Page 2575 - Hematology_ Basic Principles and Practice ( PDFDrive )

2298 Part XIII Consultative Hematology

erythematous indurated lesions have been described during T. cruzi preparation of needle aspirates. Parasites may occasionally be found
recrudescence after solid-organ transplant. Here tissue amastigotes in lachrymal fluid.
can be demonstrated by fine-needle aspiration. Sensitivity is increased by the concentration methods described
for T. brucei earlier. Organisms may also be sought in centrifuged
serum after blood has clotted or by centrifugation after lysis of RBCs
HIV with 0.8% ammonium chloride. Trypomastigotes can also be detected
in other specimens, including CSF, bone marrow, pericardiac fluid,
Coinfection with T. cruzi and HIV has been reported from urban and tissue biopsy specimens. Organisms must be distinguished from
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centers in Brazil. T. cruzi develops in end-stage disease with CD4 the morphologically similar nonpathogenic T. rangeli (see Fig. 158.14
T-cell counts of less than 400/µL. Patients may be severely ill, the and earlier).
majority with meningoencephalitis and often with a space-occupying After the acute phase, circulating parasites are not visible, although
lesion. Typically the CSF shows a mild lymphocytosis (<100 cells/µL). inoculation of blood into susceptible animals (xenodiagnosis), in
Parasites may be seen in the blood and occasionally the CSF. Cardiac vitro culture, or molecular methods may demonstrate patent infec-
involvement and heart failure are common. tion. Parasitemia may be obvious in immunocompromised patients
in the chronic phase of disease.
Hematologic and Laboratory Features
Xenodiagnosis
A mild, normocytic, normochromic anemia is typical of acute illness.
The pathogenesis of the anemia and contributions of hemolysis and Infection of laboratory triatomine bugs by a seropositive patient is
bone marrow depression have not been studied in humans, but in more sensitive than morphologic examination in chronically infected
experimental infections in mice, uncontrolled infection and TNF-α patients. It is also possible to infect susceptible laboratory animals.
can be shown to contribute to depressed hematopoiesis. A modest However, these techniques are available only in specialized centers in
lymphocytosis and increases in liver and muscle enzymes may be Latin America.
present. Nonspecific electrocardiographic changes, first-degree heart
block, and cardiomegaly suggest early myocardial involvement.
Hematologic abnormalities are not usually found in the late stage In Vitro Culture
of disease, in which cardiomyopathy with cardiac failure, rhythm
disturbance, and angina and systemic emboli from intramural throm- Epimastigotes can be cultured using blood agar (NNN) medium or
bus may occur. Trials of systemic anticoagulation have not been other media such as Schneider insect medium. After 4 weeks or more
conducted. of culture at 26°C, epimastigotes may be detected. 222,223

Diagnosis Serology

Microscopy Serologic testing is a sensitive method of detecting infection after the
acute phase. In Latin America, a number of commercial assays are
During the acute phase of the disease, motile trypanosomes can be available using crude epimastigote lysates in a variety of different
identified in wet preparations or buffy coat preparations using con- formats. Serologic tests have used IFAT and ELISA using crude
centration methods and detailed morphologic examination, including antigen prepared from in vitro cultures of epimastigotes. These tests
Giemsa-stained, gently prepared thick and thin films to avoid damage must be carefully controlled with appropriate positive or negative
to parasites (Fig. 158.15). Trypanosomes can be aspirated from the sera. Chronically infected patients usually give a positive test result if
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chagoma in the acute phase of disease and visualized in a wet titers are greater than 1 : 80. These have a sensitivity and specificity
of more than 95%. These antibodies may cross-react with antibodies
to malaria, leishmaniasis, syphilis, and some autoimmune conditions.
ELISA should be used in conjunction with a confirmatory test such
as Western blot.
In South and North America, a number of companies market
ELISA-based assays using recombinant antigens, synthetic peptides,
or a concentrated extract of excretory-secretory antigens from either
Brazil or Tulahuen strain T. cruzi trypomastigotes (total trypomasti-
gote excretory-secretory antigens [TESAs]). These assays may provide
more rapidly available and cheaper tests without loss of sensitivity
and specificity (see Trypanosomiasis as a Transfusion-Transmitted
Infection section for further discussion).
Serologic testing may be useful in the evaluation of people who
may have been exposed to Chagas disease, pregnant women, and
patients about to undergo immunosuppressive treatment or to receive
chemotherapy or who have been diagnosed with HIV or other
immunosuppressive illness. Children born to seropositive women will
have maternally derived IgG anti–T. cruzi antibodies but demonstrate
IgM anti–T. cruzi antibodies if congenitally infected. 225

Molecular Diagnosis

Fig. 158.15 TRYPANOSOMA CRUZI IN HUMAN BLOOD FILM. The Amplification of T. cruzi–specific sequences by PCR is potentially the
causative agent occurs in blood films, characteristically as short C-shaped or most widely applicable, sensitive, and specific method for detecting
S-shaped trypomastigotes with a prominent kinetoplast. It is otherwise parasites. A number of assays have been developed, based on
monomorphic. the application of repetitive sequences in kinetoplast DNA. A