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Chagas Disease Information for Medical Providers

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Chagas disease, also called American trypanosomiasis, is caused by infection with Trypanosoma cruzi, a hemoflagellate protozoan parasite. The disease is endemic only to the Americas, from north of the Patagonia region of South America to the southern half of the United States (U.S.), including all regions of Texas. Human infection occurs commonly in parts of Latin America, but relatively rarely within the U.S. The Pan American Health Organization (PAHO) estimates that approximately 8 million people in Latin America are infected, with approximately 12,000 deaths per year throughout the Americas. The U.S. Centers for Disease Control and Prevention (CDC) estimates that approximately 300,000 people within the U.S.—predominantly immigrants from highly endemic areas of Latin America—are infected. Locally-acquired human cases occur in Texas, but are relatively uncommon. In the first five calendar years (2013-2017) since Chagas disease became reportable to the Department of State Health Services (DSHS), 124 human cases have been reported: 78 foreign-acquired, 22 locally-acquired, and 24 for which the location of acquisition is unknown.

Transmission
T. cruzi is transmitted in the feces of numerous species of blood-feeding triatomine bugs (also called reduviid bugs, kissing bugs, or cone-nosed bugs) and is predominantly maintained in a triatomine-mammalian wildlife transmission cycle. Since 2013, approximately 50% of the triatomines submitted to DSHS for testing at CDC have been positive for T. cruzi. Human infection most commonly occurs when feces from infected bugs are inoculated into the bite wound inflicted during feeding, other skin wound, or a mucous membrane. Transmission can also occur via blood transfusion, organ transplantation, congenital transmission, ingestion of food or beverages contaminated with infected bugs or bug feces and, rarely, exposure to infected tissues or fluids in laboratory or medical settings. The factors affecting the lower triatomine-to-human transmission rates in the U.S. are not completely understood, but presumably includes infrequent human exposure due to better housing construction.

Clinical Disease
There are two phases of Chagas disease: acute and chronic. Both phases can be symptom-free or life-threatening.

The acute phase occurs in the first 8 weeks of infection. This phase may go unnoticed because it is often symptom-free or may be characterized by mild, non-specific signs and symptoms, including:

  • fever
  • Malaise
  • body aches
  • rash
  • headache
  • loss of appetite
  • vomiting
  • diarrhea

Medical examination may reveal mild enlargement of the liver or spleen, swollen lymph nodes, and local swelling (a chagoma) where the parasite entered the body. The most recognized marker of acute Chagas disease is Romaña's sign, which includes swelling of the eyelids on the side of the face near the bite wound or where bug feces were deposited or accidentally rubbed into the eye. Rare occurrence of cardiac, cerebral, or meningeal inflammation can be life-threatening. Symptoms can last weeks to months and then abate, even without treatment. Symptoms during the acute phase can be more pronounced in people with weakened immune systems.

The chronic phase follows the acute phase of disease and includes an asymptomatic form (“indeterminate” or “latent”) and a symptomatic form. The majority of people in this phase will remain asymptomatic for life, but 20-30% will develop illness including:

  • cardiac complications, which can include an enlarged heart (cardiomyopathy), heart failure, altered heart rate or rhythm, and cardiac arrest (sudden death)
  • intestinal complications, which can include an enlarged esophagus (megaesophagus) or colon (megacolon) and can lead to difficulties with eating or with passing stool.

Laboratory Diagnosis
Laboratory diagnosis of acute Chagas disease can be made via microscopic identification of T. cruzi in blood smears or detection of T. cruzi DNA by polymerase chain reaction (PCR).  Prior to collecting diagnostic specimens for the diagnosis of acute Chagas disease (i.e. in neonates born to a Chagas-positive mother; in recipients of organs or blood from a Chagas-positive donor; in lab/occupational exposures; and in persons with confirmed exposure to a T. cruzi-infected triatomine bug), clinicians should consult with DSHS Regional Zoonosis Control (ZC) program staff to discuss testing options.

Laboratory diagnosis of chronic Chagas disease is based upon serologic testing. Because no currently-available serologic test is sensitive or specific enough to confirm a diagnosis, two different format serologic tests which use different parasite antigen preparations to detect T. cruzi-specific antibody are used to determine infection status. Serum specimens collected for the diagnosis of chronic Chagas disease should first be screened at one of the commercial laboratories which offer testing. Samples that test positive at a commercial laboratory can then be forwarded to the DSHS Laboratory for routing to CDC for confirmatory testing.

Blood Donor Testing
Blood banks screen first-time blood donors for evidence of T. cruzi infection. Donors testing positive are notified by the blood bank and are advised to consult their medical provider for additional laboratory testing and clinical evaluation. Blood donor screening tests are not suitable for confirmation of clinical diagnosis. Blood donors who receive a letter stating that they tested positive for Chagas disease should have serum tested at a commercial laboratory.

Clinical Evaluation of Laboratory-Diagnosed Patients
For patients who test positive on blood donor screening tests or laboratory tests, medical providers should obtain a thorough history to evaluate potential routes of exposure, travel to or residence in areas endemic for human disease, previous history of blood transfusions or organ/tissue transplants, and the possibility of maternal transmission. Baseline clinical workup should include a complete physical exam and a 12-lead ECG with a 30-second lead II rhythm strip. Additional cardiac and gastrointestinal studies may be performed if indicated by the patient’s symptoms or clinical signs. Evaluation and testing of household contacts may be indicated for those sharing similar risk profiles and is strongly recommended if maternal transmission is a possibility, either from the index case or to the index case. Patients should be counseled not to donate blood or tissues for the remainder of their lifetime.

Treatment
Antiparasitic treatment is indicated for all acute infections, for chronic infections in children up to 18 years of age, for chronic infection in adults up to age 50 who have no indication of advanced cardiomyopathy, and for reactivated infections in immunocompromised patients. The decision to treat patients falling outside of these guidelines should be made after consultation with the CDC, weighing the potential benefits and risks to the individual patient.

Two drugs—nifurtimox and benznidazole—are available for treatment of U.S. patients. Benznidazole has been approved by the U.S. Food and Drug Administration (FDA) for use in children 2-12 years of age, although it may be used “off-label” for other age groups, and is available commercially. Nifurtimox is not FDA-approved and is only available through the CDC under investigational protocols. Both drugs may cause significant side effects that some patients may not tolerate.

Additional Resources
For additional information about Chagas disease in Texas, please contact the DSHS Zoonosis Control program at 512-776-7255 or visit the program’s Chagas disease webpage, listed below. More detailed information about Chagas disease may be found on the following websites:

DSHS website
CDC website
Kissing Bugs and Chagas Disease in the U.S.
Pan American Health Organization website
World Health Organization website

Continuing Medical Education (CME)
Chagas disease CME is available via an online course offered on the CDC Chagas disease website.

Last updated April 10, 2019