Chagas disease (American trypanosomiasis)
- About 6 million to 7 million people worldwide, mostly in Latin America, are estimated to be infected with Trypansosoma cruzi, the parasite that causes Chagas disease.
- Vector-borne transmission occurs in the Americas. The insect vector is a triatomine bug that carries the parasite Trypanosoma cruzi which causes the disease.
- Chagas disease was once entirely confined to the Region of the Americas – principally Latin America – but has since spread to other continents.
- Trypanosoma cruzi infection is curable if treatment is initiated soon after infection.
- In the chronic phase, antiparasitic treatment can also prevent or curb disease progression.
- Up to 30% of chronically infected people develop cardiac alterations and up to 10% develop digestive, neurological or mixed alterations which may require specific treatment.
- Vector control is the most useful method to prevent Chagas disease in Latin America.
- Blood screening is vital to prevent infection through transfusion and organ transplantation.
- Diagnosis of infection in pregnant women, their newborns and siblings is essential.
Chagas disease, also known as American trypanosomiasis, is a potentially life-threatening illness caused by the protozoan parasite Trypanosoma cruzi (T. cruzi).
About 6 million to 7 million people worldwide are estimated to be infected with Trypansosoma cruzi, the parasite that causes Chagas disease. Chagas disease is found mainly in endemic areas of 21 Latin American countries (1), where it is mostly vector-borne transmitted to humans by contact with faeces or urine of triatomine bugs, known as 'kissing bugs', among many other names, depending on the geographical area.
The cost of treatment for Chagas disease remains substantial. In Colombia alone, the annual cost of medical care for all patients with the disease was estimated to be about US$ 267 million in 2008. Spraying insecticide to control vectors would cost nearly US$ 5 million annually – less than 2% of the medical care cost.
Chagas disease is named after Carlos Ribeiro Justiniano Chagas, a Brazilian physician and researcher who discovered the disease in 1909.
Chagas disease occurs principally in the continental part of Latin America, and not in the Caribbean isles. In the past decades, however, it has been increasingly detected in the United States of America, Canada, and many European and some Western Pacific countries. This is due mainly to population mobility between Latin America and the rest of the world.
Signs and symptoms
Chagas disease presents itself in 2 phases. The initial acute phase lasts for about 2 months after infection. During the acute phase, a high number of parasites circulate in the blood but in most cases symptoms are absent or mild and unspecific. In less than 50% of people bitten by a triatomine bug, characteristic first visible signs can be a skin lesion or a purplish swelling of the lids of one eye. Additionally, they can present fever, headache, enlarged lymph glands, pallor, muscle pain, difficulty in breathing, swelling, and abdominal or chest pain.
During the chronic phase, the parasites are hidden mainly in the heart and digestive muscles. Up to 30% of patients suffer from cardiac disorders and up to 10% suffer from digestive (typically enlargement of the oesophagus or colon), neurological or mixed alterations. In later years the infection can lead to sudden death due to cardiac arrhythmias or progressive heart failure caused by the destruction of the heart muscle and its nervous system.
In Latin America, T. cruzi parasites are mainly transmitted by contact with faeces/urine of infected blood-sucking triatomine bugs. These bugs, vectors that carry the parasites, typically live in the wall or roof cracks of poorly-constructed homes in rural or suburban areas. Normally they hide during the day and become active at night when they feed on human blood. They usually bite an exposed area of skin such as the face, and the bug defecates close to the bite. The parasites enter the body when the person instinctively smears the bug faeces or urine into the bite, the eyes, the mouth, or into any skin break.
T. cruzi can also be transmitted by:
- consumption of food contaminated with T. cruzi through, for example, contact with faeces or urine of infected triatomine bugs or marsupials;
- blood transfusion from infected donors;
- passage from an infected mother to her newborn during pregnancy or childbirth;
- organ transplants using organs from infected donors; and
- laboratory accidents.
To kill the parasite, Chagas disease can be treated with benznidazole and also nifurtimox. Both medicines are almost 100% effective in curing the disease if given soon after infection at the onset of the acute phase including the cases of congenital transmission. The efficacy of both diminishes, however, the longer a person has been infected.
Treatment is also indicated for those in whom the infection has been reactivated (for example, due to immunosuppression), and for patients during the early chronic phase. Infected adults, especially those with no symptoms, should be offered treatment because antiparasitic treatment can also prevent or curb disease progression and prevent congenital transmission in pregnant women. In those cases the potential benefits of medication in preventing or delaying the development of Chagas disease should be weighed against the long duration of treatment (up to 2 months) and possible adverse reactions (occurring in up to 40% of treated patients).
Benznidazole and nifurtimox should not be taken by pregnant women or by people with kidney or liver failure. Nifurtimox is also contraindicated for people with a background of neurological or psychiatric disorders. Additionally, specific treatment for cardiac or digestive manifestations may be required.
Control and prevention
There is no vaccine for Chagas disease. Vector control is the most effective method of prevention in Latin America. Blood screening is necessary to prevent infection through transfusion and organ transplantation.
Originally (more than 9000 years ago), T. cruzi only affected wild animals. It later spread to domestic animals and people. The large reservoir of T. cruzi parasites in wild animals of the Americas means that the parasite cannot be eradicated. Instead, the control targets are elimination of the transmission and early health-care access for the infected and ill population.
T. cruzi can infect several species of the triatomine bugs, the vast majority of which are found in the Americas. Depending on the geographical area, WHO recommends the following approaches to prevention and control:
- spraying of houses and surrounding areas with residual insecticides;
- house improvements and house cleanliness to prevent vector infestation;
- personal preventive measures such as bednets;
- good hygiene practices in food preparation, transportation, storage and consumption;
- screening of blood donors;
- testing of organ, tissue or cell donors and receivers; and
- screening of newborns and other children of infected mothers to provide early diagnosis and treatment.
Since the 1990s there have been important successes in parasite and vector control in Latin America, in the territories of the Southern Cone, Central America, Andean Pact and Amazonian Intergovernmental Initiatives, with the Pan American Health Organization Secretariat. These multinational initiatives led to substantial reductions in transmission by domestic vectors.
In addition, the risk of transmission by blood transfusion has been extremely reduced through the universal screening in all blood banks of the Latin American countries and most European and Western Pacific countries with the disease. These advances have been possible because of the strong commitment of Member States affected by the disease and the strength of their research and control organizations, together with support from many international partners.
At the same time, a series of additional challenges have to be faced. These include:
- maintaining and consolidating advances made in disease control;
- emergence of Chagas disease in regions previously considered to be free of the disease – such as the Amazon basin;
- persistence in regions where control had been in progress, such as the Chaco region of Argentina, Paraguay and the Plurinational State of Bolivia;
- spread of the disease mainly due to increasing population mobility between Latin America and the rest of the world; and
- enhanced access to diagnosis and treatment for millions of infected people.
To attain the goal of elimination of Chagas disease transmission and provide health care for infected/ill patients, both in endemic and non-endemic countries, WHO aims to increase networking at the global level and reinforce regional and national capacities, focusing on:
- strengthening world epidemiological surveillance and information systems;
- preventing transmission by blood transfusion and organ transplantation in endemic and non-endemic countries;
- promoting the identification of most adequate diagnostic tests to increase screening and diagnosis of infections;
- expanding primary prevention of congenital transmission and case management of congenital and non-congenital infections; and
- promoting consensus on adequate updated case management.
(1) Argentina, Belize, Bolivia (Plurinational State of), Brazil, Chile, Colombia, Costa Rica, Ecuador, El Salvador, French Guiana, Guatemala, Guyana, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, Suriname, Uruguay, and Venezuela (Bolivarian Republic of).