Chagas disease is an infection caused by the protozoan Trypanosoma cruzi, which is transmitted by the bite of a kissing bug (also called an assassin or Triatominae bug).
- The protozoa may enter the body through the bite wound or through tissues around an eye or less commonly by eating food or drinking fresh fruit juices that are contaminated.
- 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, but does not reverse heart or digestive tract damage.
(See also Overview of Parasitic Infections.)
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.
Worldwide, 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. Among them are an estimated 40,000 women of child bearing age. It is estimated that 1 to 5% of their children are born with the infection. Immigrants to Europe have also carried the disease with them. Fortunately, measures to control the spread of infection are reducing the number of Chagas cases.
Transmission of Chagas disease
Chagas disease is most commonly spread when a kissing bug bites an infected person or animal (such as dogs, cats, opossums, rats, and many other animals), then bites another person. When infected bugs bite, they deposit feces that contains the protozoa. The protozoa then enter the body through the bite wound.
The protozoa may also enter the body through mucous membranes, such as the clear membrane that covers the eye (conjunctiva). The protozoa then get into cells at the point of entry and eventually reach the bloodstream. Trypanosoma cruzi infect many types of cells throughout the body including cells of the immune system, heart, muscles, and nervous system.
People can also become infected through blood transfusions or an organ transplant from an infected donor. People can be infected by eating uncooked food or drinking liquids (such as sugar cane juice) 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 the first stage of Chagas disease disappear without treatment. However, a few people, usually children, die during this stage. Death may result from a severe infection of the heart, 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), the first stage may be severe, and people may have fever, a rash, or brain lesions
Most babies infected before they are born (congenital infection) do not have symptoms, but some are born prematurely or have nonspecific findings including low birth weight, fever, enlargement of the liver and spleen, anemia, or abnormal blood counts. In most infected infants, symptoms eventually disappear without treatment; however, a few infants die during this stage.
Second stage (latent period)
During the second stage, people have no symptoms of Chagas disease and results of electrocardiography (ECG) and imaging tests of the heart and digestive system are normal. However, protozoa are present in their body and sometimes blood.
Many people remain in this stage, without any symptoms, for the rest of their life.
Years later, chronic Chagas disease develops in 20 to 40% of people.
The main areas affected are
- The heart
- The digestive system
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.
- During the first stage, examination of a blood sample using a microscope or blood tests
- During the second stage, blood tests
- During the third stage, blood tests, electrocardiography, and imaging tests of the heart or digestive system
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.) Antibody tests for Chagas disease may be positive in people who are not infected (false positive). So if the initial test is positive, a different antibody test is then done to confirm the diagnosis.
If the infection is diagnosed, doctors do other tests to check for damage to the heart or gastrointestinal tract. For example, electrocardiography and echocardiography are done and a chest x-ray may be taken to check for problems with the heart. Other tests may include imaging tests such as computed tomography (CT) or magnetic resonance imaging (MRI) of the heart.
If people have difficulty swallowing or constipation, a CT scan or x-rays of the gastrointestinal tract may be done.
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.
Locals and travelers in areas where infection occurs should avoid consuming freshly prepared fruit and cane juices from unsanitary sources, such as street vendors.
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.
Screening at-risk women of child bearing-age before pregnancy, and treating those who are infected, decreases the likelihood of congenital infection.
- Drugs that are effective against these protozoa
- Treatment of problems caused by chronic infection of the heart or digestive tract if present
Only two antiparasitic drugs—benznidazole or nifurtimox—are effective against Chagas disease. In the US, nifurtimox is available only from the Centers for Disease Control and Prevention. Neither of these drugs reverses heart or digestive tract disease that has already developed. People take one of these two drugs by mouth for 1 or 3 months, respectively. 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. Neither drug is given to people with severe liver or kidney disease nor to women who are pregnant or breastfeeding. Children usually tolerate treatment better than adults.
During the first stage of the disease, all people are treated with benznidazole or nifurtimox. These drugs do the following:
- Quickly reduce the number of protozoa in the blood
- Shorten the duration of symptoms
- Make developing chronic infection less likely
- If the infection becomes chronic, may reduce the risk of dying
When women are diagnosed with Chagas during pregnancy, treatment is usually delayed until after delivery, and the infant is then treated if infected.
During the second stage, children and adults up to age 50 who do not have evidence of advanced cardiac or gastrointestinal disease 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 adults over 50 years old, doctors must weigh the benefits with the risks of treatment.
Once chronic infection causes severe heart damage 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
- A greatly enlarged colon: Surgery
- Centers for Disease Control and Prevention: Chagas disease