The protozoan parasite, Trypanosoma cruzi, causes Chagas disease, a zoonotic disease that can be transmitted to humans by blood-sucking triatomine bugs.
An infected triatomine insect vector (or “kissing” bug) takes a blood meal and releases trypomastigotes in its feces near the site of the bite wound. Trypomastigotes enter the host through the wound or through intact mucosal membranes, such as the conjunctiva . Common triatomine vector species for trypanosomiasis belong to the genera Triatoma, Rhodnius, and Panstrongylus. Inside the host, the trypomastigotes invade cells near the site of inoculation, where they differentiate into intracellular amastigotes . The amastigotes multiply by binary fission and differentiate into trypomastigotes, and then are released into the circulation as bloodstream trypomastigotes . Trypomastigotes infect cells from a variety of tissues and transform into intracellular amastigotes in new infection sites. Clinical manifestations can result from this infective cycle. The bloodstream trypomastigotes do not replicate (different from the African trypanosomes). Replication resumes only when the parasites enter another cell or are ingested by another vector. The “kissing” bug becomes infected by feeding on human or animal blood that contains circulating parasites . The ingested trypomastigotes transform into epimastigotes in the vector’s midgut . The parasites multiply and differentiate in the midgut and differentiate into infective metacyclic trypomastigotes in the hindgut .
Trypanosoma cruzi can also be transmitted through blood transfusions, organ transplantation, transplacentally, and in laboratory accidents.
The Americas from the southern United States to southern Argentina. Mostly in poor, rural areas of Mexico, Central America, and South America. Chronic Chagas disease is a major health problem in many Latin American countries.
The acute phase is usually asymptomatic, but can present with manifestations that include fever, anorexia, lymphadenopathy, mild hepatosplenomegaly, and myocarditis. Romaña’s sign (unilateral palpebral and periocular swelling) may appear as a result of conjunctival contamination with the vector’s feces. A nodular lesion or furuncle, usually called chagoma, can appear at the site of inoculation. Most acute cases resolve over a period of a few weeks or months into an asymptomatic chronic form of the disease. The symptomatic chronic form may not occur for years or even decades after initial infection. Its manifestations include cardiomyopathy (the most serious manifestation); pathologies of the digestive tract such as megaesophagus and megacolon; and weight loss. Chronic Chagas disease and its complications can be fatal.
Trypanosoma cruzi in thick blood smears stained with Giemsa.
T. cruzi in thin blood smears stained with Giemsa.
T. cruzi in thin blood smears stained with Giemsa.
T. cruzi in cerebrospinal fluid (CSF) stained with Giemsa.
T. cruzi amastigotes in heart tissue.
T. cruzi epimastigotes, from culture.
Triatomine bug, the T. cruzi vector.
In the acute stage of the disease, diagnosis may be made by the finding of trypomastigotes in circulating blood or cerebral spinal fluid (CSF). During the chronic stage, trypomastigotes are usually not found circulating in blood and serologic testing is recommended. Amastigotes may be found in biopsy specimens stained with hematoxylin-and-eosin (H&E) or Giemsa.
Serology (Antibody Detection)
Positive IFA result with T. cruzi antigen (magnification 400x).
Infections with Trypanosoma cruzi are common in Mexico, Central America, and South America, and most people with Chagas disease in the United States acquired their infections in endemic countries. The transmission of Chagas disease via blood transfusion is a recognized risk, however screening tests were approved by the Food and Drug Administration and they are currently in use by blood banks. During the acute phase of illness, blood film examination generally reveals the presence of trypomastigotes. During the chronic phase of infection, parasitemia is low; immunodiagnosis is a useful technique for determining whether the patient is infected.
Diagnosis of chronic Chagas disease is made after consideration of the patient’s clinical findings, as well as by the likelihood of being infected, such as having lived in an endemic country. Diagnosis is generally made by testing with at least two different serologic tests. The indirect fluorescent antibody (IFA) test and a commercial enzyme immuno assay (EIA) are available at CDC. When using this test cross-reactivity can occur with sera from patients with leishmaniasis, a protozoan disease that occurs in some of the same geographical areas as T. cruzi. CDC also utilizes an FDA-cleared enzyme immunoassay (EIA). This assay uses recombinant antigens for antibody detection and provides additional information to inform the diagnosis. Various serologic methods are commercially available in other countries for laboratory diagnosis of Chagas disease. The sensitivity and specificity of these tests are highly variable. CDC recommends confirmatory testing if positive or negative results obtained elsewhere are suspicious.
Molecular diagnosis of Chagas disease is performed for cases of transfusion or transplant transmission are suspected and for congenital Chagas. Laboratory exposures can also be monitored using PCR. At CDC molecular detection of T. cruzi DNA is performed using a combination of three real-time PCR assays. Acceptable specimen types are EDTA blood (minimum of 2.2 ml), heart biopsy tissue (in saline or paraffin-embedded) and, in cases of suspected cerebral involvement, CSF. Using PCR to detect Trypanosoma cruzi DNA in EDTA blood is appropriate only when the parasitemia is expected to be high, such as in the acute phase of the infection or in re-activation of chronic Chagas disease due to immunosuppression. PCR can also be useful for early detection of T. cruzi in transplant-transmitted recipients of organs from donors with chronic Chagas disease. The diagnosis of chronic Chagas disease in patients without immunosuppression should be performed with serology.
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DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.