Time-course analysis of antibody response by EITB and ELISA before and after chemotherapy in sheep infected with Fasciola gigantica

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.

Serodiagnosis of Fasciola gigantica Infection in Buffaloes with Native Cathepsin-L Proteases and Recombinant Cathepsin L1-D

AIM

Serodiagnosis of Fasciola gigantica natural infection in buffaloes with recombinant cathepsin L1-D and native cathepsin-L protease antigens.

METHODS

The recombinant cat L1-D antigen was expressed in prokaryotic expression system and native cathepsin-L proteases were purified by alcoholic fractionation from adult F. gigantica flukes. Buffaloes (n  = 325) were screened for anti-Fasciola antibodies with the above antigens in immunoglobulin-G-enzyme linked immunosorbent assay (IgG-ELISA).

RESULTS

The recombinant cat L1-D antigen showed positive reactivity with 101/122 necropsy positive animals but 21/122 necropsy confirmed positive animals were negative in this ELISA (sensitivity 82.8%). However, 30/203 (14.8%) necropsy negative animals for Fasciola were seropositive with specificity of 85.2%. With native cat-L protease, 104/122 necropsy confirmed positive animals were ELISA positive but 18/122 necropsy positive animals were seronegative, thereby depicting the sensitivity of 85.2%. But ELISA with this antigen showed 27/203 (13.3%) necropsy negative animals as positive (specificity 86.7%).

CONCLUSIONS

Comparative evaluation of both the antigens showed that they are suitable for serodiagnosis of F. gigantica infection in buffalo herds.

Development of a Nanobody-based lateral flow assay to detect active Trypanosoma congolense infections

Animal African trypanosomosis (AAT), a disease affecting livestock, is caused by parasites of the Trypanosoma genus (mainly T. vivax and T. congolense). AAT is widespread in Sub-Saharan Africa, where it continues to impose a heavy socio-economic burden as it renders development of sustainable livestock rearing very strenuous. Active case-finding and the identification of infected animals prior to initiation of drug treatment requires the availability of sensitive and specific diagnostic tests. In this paper, we describe the development of two heterologous sandwich assay formats (ELISA and LFA) for T. congolense detection through the use of Nanobodies (Nbs). The immunisation of an alpaca with a secretome mix from two T. congolense strains resulted in the identification of a Nb pair (Nb44/Nb42) that specifically targets the glycolytic enzyme pyruvate kinase. We demonstrate that the Nb44/Nb42 ELISA and LFA can be employed to detect parasitaemia in plasma samples from experimentally infected mice and cattle and, additionally, that they can serve as ‘test-of-cure’ tools. Altogether, the findings in this paper present the development and evaluation of the first Nb-based antigen detection LFA to identify active T. congolense infections.

Structural basis for the high specificity of a Trypanosoma congolense immunoassay targeting glycosomal aldolase

BACKGROUND

Animal African trypanosomosis (AAT) is a neglected tropical disease which imposes a heavy burden on the livestock industry in Sub-Saharan Africa. Its causative agents are Trypanosoma parasites, with T. congolense and T. vivax being responsible for the majority of the cases. Recently, we identified a Nanobody (Nb474) that was employed to develop a homologous sandwich ELISA targeting T. congolense fructose-1,6-bisphosphate aldolase (TcoALD). Despite the high sequence identity between trypanosomatid aldolases, the Nb474-based immunoassay is highly specific for T. congolense detection. The results presented in this paper yield insights into the molecular principles underlying the assay's high specificity.

METHODOLOGY/PRINCIPAL FINDINGS

The structure of the Nb474-TcoALD complex was determined via X-ray crystallography. Together with analytical gel filtration, the structure reveals that a single TcoALD tetramer contains four binding sites for Nb474. Through a comparison with the crystal structures of two other trypanosomatid aldolases, TcoALD residues Ala77 and Leu106 were identified as hot spots for specificity. Via ELISA and surface plasmon resonance (SPR), we demonstrate that mutation of these residues does not abolish TcoALD recognition by Nb474, but does lead to a lack of detection in the Nb474-based homologous sandwich immunoassay.

CONCLUSIONS/SIGNIFICANCE

The results show that the high specificity of the Nb474-based immunoassay is not determined by the initial recognition event between Nb474 and TcoALD, but rather by its homologous sandwich design. This (i) provides insights into the optimal set-up of the assay, (ii) may be of great significance for field applications as it could explain the potential detection escape of certain T. congolense strains, and (iii) may be of general interest to those developing similar assays.

Expression, purification and in vitro refolding of the recombinant truncated Saposin-like protein 2 antigen for development of diagnosis of human fascioliasis

Early diagnosis of fascioliasis is critical in prevention of injury to the liver and bile ducts. Saposin-like protein (FhSAP-2) is probably the most ideal antigen of Fasciola hepatica for development of ELISA kits. SAP-2 has a conserved tertiary structure containing three disulfide bonds and conformational epitopes. Therefore, antigenicity of SAP-2 is greatly depends on disulfide bond formation and proper folding. We produced the recombinant truncated SAP-2 (rtSAP-2) in the SHuffle^® T7 and Rosetta strain of Escherichia coli, in soluble and insoluble forms, respectively and purified by immobilized metal affinity chromatography (IMAC). The refolding process of denatured rtSAP-2 was performed using dialysis and dilution methods in the presence of chemical additives, along with reduced/oxidized glutathione (in vitro). Physicochemical studies, including non-reducing gel electrophoresis, Ellman's assay, Western blotting and ELISA showed the most antigenicity and likely correct folding of rtSAP-2, which was obtained by dialysis method. An IgG ELISA test was developed using rtSAP-2 refolded by dialysis and compared with excretory/secretory products of parasite with 52 positive fascioliasis samples, 79 other parasitic samples and 70 negative controls samples. The results exhibited 100% sensitivity and 98% specificity for rtSAP-2, also, 100% and 95.3% for excretory/secretory (E/S) antigen, respectively. In conclusion, it is suggested that rtSAP-2 with the correct folding could be used as a candidate antigen for detection of human fascioliasis.

Serologic detection of antibodies against Fasciola hepatica in sheep in the middle Black Sea region of Turkey

BACKGROUND/PURPOSE

The aim of the present study was to estimate the prevalence of Fasciola hepatica infection in sheep in the Black Sea region of Turkey.

METHODS

Samples from 213 sheep were collected randomly in Samsun, Tokat, and Sinop from September 2005 to January 2007 and tested by indirect enzyme-linked immunosorbent assay (ELISA) and Western blot analysis using F. hepatica excretory-secretory (E/S) antigens.

RESULTS

The distribution of ELISA-positive samples for F. hepatica infections out of a total of 213 sheep serum samples was 23/71 (32.4%), 15/59 (25.4%), and 29/83 (34.9%) in Samsun, Sinop, and Tokat, respectively. The immunodominant proteins were determined by Western blot analysis using molecular weight markers of 14 kDa, 20 kDa, 24 kDa, 27 kDa, 33 kDa, 45 kDa, and 66 kDa and extracted from sera of sheep that were positive for Fasciola spp. eggs and also hyperimmune sera from rabbits immunized with E/S antigens.

CONCLUSION

The ELISA-positive results were confirmed by Western blot analysis. As a result, seroprevalence of F. hepatica infection was found in 31.4% of sheep from the Karayaka breed in the Middle Black sea region of Turkey.

An Anti-proteome Nanobody Library Approach Yields a Specific Immunoassay for Trypanosoma congolense Diagnosis Targeting Glycosomal Aldolase

BACKGROUND

Infectious diseases pose a severe worldwide threat to human and livestock health. While early diagnosis could enable prompt preventive interventions, the majority of diseases are found in rural settings where basic laboratory facilities are scarce. Under such field conditions, point-of-care immunoassays provide an appropriate solution for rapid and reliable diagnosis. The limiting steps in the development of the assay are the identification of a suitable target antigen and the selection of appropriate high affinity capture and detection antibodies. To meet these challenges, we describe the development of a Nanobody (Nb)-based antigen detection assay generated from a Nb library directed against the soluble proteome of an infectious agent. In this study, Trypanosoma congolense was chosen as a model system.

METHODOLOGY/PRINCIPAL FINDINGS

An alpaca was vaccinated with whole-parasite soluble proteome to generate a Nb library from which the most potent T. congolense specific Nb sandwich immunoassay (Nb474H-Nb474B) was selected. First, the Nb474-homologous sandwich ELISA (Nb474-ELISA) was shown to detect experimental infections with high Positive Predictive Value (98%), Sensitivity (87%) and Specificity (94%). Second, it was demonstrated under experimental conditions that the assay serves as test-of-cure after Berenil treatment. Finally, this assay allowed target antigen identification. The latter was independently purified through immuno-capturing from (i) T. congolense soluble proteome, (ii) T. congolense secretome preparation and (iii) sera of T. congolense infected mice. Subsequent mass spectrometry analysis identified the target as T. congolense glycosomal aldolase.

CONCLUSIONS/SIGNIFICANCE

The results show that glycosomal aldolase is a candidate biomarker for active T. congolense infections. In addition, and by proof-of-principle, the data demonstrate that the Nb strategy devised here offers a unique approach to both diagnostic development and target discovery that could be widely applied to other infectious diseases.

Evaluation of antibody response to various developmental stage specific somatic antigens of Paramphistomum epiclitum in goats

Electrophoretic analysis of various developmental stage specific somatic antigens of Paramphistomum epiclitum (Digenea: Paramphistomidae), namely, metacercariae (McAg), immature intestinal flukes (ImIAg), immature ruminal flukes (ImRAg), and adult flukes (AAg), was done by native polyacrylamide gel electrophoresis. Result revealed presence of 3 (range 15.2-40.3 kDa), 13 (9.3-121.2 kDa), 14 (9.3-169.3 kDa), and 15 (8.0-169.3 kDa) polypeptides in McAg, ImIAg, ImRAg, and AAg, respectively. With an aim to identify a suitable immunodiagnostic antigen for early diagnosis of amphistomosis, the IgG antibody response to various developmental stage antigens in goats experimentally infected with metacercariae of P. epiclitum was evaluated by ELISA. The highest OD values were recorded with ImIAg which ranged between 0.23 and 0.55 with a significant increase from the 2nd week till 8th week of infection with a peak at 6th week. The analysis of statistical significance using a one-way analysis of variance with multiple pair wise comparisons revealed that IgG response was significantly higher with all antigens (P < 0.01) except McAg (P > 0.05) with a maximum mean difference of 0.1838 in comparison to control with ImIAg, thus, indicating that ImIAg which could be further exploited for its potential is a candidate for immunodiagnostic antigen for early diagnosis of amphistomosis.

The global burden of fasciolosis in domestic animals with an outlook on the contribution of new approaches for diagnosis and control

Fasciolosis is an economically important disease for livestock, as well as being zoonotic. Recent figures on the prevalence of this disease have caused alarm concerning its potential for an increased prevalence in the future. The prevalence of fascioliosis has been documented from different regions of the world, helping us identify areas where future research needs to be focused. This manuscript is a review of the current status of the disease, the pathogenic species involved, diagnostic techniques (with new modifications and comparative specificity, sensitivity, and rapidity of these tests), chemotherapy, and vaccination. This also encompasses inaccurate reports on vaccination and drug development as well as the latest technologies to find promising candidates for drugs and vaccines. Drugs with lower efficacy have been used on some farms which lead to exacerbation of the clinical disease, presumably due to the development of drug resistance. Future studies should be focused on (1) the use of the most reliable diagnostic tests for periodic monitoring of the disease, (2) insights of the ecobiology and transmission dynamics of the snail intermediate host and the best possible methods of their control, (3) in vitro and in vivo testing of chemotherapeutic compounds using sensitive methods, and (4) the identification of novel drug and vaccine candidates using modern molecular markers. This approach may help increase the reliability of chemotherapeutic agents and control nuisance, ultimately reducing the economic losses attributable to the livestock industry around the world.

Antigenic components, isolation and partial characterization of excretion-secretion fraction of Paramphistomum cervi

The immunogenic components of adult Paramphistomum cervi excretion-secretion (ES) fraction were revealed by SDS-PAGE and immunoblotting technique using sera from cattle naturally infected with P. cervi, Fasciola gigantica, strongylids, Trichuris sp., and Strongyloides sp. By SDS-PAGE, it was found that the ES fraction comprised 13 distinct protein bands. Immunoblotting analysis of these proteins exhibited nine prominent antigenic bands which were recognized by paramphistomosis antisera. These antigenic proteins had molecular weights ranging from 10-170 kDa. One antigenic protein band of 40 kDa was found to give a consistent reaction with sera from all infected cattle. Its diagnostic sensitivity, specificity and accuracy using this test were 100%, 98.9% and 99.3%, respectively. The positive and negative predictive values were 98% and 100%, respectively. The 40 kDa antigen was partially purified by gel filtration and ion-exchange chromatography. The antigenicity of 40 kDa protein for diagnosis of P. cervi infection was confirmed by immunoblotting and indirect ELISA (at 1:78,125 dilution) using a pool of sera and individual serum samples from infected cattle. The present findings suggest that the 40 kDa protein may be used as a diagnostic antigen for paramphistomosis.

Studies on the viability of metacercariae of Fasciola gigantica

The viability of metacercariae of Fasciola gigantica was tested by in vitro and in vivo methods. In vitro testing was based upon the motility of juvenile flukes within the inner cyst as examined under the light microscope. In vivo testing was undertaken through experimental infections of rabbits (two groups) and natural definitive hosts, lambs (one group). In the first group, out of six rabbits each given 25 metacercariae, worm establishment only took place in one rabbit with a single fluke recovery on 60 days post infection. In the second group of six rabbits each given 200 metacercariae, five were infected, with two or three flukes per host. All the lambs given 250 metacercariae became infected showing prevalences of 7.2–40% in comparison with rabbits in which low prevalences (0–4%) were recorded. The results indicated that even viable metacercariae which were already tested in vitro could not readily establish in rabbits. Such variability in worm establishment suggests that immunological and chemotherapeutic studies in rabbits infected with F. gigantica are likely to be unreliable.

Humoral and cellular immune responses to Fasciola gigantica experimental infection in buffaloes

Humoral and cellular immune responses to Fasciola gigantica experimental infection in buffaloes were studied. The results showed that 33.4+/-9.1% of the infection dose was recovered as adult flukes from infected animals at necropsy. Significant differences of weight gain between infected and non-infected buffaloes was observed at 4 MPI (months post-infection). Anti F. gigantica excretory-secretory products (FgESP)-IgG levels increased significantly from 3 WPI (weeks post-infection) and displayed a peak at 13 WPI. Western blot indicated that in FgESP six major bands of 11.5, 19.0, 23.4, 29.8, 47.5 and 53.2kDa were recognized by F. gigantica-infected buffaloes sera after 0 WPI. Eosinophil numbers increased significantly from 3 WPI in F. gigantica-infected buffaloes and displayed a peak at 8 WPI. Peripheral blood mononuclear cells (PBMC) proliferation induced by FgESP increased from 2 WPI with a peak at 5 WPI. IFNgamma secretion by FgESP-stimulated PBMC appeared early from 1 WPI with three peaks at 2, 5 and 8 WPI, respectively. IL-10 production was observed from 2 WPI with two peaks at 4 and 9 WPI, respectively. Our results suggested that buffaloes were highly susceptible to F. gigantica infection, and this susceptibility could be associated with the late and weak cellular immune response in the early phase of infection and the Th0-like response throughout the infection.

Detection of circulating 54kDa antigen in sera of bovine calves experimentally infected with F. gigantica

The antibody response and circulating antigen levels in bovine calves, infected experimentally with Fasciola gigantica, were monitored using enzyme-linked immunoelectrotransfer blot (EITB) and sandwich ELISA, respectively. By EITB, the infected calves' sera recognized the polypeptides in the range of 54-58 kDa as early as 2 weeks post-infection. By 12th week post-infection, the lower two polypeptides of 12 and 8 kDa had disappeared. In sandwich ELISA, the circulating 54 kDa and whole worm antigen of F. gigantica were detected in the sera samples of infected calves as early as 2 weeks post-infection and persisted until the end of experiment (26th week PI). The 54 kDa antigen of F. gigantica appears to be specific and possesses promising immunodiagnostic potential for early prepatent diagnosis of bovine fasciolosis.

Evaluation of cercarial antigen for the serodiagnosis of fasciolosis in experimentally and naturally infected sheep

The value of cercarial antigen for diagnosis of experimental and natural sheep fasciolosis was studied by enzyme linked immunosorbent assay (ELISA) and enzyme linked immunotransfer blot (EITB). In ELISA, the antibody levels of experimentally infected sheep with Fasciola gigantica appeared at 2 weeks post infection (PI), gradually increased till 7 weeks PI and nearly remained at the same level from 7 to 13 weeks PI (the end of experiment). Also, the sensitivity and specificity of cercarial antigen for diagnosis of naturally sheep fasciolosis were 100 and 90%, respectively. In EITB, in the sheep experimentally infected with F. gigantica, the band of 32.5kDa molecular weight polypeptide appeared at 2 weeks PI and continued till the end of experiment. Also, the cercarial antigen recognized 32.5kDa molecular weight band with all sera from naturally infected sheep with fasciolosis (n = 25). This band did not cross-react when tested with sera from infected sheep with Cysticercus tenuicollus (n = 20). This study suggests that, the 32.5kDa molecular weight polypeptide could be used as sensitive and specific epitope for the serodiagnosis of sheep fasciolosis.

The isolation of Fasciola gigantica-specific antigens and their use in the serodiagnosis of fasciolosis in sheep by the detection of circulating antigens

The 17kDa and 69kDa polypeptide antigens which are specific to Fasciola gigantica were excised from polyacrylamide gels and used for the immunization of rabbits to raise monospecific antisera against these polypeptides. These sera were labelled with horseradish peroxidase and used for the detection of circulating 17 kDa and 69 kDa antigens by a direct enzyme-linked immunosorbent assay in the sera of sheep that were experimentally or naturally infected with F. gigantica. The 17 kDa antigen was detected in the sera of infected sheep as early as 1 week after infection and, following chemotherapy with oxyclozanide, negative seroconversion occurred 2 weeks later. The 69 kDa antigen was detectable as from the fourth week of infection and its detection ceased 3 weeks after chemotherapy. The serodiagnosis of F. gigantica, based on the detection of the 17 kDa antigen in sheep sera, was more specific and sensitive than that based on the detection of the 69 kDa antigen.

Antibody and circulating antigen profiles before and after chemotherapy in goats infected with Fasciola gigantica

The profiles of antibody response and circulating antigen levels in goats infected with Fasciola gigantica were studied by enzyme-linked immunoelectrotransfer blot (EITB) and enzyme-linked immunosorbent assay (ELISA). In the antibody assay, sera from goats experimentally infected with F. gigantica were reacted with whole worm antigen of the worm before and after chemotherapy with oxyclozanide. In ELISA, there was a significant increase in antibody level 2 weeks after infection. After chemotherapy, there was a gradual decrease in antibody within 3 weeks followed by a rapid decline by the 4th week after treatment. By EITB, the infected goat sera recognized three polypeptides in the range of 42-80 kDa as early as 2 weeks after infection. Recognition of the complete components of F. gigantica antigen repertoire occurred as early as the 4th week after infection. By the 8th week after chemotherapy, distinct polypeptide band recognition was no longer possible. Comparative immunoblotting with goat anti-Paramphistomum, anti-Dicrocoelium and anti-Fasciola sera revealed that the 14 kDa, 17 kDa, 21 kDa, 28 kDa and 30 kDa proteins are specific to F. gigantica. In the antigen assay, circulating antigen was detectable by the direct ELISA method one week after infection and negative absorbance values were observed 4 weeks after chemotherapy.