis should be as integrative as possible to dissect the realities featuring each epidemiological scenario. Such a comprehensive appraisal is presented in this review and constitutes its main asset to serve as a fresh integrative understanding of fasciolosis.

Goat γδ T cells

Goats are important food animals and are disseminated globally because of their high adaptability to varying environmental conditions and feeding regimes that provide them with a comparative advantage. Productivity is impacted by infectious diseases; this then contributes to societal poverty, food insecurity, and international trade restrictions. Since γδ T cells have been shown to have vital roles in immune responses in other mammals we reviewed the literature regarding what is known about their functions, distribution in tissues and organs and their responses to a variety of infections in goats. It has been shown that caprine γδ T cells produce interferon-γ and IL-17, are found in a variety of lymphoid and nonlymphoid tissues and constitute a significant population of blood mononuclear cells. Their representation in tissues and their functional responses may be altered concomitant with infection. This review summarizes caprine γδ T cell responses to Brucella melitensis, Fasciola hepatica, Mycobacterium avium paratuberculosis, caprine arthritis encephalitis virus (CAEV), and Schistosoma bovis in infected or vaccinated goats. Caprine γδ T cells have also been evaluated in goats infected with M. caprae, Ehrilichia ruminantium, Haemonchus contortus and peste des petits ruminants (PPR) virus but found to have an unknown or limited response or role in either protective immunity or immunopathogenesis in those cases.

Fasciola hepatica-Derived Molecules as Regulators of the Host Immune Response

Helminths (worms) are one of the most successful organisms in nature given their ability to infect millions of humans and animals worldwide. Their success can be attributed to their ability to modulate the host immune response for their own benefit by releasing excretory-secretory (ES) products. Accordingly, ES products have been lauded as a potential source of immunomodulators/biotherapeutics for an array of inflammatory diseases. However, there is a significant lack of knowledge regarding the specific interactions between these products and cells of the immune response. Many different compounds have been identified within the helminth "secretome," including antioxidants, proteases, mucin-like peptides, as well as helminth defense molecules (HDMs), each with unique influences on the host inflammatory response. HDMs are a conserved group of proteins initially discovered in the secretome of the liver fluke, Fasciola hepatica. HDMs interact with cell membranes without cytotoxic effects and do not exert antimicrobial activity, suggesting that these peptides evolved specifically for immunomodulatory purposes. A peptide generated from the HDM sequence, termed FhHDM-1, has shown extensive anti-inflammatory abilities in clinically relevant models of diseases such as diabetes, multiple sclerosis, asthma, and acute lung injury, offering hope for the development of a new class of therapeutics. In this review, the current knowledge of host immunomodulation by a range of F. hepatica ES products, particularly FhHDM-1, will be discussed. Immune regulators, including HDMs, have been identified from other helminths and will also be outlined to broaden our understanding of the variety of effects these potent molecules exert on immune cells.

Fasciola hepatica and Fasciola gigantica coexistence in domestic ruminants in Nigeria: application of a PCR-based tool

The distinction between Fasciola hepatica and Fasciola gigantica has been traditionally based on morphological criteria, although accurate recognition of the two flukes is usually difficult because of substantial variations in morphological features. The main aim of this study was to develop a PCR-based assay for discrimination between both species collected in sheep and cattle from Nigeria. A total of 47 animals, 33 cattle and 14 sheep, were sampled, and a single adult fluke was collected from each animal. DNA was extracted from flukes, and primers were designed based on mitochondrial DNA sequences to amplify a 304 bp fragment for the identification of F. hepatica and 752 bp for F. gigantica. PCR products from 12 flukes were sequenced for phylogenetic analysis. A total of 29 out of 47 flukes were identified as F. hepatica and 18 as F. gigantica. Within each host, the percentage of each fluke species was as follows: In cattle, 18/33 (54.5%) and 15/33 (45.5%) were F. hepatica and F. gigantica, respectively. In sheep, 11/14 (78.6%) were F. hepatica and 3/14 F. gigantica (21.4%). The phylogenetic analysis confirmed these results. Although the number of flukes collected in sheep was limited, it seems that F. hepatica is more prevalent in sheep than F. gigantica, whereas the percentage of each species was similar in cattle. This study confirms the presence of F. hepatica in Nigeria.

Linking murine resistance to secondary cystic echinococcosis with antibody responses targeting Echinococcus granulosus tegumental antigens

Successful establishment of a parasite infection depends partially on the host intrinsic susceptibility to the pathogen. In cystic echinococcosis (CE), a zoonotic disease caused by the cestode parasite Echinococcus granulosus, the infection outcome in the murine model of secondary CE varies according to the mouse strain used. In this regard, intrinsic differences in susceptibility to the infection were previously reported for Balb/c and C57Bl/6 mice, being C57Bl/6 animals less permissive to secondary CE. Induction of parasite-specific antibodies has been suggested to play relevant roles in such susceptibility/resistance phenomena. Here, we report an in deep comparison of antibody responses induced in both mouse strains. Firstly, only C57Bl/6 mice were shown to induce specific-antibodies with efficient anti-parasite activities during early secondary CE. Then, through ImmunoTEM and Serological Proteome Analysis (SERPA), an evaluation of specific antibody responses targeting parasite tegumental antigens was performed. Both strategies showed that infected C57Bl/6 mice -unlike Balb/c animals- narrowed their IgG recognition repertoire against tegumental antigens, targeting fewer but potentially more relevant parasite components. In this sense, tegumental antigens recognition between Balb/c and C57Bl/6 mice, either by natural and/or induced antibodies, was analyzed through SERPA and MALDI-TOF/TOF studies. A total of 13 differentially recognized proteins (DRPs) uniquely targeted by antibodies from C57Bl/6 mice were successfully identified, wherein a subset of 7 DRPs were only recognized by infection-induced antibodies, suggesting their potential as natural protective antigens. In this regard, immunoinformatic analyses showed that such DRPs exhibited higher numbers of possible T cell epitopes towards the H-2-IA^b haplotype, which is present in C57Bl/6 mice but absent in Balb/c animals. In summary, our results showed that the genetic predisposition to generate better T-dependent antibody responses against particular tegumental antigens might be a key factor influencing host susceptibility in the murine model of secondary CE.

Evasion of Host Immunity During Fasciola hepatica Infection

Fasciola hepatica, the common liver fluke, causes infection of livestock throughout temperate regions of the globe. This helminth parasite has an indirect lifecycle, relying on the presence of the mud snail to complete its transition from egg to definitive host (Beesley et al., Transbound Emerg Dis 65:199-216, 2017). Within the definitive host, the parasite excysts in the intestine forming a newly excysted juvenile (NEJ) and migrates via the peritoneal cavity to the liver. Disease resulting from infection can be acute or chronic depending on the host and the number of parasites present. Sheep may succumb to a fatal acute infection if the challenge of metacercariae is great enough. However, in cattle chronic disease is the most likely outcome with parasites surviving for long periods of time. Annual losses are estimated to be in the region of US$ 2000 million to the agricultural industry (Beesley et al., Transbound Emerg Dis 65:199-216, 2017). Management of the disease depends heavily on chemotherapy with triclabendazole being the drug of choice, consistent use for over 20 years has resulted in drug-resistant strains emerging worldwide (Beesley et al., Int J Parasitol 47:11-20, 2017). A more sustainable approach to control would be through vaccination and indeed a lead candidate has been identified, cathepsin L1. Despite these promising results the parasite continues to confound our own and host efforts to generate long-lasting and effective immunity. In this brief review we focus our attention on those mechanisms that the parasite utilises to circumvent the innate based defense mechanisms within the host.

Immunization with the recombinant myosin regulatory light chain (FhrMRLC) in Adjuplex® adjuvant elicits a Th1-biased immune response and a reduction of parasite burden in Fasciola hepatica infected rats

The aim of this study was to assess the immune response and the protective efficacy elicited by the vaccination with the recombinant Fasciola hepatica myosin regulatory light chain (FhrMRLC) in Adjuplex® adjuvant against the infection with F. hepatica in rats. Four groups of 15 animals each were used for the study, one group was immunized with the recombinant F. hepatica MRLC in Adjuplex® adjuvant and the other groups remained as adjuvant, positive and negative control groups. The parasitological study showed that a statistically significant reduction of 65.1% and 82.1% in fluke burden and fecal egg count, respectively, was detected in vaccinated animals. In addition, vaccination with FhrMRLC induced a well-defined humoral and cellular immune response characterized by a significant production of specific IgG and IL-2, IL-12, TNF-α and IFN-γ; which confirms the immunogenic capacity of the FhrMRLC.

Immunomodulatory effects of Moringa oleifera leaves aqueous extract in sheep naturally co-infected with Fasciola gigantica and Clostridium novyi

The current study was designed to evaluate the in vivo fasciolicidal activity of Moringa (M.) oleifera leaf aqueous extract oral administration as well as its antibacterial activity against Clostridium (C.) novyi in sheep naturally co-infected with fascioliasis and C. novyi. Sheep naturally infected with fascioliasis were divided into 3 groups, heavily infected treated group, lightly infected treated group and mixed infection control (non-treated) group. Treatment groups were orally administered M. oleifera leaves aqueous extract at a dose of 150 mg/kg every 48 h for 21 days. Animal body weights, fecal egg count, serum levels of anti-Fasciola IgG, cytokines (IL-2, IL-17, IL-10), and bacterial count of C. novyi were evaluated. The results showed that treatment with M. oleifera improved the body weight gain and decreased fecal egg count in lightly and heavily infected groups compared to the nontreated group with 100% reduction in egg count in lightly infected sheep. Furthermore, the treatment with M. oleifera significantly reduced the serum levels of IgG, IL-2, and IL-17. Interestingly, elevated levels of IL-10 were recorded in both heavily and lightly infected sheep. The treatment with Moringa extract significantly decreased the fecal bacterial count of C. novyi in both heavily and lightly infected groups. In conclusion, this study highlights the potential beneficial effects of M. oleifera leaf against Fasciola (F.) gigantica and C. novyi.

Identification of reference genes for real-time PCR cytokine gene expression studies in sheep experimentally infected with Fasciola hepatica

The aim of this study was to validate reference genes for gene normalisation using qRT-PCR in hepatic lymph nodes (HLN) and livers from sheep infected with Fasciola hepatica during early and late stages of infection. To this end, a comprehensive statistical approach (RefFinder) encompassing four different methods of analysis (geNorm, BestKeeper, ΔCt method and NormFinder) was used to validate ten candidate reference genes. Stability analysis of gene expression followed by pairwise variation (Vn/Vn + 1) analysis revealed that PGK1, HSP90AA1 and GYPC were the most stable reference genes and suitable for qRT-PCR normalisation in both HLN and liver tissues. These three genes were validated against FoxP3, IL-10, TGF-β, TNF-α and IL-1β genes in the HLN tissue of sheep vaccinated with Cathepsin L1 from F. hepatica and unvaccinated infected and uninfected controls during early stages of infection. In the liver, the three reference genes were validated against TNF-α and IL-1β during chronic stages of infection with F. hepatica and in uninfected controls. Our study is the first to evaluate and validate sheep reference genes in order to provide tools for monitoring cytokines in Fasciola hepatica infected sheep target organs. Our results present an approach to elucidate the role of different cytokines in F. hepatica vaccinated and infected sheep.

Fasciola and fasciolosis in ruminants in Europe: Identifying research needs

Fasciola hepatica is a trematode parasite with a global distribution, which is responsible for considerable disease and production losses in a range of food producing species. It is also identified by WHO as a re-emerging neglected tropical disease associated with endemic and epidemic outbreaks of disease in human populations. In Europe, F. hepatica is mostly associated with disease in sheep, cattle and goats. This study reviews the most recent advances in our understanding of the transmission, diagnosis, epidemiology and the economic impact of fasciolosis. We also focus on the impact of the spread of resistance to anthelmintics used to control F. hepatica and consider how vaccines might be developed and applied in the context of the immune-modulation driven by the parasite. Several major research gaps are identified which, when addressed, will contribute to providing focussed and where possible, bespoke, advice for farmers on how to integrate stock management and diagnosis with vaccination and/or targeted treatment to more effectively control the parasite in the face of increasing the prevalence of infection and spread of anthelmintic resistance that are likely to be exacerbated by climate change.

Dynamic expression of cytokine and transcription factor genes during experimental Fasciola gigantica infection in buffaloes

BACKGROUND

Determining the mechanisms involved in the immune-pathogenesis of the tropical liver fluke, Fasciola gigantica, is crucial to the development of any effective therapeutic intervention. Here, we examined the differential gene expression of cytokines and transcription factors in the liver of F. gigantica-infected buffaloes, over the course of infection.

METHODS

Water buffaloes (swamp type) were infected orally with 500 F. gigantica encysted metacercariae. Liver tissue samples were collected 3, 10, 28, 42, 70 and 98 days post-infection (dpi). Levels of gene expression of nine cytokines (IFN-γ, TGF-β, IL-1β, IL-4, IL-6, IL-10, IL-12B, IL-13 and IL-17A) and four transcription factors (T-bet, GATA-3, Foxp3 and ROR-γτ) were determined using quantitative real-time PCR (qRT-PCR). We evaluated any correlation between gene expression of these immune-regulatory factors and the severity of liver pathology.

RESULTS

Histopathological examination revealed that cellular infiltration, hemorrhage and fibrosis without calcification in the liver parenchyma of infected buffaloes, increased over the course of infection. This progressive pathology was attributed to dysregulated and excessive inflammatory responses induced by infection. The early infection phase (3-10 dpi) was marked by a generalized immunosuppression and elevated TGF-β expression in order to facilitate parasite colonization. A mixed Th1/Th2 immune response was dominant from 28 to 70 dpi, to promote parasite survival while minimizing host tissue damage. During late infection (98 dpi), the response was biased towards Th1/Treg in order to inhibit the host's Th2 protective response and promote chronic infection. Both IL-10 and IL-17A and the Th17/Treg balance, played key roles in mediating the inflammatory and immunoregulatory mechanisms in the liver during chronic fasciolosis.

CONCLUSIONS

Our data showed distinct CD4⁺ T helper (Th) polarization and cytokine dysregulation in response to F. gigantica infection in water buffaloes over the course of infection. Characterizing the temporal expression profiles for host immune genes during infection should provide important information for defining how F. gigantica adapts and survives in the liver of buffaloes and how host immune responses influence F. gigantica pathogenicity.

Time-Course Study of the Transcriptome of Peripheral Blood Mononuclear Cells (PBMCs) from Sheep Infected with Fasciola hepatica

Fasciola hepatica is a parasitic trematode that infects a wide range of mammalian hosts, including livestock and humans, in temperate and tropical regions globally. This trematode causes the disease fascioliasis, which consists of an acute phase (≤ 12 weeks) during which juvenile parasites migrate through the host liver tissues, and a chronic phase (> 12 weeks) following the establishment of adult parasites in the liver bile ducts. Few studies have explored the progression of the host response over the course of Fasciola infection in the same animals. In this study, we characterized transcriptomic changes in peripheral blood mononuclear cells (PBMCs) collected from sheep at three time points over the first eight weeks of infection relative to uninfected controls. In total, 183 and 76 genes were found to be differentially transcribed at two and eight weeks post-infection respectively. Functional and pathway analysis of differentially transcribed genes revealed changes related to T-cell activation that may underpin a Th2-biased immune response against this parasite. This first insight into the dynamics of host responses during the early stages of infection improves the understanding of the pathogenesis of acute fascioliasis, informs vaccine development and presents a set of PBMC markers with diagnostic potential.

Immune responses in rats and sheep induced by a DNA vaccine containing the phosphoglycerate kinase gene of Fasciola hepatica and liver fluke infection

Immune responses of rats and sheep following vaccination with cDNA encoding phosphoglycerate kinase of Fasciola hepatica (cDNA-FhPGK/pCMV) and F. hepatica infection were investigated in the present study. cDNA-FhPGK/pCMV vaccinated female Sprague-Dawley rats were better protected by vaccination than their male counterparts - 48% reduction in fluke burden for females and no protection for males when compared with appropriate infection control groups. Moreover, male rats developed marked leukocytosis during the study with higher neutrophil, eosinophil and monocyte responses than females. Additionally, dynamics of eosinophil and monocyte responses varied between sexes. Increased titres of anti-FhPGK IgG1 and IgG2a correlated with the protective effect of vaccination that was observed among female rats. In the case of male sheep, no differences in worm burdens and in the course of the immune response were observed following vaccination. Titres of specific antibodies detected were low, and cellular responses were not significant. Apparently, sheep immune responses induced by cDNA-FhPGK/pCMV vaccination are not effective at controlling F. hepatica infection. Poor immunogenicity of DNA vaccines in large animals is still a major obstacle of this technology that has to be overcome.

Current status of fasciolosis in Vietnam: an update and perspectives

Vietnam is recognized to be endemic for fasciolosis. However, most of the available publications have not been published in international journals. This review is based on national and international Vietnamese publications and highlights the current status of fasciolosis in Vietnam. It also provides some information available for neighbouring countries. Updated data on responsible species, distribution, transmission and control aspects are summarized. The central region of Vietnam is reported as being highly endemic for fasciolosis, with a high number of human patients (more than 20,000 in 2011). Fasciola gigantica is reported to be the main species in Vietnam. However, hybrids between F. gigantica and F. hepatica were identified. Both humans and animals are infected by the ingestion of raw vegetables and possibly contaminated drinking water. Three lymnaeid snail species (Austropeplea viridis, Radix auricularia and Radix rubiginosa) may act as intermediate hosts of Fasciola spp. However, due to the likely misidentification of snail species and cercariae during the past decade the critical analysis of published data is difficult. A better understanding of transmission aspects of fasciolosis would allow the implementation of preventive measures of this important neglected zoonotic disease.

Activity of cholinesterases, pyruvate kinase and adenosine deaminase in rats experimentally infected by Fasciola hepatica: Influences of these enzymes on inflammatory response and pathological findings

The aim of this study was to investigate acetylcholinesterase (AChE) in total blood and liver tissue; butyrylcholinesterase (BChE) in serum and liver tissue; adenosine deaminase (ADA) in serum and liver tissue; and pyruvate kinase (PK) in liver tissue of rats experimentally infected by Fasciola hepatica. Animals were divided into two groups with 12 animals each, as follows: group A (uninfected) and group B (infected). Samples were collected at 20 (A1 and B1;n=6 each) and 150 (A2 and B2; n=6 each) days post-infection (PI). Infected animals showed an increase in AChE activity in whole blood and a decrease in AChE activity in liver homogenates (P<0.05) at 20 and 150 days PI. BChE and PK activities were decreased (P<0.05) in serum and liver homogenates of infected animals at 150 days PI. ADA activity was decreased in serum at 20 and 150 days PI, while in liver homogenates it was only decreased at 150 days PI (P<0.05). Aspartate aminotransferase and alanine aminotransferase activities in serum were increased (P<0.05), while concentrations of total protein and albumin were decreased (P<0.05) when compared to control. The histological analysis revealed fibrous perihepatitis and necrosis. Therefore, we conclude that the liver fluke is associated with cholinergic and purinergic dysfunctions, which in turn may influence the pathogenesis of the disease.

Influence of levamisole and Freund's adjuvant on mouse immunisation with antigens of adults of the liver fluke Fasciola hepatica Linnaeus, 1758

We have studied the influence of both levamisole (AL) and Freund's adjuvant (AF) on the immunisation of mice with the secretory antigens of adults of the liver fluke Fasciola hepatica Linnaeus, 1758. Total IgG antibodies were detected in all groups where the F. hepatica antigen was administered, been levels of IgG1 increased respect to IgG2a antibodies. During immunisation, IL-4 and IFN-γ were only detected in AL and AF groups, but after infection, IL-4 boosted in all groups. IFN-γ increased two fold in AF and AL groups compared to the saline solution (AS) group. Worm recovering was of 32-35% in groups administered without antigen whereas in AS, AL and AF groups recovering was of 25%, 12% and 8%, respectively. Macroscopical lesions in the liver were scarce in AL and AF groups. Our data suggest that immunisation of mice with antigens of F. hepatica enhances the immune response avoiding both liver damage and worm establishment after challenge infection. The murine model of fasciolosis has appeared to be useful to elucidate the mechanism by which the parasite modulates immune responses toward a Th2 type but also the development of Th1 type-inducing vaccines.

Hematological, biochemical and pathological findings in goats naturally infection with Cysticercus tenuicollis

In Iran, Cysticercus tenuicollis, the metacestode stage of Taenia hydatigena is endemic. The migration of this parasite causes traumatic hepatitis and death in young animals. The objective of this work was to evaluate hematological, biochemical and pathological findings in 50 goats infected with C. tenuicollis in comparison with 50 non-infected goats, as control group. This study was carried out as case-control. Blood and liver samples were taken from the goats, analyzed for hematology and biochemical parameters and liver samples were prepared for paraffin blocks, sectioning and staining for further microscopic study in pathology laboratory. Significant decrease in red blood cell count, hemoglobin, packed cell volume and total protein (P < 0.05) and significant increase in white blood cell count, aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase were observed in infected goats (P < 0.05), compared with those in non-infected control group. The microscopic lesion in liver included large concentric foci of hemorrhage in migration stage and decreased number of hepatocytes, dilation of sinusoids, presence of inflammatory cells in portal areas and double layered parasitic cyst formation in chronic stages. In conclusion, various changes in parameters could have deleterious effect on morbidity and mortality of the herd.

Update on trematode infections in sheep

Trematode parasites live in the liver, fore stomachs or blood vessels of a wide range of animals and humans. Most of them have a special economic and veterinary significance. Liver fluke disease of sheep and other animal species is caused by the common liver fluke Fasciola hepatica. Hepatic fasciolosis occurs throughout the world, where climatic conditions are suitable for the survival of aquatic intermediate host snails. Also of importance for ruminants, in some parts of the world, are Fasciola gigantica and Fascioloides magna. Other trematodes infecting ruminants include Dicrocoelium dendriticum; Eurytrema pancreaticum and Eurytrema coelomaticum. Among the Paramphistomidae, some species can infect sheep and other ruminants. Finally, Schistosoma spp. are found in the blood vessels of ruminants and are of minor importance in temperate regions. The manuscript concentrates on trematode species of veterinary importance for domestic sheep.

Evaluation of local immune response to Fasciola hepatica experimental infection in the liver and hepatic lymph nodes of goats immunized with Sm14 vaccine antigen

Protection against Fasciola hepatica in goats immunized with a synthetic recombinant antigen from Schistosoma mansoni fatty acid-binding protein 14 (rSm14) was investigated by assessing worm burdens, serum levels of hepatic enzymes, faecal egg count and hepatic damage, which was evaluated using gross and microscopic morphometric observation. The nature of the local immune response was assessed by examining the distribution of CD2+, CD4+, CD8+ and γ´+ T lymphocytes along with IgG+, IL-4+ and IFN-γ+ cells in the liver and hepatic lymph nodes (HLN). The goats used consisted of group 1 (unimmunized and uninfected), group 2 [infected control - immunized with Quillaia A (Quil A)] and group 3 (immunized with rSm14 in Quil A and infected), each containing seven animals. Immunization with rSm14 in Quil A adjuvant induced a reduction in gross hepatic lesions of 56.6% (p < 0.001) and reduced hepatic and HLN infiltration of CD2+, CD4+, CD8+ and γ´+ T lymphocytes as well as IL-4+ and IFN-γ+ cells (p < 0.05). This is the first report of caprine immunization against F. hepatica using a complete rSm14 molecule derived from S. mansoni. Immunization reduced hepatic damage and local inflammatory infiltration into the liver and HLN. However, considering that Quil A is not the preferential/first choice adjuvant for Sm14 immunization, further studies will be undertaken using the monophosphoryl lipid A-based family of adjuvants during clinical trials to facilitate anti-Fasciolavaccine development.

Innate and adaptive resistance of Indonesian Thin Tail sheep to liver fluke: a comparative analysis of Fasciola gigantica and Fasciola hepatica infection

In the current study, three independent trials directly compared Fasciola gigantica and Fasciola hepatica infection of ITT sheep. In all trials, F. hepatica infection resulted in higher worm burden recoveries and greater physiological damage to ITT sheep. Developmental differences of the two Fasciola species were also observed during the first twelve weeks of a primary infection, where the migration and growth of F. hepatica was more rapid than F. gigantica. Various immunological blood parameters were measured and indicated similar kinetics in the humoral and cellular responses during the time course of infection with each Fasciola species. In contrast to F. hepatica infection, we demonstrate an innate and adaptive comparative ability of ITT sheep to resist the early stages of infection with F. gigantica infection. Unraveling the mechanisms leading to this differential resistance may potentially lead to new methods for the control of fasciolosis and other human liver flukes.

Evaluation of hepatic damage and local immune response in goats immunized with native glutathione S-transferase of Fasciola hepatica

Worm burden, hepatic damage and local cellular and humoral immune responses were assessed in goats immunized with glutathione-S-transferase and challenged with Fasciola hepatica. Infected but unimmunized and uninfected control groups were also studied. Hepatic damage was evaluated grossly and microscopically. Local immune response was evaluated by (1) microscopical examination of hepatic lymph nodes (HLNs); (2) analysis of the distribution of CD2(+), CD4(+), CD8(+), T-cell receptor gammadelta(+) lymphocytes and immunoglobulin (Ig) G(+) plasma cells; and (3) investigation of the distribution of cells expressing interleukin (IL)-4 and interferon (IFN)-gamma in the hepatic inflammatory infiltrates and HLNs. Immunized animals did not have significant reduction in fluke number, but there was significant (P<0.05) reduction of fluke size relative to the control groups. The lesions in the two infected groups were similar and consisted of fibrous perihepatitis and white tortuous tracts, mainly involving the left hepatic lobe. Microscopical lesions were similar in both infected groups and were typical of chronic fascioliosis. These included portal fibrosis, inflammatory infiltration with plasma cells, formation of lymphoid follicles, accumulation of haemosiderin-laden macrophages and granulomatous foci. Both infected groups had a marked local immune response characterized by infiltration of CD2(+), CD4(+) and CD8(+) T lymphocytes, and IgG(+) plasma cells in hepatic lesions and in HLNs. There was no expression of IL-4 or INF-gamma by cells in the hepatic inflammatory infiltrate, but expression of INF-gamma in HLNs was much lower than that of IL-4, suggesting an immune response dominated by T helper 2 cells.

Coordinating innate and adaptive immunity in Fasciola hepatica infection: implications for control

The helminth parasite Fasciola hepatica is responsible for major economic losses in agriculture throughout temperate regions of the globe. Control measures are heavily reliant on chemotherapy resulting in the emergence of drug resistant parasite populations. Novel control strategies based on vaccination ultimately require a deeper knowledge of host-parasite interactions. Herein we discuss recent advances in the understanding of the immune response to F. hepatica placing them in context with previous knowledge and developments from other model systems. Advances in RNAi and proteomics in the context of helminth research should make target identification and characterisation more rapid. In parallel, integration of these technologies with better immunological understanding will be crucial for future research into F. hepatica control measures.

Immunity against helminths: interactions with the host and the intercurrent infections

Helminth parasites are of considerable medical and economic importance. Studies of the immune response against helminths are of great interest in understanding interactions between the host immune system and parasites. Effector immune mechanisms against tissue-dwelling helminths and helminths localized in the lumen of organs, and their regulation, are reviewed. Helminth infections are characterized by an association of Th2-like and Treg responses. Worms are able to persist in the host and are mainly responsible for chronic infection despite a strong immune response developed by the parasitized host. Two types of protection against the parasite, namely, premune and partial immunities, have been described. Immune responses against helminths can also participate in pathogenesis. Th2/Treg-like immunomodulation allows the survival of both host and parasite by controlling immunopathologic disorders and parasite persistence. Consequences of the modified Th2-like responses on co-infection, vaccination, and inflammatory diseases are discussed.

Immune response of goats immunised with glutathione S-transferase and experimentally challenged with Fasciola hepatica

Glutathione S-transferase (FhGST) purified from Fasciola hepatica adult worms was used to immunise goats against F. hepatica in an experimental infection; the level of protection, in terms of fluke burden, faecal egg counts and hepatic damage was determined, as well as the humoral and cellular immune response elicited. Animals were allocated into three groups of six animals each: group 1 (immunised with FhGST and infected), group 2 (unimmunised and infected), and group 3 (unimmunised and uninfected). There was no significant reduction of fluke burden (9.3%) or faecal egg counts; hepatic damage was also similar in both infected groups. However, immunisation with FhGST induced the development of a well-defined immune response, characterized by the production of specific-FhGST antibodies as well as the appearance of circulating IL-4.

Study of the local immune response to Fasciola hepatica in the liver and hepatic lymph nodes of goats immunised with a peptide of the Sm14 antigen

The nature of the local immune response was assessed studying the distribution of CD2(+), CD4(+), CD8(+), gammadelta(+) T lymphocytes, IgM(+) B cells, IL-4(+) and IFN-gamma(+) cells in the liver and hepatic lymph nodes (HLN) of goats immunised with a synthetic peptide of the Sm14 antigen from Schistosoma mansoni and challenged with Fasciola hepatica. A morphometric study of HLN was also carried out in order to evaluate the hyperplasia of lymphoid follicles. Despite the decrease in fluke burdens found in the immunised group (45.9%) respect to the infected control group, this difference was not statistically significant due to the high individual variability. In liver, a significant increase of CD2(+), CD4(+), CD8(+), gammadelta(+) T lymphocytes was found in the infected groups respect to the uninfected control and in the infected control respect to the immunised group. HLN showed a significant enlargement due to the hyperplasia of lymphoid follicles and infiltration of CD2(+), CD4(+), CD8(+), gammadelta(+) T lymphocytes in both infected groups respect to the uninfected control, with no significant differences between the infected control and immunised group. IFN-gamma(+) lymphoid cells was absent or very occasional in HLN where the number of IL-4(+) cells was higher than that of IFN-gamma, suggesting a polarized Th2 response in immunised and in infected control group.

Host responses during experimental infection with Fasciola gigantica and Fasciola hepatica in Merino sheep II. Development of a predictive index for Fasciola gigantica worm burden

This study reports on the predictive relationship between serological, immunological and pathological responses following experimental inoculation with incremental doses of Fasciola gigantica in sheep. Fifty, 6-month-old, naive Merino wethers were allocated to one of 5 experimental groups, four of which received 50, 125, 225 and 400 metacercariae, respectively, whilst a 5th group acted as non-inoculated control. Strong individual correlations were observed between liver score, GLDH (glutamate dehydrogenase), GGT (gamma glutamyl transferase), CatL5 (cathepsin L5) antibody titre (IgG1, IgA), eosinophilia, and the total worm count or worm biomass. A combination of multiple indicator traits performed significantly better than any single indicator trait alone. The best predictive index accounted for up to 88% of observed worm burden (Wb) if information on inoculation dose was available. Without knowledge of inoculation dose, such as under field conditions, up to 67% of variation in worm burden could be predicted. In contrast, the best single predictor variable (liver damage score) accounted for up to 50% of worm burden, and in the absence of post-slaughter information, serum levels of anti-cathepsin IgA antibody titres accounted for 35% of predicted variation in worm burden. The utility of a predictive index under both field and experimental inoculation conditions is discussed.

Fasciola gigantica excretory-secretory products for immunodiagnosis and prevention of sheep fasciolosis

Excretory-secretory products (ESP) products of ex vivo Fasciola gigantica adult worms were used for immunodiagnosis of sheep experimental infection with F. gigantica and natural infection with Fasciola spp. by enzyme-linked immunosorbent assay (ELISA) and Western blotting. Specific IgG antibody binding to native or denatured ESP was detected as early as 2 weeks after experimental sheep infection with 100 or 200 metacercariae. No specific IgG antibody binding was displayed by sera obtained from 192 sheep considered to be Fasciola- and other parasite-free by microscopic examination of bile and feces. Additionally, sera from 200 apparently Fasciola-free sheep, yet infected with other parasites, were all negative. The data, thus, indicated that ESP-based ELISA reached nearly 100% sensitivity and specificity in immunodiagnosis of sheep fasciolosis. As expected, the ESP molecules were immunogenic in sheep eliciting interleukin-12p40 mRNA response and considerable amounts of antibodies, which were able to bind to the surface of newly excysted juvenile worms as judged by membrane indirect immunofluorescence, and mediate their attrition via antibody-dependent cell-mediated cytotoxicity. The ESP-induced cellular and humoral immune responses were associated with a modest reduction in worm count, yet with a highly significant (P<0.0001) decrease in size of recovered worms, thus suggesting that ESP immunization might be a safe and cost-effective strategy for reducing transmission of the infection.

Hematological and biochemical changes in organically farmed sheep naturally infected with Fasciola hepatica

A naturally occurring outbreak of fasciolosis in a group of 20 Merinolandschaf (German Merino) sheep was studied. Hematological and blood biochemical values in sheep spontaneously infected with liver fluke Fasciola hepatica were compared with equivalent values in 20 parasite-free sheep from organically farmed flock. Investigated animals were kept in outdoor system, on pastures covered with swamps, which remain flooded after rainy season. Significantly lower red blood cell (RBC) count, lymphocytes, hemoglobin (Hb), packed cell volume (PCV), mean corpuscular hemoglobin concentration (MCHC), aspartate aminotransferase (AST), blood urea nitrogen (BUN), creatinine, and albumin were recorded in sheep from the infected herd, whereas white blood cell (WBC) count, eosinophil, segmented and band neutrophil count, mean corpuscular volume (MCV), gamma-glutamyl transferase (GGT), concentrations of glucose, and globulins were significantly higher than in the parasite free herd. No significant correlation between the investigated blood parameters and the number of F. hepatica eggs in the feces was detected. This study shows that hematological and biochemical values can be useful in early diagnosis and prognosis of sheep fasciolosis.

Vaccines against the zoonotic trematodesSchistosoma japonicum,Fasciola hepaticaandFasciola gigantica

Schistosoma japonicum,Fasciola hepaticaandF. giganticaare digenetic trematodes and, therefore, possess similar life cycles. While schistosomiasis japonica has for a long time been recognised as a major disease of both humans and animals, infection with fasciolids has only been considered of relevance to animals. However, a number of recent reports indicate that fasciolosis is becoming a serious public health problem, especially in South America, Egypt and Iran (sporadic cases are also on the increase throughout Europe). Vaccines targeted at animals could play an important role in controlling these three diseases in animals and, by blocking transmission of infection, have a concurrent beneficial effect on disease in humans. Approaches towards identifying and producing vaccines against these parasites are similar and are discussed in this reveiw.

A case of human fasciolosis: discrepancy between egg size and genotype of Fasciola sp

In human fasciolosis, differential diagnosis of the causative flukes, Fasciola hepatica and Fasciola gigantica, is problematic. We report a rare case of human fasciolosis in which an adult worm was recovered from the bile duct of a Japanese man. Morphometric data of the worm were consistent with those of F. hepatica, whereas the size of eggs in the stool indicated infection with F. gigantica. Nucleotide sequences of ITS-1 and -2 and CO1 genes of the DNA extracted from the eggs revealed that the genotype was that of F. hepatica. These findings suggest that the size of eggs is not a suitable marker for species identification in human fasciolosis, especially in settings such as the East Asian region where different karyotypes and hybrid genotypes of F. hepatica and F. gigantica have been found.

Host responses during experimental infection with Fasciola gigantica or Fasciola hepatica in Merino sheep I. Comparative immunological and plasma biochemical changes during early infection

This study reports the early biochemical changes in plasma, comparative host-immune responses and parasite recovery data in Merino sheep during the first 10 weeks of infection with Fasciola gigantica and Fasciola hepatica. One group of sheep were uninfected, four groups of sheep received incremental challenge doses of F. gigantica metacercariae (50, 125, 225 and 400, respectively) and the sixth group was challenged with 250 F. hepatica metacercariae. At 10 weeks post infection (wpi), sheep challenged with F. hepatica showed the greatest fluke recovery (mean 119, range 84-166); a significantly higher biomass of parasites recovered (2.5-fold greater than the highest dose of F. gigantica); and a greater mean % parasite recovery (39.3%, range 27-55%) than any group challenged with F. gigantica. Within the groups dosed with F. gigantica a strong dose-dependent response was observed in both fluke recovery and fluke biomass with increasing dose of metacercariae. The mean % parasite recovery of F. gigantica infected groups 1-5 were 26, 23, 26 and 25%, respectively, suggesting a uniform viability of parasite establishment independent of infection dose. At 6 wpi, elevated levels of plasma GLDH were observed in the F. gigantica infected groups compared to the uninfected sheep (p<0.005) whereas the F. hepatica challenged group had four-fold higher levels of GLDH compared to the F. gigantica infected group (p<0.001). Elevated levels of GGT as an indicator of epithelial damage in the bile duct was only seen in the group challenged with F. hepatica at 10 wpi when it rose from below 100 IU/l to approximately 250 IU/l (p<0.0001) whereas no detectable increase in GGT was observed in any of the groups challenged with F. gigantica. The white blood cell response to F. hepatica infection was biphasic with the initial peak at 4 wpi and a second peak at 9 wpi, corresponding to the period of migration of juvenile fluke in the liver and the time when adult flukes are migrating into the bile duct, respectively. This biphasic response was also evident in the changes in the eosinophil counts and serum haemoglobin levels. There was a trend toward higher parasite-specific IgG2 titres in sheep infected with lower worm burdens, suggesting that higher F. gigantica or F. hepatica burdens suppress IgG2 responses. The findings of this study suggest that, in early infection in a permissive host, F. hepatica appears to be more pathogenic than F. gigantica because of its rapid increase in size and the speed of its progression through the migratory phases of its life cycle.