Immunoagglutination test to diagnose Chagas disease: comparison of different latex-antigen complexes

Chagas Disease: A Silent Threat for Dogs and Humans

Chagas disease (CD) is a vector-borne Neglected Zoonotic Disease (NZD) caused by a flagellate protozoan, Trypanosoma cruzi, that affects various mammalian species across America, including humans and domestic animals. However, due to an increase in population movements and new routes of transmission, T. cruzi infection is presently considered a worldwide health concern, no longer restricted to endemic countries. Dogs play a major role in the domestic cycle by acting very efficiently as reservoirs and allowing the perpetuation of parasite transmission in endemic areas. Despite the significant progress made in recent years, still there is no vaccine against human and animal disease, there are few drugs available for the treatment of human CD, and there is no standard protocol for the treatment of canine CD. In this review, we highlight human and canine Chagas Disease in its different dimensions and interconnections. Dogs, which are considered to be the most important peridomestic reservoir and sentinel for the transmission of T. cruzi infection in a community, develop CD that is clinically similar to human CD. Therefore, an integrative approach, based on the One Health concept, bringing together the advances in genomics, immunology, and epidemiology can lead to the effective development of vaccines, new treatments, and innovative control strategies to tackle CD.

Rapid immunochromatographic tests for the diagnosis of chronic Chagas disease in at-risk populations: A systematic review and meta-analysis

BACKGROUND

Despite of a high disease burden, mainly in Latin America, Chagas disease (CD) is underdiagnosed and undertreated. Rapid diagnostic tests (RDTs) might improve the access to diagnosis. The aim of this study is to review the accuracy of commercially available RDTs used in field conditions for the diagnosis of chronic CD in populations at risk, in endemic and non-endemic countries.

METHODS/PRINCIPAL FINDINGS

We undertook a comprehensive search of the following databases: PubMed, SCOPUS, LILACS (last up-date on the 01st July, 2017), without language or date limits. Non-electronic sources have been also searched. This review included clinical studies with cohort recruitment of individuals at risk of T. cruzi exposure, without age limits; adequate reference standards for the diagnosis of CD. We excluded case-control studies and those testing RDTs during acute CD. Data on test accuracies were pooled through a bivariate random-effects model. Only one index test was evaluated separately. Geographical area, commercial brand, disease prevalence, study size, and risk of bias were explored as possible source of heterogeneity. Values of sensitivity and specificity were computed to obtain summary positive/negative likelihood ratios, and summary diagnostic odds ratio. Ten studies were included on six different immunochromatographic RDTs. The pooled sensitivity and specificity of the RDTs resulted 96.6% (95% CI 91.3-98.7%) and 99.3% (95% CI 98.4-99.7%), respectively. Test accuracy was particularly good in endemic areas (98.07%/99.03% of sensitivity/specificity, respectively). One test (Stat-Pak) showed an overall sensitivity of 97% (95% CI 87.6-99.3) and specificity of 99.4% (95% CI 98.6-99.8).

CONCLUSIONS/SIGNIFICANCE

RDTs demonstrated to be sufficiently accurate to recommend their use for screening in endemic areas, even as stand-alone tests. This approach might increase the accessibility to the diagnosis. However, an additional confirmatory test in case of positive result remains a prudent approach.

Performance Assessment of a Trypanosoma cruzi Chimeric Antigen in Multiplex Liquid Microarray Assays

Diagnosing chronic Chagas disease (CD) requires antibody-antigen detection methods, which are traditionally based on enzymatic assay techniques whose performance depend on the type and quality of antigen used. Previously, 4 recombinant chimeric proteins from the Instituto de Biologia Molecular do Paraná (IBMP-8.1 to 8.4) comprising immuno-dominant regions of diverse Trypanosoma cruzi antigens showed excellent diagnostic performance in enzyme-linked immunosorbent assays. Considering that next-generation platforms offer improved CD diagnostic accuracy with different T. cruzi-specific recombinant antigens, we assessed the performance of these chimeras in liquid microarrays (LMAs). The chimeric proteins were expressed in Escherichia coli and purified by chromatography. Sera from 653 chagasic and 680 healthy individuals were used to assess the performance of these chimeras in detecting specific anti-T. cruzi antibodies. Accuracies ranged from 98.1 to 99.3%, and diagnostic odds ratio values were 3,548 for IBMP-8.3, 4,826 for IBMP-8.1, 7,882 for IBMP-8.2, and 25,000 for IBMP-8.4. A separate sera bank (851 samples) was employed to assess cross-reactivity with other tropical diseases. Leishmania, a pathogen with high similarity to T. cruzi, showed cross-reactivity rates ranging from 0 to 2.17%. Inconclusive results were negligible (0 to 0.71%). Bland-Altman and Deming regression analysis based on 200 randomly selected CD-positive and negative samples demonstrated interchangeability with respect to CD diagnostic performance in both singleplex and multiplex assays. Our results suggested that these chimeras can potentially replace antigens currently used in commercially available assay kits. Moreover, the use of multiplex platforms, such as LMA assays employing 2 or more IBMP antigens, would abrogate the need for 2 different testing techniques when diagnosing CD.

Accuracy of chimeric proteins in the serological diagnosis of chronic chagas disease - a Phase II study

BACKGROUND

The performance of current serologic tests for diagnosing chronic Chagas disease (CD) is highly variable. The search for new diagnostic markers has been a constant challenge for improving accuracy and reducing the number of inconclusive results.

METHODOLOGY/PRINCIPAL FINDINGS

Here, four chimeric proteins (IBMP-8.1 to -8.4) comprising immunodominant regions of different Trypanosoma cruzi antigens were tested by enzyme-linked immunosorbent assay. The proteins were used to detect specific anti-T. cruzi antibodies in the sera of 857 chagasic and 689 non-chagasic individuals to evaluate their accuracy for chronic CD diagnosis. The antigens were recombinantly expressed in Escherichia coli and purified by chromatographic methods. The sensitivity and specificity values ranged from 94.3% to 99.3% and 99.4% to 100%, respectively. The diagnostic odds ratio (DOR) values were 6,462 for IBMP-8.1, 3,807 for IBMP-8.2, 32,095 for IBMP-8.3, and 283,714 for IBMP-8.4. These chimeric antigens presented DORs that were higher than the commercial test Pathozyme Chagas. The antigens IBMP-8.3 and -8.4 also showed DORs higher than the Gold ELISA Chagas test. Mixtures with equimolar concentrations were tested in order to improve the diagnosis accuracy of negative samples with high signal and positive samples with low signal. However, no gain in accuracy was observed relative to the individual antigens. A total of 1,079 additional sera were used to test cross-reactivity to unrelated diseases. The cross-reactivity rates ranged from 0.37% to 0.74% even for Leishmania spp., a pathogen showing relatively high genome sequence identity to T. cruzi. Imprecision analyses showed that IBMP chimeras are very stable and the results are highly reproducible.

CONCLUSIONS/SIGNIFICANCE

Our findings indicate that the IBMP-8.4 antigen can be safely used in serological tests for T. cruzi screening in blood banks and for chronic CD laboratory diagnosis.

Chronic Chagas Disease Diagnosis: A Comparative Performance of Commercial Enzyme Immunoassay Tests

There is a significant heterogeneity in reported performance of serological assays for Chagas disease diagnosis. The conventional serology testing in laboratory diagnosis and in blood banks is unsatisfactory because of a high number of inconclusive and misclassified results. We aimed to assess the quality of four commercially available enzyme-linked immunosorbent assay tests for their ability to detect Trypanosoma cruzi antibodies in 685 sera samples. Cross-reactivity was assessed by using 748 sera from patients with unrelated diseases. Initially, we found that the reactivity index against T. cruzi antigen was statistically higher in sera from Chagas disease patients compared with those from non-chagasic patients, supporting the notion that all evaluated tests have a good discriminatory ability toward the diagnosis of T. cruzi infection in patients in the chronic phase of the disease. Although all tests were similarly sensitive for diagnosing T. cruzi infection, there were significant variations in terms of specificity and cross-reactivity among them. Indeed, we obtained divergent results when testing sera from patient with unrelated diseases, particularly leishmaniasis, with the levels of cross-reactivity being higher in tests using whole T. cruzi extracts compared with those using recombinant proteins. Our data suggest that all four tests may be used for the laboratory diagnosis and routine blood screening diagnose for Chagas disease. We also emphasize that, despite their general good performance, caution is needed when analyzing the results when these tests are performed in areas where other diseases, particularly leishmaniasis, are endemic.