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 Trypanosoma cruzi, the parasite that causes Chagas disease. Chagas disease is found mainly in endemic areas of 21 continental Latin American countries1, where it has been mostly transmitted to humans by contact with faeces or urine of triatomine bugs (vector-borne), known as 'kissing bugs', among many other popular names, depending on the geographical area.
Chagas disease is named after Carlos Ribeiro Justiniano Chagas, a Brazilian physician and researcher who discovered the disease in 1909. In May 2019, following up on decision of the 72 World Health Assembly, the World Chagas Disease Day was established to be celebrated on 14 April (the date of the year 1909 when Carlos Chagas diagnosed the first human case of the disease, a two-year old girl called Berenice).
Chagas disease was once entirely confined to continental rural areas of the Region of the Americas – principally Latin America (not in the Caribbean islands). Mainly because of the increased population mobility in the last decades, most infected people live in urban settings (urbanization) and the disease has been increasingly detected in the United States of America, Canada, and many European and some African, Eastern Mediterranean and Western Pacific countries.
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 homes and peridomiciliary structures, such as chicken coops, pens and warehouses, in rural or suburban areas. Normally they hide during the day and become active at night when they feed on mammalian blood, including human blood. They usually bite an exposed area of skin such as the face (hence its common name ‘kissing bug’), and the bug defecates or urinates 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 (causing outbreaks of foodborne transmission with more severe morbidity and higher mortality - infecting groups of people simultaneously with more frequent cases of severe disease and higher number of deaths);
- blood or blood product 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.
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.
To kill the parasite, Chagas disease can be treated with benznidazole and also nifurtimox. Both medicines are nearly 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 and the adverse reactions are more frequent at older age.
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 other cases the potential benefits of medication in preventing or delaying the development of Chagas disease should be weighed against the duration of treatment (up to 2 months) and possible adverse reactions (occurring in up to 40% of treated adult 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 or neurological manifestations may be required.
Control and prevention
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 of the infected and ill population.
There is no vaccine for Chagas disease. T. cruzi can infect several species of the triatomine bugs, the vast majority of which are found in the Americas. Vector control has been the most effective method of prevention in Latin America. Blood screening is necessary to prevent infection through transfusion and organ transplantation and to increase detection and care of the affected population.
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;
- access to diagnosis and treatment of people with medical indication or recommendation to do antiparasitic treatment, especially children and women of child-bearing age before pregnancy; and
- screening of newborns and other children of infected mothers without previous antiparasitic treatment to do early diagnosis and provide treatment.
The medical care cost of patients with chronic cardiac, digestive, neurologic or mixed forms of the disease has been calculated to be >80% higher than the cost of spraying residual insecticide to control vectors and prevent infection.
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 and increased access to diagnosis and antiparasitic treatment.
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 disease cases. 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.
In 2005 the World Health Organization recognized Chagas disease one neglected tropical disease. This facilitated a greater recognition of the disease on the international scene and facilitated to combat misinformation, lack of social demand and weak political commitment to solve the problems related with Chagas, as well as insufficient scientific research and development related with prevention, detection and comprehensive care, including diagnosis, treatment, medicine presentations, social aspects, information, education and communication tools.
At the same time, a series of additional challenges have to be faced. These include:
- maintaining and consolidating advances made in disease control and prevention;
- 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 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;
- prevention of the consequences of the ignorance, stigma and/or discrimination associated with the disease; 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 or people suffering from the disease, both in endemic and non-endemic territories, WHO aims to increase networking at the global level and reinforce regional and national capacities, focusing on:
- strengthening world epidemiological surveillance and information systems;
- raising awareness about Chagas disease and affected populations;
- preventing transmission by blood transfusion and organ transplantation;
- promoting the identification of most adequate diagnostic tests and algorithms/protocols 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; and,
- promoting the development of multidimensional approaches.
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).