From the Guidelines
The most effective way to test for Chagas disease is through a combination of microscopy, serology, and nucleic acid amplification tests (NAAT), with the specific test depending on the stage of infection, as outlined in the 2018 update by the Infectious Diseases Society of America and the American Society for Microology 1.
Diagnostic Approaches
During the acute phase of infection, microscopy of Giemsa-stained thick and thin blood films is the standard method for diagnosis, as it allows for the direct detection of extracellular trypanosomes 1.
- Microscopy should be performed on fresh blood samples, with slides and wet preps made within 1 hour of collection.
- The presence of motile trypomastigote forms with a large posterior kinetoplast is indicative of T. cruzi infection. In contrast, during the latent and chronic stages of infection, serology by commercially available enzyme-linked immunoassay (ELISA) kits is more useful, as parasites are no longer easily detected in peripheral blood preparations by microscopy 1.
- Positive ELISA results are considered evidence of active infection and can be used to exclude potential blood or tissue donors.
- A second confirmatory test, such as a radioimmunoprecipitation assay (RIPA) or immunoblot, may be performed to ensure accuracy.
Additional Diagnostic Methods
Other diagnostic methods, such as culture in Novy-MacNeal-Nicolle medium or NAAT, can also be used to detect T. cruzi infection 1.
- Culture can be performed on blood or tissue specimens and may be available through specialized reference laboratories.
- NAAT can be performed on venipuncture blood in EDTA tubes and can provide rapid results.
Importance of Early Detection
Early detection of Chagas disease is crucial, as treatment is most effective when started early, using medications like benznidazole or nifurtimox to eliminate the parasite before it causes serious organ damage 1.
- Testing is particularly important for people from endemic areas in Latin America, those who have received blood transfusions in endemic regions, or babies born to infected mothers.
From the FDA Drug Label
The conventional serologic tests used include indirect hemagglutination assay (IHA), immunofluorescence antibody assay (IFA), and/or enzyme linked immunosorbent assay (ELISA) and were based on the detection of antibodies against T. cruzi parasites Chagas disease diagnosis was confirmed by direct observation of T. cruzi by concentration test in patients <8 months of age at randomization and by demonstrating positive results for both the lysate enzyme-linked immunosorbent assay (ELISA) and the recombinant ELISA in patients ≥8 months to <18 years of age at randomization Seroconversion to negative confirmed by three assays, lysate ELISA, recombinant ELISA and IHA, was evaluated in patients in the 60-day treatment arm by age group
To test for Chagas disease, the following methods can be used:
- Indirect hemagglutination assay (IHA)
- Immunofluorescence antibody assay (IFA)
- Enzyme linked immunosorbent assay (ELISA)
- Lysate ELISA
- Recombinant ELISA
- Direct observation of T. cruzi by concentration test (for patients <8 months of age) These tests detect antibodies against T. cruzi parasites or directly observe the parasite. 2 3
From the Research
Diagnostic Methods for Chagas Disease
- The diagnosis of Chagas disease can be performed using various methods, including serological tests, molecular methods like PCR, and biomarker tests 4, 5, 6, 7, 8.
- Serological tests, such as enzyme-linked immunosorbent assays (ELISAs) and rapid tests, detect the presence of antibodies against Trypanosoma cruzi in the blood 5, 6, 7, 8.
- Molecular methods, like PCR, detect the parasite's DNA in blood or tissue samples and are highly sensitive and specific 4, 6.
Serological Tests
- ELISAs, such as Wiener and bioMérieux, have high sensitivity and specificity, with the Wiener ELISA showing a sensitivity of 98.92% and the bioMérieux ELISA showing a specificity of 99.45% 5.
- The TESA-blot test showed superior performance, with lower false-negative and false-positive rates, and can be used in conjunction with ELISAs for more accurate diagnosis 5.
- In-house ELISA methods can also be used for diagnosis and monitoring of Chagas disease morbidity, with high sensitivity and specificity 7.
Molecular Methods
- PCR tests, such as the NDO-PCR, have high sensitivity, specificity, and accuracy for detecting T. cruzi DNA in serum samples 6.
- The NDO-PCR showed a sensitivity of 92.3%, specificity of 100%, and accuracy of 94.3% in detecting T. cruzi DNA in serum samples 6.
- PCR tests can be used in conjunction with serological tests for more accurate diagnosis and monitoring of Chagas disease 4, 6.