Chagas disease laboratory tests
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
|
Chagas disease Microchapters |
|
Diagnosis |
|---|
|
Treatment |
|
Case Studies |
|
Chagas disease laboratory tests On the Web |
|
American Roentgen Ray Society Images of Chagas disease laboratory tests |
|
Risk calculators and risk factors for Chagas disease laboratory tests |
Overview
Laboratory Findings
Diagnosis of chronic Chagas disease is made after consideration of the patient's clinical findings, as well as by the likelihood of being infected, such as having lived in an endemic country. Diagnosis is generally made by testing with at least two different serologic tests.
Demonstration of the causal agent is the diagnostic procedure in acute Chagas' disease. It almost always yields positive results, and can be achieved by:
- Microscopic examination: a) of fresh anticoagulated blood, or its buffy coat, for motile parasites; and b) of thin and thick blood smears stained with Giemsa, for visualization of parasites; it can be confused with the 50% longer Trypanosoma rangeli, which has not shown any pathogenicity in humans yet.
- Isolation of the agent by: a) inoculation into mice; b) culture in specialized media (e.g., NNN, LIT); and c) xenodiagnosis, where uninfected Reduviidae bugs are fed on the patient's blood, and their gut contents examined for parasites 4 weeks later.
- Various Immunodiagnostic tests; (also trying to distinguish strains (zymodemes) of T.cruzi with divergent pathogenicities).
- Complement fixation
- indirect hemagglutination
- IFA, Indirect fluorescent assay
- RIA, Radio-immunoassay
- ELISA, Enzyme-Linked Immunosorbent Assay
- Diagnosis based on Molecular Biology techniques.
- PCR, Polymerase chain reaction, most promising
Antibody Detection:
Infections with Trypanosoma cruzi are common in Mexico, Central America, and South America. Many immigrants from areas where Chagas disease is endemic currently reside in the United States and are potential sources for parasite transmission via contaminated blood. During the acute phase of illness, blood film examination generally reveals the presence of trypomastigotes. During the chronic phase of infection, parasitemia is low; immunodiagnosis is a useful technique for determining whether the patient is infected.
The indirect fluorescent antibody (IFA) test is available at CDC. IFA antigen slides are prepared from a suspension of epimastigotes. Although IFA is very sensitive, cross-reactivity can occur with sera from patients with leishmaniasis, a protozoan disease that occurs in some of the same geographical areas as T. cruzi. Various serologic methods are commercially available in the U.S. and other countries for laboratory diagnosis of Chagas disease. The sensitivity and specificity of these tests are highly variable.