What is Chagas Disease?
Chagas disease, named for Carlos Chagas, the Brazilian doctor who first described the disease in 1909, is caused by Trypanosoma cruzi, a flagellate protozoan parasite. This organism belongs to the taxonomic family Trypanosomatidae within the order Kinetoplastida. It exhibits a high level of intraspecific variation, making it a difficult disease for scientists to battle. Chagas, because it often causes early mortality and disability in youth, imposes a high economic cost on the countries where the disease is found. Blood sucking reduviid insects known as kissing bugs act as the vectors of Chagas to humans.
Chagas disease is characterized by both an acute stage and a chronic stage. Approximately 1% of infected humans, frequently children, develop acute symptoms, which last four to eight weeks. A swollen eye is the key indicator. When the parasite enters other tissues, symptoms include fever, fatigue, swollen lymph glands, enlarged liver and spleen, and brain swelling. This can cause death in very young children. Approximately one-third of people who suffer from the acute stage of Chagas develop the chronic set of symptoms ten to 20 years after the initial infection. Most damaging are the lesions that strike the digestive and cardiac systems. The colon and esophagus are particularly affected, leading to severe constipation and problems with swallowing. Problems resulting from cardiac lesions can bring on sudden death.
How do people contract Chagas Disease?
People contract Chagas disease from insects of the family Reduviidae, in the suborder Heteroptera (the true bugs). These bugs are often called "kissing bugs" because they tend to bite skin where it is thinnest, around the mouth and eyes. The parasite develops over a few weeks within the kissing bug's intestine. When an infected bug bites a person, contaminated feces may enter the body through the wound, other areas of broken skin, or the conjunctiva of the eyes, introducing the parasite into the human. Secondary means of transmission include blood transfusions, maternal transfer, organ transplants, and undercooked food that contain feces of an infected bug. Domestic and wild animals can also act as carriers, although this is not as common a pathway of disease transmission.
The primary risk factor for contracting Chagas is poor housing made of mud, adobe, or thatch. The vector insects prefer this type of environment. Hundreds of reduviid bugs can rest in the housing cracks during the day and come out at night when the people in the hut are sleeping. A secondary risk factor is contaminated blood; the level of Chagas contamination in blood stocks in Central and South America exceeds that of AIDS or hepatitis.
What is the geographic distribution of Chagas Disease?
Although the disease can be detected throughout much of the American continent, Chagas is most prevalent in 21 countries in Central and South America. Once a rural disease, Chagas became an urban problem when human populations undertook significant migrations in the 1970s and 1980s. This tropical disease affects 16 to18 million people, 50,000 of whom die each year. It is estimated that as much as 25% of the Latin American population, or 90 million people, is at risk for Chagas. It is estimated that there may be 100,000 people infected with Chagas disease in the United States; most are believed to have contracted the parasite through contaminated blood transfusions.
How can Chagas Disease be treated and controlled?
There is currently no vaccine and no effective treatment for Chagas. The antiprotozoal drugs benznidazole and nifurtimox have been used for treating the disease, but they can only be used during the early stages of the acute form of the disease, they can cause side effects, and they are not always completely effective. Drugs that inhibit steroid synthesis in T. cruzi,and that could be used to combat both the acute and chronic stages of Chagas, have shown promise in mice. Until these and/or other medicines become available, however, the standard course of treatment will remain management of the disease's symptoms.
Note: This description of medicines is given for general information purposes only; contact your health care provider for details on specific treatment options.
Because vaccines and effective treatments are not available, the best means of preventing Chagas is to eliminate transmission by controlling the vector organism and by screening blood donors. Personal protection measures include avoiding or improving poor housing, using bed nets and residual insecticides, and avoiding blood transfusions from contaminated blood. Housing improvements include pouring a cement floor, plastering cracks in walls, and replacing thatched roofs with metal ones. Generally, the use of insecticides for control can have drawbacks due to their cost, the concern that reduviid vectors could develop resistance to the chemicals, and the potentially toxic effects of the insecticides on species other than the intended target. However, a tool for controlling Chagas vectors that is inexpensive and effective is a fumigant canister called CIPEIN Pf-6. Its simple operation allows local communities to play an active role in controlling Chagas. Another strategy for vector control that is being investigated is trying to eliminate vectors by killing symbiotic bacteria within the insects' digestive system.
The health ministers of the six countries of South America's "southern cone" (Brazil, Chile, Uruguay, Paraguay, Argentina, and Bolivia) implemented an initiative in 1991 to eliminate Chagas in their countries. There is also an initiative underway in the Andean countries, and an initiative in Central America. Fortunately, control programs are showing great success. Overall, positive trends include a reduction in infested houses and a reduction in infected young children (reductions between 60 and 99%). In 1997, Uruguay was declared Chagas-free, and Chile was free of the disease by 1999. By 2000, most of Brazil had eliminated transmission of the disease, as well. These are encouraging trends in the battle against this serious and potentially fatal disease.
Where can you find out more about Chagas?
Kirchhoff, L. V. 1993. American trypanosomiasis (Chagas' disease)-a tropical disease now in the United States. New England Journal of Medicine329: 639-644.
Schmunis, G., Zicker, F., Moncayo, A. 1997. Interruption of Chagas' disease transmission through vector elimination, The Lancet348: 1171.
Moncayo, A. 1997. Progress towards the elimination of transmission of Chagas disease in Latin America. World Health Statistics Quarterly50: 195-198
Hagar, J. M., Rahimtoola, S. H. 1995 Chagas' heart disease. Current Problems in Cardiology20: 825-924.
Kirchoff, L. V. 1996. American trypansomiasis (Chagas' disease). Gastroenterology Clinics of North America25: 517-532.
Guerrant, R. L., Walker, D. H., and Weller, P. F. (Eds.) 2001.Essentials of Tropical Infectious Diseases. W. B. Saunders, Philadelphia.
Beaty, B. J., and Marquardt, W. C. (Eds.) 1996. The Biology of Disease Vectors. Univ. of Colorado Press, Niwot, Colorado.
Perleth, M. 1997. Historical Aspects of American Trypanosomiasis (Chagas' Disease) (Medizin in Entwicklungslandern, Bd. 43).Peter Lang Publishers, Frankfort, Germany.
Bastien, J. W. 1998. The Kiss of Death : Chagas' Disease in the Americas.Univ. of Utah Press, Salt Lake City.
The Centers for Disease Control: http://www.cdc.gov/ncidod/dpd/parasites/chagasdisease/default.htm
—Prepared by Susan L. Thomas
Last updated: March 1, 2002