Antibody Detection
Infections with Trypanosoma cruzi are common in Mexico, Central America, and South America, and most people with Chagas disease in the United States acquired their infections in endemic countries.  The transmission of Chagas disease via blood transfusion is a recognized risk, however a screening test was approved by the Food and Drug Administration in December 2006 and is currently in use by blood banks.  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.  CDC also utilizes an FDA-cleared commercial diagnostic enzyme immunoassay (EIA).  This assay uses purified antigens and provides additional information to inform the diagnosis.  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.

A

A: Positive IFA result with T. cruzi antigen (magnification 400×).