American trypanosomiasis

Epidemiology and mechanism of infection

American trypanosomiasis is a typical zoonosis. The natural reservoirs of Trypanosoma cruzi in the wild include armadillos, opossums, skunks, and a wide range of other wild mammals. In addition, an infected human can become a fully competent source of the pathogen.

The primary mechanism of transmission is vector-borne, though the process has important specific features. Infection occurs not at the moment of the bite itself, but via specific contamination. The infective stage for humans is the metacyclic trypomastigote, which is excreted in the feces of infected triatomine bugs (Triatoma sp.). The insect feces enter the human body through:

• damaged skin;
• the skin directly at the site of the bite (when feces are rubbed into the wound as a result of scratching);
• various mucous membranes (eyes, oral cavity).

Life cycle and localization

The development of the pathogen involves two hosts:

1. Specific vector — triatomine bug.
2. Vertebrate host (including humans).

Once inside the human body, the parasites lead a strictly intracellular lifestyle. Although trypanosomes are capable of infecting virtually any cells in the body, their most frequent and favored localization is smooth muscle cells.

Clinical presentation

The disease is characterized by a chronic course with two distinct main forms.

1. Acute phase The disease manifests acutely: the patient develops fever, pronounced chills, malaise, eye pain, as well as muscle and headaches. A specific local manifestation forms at the site of pathogen entry into the skin — chagoma. This is an area of pronounced infiltration that visually resembles a boil. With a favorable outcome, after 4–5 weeks the level of parasitemia in the blood decreases, and the disease transitions to the chronic stage.

2. Chronic phase This stage can remain completely asymptomatic for many years (from 10 to 20 years). Subsequently, the leading clinical syndrome of Chagas disease develops — «megasyndrome». It consists of the pathological enlargement of internal organs. The heart is affected primarily (marked cardiac enlargement, dilation of the right atrium and both ventricles are observed). In the digestive system, megasyndrome manifests as dilation of the esophagus and colon.

Diagnostic methods and prevention

Laboratory diagnosis of American trypanosomiasis requires a comprehensive approach and includes the following methods:

• Parasitological method. Consists of microscopic examination of the patient's blood smear, as well as preparations made from aspirates of the primary chancre or lymph nodes (Romanowsky-Giemsa stain is used).
• Xenodiagnosis. A specific method based on feeding uninfected laboratory triatomine bugs directly on the patient. For this, about 40 insects are used, and the container with them is fixed to the skin. After feeding, laboratory technicians examine the insect's gut for the presence of multiplied parasites.
• Biological assay. Involves inoculating laboratory animals with blood from infected patients. If infection is present, trypanosomes are detected in the animals within two weeks.
• Culture method. Inoculation of clinical material onto NNN medium (agar supplemented with defibrinated blood).
• Immunological method.

Prevention is primarily epidemiological in nature and aimed at vector control (bugs) and housing improvement in endemic regions.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Morphology of metacyclic trypomastigotes
• Features of NNN medium preparation
• Immunological tests in the diagnosis of trypanosomiasis
• Romanowsky-Giemsa blood smear staining technique

Other topics in the "Medical Protozoology" section

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