Trypanosoma cruzi

Trypanosoma cruzi illustration exhibiting the characteristic large kinetoplast – Illustration by W. Vientos

Trypanosoma cruzi is protozoan hemo-flagellate

Disease / Pathology

Trypanosoma cruzi is a hemo-flagellate that is the causative agent of Chagas disease (named after the Brazilian physician Carlos Chagas). The disease also goes by the name American trypanosomiasis.

It can occur as an acute or chronic disease. In either case the disease can can prove to be fatal if not treated in a timely fashion. Acute infections are mild or symptomatic initially as the parasites circulate in the blood of the host. Swellings in or around the entry site of the parasite may occur and these entry sites are usually around the mucous membranes (eye). When these swellings occur around the eye they are described as Romana’s sign. Acute infections can progress to heart muscle involvement with severe inflammation, or the brain causing severe inflammation of the lining around the brain.

Acute infections can progress to a chronic phase which can be prolonged and asymptomatic. While this chronic phase may not produce disease in most, in about 25% of those with chronic disease there can be the development of severe and life-threatening medical problems such as heart rhythm abnormalities that can lead to sudden death; a compromised heart due to it being dilated (cardiomegaly); a dilated esophagus or colon (mega esophagus – mega colon). Persons with chronic infections can have reactivations of their infections if for some reason they become immunocompromised by either an infection or drug.

It is a disease considered endemic in South America, Central America, and Mexico where the vector is found. The vector for T. cruzi is the triatomine bug or kissing bug.

Infections of T. cruzi can be transmitted through other means, albeit not as common, such as blood product transfusions; congenital transfer; organ transplantation. There are rare reports of transmission through laboratory accidents or the ingestion of contaminated food/drink.

As the disease becomes more prevalent in the Southern United States, it will become more important to consider Chagas disease in a person presenting with cardiac abnormalities. It will be even more important to screen organ and blood product donors for Chagas disease or risk the chance of infecting a recipient of the product with the parasite.

Location in the Host

The Trypanosoma cruzi location of the organism in the host is the peripheral blood as well as throughout the body (organs such as the heart and brain).

Geographic Distribution

Trypanosoma cruzi is predominantly found in South and Central America as well as Mexico. As a result of global warming and the spread of the vector – the triatomine bug – its geographic distribution continues to expand. Cases are now being seen in the southwest parts of the United States.

The triatomine bug is nocturnal and prefers to inhabit cracks/crevices of dwellings. It will bite and take it’s meal from other animals as well as humans. The bug is attracted to the elevated CO2 levels around the face as the host sleeps and thus most bites and introductions of the T. cruzi parasite occur around the face. As the bug feeds it has the habit of defecating. The bug’s feces is where the T. cruzi parasite is found. The next morning the area around the bite is itchy due to an allergic reaction initiated by the saliva of the triatomine bug. As the host scratches the site, the feces is introduced into the bite site along with the T. cruzi parasite which then gains entry to the peripheral blood.

Life Cycle

Trypanosoma cruzi life cycle

Image courtesy of the CDC

Morphology & Diagnosis

Trypanosoma cruzi can be seen in the peripheral blood during the acute phase as delicate tripomastigotes with a visible undulating membrane on the side; flagella at the posterior end; and a prominent kinetoplast at the anterior end. Trypomastigotes invade the cells of various tissues and transform into the amastigote stage. Blood stream trypomastigotes do not replicate. Replication occurs within the invaded host cell.

Amastigotes (tissue forms) can be seen in various suspected infected tissues if biopsies or tissue impressions are taken. This can be useful in suspected cases of chronic infections or if the person has had a history of living in an endemic area. However, diagnosis is generally made by testing for parasite specific antibodies.


Trypanosoma cruzi trypomastgotes in the peripheral smear – notice the prominent kinetoplast that distinguishes it from T. gambiensie.

Trypanosoma cruzi trypomastigotes in a peripheral smear. The large kinetoplast is an identifying characteristic of the species – Photo by W. Vientos
Trypanosoma cruzi amastigotes in smear – photo by W. Vientos
A child with Romana’s Sign as evident by the swelling of the right upper eyelid – Photo by CDC/Dr. Mae Melvin