Diagnosis

Diagnostic tests should be performed in all patients from Chagas disease–endemic areas and patients with epidemiologic risk factors for infection (e.g. former residence in an endemic area, maternal history of Chagas disease, unmonitored blood transfusion).

Depending on the stage of disease, Chagas disease can be diagnosed using direct or indirect parasitological methods.

• Direct parasitological methods: microscopic observation of the parasite in a peripheral blood smear, microhematocrit tube method, hemoculture with a specialized culture medium, xenodiagnosis, polymerase chain reaction (PCR) assay. These techniques are only valid for detecting acute infection, when large numbers of trypomastigotes are present in the blood (primarily ­­in the first 6 to 10 weeks of infection). Patients with chronic Chagas disease have low to moderate parasitemia. If immunocompromised, however, they may experience reactivation, in which case direct parasitological diagnosis would be indicated.
• Indirect parasitological methods: enzyme-linked immunosorbent assay, indirect immunofluorescence, and indirect hemagglutination test. Indirect methods are particularly indicated for the chronic phase of disease, when there are high titres of IgG anti-Trypanosoma cruzi antibodies. Based on the diagnostic criteria of the World Health Organisation, confirmation of T. cruzi infection should be based on a positive result in 2 separate serologic tests. Although patients with acute disease may have detectable IgM antibodies, direct parasitological methods are preferred in such cases.

A person is considered to have T. cruzi infection when there is laboratory confirmation of infection and a compatible epidemiological history.

• Development of a real-time PCR assay for Trypanosoma cruzi detection in blood samples. Piron M, Fisa R, Casamitjana N, López-Chejade P, Puig L, Vergés M, Gascón J, Gómez i Prat J, Portús M, Sauleda S. Acta Trop. 2007 Sep;103(3):195-200. Epub 2007 Jun 23.
• International study to evaluate PCR methods for detection of Trypanosoma cruzi DNA in blood samples from Chagas disease patients. Schijman AG, Bisio M, Orellana L, Sued M, Duffy T, Mejia Jaramillo AM, Cura C, Auter F, Veron V, Qvarnstrom Y, Deborggraeve S, Hijar G, Zulantay I, Lucero RH, Velazquez E, Tellez T, Sanchez Leon Z, Galvão L, Nolder D, Monje Rumi M, Levi JE, Ramirez JD, Zorrilla P, Flores M, Jercic MI, Crisante G, Añez N, De Castro AM, Gonzalez CI, Acosta Viana K, Yachelini P, Torrico F, Robello C, Diosque P, Triana Chavez O, Aznar C, Russomando G, Büscher P, Assal A, Guhl F, Sosa Estani S, DaSilva A, Britto C, Luquetti A, Ladzins J. PLoS Negl Trop Dis. 2011 Jan 11;5(1):e931.

• Estimation of the parasitemia in Trypanosoma cruzi human infection: high parasitemias are associated with severe and fatal congenital Chagas disease. Torrico MC, Solano M, Guzmán JM, Parrado R, Suarez E, Alonzo-Vega C, Truyens C, Carlier Y,Torrico F. Rev Soc Bras Med Trop. 2005;38 Suppl 2:58-61.

• WHO comparative evaluation of serologic assays for Chagas disease. Otani MM, Vinelli E, Kirchhoff LV, del Pozo A, Sands A, Vercauteren G, Sabino EC. Transfusion. 2009 Jun;49(6):1076-82.