Chagas Disease: The Scope and Impact of the Problem
It is estimated that, in Latin America alone, between 6 and 8 million people are infected with the parasite, and 99% of these are not receiving treatment, either because they are unaware of their infection or because they do not know that treatment exists. The potential spread of the disease is also a cause for considerable concern: 65 million people live in areas of exposure and are at risk of contracting Chagas disease, and 28,000 new cases occur every year.
While significant progress has been made in the Americas on controlling vector-borne transmission, disease prevalence remains high in endemic areas due to a lack of sustained control. At the same time, the movement of affected populations to urban areas and other countries has led to the spread of the disease. As a result of these migratory flows, Chagas disease is now also a public health problem in countries where vector-borne transmission has never been documented.
Diverse and complex political, social and economic factors have favoured these migratory flows, with the search for higher-paying jobs and a better quality of life playing a decisive role in the spread of the infection. Chagas disease is now found in areas receiving migrant populations where no vector-borne transmission occurs. Nonetheless, even there, the infection continues to be transmitted in other ways. The disease is an emerging health problem in the United States, Canada and Spain as well as in other countries in Europe and the Western Pacific.
Chagas disease is caused by infection with the protozoan Trypanosoma cruzi, a parasite that nests in various tissues, causing irreversible cardiac damage in 30% of patients with chronic disease and neurological or digestive lesions in 10%. Social and environmental factors are important in the areas where the disease is endemic and there is evidence of vector-borne transmission. Living in poor quality housing, in close proximity to animals and in rural or suburban areas, especially those affected by poverty and marginalisation, are all factors that increase the risk of infection. The disease particularly targets the poorest and most vulnerable populations because the principal insect vector is a bloodsucking bug that lives in the adobe walls and thatched roofs typical of poor dwellings in rural areas and it feeds on people living in such houses. The deplorable consequence of the current situation is that, according to data published by the Pan American Health Organization (PAHO), Chagas disease still causes some 12,000 deaths annually worldwide. A recent study by the Brazilian Ministry of Health estimated that, in Brazil alone, 6,000 people die every year from Chagas disease.
What Is the Cost?
The real economic burden of Chagas disease can be hidden for years because many of those infected remain asymptomatic for over a decade. Since diagnostic tests are rarely used, many people are unaware of their infection because it has never been diagnosed. However, once the patient starts to have clinical signs—including cardiomyopathy, heart failure or dilation of the oesophagus or colon—the costs of health care, disability support and death are high.
Moreover, since these medical problems are chronic and progressive, the cost accumulates over many years. On average, the annual cost of health care per infected person is US$474, and the cumulative lifetime cost is US$3,456. This figure represents the average cost taking into account both the patients who develop complications that require complex and expensive interventions (approximately 30% to 35% of cases) and those living with the infection who never develop symptoms (65% to 70%). It does not, therefore, reflect the great range between the two extremes. Moreover, this figure only reflects the direct cost of health care. Low productivity, permanent disability, loss of income due to work absenteeism and other associated social costs amount to an average annual cost of US$4,660 per year per infected person and an accumulated average lifetime cost of US$27,770.
How is Chagas Disease Treated?
Chagas disease can be treated with the antiparasitic drugs benznidazole and nifurtimox. Both drugs are almost 100% effective in infected newborn babies and highly effective in the treatment of patients in the acute stage of the disease. However, the efficacy of both drugs decreases the longer a person has been infected. Patients with chronic disease may also require treatment for cardiac or gastrointestinal manifestations. Aetiological treatment should be offered to infected adults, especially those who have no symptoms. In addition to the social and medical benefits of controlling Chagas disease, the economic benefits are also important. The cost of aetiological treatment is equivalent to less than 1% of the social cost associated with the disease. This means that every dollar invested in such treatment can yield a savings of up to US$830 per patient who develops the disease.
Why Is it Important to Act Now?
Immediate action to combat Chagas disease is important because people are still dying as a result of this parasitic infection without ever being diagnosed or receiving treatment. Moreover, the scientific challenges that need to be addressed if we are to reduce the burden of Chagas disease do not receive sufficient global funding and the problem continues to suffer from a lack of visibility. Funding for research and development (R&D) in Chagas disease represents only 0.5% of the global budget for neglected diseases. National programmes in endemic countries have typically focused more on vector control and less on the diagnosis and treatment of patients. However, it has now been shown that treatment can effectively control the disease in most settings. Technical limitations no longer seem to be an obstacle to improving the treatment of those affected. Rather than being a due to technical constraints, the current lack of adequate treatment appears to be due to insufficient capacity for action on the part of the stakeholders and institutions responsible. At the same time, it is essential to continue researching and developing new tools. The available drugs are not very effective in the chronic phase of the disease and involve lengthy treatment cycles (two months). Furthermore, treatment must be supervised by medical personnel because of the possibility of adverse effects. The development of new tools for diagnosing the disease and monitoring treatment remains crucial; we need to identify biomarkers of disease progression and cure that can be used to monitor the effectiveness of therapy in patients with chronic disease.
What is Needed?
What is urgently needed today is an integrated approach to the disease comprising three main lines of action:
1. Prevention of new cases
A multifaceted strategy is needed to interrupt the transmission of Chagas disease, including vector control, blood screening to prevent infection through transfusion and organ transplantation, and control of vertical transmission from mother to child. Vector control, which is the most effective method of preventing vector-borne transmission in Latin America, involves three types of interventions: spraying houses with insecticides to eliminate the vector, improving housing to prevent reinfestation, and improving food hygiene standards. Blood and organs donated by individuals at risk of exposure should be screened for the parasite to prevent the transmission of infection. Congenital transmission is managed by screening pregnant women and monitoring both mother and child after delivery.
2. Aetiological treatment
The infection can be cured, but patients cannot be treated until they have been diagnosed. An active search programme is required to identify infected people who should be treated, but this is a strategy rarely implemented in the affected countries. Once a patient has been diagnosed, aetiological treatment should be started immediately regardless of whether the disease is in the acute or chronic stage. To continue the process of diagnosis and treatment, the next step is to screen family members and the local population who may be at risk.
3. Coordination of R&D
To coordinate R&D it is essential to gather information on the areas already covered, to identify potential gaps, and to draw up an R&D agenda defining the priorities that respond to the needs of the affected countries. Coordination is also required to ensure that experiences are exchanged and that intervention programmes are implemented to evaluate the new tools that have been developed.