The immunodiagnostic potential of Echinococcus granulosus adult-worm antigens in human cystic echinococcosis

Diagnostic performance of Echinococcus granulosus protoscolices antigens in the serodiagnosis of human cystic echinococcosis

The development of suitable serological tests for the diagnosis of CE is still necessary. This study aimed to evaluate the efficacy of ELISA in the diagnosis of human cystic echinococcosis (CE), using parasite protoscolices antigens. Liver hydatid cysts were isolated from sheep infected with hydatid cysts and the protoscolices were isolated from the hydatid cyst fluid. Protoscolices crude antigen was prepared by mechanical disruption, plus freeze-thawing and sonication methods. Thirty sera samples of confirmed hydatid cyst patients, 30 samples of healthy individuals, and 30 samples of people with other infections were collected and the samples were evaluated in an ELISA system, using the crude protoscolices antigen. The sera samples were also simultaneously evaluated by antigen B-ELISA. The estimated value of sensitivity and specificity for the ELISA, using the crude protoscolices antigens, was 93.3% (95% CI: 76.4-98.8%) and 90% (95% CI: 78.8-95.8%), respectively. These values were 86.6 (95% CI: 68.3-95.6) and 91 (95% CI: 80.81-96.9) for the antigen-B based ELISA. Antigens prepared from protoscolices of hydatid cyst are suitable candidates for the serologic diagnosis of human CE. Further studies are needed to identify a single specific antigen among the protoscolices antigens to improve the diagnostic performance of these antigens.

Degree of calcification and cyst activity in hepatic cystic echinococcosis in humans

To evaluate the relationship between cyst activity and calcification degree in cystic echinococcosis (CE) in humans, 99 hepatic cysts at successive stages of involution, surgically excised from 72 Sardinian patients, have been analyzed. Cysts were classified into 4 groups according to calcification extent: CALC 0 (no calcification); CALC 1 (scattered punctate calcifications); CALC 2 (large coarse segmental/partial calcifications); CALC 3 (complete or nearly complete circumferential ring of calcification up to thick wall of osseous consistency/calcified content of cyst). In addition the possible correlation with antibody response has been explored analyzing IgG1, IgG4 and IgE produced against somatic PSCAg. Results showed that calcification is not restricted to the inactive WHO cyst types CE4 and CE5, but occurs to a varying extent in all morphotypes of metacestode, from active classic unilocular or multivesicular cysts to the more complicated and highly degenerate stages, where cyst wall appears massively calcified. Prevalence of calcification increases with progression of cyst degenerative process, but is not synonymous with parasite inactivity and can be misleading as signs of calcification may coexist with still metabolically active cysts. On the contrary, detection of entirely firmly solidified content seems a reliable indication of cyst inactivity. IgG4 is the dominant isotype associated particularly with the evolutive phase. Positive rates and OD levels, higher in active vs inactive stages, are stable or increase slightly in weakly and moderately calcified cysts (CALC 1/CALC 2), compared to non-calcified ones (CALC 0), strongly decreasing in highly calcified forms (CALC 3). In conclusion, evaluation of calcification extent may be pertinent for staging CE, and immunological tests, particularly for IgG4, and IgE may help to better define cyst activity.

Laboratory Diagnosis of Echinococcus spp. in Human Patients and Infected Animals

Among the species composing the genus Echinococcus, four species are of human clinical interest. The most prevalent species are Echinococcus granulosus and Echinococcus multilocularis, followed by Echinococcus vogeli and Echinococcus oligarthrus. The first two species cause cystic echinococcosis (CE) and alveolar echinococcosis (AE) respectively. Both diseases have a complex clinical management, in which laboratory diagnosis could be an adjunctive to the imaging techniques. To date, several approaches have been described for the laboratory diagnosis and followup of CE and AE, including antibody, antigen and cytokine detection. All of these approaches are far from being optimal as adjunctive diagnosis particularly for CE, since they do not reach enough sensitivity and/or specificity. A combination of several methods (e.g., antibody and antigen detection) or of several (recombinant) antigens could improve the performance of the adjunctive laboratory methods, although the complexity of echinococcosis and heterogeneity of clinical cases make necessary a deep understanding of the host-parasite relationships and the parasite phenotype at different developmental stages to reach the best diagnostic tool and to make it accepted in clinical practice. Standardization approaches and a deep understanding of the performance of each of the available antigens in the diagnosis of echinococcosis for the different clinical pictures are also needed. The detection of the parasite in definitive hosts is also reviewed in this chapter. Finally, the different methods for the detection of parasite DNA in different analytes and matrices are also reviewed.

Serological Diagnosis and Follow-Up of Human Cystic Echinococcosis: A New Hope for the Future?

Cystic echinococcosis (CE) is an important helminthic zoonotic disease caused by the Echinococcus granulosus complex. In humans, CE is a chronic disease driven by the growth of echinococcal cysts in different organs. Prognosis of this disease depends on multiple factors, including location, number, size, and stage of the cysts, making CE a disease of complex management. CE is usually asymptomatic for years and attracts limited attention from funding organizations and health authorities. For this reason, only experts' recommendations are available but no evidence-based conclusions have been drawn for CE clinical management. One of those pitfalls refers to the lack of evidence to support the use of serological tools for the diagnosis and follow-up of CE patients. In this respect, crude antigens are used to detect specific antibodies in patients, giving rise to false positive results. The advent of molecular techniques allowing the production of recombinant proteins has provided a number of candidate antigens that could overcome the problems associated with the use of crude parasite extracts in the serological assays. In this review, we present the last advances in this field, proposing the use of serology to support cyst stage-specific diagnosis and follow-up.

Human Cystic Echinococcosis in the Nalut District of Western Libya: A Clinico-epidemiological Study

Human cystic echinococcosis (CE) is an endemic disease in the Mediterranean area that has not yet been fully documented in western Libya. The present study describes the clinico-epidemiologic profile of CE in western Libya’s Nalut district. From April 2008 to July 2011, 36 cases of CE were confirmed following surgical removal of cysts. The cysts were most frequently found in the liver (61.1%), followed by the lungs (19.4%), kidneys (11.1%), peritoneal cavity (11.1%), and spleen (5.6%). Among the 36 patients, 6 possessed plural cysts and 3 had cysts in 2 organs. Blood samples from this group were examined for the presence of serum anti-hydatid IgG antibodies, which revealed positivity in 25 patients (69.4%). An additional 300 blood samples were collected randomly from the inpatient and outpatient clinics at Nalut Hospital. Twenty-seven samples (9%) were found to be positive for the anti-hydatid IgG antibody among which the prevalence of infection tended to be higher in men (12%) than in women (6%). This study demonstrates that CE is a major parasitic infectious disease of public health significance in Libya, notably in the western part of the country, and that disease awareness needs to be raised nationwide.

Serodiagnosis of human hydatidosis with an ELISA developed based on antigens derived from sheep hydatid cysts and comparison with a commercial human ELISA kit

OBJECTIVE

To explore the serodiagnosis of hydatid cyst in human using different antigens of sheep (hydatid fluid, Somatic and Excretory/secretory antigens of protoscolex) by ELISA and compares this result with commercial human ELISA kit.

METHODS

One hundred blood samples from patients with history of severe abdominal pain and eosinophilia were obtained. Ten serum samples were obtained from surgically and pathologically confirmed cystic echinococcosis patients from Mashhad university hospital as positive control and 5 serum samples from infant under one year old as negative control. Blood samples were centrifuged at 3 000μg at 20 °C for 15 min and sera were stored at -20 °C. First, these samples were tested for the presence of antibody by commercial human ELISA. Then, ELISA was developed on microplates coated with hydatid fluid, Somatic and Excretory/secretory antigens of protoscolex of sheep.

RESULTS

The results of this study as analyzed by Kappa test showed that, hydatid fluid antigen could be used as a precise source of detection in indirect ELISA test.

CONCLUSIONS

Hydatid fluid in comparison with Excretory-secretory and somatic antigens showed more compatibility agreement in kappa test which can be used for further studies in development of any ELISA test for diagnosis of human hydatidosis.

Differential diagnosis of cystic and alveolar echinococcosis using an immunochromatographic test based on the detection of specific antibodies

Human cystic and alveolar echinococcoses are zoonotic diseases caused by the larval stages of Echinococcus granulosus and Echinococcus multilocularis, respectively. As the diseases are co-endemic in many areas of the world, a simple and rapid test for the differential diagnosis of cystic echinococcosis (CE) and alveolar echinocoocosis (AE) is needed. Here, we describe the development of an immunochromatographic test (ICT) using crude hydatid cyst fluid and a recombinant 18-kDa protein (rEm18) as antigens for the detection of E. granulosus and E. multilocularis antibodies in serum samples. The ICT was evaluated with serum samples from 195 echinococcosis patients from different endemic areas in northwestern China. These included 144 from CE patients, 51 from AE patients, 67 from patients with other parasitic diseases, 13 from patients with serous hepatic cysts, and 60 from healthy individuals. The sensitivity and specificity of the ICT for CE were 91.0 and 96.9% and for AE were 98.0 and 99.3% with diagnostic efficiencies of 94.1 and 99.1%, respectively. No significant differences and high degrees of agreement were found between the ICT and an enzyme-linked immunosorbent assay for both CE and AE. Five serum samples from cysticercosis patients and one serum sample from a healthy control were found positive for CE with the ICT. These findings indicate that this test allows for discrimination between both forms of human echinococcosis. In conclusion, the ICT developed in this study is a promising tool for the simultaneous detection and discrimination of CE and AE. This test will be useful for serodiagnosis of CE and AE in clinical settings and screening programs.

A review on diagnostic and preventive aspects of cystic echinococcosis and human cysticercosis

Cystic echinococcosis and human cysticercosis have recently been included in the list of "neglected tropical diseases" by the World Health Organization (WHO). Both are zoonoses which are prevalent throughout the world and lead to considerable mortality, morbidity, and economic losses as well. This review deals with the disease burden of these two neglected cestode infections. Diagnostic modalities with their specific advantages and disadvantages have also been discussed. Recent developments in immunodiagnostic assays for the two diseases have been dealt with. Various control strategies including the use of veterinary vaccines have been highlighted.

Gene cloning, expression, and localization of antigen 5 in the life cycle of Echinococcus granulosus

Antigen 5 (Ag5) has been identified as a dominant component of cyst fluid of Echinococcus granulosus and is considered as a member of serine proteases family, which in other helminth, plays an important role in the egg hatch and larva invasion. However, whether Ag5 is expressed and secreted in all life stages is unknown. In this study, according to the sequence in GenBank, we cloned and sequenced the open reading frame (ORF) of Ag5 gene from the protoscolices of E. granulosus isolated from the sheep in Qinhai Province of China, and found several substitutions and a base insert and deletion in a short region near the stop code, leading to a frameshift mutation which is conserved with the homologue of other cestode. The ORF is 1,455 bp in length, encoding 484 amino acids with a secretory signal peptide. Bioinformatics analysis predicted several phosphorylation and myristoylation sites and a N-glycosylation site and a species-specific linear B epitope in the protein. The ORF was cloned into the plasmid pET28a(+) vector and expressed in Escherichia coli . The recombinant protein was purified by affinity chromatography. Anti-rEgAg5 antiserum was prepared in rats and used to analyze the localization of Ag5 in protoscolex and adult worm by immunofluorescence technique. Results demonstrated that the Ag5 is strongly expressed in the tegument of protoscolex and the embryonic membrane of egg and surface of oncosphere; meanwhile, it is also weakly expressed in tegument of the adult. This study showed that Ag5 is expressed in all stages of life cycle, secreted from the surface of the worm and may be anchored in membrane by its myristoylation sites; these characteristics make it a candidate antigen for diagnosis and vaccine for both intermediate and definitive hosts.

Dot-Elisa for evaluation of hydatid cyst wall, protoscoleces and hydatid cyst fluid antigens in the serodiagnosis of cystic echinococcosis

The aim of the present study is to evaluate cyst wall and protoscolex as an alternate source of antigen in serodiagnosis of cystic echinococcosis (CE). A total of 90 blood samples, 30 each of confirmed CE cases, disease controls and healthy controls were collected. Dot-ELISA using cyst wall, protoscolex and cyst fluid were used to demonstrate anti-hydatid antibodies. The sensitivity of Dot-ELISA using cyst wall, protoscolex and cyst fluid was 96.66%, 86.66% and 93.33% respectively and the specificity of the assay was 70% for Dot-ELISA using cyst fluid, protoscolex and cyst wall antigens. Results of the present study show that cyst wall and protoscolex can also be an useful source of antigen in detection of hydatid antibodies in the serodiagnosis of CE.

Assessment of Echinococcus granulosus somatic protoscolex antigens for serological follow-up of young patients surgically treated for cystic echinococcosis

Echinococcus granulosus protoscolex soluble somatic antigens (PSSAs) were assessed for their prognostic value in the serological follow-up of young patients treated for cystic echinococcosis (CE), compared to conventional hydatid fluid (HF) antigen. Based on different clinical courses and outcome of infection, as well as imaging findings, patients were retrospectively classified into two different groups including either cured CE (CCE; i.e., absence of active cysts or presence of inactive cysts, respectively) and noncured CE (NCCE) patients still presenting active cysts at the end of an up to 5-year follow-up period. An immunoglobulin G (IgG)-PSSA enzyme-linked immunosorbent assay (ELISA) showed a gradual decrease in antibody levels in CCE cases, reaching seronegativity in 20% of the cases at least within 5 years postsurgery. In comparison, the conventional IgG-HF ELISA showed a significantly lower progressive decrease in antibody levels, serology becoming negative in only 15% of CCE patients at the endpoint of the follow-up period. Serological analysis of PSSA by immunoblotting yielded an interesting immunoreactive double band of 27 and 28 kDa that, in 15 (75%) of 20 CCE cases, exhibited a rapid decrease and subsequent disappearance of respective antibody reactivities within 3 years postsurgery. Conversely, anti-27- and -28-kDa antibody reactivity strongly persisted until the endpoint of the follow-up period in all of the five NCCE patients. Further analysis of the 27- and 28-kDa doublet by using affinity-purified antibodies showed that the double band was not detectable in HF. Furthermore, a predominantly IgG4 subclass-restricted humoral immune response against the 27- and 28-kDa antigens was demonstrated in seroreactive CE patients. Overall, an anti-27- and -28-kDa response appeared to correlate with cyst activity. In conclusion, PSSA represents a useful candidate to carry out a serologic follow-up of CE subsequent to treatment and deserves further respective evaluation for other age groups of CE patients.

Antigens for the immunodiagnosis of Echinococcus granulosus infection: An update

The taeniid tapeworm Echinococcus granulosus is the causative agent of the echinococcal disease, an important zoonosis with worldwide distribution. Accurate immunodiagnosis of the infection requires highly specific and sensitive antigens to be used in immunodiagnostic assays. The choice of an appropriate source of antigenic material is a crucial point in the improvement of the diagnostic features of tests, and must be based on the developmental stage of the parasite and the host. The most common antigenic sources used for the immunodiagnosis of echinococcal disease are hydatid cyst fluid, somatic extracts and excretory-secretory products from protoscoleces or adults of E. granulosus. Hydatid cyst fluid is the antigenic source of reference for immunodiagnosis of human hydatidosis, which is mainly based on the detection of antigens B and 5. Somatic extracts have been widely used in the serodiagnosis for E. granulosus infection in dogs and ruminant intermediate hosts, although in the last few years the detection of excretory-secretory products of the worm in faeces (coproantigens) have become the most reliable method for the detection of the parasite in the definitive host. This review emphasizes recent advances in the identification and characterization of novel antigens with potential for the immunodiagnosis of echinococcal disease. Progress in recombinant technologies and synthetic peptides are also discussed. The paper highlights the need to search for new antigenic components with high diagnostic sensitivity and specificity, a fact that remains a crucial task in the improvement of the immunodiagnosis of the disease.

Echinococcus granulosus in Jordan: assessment of various antigenic preparations for use in the serodiagnosis of surgically confirmed cases using enzyme immuno assays and the indirect haemagglutination test

The Enzyme linked immunosorbent Assay (ELISA), indirect haemagglutination (IHA), and immunoblot techniques (IB) were used for the serodiagnosis of surgically confirmed cystic echinococcosis (CE) caused by the tapeworm Echinococcus granulosus. Antigens used for the detection of IgG or total antibodies included crude sheep hydatid fluid (CSHF), autoclaved antigen B (AAB), boiled antigen B (BAB), and homogenate protoscoleces antigen (HPA). The overall sensitivity of the ELISA and IHA tests used for the serodiagnosis of 57 surgically confirmed human cases was 91.2% and 68.4%, respectively. The sensitivity of both tests was comparable in groups whose sera were collected one week before surgery and up to one year after surgery at 95.8% and 87.5%, respectively. In contrast, the sensitivity of the ELISA was significantly higher than that of IHA for sera of patients collected after one year of surgery. There was a positive correlation (r = 0.61) between the titers of antibodies detected by the ELISA and IHA. Using the IB technique, antigen B fractions (8/12, 16, and 24 KDa) were detectable by sera of 68.4% using either CSHF or AAB, 49.1% using BAB and 22.8% using HPA as detecting antigens. The overall sensitivity of the three AgB fractions was identical or similar to that of the 8/12 KDa fraction alone, indicating that the detection of the latter fraction is sufficient for the serodiagnosis of CE infection in humans. In conclusion, the ELISA is the test of choice for the serodiagnosis of CE and the follow up of cases following surgery using CSHF as an antigen. The IB test is a confirmatory test when antigen B fractions of CSHF or AAB are detected.