Sandwich enzyme-linked immunosorbent assay for detection of excretory secretory antigens in humans with fascioliasis

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.

Field evaluation of the enhanced MM3-COPRO ELISA test for the diagnosis of Fasciola hepatica infection in sheep

Fasciolosis is a severe zoonosis responsible for major economic losses in livestock. The enhanced MM3-COPRO test (eMM3-COPRO) and the commercial version BIO K 201 (Bio-X Diagnostics, Rochefort, Belgium) are widely used as immunodiagnostic tools for the specific detection of coproantigens released by Fasciola during the late prepatent and patent stages of infection. However, performance of the eMM3-COPRO has never been evaluated under field conditions. To address this gap, a large number of ovine faecal samples, collected in a region where fasciolosis is endemic (Galicia, NW Spain), were analyzed. Two groups of sheep flocks were selected according to the Fasciola infection status: ‘Fasciola-free’ and ‘Fasciola-infected’ flocks. ‘Fasciola-free’ flocks were seronegative flocks with no history of fasciolosis detected by either coproscopy or necropsy in the last 5 years. Faecal samples from these sheep were used to calculate a cut-off value for infection (OD = 0.021). The cut-off was calculated using a bootstrap resampling method that enables estimation of the sampling distribution of the statistical parameters without making assumptions about the underlying data distribution. ‘Fasciola-infected’ flocks were characterized by high seroprevalence, a history of fasciolosis and periodical treatment with flukicides. Samples from these flocks were used to estimate the diagnostic accuracy of the eMM3-COPRO relative to coproscopy, which although limited by poor sensitivity is the only reference test available for diagnosing fasciolosis in vivo. To overcome this limitation, all animals classified positive by eMM3-COPRO were treated with triclabendazole and then retested. The eMM3-COPRO displayed higher sensitivity than coproscopy, as it detected coproantigens in all samples with positive coproscopy and in 12% of samples with negative coproscopy. The test also proved highly specific as coproantigens disappeared after the treatment. The eMM3-COPRO was less time consuming than coproscopy, particularly when the procedure involved numerous samples, and showed promise as a tool for monitoring flukicide efficacy.

Bilious mask: parasite masquerading as malignant gall bladder polyp

A 31-year-old woman, presenting with right upper quadrant pain, was suspected to have malignant gall bladder polyp based on MRI and CT scan findings. She underwent radical cholecystectomy with excision of bile duct and hepaticojejunostomy. Surprisingly, histology revealed parasitic remnants within the bile duct wall with no evidence of malignancy. A year later, this young woman suffers significant impairment of quality of life, perhaps an aftermath to the radicality of the surgery. Our case demonstrates a masquerade of 'malignant biliary polyp' by a parasite. This raises the need for extensive investigations such as endoscopic ultrasound guided biopsies, parasitic serology and positron emission tomography (PET) scans when patients present with probable malignant biliary lesions, even in difficult-to-access areas. A preoperative diagnosis might have averted an unnecessary major surgery in this young woman.

Recent Developments in Recombinant Proteins for Diagnosis of Human Fascioliasis

Fascioliasis is an important neglected tropical disease that causes severe injury to the bile ducts and liver. Therefore, a rapid and accurate method for detection of Fasciola hepatica infection plays a vital role in early treatment. Currently, the diagnosis of fascioliasis is mainly conducted via serological tests using the excretory/secretory (E/S) products, which might cross-react with antigens from other helminth parasitic diseases. Hence, the development of serodiagnosis test using recombinant antigens may contribute to differentiate fascioliasis from other helminth infections. In the past 20 years, many attempts have been made to exert different F. hepatica recombinant antigens to obtain a well-established standard assay with high accuracy. In this review, we address recent studies that refer to the development of serodiagnosis tests for diagnosis of human fascioliasis based on the candidate recombinant antigens produced by different approaches. Meanwhile, in the present review, some main factors have been highlighted to improve the accuracy of diagnostic tests such as the effect of refolding methods to recover antigens' tertiary structure as well as applying a mixture of recombinant antigens with the highest sensitivity and specificity to improve the accuracy of diagnostic tests.

Fascioliasis and fasciolopsiasis: Current knowledge and future trends

Food-borne zoonotic trematodiases are classified as neglected diseases by the World Health Organization. Among them, fascioliasis is caused worldwide by Fasciola hepatica and F. gigantica, and represent a huge problem in livestock production and human health in endemic areas. Fasciolopsis buski, restricted to specific regions of Asia, causes fasciolopsiasis. The incidence of these trematodiases is underestimated due to under-reporting and to the lack of sensitive and widely accepted tool for their diagnosis. This, together with a rising trend in reporting of drug resistance and the need for an effective vaccine against these parasites, pose a challenge in the effective control of these diseases. Here, the latest reports on fascioliasis outbreaks between 2000 and 2020 and the most recent advances in their epidemiology, diagnosis, treatment and control are revised. Finally, future needs in the field of fascioliasis and fasciolopsiasis are presented, which could be addressed based on current knowledge and by means of new emerging technologies.

A sensitive serodiagnostic tool for the detection of active infection of zoonotic visceral and nasopharyngeal linguatulosis

Aim:

This study aimed to evaluate the different serological techniques for early diagnosis of acute concurrent infections with linguatulosis in the definitive host (dogs) and an intermediate host (goats). This evaluation compared between the gold standard (GS) test (GS; examination of nasal and fecal samples in dogs and examination of lymph nodes in goats), sandwich enzyme-linked immunosorbent assay (S-ELISA), and indirect ELISA.

Materials and Methods:

Fifty goats and fifty dogs were examined for the presence of Linguatula serrata nymphs and adults, respectively, besides the collection of blood samples from the examined animals for serologic testing.

Results:

In goats; GS, S-ELISA, and indirect ELISA showed positivity in 32 (64%), 28 (56%), and 39 (78%) samples, respectively. In dogs; GS, S-ELISA, and indirect ELISA showed positivity in 25 (50%), 25 (50%), and 30 (60%) samples, respectively. S-ELISA displayed significant higher agreement with the GS test (≥0.83) than indirect ELISA (≤0.67) in both hosts. Infection with linguatulosis showed significant relation with the age of goats and dogs and the sex of goats (p<0.05).

Conclusion:

S-ELISA displayed more sensitivity and specificity for the detection of concurrent infections with linguatulosis in both dogs and goats than indirect ELISA, which could detect the prior infections. Similarly, these assays could be used for diagnosis of concurrent infections with linguatulosis in human, especially the chronic ones.

Identification of the Apa protein secreted by Mycobacterium avium subsp. paratuberculosis as a novel fecal biomarker for Johne's disease in cattle

Paratuberculosis (PTB) or Johne's disease is a chronic intestinal infection of ruminants, caused by Mycobacterium avium subsp. paratuberculosis. The shedding of mycobacteria in the feces starts at the initial stages and increases with disease progression, suggesting that antigens secreted by mycobacteria could be excreted in the feces. Previously, we demonstrated that the alanine and proline-rich antigen (Apa), a secretory antigen of Map, could be detected in the intestine of cows with PTB using a monoclonal antibody. In this study, we verified whether this protein can be found in consistently detectable levels in the feces of cattle with PTB. Feces were obtained from cows with Johne's disease confirmed by laboratory tests, cows with suspected PTB based on seropositivity and from PTB-free control cows. Samples were immunoprecipitated using anti-Apa monoclonal antibody and analyzed by immunoblot. The Apa was detected as a 60/70 kDa doublet band in all samples obtained from animals with laboratory-confirmed disease and in a substantial proportion of seropositive asymptomatic animals, but not in the control samples. Additionally, the antigen was detected in the feces of animals with Johne's disease by ELISA. This study strongly suggests that Apa is a potential fecal biomarker of Johne's disease that could serve for immunodiagnosis.

Comparison of recombinant cathepsins L1, L2, and L5 as ELISA targets for serodiagnosis of bovine and ovine fascioliasis

Infections caused by Fasciola hepatica are of great importance in the veterinary field, as they cause important economic losses to livestock producers. Serodiagnostic methods, typically ELISA (with either native or recombinant antigens), are often used for early diagnosis. The use of native antigens, as in the MM3-SERO ELISA (commercialized as BIO K 211, BIO-X Diagnostics), continues to be beneficial in terms of sensitivity and specificity; however, there is interest in developing ELISA tests based on recombinant antigens to avoid the need to culture parasites. Of the antigens secreted by adult flukes, recombinant procathepsin L1 (rFhpCL1) is the most commonly tested in ELISA to date. However, although adult flukes produce three different clades of CLs (FhCL1, FhCL2, and FhCL5), to our knowledge, the diagnostic value of recombinant FhCL2 and FhCL5 has not yet been investigated. In the present study, we developed and tested three indirect ELISAs using rFhpCL1, rFhpCL2, and rFhpCL5 and evaluated their recognition by sera from sheep and cattle naturally infected with F. hepatica. Although the overall antibody response to these three rFhpCLs was similar, some animals displayed preferential recognition for particular rFhpCLs. Moreover, for cattle sera, the highest sensitivity was obtained using rFhpCL2 (97%), being equal for both rFhpCL1 and rFhpCL5 (87.9%), after adjusting cut-offs for maximum specificity. By contrast, for sheep sera, the sensitivity was 100% for the three rFhpCLs. Finally, the presence of truncated and/or partially unfolded molecules in antigen preparations is postulated as a possible source of cross-reactivity.

Standardization of a latex agglutination test for coproantigen detection of Fasciola sp. in bovine cattle stool

Fasciolosis is a zoonotic parasitic disease, which affects humans and animals; diagnosed through noncommercial immunoassay tests that cannot be used on the field. Thereby, establishing the optimal conditions to develop a latex agglutination technique with IgG and IgM antibodies directed against excretion/secretion antigens of Fasciola sp. is a priority. Latex particles were sensitized with IgG and IgM antibodies directed against excretion/secretion antigens of Fasciola sp. The specificity of the antibodies was determined against antigens of different helminths and protozoa; the sensitivity and specificity of the test was evaluated against a previously standardized direct ELISA. The coupling rates of the IgG and IgM antibodies were 85.77 and 100%, respectively. The minimum detectable concentration of Fasciola sp. excretion/secretion antigens, diluted in a phosphate-buffered saline, was 1.589 mg/mL(IgG) and 0.158 mg/mL(IgM) and for the antigens incorporated in the bovine cattle stool it was 3.178 mg/mL(IgG) and 1.589 mg/mL(IgM). The test showed crossed reaction against Giardia sp., and Cryptosporidium sp. antigens. Agreement of the IgG and IgM latex test against the ELISA test was of 78.78 and 96.96%, respectively; the specificity found was of 100% for both tests and sensitivity was 78.79% (IgG) and 96.97% (IgM). This work standardized the latex agglutination technique to detect Fasciola sp. antigens in bovine cattle stool.

Immunodiagnosis of paramphistomosis using monoclonal antibody-based sandwich ELISA for detection ofParamphistomum gracilecirculating 16 kDa antigen

In this study, we have produced a monoclonal antibody (MoAb) against 16 kDa antigen ofParamphistomum gracile(16 kDaAgPg), and developed an accurate sandwich enzyme-linked immunosorbent assay (sandwich ELISA) for the detection of circulating 16 kDaAg in the serum and fecal samples from cattle naturally infected withP. gracile. MoAb 1D10 was immobilized on a microtitre plate, and the antigen in the samples was captured and detected with biotinylated rabbit anti-16 kDaAgPg antibody. The lower detection limit of sandwich ELISA was 3·5 pg mL−1, and no cross-reaction with other parasite antigens was evaluated. The reliability of the assay was examined using the serum and fecal samples from cattle naturally infected withP. gracile, Fasciola gigantica, Moniezia benedeni, Trichurissp.,Strongyloidessp., strongylids and non-infected animals. The sandwich ELISA showed the sensitivity, specificity and accuracy at 98·33, 100 and 99·55% (serum samples), and 96·67, 100 and 99·09% (fecal samples). Therefore, this detection method is a rapid and excellent potential assay for the accurate diagnosis of paramphistomosis.

Repertory of eukaryotes (eukaryome) in the human gastrointestinal tract: taxonomy and detection methods

Eukaryotes are an important component of the human gut, and their relationship with the human host varies from parasitic to commensal. Understanding the diversity of human intestinal eukaryotes has important significance for human health. In the past few decades, most of the multitudes of techniques that are involved in the diagnosis of the eukaryotic population in the human intestinal tract were confined to pathological and parasitological aspects that mainly rely on traditionally based methods. However, development of culture-independent molecular techniques comprised of direct DNA extraction from faeces followed by sequencing, offer new opportunities to estimate the occurrence of eukaryotes in the human gut by providing data on the entire eukaryotic community, particularly not-yet-cultured or fastidious organisms. Further broad surveys of the eukaryotic communities in the gut based on high throughput tools such as next generation sequencing might lead to uncovering the real diversity of these ubiquitous organisms in the human intestinal tract and discovering the unrecognized roles of these eukaryotes in modulating the host immune system and inducing changes in host gut physiology and ecosystem.

Rapid Enhanced MM3-COPRO ELISA for Detection of Fasciola Coproantigens

ELISA-based methods of detecting Fasciola cathepsins in feces are powerful techniques for diagnosing infections by F. hepatica and F. gigantica. In the last decade, the in-house MM3-COPRO ELISA and its commercial version BIO K 201 (BIO X Diagnostics, Belgium) have been recognized as useful tools for detecting early infections by such trematodes and for monitoring the efficacy of anthelmintic treatments in human and animal species, as they provide some advantages over classic fecal egg counts. However, the sensitivity of MM3-COPRO ELISA can sometimes be compromised by the high variability in the concentration of cathepsins in fecal samples throughout the biological cycle of Fasciola (mainly in cattle) and by differences in the between-batch performance of peroxidase-labeled anti-mouse IgG polyclonal antibodies. To prevent such problems, we investigated whether the incorporation of a commercial streptavidin-polymerized horseradish peroxidase conjugate, in order to reveal bound biotinylated monoclonal antibody MM3, can improve the sensitivity of the MM3-COPRO ELISA. We observed that inclusion of this reagent shifted the previous detection limit of the assay from 0.6 ng/mL to 150 pg/mL and that the modified test is able to identify infection in cows harboring only one fluke. Moreover, we demonstrated that maximal OD values can be achieved with short incubations (30 min each step) at RT with shaking, rather than standard incubations, which significantly accelerates the diagnostic procedure. Finally, we did not find a significant correlation between coproantigen concentration and parasite burden in cattle, which may be due to the low parasite burden (1–10 adult flukes) of the animals used in the present study. As the usefulness of the classic MM3-COPRO test for detecting animal and human infections has already been demonstrated, it is expected that the improvements reported in this study will add new insights into the diagnosis and control of fasciolosis.

We have previously reported how the combined use of mAb MM3 with polyclonal antibodies obtained from rabbit immunized with Fasciola hepatica excretory-secretory antigens led to the development of the in-house MM3-COPRO ELISA and its commercial version BIO K 201 (BIO X Diagnostics, Belgium), which are widely used to detect human and animal infections caused by F. hepatica. After more than a decade in use, both tests have proven to be useful tools for specifically detecting Fasciola infections, although it has also been found that: i) the conditions of use of the commercial test in some field studies did not enable the sensitivity obtained with the in-house test to be reached, and ii) the batches of the secondary reagent (peroxidase-labeled anti-mouse antibodies) currently available for use in the in-house test do not perform the same as previous batches. To solve these problems, we provide data showing that the incorporation of an enhancement system consisting of streptavidin-polymerized horseradish peroxidase conjugate greatly improved the sensitivity of the MM3-COPRO ELISA and enabled reduction of the incubation time. These modifications enabled the detectability of the assay to be 150 pg/mL, thus enabling detection of infection in animals harboring only one fluke.

Immunodiagnostic monoclonal antibody-based sandwich ELISA of fasciolosis by detection ofFasciola giganticacirculating fatty acid binding protein

Up to now, parasitological diagnosis of fasciolosis is often unreliable and possesses low sensitivity. Hence, the detection of circulating parasite antigens is thought to be a better alternative for diagnosis of fasciolosis, as it reflects the real parasite burden. In the present study, a monoclonal antibody (MoAb) against recombinantFasciola giganticafatty acid binding protein (rFgFABP) has been produced. As well, a reliable sandwich enzyme-linked immunosorbent assay (sandwich ELISA) has been developed for the detection of circulating FABP in the sera of mice experimentally and cattle naturally infected withF. gigantica. MoAb 3A3 and biotinylated rabbit anti-recombinant FABP antibody were selected due to their high reactivities and specificities. The lower detection limit of sandwich ELISA was 5 pg mL−1, and no cross-reaction with other parasite antigens was observed. This assay could detectF. giganticainfection from day 1 post infection. In experimental mice, the sensitivity, specificity and accuracy of this assay were 93·3, 100 and 98·2%, while in natural cattle they were 96·7, 100 and 99·1%. Hence, this sandwich ELISA method showed high efficiencies and precisions for diagnosis of fasciolosis byF. gigantica.

Immunodiagnosis of Fasciola gigantica Infection Using Monoclonal Antibody-Based Sandwich ELISA and Immunochromatographic Assay for Detection of Circulating Cathepsin L1 Protease

BACKGROUND

Tropical fasciolosis caused by Fasciola gigantica infection is one of the major diseases infecting ruminants in the tropical regions of Africa and Asia including Thailand. Parasitological diagnosis of fasciolosis is often unreliable and possesses low sensitivity. Therefore, the detection of circulating parasite antigens is thought to be a better alternative for diagnosis of fasciolosis, as it reflects the real parasite burden.

METHODS

In this study, we have produced a monoclonal antibody (MoAb) against recombinant F. gigantica cathepsin L1 (rFgCatL1), and developed both sandwich enzyme-linked immunosorbent assay (sandwich ELISA) and immunochromatographic (IC) test for rapid detection of circulating cathepsin L1 protease (CatL1) in the sera from mice experimentally and cattle naturally infected with Fasciola gigantica. MoAb 4E3 and biotinylated rabbit anti-recombinant CatL1 antibody were selected due to their high reactivities and specificities.

RESULTS

The lower detection limits of sandwich ELISA and IC test were 3 pg/ml and 0.256 ng/ml, respectively. Sandwich ELISA and IC test could detect F. gigantica infection from day 1 to 35 post infection. In experimental mice, the sensitivity, specificity and accuracy were 95%, 100% and 98.6% (for sandwich ELISA), and 93%, 100% and 98.2% (for IC test), while in natural cattle they were 98.3%, 100% and 99.5% (for sandwich ELISA), and 96.7%, 100% and 99.1% (for IC test).

CONCLUSIONS

These two assay methods showed high efficiencies and precisions for diagnosis of fasciolosis by F. gigantica.

Prevalence and risk factors for intestinal parasitic infections in a rural community in "consolación del sur" municipality, cuba

Intestinal parasites are very common infections worldwide and they are responsible for significant public health problems. The World Health Organization estimates that one-third of the world population is infected and some epidemiologic factors related to the transmission have been identified. The purpose of this investigation was to study the prevalence of intestinal parasitic infections in people living in the rural community of "El Canal", Consolación del Sur municipality and the association with some epidemiologic risk factors. All participants were subjected to three methods of parasitological examinations on the stool samples and by immunodiagnostic tests which allow the detection of excretory-secretory antigens of adults with Fasciola hepatica. The global prevalence rate of intestinal parasitic infections (IPIs) was 18%, and 16.7% for protozoan infections, while the rate of helminth infection was lower (5.3%) in the population studied. The univariate analysis identified three factors associated with intestinal pathogenic protozoan infections which include livestock work, drinking water from well\river and eating unwashed fruits\vegetables. The multivariate analysis using introduction test logistic regression ratified the association of these risk factors. Contrary to what have been published in the majority of Cuban studies carried out in rural places, a higher prevalence of protozoan than helminth infection was found. This discrepancy may be explained because the majority of the workers in this rural community were stock-breeders and they are not involved in other agricultural work. The identification of risk factors is important in order to design appropriate strategies for control of IPIs in communities.

Detection of Coproantigens by Sandwich ELISA in Rabbits Experimentally Infected with Fasciola gigantica

BACKGROUND

The study was targeted to report the appearance of coproantigens in feces and circulating antibodies in the serum of Fasciola gigantica experimentally infected rabbits.

METHODS

Copro Hyper Immune Serum (HIS) and Excretory-Secretory Hyper Immune Serum (ES HIS) antigens were used in a sandwich ELISA for the detection of F. gigantica antigens in feces of 12 rabbits experimentally infected with different doses of F. gigantica encysted metacercariae (EMC) (10, 25 and 30 EMC). The relation between time of appearance of coproantigens in feces and anti-Fasciola antibodies in serum was evaluated.

RESULTS

The earliest diagnostic coproantigen was recorded at 21(st), 25(th) and 28(th) day post-infection (p.i.) in groups of rabbits infected with 30, 25 and 10 F. gigantica EMC respectively. Both HIS and ES HIS were able to detect coproantigens in feces of rabbits infected with 30 EMC at day 21 p.i. The appearance of F. gigantica coproantigens in feces of infected rabbits was concurrent to the appearance of anti-Fasciola antibodies in blood (3(rd) week p.i.). However, coproantigen has specific ability for direct assessment of active infection with minimal cross-reaction with other heterologous parasitic infections.

CONCLUSION

The findings hold promise for a more accurate diagnostic technique in the near future for suspected Fasciola infection.

Techniques for the diagnosis of Fasciola infections in animals: room for improvement

The common liver fluke, Fasciola hepatica, causes fascioliasis, a significant disease in mammals, including livestock, wildlife and humans, with a major socioeconomic impact worldwide. In spite of its impact, and some advances towards the development of vaccines and new therapeutic agents, limited attention has been paid to the need for practical and reliable methods for the diagnosis of infection or disease. Accurate diagnosis is central to effective control, particularly given an emerging problem with drug resistance in F. hepatica. Traditional coprological techniques have been widely used, but are often unreliable. Although there have been some advances in establishing immunologic techniques, these tools can suffer from a lack of diagnostic specificity and/or sensitivity. Nonetheless, antigen detection tests seem to have considerable potential, but have not yet been adequately evaluated in the field. Moreover, advanced nucleic acid-based methods appear to offer the most promise for the diagnosis of current infection. This chapter (i) provides a brief account of the biology and significance of F. hepatica/fascioliasis, (ii) describes key techniques currently in use, (iii) compares their advantages/disadvantages and (iv) reviews polymerase chain reaction-based methods for specific diagnosis and/or the genetic characterization of Fasciola species.

Diagnosis of human fascioliasis by stool and blood techniques: update for the present global scenario

Before the 1990s, human fascioliasis diagnosis focused on individual patients in hospitals or health centres. Case reports were mainly from developed countries and usually concerned isolated human infection in animal endemic areas. From the mid-1990s onwards, due to the progressive description of human endemic areas and human infection reports in developing countries, but also new knowledge on clinical manifestations and pathology, new situations, hitherto neglected, entered in the global scenario. Human fascioliasis has proved to be pronouncedly more heterogeneous than previously thought, including different transmission patterns and epidemiological situations. Stool and blood techniques, the main tools for diagnosis in humans, have been improved for both patient and survey diagnosis. Present availabilities for human diagnosis are reviewed focusing on advantages and weaknesses, sample management, egg differentiation, qualitative and quantitative diagnosis, antibody and antigen detection, post-treatment monitoring and post-control surveillance. Main conclusions refer to the pronounced difficulties of diagnosing fascioliasis in humans given the different infection phases and parasite migration capacities, clinical heterogeneity, immunological complexity, different epidemiological situations and transmission patterns, the lack of a diagnostic technique covering all needs and situations, and the advisability for a combined use of different techniques, at least including a stool technique and a blood technique.

Recent advances in the diagnosis, impact on production and prediction of Fasciola hepatica in cattle

Fasciola hepatica is a pathogenic trematode parasite of ruminants with a global distribution. Here, we briefly review the current epidemiology of bovine fasciolosis in Europe and discuss the progress made over the last decade in the diagnosis, impact on production and prediction of F. hepatica in cattle. Advances in diagnosis have led to significantly improved coprological and serological methods to detect presence of infection. Diagnostic test results have been correlated with intensity of infection and associated production losses, unravelling the impact on carcass weight and milk yield in modern cattle production systems. The economic impact of fasciolosis may, however, go beyond the direct impacts on production as evidence shows that F. hepatica can modulate the immune response to some co-infections. Control of bovine fasciolosis remains hampered by the limitations of the currently available flukicidal drugs: few drugs are available to treat dairy cows, many have low efficacies against juvenile stages of F. hepatica and there is evidence for the development of drug resistance. This makes research into the prediction of risk periods, and thus the optimum application of available drugs more pertinent. In this field, the recent research focus has been on understanding spatial risk and delivering region-specific spatial distribution maps. Further advances in epidemiological and economic research on bovine fasciolosis are expected to deliver farm-specific economic assessments of disease impact, to leverage non-chemotherapeutic management options and to enhance a more targeted use of anthelmintics.

Fascioliasis and intestinal parasitoses affecting schoolchildren in Atlixco, Puebla State, Mexico: epidemiology and treatment with nitazoxanide

BACKGROUND

The Atlixco municipality, Puebla State, at a mean altitude of 1840 m, was selected for a study of Fasciola hepatica infection in schoolchildren in Mexico. This area presents permanent water collections continuously receiving thaw water from Popocatepetl volcano (5426 m altitude) through the community supply channels, conforming an epidemiological scenario similar to those known in hyperendemic areas of Andean countries.

METHODOLOGY AND FINDINGS

A total of 865 6-14 year-old schoolchildren were analyzed with FasciDIG coproantigen test and Lumbreras rapid sedimentation technique, and quantitatively assessed with Kato-Katz. Fascioliasis prevalences ranged 2.94-13.33% according to localities (mean 5.78%). Intensities were however low (24-384 epg). The association between fascioliasis and the habit of eating raw vegetables was identified, including watercress and radish with pronouncedly higher relative risk than lettuce, corncob, spinach, alfalfa juice, and broccoli. Many F. hepatica-infected children were coinfected by other parasites. Entamoeba histolytica/dispar, Giardia intestinalis, Blastocystis hominis, Hymenolepis nana and Ascaris lumbricoides infection resulted in risk factors for F. hepatica infection. Nitazoxanide efficacy against fascioliasis was 94.0% and 100% after first and second treatment courses, respectively. The few children, for whom a second treatment course was needed, were concomitantly infected by moderate ascariasis burdens. Its efficacy was also very high in the treatment of E. histolytica/E. dispar, G. intestinalis, B. hominis, H. nana, A. lumbricoides, Trichuris trichiura, and Enterobius vermicularis. A second treatment course was needed for all children affected by ancylostomatids.

CONCLUSIONS

Fascioliasis prevalences indicate this area to be mesoendemic, with isolated hyperendemic foci. This is the first time that a human fascioliasis endemic area is described in North America. Nitazoxanide appears as an appropriate alternative to triclabendazole, the present drug of choice for chronic fascioliasis. Its wide spectrum efficacy against intestinal protozooses and helminthiasis, usually coinfecting liver fluke infected subjects in human endemic areas, represents an important added value.

Immunodiagnosis of fascioliasis using sandwich enzyme-linked immunosorbent assay for detection of Fasciola gigantica paramyosin antigen

Background:

Many immunological techniques have been developed over years using the different Fasciola antigens for diagnosis of parasitic infection and to replace the parasitological techniques, which are time consuming and usually lack sensitivity and reproducibility.

Materials and Methods:

In this study, Fasciola gigantica paramyosin (Pmy) antigen was early detected in cattle sera using sandwich enzyme-linked immunosorbent assay (ELISA), to evaluate the Pmy antigen performance in diagnosis. This work was conducted on 135 cattle blood samples, which were classified according to parasitological investigation into, healthy control (30), fascioliasis (75), and other parasites (30) groups.

Results:

The sensitivity of Sandwich ELISA was 97.33%, and the specificity was 95%, in comparison with parasitological examination, which recorded 66.66% sensitivity and 100% specificity, respectively.

Conclusions:

It was clear that the native F. gigantica Pmy is considered as a powerful antigen in early immunodiagnosis of fascioliasis, using a highly sensitive and specific sandwich ELISA technique.

Immunodetection of Fasciola gigantica circulating antigen in sera of infected individuals for laboratory diagnosis of human fascioliasis

Currently, the laboratory diagnosis of human fascioliasis is based on the parasitological examination of parasite eggs in stool specimens and serological detection of specific antibodies in serum samples, which are often unreliable diagnostic approaches. Ideally, a sensitive and specific diagnostic test for Fasciola infection should be based on the detection of circulating Fasciola antigen, which implies active infection. Here, a 27-kDa-molecular-mass antigen was identified in a Fasciola gigantica adult worm antigen preparation, excretory-secretory products, and sera from F. gigantica-infected individuals, and it was not detected in antigenic extracts of other parasites and sera from noninfected individuals. The target antigen was isolated and partially characterized as a protein. Immunoperoxidase staining located the target epitope within teguments and guts of F. gigantica adult worms. The performance characteristics of a newly developed enzyme-linked immunosorbent assay (ELISA) based on F. gigantica circulating antigen detection in serum (FgCA-27 ELISA) were investigated using sera of 120 parasitologically diagnosed F. gigantica-infected individuals and 80 noninfected individuals. The area under the receiving operating characteristic (ROC) curve (AUC) for ELISA was significantly high (AUC = 0.961, P < 0.0001) for discriminating Fasciola-infected and noninfected individuals. The developed assay showed high degrees of sensitivity, specificity, and efficiency (>93%), and a significant correlation (r = 0.715, P < 0.0001) between antigen level and parasite egg count was shown. In conclusion, a 27-kDa Fasciola antigen was identified in sera of F. gigantica-infected individuals. A highly sensitive and specific Fasciola antigen detection assay, FgCA-27 ELISA, was developed for laboratory diagnosis of human fascioliasis.

Diagnosis of Fasciola gigantica infection using a monoclonal antibody-based sandwich ELISA for detection of circulating cathepsin B3 protease

A reliable monoclonal antibody (MoAb)-based sandwich enzyme-linked immunosorbent assay (sandwich ELISA) was developed for the detection of circulating cathepsin B3 protease (CatB3) in the sera from mice experimentally infected with Fasciola gigantica and cattle naturally infected with the same parasite. The MoAb 2F9 and biotinylated rabbit polyclonal anti-recombinant CatB3 antibody were selected due to their high reactivities and specificities to F. gigantica CatB3 antigen based on indirect ELISA and immunoblotting. The lower detection limit of the sandwich ELISA assay was 10, 100 and 400pg/ml, when applied for the detection of rCatB3 antigen and CatB3 in whole body (WB) of newly excysted juveniles (NEJ) and metacercariae (Met) of F. gigantica, respectively. This sandwich ELISA assay could detect F. gigantica infection from day 1 to 35 post infection and revealed that circulating level of CatB3 peaked at day 1 post infection. In contrast, the antibody detection by indirect ELISA could only demonstrate the antibody level from 35 days post infection. The reliability of the assay method was evaluated using serum samples from mice infected with F. gigantica or Schistosoma mansoni, and hamsters infected with Opisthorchis viverrini, as well as normal mice and hamsters. In addition, sera from cattle infected with Paramphistomum cervi, Strongylid, Trichuris sp. and Strongyloides sp., as well as sera from normal cattle were also assessed. In experimental mice, the diagnostic sensitivity, specificity, positive predictive value, negative predictive value, false positive rate, false negative rate and accuracy of ELISA were 95%, 100%, 100%, 97.9%, 0%, 5.3% and 98.5%, while in natural cattle they were 96.7%, 100%, 100%, 98.5%, 0%, 3.4% and 98.9%, respectively. Hence, this assay method showed high efficient and precision for early diagnosis of fasciolosis by F. gigantica.

Field evaluation of a coproantigen detection test for fascioliasis diagnosis and surveillance in human hyperendemic areas of Andean countries

Background

Emergence of human fascioliasis prompted a worldwide control initiative including a pilot study in a few countries. Two hyperendemic areas were chosen: Huacullani, Northern Altiplano, Bolivia, representing the Altiplanic transmission pattern with high prevalences and intensities; Cajamarca valley, Peru, representing the valley pattern with high prevalences but low intensities. Coprological sample collection, transport and study procedures were analyzed to improve individual diagnosis and subsequent treatments and surveillance activities. Therefore, a coproantigen-detection technique (MM3-COPRO ELISA) was evaluated, using classical techniques for egg detection for comparison.

Methodology and Findings

A total of 436 and 362 stool samples from schoolchildren of Huacullani and Cajamarca, respectively, were used. Positive samples from Huacullani were 24.77% using the MM3-COPRO technique, and 21.56% using Kato-Katz. Positive samples from Cajamarca were 11.05% using MM3-COPRO, and 5.24% using rapid sedimentation and Kato-Katz. In Huacullani, using Kato-Katz as gold standard, sensitivity and specificity were 94.68% and 98.48%, respectively, and using Kato-Katz and COPRO-ELISA test together, they were 95.68% and 100%. In Cajamarca, using rapid sedimentation and Kato-Katz together, results were 94.73% and 93.58%, and using rapid sedimentation, Kato-Katz and copro-ELISA together, they were 97.56% and 100%, respectively. There was no correlation between coproantigen detection by optical density (OD) and infection intensity by eggs per gram of feces (epg) in Cajamarca low burden cases (<400 epg), nor in Huacullani high burden cases (≥400 epg), although there was in Huacullani low burden cases (<400 epg). Six cases of egg emission appeared negative by MM3-COPRO, including one with a high egg count (1248 epg).

Conclusions

The coproantigen-detection test allows for high sensitivity and specificity, fast large mass screening capacity, detection in the chronic phase, early detection of treatment failure or reinfection in post-treated subjects, and usefulness in surveillance programs. However, this technique falls short when evaluating the fluke burden on its own.

A coproantigen-detection technique (MM3-COPRO ELISA) was evaluated in 436 and 362 schoolchildren of Huacullani, Bolivia, and Cajamarca valley, Peru, respectively. Classical techniques for egg detection were used for comparison. In Huacullani, using Kato-Katz as gold standard, sensitivity and specificity were 94.68% and 98.48%, respectively, and using Kato-Katz and COPRO-ELISA test together, they were 95.68% and 100%, respectively. In Cajamarca, using rapid sedimentation and Kato-Katz together, these results were 94.73% and 93.58%, respectively, and using rapid sedimentation, Kato-Katz and copro-ELISA together, results were 97.56% and 100%, respectively. There was no correlation between coproantigen detection by optical density (OD) and infection intensity by eggs per gram of feces (epg) in Cajamarca low burden cases (<400 epg), nor in Huacullani high burden cases (≥400 epg), although there was in Huacullani low burden cases (<400 epg). Six cases of egg emission appeared negative by MM3-COPRO, including one with a high egg count (1248 epg). The coproantigen-detection test allows for high sensitivity and specificity, fast large mass screening capacity, detection in the chronic phase, early detection of treatment failure or reinfection in post-treated subjects, and usefulness for surveillance programs. However, this technique falls short when evaluating the fluke burden on its own.

Evaluation of rabbit antibody response against 8 and 16 kDa recombinant subunits of antigen B from Echinococcus granulosus

OBJECTIVE

To immunize rabbits with 12 and 16 kDa recombinant subunits of antigen B from Echinococcus granulosus (E. granulosus) and measuring polyclonal antibody and humoral immune response using ELISA and gel diffusion.

METHODS

Two mentioned antigens were cloned and expressed in expression vector and purified by affinity chromatography. Four young rabbits were selected and challenged intradermally with yielded recombinant antigens. Rabbits' sera were collected post infection and were tested using ELISA and gel diffusion for polyclonal antibody detection 10 days after last injection.

RESULTS

The specific antibody against the recombinant peptides was efficiently produced within 4 weeks post infection.

CONCLUSIONS

Produced recombinants proteins could induce the immune response of the rabbits successfully. This process might improve the clarification of diagnosis and vaccination as regards hydatidosis.

Diagnostic potential ofFasciola gigantica-derived 14.5 kDa fatty acid binding protein in the immunodiagnosis of bubaline fascioliasis

The 14.5 kDa fatty acid binding protein (FABP) was isolated from the crude extract of adultFasciola giganticaworms. Polyclonal anti-FABP IgG was generated in rabbits immunized with prepared FABP antigen. Sandwich enzyme-linked immunosorbent assay (ELISA) was applied to detect coproantigen in stools and circulatingFasciolaantigen (CA) in sera of 126 water buffaloes by using purified and horseradish peroxidase (HRP)-conjugated anti-FABP IgG. Sandwich ELISA sensitivity was 96.97% and 94.95%; while specificity was 94.12% and 82.35% for coproantigen and CA detection, respectively. However, sensitivity and specificity of the Kato–Katz technique was 73.74% and 100%, respectively. The diagnostic efficacy of sandwich ELISA was 96.55% and 93.1% for coproantigen and CA detection, respectively. In contrast, the diagnostic efficacy of the Kato–Katz technique was 77.59%. In conclusion, these results demonstrate that the purified 14.5 kDa FABP provides a more suitable antigen for immunodiagnosis of early and current bubaline fascioliasis by using sandwich ELISA.

Diagnostic efficacy of monoclonal antibody based sandwich enzyme linked immunosorbent assay (ELISA) for detection of Fasciola gigantica excretory/secretory antigens in both serum and stool

Background

This research was carried out to develop a reliable monoclonal antibody (MoAb)-based sandwich enzyme linked immunosorbent assay (ELISA) for the diagnosis of active Fasciola gigantica infection in both serum and stool for comparative purposes.

Methods

From a panel of MoAbs raised against F. gigantica excretory/secretory antigens (ES Ags), a pair (12B/11D/3F and 10A/9D/10G) was chosen due to its high reactivity and strict specificity to F. gigantica antigen by indirect ELISA.

Results

The two MoAbs were of the IgG₁ and IgG_2a subclasses, respectively. Using SDS-PAGE and EITB, the selected MoAbs recognized 83, 64, 45 and 26 kDa bands of ES Ags. The lower detection limit of ELISA assay was 3 ng/ml. In stool, the sensitivity, specificity and diagnostic efficacy of ELISA was 96%, 98.2 and 97.1%; while in serum they were 94%, 94.6% and 94.3%, respectively. Moreover, a positive correlation was found between ova count in stool of F. gigantica infected patients and the OD readings of ELISA in both stool and serum samples (r = 0.730, p < 0.01 and r = 0.608; p < 0.01, respectively).

Conclusions

These data showed that the use of MoAb-based sandwich ELISA for the detection of F. gigantica coproantigens in stool specimens was superior to serum samples; it provides a highly efficient, non-invasive technique for the diagnosis of active F. gigantica infection.

Molecular and immunological characterization of Fasciola antigens recognized by the MM3 monoclonal antibody

Fascioliasis is a re-emerging parasitosis produced by liver flukes of the genus Fasciola. In this study we used protein fingerprinting (PMF) and MS/MS analysis to investigate the Fasciola secretory antigens that are recognized by mAb MM3. The results showed that mAb MM3 binds to several Fasciola cathepsins L1 and L2, but also co-purifies a Kunitz-type protein previously described in F. hepatica, which appears to bind to Fasciola cathepsins L. After identifying the target antigens for mAb MM3, we cloned and expressed a cathepsin L1 isoform in E. coli (gb|FR848428), which after refolding exhibited the MM3-recognized epitope and displayed cysteine protease activity. Using native, folded-recombinant and denatured-recombinant Fasciola cathepsins L as targets, we demonstrated that during F. hepatica infections in sheep, antibody responses to linear and conformational epitopes present on cathepsins L are promoted. However, the antibody response to linear epitopes was only detected in significant amounts in animals suffering from repeated infections. A different antibody response to linear and conformational epitopes also appears to occur in rabbits immunized with native or recombinant unfolded cathepsins, as sera from animals immunized with the latter did not react with native cathepsins and vice versa. In addition, the ELISA inhibitions showed that the MM3 epitope is not recognized by rabbits, which explains the usefulness of these species for producing capture antibodies for use in MM3-ELISA assays.

A coproantigen diagnostic test for Strongyloides infection

Accurate diagnosis of infection with the parasite Strongyloides stercoralis is hampered by the low concentration of larvae in stool, rendering parasitological diagnosis insensitive. Even if the more sensitive agar plate culture method is used repeated stool sampling is necessary to achieve satisfactory sensitivity. In this manuscript we describe the development of a coproantigen ELISA for diagnosis of infection. Polyclonal rabbit antiserum was raised against Strongyloides ratti excretory/secretory (E/S) antigen and utilized to develop an antigen capture ELISA. The assay enabled detection of subpatent rodent S. ratti and human S. stercoralis infection. No cross-reactivity was observed with purified E/S from Schistosoma japonicum, the hookworms Ancylostoma caninum, A. ceylanicum, nor with fecal samples collected from rodents harboring Trichuris muris or S. mansoni infection. Strongyloides coproantigens that appear stable when frozen as formalin-extracted fecal supernatants stored at -20 °C remained positive up to 270 days of storage, whereas supernatants stored at 4 °C tested negative. These results indicate that diagnosis of human strongyloidiasis by detection of coproantigen is an approach worthy of further development.

Fasciola hepatica infection in a 65-year-old woman

Fascioliasis is an infectious disease caused by fasciola or liver fluke. Humans are accidental hosts to these flatworms. The World Health Organisation considers fascioliasis an important human parasitic disease. In Europe, Australia and Northern America, the disease is rare, but should have a high index of suspicion in patients who have lived in or travelled to endemic areas. Although it can be self-limiting, fascioliasis is associated with an increased risk of bile duct cancer. Before a clear-cut diagnosis is made using ELISA-based arrays, radiologic studies can provide the clinician with a number of suggestive features, thereby avoiding the need for liver biopsy or even surgery, which have nowadays become obsolete for the diagnosis of fascioliasis. We provide an overview of the major radiologic hallmarks and we demonstrate the role of iron-oxide enhanced MRI.

Evaluation of an ELISA to assess the intensity of Fasciola hepatica infection in cattle

An elisa with a diagnostic sensitivity of 98 per cent and specificity of 96 per cent was evaluated as a means of assessing the intensity of Fasciola hepatica infection in cattle. A total of 294 blood samples were collected from infected cattle at a local abattoir, and the level of infection in each animal was assessed on the basis of the extent of liver pathology and the presence of flukes; 120 blood samples were also collected from uninfected cattle kept on a farm known to be free of F hepatica. The results indicated that there was a significant correlation (P<0.001) between the elisa values and the intensity of infection. Values between 15 and 28 per cent of a positive control sample indicated a low intensity of infection, values between 28 and 50 per cent indicated a medium intensity of infection and values above 50 per cent indicated a high intensity of infection.

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.

Detection of coproantibodies and faecal immune complexes in human trichinellosis

Trichinella spiralisis the nematode causative agent of trichinellosis, an intestinal and tissular parasitosis. Even though an early diagnosis during the intestinal phase is essential to limit the infection in humans, to date, there are no available tests to achieve this goal. Based on the immune response generated by the host's intestinal mucosa, the aim of this work was to develop ELISAs to assess the presence of coproantigens (CAgs), coproantibodies (CAbs) and faecal immune complexes in stool samples of 18 individuals belonging to different outbreaks that have arisen in Argentina. By the methodologies developed in this work it was found that anti-muscle larva excretory-secretory products (ML-ESP) CAbs were detected in 89% of the samples analysed regardless of the time p.i. Anti-ML-ESP IgA, IgG, IgE and IgM were detected in 56%, 56%, 28% and 22% of the individuals respectively. Those samples negative for anti-ML-ESP total immunoglobulins proved positive for anti-adult worm-ESP CAbs. No CAgs were detected in any of the samples. The results obtained in this work indicate that the intestinal immune response in human trichinellosis is featured by all the isotypes of specific immunoglobulins. Furthermore, the detection of antibodies in stool samples, in either the free or complexed form, could be applied to confirm early human trichinellosis.

Endemic human fasciolosis in the Bolivian Altiplano

Fasciolosis, caused by trematodes of the genus Fasciola, is an emerging disease of humans. One of the highest levels of human fasciolosis hepatica is found amongst the indigenous Aymaran people of the Northern Bolivian Altiplano. A meta-analysis of epidemiological surveys from 38 communities in the region demonstrates that fasciolosis has been endemic in the region since at least 1984 and is a zoonosis of rural communities. Human and bovine fasciolosis is associated with the communities lying in the plain from Lake Titicaca to La Paz, predominantly in the Los Andes province. In Los Andes incidences of up to 67% of population cohorts were found, and prevalence is age-related with the highest infection rate in children aged 8-11 years.

A 2.9 kDa Fasciola hepatica-recombinant protein based ELISA test for the detection of current-ovine fasciolosis trickle infected

The suitability of an enzyme linked immunosorbent assay (ELISA) test with a 2.9 kDa Fasciola hepatica-recombinant protein (FhrAPS) for diagnosing early and current-ovine fasciolosis was analyzed, and compared to that obtained by using a direct ELISA for detecting F. hepatica-circulating FhES antigens and to the coprological sedimentation for fluke egg quantitation. Fourteen Gallega autochthonous breed sheep were experimentally infected with metacercariae by a trickle system (small repetitive infections) and divided into two groups: G-I represented a primary infection for 34 weeks; G-R, animals with primary infection and reinfected 18 w.a.p.i. Seven sheep were left uninfected as the control group (G-C). Serum IgG antibody values against the FhrAPS rose rapidly by 1st w.a.p.i. in all infected sheep. Antibody levels in those with primary infection (G-I, G-C) peaked at 10 weeks, diminishing slightly and levelling from 16 to 34 weeks. Those with primary infection reinfected at 18 weeks had a rebound effect with the highest values observed. Circulating F. hepatica-ES antigens were detected by the 1st w.a.p.i. in all infected groups peaking at 6 weeks, decreasing rapidly to uninfected control values by 10 weeks of infection. Faecal egg-output started 11 weeks after primary infection. An increase in the IgG antibody as well as antigen responses to the FhrAPS and to anti-FhES from the 18 w.a.p.i. was recorded in G-T and G-R after the challenge infection. Antibody levels remained high whereas antigenemia values diminished after 6 weeks. A positive significant correlation between the IgG response against the FhrAPS and the F. hepatica circulating antigens (r2 = 0.428, p = 0.001) was obtained. In conclusion, our standardized diagnostic ELISA for fasciolosis based on the detection of IgG responses to the FhrAPS would be a valuable tool to diagnosis early and current F. hepatica-infections in sheep.

A novel Fasciola hepatica saposinlike recombinant protein with immunoprophylactic potential

A member of the Fasciola hepatica saposinlike/NK-lysin protein family with lytic activity on human peripheral blood mononuclear cells and erythrocytes was recently described. The current study was designed to test the immunoprophylactic potential of this protein termed FhSAP-2 against infection with F. hepatica in rabbits. Two doses of 50 microg of recombinant FhSAP-2 (rFhSAP-2) emulsified in TiterMax were injected subcutaneously on the dorsal surface of 4 rabbits at 2-wk intervals. Four weeks after the second immunization, the rabbits were infected orally with 25 F. hepatica metacercariae. Four non-immunized-infected rabbits were used as controls. An enzyme-linked immunosorbent assay revealed high levels of antibodies to both rFhSAP-2 and F. hepatica excretory-secretory antigens by 2 wk after the first immunization, which were always significantly higher in immunized-infected rabbits than in control-infected rabbits. On the completion of the trial, vaccinated rabbits had 81.2% less flukes than controls. Moreover, F. hepatica egg counts in feces, as well as in bile collected from the gall bladders from vaccinated animals, were lower, 83.8 and 73%, respectively, compared with controls. The vaccinated rabbits also had significantly lower amounts of parasite antigen in stool and bile samples than controls. Last, evaluation of macroscopic liver lesions revealed that the rabbits vaccinated with rFhSAP-2 had milder lesions than the infected-control rabbits. These findings support the hypothesis that this novel rFhSAP-2 protein has immunoprophylactic potential against fascioliasis in rabbits including antifecundity and antipathology effects. This is the first report on experimental vaccination of rabbits against F. hepatica with a purified, defined, recombinant protein related to a member of the saposinlike protein family.

A RECOMBINANT ANTIGEN RECOGNIZED BY FASCIOLA HEPATICA–INFECTED HOSTS

This work reports the detection of specific immunoglobulins (Ig) against rFh8, a recombinant Fasciola hepatica adult worm excretion-secretion antigen, in sera from experimentally (rabbit, Wistar rat, cattle, and sheep), or naturally (human) infected hosts. In the case of laboratory experimental models the study revealed significant differences between rabbits, which recognized the recombinant antigen all along the infection, and Wistar rats, which showed high anti-rFh8 Ig levels only for a short period of the infection. Available sera from experimentally infected cattle and sheep, as well as sera from naturally F. hepatica-infected humans, also contained significant levels of Ig against rFh8, suggesting that Fh8 was produced by F. hepatica at a very early stage of infection in all hosts so far analyzed and that the rFh8 antigen could be used as a tool for the diagnosis of F. hepatica infections.

AN ULTRASENSITIVE CAPTURE ELISA FOR DETECTION OF FASCIOLA HEPATICA COPROANTIGENS IN SHEEP AND CATTLE USING A NEW MONOCLONAL ANTIBODY (MM3)

A capture enzyme-linked immunosorbent assay (ELISA) using a new monoclonal antibody (mAb MM3) is reported for the detection of Fasciola hepatica excretory-secretory antigens (ESAs) in feces of infected hosts. The mAb MM3 was produced by immunization of mice with a 7- to 40-kDa purified and O-deglycosylated fraction of F. hepatica ESAs, which has previously been shown to be specific for the parasite. The specificity and sensitivity of the MM3 capture ELISA were assessed using feces from sheep and cattle. Sheep feces were obtained from a fluke-free herd (with most animals harboring other nematodes and cestodes), from lambs experimentally infected with 5-40 F. hepatica metacercariae and in some cases treated with triclabendazole at 14 wk postinfection (PI), and from uninfected control lambs. Cattle feces were collected at the slaughterhouse from adult cows naturally infected with known numbers of flukes (from 1 to 154) or free of F. hepatica infection (though in most cases harboring other helminths). The MM3 capture ELISA assay had detection limits of 0.3 (sheep) and 0.6 (cattle) ng of F. hepatica ESA per milliliter of fecal supernatant. The assay detected 100% of sheep with 1 fluke, 100% of cattle with 2 flukes, and 2 of 7 cattle with 1 fluke. The false-negative animals (5/7) were probably not detected because the F. hepatica individuals in these animals were immature (5-11 mm in length). As expected, coproantigen concentration correlated positively (r = 0.889; P < 0.001) with parasite burden and negatively (r = 0.712; P < 0.01) with the time after infection at which coproantigen was first detected. Nevertheless, even in animals with low fluke burdens (1-36 parasites), the first detection of F. hepatica-specific coproantigens by the MM3 capture ELISA preceded the first detection in egg count by 1-5 wk. In all sheep that were experimentally infected and then untreated, coproantigen remained detectable until at least 18 wk PI, whereas in sheep that were experimentally infected and then flukicide treated, coproantigen became undetectable from 1 to 3 wk after treatment. None of the fecal samples from sheep or cattle negative for fascioliasis but naturally infected with other parasites including Dicroelium dendriticum showed reactivity in the MM3 capture ELISA. These results indicate that this assay is a reliable and ultrasensitive method for detecting subnanogram amounts of F. hepatica antigens in feces from sheep and cattle, facilitating early diagnosis.

Passive protection against fasciolosis in mice by immunization with a monoclonal antibody (ES-78 MoAb)

Recently, we reported a partial characterization of the epitope recognized by the ES-78 monoclonal antibody (MoAb). This monoclonal antibody was obtained from spleen lymphocytes of a mouse immunized with excretory-secretory antigens of Fasciola hepatica adult worms. In the present study, we report the results obtained in experiments of passive protection using this MoAb in BALB/c mice infected with 15 Fasciola hepatica metacercariae. The monoclonal antibody was able to reduce the parasite burden when administered 24 h before challenge but not when delivered 7 days after challenge. The antibody recognition of digestive tract structures in 3-week-old parasites was demonstrated by immune histochemical techniques. The antigens purified by affinity chromatography using this antibody had molecular weights of 14-20, 25-29 and 36-45 kDa and demonstrated proteinase activity similar to cathepsin L. These results suggest that the antigens carrying the epitope recognized by the ES-78 MoAb may be used as target in the protection against fasciolosis.

Effect of parasite burden on the detection of Fasciola hepatica antigens in sera and feces of experimentally infected sheep

The effect of Fasciola hepatica parasite burden on the detection of excretory/secretory (E/S) antigens in sera and feces of experimentally infected sheep was evaluated using a double antibody-based capture enzyme-linked immunosorbent assay (ELISA). Four groups of five sheep each were used. The first three groups were infected with 50, 100 and 200 metacercariae of F. hepatica, and the fourth group remained as non-infected control. On the day of infection and weekly thereafter, serum and fecal samples were taken. ELISA detected F. hepatica E/S antigen levels in serum from the first week post-infection (wpi) and in fecal supernatant from the fourth wpi, which were significantly (p<0.05) higher than controls. F. hepatica eggs were not detected until after the eighth wpi. The correlation between absorbance of E/S antigens in serum with the fluke burden was 0.77 (p<0.0001) and in feces 0.76 (p<0.0001) at 12th wpi. The sensitivity of the assay to detect E/S antigens in serum was 86.6% and in feces 93.3%. It is concluded that the ELISA technique used in this study offers a diagnostic alternative for detecting early infections of F. hepatica in sheep.

Immunodiagnosis of human fascioliasis by an enzyme-linked immunosorbent assay (ELISA) and a micro-ELISA

Enzyme-linked immunosorbent assay (ELISA) and micro-ELISA were evaluated for their ability to detect anti-Fasciola hepatica antibodies in humans by using excretory-secretory antigen. The sensitivity of each method was 100%, but the specificity was 100% for ELISA and 97% for micro-ELISA. The micro-ELISA could be used as a screening assay and ELISA could be used as a confirmatory method for the serodiagnosis of human fascioliasis.

Serological responses of cattle after treatment and during natural re-infection with Fasciola hepatica, as measured with a dot-ELISA system

The dot-ELISA reaction was used to study the dynamics of IgG titers in cattle naturally infected with Fasciola hepatica after anthelmintic treatment and during reinfection. Excretion/secretion products (ES) of the parasite were used as antigens for the dot-ELISA. IgG antibodies were no longer detectable by dot-ELISA, 4-6 months after nine animals received the first of three weekly doses of triclabendazole (15 mg kg(-1)) and were then maintained on a pasture free of F. hepatica metacercariae. Six fluke-free cattle began shedding F. hepatica eggs 3-6 months after grazing a pasture contaminated with metacercariae of the parasite. A detectable increase in dot-ELISA IgG antibody levels was observed 2-4 weeks after natural reinfection by grazing a similar pasture contaminated with F. hepatica metacercariae. The usefulness of the dot-ELISA system to diagnose chronic infection by serology is complicated by previous treatment against the parasite. It is concluded that the ES antigens can be useful to detect early infection of cattle with F. hepatica in a dot-ELISA system

Fascioliasis: sonographic abnormalities of the biliary tract and evolution after treatment with triclabendazole

Diagnosis of infection with the liver fluke Fasciola hepatica is usually difficult. Ultrasonography (US) might be a useful diagnostic alternative, and we assessed the value of sequential US in the diagnosis and monitoring of fascioliasis in 76 patients at baseline and for 60 days after treatment with triclabendazole. At baseline, biliary abnormalities were observed in 52 patients. Crescent-shaped parasites were seen in 11 patients; in 2 cases parasites were spontaneously moving and in 4 patients parasites were motionless. Postprandial examination revealed parasites adhering to the gallbladder wall in a further 5 cases. In 3 further cases, gallbladder contents were mobile but did not sediment downwards after patients changed position. Non-specific abnormalities were: impaired gallbladder contractility (n = 23), gallbladder tenderness (n = 19), debris (n = 6), calculi (n = 5), wall thickening (n = 2) and bile duct dilatation (n = 12). During day 1-7, Fasciola-like crescents in the gallbladder or passing through the bile duct were detected in another 15 patients, impaired gallbladder contractility in 16, gallbladder tenderness in 16, and bile duct dilatation in an additional 28 patients. Thirty-two patients with these US abnormalities experienced colic-like abdominal pain accompanied by increased alkaline phosphatase in 25 cases. During day 30-60, abnormalities regressed completely in 45 patients; 2/6 triclabendazole failures were evident by detection of living parasites. Biliary tract abnormalities are frequently observed by US, but the detection-rate of Fasciola hepatica is disappointingly low despite the parasite's relatively large size. US findings must therefore be interpreted together with other clinical measurements. The visualization of parasites being expelled through the dilated common bile duct allowed the causal interpretation of post-therapeutic abdominal pain and increase of liver enzymes. When triclabendazole is given on suspicion, visualization of worm expulsion and bile duct dilatation by US may be used to confirm diagnosis.

Detection of circulating E/S antigens in the sera of patients with fascioliasis by IELISA: a tool of serodiagnosis and assessment of cure

An IELISA was developed to evaluate the performance of Fasciola E/S antigens in diagnosis and cure assessment of human Fasciola infection. Twenty patients with acute (prepatent) fascioliasis and another 20 with patent infection were enrolled in the study. Patients were treated with TCZ and followed at 1, 3 and 6 months after therapy. At inspection, the sensitivity of the test to diagnose prepatent cases was 100% compared to 70% for patent infections. There was a gradual decrease of antigenaemia over the follow-up period in acute cases. In chronic cases antigen disappeared from 13 cases (65%) at 1 month; this proportion did not change at 3 or 6 months.