Chagas Disease: Creeping into Family Practice in the United States

DIAGNOSING ACUTE, CHRONIC, AND CONGENITAL CHAGAS

Accurate diagnosis of Chagas disease requires a thorough history and physical exam, as well as a high index of suspicion. Recent travel to an endemic area of Chagas disease in combination with the typical signs and symptoms—such as fever, headache, lymphadenopathy, shortness of breath, myalgia, swelling, and abdominal or chest pain—should prompt the provider to perform more specific tests.⁴ Inquiry about past medical history, blood transfusions, and surgeries is also imperative to make the correct diagnosis.⁵

The approach to diagnosis of Chagas disease depends on whether the patient presents during the acute or chronic phase. During the acute phase, the count of the trypomastigote, the mature extracellular form of the parasite T cruzi, is at its highest, making this the best time to obtain an accurate diagnosis if an infection is suspected.³ Microscopy of fresh preparations of anticoagulated blood or buffy coat may show motile parasites.¹⁰ Other options include visualization of parasites in a blood smear with Giemsa stain or hemoculture. Hemoculture is a sensitive test but takes several weeks to show growth of the parasites. Therefore, polymerase chain reaction (PCR) assay is the preferred diagnostic test due to its high sensitivity and quick turnaround time.⁵

Because no diagnostic gold standard exists for chronic disease, confidently diagnosing Chagas in the United States can be difficult.⁵ Past the acute phase (about three months after infection), microscopy and PCR cannot be used due to low parasi­temia. If an infection with T cruzi is suspected but nine to 14 weeks have passed since exposure, serology is the method of choice for diagnosis. The enzyme-linked immunosorbent assay (ELISA) and immunofluorescent-antibody assay (IFA) are most often used to identify immunoglobulin (Ig) G antibodies to the parasite.

The difficulty of diagnosing Chagas disease in the chronic phase lies in the fact that neither ELISA or IFA alone is sensitive or specific enough to confirm the diagnosis.⁵ In order to make a serologic diagnosis of infection, positive results are needed from two serologic tests based on two different antigens or by using two different techniques (eg, ELISA or IFA). If the two tests are discordant, a third test must be done to determine the patient’s infection status. The radioimmunoprecipitation assay (RIPA) and trypomastigote excreted-secreted antigen immunoblot (TESA-blot) have been traditionally used as confirmatory tests, but even they do not have high sensitivity and specificity. A case of indeterminate Chagas disease is confirmed with positive serologic testing in a patient without symptoms and with normal ECG, chest x-ray, and imaging of the colon and esophagus.¹⁵

The preferred protocol for diagnosis of congenital Chagas disease first requires positive serologic testing confirming the infection in the mother (see Figure 2).¹⁶ Once that is determined, microscopic and PCR-based examinations of cord blood and peripheral blood specimens are carried out during the first one to two months of the infant’s life.¹⁰ PCR is the preferred test for early congenital Chagas disease, recipients of organ transplants, and after accidental exposure since results can determine if the patient is infected earlier than trypomastigotes (developmental stage of trypanosomes) can be seen on a peripheral blood smear.⁵