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Chagas Disease

(American Trypanosomiasis)

By Richard D. Pearson, MD, University of Virginia School of Medicine

Chagas disease is an infection caused by the protozoa Trypanosoma cruzi, which are transmitted by the bite of a kissing bug (assassin or Triatominae bug).

  • The protozoa may enter the body through the bite wound or through tissues around an eye.

  • The area around the bite wound may swell, and people may have a fever.

  • After a long period of no symptoms, serious complications, mainly heart or digestive problems, may develop years later.

  • Doctors usually confirm the diagnosis by identifying the protozoa in a sample of blood or fluid taken from an infected organ and sometimes by doing tests for certain antibodies.

  • A drug (nifurtimox or benznidazole) is used to kill the protozoa in the blood.

Chagas disease occurs in North, Central, and South America, mainly in rural areas of Latin America where poverty is widespread. These areas provide a favorable environment for kissing bugs, which transmit Trypanosoma cruzi. The kissing bug thrives in cracks and crevices in mud walls, in thatched roofs of houses (such as adobe houses) and farm buildings, and in rock or wood piles, chicken coops, and dog kennels.

In the Americas, between 8 and 11 million people are infected. This number includes more than 300,000 people who have immigrated to the United States or to Europe from regions of Latin America where the infection is common. However, measures to control the infection are reducing the number of infections. In some rural parts of South America, Chagas disease used to be a common cause of death.

Transmission

When infected bugs bite a person, they deposit feces that contains the protozoa. The protozoa enter the body through the bite wound. If the bug deposits feces near the eyes or nose, protozoa may enter the body through the mucous membranes in those areas. The protozoa then enter the bloodstream and spaces around tissues and infect other cells, including cells of the immune system, heart, muscles, and nervous system. Dogs, cats, opossums, rats, and many other animals may also be bitten and infected. The infection is spread when a kissing bug bites an infected person (or animal), then bites another person.

People can also become infected through blood transfusions or an organ transplant from an infected donor. Rarely, people are infected by eating uncooked food or drinking liquids contaminated by infected bugs or their feces.

The protozoa can also cross the placenta in a pregnant woman and infect the fetus, resulting in miscarriage, stillbirth, or serious, sometimes fatal problems in the newborn.

Symptoms

This infection has three stages. Symptoms can occur in the first and third stages.

First stage

Chagas disease symptoms usually start 1 to 2 weeks after the protozoa enter the body, usually through the bite wound or tissues around the eyes. A swollen, red bump may appear at the bite wound. If the protozoan entered through tissues around the eyes, the area around the eyes may swell (called Romaña's sign). A fever may develop. Some people have no symptoms, but the protozoa can be identified in their blood.

In most people, Chagas disease symptoms disappear on their own. However, a few people die during this stage. Death results from a severe infection of the heart muscle, which causes heart failure, or from infection of the brain and tissues covering the brain and spinal cord (meningoencephalitis).

If people have a weakened immune system (as occurs in people with AIDS), this stage may be severe. People may have a severe rash or, rarely, brain abscesses.

Second stage (latent period)

People have no symptoms of Chagas disease and results of imaging tests (such as a chest x-ray or echocardiography) and electrocardiography (ECG) are normal. However, protozoa can be identified in their blood. Many people remain in this stage, without any symptoms.

Third stage

Years later, chronic infection develops in about 20 to 40% of people.

The main areas affected are

  • The heart

  • The digestive system

The heart becomes enlarged and weak, so people tire easily and are short of breath. The heart's electrical system may be affected, causing fainting or sudden cardiac arrest.

The muscles of the digestive tract (such as those of the esophagus) may malfunction, causing difficulty swallowing and/or severe constipation. If swallowing is difficult, people may breathe in (aspirate) food, liquids, or saliva, causing pneumonia, or become severely undernourished. The large intestine may enlarge.

Diagnosis

  • During the first stage, examination of a blood sample using a microscope or blood tests

  • During the second and third stages, blood tests or examination of a sample from an infected organ

Doctors can usually diagnose the infection during the first stage by seeing the protozoa in a sample of blood examined with a microscope.

During the second and third stages the protozoa are seldom seen in a sample of blood examined with a microscope. So doctors do other, more sensitive blood tests to check for antibodies, or they examine samples taken from infected organs, such as the lymph nodes, to check for the protozoa.

If the infection is diagnosed, doctors do other tests to check for problems. For example, electrocardiography may be done and a chest x-ray may be taken to check for problems with the heart. Other tests may include echocardiography and imaging tests such as computed tomography (CT).

If people have difficulty swallowing or constipation, a CT scan or x-rays may be taken after barium (an opaque substance that outlines the digestive tract) is swallowed or inserted in the rectum.

Prevention

Plastering walls, replacing thatched roofs, and/or repeatedly spraying houses with insecticides that have long-lasting effects can help reduce the number of kissing bugs and thus help control spread of the infection.

Rarely, travelers to areas where the infection occurs become infected. Not sleeping in adobe houses or, if sleeping in such houses, using bed nets can help travelers avoid infection.

Blood and organ donors are screened in many affected areas and in the United States to prevent the infection from being spread through blood transfusions or organ transplants.

Treatment

  • Drugs that are effective against these protozoa

  • Treatment of problems caused by the infection if present

Chagas disease treatment is most effective during the first stage. Doctors use one of two drugs: nifurtimox or benznidazole. These drugs are taken by mouth for several months. They quickly reduce the number of protozoa in the blood, shorten the duration of symptoms, and, if the infection becomes chronic, reduce the risk of dying. However, both drugs can have serious side effects, which most often involve the digestive tract and nerves. Also, many people have difficulty taking the drugs for the several months that are required.

During the second stage, doctors usually treat children and young adults, but treatment does not always eliminate the infection. Treatment of older adults during this stage is controversial.

Once chronic infection causes problems, drugs are not helpful. Problems are treated as needed:

  • Heart failure: Drugs to reduce the heart's workload or heart transplantation

  • Irregular heart rhythms: Drugs to correct the heart's rhythm (antiarrhythmic drugs)

  • Problems with the esophagus: Botulinum toxin (to relax the lower esophageal muscle)

  • An enlarged colon: Surgery

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