How do health-care professionals diagnose Chagas disease?
Unless the person lives in an area where the chagomas associated with Chagas disease are well recognized, the acute phase is not often diagnosed. The majority of acute-phase infections are not diagnosed because many people develop nonspecific symptoms, and the people who get the infection usually are very poor, have primitive living conditions, and no access to medical care. Unfortunately, if Chagas disease is not diagnosed and treated in the early phase, those infections that progress to chronic phase are then are diagnosed in this later stage when they are not easily treated because the damage to the body organs is usually irreversible.
There are multiple types of blood tests available to test for Chagas disease. Most are based on the host (human) production of antibodies directed against the infecting parasites, although direct microscopic examination of blood smears may visualize the parasites. However, microscopic visualization of the parasites usually requires confirmation by immunological studies because visually, the parasites may be confused with those seen in people with malaria, leishmaniasis, babesiosis, giardiasis, or African sleeping sickness. Microscopic preparation and examination should be performed by experienced lab technicians or experts in parasitology.
Giemsa-stained microscopic picture of Trypanosoma cruzi in a blood smear; SOURCE: CDC/Dr. Mae Melvin
In the U.S., the FDA approved an immunologic test (enzyme-linked immunosorbent assay or ELISA test) for Chagas disease by Ortho-Clinical Diagnostics in 2006. It detects antibodies formed against T. cruzi with high sensitivity and specificity and currently is the only FDA-approved test. Since 2007, about 800 blood-donor samples have been detected as Chagas-positive across the U.S. (see map, reference five). Other tests used in other countries (indirect immunofluorescence, hemagglutination) are less sensitive and specific but are still used. A Chagas radioimmune precipitation assay (Chagas RIPA) is used in research and with FDA permission in some clinical testing but is not widely available.
Most cases of Chagas disease are diagnosed when individuals donate blood; most people are not aware they have been infected with T. cruzi. However, since blood and organ donation can pass the disease to other people, most labs now test donated blood and organs for Chagas disease with the approved ELISA assay. If the donors are positive, they are notified (diagnosed). The prevalence of Chagas-positive blood donors is estimated by various studies to widely range between about one positive case per 2,000-29,000 donors.
Chronic-phase Chagas disease is diagnosed also with the above-mentioned blood tests, but these patients also often have physical findings that indicate the patient has chronic disease. Physical findings may include swelling of the extremities (peripheral edema), ascites, pulmonary congestion, and arrhythmias in patients with heart involvement. Patients with mainly chronic gastrointestinal involvement may have weight loss, severe gastroesophageal reflux, esophageal erosions, inability to swallow normally, or an enlarged colon (megacolon) with an enlarged abdomen. Many different diseases can cause these physical findings so it is important to know that the patient has a positive blood test for T. cruzi before concluding the person has Chagas disease. Conversely, if such physical findings and history of possible contact with Chagas vectors is present, then the blood tests could be done to either prove or rule out the diagnosis of Chagas disease in chronic phase.
Other tests such as electrocardiography and Holter or heart-event monitoring, endoscopy, esophageal manometry (pressure measurements within the esophagus), or gastrointestinal motility studies are used to help determine the functionality of heart or gastrointestinal tissues in patients with chronic-phase Chagas disease.