Chagas Control in the Southern Cone Countries: History of an International Initiative, 1991/2001
(Abstracts in English, overview plus six country profiles)
Chapter Index with Links to Abstracts
Chagas disease apparently presents low vulnerability to control, considering that the only intervention possibility is reduced, by limitations imposed by its own epidemiology and by the available technology, to the reduction of a person's chances of contact with the infected vector in the domicile atmosphere. However, 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. This is especially true in cases of species that are introduced in a certain area and strictly housed.
Basically, two control alternatives are possible:
These measures are not exclusive and can even be complementary.
What limits physical control is primarily the volume of resources necessary for this purpose, when there is an extensive area with risk transmission that imposed the adoption of measures of more rapid and economically viable impact. There has been enough knowledge and technological resources for vector control since the 1940s, but the low clinical visibility of the disease, its chronic and long course evolution, and the affected population strata—almost always rural, disempowered and without a political voice—have brought about a delay in the control demanded by the magnitude and transcendence of the disease.
The Southern Cone countries have been pioneers in the control of Chagas disease, with an institutional commitment since the 1960s in the form of national campaigns implemented in some of the countries of the subregion since the 1970s and 1980s. The "Southern Cone Initiative"—inaugurated in 1991 through decisions by the Ministers of Health of Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay—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. After ten years, the progress made has been undeniable.
On a broad scale, there has been proven interruption of Triatoma infestans, the only domiciled species in nearly the whole area. In Chile, Uruguay, and parts of Argentina and Brazil, there is no longer the risk of household transmission of the disease by this species. In many areas, it can be said that the vector has been eliminated, although it has not been demonstrated with absolute safety so far.
There has also been a great impact on transfusional transmission, through donor screening in blood banks. Congenital transmission has also been the object of some attention, with routine detection activities and treatment of cases in some of the countries.
The biggest challenge to be faced now is the sustainability of results. For this reason, it is of fundamental importance to take action in areas still infested—above all in Bolivia and Peru, a country not part of the Southern Cone but that contains areas highly infested by T. infestans. Of equal importance is the review and re-measurement of activities involving epidemiological surveillance, adapting them to the control levels achieved and to the risk—be it major or minor—in different areas, in order to stop transmission there.
Chagas Control in Argentina (E. Segura)
The National Chagas Program (Programa Nacional de Chagas, or PNC) was officially organized in 1962, after more than a decade of investigation and development of various pilot control programs for Triatoma infestans. The PNC initially had about 2,000 technicians in 19 provinces; and, in the 1960s, 1970s and 1980s, it applied a vertical control strategy with an approximate budget of US$ 120, 280 and 100 million, respectively. The annual rate of insecticide treatment decreased from 216,000–300,000 sprays in 1978–1981, to about 37,000 sprays in 1985, and then increased until reaching about 120,000 sprays in 1993. The interventions against the vector and transfusion-mediated transmission was reflected in a drop in the prevalence of < i>T. cruzi infection in young man annually drafted into obligatory military service: from 10.1% in those aged 20 years in 1965–1969, to 5.8% in 1981 and 1.9% in 1993 in those aged 18 years.
This general tendency towards decline was heterogeneous among regions and provinces. Despite improvements in epidemiological indicators, acute cases of Chagas still occurred because of repeated infestation in the communities treated and the absence of a sustainable entomological surveillance system. In a continental political scenario characterized by a clear tendency towards the reduction and decentralization of resources invested in health, in the 1980s we initiated operation research projects based on an intervention strategy that integrated the primary health-care system, and then in the horizontalization of control actions with direct community participation with the appropriate technology provided.
The transferal and execution of the horizontal strategy from the researchers that developed it to the 600 national and provincial PNC supervisors—and from these to the sanitary and municipal agencies, community leaders and members of the communities—were carried it in an eight-year process. From 1993 to 1998, a total of about 15,500 health or municipal agencies and leaders were trained in 5,000 participant workshops. There, together with PNC technicians, they treated approximately 675,000 houses with insecticides. By 2000, nearly one million houses were sprayed, and surveillance was installed in 830,000 units. The prevalence of T. infestans infestation decreased from 6.11% in 1992 to 1.19% in 1999. The annual national notification of vector-mediated acute cases of Chagas was 22, 19, 8, and 22 cases between 1997 and 2000, respectively. The impact of PNC between 1992 and 2000 was greater than between 1964 and 1992, because in less than 10 years, it achieved a greater reduction in infestation and seroprevalence rates, a greater number of houses sprayed with insecticides, with five times few the number of national technicians and a total cost of US$ 144 million—four times less than was spent between 1961 and 1990. Within the framework of the "Southern Cone Initiative," the number of blood donors checked for T. cruzi infection increased from 200,000 in 1991 to about 500,000 in 2000, spanning all public services. There was also regulation of checkups for pregnant women and newborns, as well as organ donors.
Although by 2000 the epidemiological indicators apparently had generally shown a very favorable tendency, it should be understood that national infestation averages and surveillance coverage can dilute and disguise the heterogeneity of transmission and infestation conditions at the local level, as well as its relatively rapid temporal variation in the absence of control actions. The interruption of the vectoral transmission of T. cruzi in Argentina can only be consolidated through the continuity of a surveillance system with an ample social base, which should be the conscious owner of instruments and decisions for action, as well as of an information, monitoring and evaluation systems that may give credibility to the efforts. Therefore, in the context of an extended and profound socio-economic crisis that threatens the achievements of the last decade, the Argentine PNC should return to the strategy of participation to ensure the sustainability of its control measures.
Chagas Control in Bolivia (G. Guillén)
According to the available data, there has been knowledge of the presence of the vector within the territory of Bolivia since pre-Columbian times. Its name, vinchuca, comes precisely from a Quechua word. There are also chronicles dating from colonial times.
National scientific and medical history includes researcher Artur Neiva denouncing the presence of infected vinchucas back in 1916. Since then, several national researchers and foreign institutions—such as CENETROP, INLASA, CUMETROP, and CIDECH—have continued to carry out research for more and improved knowledge of this pathology in our country. The initial reports made by Dr. Rafael Torricos, in the national study directed by Dr. Angel Valencia, are undoubtedly notable in this regard.
Between 1984 and 1992, several institutions have had significant experience in the area of vector control. Among the most import, we would like to mention the following projects: Cotagaita San Juan de Loro, Cardenal Maurer, CCH/USAID, and Pro Habitat. All of these contributed a great deal of scientific knowledge and developed sufficient technical expertise to fact this nationwide problem with all due seriousness.
Since 1992, coinciding with the landmark decision to implement the control programs of the "Southern Cone Initiative for the Elimination of T. infestans and Control of Transfusional Transmission of Chagas Disease" (INCOSUR/Chagas) in member states, Bolivia has begun a systematic process to structure the National Chagas Program, with cooperation from PMA and UNDP in 1997. Finally, the country has made a solid decision to consolidate a program and obtain funding from the IDB, along with PAHO/WHO technical assistance and UNDP administrative support. Thus, Bolivia began to build up the program until results were obtained within the framework of the Southern Cone Initiative. This program has components of vector control, transfusion control, treatment of children under five, information/communication/education/training, and monitoring and evaluation. It is important to mention that program execution is based primarily on the importance of community participation and interagency collaboration, e.g. between the armed forces and several NGOs.
Despite a short execution time, the benefits obtained up to now have been significant, clearly showing that the methodological and design strategies are on target, as are the guidelines, instruments, and procedures. Current coverage for spraying dwellings stands at 30%, in two cycles. Dwelling infestation has fallen from about 75% to between 3% and 5%. Around 1,500 dwellings have undergone improvement with good-quality materials, an activity entrusted to the Minister of Housing and the PROCOSI network.
Chagas Control in Brazil (J.C. Pinto Dias)
This paper describes the epidemiological, political, technical, and administrative aspects of the fight against Chagas in Brazil. It summarily analyzes the historical background of expansion and the discovery of human Chagas Disease (DCH), in parallel with the evolution of knowledge and control actions aimed at the epidemic. It covers what is expected over the coming years.
Socio-economic history and the production model explain the expansion of household infestation by Triatomines and how DCH has consequently become endemic since the nineteenth century. This discovery and evolution of research on the disease are part of the emergency of Brazilian tropical medicine, which always is approached from a control perspective. Since Bambuí (1944), the description of the clinical scenario and the main lines of vector control have been consolidated. Between 1950 and 1970, the definitive basis of the fight against Chagas was established, where the participation of researchers taking concrete action in the field has been fundamental—especially in the state of São Paulo. In the 1980s, priority was placed on the National Program, with a focus on transfusion control, resulting in a drastic reduction of DCH transmission in the country and making the elimination of Triatoma infestans a reality in several areas.
In this way, Brazil became part of the "Southern Cone Initiative," an agreement among six countries with PAHO as its Secretariat. In parallel, the program has been decentralized, which has led to political, operation, and administrative challenges. Today, DCH transmission in Brazil has been virtually interrupted. There remain areas requiring consolidation, mainly for permanent, sustainable epidemiological surveillance. What has been accomplished with this effort has had a major impact on the epidemic and shows and excellent cost-benefit ratio, despite the fact that two million infected people still require medical and social attention. The history of DCH and its control in Brazil show that it can be stopped within the next five years, depending on the continuity of actions, the competence of the technicians, and the will of the political decision-makers.
Chagas Control in Chile (M. Lorca, H. Schenone & J. Valdés)
In 1938, Gasic—who discovered the first acute case of Chagas in the town of Domeyko (in the north sector or Region IV)—first described the disease. From 1939 until the 1980s, clusters of cases were described, both acute and chronic, throughout the northern part of Chile. In parallel, Neghme and Schenone were pioneers in their epidemiological studies identifying the distribution of infection in the country across Regions I and VI, which include the metropolitan region.
During the 1980s, with support from WHO/TDR, a study was carried out covering a total of 5,601 rural dwellings in which residents' statements indicate an infestation rate 37.4%; and the presence of bugs (feces and urine prints, dead or captured insects), 29.4%. The more important Triatominae (and almost the only one) was Triatoma infestans; the other, Triatoma spinolai, which is more scarce and present no real importance in terms of transmission. Of the 3,822 Triatoma infestans captured and examined, 659 (17.2%) showed T. cruzi in their abdominal content (feces and/or urine).
Serological studies were carried out with RHAI for Chagas disease. In 5,050 domestic animals, it showed up positive for 7.9% of the cats, 7.0% of the dogs, 7.0% of the goats, 4.1% of the sheep, and 4.1% of the rabbits. In the case of the human population, the RHAI for Chagas disease was positive in 2,579 (16.9%) of the 15,418 people studied, with a similar frequency in men and women, with positive rates that increased progressively in proportion to the increase in age of the individuals examined.
Control work began in an isolated way between 1940 and 1950 but, by the 1960s, had already become systematic. In the period between 1991 and 2001, the efforts were already part of the Initiative and overall proved to be very effective, managing to reduce the percentage of infected housing to 5% by 1994 and progressively decreasing household 'Triatomism' in the seven regions mentioned, practically eliminating it by the end of 1999.
Program evaluation made use of the conventional entomological methods and serological evaluation of the child population. At present, in the entomological area and in dwellings where re-infestation has occurred, the number of Triatomines captured come mainly from peridomestic areas, not surpassing two insects per house; only in two dwellings were there three insects. Due to good education programs and surveillance efforts, the number of re-infested dwellings could feasibly be reduced to less than 1%. At present, the development of the aforementioned activities have allowed for a low level of surveillance over the entire area. This accounted for a positive rate of only 0.3% of dwellings in 2000.
As for the serological study on children in endemic areas, a comparative evaluation of the prevalence of anti-Trypanosoma cruzi antibodies was carried out in children under five between 1994 and 1995, and again between 1995 and 1999. During the first period, 5,948 children were studied, of which 67 (1.12%) tested positive for Chagas disease. During the second period, of the 5,069 children studied, 20 (0.4%) tested positive for T. cruzi antibodies. These data were compared, showing a reduction in prevalence of 94.6%—showing the effect of vector-control measures. In only 3 of the 209 cases was vector transmission confirmed, representing a real reduction of 99.4% for this mode of transmission. Because of this, in 1999 an International Certification Commission declared Chile to be free of vector transmission of Chagas disease. By 2005, Chile expects to have obtained certification of having eliminated the vector.
Chagas Control in Paraguay (A. Rojas de Arias & G. Russomando)
Chagas disease in Paraguay was first described in 1939 in a soldier from the Paraguayan Chaco. This finding impelled numerous works aimed at describing the natural history of the disease in the country. Between 1960 and 1982, the magnitude of the disease was shown; and between 1983 and 1991, important contributions were made in the area of generating knowledge on the disease in the country. Since 1991, Paraguay has become part of the "Southern Cone Initiative for the Elimination of Triatoma infestans and the Interruption of Transfusional Transmission" (INCOSUR/Chagas), thus increasing the effectiveness of operational actions against the vector that began in 1993.
In 1978, triatomic infestation stood at 39.5%; and in the period from 1982–1985, 60% of the departments in the country ranged between 11% and 30% in terms of infestation rates. Regarding T. cruzi infection, serological surveys showed for 1986 an anti-T. cruzi serology of between 20% and 22% in endemic areas. In 1992, the National Control Plan was developed, with the intention of spraying 250,000 dwellings over a period of 10 years. In 1993, spraying began; and by 1998, 30% of the original goal had been met. Serological surveys in conscripts conducted over a 25-year period show a 60% decrease (from 9% to 3.9%). In 1995, a program of prenatal checkups was set up in the departments of Cordillera and Paraguarí; and by 1999, a total of 5,191 seropositive women seropositive for T. cruzi had been diagnosed, with an overall prevalence rate of 15.5% and 13%, respectively. This program has spread to the departments of Paraná and Canindeyú.
Quality control in blood banks has permitted effective coverage of blood used in transfusions, with coverage at around 95% for approximately 33,000 donors. Since 1998, the National Chagas Program was restructured on the basis of an entomological survey, with spraying of positive dwellings including a range of 200 meters around them and the total spraying of localities with an infestation rate above 5%. The Program has concluded its field activities in Cordillera and Paraguarí, with a respective total of 41,303 and 53,575 evaluated dwellings with infestation levels reaching 1%, from 5.4% to 6.6%, respectively.
With regard to the surveillance system, it is noteworthy that the surveillance system in indigenous communities of the Chaco, where after general spraying for infestations with averages of 50%, coverage reached 72% with a re-infestation rate for Triatoma infestans of 2.8%. In the eastern region, the surveillance system has started up, with moderated educational workshops and the preparation of manuals for community leaders. The school, responsible for monitoring "National Chagas Week," taught people how to detect the bugs in dwellings after spraying. The municipalities and governments were nominated as receptor entities for post-spraying reporting.
Over the past three years, the National Chagas Program had invested around US$ 120,000 in the departments involved, in getting their input, paying travel expenses and per diems for their personnel. By 2003, it expects to have covered 50% of all the departments in the country. The success of the National Chagas Program lies in its strategic planning and the political decision by the health authorities to identify Chagas disease as a common denominator with an impact on most of its national territory. The support of the Southern Cone Initiative has been invaluable for the country, since its repeated evaluations and technical incentives have contributed to strengthening the methodology and the operationalization of expected goals.
Chagas Control in Uruguay (R. Salvatella)
Uruguay has been a pioneer in research on Chagas disease, a fact internationally recognized in the years between 1923 and 1950. Uruguay also developed anti-vector chemical control measures at an early stage, though it suffered a decline over subsequent decades in both research and control over its social, economic, and political reality. It is with the advent of a new generation of researchers and control-program managers, fortunately coinciding with the national restoration of democracy, that research and control achieved success in1997 in drastically reducing the vectoral and transfusional transmission of Chagas disease. Even more remarkably, this took place in a small country that, despite reduced possibilities, concentrated its efforts in parasitological research on a subject where control has been managed appropriately from 1983 up to the present.
It is desirable that this new stage leading to the total elimination of Triatoma infestans, within the framework of the Southern Cone Initiative—together with continuity in transfusion control and implementation of effective congenital control—should continue to show solid contributions in this area in terms of management, support, and research adapted to and in accordance with the needs of the country.