Identification of Fasciola spp. based on ITS-2 reveals the Fasciola gigantica infection in buffaloes in Nanning city, South China

The eukaryotic expression of SAP-2 shows higher sensitivity than the prokaryotic expressed SAP-2 protein in the detection of antibodies against bovine fasciolosis

Bovine fasciolosis, caused by Fasciola gigantica and Fasciola hepatica, represents a major economic burden to the livestock industry. Developing a reliable diagnostic antigen is crucial for advancing diagnostic kits for bovine fasciolosis, which could effectively mitigate these economic losses. FgSAP-2 has demonstrated​​​ considerable potential as a diagnostic antigen when expressed in prokaryotic systems. Computational analyses suggest that FgSAP-2 undergoes glycosylation, promoting the investigation of whether eukaryotic expression systems--capable of performing post-translational modifications--might enhance its antigenic properties and improve its suitability for diagnostic kit development. To explore this possibility, FgSAP-2 was expressed in Pichia pastoris (reFgSAP-2), purified and used to establish an indirect ELISA. The sensitivity, specificity, and stability of the ELISA were subsequently evaluated. Field serum samples from Guangxi were tested using the reFgSAP-2-based ELISA and compared to results from ELISAs employing prokaryotically expressed FgSAP-2 (rpFgSAP-2) and Excretory-Secretory Products (FgESP). The reFgSAP-2 ELISA exhibited positive detection at a serum dilution of 1:1600, with a coefficient of variation (CV) below 10 % in both intra-batch and inter-batch repeatability tests. Furthermore, no cross-reactivity was observed with sera positive for Schistosoma japonicum and Toxoplasma gondii. The positive detection rates of the reFgSAP-2-ELISA were comparable to those of the FgESP-ELISA, both surpassing the detection performance of the rpFgSAP-2-ELISA. CONCLUSION: An indirect ELISA detection method based on eukaryotically expressed FgSAP-2 was successfully developed, demonstrating high sensitivity, specificity, and repeatability. This approach shows promise for further development in the preparation of diagnostic kits.

Immune modulation of buffalo peripheral blood mononuclear cells by two asparaginyl endopeptidases from Fasciola gigantica

BACKGROUND

Fascioliasis is a zoonotic parasitic disease caused by Fasciola hepatica and Fasciola gigantica, which poses a serious threat to global public health and livestock farming. Fasciola gigantica secretes and excretes various components to manipulate the immune response, thereby enhancing its invasion, migration, and survival in vivo. However, the roles of specific components in immune modulation, such as asparagine endopeptidase, remain unknown.

METHODS

The transcriptional abundance of members of the asparagine endopeptidase family (also known as the legumain family) from F. gigantica was analyzed. Two highly transcribed asparagine endopeptidases in metacercariae, juveniles and adults were cloned, and their recombinant proteins-recombinant F. gigantica legumain (rFgLGMN-1) and (rFgLGMN-2)-were expressed in prokaryotic expression system. Their regulatory effects on buffalo peripheral blood mononuclear cells (PBMCs), including proliferation, migration, total nitric oxide (NO) production, cytokine secretion, and phagocytosis were explored in vitro.

RESULTS

Ten members of the legumain family were detected in F. gigantica, among of which FgLGMN-1 and FgLGMN-2 exhibited high transcription levels in juveniles and adults. The isolation of sequences indicated that FgLGMN-1 encodes 409 amino acids, while FgLGMN-2 encodes 403 amino acids. Both recombinant FgLGMN-1 (rFgLGMN-1) and rFgLGMN-2 were recognized by serum from buffaloes infected with F. gigantica. Both rFgLGMN-1 and rFgLGMN-2 inhibited the proliferation of PBMCs, and rFgLGMN-1 also inhibited the migration of PBMCs. While rFgLGMN-1 increased the production of total NO, rFgLGMN-2 decreased NO production. Both rFgLGMN-1 and rFgLGMN-2 increased the transcription of the cytokines interleukin-10 and transforming growth factor β. The effect of rFgLGMN-1 and rFgLGMN-2 on the phagocytosis of PBMCs varied depending on their concentrations.

CONCLUSIONS

rFgLGMN-1 and rFgLGMN-2 modulate several cellular and immunological functions of PBMCs, and exhibited distinct regulatory effects on these in vitro, which indicated that they may play roles in immune modulation and facilitate fluke development. However, due to uncertainties associated with in vitro experiments, further studies are necessary to elucidate the precise functions of these legumains.

Secondary infection of Fasciola gigantica in buffaloes shows a similar pattern of serum cytokine secretion as in primary infection

Background

As a natural host of Fasciola gigantica, buffalo is widely infected by F. gigantica. Its impact on buffalo production has caused great losses to the husbandry sector, and repeat infection is non-negligible. In buffaloes experimentally infected with F. gigantica, primary and secondary infection have yielded the same rate of fluke recovery, indicating a high susceptibility of buffalo to F. gigantica, which contributes to the high infection rate. Determining the immunological mechanism of susceptibility will deepen the understanding of the interaction between F. gigantica and buffalo. Here, we explored the immune response of buffaloes against primary and secondary F. gigantica infection, with a focus on cytokines' dynamics explored through serum cytokine detection.

Methods

Buffaloes were assigned to three groups: group A (noninfected, n = 4), group B (primary infection, n = 3), and group C (secondary infection, n = 3). Group B was infected via oral gavage with 250 viable F. gigantica metacercariae, and group C was infected twice with 250 metacercariae at an interval of 4 weeks. The second infection of group C was performed simultaneously with that of group B. Whole blood samples were collected pre-infection (0 weeks) and at 1-6, 10, and 12  weeks after that. The serum levels of seven cytokines (IFN-γ, IL-4, IL-5, IL-10, IL-13, TGF-β, and IL-17) were simultaneously determined using ELISA and further analyzed.

Results

In the present study, no significant changes in Th1-type cytokines production were detected in early infection, both in primary and secondary infections, while the Th2-type response was strongly induced. A comparison of primary and secondary infection showed no significant difference in the cytokine secretion, which may indicate that the re-infection at 4 weeks after primary infection could not induce a robust adaptive immune response. The full extent of interaction between buffalo and F. gigantica in re-infection requires further study.

Development of a colloidal gold immunochromatographic strip for the rapid detection of antibodies against Fasciola gigantica in buffalo

Background

Fasciola gigantica, a tropical liver fluke, infects buffalo in Asian and African countries, causing significant economic losses and posing public health threats. The diagnostic of buffalo fascioliasis caused by F. gigantica is vital in fascioliasis control and preventation. The 22nd gel filtration chromatography fraction of F. gigantica Excretory-Secretory Products (FgESP), namely Fasciola 22 (F22), which was used as a diagnostic antigen in indirect ELISA, has demonstrated great potential for fascioliasis diagnosing. In the absence of rapid diagnostic methods, the use of a colloidal gold immunochromatographic strip based on F22 was applied to detect F. gigantica infection in buffalo.

Methods

In the present study, the 22nd gel filtration chromatography fraction of FgESP (F22) was used as an antigen to establish the colloidal gold-based immunochromatographic strip (ICS). The nitrocellulose membrane was incubated with F22 at the test line (T line) and goat anti-mouse secondary antibody at the control line (C line). The mouse anti-buffalo secondary antibody 2G7 conjugated to colloidal gold particles was used as the detection system for line visualization. The strip was assembled and developed by optimizing reaction conditions. The sensitivity, specificity, stability, and early diagnostic value of the strip were evaluated employing buffalo-derived sera.

Results

An immunochromatographic strip for the rapid detection of antibodies against F. gigantica-FgICS was developed. The strip demonstrated high sensitivity and specificity. Sensitivity tests confirmed positive results even when the positive reference serum was diluted 4,096 times. Except for one Schistosoma japonicum-positive serum that tested positive via FgICS, specificity tests confirmed no cross-reactivity with other positive sera of Schistosoma japonicum and Babesia bovis. The strip remained stable after storage at 4°C for up to 3 months. In infected buffalo, antibodies could be detected as early as 14–21 days post-infection. The detection of 17 positive sera yielded an 82.4% positive rate via FgICS vs. a 100.0% positive rate via ELISA based on FgESP. For FgICS, the 95% confidence interval of sensitivity was 84.8–95.4%, while specificity was 4.2–14.7%.

Conclusion

The immunochromatographic strip FgICS developed in this study provides a simple and rapid method of F. gigantica antibody detection and infected buffalo monitoring in the field.

Effect of primary and secondary Fasciola gigantica infection on specific IgG responses, hepatic enzyme levels and weight gain in buffaloes

Buffaloes, as highly susceptible definitive hosts of Fasciola gigantica, suffer from a high infection rate of fasciolosis, which causes enormous economic losses. Repeat infection is responsible for this high rate; thus, elucidating the protective immunity mechanism in repeat infection is decisive in fasciolosis prevention. Herein, a secondary experimental infection model was established to preliminarily reveal the protective immunity that occurs in repeat infection. In brief, animals were assigned to three groups: group A (uninfected control), group B (primary infection) and group C (secondary infection). Buffaloes were autopsied 20 weeks post-infection for measurements of the recovered flukes and hepatic examination. In addition, the detection of specific antibody (IgG) responses to F. gigantica excretory-secretory product (FgESP) throughout the whole period and weight gain throughout the first 4 months as a percentage (%) of the starting weight were also determined. The serum hepatic enzyme gamma glutathione transferase (GGT) levels were monitored to assess hepatic damage throughout the study period. Infection establishment was compared between group B and group C. Similar specific IgG patterns were observed between group B and group C, and hepatic damage was more severe in group C than group B. Significant differences in weight gain as a percentage of the start weight were observed between group A and group B at the 3rd and 4th months postprimary infection, while significant differences were not observed between group A and group C or group B and group C. Our results suggest that challenge infection cannot induce resistance against F. gigantica in buffaloes, which is consistent with the protective immunity against Fasciola hepatica reinfection observed in sheep and goats.