Trypanosoma cruzi - Chagas Disease

Chagas disease, also called American trypanosomiasis, is an infection caused by the protozoan parasite Trypanosoma cruzi, often following contact with triatomine insects (ie, kissing bugs). Although diagnosis is important to prevent possible chronic manifestations of the disease (eg, cardiomyopathy), the diagnostic process may be complicated by a lack of symptoms in the acute and chronic phases. Chagas disease poses a particular threat to immunocompromised individuals, such as organ transplant recipients. Appropriate laboratory testing for Chagas disease depends on the suspected phase of infection but can include microscopic parasite identification via blood smear, molecular detection by polymerase chain reaction (PCR), and/or serologic testing involving two or more methods that detect antibodies to different antigens. 

Quick Answers for Clinicians

Who is at risk of Chagas disease?

Chagas disease is predominantly transmitted by triatomine insects (ie, kissing bugs), which are endemic  to Latin America but may also be found in parts of the southern United States.

At-risk individuals include those who:

  • Have lived in or emigrated from an endemic region  
  • Were born to a mother who has lived in or emigrated from an endemic region and has not tested negative for Chagas disease  
  • Have received a blood transfusion within an endemic region  
How does the suspected phase of Chagas disease impact testing?

Because parasitemia peaks during the acute phase of Chagas disease, testing techniques that detect Trypanosoma cruzi within a blood sample (eg, blood smear or polymerase chain reaction [PCR]) can be applied. By contrast, typically few or no parasites are detectable after 8-12 weeks of infection.  Therefore, during the chronic phase, serology is necessary to diagnose Chagas disease. For more information about the preferred testing for either phase, see the Preferred Acute- and Chronic-Phase Testing Strategy table.

Is screening for Chagas disease recommended in pregnant individuals?

Routine screening of pregnant individuals for Chagas disease is not recommended. However, targeted screening may be appropriate in individuals who are pregnant or considering pregnancy when patient history reveals one or more risk factors for the disease. In general, individuals who have lived in Mexico, Central America, or South America face an increased risk of infection. 

Is screening for Chagas disease recommended in the setting of organ transplantation?

Yes. The American Society of Transplantation (AST) recommends targeted screening of any prospective transplant recipients who are at risk for Chagas disease (eg, those who report a personal or maternal history of living in an endemic region).  Additionally, the Chagas in Transplant Working Group recommends screening prospective organ donors who may be at risk for Chagas disease. 

Indications for Testing

Laboratory testing for Chagas disease is indicated in individuals who are at risk when clinical findings point to acute- or chronic-phase infection. 

Additionally, selective screening is recommended for at-risk individuals who are:

  • Pregnant or plan to become pregnant 
  • Organ transplant candidates or recipients 
  • Prospective living organ donors 

Laboratory Testing

Accurate diagnosis of Chagas disease requires the use of appropriate testing for the suspected stage of infection (either acute or chronic), which corresponds to detectable parasitemia. In general, the same testing methods apply across patient populations (eg, infants, immunocompromised individuals, etc.). Blood smear and PCR testing may be used when acute-phase Chagas disease is suspected, whereas serology is preferred to detect chronic-phase infection. Because no single serologic test is adequately sensitive or specific to diagnose Chagas disease, two or more serologic methods are needed to confirm infection.

Preferred Acute- and Chronic-Phase Testing Strategy
Phase of Chagas Disease Duration Presentation Preferred Testing Strategy

Acute

Lasts 8-12 wks after infection

Asymptomatic or mild febrile illnessa with possible swelling at the initial site of infection

T. cruzi is demonstrable within a blood sample

Use blood smear (eg, Giemsa stain)b or molecular detection by PCRc

Chronic (follows acute illness)

Lasts indefinitely without treatment

Typically asymptomatic

20-30% of infections result in cardiovascular and/or gastrointestinal manifestations, such as:

  • Cardiomyopathy
  • Arrhythmia
  • Megaesophagus
  • Megacolon

Use ≥2 serologic methods that detect antibodies to different antigensd

Common methods include EIA, IFA, and immunoblot

aInfants born with Chagas disease can be asymptomatic or may present with symptoms such as prematurity, low weight, anemia, thrombocytopenia, etc.

bBlood smear is the most common method of identifying acute Chagas disease and is commercially available.

cPCR testing is the most sensitive option to detect early acute-phase Chagas disease and can be ordered through the CDC.

dSerology may yield false-positive results in infants <12 mos of age, before the dissipation of maternal antibodies.

EIA, enzyme immunoassay; IFA, immunofluorescent antibody test

Sources: CDC Yellow Book, 2019 ; La Hoz, 2019 ; CDC, Congenital Chagas disease, 2021 ; CDC, Chagas disease molecular detection, 2021 

Organ Transplantation

Selective screening is recommended for both organ transplant recipients  and living donors  who are at risk for Chagas disease to identify the possibility of transmission or reactivation and mitigate potential serious complications.

The American Society of Transplantation (AST) recommends dual-method serologic testing to screen for chronic Chagas infection in any transplant candidate who may be at risk for the disease. A combined testing approach involving PCR alongside blood smear should be used when reactivation of Chagas disease is suspected. 

Systematic monitoring is recommended in transplant recipients when reactivation or donor transmission of the disease is possible. PCR testing, available through the CDC,  is the preferred means of detecting acute infection in at-risk transplant recipients and should be used alongside blood smears in a coordinated testing schedule, as indicated in the following table. 

Posttransplantation Monitoring Schedule for At-Risk Transplant Recipientsa
Time Since Transplant (Mos) Testing Frequencyb,c

1-2

Weekly

3

Biweekly

4-9

Monthly

10+

≥Monthlyd

aRecommendations are from the AST. CDC recommendations vary; for additional details, see Preventing Chagas disease in transplant recipients: donor screening and recipient monitoring. 

bMore frequent monitoring may be indicated in transplant recipients with chronic Chagas disease when adjusting immunosuppression to treat transplant rejection.

cTesting in addition to scheduled monitoring should be performed if an at-risk transplant recipient develops unexplained febrile illness.

dFrequency of testing can be reduced in stable patients with consistent negative test results.

Sources: La Hoz, 2019 

ARUP Laboratory Tests

Use to identify T. cruzi within a blood sample during the acute phase of infection

Aids in the diagnosis of chronic-phase Chagas disease

Medical Experts

Contributor

Couturier

Marc Roger Couturier, PhD, D(ABMM)
Professor of Pathology (Clinical), University of Utah
Medical Director, Parasitology/Fecal Testing, Infectious Disease Antigen Testing, Bacteriology, and Molecular Amplified Detection, ARUP Laboratories

References