Chagas (SHA-gus) disease is caused by infection with the parasite Trypanosoma cruzi, which is transmitted from an animal reservoir to a human or other animal host by insects. Chagas disease occurs mostly in Latin America and is endemic (occurs naturally in a region) to rural areas in Mexico, Central America, and South America. However, through migration and other mass movements of people, the disease has been spread all over the world. Since parasites can be transmitted via the bloodstream, another mode of infection is via exposure to infected blood. This is the main mode of infection in non-endemic countries.
Drug treatment for Chagas disease is usually only effective during acute stages of the disease and is aimed at removing the parasite. However, during the chronic stages treatment targets the effects of the disease, such as damaged organs. Chagas disease is best prevented through avoidance of insects that may be infected with T. cruzi, or through preventing infection from contaminated blood.
Chagas disease was first identified in 1909 by the Brazilian physician Carlos Chagas. This disease, also known as American trypanosomiasis, is caused by the parasite Trypanosoma cruzi, which is transmitted to animals and humans by an insect vector (Triatoma infestans).
WORDS TO KNOW
ARTHROPOD: A member of the largest single animal phylum, consisting of organisms with segmented bodies, jointed legs or wings, and exoskeletons. Includes insects and spiders.
VECTOR: Any agent, living or otherwise, that carries and transmits parasites and diseases. Also, an organism or chemical used to transport a gene into a new host cell.
Human infection usually occurs in one of two ways—parasites in the feces of insects enter the body by ingestion or through the skin, or parasites are passed from an infected bloodstream into an uninfected bloodstream. In endemic areas, contact with an insect vector is the source of most infections. When blood-sucking insects feed on infected animals, they become infected with the parasites. These insects then bite another animal or human and leave behind feces. These feces are usually rubbed into the open bite wound or into mucous membranes, such as are found in the eyes or mouth, when the animal or human scratches the area. The parasite enters the bloodstream of the host and infects tissue cells.
Transmission can also occur when blood from an infected person is introduced into an uninfected person. Such infections can occur during blood transfusions, between mothers and babies, during organ transplants, and from blood exposure in laboratories.
Chagas disease is characterized by acute and chronic stages, both of which can be symptom-free. Though the acute phase tends to be symptom-free, some people experience fever, fatigue, body aches, headaches, rashes, diarrhea, vomiting, and loss of appetite during this phase. Swelling can also occur in areas where the parasite entered the body. The most common swelling is known as Romana's sign—a swelling of the eyelid on the side of the face closest to the site of the parasite's entry. Symptoms usually fade, although infection persists if untreated.
The chronic phase usually occurs many years after infection, although some people never develop this chronic phase of the disease at all. The most common chronic problems are cardiac, including an enlarged heart, heart failure, altered heart rate, or cardiac arrest; and intestinal effects, such as an enlarged esophagus or colon, which causes problems eating or passing stool.
Since Chagas disease can be transmitted by infected blood as well as by insect vectors, it can exist outside endemic areas. However, vector-borne infections of Chagas disease generally occur only in endemic areas from the southern United States to southern Argentina. Rural areas in Mexico, Central America, and South America are the principle locations of vector-borne infections.
The human populations at highest risk for developing Chagas disease are low-income people living in rural areas. Housing is often of poor quality and provides ideal habitats for insects carrying the disease. Rural areas in Central and South America, where houses are often built of mud, adobe, or thatch, have a high incidence of infection. It is estimated that as many as 11 million people in Mexico, Central America, and South America are infected with Chagas disease.
As populations have begun to make large-scale migrations, Chagas disease has spread from rural areas into previously uninfected areas. This has increased its global distribution and given rise to other modes of infection, resulting in a need to adopt new infection control strategies. Countries into which the disease is introduced must take steps to identify infected persons in order to prevent the spread of the disease. Any activities that involve potential mixing of blood, such as transfusions, require stringent monitoring.
Chagas disease can be effectively treated with medication during the acute stages of infection. The drugs most commonly used to treat Chagas disease are benznidazole and nifurtimox. These are antiparasitic drugs aimed at killing the parasite. However, they are toxic and must be taken under medical supervision, since they may cause adverse side effects. Chemotherapy can also be used in an attempt to remove the parasite, although this treatment is not 100 percent effective.
Treatment during the chronic stages of Chagas disease focuses on controlling the effects of the disease, such as cardiac and intestinal complications. This may include insertion of a pacemaker, to control the heart's rhythm and to prevent chronic heart failure; or surgery on enlarged organs, such as the esophagus or colon. Organ transplants are also sometimes performed to replace damaged organs.
As there is no vaccine or drug available to prevent infection, prevention efforts focus on preventing parasite transmission. In terms of vector-borne infection, avoiding rural areas in which the disease is likely to exist, or treating houses, clothes, and bodies with insect repellants may prevent contact with a vector. Feces-contaminated food can also carry the parasite. Therefore, careful handling and preparation of food, plus an awareness of whether insects have been near the food, may prevent infection.
Bloodborne transmission of Chagas disease can also occur. Therefore, medical procedures, such as blood transfusions and organ transplants, require strict screening to prevent transmission of the parasite. In addition, mothers infected with Chagas disease can potentially pass the parasite to their babies while breastfeeding, if the skin around the nipple is broken. Avoiding breast-feeding when the nipples have broken skin can prevent infection.
IN CONTEXT: REAL-WORLD RISKS
Chagas disease occurs most often in Mexico, Central America, and South America; infection in the United States is rare.
- An estimated 11 million people are infected worldwide; of these, 15–30% have clinical symptoms.
- Travelers rarely acquire Chagas disease. Triatomine bugs typically infest poor-quality buildings constructed of mud, adobe brick, or palm thatch, particularly those with cracks or crevices in the walls and roof.
- Because the bugs primarily feed at night, travelers can greatly reduce their risk for acquiring infection by avoiding overnight stays in such dwellings and by not camping or sleeping outdoors in endemic areas.
- Travelers should be aware that blood products might not be routinely or adequately tested for T. cruzi prior to transfusion.
Large-scale population movements have led to an increased risk of Chagas disease in areas outside Latin America where the disease is not endemic. In nonendemic areas, the disease is largely spread by infected blood, making strict screening of the blood supply imperative. However, some countries do not perform routine tests for Chagas disease in their blood banks, and, thus, the risk of infection is high in those countries. The World Health Organization ranks the infection rate for Chagas disease from Latin American blood banks higher than HIV, hepatitis B, and hepatitis C.
T. cruzi, the parasite that causes Chagas disease, has also been discovered in wild animals in some American states. This discovery suggests that wild reservoirs of this parasite may exist in the United States, raising the possibility of an outbreak of vector-borne infections, if insects feeding on these wild animals come in contact with humans.
Transmission between a vector and human is less likely to occur in densely vegetated habits, such as rainforests, or in city areas. However, regions in which the habitat is thinned out and the abundance of fauna is reduced while the human population increases are hotspots for an outbreak of Chagas disease. In these areas, a decrease in the abundance of animals drives the vector insects to seek a new food source, and the growing human population provides a ready target. Deforestation of the Amazon and other areas of tropical rainforest in Central and South America may create just such hotspots, and more people may be infected with Chagas disease as a result.
See AlsoArthropod-borne Disease; Blood Supply and Infectious Disease; Bloodborne Pathogens; Economic Development and Disease; Host and Vector; Immigration and Infectious Disease; Parasitic Diseases; Vector-borne Disease; Zoonoses.
Arguin, P.M., P.E. Kozarsky, and A.W. Navin. Health Information for International Travel 2005–2006. Washington, DC: U.S. Department of Health and Human Services, 2005.
Aufderheide, A.C., et al. “A 9,000-year Record of Chagas’ Disease.” Proceedings of the National Academy of Sciences of the United States of America 101 (2004): 2034–2039.
Centers for Disease Control and Prevention (CDC). “Chagas Disease (American Trypanosomiasis).” December 13, 2006. <http://www.cdc.gov/ncidod/dpd/parasites/chagasdisease/factsht_chagas_disease.htm> (accessed January 31, 2007).
Directors of Health Promotion and Education. “Chagas Disease.” <http://www.dhpe.org/infect/Chagas.html> (accessed January 31, 2007).
Pan American Health Organization. “Chagas Disease (American Trypanosomiasis).” <http://www.paho.org/english/ad/dpc/cd/chagas.htm> (accessed January 31, 2007).
Chagas’ (SHAH-gas) disease is a parasitic infection common in South and Central America. It is chronic (long-lasting) and can seriously damage the heart and the digestive system many years after a person gets infected. Another name for it is American trypanosomiasis (tri-pan-o~so-MY-a-sis).
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Chagas’ disease is an infection with a protozoan (pro-to-ZO-an), a tiny parasite called Trypanosoma cruzi. This parasite infects many kinds of mammals in South and Central America. It is spread to people by blood-sucking insects called reduviid (re-DOO-vi-id) bugs. These bugs, also called kissing or assassin bugs, pick up the parasite when they bite an infected person or animal. The parasites multiply inside the bugs. When the bugs bite other people, they deposit parasite-laden feces on the skin. If the people accidentally rub the feces into a cut or scratch, or into their eyes or mouth, they can get infected too.
Reduviid bugs tend to live in the cracks and crevices of poorly built houses in rural South and Central America and in Mexico. So Chagas’ disease used to be largely an illness of the rural poor in those areas. But in the 1970s and 1980s, many people moved from the countryside to Latin American cities, bringing the infection with them. In the cities, it started to spread through transfusions of contaminated blood. More rarely, it can also spread from a pregnant woman to her fetus. Chagas’ disease is estimated to kill up to 50,000 people a year.
Chagas’ disease has acute, indeterminate, and chronic phases.
People usually get infected as children. Most have no symptoms, but some have fever, swelling of the lymph nodes, or swelling around the eyes, if that was where the parasite entered the body. Symptoms usually go away in four to eight weeks. In rare cases, there may be heart damage or seizures. In people with weakened immune systems, such as those with AIDS, the acute stage can recur later, in a very severe form.
The parasite is still present in the body but causes no symptoms. This stage lasts a lifetime in most infected people.
In about one third of infected people, serious symptoms develop 10 to 20 years or more after they became infected. The most common problems are:
- enlargement and weakening of the heart, a condition called cardiomyopathy (kard-ee-o-my-OP-a-thee), which can make a person feel weak and short of breath
- ventricular dysrhythmias (dis-RITH-me-as)—a form of irregular heartbeat that can cause sudden death
- megacolon—an enlargement of the colon (large intestine) that can cause extreme constipation and require surgical treatment
- enlargement of the esophagus (the tube carrying food from the throat to the stomach), which can make eating difficult.
In the acute stage, the parasites can be seen when blood is examined under a microscope. In the later stages, diagnosis is more difficult, and an array of different blood tests is used.
The U.S. and the World
Chagas’ disease occurs only in the Americas, mainly in South and Central America and in Mexico. It is believed to create a greater economic burden than any other tropical disease except malaria and schistosomiasis.
- In South and Central America, about 16 million to 18 million people are infected with Chagas’ disease. Many live in thatch, mud, or adobe houses in poor areas.
- In the United States, many people who emigrated from South and Central America are thought to be infected with Chagas’ disease, chiefly in the indeterminate or chronic stages. But it is extremely rare for someone to catch the disease in the United States. In a recent 20-year period, fewer than 20 newly acquired U.S. cases were reported, including three from blood transfusions.
- About 50,000 people die each year from the disease.
- The World Health Organization (WHO) reports that about 100 million people are at risk of developing Chagas’ disease.
In the acute stage, the parasites often can be eliminated by prescription medication taken for several months. In later stages, there is no proven cure. Instead, doctors try to treat the symptoms of the organ damage the parasites cause.
In Latin America, many countries are taking part in a campaign to wipe out Chagas’ disease. They are using pesticides to kill the bugs that transmit the disease, and they are upgrading housing so the bugs cannot hide in cracked walls and thatched roofs. They also are trying to screen blood supplies more thoroughly.
This campaign is farthest along in the countries of the “Southern Cone”: Argentina, Brazil, Chile, Paraguay, and Uruguay. In this area, new infections of children and young adults reportedly were reduced by almost 70 percent in the late 1990s.
Travelers to areas where Chagas’ disease is common should use insect repellent (bug spray). If possible, they should avoid sleeping in thatch, mud, or adobe homes, or they should use bed nets at night.
The World Health Organization posts information about Chagas’ disease at its website. http://www.who.int/ctd/html/chag.html
The U.S. Centers for Disease Control and Prevention (CDC) has a Division of Parasitic Diseases that posts information about Chagas’ disease at its website. http://www.cdc.gov/ncidod/dpd/chagas.htm
Chagas' disease is named after Dr. Carlos Chagas who first found the organism in the early 1900s. It involves damage to the nerves that control the heart, digestive and other organs, and eventually leads to damage to these organs. Worldwide, Chagas' disease affects over 15 million persons, and kills 50,000 each year. Researchers believe that the parasite that causes the disease is only found in the Americas.
When a person is infected with Chagas' disease, the parasite known as Trypanosoma cruzi first causes a mild, short-lived period of "acute" illness; then after a long period without symptoms, the effects of the infection begin to appear. The heart, esophagus, and colon are most frequently involved. These organs become unable to contract properly, and begin to stretch or dilate.
Causes and symptoms
T. cruzi is carried by insects or bugs known as reduviid or "kissing bugs." These insects are very common in Central and South America where they inhabit poorly constructed houses and huts. The insects deposit their waste material, exposing inhabitants to the parasites. The parasites then enter the body by way of a cut or via the eyes or mouth. T. cruzi can also be transmitted by blood transfusion. Eating uncooked, contaminated food or breastfeeding can also transmit the disease. The reduviids, in turn, become infected with the parasite by biting infected animals and humans.
There are three phases related to infection:
- Acute phase lasts about two months, with non-specific symptoms of low grade fever, headache, fatigue, and enlarged liver or spleen.
- Indeterminate phase lasts 10-20 years, during which time no symptoms occur, but the parasites are reproducing in various organs.
- Chronic phase is the stage when symptoms related to damage of major organs (heart, esophagus, colon) begin.
In the chronic phase, irregularities of heart rhythm, heart failure, and blood clots cause weakness, fainting, and even sudden death.
Esophageal symptoms are related to difficulty with swallowing and chest pain. Because the esophagus does not empty properly, food regurgitates into the lungs causing cough, bronchitis, and repeated bouts of pneumonia. Inability to eat, weight loss, and malnutrition become a significant factor in affecting survival.
Involvement of the large intestine (colon) causes constipation, distention, and abdominal pain.
The best way to diagnose acute infection is to identify the parasites in tissue or blood. Occasionally it is possible to culture the organism from infected tissue, but this process usually requires too much time to be of value. In the chronic phase, antibody levels can be measured. Efforts to develop new, more accurate tests are ongoing.
In most cases treatment of symptoms is all that is possible. Present medications can reduce the duration and severity of an acute infection, but are only 50% effective, at best, in eliminating the organisms.
Cardiac effects are managed with pacemakers and medications. Esophageal complications require either endoscopic or surgical methods to improve esophageal emptying, similar to those used to treat the disorder known as achalasia. Constipation is treated by increasing fiber and bulk laxatives, or removal of diseased portions of the colon.
Those patients with gastrointestinal complications often respond to some form of treatment. Cardiac problems are more difficult to treat, particularly since transplant would rekindle infection.
Visitors traveling to areas of known infection should avoid staying in mud, adobe, or similar huts. Mosquito nets and insect repellents are useful in helping to avoid contact with the bugs. Blood screening is not always effective in many regions where infection is common. It is necessary to carefully screen people who have emigrated from Central and South America before they make blood donations.
Achalasia— An esophageal disease of unknown cause, in which the lower sphincter or muscle is unable to relax normally, and leads to the accumulation of material within the esophagus.
Endoscopy— Exam using an endoscope (a thin flexible tube which uses a lens or miniature camera to view various areas of the gastrointestinal tract). When the procedure is performed to examine certain organs such as the bile ducts or pancreas, the organs are not viewed directly, but rather indirectly through the injection of x ray.
Parasite— An organism that lives on or in another and takes nourishment (food and fluids) from that organism.
Regurgitation— Flow of material back up the esophagus and into the throat or lungs.
Centers for Disease Control. 〈http://www.cdc.gov/nccdphp/ddt/ddthome.htm〉.
Chagas disease is a human infection that is caused by a microorganism that establishes a parasitic relationship with a human host as part of its life cycle. The disease is named for the Brazilian physician Carlos Chagas, who described in 1909 the involvement of the flagellated protozoan known as Trypanosoma cruzi in a prevalent disease in South America.
The disease is confined to North, South, and Central America. Reflecting this, and the similarity of the disease to trypanosomiasis, a disease that occurs on the African continent, Chagas disease has also been dubbed American trypanosomiasis. The disease affects some 16 to 18 million each year, mainly in Central and South American. Indeed, in these regions the prevalence of Chagas disease in the population is higher than that of the Human Immunodeficiency Virus and the Hepatitis B and C viruses . Of those who acquire Chagas disease, approximately 50,000 people die each year.
The agent of Chagas disease, Trypanosoma cruzi, is a member of a division, or phylum, called Sarcomastigophora. The protozoan is spread to human via a bug known as Reduviid bugs (or "kissing bugs"). These bugs are also known as triatomines. Examples of species include Triatoma infestans, Triatoma brasiliensis, Triatoma dimidiata, and Triatoma sordida.
The disease is spread because of the close proximity of the triatomine bugs and humans. The bugs inhabit houses, particularly more substandard houses where cracks and deteriorating framework allows access to interior timbers. Biting an already infected person or animal infects the bugs themselves. The protozoan lives in the digestive tract of the bug. The infected bug subsequently infects another person by defecating on them, often while the person is asleep and unaware of the bug's presence. The trypanosomes in the feces gain entry to the bloodstream when feces are accidentally rubbed into the bite, or other orifices such as the mouth or eyes.
Chagas disease can also be transmitted in the blood. Acquisition of the disease via a blood transfusion occurs in thousands of people each year.
The association between the Reduviid bug and poor quality housing tends to make Chagas disease prevalent in underdeveloped regions of Central and South America. To add to the burden of these people, some 30% of those who are infected in childhood develop a chronic form of the disease 10 to 20 years later. This long-lasting form of Chagas disease reduces the life span by almost a decade.
Chagas disease may be asymptomatic (without symptoms)—or can produce a variety of symptoms. The form of the disease that strikes soon after infection with Trypanosoma cruzi tends to persist only for a few months before disappearing. Usually, no treatment is necessary for relief from the infection. Symptoms of this type of so-called acute infection include swelling at the site of the bug bite, tiredness, fever, enlarged spleen or liver, diarrhea, and vomiting. Infants can experience a swelling of the brain that can be fatal.
The chronic form of Chagas disease can produce more severe symptoms, including an enlarged heart, irregularities in heart function, and the enlargement and malfunction of the digestive tract. These symptoms are of particular concern in those people whose immune system is not functioning properly.
Currently, there is no vaccine or other preventative treatment for Chagas disease. Avoidance of habitats where the Reduviid bug lives is the most prudent precaution. Unfortunately, given the economic circumstances of those most at risk, this option is not easily attainable. Trypanosoma cruzi can also be transmitted in the blood. Therefore, screening of blood and blood products for the presence of the protozoan is wise. Once again, however, the poverty that often plays a role in the spread of Chagas disease may also be reflected in less than adequate medical practices, including blood screening.
See also Parasites; Zoonoses