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Microbiology · Hemoflagellates (trypanosomes and Leishmania)

Trypanosoma cruzi !

  • Parasite
  • Exam priority: high

The parasite of Chagas disease. It spreads through the feces of kissing bugs («pito» in Colombia), contaminated food and from mother to baby.

Updated 2026-11-01

Also called: Chagas disease agent, American trypanosomiasis

At a glance

Shape
C- or S-shaped trypomastigote in blood; round amastigote in tissue
Family
Trypanosomatidae
Type
Flagellated protozoan (hemoflagellate), intracellular and bloodborne
Stain
Giemsa: large, posterior kinetoplast
Size
Trypomastigote about 20 µm long

Morphology

  • C-shaped blood trypomastigote with a free flagellum, undulating membrane and a large kinetoplast at the posterior end.
  • Small intracellular amastigote without a free flagellum, in nests inside heart and muscle fibers.
  • Epimastigote only in the vector's gut or in culture.

Transmission

  • Vector-borne: the triatomine bites at night and defecates nearby; infected feces enter through the bite, conjunctiva or mucosa.
  • Oral: food or drinks contaminated with bug feces or crushed bugs (fruit juices, sugarcane drinks); causes outbreaks with high fatality.
  • Congenital: from an infected mother to the fetus during pregnancy or birth.
  • Blood transfusion, organ transplant and laboratory accidents.

Reservoir: Wild and domestic mammals: opossums, armadillos, rodents, dogs; Humans

Vector: Triatomine bugs (subfamily Triatominae), called «pito» in Colombia: Rhodnius prolixus (the main domestic vector), Triatoma dimidiata and Panstrongylus geniculatus, among others.

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. An infected triatomine bites and leaves metacyclic trypomastigotes in its feces.
  2. Trypomastigotes enter through the bite wound or mucosa and invade nearby cells.
  3. Inside the cell they turn into amastigotes and multiply by binary fission.
  4. They change back into trypomastigotes, burst the cell and enter the blood, where they do not divide.
  5. Through the blood they reach the heart, gut smooth muscle and nervous system and repeat the intracellular cycle.
  6. A triatomine biting an infected person or animal takes up trypomastigotes, which become epimastigotes in its midgut.
  7. New infective metacyclic trypomastigotes form in the vector's hindgut.

Virulence factors

  • Intracellular multiplication as amastigotes, shielded from antibodies.
  • Trans-sialidase and surface proteins that help it evade complement and enter cells.
  • Lifelong persistence in myocardium and gut smooth muscle with chronic inflammation, fibrosis and loss of autonomic ganglia.
  • Reactivation when cell-mediated immunity drops (HIV, transplant, immunosuppressants).

Diseases it causes

  • Acute and chronic Chagas disease (indeterminate, cardiac, digestive or mixed form). Chagas disease →
  • Chagas cardiomyopathy: dilation, conduction disease, arrhythmias, apical aneurysm, thromboembolism and sudden death. Chagas cardiomyopathy →
  • Megaesophagus and megacolon from destruction of the gut's nerve plexuses.

Clinical picture

  • Acute phase (about 8 weeks): often silent, or fever, lymphadenopathy and hepatosplenomegaly; a skin chagoma or Romaña's sign (one-sided swelling of both eyelids).
  • Oral acute Chagas: prolonged fever, facial and limb edema, myocarditis and pericardial effusion, sometimes fatal.
  • Chronic indeterminate phase: positive serology with no organ damage; the most common form.
  • Chronic determinate phase, years to decades later: right bundle branch block, left anterior fascicular block, arrhythmias, heart failure, dysphagia or chronic constipation.
  • Congenital: most babies look well at birth; low birth weight, hepatosplenomegaly or myocarditis may occur.

Diagnosis

  • Acute phase: direct search for the parasite in blood (thick film, thin film, microhematocrit, Strout) and PCR.
  • Chronic phase: parasitemia is low; it is confirmed with two serologic tests based on different principles (for example ELISA plus another method), with a third if they disagree.
  • Newborn of a seropositive mother: microhematocrit or PCR in the first months; serology from 10 months, once maternal IgG is gone.
  • Damage work-up: ECG, echocardiogram, Holter; contrast studies of the esophagus and colon if symptomatic.

Treatment

Nitroheterocyclic antiparasitics: benznidazole or nifurtimox. They work very well in the acute phase, in congenital infection and in children; efficacy falls the longer the infection has lasted, and they are not used in pregnancy. Cardiomyopathy is managed as heart failure and arrhythmia (antiarrhythmics, pacemaker, defibrillator, anticoagulation as needed).

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Vector control: residual insecticide spraying and housing improvement (plastered walls, no palm-thatch roofs).
  • Food hygiene: protecting juices, sugarcane drinks and fruit from bugs in endemic areas.
  • Screening of blood and organ donors.
  • Screening of pregnant women and women of childbearing age in endemic areas, and testing of their children.
  • Bed nets and community education to recognize and report the bug.

Vaccine: There is no vaccine.

Test yourself

Think of the answer, then tap the question to see it.

How does T. cruzi enter the body in vector-borne transmission?

Through triatomine feces left near the bite; the person rubs them into the wound, conjunctiva or mucosa.

What is Romaña's sign?

Painless swelling of both eyelids of one eye, with conjunctivitis, when the parasite enters through the eye in the acute phase.

How is chronic Chagas disease confirmed?

With two positive serologic tests based on different principles; direct parasite searches are usually negative because parasitemia is low.

Which ECG finding is classic for Chagas cardiomyopathy?

Right bundle branch block, often with left anterior fascicular block; ventricular ectopy and AV blocks are also common.

From what age is serology useful in the child of a mother with Chagas?

From 10 months, once maternal antibodies have cleared; before that, parasites are sought in blood or PCR is used.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - American Trypanosomiasis (CDC, 2024); Chagas disease (also known as American trypanosomiasis) (WHO, 2025); Chagas disease - PAHO/WHO | Pan American Health Organization (PAHO, 2025); Informe de Evento 2023 Chagas (Instituto Nacional de Salud (INS) Colombia, 2024).

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