Evaluation of three commercial enzyme-linked immunosorbent assays for diagnosis of Chagas' disease

Accuracy of Diagnostic Tests for the Detection of Chagas Disease: A Systematic Review and Meta-Analysis

The present systematic review and meta-analysis about the accuracy of diagnostic tests aim to describe the findings of literature over the last thirty years for the diagnosis of Chagas disease (CD). This work aimed to determine the accuracy of diagnostic techniques for CD in the disease's acute and chronic phases. The PubMed database was searched for studies published between 1990 and 2021 on CD diagnostics. Fifty-six published studies that met the criteria were analyzed and included in the meta-analysis, evaluating diagnostic accuracy through sensitivity and specificity. For Enzyme-Linked Immunosorbent Assay (ELISA), Fluorescent Antibody Technique (IFAT), Hemagglutination Test (HmT), Polymerase Chain Reaction (PCR), and Real-Time Polymerase Chain Reaction (qPCR) diagnosis methods, the sensitivity had a median of 99.0%, 78.0%, 75.0%, 76.0%, and 94.0%, respectively; while specificity presented a median of 99.0%, 99.0%, 99.0%, 98.0%, and 98.0%, respectively. This meta-analysis showed that ELISA and qPCR techniques had a higher performance compared to other methods of diagnosing CD in the chronic and acute phases, respectively. It was concluded utilizing the Area Under the Curve restricted to the false positive rates (AUCFPR), that the ELISA diagnostic test presents the highest performance in diagnosing acute and chronic CD, compared to serological and molecular tests. Future studies focusing on new CD diagnostics approaches should be targeted.

Commercial enzyme-linked immunosorbent assay versuspolymerase chain reaction for the diagnosis of chronic Chagas disease: a systematic review and meta-analysis

Chronic Chagas disease diagnosis relies on laboratory tests due to its clinical characteristics. The aim of this research was to review commercial enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) diagnostic test performance. Performance of commercial ELISA or PCR for the diagnosis of chronic Chagas disease were systematically searched in PubMed, Scopus, Embase, ISI Web, and LILACS through the bibliography from 1980-2014 and by contact with the manufacturers. The risk of bias was assessed with QUADAS-2. Heterogeneity was estimated with the I2 statistic. Accuracies provided by the manufacturers usually overestimate the accuracy provided by academia. The risk of bias is high in most tests and in most QUADAS dimensions. Heterogeneity is high in either sensitivity, specificity, or both. The evidence regarding commercial ELISA and ELISA-rec sensitivity and specificity indicates that there is overestimation. The current recommendation to use two simultaneous serological tests can be supported by the risk of bias analysis and the amount of heterogeneity but not by the observed accuracies. The usefulness of PCR tests are debatable and health care providers should not order them on a routine basis. PCR may be used in selected cases due to its potential to detect seronegative subjects.

Chagas disease in the 21st century: a public health success or an emerging threat?

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is a major public health burden in Latin America and a potentially serious emerging threat to a number of countries throughout the world. Although public health programs have significantly reduced the prevalence of Chagas disease in Latin America in recent decades, the number of infections in the United States and non-endemic countries in Europe and the Western Pacific Region continues to rise. Moreover, there is still no vaccine or highly effective cure available for the approximately 10 million people currently infected with T. cruzi, a third of which will develop potentially fatal cardiomyopathy and/or severe digestive tract disorders. As Chagas disease becomes an increasingly globalized public health issue in the twenty-first century, continued attentiveness from governmental and health organizations as well as improved diagnostic tools, expanded surveillance and increased research funding will be required to maintain existing public health successes and stymie the spread of the disease to new areas and populations.

Performance of different Trypanosoma cruzi antigens in the diagnosis of Chagas disease in patients with American cutaneous leishmaniasis from a co-endemic region in Argentina

OBJECTIVE

To determine the ability of recombinant antigens to detect cases of infection with Trypanosoma cruzi among cases of infection with Leishmania spp. by serological methods.

METHODS

Sera from 41 patients infected with Leishmania spp. were evaluated with ELISA using single (FRA, CP1 and TSSAVI) or pooled (commercial Rec-ELISA) recombinant proteins or homogenate antigens (commercial H-ELISA). As there is no gold standard antigen to discriminate Chagas disease from leishmaniasis, the correlation of results between defined antigens and the homogenate was made with Kappa Index (KI), the level of correlation considered being used as a criterion of specificity.

RESULTS

Single recombinant antigens and Rec-ELISA showed good correlation (KI > 0.8). A low correlation (KI < 0.66) was observed between the results from single recombinant antigens or the commercial recombinant kit and H-ELISA.

CONCLUSIONS

The highly correlated results between T. cruzi single or pooled recombinant proteins are indicative of the usefulness of recombinant antigens for Chagas diagnosis. Our results also indicate that in the city of Oran in Argentina, between 12% and 17% of patients with leishmaniasis are also infected with Chagas disease. The high KI values between TSSAVI and the other recombinant proteins suggest that in these patients, the infection may be caused by T. cruzi II and/or V and/or VI lineages.

A systematic review of high quality diagnostic tests for Chagas disease

Background

There is significant heterogeneity in reported sensitivities and specificities of diagnostic serological assays for Chagas disease, as might be expected from studies that vary widely according to setting, research design, antigens employed, and reference standard. The purpose of this study is to summarize the reported accuracy of serological assays and to identify sources of heterogeneity including quality of research design. To avoid associated spectrum bias, our analysis was limited to cohort studies.

Methods

We completed a search of PubMed, a bibliographic review of potentially relevant articles, and a review of articles identified by a study author involved in this area of research. Studies were limited to prospective cohort studies of adults published since 1985. Measures of diagnostic accuracy were pooled using a Der Simonian Laird Random Effects Model. A subgroup analysis and meta regression were employed to identify sources of heterogeneity. The QUADAS tool was used to assess quality of included studies and Begg's funnel plot was used to assess publication bias.

Results

Eighteen studies and 61 assays were included in the final analysis. Significant heterogeneity was found in all pre-determined subgroups. Overall sensitivity was 90% (95% CI: 89%–91%) and overall specificity was 98% (95% CI: 98%–98%).

Conclusion

Sensitivity and specificity of serological assays for the diagnosis of Chagas disease appear less accurate than previously thought. Suggestions to improve the accuracy of reporting include the enrollment of patients in a prospective manner, double blinding, and providing an explicit method of addressing subjects that have an indeterminate diagnosis by either the reference standard or index test.

Chagas disease, an infectious disease endemic to Latin America, is caused by the protozoan parasite Trypanosoma cruzi. T. cruzi can be transmitted through blood transfusions, organ transplants, or from mother to fetus, although it is most commonly transmitted through insect vectors. Infections can remain silent for many years before manifesting as potentially fatal damage to the cardiac and/or digestive system. Diagnosis of Chagas disease during its chronic asymptomatic phase is crucial to preventing future infections with T. cruzi and is often performed using serological tests that detect antibodies in the blood. Because there is currently no gold standard for serological diagnostic tests, multiple forms of serologic testing are often used in conjunction. The purpose of this study was to compare reports on the accuracy of serological tests. After limiting studies by certain criteria, the authors found a lower estimate of accuracy than has previously been reported in the literature and suggest quality improvements that can be made to standardize future reports.

Profile of Trypanosoma cruzi reactivity in a population at high risk for endemic pemphigus foliaceus (Fogo selvagem)

Fogo selvagem (FS) is an autoimmune bullous disease with pathogenic IgG autoantibodies recognizing desmoglein 1 (Dsg1), a desmosomal glycoprotein. In certain settlements of Brazil, a high prevalence of FS (3%) is reported, suggesting environmental factors as triggers of the autoimmune response. Healthy individuals from endemic areas recognize nonpathogenic epitopes of Dsg1, and exposure to hematophagous insects is a risk factor for FS. Fogo selvagem and Chagas disease share some geographic sites, and anti-Dsg1 has been detected in Chagas patients. Indeterminate Chagas disease was identified in a Brazilian Amerindian population of high risk for FS. In counterpart, none of the FS patients living in the same geographic region showed reactivity against Trypanosoma cruzi. The profile of anti-Dsg1 antibodies showed positive results in 15 of 40 FS sera and in 33 of 150 sera from healthy individuals from endemic FS sites, and no cross-reactivity between Chagas disease and FS was observed.

ELISA versus PCR for diagnosis of chronic Chagas disease: systematic review and meta-analysis

Background

Most current guidelines recommend two serological tests to diagnose chronic Chagas disease. When serological tests are persistently inconclusive, some guidelines recommend molecular tests. The aim of this investigation was to review chronic Chagas disease diagnosis literature and to summarize results of ELISA and PCR performance.

Methods

A systematic review was conducted searching remote databases (MEDLINE, LILACS, EMBASE, SCOPUS and ISIWeb) and full texts bibliography for relevant abstracts. In addition, manufacturers of commercial tests were contacted. Original investigations were eligible if they estimated sensitivity and specificity, or reliability -or if their calculation was possible - of ELISA or PCR tests, for chronic Chagas disease.

Results

Heterogeneity was high within each test (ELISA and PCR) and threshold effect was detected only in a particular subgroup. Reference standard blinding partially explained heterogeneity in ELISA studies, and pooled sensitivity and specificity were 97.7% [96.7%-98.5%] and 96.3% [94.6%-97.6%] respectively. Commercial ELISA with recombinant antigens studied in phase three investigations partially explained heterogeneity, and pooled sensitivity and specificity were 99.3% [97.9%-99.9%] and 97.5% [88.5%-99.5%] respectively. ELISA's reliability was seldom studied but was considered acceptable. PCR heterogeneity was not explained, but a threshold effect was detected in three groups created by using guanidine and boiling the sample before DNA extraction. PCR sensitivity is likely to be between 50% and 90%, while its specificity is close to 100%. PCR reliability was never studied.

Conclusions

Both conventional and recombinant based ELISA give useful information, however there are commercial tests without technical reports and therefore were not included in this review. Physicians need to have access to technical reports to understand if these serological tests are similar to those included in this review and therefore correctly order and interpret test results. Currently, PCR should not be used in clinical practice for chronic Chagas disease diagnosis and there is no PCR test commercially available for this purpose. Tests limitations and directions for future research are discussed.

Chagas disease: changes in knowledge and management

More than 100 years after the discovery of human American trypanosomiasis by Carlos Chagas, our knowledge and management of the disease are profoundly changing. Substantial progress made by disease control programmes in most endemic areas contrasts with persisting difficulties in the Gran Chaco region in South America and the recent emergence of the disease in non-endemic areas because of population movements. In terms of pathogenesis, major discoveries have been made about the life cycle and genomics of Trypanosoma cruzi, and the role of the parasite itself in the chronic phase of the disease. From a clinical perspective, a growing number of arguments have challenged the notion of an indeterminate phase, and suggest new approaches to manage patients. New methods such as standardised PCR will be necessary to ensure follow-up of this chronic infection. Although drugs for treatment of Chagas disease are limited, poorly tolerated, and not very effective, treatment indications are expanding. The results of the Benznidazole Evaluation For Interrupting Trypanosomiasis (BENEFIT) trial in 2012 will also help to inform treatment. Mobilisation of financial resources to fund research on diagnosis and randomised controlled trials of treatment are international health priorities.

Estimation of sensitivity and specificity of several Trypanosoma cruzi antibody assays in blood donors in Argentina

BACKGROUND

The absence of a gold standard test for Trypanosoma cruzi antibodies represents a problem not only for the evaluation of screening tests, but also for appropriate blood donor counseling. The aim of this study was to estimate the sensitivity and specificity of multiple blood donor screening tests for T. cruzi antibodies in Argentina.

STUDY DESIGN AND METHODS

From June 2006 to March 2007 a sample of 1455 blood donors was recruited from two blood banks in Chaco province, an area of Argentina with highly endemic T. cruzi infection. Samples were tested by three epimastigote lysate enzyme immunoassays (EIAs), one recombinant antigen EIA, two indirect hemagglutination assay (IHA) tests, a particle agglutination assay (PA), and a research trans-sialidase inhibition assay (TIA). Sensitivity and specificity were estimated using latent class analysis (LCA).

RESULTS

LCA estimated the consensus prevalence of T. cruzi infection at 24.5%. Interassay correlation was higher among the four EIA tests and TIA compared to IHA tests. Assay sensitivities varied from 96 to 99.7 for different EIAs, 91% for TIA, 84% for PA, and 66 to 74% for IHA tests. Relative to the LCA, assay specificities were from 96% to almost 100%.

CONCLUSION

Based on the comparison of several tests in a large population from an endemic area for T. cruzi infection, our data showed an adequate sensitivity for EIA tests in contrast to PA and IHA assays. The latter tests should no longer be used for blood donor screening.

Comparison of two immunochromatographic assays and the indirect immunofluorescence antibody test for diagnosis of Trypanosoma cruzi infection in dogs in south central Louisiana

Two rapid tests evaluated in dogs considered to be of high risk of infection with the Chagas parasite Trypanosoma cruzi using two immunochromatographic assays: Trypanosoma Detect for canine, InBios, Seattle, WA and CHAGAS STAT-PAK assay, Chembio Diagnostic Systems, Medford, NY, in south central Louisiana. For this purpose a serological survey was carried out in a total of 122 dogs and a serum bank was created. These 122 animals were first tested by IFAT that was used as the standard test. From the serum bank 50 samples were tested using the two rapid Chagas assays and results compared to the standard test IFAT. The serological survey using IFAT showed a prevalence of T. cruzi infection in 22.1% of the tested dogs. In the immunochromatographic assays, 13 and 11 animals were positive on rapid assay: Trypanosoma Detect for canine, InBios and CHAGAS STAT-PAK, Chembio Diagnostic Systems, respectively compared to 11 positive by IFAT. These two immunochromatographic tests have shown high susceptibility and specificity compared to our standard method IFAT. The rapid, easy and accurate screening assays used in conjunction with confirmatory tests, would be an excellent tool for veterinarians to diagnose T. cruzi infection. Early detection of T. cruzi infection may prevent complications through an effective treatment. Greater awareness by veterinarians of the risk, clinical findings, history along with diagnostic methods will contribute greatly to an understanding of the true prevalence of Chagas disease in dogs in Louisiana.

[Evaluation of SD BIOLINE Chagas Ab Rapid kit]

BACKGROUND

Chagas' disease is caused by Trypanosoma cruzi, a protozoan parasite, which is transmitted by blood-sucking bugs or through blood transfusion or organ transplantation. It is endemic in Central and South America. The objective of this study was to compare the performance of immunochromatographic SD Bioline Chagas Ab Rapid (Standard Diagnostics, Korea) with three immunochromatographic kits for the detection of antibodies to T. cruzi.

METHODS

A total of 320 serum specimens (140 positive and 180 negative) from National Reference Laboratory for Chagas and Leishmaniasis (NRLCL, Honduras) were used for the evaluation of four different test kits: SD Bioline Chagas Ab Rapid, Chagas Stat-Pak Assay (Chembio Diagnositc Systems, USA), OnSite Chagas Ab Rapid test-Cassette (CTK Biotech, USA), and Trypanosoma Detect Rapid Test (InBios International, USA). The results of four kits were compared with those of NRLCL. Cross-reactivity with other parasites was also evaluated.

RESULTS

Compared with the results of NRLCL, sensitivity and specificity were 99.3% and 100% for both of SD and Chembio kits, 97.2% and 100% for InBios kit, and 97.9% and 98.8% for CTK kit. None of other parasites showed cross-reactivity.

CONCLUSIONS

SD Bioline Chagas Ab Rapid kit showed test results highly correlating with those of National Reference Laboratory for Chagas and Leishmaniasis. It can be used for a rapid detection of Chagas' disease in endemic region and monitoring the disease among overseas travelers in Korea.

Evaluation of serological tests to identify Trypanosoma cruzi infection in humans and determine cross-reactivity with Trypanosoma rangeli and Leishmania spp

Five commercially available enzyme-linked immunosorbent assays (ELISAs), one in-house ELISA, and two hemagglutination assays were evaluated to determine their diagnostic accuracy for Chagas' disease in two studies. In study 1, ELISA kits showed 100% sensitivity, but specificities ranged from 82.84% to 100% when leishmaniasis cases were included and from 95.57% to 100% when leishmaniasis cases were excluded. Kits using recombinant antigens or synthetic peptides are more specific than those using crude extracts from Trypanosoma cruzi epimastigote forms. Kits evaluated in Panama, in study 2, showed 75% to 100% sensitivity and 97.12% to 100% specificity. These data were obtained by using a Western blot assay with T. cruzi trypomastigote excreted-secreted antigens as a reference test to confirm T. cruzi infection.

Clinical forms of Trypanosoma cruzi infected individuals in the chronic phase of Chagas disease in Puebla, Mexico

In Mexico, despite the relatively high seroprevalence of Trypanosoma cruzi infection in humans in some areas, reported morbidity of Chagas disease is not clear. We determined clinical stage in 71 individuals seropositive to T. cruzi in the state of Puebla, Mexico, an area endemic for Chagas disease with a reported seroprevalence of 7.7%. Diagnosis of Chagas disease was made by two standardized serological tests (ELISA, IHA). Individuals were stratified according to clinical studies. All patients were submitted to EKG, barium swallow, and barium enema. Groups were identified as indeterminate form (IF) asymptomatic individuals without evidence of abnormalities (n = 34 cases); those with gastrointestinal alterations (12 patients) including symptoms of abnormal relaxation of the lower esophageal sphincter and absent peristalsis in the esophageal body, grade I megaesophagus, and/or megacolon; patients with clinical manifestations and documented changes of chronic Chagas heart disease who were subdivided as follows: mild (8 patients)--mild electrocardiographic changes of ventricular repolarization, sinus bradychardia); moderate (6 patients)--left bundle branch block, right bundle branch block associated with left anterior fascicular block); severe (8 patients)--signs of cardiomegaly, dilated cardiomyopathy); and the associated form (3 cases) that included presence of both cardiomyopathy and megaesophagus. These data highlight the importance of accurate evaluation of the prevalence and clinical course of Chagas disease in endemic and non-endemic areas of Mexico.

Field evaluation of four novel enzyme immunoassays for Chagas' disease in Venezuela blood banks: comparison of assays using fixed-epimastigotes, fixed-trypomastigotes or trypomastigote excreted?secreted antigens from two Trypanosoma cruzi strains

Many serological tests have been developed for the diagnosis of Chagas' disease, but few have been subjected to a rigorous field evaluation. We have recently described several novel enzyme immunoassays (EIAs) based on fixed-whole organisms or trypomastigote excretory-secretory antigens (TESA) from different Trypanosoma cruzi strains (Tulahuen or Brazil). This study evaluated the most promising of these novel assays (e.g. fixed-epimastigotes, fixed-trypomastigotes, TESA Brazil and TESA Tulahuen antigens) in a field study of Venezuelan blood bank specimens. The assays were tested in an operator-blinded fashion using 2038 blood bank samples obtained from low and high T.cruzi prevalence regions of Venezuela (n= 1050 and n= 988 from Bolivar and Portuguesa states, respectively). Based on National Laboratory for Chagas Immunodiagnosis (NLCI) 'gold standard' results, all novel EIAs were superior to the commercial kit currently used in Venezuela, achieving 100% sensitivity and >99% specificity at optimal cut-off values. The novel assays identified seven false-negative samples compared with the routine screening performed by the Venezuelan blood bank although two samples were also misclassified as positive. Minor differences in the performance of the four novel assays were observed at lower arbitrary cut-off values. This study confirms the potential utility of both the fixed-organism and the TESA-based assays in the diagnosis of T.cruzi infection.

Serological diagnosis of Trypanosoma cruzi: evaluation of three enzyme immunoassays and an indirect immunofluorescent assay

Chagas' disease is an important cause of heart failure in Latin America, but is rare in the United States. The immigration of persons from endemic countries increases the potential of encountering patients with the disease. Concerns have also been raised about the introduction of Trypanosoma cruzi, the parasite that causes the disease, into the blood supply and during organ transplantation. To compare Chagas' antibody tests that are available in the United States, we evaluated three IgG ELISAs, CeLLabs T. cruzi ELISA, Hemagen Chagas' kit and IVD Research Chagas' Serum Microwell ELISA, and MarDx indirect immunofluorescent assays. The CeLLabs and Hemagen IgG ELISAs had 100 % agreement, sensitivity and specificity. The IVD Research IgG ELISA had 94·6 % agreement, 100 % sensitivity and 93 % specificity.

Chimeric synthetic peptides as antigens for detection of antibodies to Trypanosoma cruzi

Six chimeric synthetic peptides (QCha-1, QCha-2, QCha-3, QCha-4, QCha-5, and QCha-6) incorporating antigenic sequences of two immunodominant repeat B-cell epitopes of Trypanosoma cruzi were synthesized by conventional solid-phase peptide synthesis. The antigenic activity of these peptides was evaluated by UltramicroEnzyme-linked immunosorbent assay (UMELISA) by using panels of positive Chagasic sera (n=82), while specificity was evaluated with samples from healthy blood donors (n=44) and patients with other infectious diseases (n=86). The antigenicity of the chimeric peptides in solid-phase immunoassays was compared with that of the monomeric peptides. Data demonstrated that the chimeric peptide QCha-5 was the most reactive because it detected antibodies to parasite efficiently. The results indicate that chimeric peptide as coating antigen is very useful for the immunodiagnosis of Chagas' disease.

The validity of serologic tests for Trypanosoma cruzi and the effectiveness of transfusional screening strategies in a hyperendemic region

BACKGROUND

This study aims at obtaining unbiased estimates of the sensitivity and specificity of existing screening tests for Trypanosoma cruzi and at simulating the effectiveness of alternative screening strategies at different prevalence rates.

STUDY DESIGN AND METHODS

A systematic random sample of 400 was taken from 1200 banked serum samples of donors screened between August 1998 and January 1999 in Santa Cruz, Bolivia. Samples were tested with indirect hemagglutination test (IHA), indirect immunofluorescence assay (IFA), and four enzyme-linked immunosorbent assays (ELISAs). Sensitivity and specificity of tests were estimated through latent class analysis.

RESULTS

The sensitivity of individual tests ranged from 96.5 to 100 percent, and their specificity from 87.0 to 98.9 percent. Combinations of two tests used in parallel would, even at 40 percent prevalence, only miss approximately 1 infected unit per 10,000 screened. At 5 percent prevalence, however, they would yield 75 to 120 false-positive units per 1000 units screened. Parallel testing with IHA plus ELISA or with IHA plus IFA is marginally more cost-effective, compared to single IHA testing, than single ELISA or single IFA testing, regardless of the T. cruzi prevalence.

CONCLUSIONS

Routine blood donor screening for T. cruzi with a single test results in unacceptable numbers of false-negative samples in highly endemic areas or in at risk population groups. Adding a second test seems mandatory, but which one to choose depends on local cost components and feasibility.

Safety of the blood supply in Latin America

Appropriate selection of donors, use of sensitive screening tests, and the application of a mandatory quality assurance system are essential to maintain the safety of the blood supply. Laws, decrees, norms, and/or regulations covering most of these aspects of blood transfusion exist in 16 of the 17 countries in Latin America that are the subject of this review. In 17 countries, there is an information system that, although still incomplete (there are no official reports on adverse events and incidents), allows us to establish progress made on the status of the blood supply since 1993. Most advances originated in increased screening coverage for infectious diseases and better quality assurance. However, in 2001 to 2002, tainted blood may have caused infections in 12 of the 17 countries; no country reached the number of donors considered adequate, i.e., 5% of the population, to avoid blood shortages, or decreased significantly the number of blood banks, although larger blood banks are more efficient and take advantage of economies of scale. In those years, paid donors still existed in four countries and replacement donors made up >75% of the blood donors in another eight countries. In addition, countries did not report the number of voluntary donors who were repeat donors, i.e., the healthiest category. In spite of progress made, more improvements are needed.

Using polymerase chain reaction in early diagnosis of re-activated Trypanosoma cruzi infection after heart transplantation

BACKGROUND

Heart transplantation is an effective treatment for patients with end-stage Chagas' heart disease. Re-activation of Chagas' disease in transplant recipients is frequent, triggered by immunosuppression level. Therefore, highly sensitive methods for early diagnosis of Chagas' disease relapse are necessary to initiate appropriate therapy. We analyzed the use of polymerase chain reaction (PCR) in the clinical follow-up of heart transplant recipients.

METHODS

We prospectively evaluated 4 heart transplant recipients at the Hospital Privado, Cordoba, Argentina, who had terminal Chagas' disease. The parameters analyzed were presence of parasites in the blood (blood culture, Strout) and in endomyocardial biopsy (EMB) samples, and PCR was performed with oligonucleotides directed to a nuclear repetitive sequence of Trypanosoma cruzi. We evaluated these parameters weekly from the day of transplantation until results were negative and then during regular follow-up visits.

RESULTS

In 2 patients, we detected T cruzi using PCR in peripheral blood 30 days before clinical evidence of re-activation. In the 3rd case, PCR results in peripheral blood were positive from the day before transplantation, followed by positive results in EMB and sub-cutaneous chagomas biopsy specimens. Only 1 patient had positive Strout results for parasites in skin lesions, and none showed amastigotes in the biopsy specimens. After clinical diagnosis, all patients received 5 mg/kg/day benzimidazole for 6 months, with acceptable tolerance and good clinical outcome. All patients had negative peripheral blood PRC results after 30 days of treatment. One patient had intermittent positive PCR results during follow-up, with no evidence of clinical re-activation.

CONCLUSION

Polymerase chain reaction detection of T Cruzi in heart transplant recipients is a more sensitive and specific procedure in diagnosing Chagas' disease re-activation.

Chagas' disease: application of TESA-blot in inconclusive sera from a Brazilian blood bank

BACKGROUND AND OBJECTIVES

The procedure used for screening Trypanosoma cruzi-infected blood donors by using two serological techniques has frequently led to discordant results. The TESA-blot, a confirmatory test for Chagas' disease, was applied in a survey of inconclusive sera from a Brazilian blood bank.

MATERIALS AND METHODS

Four hundred and forty-eight sera, obtained from blood donors at the HRU-Fundação Hemominas, were tested by using the TESA-blot assay, a Western blotting method. Of these 448 sera, 348 had previously been determined as inconclusive for Chagas' disease owing to discordance between the indirect immunofluorescence assay (IFA) and the enzyme-linked immunosorbent assay (ELISA).

RESULTS

The TESA-blot was positive for 2.87% (10/348) of the inconclusive sera, and 100% positive and negative for the sera from chagasic (n=50) and non-chagasic (n=50) donors, respectively.

CONCLUSIONS

Our results clearly indicate the need to improve the diagnosis of Chagas' disease in blood banks by using new confirmatory diagnostic test(s). The TESA-blot, a new test with trypomastigote fractions of the T. cruzi Y strain, has made new approaches to the confirmation of Chagas' disease possible.

Development and comparison of enzyme immunoassays for diagnosis of Chagas' disease using fixed forms of Trypanosoma cruzi (Epimastigotes, Amastigotes, and Trypomastigotes) and assessment of antigen stability for the three assays

Three enzyme immunoassays (EIAs) for diagnosis of Chagas' disease were developed with fixed forms of Trypanosoma cruzi using a panel of 435 sera from the following groups: Venezuelan subjects positive by immunofluorescence (n = 70), Venezuelan healthy controls (n = 85), healthy Canadians (n = 166), and subjects with other parasitic diseases (n = 114). All assays achieved 100% sensitivity and reasonable specificity for amastigotes (97.6%), epimastigotes (98.3%), and trypomastigotes (99.3%). The fixed-trypomastigote assay was stable over 4 months at 4 degrees C and room temperature. These data suggest that a fixed-trypomastigote EIA may be a suitable candidate for blood bank screening.

Serodiagnosis of chronic and acute Chagas' disease with Trypanosoma cruzi recombinant proteins: results of a collaborative study in six Latin American countries

An enzyme-linked immunosorbent assay to diagnose Chagas' disease by a serological test was performed with Trypanosoma cruzi recombinant antigens (JL8, MAP, and TcPo). High sensitivity (99.4%) and specificity (99.3%) were obtained when JL8 was combined with MAP (JM) and tested with 150 serum samples from chagasic and 142 nonchagasic individuals. Moreover, JM also diagnosed 84.2% of patients in the acute phase of T. cruzi infection.

Diagnosis of parasitic zoonoses by immunoenzymatic assays--analysis of cross-reactivity among the excretory/secretory antigens of Fasciola hepatica, Toxocara canis, and Ascaris suum

Several parasitic infections such fasciolosis, toxocariosis or ascariosis are important zoonoses. During the infection with Fasciola hepatica, Toxocara canis and Ascaris suum, an important intraorganic phase in their hosts takes place, releasing antigens responsible for a humoral immune response, which enables the diagnosis of that parasitosis. A study to identify the existence of cross-reactivity among the excretory/ secretory antigens of F. hepatica, T. canis and A. suum was developed. One group of Sprague-Dawley rats was infected with 20 metacercariae of F. hepatica and another group remained uninfected as control. By means of an Indirect-ELISA, the rat humoral immune response (IgG and IgM) against the excretory/secretory antigens of F. hepatica was analysed and measured for cross reactivity with T. canis and A. suum. IgM cross-reaction was mainly observed in the first 10 weeks post-infection. IgG cross-reaction was observed throughout the study, and was maximal at the 2-3 weeks and 3-6 weeks post-infection, which corresponds to the intraorganic migratory phase of these parasites. The western-blot showed that the rat IgG recognised three proteins of 190, 160 and 33 kDa in the antigens from F. hepatica, T. canis and A. suum. The existence of cross-reactivity among these antigens seems to demonstrate also the presence of structural similarities, such as tegumental proteins. These results should be consider when immunoassay probes are used in the diagnosis of parasitic infections.

An improved serodiagnostic test for Chagas' disease employing a mixture of Trypanosoma cruzi recombinant antigens

BACKGROUND

Blood transfusion is one of the most important transmission routes of Chagas' disease, a major parasitic infection in Latin America. Therefore, screening for antibodies to Trypanosoma cruzi is mandatory in blood banks in South America. Most of the commercial serologic tests employ epimastigote antigens and show a high number of inconclusive and false-positive results, with high economic and social costs.

STUDY DESIGN AND METHODS

An ELISA using a mixture of three T. cruzi recombinant antigens, B13, 1F8, and H49 (mix-ELISA), was evaluated, first with a panel of well-characterized sera from 617 patients with Chagas' disease and 277 nonchagasic individuals, living in nine countries of South and Central America. Subsequently, the mix-ELISA was evaluated with 451 samples, from an endemic area of Brazil (Goiás), that were rejected from several blood banks because they presented discrepant results by two commercially available kits (indirect immunofluorescence assay, indirect hemagglutination assay, and/or ELISA).

RESULTS

The mix-ELISA exhibited 99.7 percent sensitivity and 98.6 percent specificity in the first evaluation with the 894 samples. In the second evaluation, 451 sera that had discrepant results in the first screening for Chagas' disease were further analyzed with the mix-ELISA. Upon consideration of the consensus results obtained with the trypomastigote excreted-secreted antigens blot test, a confirmatory test for Chagas' disease, the mix-ELISA led to a reduction in 99.6 percent in the number of discordant sera.

CONCLUSION

The combination of three T. cruzi recombinant antigens in a multiantigen immunoassay was highly sensitive and specific for Chagas' disease diagnosis. It is proposed that it can be applicable in blood bank screening in conjunction with the conventional serologic tests.

High prevalence anti-Trypanosoma cruzi antibodies, among blood donors in the State of Puebla, a non-endemic area of Mexico

Blood transfusion is the second most common transmission route of Chagas disease in many Latin American countries. In Mexico, the prevalence of Chagas disease and impact of transfusion of Trypanosoma cruzi-contaminated blood is not clear. We determined the seropositivity to T. cruzi in a representative random sample, of 2,140 blood donors (1,423 men and 647 women, aged 19-65 years), from a non-endemic state of almost 5 millions of inhabitants by the indirect hemagglutination (IHA) and enzyme linked immunosorbent assay (ELISA) tests using one autochthonous antigen from T. cruzi parasites, which were genetically characterized like TBAR/ME/1997/RyC-V1 (T. cruzi I) isolated from a Triatoma barberi specimen collected in the same locality. The seropositivity was up to 8.5% and 9% with IHA and ELISA tests, respectively, and up to 7.7% using both tests in common. We found high seroprevalence in a non-endemic area of Mexico, comparable to endemic countries where the disease occurs, e.g. Brazil (0.7%), Bolivia (13.7%) and Argentina (3.5%). The highest values observed in samples from urban areas, associated to continuous rural emigration and the absence of control in blood donors, suggest unsuspected high risk of transmission of T. cruzi, higher than those reported for infections by blood e.g. hepatitis (0.1%) and AIDS (0.1%) in the same region.

Enzyme-linked immunosorbent assay for serological diagnosis of Chagas' disease employing a Trypanosoma cruzi recombinant antigen that consists of four different peptides

Serological tests to detect Trypanosoma cruzi antibodies have been used for screening blood donors, for epidemic studies, and for diagnosis of probably infected persons. Among different tests, the enzyme-linked immunosorbent assay (ELISA) with total, semipurified, or synthetic antigens has been widely used, mainly due to its easy automation. Aiming to improve serological studies concerning Chagas' disease, we have developed and evaluated a new test, the TcF-ELISA, using an artificially engineered recombinant antigen, which contains tandem sequences of different T. cruzi-specific peptides. The sensibility of the TcF-ELISA was determined with 101 serum samples from chagasic patients well-defined by clinical and epidemiological criteria. The specificity was determined with 39 serum samples from leishmaniasis or kala-azar patients and 150 serum samples from nonchagasic blood donors from Sao Paulo, Brazil. The TcF-ELISA showed 100% sensitivity and 98.94% of specificity. Compared with conventional ELISA (with semipurified T. cruzi epimastigote antigens), the TcF-ELISA showed advantages; for example, it distinguishes better between reagent and nonreagent serum and provides better precision and a lower occurrence of leishmaniasis cross-reactions. Our studies demonstrate high reproducibility between two different lots of the TcF ELISA and its applicability for the serological diagnosis of Chagas' disease.

Antibodies to Trypanosoma cruzi among blood donors in Buenos Aires, Argentina

OBJECTIVES

The aim of this work was to study the prevalence of anti-Trypanosoma cruzi in the blood donor population in Buenos Aires, to compare the relative sensitivity and specificity of the two screening tests used and to confirm the results with a third assay.

MATERIAL AND METHODS

Between May 1995 and July 1999, 64,887 blood donor consecutive samples were screened with the following commercial tests: indirect hemagglutination (IHA) (Polychaco, Buenos Aires, Argentina) and enzyme-linked immunosorbent assay (ELISA) (40,222 with Chagatek, Organon Teknika, Buenos Aires, Argentina, and 24,665 with Chagas EIA, Abbott, São Paulo, Brazil). Repeatedly reactive samples in one or both tests were analyzed with a third method: dot blot (Bio Chagas, Gador, Buenos Aires, Argentina) or particle agglutination (Serodia, Fujirebio, Tokyo, Japan). Sera that reacted in at least two tests were considered positive.

RESULTS

The seroprevalence was 2.66% (1744 samples were reactive for one or both screening tests), and 1.46% (949 samples) were confirmed positive. The ELISAs proved to be more sensitive (relative sensitivity: 99.67-99.71%) whereas 192 samples (0.47%) were IHA false-negatives (relative sensitivity: 79.77%). Relative specificity for EIA was 98.47--99.23% and for IHA 99.85%.

CONCLUSIONS

Results suggest the need of performing two screening tests for Chagas disease in blood banks from endemic areas and the importance of a third confirmatory assay to avoid unnecessary medical counseling.

Prevention of transfusional Trypanosoma cruzi infection in Latin America

Trypanosoma cruzi is a protozoan infection widely spread in Latin America, from Mexico in the north to Argentina and Chile in the south. The second most important way of acquiring the infection is by blood transfusion. Even if most countries of Latin America have law/decree/norms, that make mandatory the screening of blood donors for infectious diseases, including T. cruzi (El Salvador and Nicaragua do not have laws on the subject), there is usually no enforcement or it is very lax. Analysis of published serologic surveys of T. cruzi antibodies in blood donors done in 1993, indicating the number of donors and screening coverage for T. cruzi in ten countries of Central and South America indicated that the probability of receiving a potentially infected transfusion unit in each country varied from 1,096 per 10,000 transfusions in Bolivia, the highest, to 13.02 or 13.86 per 10,000 transfusions in Honduras and Venezuela respectively, where screening coverage was 100%. On the other hand the probability of transmitting a T. cruzi infected unit was 219/10,000 in Bolivia, 24/10,000 in Colombia, 17/10,000 in El Salvador, and around 2-12/10,000 for the seven other countries. Infectivity risks defined as the likelihood of being infected when receiving an infected transfusion unit were assumed to be 20% for T. cruzi. Based on this, estimates of the absolute number of infections induced by transfusion indicated that they were 832, 236, and 875 in Bolivia, Chile and Colombia respectively. In all the other countries varied from seven in Honduras to 85 in El Salvador. Since 1993, the situation has improved. At that time only Honduras and Venezuela screened 100% of donors, while seven countries, Argentina, Colombia, El Salvador, Honduras, Paraguay, Uruguay and Venezuela, did the same in 1996. In Central America, without information from Guatemala, the screening of donors for T. cruzi prevented the transfusion of 1,481 infected units and the potential infection of 300 individuals in 1996. In the same year, in seven countries of South America, the screening prevented the transfusion of 36,017 infected units and 7, 201 potential cases of transfusional infection.

Transfusion-transmitted infectious diseases in Argentina, 1995 through 1997

BACKGROUND

Assessment of the safety of the blood supply, the quality of screening procedures, and the risk of transfusion transmission of infectious diseases in any country can be estimated by reviewing the records of blood donations and screening procedures and the prevalence of serologic markers of infectious diseases.

STUDY DESIGN AND METHODS

Information on blood donors, particularly the number of screened donors, and on the prevalence of serologic markers of infectious diseases was available from Argentina for 1995 through 1997. This information permitted the estimation of the risks and costs of preventing transfusion transmission of infectious diseases within the country during this period.

RESULTS

Screening coverage was higher in the private sector. The proportion of donors screened for HIV increased from 84.52 percent in 1995 to 97.97 percent in 1997; in the same period, serologic screening for HbsAg increased from 83.71 percent to 98.48 percent; that for HCV from 69. 92 percent to 97.83 percent; and that for syphilis from 87.94 percent to 98.71 percent. One hundred percent of donors were screened for Trypanosoma cruzi throughout the period. The overall prevalence of HIV per year varied from 2.42 to 3.36 per 1,000 donors; that of HBV, from 5.80 to 9.76 per 1,000; of HCV, from 7.39 to 16.61 per 1,000; and of syphilis, from 5.25 to 7.65 per 1,000. The overall prevalence of antibodies to T. cruzi ranged from 36.53 to 49.20 per 1,000 donors. The overall index of the spread of infectious viral disease through blood transfusion decreased from 47. 74 per 10,000 donations in 1995 to 4.75 per 10,000 in 1997. The ratio of acquired infections to donations improved from 1:209 to 1:2, 102 during the same period. The risk of T. cruzi infection from 1995 through 1997 was, in theory, nil, given the 100-percent screening. The greatest threat to the quality of the blood supply throughout the period studied was HCV.

CONCLUSION

The status of the blood supply in Argentina improved steadily from 1995 to 1997, as shown by the increase in screening coverage.

Serological confirmation of Chagas' disease by a recombinant and peptide antigen line immunoassay: INNO-LIA chagas

Although screening for Trypanosoma cruzi antibodies is mandatory in most South American countries, current tests are insensitive and have poor specificity. A recently optimized line immunoassay (the INNO-LIA Chagas assay) for the serological confirmation of Chagas' disease was evaluated at a large blood bank in São Paulo, Brazil. Sera from blood donors who reacted in at least one of three serological screening assays (n = 1,604) and who returned for a follow-up were retested, and the donors were interviewed to assess their epidemiological risk. The results obtained by the confirmatory assay evaluated in this study were compared to those obtained by the three different screening assays. Upon consideration of the consensus results obtained by the three different screening assays as a "gold standard," the INNO-LIA Chagas assay showed a sensitivity of 99.4% (95% confidence interval [CI], 98.3 to 99.9) and a specificity of 98.1% (95% CI, 96.6 to 99.0) for positive (n = 503) and negative (n = 577) sera. The INNO-LIA Chagas assay confirmed the results for significantly larger numbers of positive samples of at-risk individuals independent of the number of positive screening tests (P = 0.017, Mantel-Haenszel test). In conclusion, the INNO-LIA Chagas assay reliably confirmed the presence of antibodies to T. cruzi and can be implemented as a confirmatory assay for Chagas' disease serology.

A recombinant peptide antigen line immunoassay optimized for the confirmation of Chagas' disease

BACKGROUND

The transfusion of contaminated blood has become the major route of transmission for Chagas' disease in Brazil. Current screening tests are insensitive and yield conflicting results, while confirmatory assays do not exist. A line immunoassay (INNO-LIA Chagas Ab [INNO-LIA]) combining relevant, immunodominant recombinant and synthetic antigens on a single nylon membrane strip was evaluated for the serologic confirmation of Chagas' disease.

STUDY DESIGN AND METHODS

Sera from 1062 patients and healthy residents of four Brazilian regions endemic for Chagas' disease were used for test optimization. The established confirmation algorithm was evaluated with an independent set of positive (n = 75) and negative (n = 148) samples.

RESULTS

In the optimization phase, without an established comparative gold standard, the results with the INNO-LIA were compared with those obtained in four other screening assays. In the validation phase, the INNO-LIA showed a sensitivity of 100 percent (95% CI, 95.21-100) and a specificity of 99.32 percent (95% CI, 96.29-99.98) for well-characterized sera. Moreover, its specificity reached 100 percent with a set of 40 sera obtained from patients with documented leishmaniasis. The interpretation criteria defined in this study indicated that the INNO-LIA accurately detected the presence of antibodies to various specific antigens of Trypanosoma cruzi.

CONCLUSION

The INNO-LIA Chagas Ab assay may become the first commercial assay to reliably confirm the presence of antibodies to T. cruzi.