Laboratory Studies
During the acute phase of trypanosomiasis, the CBC count may reveal leukocytosis with relative lymphocytosis, and transaminase levels are often elevated.
During acute illness (ie, the first 6-12 wk), parasites are frequently seen in blood smears [39] , using either Giemsa staining or direct wet-mount preparations (in which motile parasites may be seen). Sensitivity is 80-90%. Thickly-stained and thinly-smeared blood can allow morphologic characterization of the parasite and differentiation from other trypanosomes, but these preparations are less sensitive (60%). Concentration using centrifugation after red-cell lysis, or clotting and examination of the buffy coat increases detection to 90-100%. Following the acute infectious period, low levels of parasitemia are present; therefore, blood smear results are often negative.
Serologic confirmation of diagnosis requires that the parasites are cultured on a special medium or identified by means of xenodiagnosis. Blood cultures have positive results in 100% of patients with acute-phase illness, but only 40-50% in those with chronic illness. Xenodiagnosis is the best method for parasitologic diagnosis in the latent or chronic phases. It consists of allowing laboratory-reared reduviid nymphs to feed on blood from an infected patient. The feces and intestines of the nymphs are examined 20-60 days later for the presence of parasites. Test results are positive in approximately 50% of individuals.
Serologic tests for anti– T cruzi immunoglobulin M (IgM) play a limited role in the diagnosis because these tests are not widely available or standardized. In recent human infections, antibodies of the IgM class appear in the blood stream 15 days after infection, peak 17-45 days after infection, and persist for years. Antibodies of the IgM isotype predominate during the acute phase. Later, in the latent and chronic stages, antibodies are primarily from the IgG and IgA classes.
Serologic tests include complement fixation (CF), indirect immunofluorescence (IFAT) and enzyme-linked immunosorbent assay (ELISA).
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The CF test, or Machado-Guerreiro test, is considered the most reliable immunodiagnostic method for diagnosis.
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The indirect fluorescent antibody test (IFAT) is rapid and easy to perform, has a high sensitivity, and can be used to differentiate IgM antibodies from IgG antibodies. IFAT reveals the earliest positive results for IgM antibodies after initial infection.
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Enzyme-linked immunosorbent assay (ELISA) is as sensitive as the IFAT and can also be used to differentiate IgM antibodies from IgG antibodies.
In the United States, CF and IFAT are available from the Centers for Disease Control and Prevention (CDC). In addition, the Food and Drug Administration (FDA) has approved assays based on the ELISA format for use in clinical testing; these are performed at Abbott Laboratories in Illinois and Gull Laboratories in Utah.
Several agglutination tests have been developed that detect the presence of antibodies against T cruzi, such as indirect hemagglutination (IHA), direct agglutination (DA), latex agglutination (LA), and flocculation tests. After initial infection, IFAT reveals the earliest positive results for IgM antibodies; also confirmed early-on by the DA method. All of these tests have been reported to provide positive results in more than 95% of the sera from infected humans.
A persistent problem with these tests is false-positive reactions. These have been observed with leishmaniasis, malaria, syphilis, infectious mononucleosis, tuberculosis, leprosy, and collagen vascular disease. The use of a minimum of 2 different, independently performed serologic tests is recommended to confirm infection. A Western blot confirmatory test has been described, to address the concern for serologic cross-reactivity. [40]
T cruzi kinetoplast DNA has been observed using polymerase chain reaction (PCR) amplification, [41, 42] which can be used to identify as few as 1 parasite in 20 mL of blood with a sensitivity of 96-100%. PCR has also been used to detect T cruzi in congenital trypanosomiasis and to follow the efficacy of patients treated for Chagas disease. [43]
Blood banks in areas of endemic disease use either the IHA or LA tests for disease detection. Recent studies involving the use of ELISA for the detection of antibodies to T cruzi and a radioimmunoprecipitation assay had a sensitivity and specificity of 100%.
In congenital Chagas disease, an indirect immunofluorescence test with anti-IgM has been introduced recently and it is effective in confirming acute congenital disease. Test infants of seropositive mothers as soon as possible for the presence of circulating parasites and specific IgM antibody, recognizing that these tests are not optimally sensitive. [44] Additionally, an ELISA using shed acute phase antigen (SAPA) for newborns has been described. [45, 46]
Atrial natriuretic factor is a sensitive marker capable of detecting gradual impairments in cardiac function and suggests poor survival in patients with Chagasic cardiomyopathy. N -terminal proBNP has been shown to be a marker of impaired left ventricular dysfunction. [47] Brain natriuretic peptide has also been shown to be a marker for severity of disease in Chagas disease. Mass spectroscopy has been used to measure serum biomarkers of disease. [48]
In people who are immunosuppressed and thought to have Chagas disease, examine other specimens, such as lymph node aspirates, bone marrow, cerebrospinal fluid, and pericardial fluid, if the presence of T cruzi cannot be confirmed in the blood.
Imaging Studies
See the list below:
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In patients with cardiac involvement, chest radiography may reveal cardiac enlargement with clear lung fields.
Electrocardiography (ECG) may be useful. The most common electrocardiographic abnormalities in acute infection include sinus tachycardia, prolongation of the PR interval, S-T segment depression and T-wave inversion, low voltage of the QRS complex, and prolongation of the QT interval. [49] The most common electrocardiographic manifestations in chronic disease are intraventricular blocks (right bundle branch block and left anterior hemiblock), sinus bradycardia, atrioventricular (AV) block (first degree, second degree, complete), sinoatrial block, atrial fibrillation, and premature ventricular beats.
Echocardiography is used to assess for evidence of acute chagasic myocarditis or chronic Chagas cardiomyopathy. [50] In the acute setting, echocardiography may reveal pleural effusions, apical or anterior dyskinesis, and left ventricular dilatation. In patients with chronic disease, echocardiography may reveal left ventricular aneurysm, segmental wall abnormalities, left ventricular dilatation, decreased left ventricular ejection fraction, diastolic dysfunction, tricuspid, and mitral regurgitation.
Thallium stress-redistribution myocardial perfusion scintigraphy may reveal reversible and irreversible perfusion defects in chronic Chagas cardiomyopathy. The perfusion defects occur in the presence of normal epicardial coronary arteries and probably represent myocardial fibrosis, coronary microvasculature abnormalities, or extensive impairment of cardiac sympathetic function.
Cardiac MRI has been shown to be the most accurate method to detect myocardial fibrosis in patients with Chagas disease. CMR offers a wide variety of imaging tools to evaluate morphology, function, and other tissue characterization abilities, such as edema and fat.
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In patients with advanced esophageal involvement, chest radiography may reveal a tubular mass along the aorta and air-fluid level, which reflects the retention of swallowed material in the esophagus.
Fluoroscopic esophagrams obtained with barium often show the absence of mucosal irregularities and a variably dilated esophagus with a narrow, conical segment at its lower end that represents the nonrelaxing sphincter (bird-beak appearance). In advanced disease, the diameter is grossly enlarged, causing it to fold over the diaphragm.
Cine-esophagrams may show tertiary contractions and accumulation of the contrast material.
Manometry in patients with Chagas disease typically reveals loss of peristalsis upon deglutition and an abnormally elevated pressure in the lower esophageal sphincter, which fails to relax.
Scintigraphy is as sensitive as manometry in depicting esophageal dysmotility and it reveals patterns of transit similar to those described in idiopathic achalasia.
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In colonic involvement, barium enema examination is the cornerstone for diagnosis. The sigmoid colon is frequently dilated and elongated in nearly all cases, and the rectum is dilated in 80% of cases.
Other Tests
See the list below:
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Complex ventricular dysrhythmias during cardiac stress testing are a clinical marker for progressive cardiomyopathy in Chagas disease.
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Lumbar puncture to assess for CNS involvement. Cerebral spinal fluid may show pleocytosis with a predominance of lymphocytes and elevated protein level; often, it reveals the presence of T cruzi.
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Autonomic dysfunction may occur in infected children. [51]
Procedures
Endoscopy is not essential to diagnose chagasic achalasia. Its main value is to identify other disorders, such as gastric and esophageal cancer, which are more common in patients with chagasic megaesophagus.
Histologic Findings
See the list below:
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The lesion at the parasite's portal of entry has a predominance of lymphocytic, monocytic, and eosinophilic infiltration, along with the presence of giant cells.
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When the heart is invaded, myocardial fibers are often edematous and undergo various stages of focal necrosis, which primarily involves the contractile and conduction systems. Interspersed among the degenerating fibers is a markedly mixed inflammatory cell exudate consisting of granulocytes, lymphocytes, monocytes, mast cells, and plasma cells.
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Diffuse inflammation of the myocardium is present, as well as dense foci of fibrosis in the interstitial spaces and invasion of lymphocytes, plasma cells, and macrophages. In two-thirds of cases, detection of parasites in the myocardium is difficult.
