The Detection of Circulating Antigen Glutathione S-Transferase in Sheep Infected with Fasciola hepatica with Double-Antibody Sandwich Signal Amplification Enzyme-Linked Immunosorbent Assay

Fasciolosis is a global zoonotic parasitic disease caused by F. hepatica infection that is particularly harmful to cattle and sheep. A biotin-streptavidin signal amplification ELISA (streptavidin-ELISA/SA-ELISA) based on circulating antigens can allow for the early detection of F. hepatica-infected animals and is suitable for batch detection. It is considered to be a better means of detecting F. hepatica infection than traditional detection methods. In this study, using the serum of sheep artificially infected with F. hepatica, the cDNA expression library of F. hepatica was screened, 17 immunodominant antigen genes of F. hepatica were obtained, and glutathione s-transferase (GST) was selected as the candidate detection antigen. Firstly, the GST cDNA sequence was amplified from F. hepatica, followed by the preparation of recombinant protein GST (rFhGST). Then, monoclonal and polyclonal antibodies against rFhGST were prepared using the GST protein. Afterward, the immunolocalization of the target protein in the worm was observed via confocal microscopy, and it was found that the GST protein was localized in the uterus, intestinal tract, and body surface of F. hepatica. Finally, a double-antibody sandwich SA-ELISA based on the detection of circulating antigens was established. There was no cross-reaction with positive sera infected with Dicrocoelium lanceatum (D. lanceatum), Haemonchus contortus (H. contortus), Neospora caninum (N. caninum), or Schistosoma japonicum (S. japonicum). Forty serum and fecal samples from the same batch of sheep in Nong'an County, Changchun City, Jilin Province, China were analyzed using the established detection method and fecal detection method. The positive rate of the SA-ELISA was 17.5%, and the positive rate of the fecal detection method was 15%. The detection results of this method were 100% consistent with commercial ELISA kits. A total of 152 sheep serum samples were tested in Nong'an County, Changchun City, Jilin Province, and the positive rate was 5.92%. This study laid the foundation for the development of serological detection preparations for F. hepatica infection based on the detection of circulating antigens.

Plasma lipopolysaccharide elevations in cattle associated with early-stage infection by Fasciola hepatica

Fasciolosis is an endemic zoonotic parasitic disease with significant impacts on human health and both animal health and production. Early post-infection impacts on the host remain unclear. The objective of this study was to determine the changes, if any, to levels of endotoxin in cattle plasma in response to early-stage infection with Fasciola hepatica. Thirty-six (36) commercial bred cattle were experimentally infected with approximately 400 viable metacercariae. Plasma lipopolysaccharide (endotoxin) levels were examined on 24 occasions from 0 h before infection to 336 h after infection using the Limulus Amoebocyte Lysate chromogenic end point assay and compared with that of six (6) uninfected control animals. Peak lipopolysaccharide levels in infected animals were reached at 52 h after infection and returned to pre-infection levels at time 144 h after infection. Infected animals had significantly elevated lipopolysaccharide levels between 24 and 120 h after infection when compared to uninfected animals. The mean change in endotoxin units (EU)/mL over time after infection was statistically significant in infected animals. Elevations of lipopolysaccharide occurred in all infected animals suggesting a possible repeatable and titratable endotoxemia conducive to therapeutic agent model development.

The global prevalence of human fascioliasis: a systematic review and meta-analysis

Background

Fascioliasis is a parasitic zoonosis that can infect humans and be a source of significant morbidity. The World Health Organization lists human fascioliasis as a neglected tropical disease, but the worldwide prevalence of fascioliasis data is unknown.

Objective

We aimed to estimate the global prevalence of human fascioliasis.

Data sources and methods

We performed a systematic review and prevalence meta-analysis. We used the following inclusion criteria: articles published in the English, Portuguese, or Spanish languages from December 1985 to October 2022 and studies assessing the prevalence of Fasciola in the general population with an appropriate diagnostic methodology, including longitudinal studies, prospective and retrospective cohorts, case series, and randomized clinical trials (RCTs). We excluded animal studies. Two reviewers independently reviewed the selected studies for methodological quality, performing critical standard measures from JBI SUMARI. A random-effects model was conducted of the summary extracted data on the prevalence proportions. We reported the estimates according to the GATHER statement.

Results

In all, 5617 studies were screened for eligibility. Fifty-five studies from 15 countries were selected, including 154,697 patients and 3987 cases. The meta-analysis revealed a pooled prevalence of 4.5% [95% confidence interval (CI): 3.1-6.1; I² = 99.4%; T² = 0.07]. The prevalence in South America, Africa, and Asia was 9.0%, 4.8%, and 2.0%, respectively. The highest prevalence was found in Bolivia (21%), Peru (11%), and Egypt (6%). Subgroup analysis showed higher prevalence estimates in children, in studies from South America, and when Fas2-enzyme-linked immunosorbent assay (ELISA) was used as a diagnostic method. A larger study sample size (p = 0.027) and an increase in female percentage (p = 0.043) correlated with a decrease in prevalence. Multiple meta-regression showed a higher prevalence for hyperendemic than hypoendemic (p = 0.002) or mesoendemic (p = 0.013) regions.

Conclusion

The estimated prevalence and projected disease burden of human fascioliasis are high. Study findings support that fascioliasis continues to be a globally neglected tropical disease. Strengthening epidemiological surveillance and implementing measures to control and treat fascioliasis is imperative in the most affected areas.

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.

Comparative analysis of the mitochondrial proteins reveals complex structural and functional relationships in Fasciola species

Mitochondria is a cellular source of energy, appears to play an essential role in dealing with cellular stress induced by environmental stimuli. The genetic diversity of mitochondrial genes involved in oxidative phosphorylation affecting the production of cellular energy and regional adaptation to various ecological (climatic) pressures affecting amino acid sequences (variants of protein). However, little is known about the combined effect of protein changes on cell-level metabolic alterations in simultaneous exposure to various environmental conditions, including mitochondrial dysfunction and oxidative stress induction. The present study was designed to address this issue by analyzing the mitochondrial proteins in Fasciola species including Cytochrome oxidase (COX1, COX2, COX3, and CYTB) and NADH dehydrogenase (ND1, ND2, ND3, ND4, ND5, and ND6). Mitochondrial proteins were used for detailed computational investigation, using available standard bioinformatics tools to exploit structural and functional relationships. These proteins in Fasciola hepatica, Fasciola gigentica, and Fasciola jacksoni were functionally annotated using public databases. The results showed that the protein of COX1 of F. hepatica, F. gigantica, and F. jacksoni consist of 510, 513, and 517 amino acids, respectively. The alignment of proteins showed that these proteins are conserved in the same regions at ten positions in COX and CYTB proteins while at twelve locations in NADH. Three-dimensional structure of COX, CYTB, and NADH proteins were compared and showed differences in additional conserved and binding sites in COX and CYTB proteins as compared to NADH in three species of Fasciola. These results based on the amino acid diversity pattern were used to identify sites in the enzyme and the variations in mitochondrial proteins among Fasciola species. Our study provides valuable information for future experimental studies, including identification of therapeutic, diagnostic, and immunoprophylactic interests with novel mitochondrial proteins.

Gene Silencing in the Liver Fluke Fasciola hepatica: RNA Interference

The chronic infection with the liver fluke of the genus Fasciola spp. is the most prevalent foodborne trematodiasis, affecting at least one-fourth of the world livestock grazing in areas where the parasite is present. Moreover, fascioliasis is considered a major zoonosis mainly in rural areas of central South America, Northern Africa, and Central Asia. Increasing evidences of resistance against triclabendazole may compromise its use as drug of choice; thus, novel control strategies are desperately needed. Functional genomic approaches play a key role in the validation and characterization of new targets for drug and vaccine development. So far, RNA interference has been the only gene silencing approach successfully employed in liver flukes of the genus Fasciola spp. Herein, we describe a detailed step-by-step protocol to perform gene silencing mediated by RNAi in Fasciola hepatica.

Distribution Status of Hybrid Types in Large Liver Flukes, Fasciola Species (Digenea: Fasciolidae), from Ruminants and Humans in Vietnam

The aim of this study is to delineate ‘admixed hybrid’ and ‘introgressive’ Fasciola genotypes present in the Fasciola population in Vietnam. Adult liver flukes collected from ruminants in 18 Provinces were morphologically sorted out by naked eyes for small (S), medium (M) and large (L) body shapes; and human samples (n=14) from patients. Nuclear ribosomal (rDNA) ITS1 and ITS2, and mitochondrial (mtDNA) nad1 markers were used for determination of their genetic status. Total 4,725 worm samples of ruminants were tentatively classified by their size: 6% (n=284) small (S)-, 13% (n=614) medium (M)-, and 81% (n=3,827) large (L)-forms. All the representative (n=120, as 40 each group) and 14 human specimens, possessed maternal mtDNA of only F. gigantica and none of F. hepatica. Paternally, all (100%) of the L-(n=40) and 77.5% (n=31) of the M-flukes had single F. gigantica rDNA indicating ‘pure’ F. gigantica. A majority (90%, n=36) of the S- and 15% (n=6) of the M-worms had single F. hepatica rDNA, indicating their introgressive; the rest (10%, n=4) of the S- and 7.5% (n=3) of the M-flukes had mixture of both F. gigantica and F. hepatica rDNAs, confirming their admixed hybrid genetic status. Fourteen human samples revealed 9 (64%) of pure F. gigantica, 3 (22%) of introgressive and 2 (14%) of admixed hybrid Fasciola spp. By the present study, it was confirmed that the small worms, which are morphologically identical with F. hepatica, are admixed and/or introgressive hybrids of Fasciola spp., and able to be the pathogens of human fascioliasis.

Anthelmintic efficacy of Moringa oleifera seed methanolic extract against Fasciola hepatica

The current study was carried out to assess in vitro and in vivo effects of Moringa oleifera seed methanolic extract on Fasciola hepatica to develop an alternative source of treatment. The in vitro ovicidal effect of M. oleifera seed extract on immature F. hepatica eggs has provided evidence of inhibitory activity on the vitality and hatchability of F. hepatica eggs. This inhibitory activity was concentration-dependent and also correlated strongly with the exposure time. In the in vivo trial, the oral administration of F. hepatica experimentally infected rabbits with doses of 150 mg/kg BW prepared extract per day for 3 consecutive days on the 63rd day post infection confirmed potent fasciolicide activity of the extract. A gradual decrease in fecal egg count (FEC) was detected from the 1st day post treatment until reaching 100% FEC reduction by the 7th day post treatment. No flukes could be found at post mortem examinations. Significant increments of serum total protein, globulin, the activities of ALT and AST, total cholesterol, triglycerides and urea were recorded during the period of infection, which were improved by treatment. Remarkable histopathological alterations were observed in the infected liver and gallbladder tissues which decreased clearly in the treated rabbits. This study proposes that the used extract has promising and potent fasciolicide activity.

PD-L2 negatively regulates Th1-mediated immunopathology during Fasciola hepatica infection

Macrophage plasticity is critical for controlling inflammation including those produced by helminth infections, where alternatively activated macrophages (AAM) are accumulated in tissues. AAM expressing the co-inhibitory molecule programmed death ligand 2 (PD-L2), which is capable of binding programmed death 1 (PD-1) expressed on activated T cells, have been demonstrated in different parasitic infections. However, the role of PD-L2 during F. hepatica infection has not yet been explored. We observed that F. hepatica infection or a F. hepatica total extract (TE) injection increased the expression of PD-L2 on peritoneal macrophages. In addition, the absence of PD-L2 expression correlated with an increase in susceptibility to F. hepatica infection, as evidenced by the shorter survival and increased liver damage observed in PD-L2 deficient (KO) mice. We assessed the contribution of the PD-L2 pathway to Th2 polarization during this infection, and found that the absence of PD-L2 caused a diminished Th2 type cytokine production by TE stimulated splenocytes from PD-L2 KO infected compared with WT mice. Besides, splenocytes and intrahepatic leukocytes from infected PD-L2 KO mice showed higher levels of IFN-γ than those from WT mice. Arginase expression and activity and IL-10 production were reduced in macrophages from PD-L2 KO mice compared to those from WT mice, revealing a strong correlation between PD-L2 expression and AAM polarization. Taken together, our data indicate that PD-L2 expression in macrophages is critical for AAM induction and the maintenance of an optimal balance between the Th1- and Th2-type immune responses to assure host survival during F. hepatica infection.

hepatica in South Africa and Zimbabwe

The aim of this study was to identify and determine the genetic diversity of Fasciola species in cattle from Zimbabwe, the KwaZulu-Natal and Mpumalanga provinces of South Africa and selected wildlife hosts from Zimbabwe. This was based on analysis of DNA sequences of the nuclear ribosomal internal transcribed spacer (ITS1 and 2) and mitochondrial cytochrome oxidase 1 (CO1) regions. The sample of 120 flukes was collected from livers of 57 cattle at 4 abattoirs in Zimbabwe and 47 cattle at 6 abattoirs in South Africa; it also included three alcohol-preserved duiker, antelope and eland samples from Zimbabwe. Aligned sequences (ITS 506 base pairs and CO1 381 base pairs) were analyzed by neighbour-joining, maximum parsimony and Bayesian inference methods. Phylogenetic trees revealed the presence of Fasciola gigantica in cattle from Zimbabwe and F. gigantica and Fasciola hepatica in the samples from South Africa. F. hepatica was more prevalent (64%) in South Africa than F. gigantica. In Zimbabwe, F. gigantica was present in 99% of the samples; F. hepatica was found in only one cattle sample, an antelope (Hippotragus niger) and a duiker (Sylvicapra grimmia). This is the first molecular confirmation of the identity Fasciola species in Zimbabwe and South Africa. Knowledge on the identity and distribution of these liver flukes at molecular level will allow disease surveillance and control in the studied areas.

Fasciola hepatica mucin-encoding gene: expression, variability and its potential relevance in host-parasite relationship

Fasciola hepatica is the causative agent of fasciolosis, a zoonosis with significant impact both in human and animal health. Understanding the basic processes of parasite biology, especially those related to interactions with its host, will contribute to control F. hepatica infections and hence liver pathology. Mucins have been described as important mediators for parasite establishment within its host, due to their key roles in immune evasion. In F. hepatica, mucin expression is upregulated in the mammalian invasive newly excysted juvenile (NEJ) stage in comparison with the adult stage. Here, we performed sequencing of mucin cDNAs prepared from NEJ RNA, resulting in six different cDNAs clusters. The differences are due to the presence of a tandem repeated sequence of 66 bp encoded by different exons. Two groups of apomucins one with three and the other with four repeats, with 459 and 393 bp respectively, were identified. These cDNAs have open reading frames encoding Ser-Thr enriched proteins with an N-terminal signal peptide, characteristic of apomucin backbone. We cloned a 4470 bp gene comprising eight exons and seven introns that encodes all the cDNA variants identified in NEJs. By real time polymerase chain reaction and high-resolution melting approaches of individual flukes we infer that fhemuc-1 is a single-copy gene, with at least two different alleles. Our data suggest that both gene polymorphism and alternative splicing might account for apomucin variability in the fhemuc-1 gene that is upregulated in NEJ invasive stage. The relevance of this variation in host-parasite interplay is discussed.

Triclabendazole Effect on Protease Enzyme Activity in the Excretory- Secretory Products of Fasciola hepatica in Vitro

BACKGROUND

Fasciola hepatica is one of the most important helminthes parasites and triclabendazole (TCBZ) is routinely used for treatment of infected people and animals. Secreted protease enzymes by the F. hepatica plays a critical role in the invasion, migration, nutrition and the survival of parasite and are key targets for novel drugs and vaccines. The aim of study was to determine the protease activity of excretory- secretory products (ESP) of F. hepatica in the presence of TCBZ anthelmintic.

METHODS

F. hepatica helminthes were collected and cultured within RPMI 1640 [TCBZ treated (test) and untreated (control)] for 6 h at 37 °C. ESP of treated and control were collected, centrifuged and supernatants were stored at -20°C. Protein concentrations were measured according to Bradford method. Protease enzymes activities of ESP samples were estimated by using sigma's non-specific protease activity assay. ESP protein bands were detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

Mean protein concentrations in control and treated of ESP samples were determined 196.1 ±14.52 and 376.4 ±28.20 μg/ml, respectively. Mean protease enzymes activities in control and treated were 0.37 ±0.1 and 0.089 ±0.03 U/ml, respectively. Significant difference between proteins concentrations and protease enzymes activities of two groups was observed (P<0.05). SDS-PAGE showed different patterns of protein bands between treated and control samples.

CONCLUSION

The TCBZ reduced secreted protease enzymes activities and possibly effects on invasion, migration, nutrition and particularly survival of the parasite in the host tissues.