(See also Overview of Parasitic Infections.)
Chagas disease is an infection caused by the protozoan Trypanosoma cruzi, which is 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 point of entry (a bite wound or an eye) may swell, and people may have a fever.
Then, after a long period of no symptoms, serious complications, mainly heart or digestive problems, may develop years later.
Doctors confirm the diagnosis by identifying the protozoa in a sample of blood or fluid taken from an infected organ or by doing blood tests.
A drug (benznidazole or nifurtimox) is used to kill the protozoa.
Chagas disease affects people in Mexico and Central and South America, mainly in rural areas 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 and farm buildings, and in rock or wood piles, chicken coops, and dog kennels.
In the Americas, about 8 million people are infected with Trypanosoma cruzi. This number includes more than 300,000 people who live in the United States after immigrating from regions of Latin America where they acquired the infection. Immigrants to Europe have also carried the disease with them. However, measures to control the infection are reducing the number of infections in Latin America.
When infected bugs bite a person, they deposit feces that contains the protozoa. The protozoa enter the body through the bite wound. The protozoa may also enter the body through the mucous membranes, such as the clear membrane that covers the eye (conjunctiva). The protozoa then enter the skin or tissues around the point of entry and the bloodstream and infect many types of 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.
Chagas disease occurs in three stages. Symptoms can occur in the first and third stages.
Chagas disease symptoms usually start 1 to 2 weeks after the protozoa enter the body, usually through the bite wound or tissues around an eye. A swollen, red bump may appear at the bite wound. If the protozoan entered through tissues around the eye, the area around the eye 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, symptoms of Chagas disease disappear on their own. However, a few people, usually children, 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, and people may have a rash or, rarely, brain abscesses.
Years later, chronic Chagas disease develops in 20 to 40% of people.
The main areas affected are
The heart may become enlarged and weak, so people tire easily and are short of breath. The heart's electrical system may be affected, causing fainting, irregular heart rhythms, 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 affected, people may breathe in (aspirate) food, liquids, or saliva, causing pneumonia, or become severely undernourished. The large intestine (colon) may enlarge, and severe constipation may develop.
Doctors can usually diagnose Chagas disease during the first stage by seeing the protozoa in a sample of blood examined with a microscope. A blood sample may also be tested for the protozoa's genetic material (DNA).
During the second and third stages the protozoa are seldom seen in a sample of blood examined with a microscope. So doctors do two or more different blood tests to check for antibodies to the protozoa. (Antibodies are proteins produced by the immune system to help defend the body against a particular attack, including that by parasites.)
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.
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 Chagas disease.
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 countries, including the United States, to prevent the infection from being spread through infected blood transfusions or organ transplants.
Only two antiparasitic drugs—benznidazole or nifurtimox—are effective against Chagas disease. People take one of these two drugs by mouth for one to three months.
During the first stage of the disease, all people are treated with benznidazole or nifurtimox. These drugs do the following:
Newborns who were infected before birth are also treated.
During the second stage, children and adults up to age 50 are treated with benznidazole or nifurtimox.. The younger the person and the earlier treatment is started, the more likely that treatment will eliminate the protozoa. For older adults during this stage, doctors must weigh the benefits with the risks of treatment.
Both benznidazole and nifurtimox can have serious side effects, which most often involve the digestive tract, skin, and nervous system. They include loss of appetite, weight loss, nausea, vomiting, rash, nerve damage, insomnia, and dizziness.
Benznidazole and nifurtimox are not given to people with severe liver or kidney disease nor to women who are pregnant or breastfeeding.
Once chronic infection causes heart or digestive problems, antiparasitic 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) or a pacemaker
Problems with the esophagus: Botulinum toxin (to relax the lower esophageal muscle) or a surgical procedure to widen (dilate) the lower esophagus
An enlarged colon: Surgery