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• Eradication of
  Chaga’s Disease
• The world’s most successful parasite
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BACKGROUND

Eradication of Chagas Disease—Is it possible?

For several reasons, particularly because of the presence of numerous animal reservoirs, it is highly unlikely that Chagas Disease can be completely eradicated from the earth. Because of T. cruzi’s ability to complete its life cycle in both sylvatic and domestic reservoirs, even if the parasite is wiped out of a community the possibility of reinfection is present and can easily occur if surveillance and control efforts in that area begin to diminish. In addition, other characteristics of the disease also present obstacles for its eradication. Such factors include:

• Low clinical visibility: not everyone that is infected presents with acute symptoms, and there is an indeterminate phase of the disease that is asymptomatic
• Lack of a vaccine
• Treatment: medications to treat the disease are expensive (up to $500), have a long course of action, and have numerous side effects [9]
• Lack of resources: because it is primarily a disease of the poor in Latin America, the incentives for investing in research of the disease have been limited [9]

However, although Chagas Disease does not appear to be a good candidate for complete eradication, elimination of the parasite from human populations is a feasible and important goal. Vector control is the most effective intervention of preventing transmission of the disease to the human population. Luckily, “attributes of the vector, such as its slow population replacement and meager capacity of active dispersion, make control of the natural transmission of the disease a concrete possibility” [11]. Efforts to screen blood donors and monitor blood banks are also crucial to stopping the transmission of T. cruzi. The past two decades have witnessed the formation of several Chagas Disease control initiatives across Latin America which have experienced a great amount of success thus far.

Eradication and Control Initiatives Across Latin America

Southern Cone Initiative

Established in 1991 by the Ministers of Health of Chile, Argentina, Uruguay, Bolivia, Brazil, and Paraguay, the Southern Cone Initiative to Control/Eliminate Chagas (INCOSUR—Iniciativa del Cono Sur) was the first successful regional commitment to effectively control the disease. National campaigns had been underway in many of these countries since the 1960s, but this initiative “permitted the activities to be maintained, broadened or carried out on a regular basis, according to the level of the national program. Moreover, it has clearly defined its objectives, ensured quality control, and shared activities in border areas” [11].

The initiative’s most important control strategy focused on vector control through two main measures:

1. routine, systematized and, for some time, continuous use of insecticides in infested areas
2. improvement of the physical condition of the houses

Transfusional transmission, another important mode of transmission, has been greatly reduced through monitoring of blood banks and donor screening. Congenital transmission has also been addressed with routine detection activities and in some countries, treatment of cases. These activities have proven to be extremely successful in the interruption of the transmission of T.cruzi to human populations in these countries. However, continued epidemiological surveillance is important for the sustainability of results achieved thus far and to continue to interrupt transmission in areas that are still Chagas-endemic.

Some of the accomplishments of Chagas control in the Southern Cone countries are highlighted below:

• Argentina: vectoral transmission interrupted in 10 of the 13 provinces
• Brazil: validated interruption of vector-borne transmission of Trypanosoma cruzi in its last Chagas-endemic state in 2006
• Bolivia: interruption of vectoral transmission has occurred in several states, and dwelling infestation decreased from about 75% in 1991 to between 3% and 5% in 2001
• Chile: vectoral transmission interrupted in 1999
• Paraguay: several states have interrupted vectoral transmission, and serological surveys in 2001 showed a 60% decrease in T.cruzi infection (from 9% to 3.9%) over a 25-year period
• Uruguay: vectoral and transfusional transmission of T.cruzi interrupted in 1997

Andean Chagas Initiative

Following the success of the Southern Cone Initiative, the Andean countries of Colombia, Ecuador, Peru, and Venezuela established The Initiative of the Andean Countries to Control Vectoral and Transfusional Transmission of Chagas Disease (IPA—Iniciativa de Países Andinos) in 1997. Control strategies of this initiative mirrored those of INCOSUR, with a heavy emphasis on vector control through insecticide spraying as well as management of the blood supply. Another important strategy employed by the Andean Initiative is the use of Geographic Information Systems (GIS) to evaluate the vector-control program. This new computer technology allows for the collection, storage, and analysis of geographical data through representation of the data with spatial attributes. GIS “can be used to locate sites where vectors are found and where cases occur, and to establish spatio-temporal relationships between vectors and cases using environmental variables” [14].

Amazon Initiative

The Initiative of the Amazon Countries for Surveillance and Control of Chagas Disease (AMCHA) was established in 2004 to address the specific needs of Amazonian regions in Chagas Disease Control. Participating countries include Brazil, Bolivia, Peru, Colombia, Ecuador, French Guiana, Suriname, and Venezuela [13].

Central American Initiative

Also launched in 1997 was the Initiative of the Countries of Central America for Control of Vector-Borne and Transfusional Transmission and Medical Care for Chagas Disease (IPCA—Iniciativa de los Países de Centro América). The Ministries of Health of Honduras, Panama, Nicaragua, El Salvador, Costa Rica, Guatemala created this initiative with additional input and financial support from PAHO and several different international NGOs. Partners in this initiative include Japan International Cooperation Agency (JICA), Canadian International Development Agency (CIDA), Doctors Without Borders, World Vision, and the Inter-American Development Bank (IDB) [15].

Case Study: Honduras

Chagas Disease was first reported in Honduras in 1960, and epidemiological studies in the 1970s and 1980s identified Rhodnius prolixus and Triatoma dimidiate as the two main vectors of T.cruzi in Honduras [6]. T. dimidiata is native to Honduras and is not considered a feasible goal for elimination because it exists in peridomestic and sylvatic settings. However, R. prolixius, a species foreign to Honduras, is a feasible elimination target because of its confinement to domestic areas. [8,21]. Blood transfusions have also been an important mode of transmission in Honduras in the past, reaching a seroprevalence among donors as high 19%-28%. However, tremendous progress has been made in this area and Honduras achieved 100% coverage of blood screening in 1991 [21].

The National Strategic Plan for Chagas Disease (PENCHAGAS) was created in 2003 to achieve in Honduras the goals set forth by the 1997 Central American Initiative. The Plan outlines a comprehensive and multipronged approach to the prevention and control of Chagas Disease in Honduras. For example, the Chagas Disease control project currently underway in the state of Intibucá has three main approaches:

1. Epidemiology and education of the population: Because of the high level of decentralization of the health system in Honduras, the project used a “school-based exploration” of interviewing schoolchildren to determine which communities had the highest infection rates and should be targeted for vector control. Education and awareness campaigns also occurred in schools as well as in community meetings, and have been extremely successful. These campaigns teach people about the nature of the disease, how it is transmitted, and how to recognize symptoms. There is also a particular emphasis on the vector insect—where it lives, what it looks like, and how they can potentially avoid it.

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1. Housing project:

• Insecticide spray: Every house in the region was sprayed with insecticide to kill the vector insect.
• Rebuilding: Houses that are particularly vulnerable to inhabitation by the vector are rebuilt with materials less prone to infestation. For example, thatched roofs are replaced with metal ones and adobe walls are replaced with concrete. Materials are donated by NGOs, but the actual building is done by community members.

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1. Surveillance and treatment: Since the limited resources in Honduras don’t allow for every infected person to be treated, the treatment aspect of the project focuses on children under age 15. This population is targeted because research has shown that there is the greatest chance of eliminating the parasite from the blood stream and preventing future organ damage in this age group. The campaign involves going around to schools and testing for the parasite with a blood smear. Those that test positive are given medications donated by CIDA-Canada.

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The project has been very successful since it began and is now in its second phase with an increased focus on community based surveillance [8,16,21].

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