[Sensitivity and specificity of new commercial tests for the detection of specific Echinococcus antibodies]

Meta-Analysis of the Prevalence of Echinococcus in Sheep in China From 1983 to 2020

Echinococcosis is a zoonosis caused by the larval stage of cestode species that belong to the genus Echinococcus. The infection of hydatid in sheep is very common in China, especially in the northwestern China. Here, we conducted the first systematic review and meta-analysis of echinococcosis in sheep in China. Six databases (PubMed, ScienceDirect, Baidu Library, CNKI, Wanfang, and VIP Chinese Journal Database) were used to retrieve the literatures on echinococcosis in sheep in China from 1983 to 2020, and 74 studies. The random effects model was used in the “meta” package of the R software and the PFT was chosen for rate conversion. The research data were analyzed through subgroup analysis and univariate meta-regression analysis to reveal the factors that lead to research heterogeneity. The combined prevalence of Echinococcus in the selected period was estimated to be 30.9% (192,094/826,406). In the analysis of sampling year, the lowest positive rate was 13.9% (10,296/177,318) after 2011. The highest prevalence of Echinococcus was 51.1% (278/531) in the southwestern China. The highest infection rate in sheep was 20.1% (58,344/597,815) in the liver. The analysis based on age showed that the infection rate of elderly sheep was significantly higher than that in younger animals (P < 0.05). We also evaluated the effects of different geographic and climatic factors on the prevalence of Echinococcus in sheep. The results showed that the prevalence of Echinococcus was higher in high altitude, cold, humid, and high rainfall areas. It is necessary to carry out long-term monitoring and control of echinococcosis, cut off the infection route, and reduce the risk of infection in the high risk areas.

Design and construction of a new recombinant fusion protein (2b2t+EPC1) and its assessment for serodiagnosis of cystic echinococcosis

The immunodiagnostic tests for cystic echinococcosis (CE) are mostly serological tests based on ELISA that use hydatid cyst antigens for primary screening because of its simple preparation and availability. The challenge to develop new serological methods (as compared to those based on the hydatid cyst fluid antigens) to meet the gold standard remains. Appropriate sources of antigenic material are necessary for application to improve the efficacy of immunodiagnostic tests at a population level. In the current study, a fusion protein containing the coding sequence of antigen B2t and two sequences of EPC1 antigen with some modifications was reconstructed. Using bioinformatics tools, these sequences were joined together by applying the sequence of a rigid α-helix-forming linker to obtain an appropriate structure of a fusion protein. Synthetic recombinant fusion protein was expressed using pET28a as a vector and evaluated by indirect ELISA test for sera from patients with hepatic CE and other parasitic infections. The sensitivity of the fusion protein was lower (88.46%) than the available ELISA kit (96.15%). However, the differences in sensitivity were not statistically significant as compared to the recombinant fusion peptide with the commercial kit (p = 0.269). The specificity of the recombinant fusion protein (95.45%) was not significantly lower than the commercial kit (96.59%; p = 1.000). Moreover, surprisingly there was no difference in the cross-reactivity values of performance between the recombinant-ELISA and commercial kit. The positive and negative predictive values of the recombinant antigen were achieved as 92% and 93.33%, respectively, while for the commercial kit, they were obtained as 94.33% and 97.70%, respectively. In conclusion, as an early evaluation of these antigens the performance of our recombinant fusion protein in ELISA is relatively promising. Although, it seemed that this peptide with specific antigenic epitopes might be more appropriate for the serological evaluation of CE by use of bioinformatics tools, our findings showed that cross-reactions and a negative reaction could occur in clinical performance. This fusion protein may have utility for diagnosis in humans, but further evaluation is needed using the WHO ultrasound classification for CE.

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.

Microbiological laboratory diagnostics of neglected zoonotic diseases (NZDs)

This review reports on laboratory diagnostic approaches for selected, highly pathogenic neglected zoonotic diseases, i.e. anthrax, bovine tuberculosis, brucellosis, echinococcosis, leishmaniasis, rabies, Taenia solium-associated diseases (neuro-/cysticercosis & taeniasis) and trypanosomiasis. Diagnostic options, including microscopy, culture, matrix-assisted laser-desorption-ionisation time-of-flight mass spectrometry, molecular approaches and serology are introduced. These procedures are critically discussed regarding their diagnostic reliability and state of evaluation. For rare diseases reliable evaluation data are scarce due to the rarity of samples. If bio-safety level 3 is required for cultural growth, but such high standards of laboratory infrastructure are not available, serological and molecular approaches from inactivated sample material might be alternatives. Multiple subsequent testing using various test platforms in a stepwise approach may improve sensitivity and specificity. Cheap and easy to use tests, usually called "rapid diagnostic tests" (RDTs) may impact disease control measures, but should not preclude developing countries from state of the art diagnostics.

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.

Evaluation of reactivity to Echinococcus spp. among rural inhabitants in Poland

A group of 172 rural inhabitants from eastern Poland (68 males and 104 females, mean age 49.0 ± 12.0 years) was examined for the presence of antibodies against Echinococcus granulosus and Echinococcus multilocularis. A population of 38 healthy urban dwellers from the city of Lublin (17 males and 21 females, mean age 36.2 ± 9.6 years) were examined as a control group. Sera of 22 rural inhabitants (12.8%) reacted positively to Echinococcus granulosus hydatid fluid antigen in the screening test. A cross-reactivity was observed with two serum samples that tested positive in ELISA for E. granulosus. Three serum samples were tested positive for E. multilocularis using the Em2plus ELISA assay and also positive for Western blot. None of the members of control group showed the presence of a seropositive reaction to Echinococcus spp. The reactivity to Echinococcus spp. among rural inhabitants decreased with age and this correlation was statistically significant (R = -0.197151, p = 0.009535). The percentage of positive findings was the highest (50.0%) in the youngest age group (14-20). No significant correlations were found between responses to interview questions (possession of domestic and farm animals, contact with wild animals, eating unwashed berries, drinking unboiled water) and the presence of seropositive reactions to Echinococcus spp. The presented results seem to indicate that echinococcosis is still a current problem in Poland that should not be neglected and, moreover, indicates the need for improvement in the routine laboratory diagnostics of Echinococcus spp. by standardizing the ELISA and Western blot tests.

Helminths and helminthoses in Central Europe: diseases caused by cestodes (tapeworms)

The second part of the overview "Helminths and helminthoses in Central Europe" is dedicated to the cestodes (tapeworms) and the diseases caused by cestodes. The overview comprises the spectrum of the most relevant species, describes their incidence, geographic distribution and the most important clinical symptoms and highlights the possibilities of diagnosis, treatment and prophylaxis of cestode-caused diseases.

An easy and efficient method for native and immunoreactive Echinococcus granulosus antigen 5 enrichment from hydatid cyst fluid

Background

Currently, the serodiagnosis of cystic echinococcosis relies mostly on crude Echinococcus granulosus hydatid cyst fluid as the antigen. Consequently, available immunodiagnostic tests lack standardization of the target antigen and, in turn, this is reflected on poor sensitivity and specificity of the serological diagnosis.

Methodology/Principal Findings

Here, a chromatographic method enabling the generation of highly enriched Antigen 5 (Ag5) is described. The procedure is very easy, efficient and reproducible, since different hydatid cyst fluid (HCF) sources produced very similar chromatograms, notwithstanding the clearly evident and extreme heterogeneity of the starting material. In addition, the performance of the antigen preparation in immunological assays was preliminarily assessed by western immunoblotting and ELISA on a limited panel of cystic echinococcosis patients and healthy controls. Following western immunoblotting and ELISA experiments, a high reactivity of patient sera was seen, with unambiguous and highly specific results.

Conclusions/Significance

The methods and results reported open interesting perspectives for the development of sensitive diagnostic tools to enable the timely and unambiguous detection of cystic echinococcosis antibodies in patient sera.

Immunodiagnosis of CNS parasitic infections

The nature of many parasitic infections of the central nervous system (CNS) requires immunodiagnosis to confirm presumptive diagnoses. The CNS is the primary site of parasite infection for some parasitic organisms and for others, neurological infection occurs only in immunocompromised hosts. Still other parasites cause ectopic infections of the CNS and occur very rarely. This review concentrates on laboratory diagnosis of diseases that are caused by parasites with a primary predilection for the CNS. Emphasis is placed on laboratory diagnostic methods that are used and suitable for clinical diagnosis, rather than a comprehensive review of all the experimental methods that have been reported in the literature. Immunodiagnosis is not appropriate for the diagnosis of all parasitic infections of the CNS; in those cases, alternative diagnostic methods are presented, but not discussed in detail. In some instances potential new antigens or methods are presented, particularly if adoption of these methods is expected in the near future.

Serodiagnosis of Echinococcus spp. infection: explorative selection of diagnostic antigens by peptide microarray

Background

Production of native antigens for serodiagnosis of helminthic infections is laborious and hampered by batch-to-batch variation. For serodiagnosis of echinococcosis, especially cystic disease, most screening tests rely on crude or purified Echinococcus granulosus hydatid cyst fluid. To resolve limitations associated with native antigens in serological tests, the use of standardized and highly pure antigens produced by chemical synthesis offers considerable advantages, provided appropriate diagnostic sensitivity and specificity is achieved.

Methodology/Principal Findings

Making use of the growing collection of genomic and proteomic data, we applied a set of bioinformatic selection criteria to a collection of protein sequences including conceptually translated nucleotide sequence data of two related tapeworms, Echinococcus multilocularis and Echinococcus granulosus. Our approach targeted alpha-helical coiled-coils and intrinsically unstructured regions of parasite proteins potentially exposed to the host immune system. From 6 proteins of E. multilocularis and 5 proteins of E. granulosus, 45 peptides between 24 and 30 amino acids in length were designed. These peptides were chemically synthesized, spotted on microarrays and screened for reactivity with sera from infected humans. Peptides reacting above the cut-off were validated in enzyme-linked immunosorbent assays (ELISA). Peptides identified failed to differentiate between E. multilocularis and E. granulosus infection. The peptide performing best reached 57% sensitivity and 94% specificity. This candidate derived from Echinococcus multilocularis antigen B8/1 and showed strong reactivity to sera from patients infected either with E. multilocularis or E. granulosus.

Conclusions/Significance

This study provides proof of principle for the discovery of diagnostically relevant peptides by bioinformatic selection complemented with screening on a high-throughput microarray platform. Our data showed that a single peptide cannot provide sufficient diagnostic sensitivity whereas pooling several peptide antigens improved sensitivity; thus combinations of several peptides may lead the way to new diagnostic tests that replace, or at least complement conventional immunodiagnosis of echinococcosis. Our strategy could prove useful for diagnostic developments in other pathogens.

Crude or purified, somatic or metabolic extracts of native antigens are routinely used for the serodiagnosis of human helminthic infections. These antigens are often cross-reactive, i.e., recognized by sera from patients infected with heterologous helminth species. To overcome limitations in antigen production, test sensitivity and specificity, chemically synthesized peptides offer a pure and standardized alternative, provided they yield acceptable operative characteristics. Ongoing genome and proteome work create new resources for the identification of antigens. Making use of the growing amount of genomic and proteomic data available in public databases, we tested a bioinformatic procedure for the selection of potentially antigenic peptides from a collection of protein sequences including conceptually translated nucleotide sequence data of Echinococcus multilocularis and E. granulosus (Plathyhelminthes, Cestoda). The in silico selection was combined with high-throughput screening of peptides on microarray and systematic validation of reactive candidates in enzyme-linked immunosorbent assay. Our study proved the applicability of this approach for selection of peptide antigens with good diagnostic characteristics. Our results suggested the pooling of several peptides to reach a high level of sensitivity required for reliable immunodiagnosis.