Pathological, immunological and parasitological study of sheep vaccinated with the recombinant protein 14-3-3z and experimentally infected with Fasciola hepatica

Advancement in Diagnosis, Treatment, and Vaccines against Fasciola hepatica: A Comprehensive Review

In this review article, we aim to provide an overview of fasciolosis in ruminants. Diagnosis through new coprological methods (such as Flukefinder®, FLOTAC®, and Mini-FLOTAC®) remains the most suitable approach for farms. Regarding treatment, there is a scarcity of available drugs, and resistance to them has prompted new approaches (including drug combinations, enhanced metabolism, or the use of natural compounds) to address this issue. Additionally, several researchers have developed vaccines to control the disease, but their efficacy varies, and none are currently sufficient for commercial use. Further studies are needed to better understand all aspects discussed in this manuscript, with the goal of improving diagnosis, treatment, and disease control. It is important to note that this manuscript does not delve into in-depth knowledge of the discussed aspects; rather, it provides an overview of the different methodologies related to these three aspects of parasitic disease.

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.

Efficacy of flukicides against Fasciola hepatica and first report of triclabendazole resistance on German sheep farms

Fasciola hepatica infections lead to severe health problems and production losses in sheep farming, if not treated effectively. Triclabendazole has been used extensively over decades due to its unique efficacy range against all definitive hostfluke stages but published data about the susceptibility of F. hepatica to anthelmintics in Germany are lacking. This study aimed to identify current F. hepatica infections in German sheep flocks by coproscopic examinations and to evaluate the efficacy of anthelmintics with a focus on triclabendazole in a field study conducted from 2020 to 2022. Initial screening included 71 sheep farms, many of them with known history of fasciolosis. In this highly biased sample set, the frequency of F. hepatica infection at individual sheep and farm level were 12.8% and 35.2%, respectively. Additionally, eggs of Paramphistominae were found at frequencies of 4.8% and 15.5% at individual sheep and farm level, respectively. Due to low egg shedding intensity, faecal egg count reduction (FECR) tests could only be conducted on a few farms. The efficacy of triclabendazole was tested on 11 farms and albendazole on one farm, including 3-53 sheep/farm. Individual faecal samples were collected before and two weeks after treatment to evaluate the FECR using the sedimentation or FLUKEFINDER® or a modified FLUKEFINDER® method. On all farms a coproantigen reduction test was conducted in parallel. Lacking efficacy of triclabendazole even at double dosage was shown on one farm associated with a high number of animal losses due to acute fasciolosis. On this farm, the Fasciola miracidium development test was additionally performed, revealing a high in vitro ovicidal activity of albendazole while closantel was effective in vivo. On all other farms, sufficient efficacy of triclabendazole was observed. In conclusion, triclabendazole resistance appears not to be widespread on German sheep farms but, when present, can have serious effects on animal health.

Fasciola hepatica antioxidant and protease-inhibitor cocktail recombinant vaccines administered five times elicit potent and sustained immune responses in sheep but do not confer protection

Our laboratory's vaccine development strategy against the livestock parasite Fasciola hepatica centres around disrupting key biological processes by combining groups of antigens with similar/complementary functional actions into a single vaccine cocktail. In this study the focus was on antioxidant protein vaccines and a protease inhibitor vaccine aimed at disrupting the parasite's ability to defend against oxidative stress and protease-inhibitor balance, respectively. Two combinations of recombinantly expressed antioxidants were assessed, namely peroxiredoxin (rFhPrx), thioredoxin (rFhTrx) and thioredoxin-glutathione reductase (rFhTGR) (Group 1) and rFhPrx, rFhTrx, and two superoxide dismutases (rFhSOD1 and rFhSOD3) (Group 2). The protease inhibitor vaccine cocktail included representatives of each of the key secreted protease inhibitor families, namely a Kunitz-type inhibitor (rFhKT1), a serpin (rFhSrp1) and a stefin, (rFhStf1) (Group 3). The vaccine combinations were formulated in adjuvant Montanide 61VG administered at five timepoints; two before experimental challenge with 60 F. hepatica metacercariae and three after infection. The vaccine combinations did not reduce the liver fluke burden, and only Group 2 displayed a marginal reduction in egg viability (8.2%). Despite previous results showing an effect of liver fluke vaccines on overall weight gain in infected animals, no significant (P value >0.05) impact on weight gain was observed in this study. Antibodies were elicited against all the vaccine antigens within the cocktails and were maintained at high levels to the end of the trial, due to our strategy of continuing vaccine administration after infection. However, these responses were not boosted by the challenge F. hepatica infection. A comparative analysis with previous vaccine data using a protease inhibitor vaccine found no repeat of the promising outcomes associated with this vaccine, indicating that the addition of rFhSrp1 to the vaccine cocktail did not improve vaccine efficacy. Assessment of liver pathology across the two trials using a modified liver enzyme score (glutamate dehydrogenase to platelet ratio) at eight weeks post infection suggests an association with liver fluke burden above 45 flukes, which could be used to predict liver pathology in future trials. The results reported in this study highlight the ambiguousness in liver fluke vaccine development and the difficulty in obtaining consistent and repeatable protection. This work stresses the need for repetition of trials and the use of sufficiently sized groups to assess vaccine efficacy with adequate statistical power.

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.

Fasciolosis—An Increasing Challenge in the Sheep Industry

Simple Summary

Fasciolosis caused by Fasciola hepatica is a serious disease and a huge challenge in the sheep industry. The disease has several clinical manifestations including acute death, anemia, ill-thrift and loss of body condition. Climate change with milder temperatures and heavier rainfall will increase the risk of fasciolosis. Grazing management and treatment with flukicide are at present the only options to restrain F. hepatica infection. However, control possibilities are challenging, and resistance to flukicide drugs is increasing. Diagnostic improvements, targeted treatment and vaccines will hopefully increase animal health and welfare on fluke infested pastures in the future.

Abstract

The liver fluke Fasciola hepatica may cause severe infection in several mammalian species, including sheep and humans. Fasciolosis is a parasitic disease occurring worldwide in temperate climates and involves intermediate lymnaeid snails as vectors, in Europe the pond snail Galba truncatula in particular. In the sheep industry, the disease is a serious welfare and health problem. Fasciolosis is usually classified as acute, subacute or chronic according to the number and stage of flukes present in the liver, but with a considerable overlap. Acute disease, associated with a large number of migrating larvae, often results in sudden death due to acute and massive hemorrhage, while chronic fasciolosis is characterized by anemia, hypoalbuminaemia and weight loss. The management of fasciolosis is an increasing challenge in the sheep industry. Early diagnostic tests are limited. Protective immunity against liver flukes in sheep is low or lacking, and vaccines are not yet available. Treatment and control possibilities are challenging, and resistance to flukicide drugs is increasing. In addition, climate change with warmer and more humid weather will have a substantial effect on the establishment of both flukes and snails and will most likely increase the future distribution of F. hepatica.

Therapeutic efficacy of triclabendazole in comparison to combination of triclabendazole and levamisole in sheep naturally infected with Fasciola sp

Fascioliasis is an important parasitic disease which affects productivity of ruminants, and imposes significant economic losses. Benzimidazoles are effective in the treatment of fascioliasis; however, there are several reports on benzimidazoles resistant flukes. Combinational therapy is an approach to delay the emergence of resistant flukes. The present study aimed to compare the efficacy of triclabendazole (TBZ) and combination of triclabendazole and levamisole (TBZ + LVM) in the treatment of sheep naturally infected with Fasciola sp. For this purpose, 40 ewes infected with Fasciola sp. in three groups received TBZ, and TBZ + LVM, or remained untreated as CON. Fecal egg count (FEC), fecal egg count reduction (FECR), liver enzymes activity, albumin, globulin, and total protein levels were measured on day 0, 7, 14, and 28 post treatments. Obtained results showed that treatment with TBZ and TBZ + LVM resulted in significant reduction in FEC (P < 0.05), and FECR reached to values of higher than 90% on 28 day post treatment. The FEC for TBZ + LMV on day 7 and 14 were 12.25 ± 3.82 and 3.08 ± 1.03, respectively which was significantly lower in comparison to TBZ and CON (P < 0.05). Efficacy of TBZ + LMV was higher than TBZ on day 7 and 14 post treatment; however, no significant difference was observed on 28 day. The liver enzyme activities on days 7 and 14 were lower in the TBZ + LVM sheep in comparison to the TBZ and CON. Treatment with TBZ or TBZ + LVM resulted in an increase in albumin and a decrease in globulin. Over all, the present study clarified the importance of combinational therapy, and demonstrated that combination of TBZ + LVM resulted in higher efficacy and earlier improvement of liver conditions in sheep naturally infected with Fasciola sp.

A Partially Protective Vaccine for Fasciola hepatica Induced Degeneration of Adult Flukes Associated to a Severe Granulomatous Reaction in Sheep

Simple Summary

Fasciolosis is a parasitic disease of livestock causing important economic losses worldwide and it is also a zoonosis. Current therapy relies on the use of anthelmintic drugs, which is no longer sustainable due to the increase of anthelmintic resistance and the risk of drug residues in food. A deep understanding of the host-parasite interaction is required to develop protective vaccines for the control of fasciolosis. The aim of the present study is to evaluate the hepatic lesions in sheep vaccinated with a partly protective vaccine for F. hepatica, a non-protective vaccine and an infected control group. The protective vaccine showed less severe hepatic lesions than the infected control group. In addition, in the protective vaccine group dead flukes surrounded by a severe granulomatous inflammation were observed, which taken together with the lower fluke burden, suggests that the host response induced by the partially protective vaccine may have been involved in the death of adult flukes of F. hepatica. This is the first study reporting the presence of degenerated flukes associated to a severe granulomatous inflammation in bile ducts in a vaccine trial, a finding that would be useful for improving vaccine efficacy in future trials.

Abstract

Fasciolosis is an important economic disease of livestock. There is a global interest in the development of protective vaccines since current anthelmintic therapy is no longer sustainable. A better knowledge of the host-parasite interaction is needed for the design of effective vaccines. The present study evaluates the microscopical hepatic lesions in sheep immunized with a partially protective vaccine (VAC1), a non-protective vaccine (VAC2), and an infected control group (IC). The nature of granulomatous inflammation associated with degeneration of adult flukes found in the VAC1 group was characterized by immunohistochemistry. Hepatic lesions (fibrous perihepatitis, chronic tracts, bile duct hyperplasia, infiltration of eosinophils and lymphocytes and plasma cells) were significantly less severe in the VAC1 group than in the IC group. Dead adult flukes within bile ducts were observed only in the VAC1 group and were surrounded by a severe granulomatous inflammation composed by macrophages and multinucleate giant cells with a high expression of lysozyme, CD163 and S100 markers, and a low expression of CD68. Numerous CD3+ T lymphocytes and scarce infiltrate of FoxP3+ Treg and CD208+ dendritic cells were present. This is the first report describing degenerated flukes associated to a severe granulomatous inflammation in bile ducts in a F. hepatica vaccine trial.

Promising Technologies in the Field of Helminth Vaccines

Helminths contribute a larger global burden of disease than both malaria and tuberculosis. These eukaryotes have caused human infections since before our earliest recorded history (i.e.: earlier than 1200 B.C. for Schistosoma spp.). Despite the prevalence and importance of these infections, helminths are considered a neglected tropical disease for which there are no vaccines approved for human use. Similar to other parasites, helminths are complex organisms which employ a plethora of features such as: complex life cycles, chronic infections, and antigenic mimicry to name a few, making them difficult to target by conventional vaccine strategies. With novel vaccine strategies such as viral vectors and genetic elements, numerous constructs are being defined for a wide range of helminth parasites; however, it has yet to be discussed which of these approaches may be the most effective. With human trials being conducted, and a pipeline of potential anti-helminthic antigens, greater understanding of helminth vaccine-induced immunity is necessary for the development of potent vaccine platforms and their optimal design. This review outlines the conventional and the most promising approaches in clinical and preclinical helminth vaccinology.

Protective Immunity Against Neospora caninum Infection Induced by 14-3-3 Protein in Mice

Neospora caninum is an apicomplexan parasite that infects many mammals and remains a threatening disease worldwide because of the lack of effective drugs and vaccines. Our previous studies demonstrated that N. caninum 14-3-3 protein (Nc14-3-3), which is included in N. caninum extracellular vesicles (NEVs), can induce effective immune responses and stimulate cytokine expression in mouse peritoneal macrophages. However, whether Nc14-3-3 has a protective effect and its mechanisms are poorly understood. Here, we evaluated the immune responses and protective effects of Nc14-3-3 against exposure to 2 × 10⁷ Nc-1 tachyzoites. Antibody (IgG, IgGl, and IgG2a) levels and Th1-type (IFN-γ and IL-12) and Th2-type (IL-4 and IL-10) cytokines in mouse serum, survival rates, survival times, and parasite burdens were detected. In the present study, the immunostimulatory effect of Nc14-3-3 was confirmed, as it triggered Th1-type cytokine (IFN-γ and IL-12) production in mouse serum 2 weeks after the final immunization. Moreover, the immunization of C57BL/6 mice with Nc14-3-3 induced high IgG antibody levels and significant increases in CD8⁺ T lymphocytes in the spleens of mice, indicating that the cellular immune response was significantly stimulated. Mouse survival rates and times were significantly prolonged after immunization; the survival rates were 40% for Nc14-3-3 immunization and 60% for NEV immunization, while mice that received GST, PBS, or blank control all died at 13, 9, or 8 days, respectively, after intraperitoneal N. caninum challenge. In addition, qPCR analysis indicated that there was a reduced parasite burden and diminished pathological changes in the mice immunized with Nc14-3-3. Our data demonstrate that vaccination of mice with Nc14-3-3 elicits both cellular and humoral immune responses and provides partial protection against acute neosporosis. Thus, Nc14-3-3 could be an effective antigen candidate for vaccine development for neosporosis.

Efficacy of a multivalent vaccine against Fasciola hepatica infection in sheep

In this work we report the protection found in a vaccination trial performed in sheep with two different vaccines composed each one by a cocktail of antigens (rCL1, rPrx, rHDM and rLAP) formulated in two different adjuvants (Montanide ISA 61 VG (G1) and Alhydrogel®(G2)). The parameters of protection tested were fluke burden, faecal egg count and evaluation of hepatic lesions. In vaccinated group 1 we found a significant decrease in fluke burden in comparison to both unimmunised and infected control group (37.2%; p = 0.002) and to vaccinated group 2 (Alhydrogel®) (27.08%; p = 0.016). The lower fluke burden found in G1 was accompanied by a decrease in egg output of 28.71% in comparison with the infected control group. Additionally, gross hepatic lesions found in vaccine 1 group showed a significant decrease (p = 0.03) in comparison with unimmunised-infected group. The serological study showed the highest level for both IgG1 and IgG2 in animals from group 1. All these data support the hypothesis of protection found in vaccine 1 group.

Immunization with a Recombinant Protein of Trichinella britovi 14-3-3 Triggers an Immune Response but No Protection in Mice

14-3-3 proteins are present in all eukaryotic organisms and are ubiquitously expressed in a broad range of tissues and cellular compartments. They are regulatory adapter proteins that play key roles in a variety of signaling pathways, and have been proposed as suitable targets for the control and detection of certain parasites. Trichinella britovi is a widely-distributed parasitic nematode, transmitted through ingestion of meat products containing invasive larvae. The present study describes the cloning and expression of Tb14-3-3, and investigates the immunological and protective potential of the recombinant protein. Immunization of mice with rTb14-3-3 triggered an IgG response, and significant differences, in the profiles of secreted cytokines observed in vitro, between experimental groups. Nonetheless, neither specific antibodies, nor increased secretion of IFNγ, IL-4, and IL-10 cytokines, conferred greater protection against infection. No reduction in larval burden was observed during recovery at 48 dpi. Additionally, rTb14-3-3 was not recognized by sera from the infected control mice, except for one, suggesting some mismatch between native and recombinant Tb14-3-3 antigenic sites. Therefore, before 14-3-3 can be considered a potential tool for Trichinella detection and vaccination, more research regarding its target proteins, and actual specific function, is needed.

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.

Proteomic identification of galectin-11 and -14 ligands from Fasciola hepatica

Fasciola hepatica is a globally distributed zoonotic trematode that causes fasciolosis in livestock, wildlife, ruminants and humans. Fasciolosis causes a significant economic impact on the agricultural sector and affects human health. Due to the increasing prevalence of triclabendazole resistance in F. hepatica, alternative treatment methods are required. Many protein antigens have been trialled as vaccine candidates with low success, however, the tegument of F. hepatica is highly glycosylated and the parasite-derived glycoconjugate molecules have been identified as an important mediator in host-parasite interactions and as prime targets for the host immune system. Galectin-11 (LGALS-11) and galectin-14 (LGALS-14) are two ruminant-specific glycan-binding proteins, showing upregulation in the bile duct of sheep infected with F. hepatica, which are believed to mediate host-parasite interaction and innate immunity against internal parasites. For the first known time, this study presents the ligand profile of whole worm and tegument extracts of F. hepatica that interacted with immobilised LGALS-11 and LGALS-14. LGALS-14 interacted with a total of 255 F. hepatica proteins. The protein which had the greatest interaction was identified as an uncharacterised protein which contained a C-type lectin domain. Many of the other proteins identified were previously trialled vaccine candidates including glutathione S-transferase, paramyosin, cathepsin L, cathepsin B, fatty acid binding protein and leucine aminopeptidase. In comparison to LGALS-14, LGALS-11 interacted with only 49 F. hepatica proteins and it appears to have a much smaller number of binding partners in F. hepatica. This is, to our knowledge, the first time host-specific lectins have been used for the enrichment of F. hepatica glycoproteins and this study has identified a number of glycoproteins that play critical roles in host-parasite interactions which have the potential to be novel vaccine candidates.

Moderate protection is induced by a chimeric protein composed of leucine aminopeptidase and cathepsin L1 against Fasciola hepatica challenge in sheep

Leucine aminopeptidase (FhLAP) and cathepsin L1 (FhCL1) of Fasciola hepatica play a critical role in parasite feeding, migration through host tissue, and immune evasion. These antigens have been tested for immune protection as single components with variable degrees of success. The chimeric-protein approach could improve protection levels against fasciolosis. Previously, we reported the design and construction of a chimeric protein composed of antigenic sequences of FhLAP and FhCL1 of F. hepatica. The goal of the present study was to express and evaluate the immune-protective capacity of this chimeric protein (rFhLAP-CL1) in sheep. Animals were randomly allocated into five groups with five animals in each group. Groups 1, 2 and 3 were immunized twice with 100 μg, 200 μg and 400 μg of rFhLAP-CL1 emulsified with Quil A adjuvant, whereas groups 4 and 5 were the adjuvant control and infection control groups, respectively. The animals were then challenged with 200 metacercariae two weeks after the rFhLAP-CL1 booster. The fluke burden was reduced by 25.5%, 30.7% (p < 0.05) and 46.5% (p < 0.01) in sheep immunized with 100 μg, 200 μg and 400 μg of chimeric protein, respectively, in comparison to the infection control group. There was a reduction of 22.7% (p < 0.05) and 24.4% (p < 0.01) in fecal egg count in groups 2 and 3, respectively, compared to the infection control group. Sheep immunized with chimeric protein produced F. hepatica excretion-secretion product-specific total IgG antibody, which were increased after challenge. Moreover, the levels of rFhLAP-CL1-specific IgG1 and IgG2 isotypes in immunized sheep increased rapidly two weeks after the first immunization and were significantly more elevated than those of the control groups, indicating a mixed Th1/Th2 response. This is a preliminary evaluation of the chimeric protein rFhLAP-CL1 as a possible immunogen against F. hepatica infection in sheep.