Chagas disease (American trypanosomiasis)

Chagas disease, also known as American trypanosomiasis, is a potentially life-threatening illness caused by the protozoan parasite, Trypanosoma cruzi or T. cruzi.

It is found mainly in Latin American countries, where it is mostly vector-borne. The main vector involved in the transmission of the parasite to humans is a triatomine bug, also known as a ‘kissing bug’. An estimated 7 million people are infected worldwide, mostly in Latin America. Chagas disease is clinically curable if treatment is initiated at an early stage. Therefore universal access to prompt diagnosis and care is essential.

Once totally confined to the Region of the Americas, Chagas disease has spread to other continents over the last century mainly because of enhanced means of travel and global population movement to and from Latin America.

It is estimated that over 10 000 people die every year from clinical manifestations of Chagas disease, and more than 100 million people are at risk of acquiring the disease.

Vector control remains the most useful method to prevent infection. Blood screening is vital to avoid infection through transfusion and organ transplantation. Screening and diagnosis in pregnant women and their children are essential control measures.

Chagas disease is named after Carlos Justiniano Chagas, a Brazilian doctor, who discovered the disease in 1909.

The Chagas disease vector is an insect of the Hemiptera order (adults have wings and fly), Reduviidae family and Triatominae subfamily (which feed on blood at all stages of their development) and mainly from the genera Triatoma, Panstrongylus and Rhodnius, but also from 12 other genera.

In the Region of the Americas, Chagas disease is transmitted by several species of the triatomine bugs that typically live in the cracks of poorly constructed dwellings in rural areas and suburban slums in Latin America.

The bugs hide during the day and emerge at night to feed on human blood, usually when people are asleep. Other infected triatomine bug species may be found in areas surrounding houses and in wild environments. Exchange of infection is therefore possible in such environment.

Distribution of vectors

The distribution of vectors and wild reservoirs of T. cruzi in the Americas extends from the United States of America to Argentina and Chile (latitudes 46°N to 46°S). Triatomine bugs have also been found outside the Region of the Americas, but up to now none of them have been found to be infected.

More than 150 species of triatomine bugs and >100 species of mammals, mostly wild species, maintain T. cruzi infection in nature.

With such a wide reservoir, Chagas disease is not eradicable.

The vector was first described in 1773 by the Swedish scientist Charles De Geer, through the observation of an insect captured in the old so-called "Indies" (assumed to refer to the East Indies, probably Indonesia).

Triatomine bug species with the capacity to transmit T. cruzi have been identified since the 18th century along maritime travel routes to parts of Africa, the Middle East, South-East Asia and the Western Pacific.

Increased global population mobility increased the possibility of establishing vector transmission to areas where Chagas disease was previously non-endemic, especially in Asia, where the vector is naturally abundant, and even infest houses in large numbers.

In the Region of the Americas, T. cruzi is mainly transmitted to humans through the infected faeces of the blood-sucking triatomine bug, which is the disease vector. This insect normally hides during the day and becomes active at night, when it feeds on human blood.

In its search for a blood meal, the bug usually bites an exposed area of the skin (such as the face - hence its common English name, “kissing bug”).

Right after its blood meal, it defecates close to the bite. The parasite, T.cruzi found in the faeces of the bug, is transmitted when the person rubs the area of the bite in an instinctive reaction to the itch (caused by the bite), thereby putting the faeces in contact with the bite.

The parasite can also be transmitted when the parasite comes in contact with the mucous membrane of the eyes or mouth or through any other skin lesion.

Transmission can occur through contaminated food infected with the vector’s faecal matter. This frequently generates oral outbreaks, especially in hot and humid climates.

Other means of transmission involve transfusion of contaminated blood and from infected mothers to child during pregnancy or during delivery (congenital transmission). Less frequently, organ transplantation or laboratory accident can result in transmission.

Outside the Region of the Americas, transmission does not occur through the faeces of the infected vector, but rather through non-vectorial routes.

Cases of infection outside Latin America have been reported among travellers returning from endemic regions, adopted children, migrants and recipients of blood transfusion or organ transplants.

Globalisation and increased international travel and trade between endemic and non-endemic countries make Chagas disease a growing concern at the global level.

Chagas disease has two successive phases: an acute phase and a chronic phase.

Most acute phases are asymptomatic or have non-specific symptoms.

During the chronic phase patients may also be symptom-free but some may progress to clinical forms of the disease (cardiac, digestive and/or neurological), which can be life threatening if left undiagnosed and untreated.

Initial acute phase

The initial acute phase lasts for about two months after infection. During this phase, a high number of parasites circulate in the blood. In most cases, symptoms are absent or mild, but may include fever, headache, enlarged lymph glands, pallor, muscle pain, cough, difficulty in breathing, liver enlargement , generalized body swelling, diarrhoea, heart inflammation (with chest pain and even heart failure) and, less frequently, meningoencephalitis (with seizures and even paralysis).

The acute phase can occur at any age but is frequently more severe in children aged <2 years, the elderly and in people who are immunosuppressed or in individuals infected with a high number of parasites. Meningoencephalitis is the most frequent manifestation in people suffering from AIDS.

Chronic phase

The acute phase is followed by the chronic phase, during which parasites are hidden mainly in the heart and digestive muscle.

Different clinical forms may be observed:

• the indeterminate form, the most frequent form, asymptomatic and without apparent signs of disease, is typically found immediately after the acute phase and is life-long in most patients;
• the cardiac form occurs in up to a third of patients, affecting the heart’s electrical conduction system, causing arrhythmia, heart muscle disorder, heart failure and embolisms;
• the digestive form (generally enlargement of the esophagus and/or the colon), observed in the South of the Amazon basin, or
• a mixed form that affects the heart, the digestive system and the autonomic nervous system occurs in ≤15% of patients.

Depending on cardiac damage, the mortality rate in a period of 10 years may range from 9 to 85%. Patients usually die, by frequency order, from sudden death caused by arrhythmias, heart failure and vascular cerebral accident, often in early adult life.

During the acute phase or during reactivation because of immunosuppression (which can be caused by old age, radiation, chemotherapy or AIDS), diagnosis is made by direct detection of the parasite circulating in the bloodstream. To this end a blood wet smear or a blood concentration technique such as microhaematocrit or Strout technique, must be used.

Stained preparations, such as malaria films, detect the parasites when parasitaemia is high (acute phase). In the Amazon Basin, microscopy technicians who diagnose malaria have been trained to detect acute individual cases of Chagas disease and, through them, identify possible foodborne outbreaks.

During the chronic phase, when the parasite is hidden in target tissues, diagnosis is made via the detection of antibodies against T. cruzi (serological techniques) using serological tests. Some of the most frequently used techniques are: enzyme-linked immunosorbent assay (ELISA), indirect haemagglutination assay, indirect immunofluorescence assay, western blot and rapid diagnostic tests such as immunochromatography.

For strict research purposes, molecular tests (qualitative and quantitative polymerase chain reaction) and parasitological tests (haemoculture and xenodiagnosis – with examination of the faeces of uninfected triatomine bugs that have fed from an infected patient’s blood) may also be used.

Treatment is urgently indicated for anyone during the acute phase and for those in whom the infection has been reactivated (immunosuppression). In these situations, treatment is almost 100% effective, and the disease can be completely cured.

However, efficacy decreases as the duration of the infection lengthens. Moreover, infants are less likely to have adverse events from treatment but this risk increases with age.

Treatment is also indicated for infants with congenital infection and for patients during the early chronic phase.

Adults, especially those with the indeterminate form of the disease, should be offered treatment, but its potential benefits in preventing or delaying the development of Chagas disease should be weighed against the long duration and frequent adverse events.

During the late chronic phase, when cardiac or digestive manifestations may occur, additional lifelong medical treatment and surgery are usually indicated.

As described earlier, the two medicines used for treatment are benznidazole, often the first-line treatment in most countries; and, nifurtimox. The main contraindications to treatment are pregnancy and kidney or liver failure. Nifurtimox is contraindicated in patients with a history of psychiatric or neurological disorders.

Both nifurtimox and benznidazole are donated to WHO by Bayer AG and Insud Pharma Group, respectively, and are made available mostly free of charge to the national health services of countries requesting these drugs.

For more information on requesting medicines please follow this link.

There is no vaccine to prevent Chagas disease.

However, the following prevention and control tools are useful depending on the geographical area(s) affected:

• insecticide spraying of houses and surrounding areas;
• home improvements to prevent vector infestation (such as plastering walls, and installing concrete floors and corrugated iron roofs);
• good hygiene practices in food preparation, transportation, storage and consumption;
• personal preventive measures such as bednets;
• screening of blood donors;
• testing of organ, tissue and cell donors and receivers;
• observance of the standard safety protocols (wearing laboratory coats, gloves, face masks, caps and glasses) for laboratory accidents prevention

Additionally, key tools of congenital transmission control are the screening of infected pregnant women and the early detection of possible infection in neonates (secondary prevention) and their siblings to provide early diagnosis and treatment.

The diagnosis of an infected newborn can be made at birth by detecting parasites directly in the umbilical cord or venous blood of the baby or when the infant is aged 8 months by detecting antibodies against T. cruzi.

In areas where malaria is also transmitted, a system of surveillance for Chagas disease has been recently implemented. Malaria microscopy technicians have been trained to identify T. cruzi parasites in malaria films and detect acute Chagas disease in individual cases. Through them, possible foodborne outbreaks and active transmission areas for the disease may be also detected and controlled.

The present low diagnosis indexes are strongly related to psychosocial rather than biomedical challenges. Among others, the following are well described determinants:

Stigma - Forgotten disease or forgotten population? (Pinto Dias)

For a long time, Chagas disease was a strictly found in rural areas, plaguing only certain regions of the countryside, usually characterized by poverty and exclusion.

To many, Chagas disease symbolises much more than an illness, almost always associated with poverty in rural areas and impoverished house infested with triatomine bugs.

Although the epidemiology of Chagas disease has changed because of migration and globalization, it is still associated with the poverty-stricken hut. Today, the disease is found in cities but the social stigma associated with infection remains strong.

The social consequences of stigma can be extremely severe; indeed, infection with T. cruzi can lead to social rejection. Infection can also mean work restriction because its association with poor health and potential difficulties in performing work, and even sudden death, creating a fear of financial losses by employers. For these reasons many people are reluctant to seek screening and medical help, which can lead to more serious complications and further spread of the disease.

Emotional burden of Chagas disease

Studies have shown that local communities in endemic countries do not have a clear understanding of Chagas disease. Instead people in rural areas merge preconceptions, forging an overall mixed and incorrect concept of the disease, its origin and consequences.

For many, Chagas disease is not necessarily associated with its vector or its symptoms, but more with feelings of despair, fear of death and suffering.

This negative approach drastically affects health-seeking behaviour as people develop adaptive behaviours, such as refusing to get screened thereby compromising both treatment and diagnosis.

Chagas disease diagnosis in non-endemic countries

Globalisation has led to a rise in awareness about Chagas disease as an emerging issue in non-endemic regions.

However, many practitioners in non-endemic countries still consider Chagas disease to be a tropical illness restricted to Latin America, and this assumption causes many misdiagnoses when presented with cardiomyopathies or other clinical manifestations of the disease.

Similarly, patients infected with T. cruzi in non-endemic countries may not be aware of their condition which can lead to further transmission through blood and organs donation, for instance.

Training health personnel to facilitate diagnosis and provide medical care can greatly help to mitigate transmission and improve prognosis.

Regulatory practices in some countries require people applying for employment to go through a compulsory T. cruzi serology. Although the aim is to protect patients with Chagas disease, this practice has resulted in discrimination against infected individuals., causing instead, hindrance and stigmatization.

Lack of understanding and knowledge of the disease, along with incorrect beliefs, are clear obstacles to promoting health-seeking behaviour.