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Initiative of the Southern Cone countries: epidemiological trends

Accepting that the epidemiological and entomological spaces did not overlap with political divisions, in Brasilia in June 1991, the Ministers of Health of Argentina, Brazil, Bolivia, Chile, Paraguay, and Uruguay launched the “Initiative for the Elimination of transmission of Chagas Disease.”38 Since the vector of T. cruzi, in these countries, T. infestans, is intradomiciliary, sustained implementation of control measures have successfully interrupted transmission of Chagas disease as indicated below.

At the time, in these countries there were 11 million infected persons and 50 million were at risk. This represented 62% of the prevalence of infected individuals of the whole continent.

Technical representatives of each Ministry were designated to constitute an Intergovernmental Commission in charge of implementation and evaluation of the control programs. The Pan American Health Organization (PAHO) was appointed as the Secretariat of this Commission and has played a leading role of promotion and coordination.

A program guide was designed by the Commission incorporating revisions submitted by the professional staff of the control programs and was used for the development of the country programs. The proposed plans for Argentina, Brazil, Bolivia, Chile, Paraguay, and Uruguay are approved on a yearly basis by their respective governments.

The objectives of the “Southern Cone Initiative” were clearly established on their inception and comprised the interruption of vectorial and transfusional transmission. The cooperation among countries was ensured by the formal commitments of the countries which introduced the agreed activities in their national control programs. Later, other objectives of this Initiative were introduced, such as etiological treatment and medical care of the infected patients as an ethical imperative.

Current data37,39-46,47 on disinfestations of houses, blood bank screening, and incidence of infection in the under-5 years age group, indicate that the vector borne and transfusional transmission of Chagas disease were interrupted in Uruguay in 1997, in Chile in 1999, and in Brazil in 2006. Chagas disease has been targeted for elimination by the World Health Assembly in Resolution WHA51.14 approved in May 199848 and recently reviewed by the WHO Executive Board in January 2009.49

The model implemented in the Southern Cone was adapted to the Initiatives of the Andean Countries in 1996 (IPA) and Central America in 1997 (IPCA).50 and more recently the Amazon Initiative in 2004 (AMCHA).

The advances in control of Chagas disease accomplished in the period 1991-2006 changed the epidemiological model of the disease.

From a general point of view the most important changes obtained by the Southern Cone Initiative are:

  • • Interruption of transmission of T. cruzi by T. infestans certified in Brazil, Chile, and Uruguay, in the eastern region of Paraguay, and in 10 of the 13 endemic provinces of Argentina. (Misiones, Santa Fe, San Luis, Santiago del Estero, Jujuy, Entre Rios, La Pampa, Neuquen, and Rio Negro.)51
  • • Important reduction of vectorial transmission in Bolivia due to the coverage of house spraying with insecticides in the endemic area and regular activities of vector control in southern Peru where the house infestation is also caused by T. infestans.
  • • Reduction of the transmission by secondary species in Brazil.
  • • Coverage of blood screening close to 100% in all the countries as shown in Table 4.2.
  • • Systematic screening in blood banks is carried out routinely in 20 out of 21 countries.
  • • The prevalence of infection in young children has been substantially reduced throughout the continent and the number of people at risk of infection by the parasite has decreased in 40%, from 108 million in 2006 to 65 million in 2010.

Progress in control in each country is reported as follows:

Argentina

The area of transmission covered 60% of the country north of parallel 44 degrees. The main vector is T. infestans. In 1980 the average house infestation rate for the country as a whole was 30%; in 1998 it was 1.2%; and in 2002 it dropped to 1.0% which is equivalent to 98% reduction in house infestation by the main vector.

The seroprevalence rates for the whole country for the age group 0—4 years is 0.9% which confirms the very low number of acute cases among children in this age group. In the age group 0—14 years the rate is 1.9%. In the age group of 18-year-old males the seroprevalence rates have dropped from 5.8% in 1981 to 1.0% in 1993 and 0.5% in 2002. The interruption of vectorial transmission has been achieved in 10 of the 13 endemic provinces of the country.52

Finally, there is 100% coverage of the blood donations screened against Chagas disease in the blood banks of the public sector and 80% coverage in the private

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ones.

Bolivia

The endemic area covers 80% of the extension of the country which corresponds to seven of the nine Departments. T. infestans is the main vector. In 1982 it was estimated there were a total of 1,300,000 infected persons and in 26% of them electrocardiograph alterations were observed. The house infestation rate for the whole country was 41.2% in that year and the infection rate in the vectors was 30.0%. Infection rates of more than 50.0% have been reported in blood donors in Santa Cruz.23

Data on serological prevalence shows a rate of 28.8% in the general population while in the age group of 0—4 years it is 22.0% in Cochabamba but 0.0% in Potosi where there is an active vector control program. In Tupiza, another department where there is an active control program, the house infestation rate is 0.8%.53

Brazil

The main vector was T. infestans. Other two common species, Triatoma brasiliensis and Panstrongilus megistus are less important in disease transmission.

In 1975 the endemic area comprised 3,600,000 km2 or 36% of the total extension of the country and the most extensive endemic area on the continent. This area included 2493 municipalities in the States of Alagoas, Bahia, Ceara, Espirito Santo, Goias, Piaui, Mato Grosso, Mato Grosso do Sul, Maranhao, Paraiba, Parana, Pernambuco, Rio de Janeiro, Rio Grande do Norte, Rio Grande do Sul, Sergipe, Tocantins, and the Federal District of Brasilia. At present only the States of Bahia and Rio Grande do Sul are still considered infested by the main vector in residual foci with low density.

House infestation due to T. infestans has been reduced from 166,000 insects captured in the endemic areas by the control program in 1975 to 611 insects captured in 1999 in the same areas which corresponds to a reduction of 99.7% of the infestation by this vector. This represents an average of 1 insect per 10,000 houses surveyed, i.e., an infestation rate far below the minimum required for effective transmission of the parasite into new patients.

The prevalence of human T. cruzi infection in the 7—14 year group in 1999 was 0.04% as compared with 18.5% in 1980. This represents a 99.8% reduction of incidence of infection in this age group.

Results of 94,000 serological tests carried out in a population sample in the population of the 0—5 year group in 2007 indicate that the seroprevalence in this age group is 0.0% which can be interpreted as a proof of the interruption of vectorial transmission of Chagas disease in Brazil (Luquetti, 2007).

The above data confirms the interruption of transmission of Chagas disease by T. infestans vectors in Brazil. Based on the above epidemiological and entomological data an international commission in charge of evaluating the interruption of vectorial transmission in this country issued a certification to declare the country as free of transmission in 20 06.42,46,47,53,54

Chile

The vector responsible for disease transmission was T. infestans which has been eliminated from human dwellings and hence the transmission has been interrupted.

The overall infestation rate for the country has been reduced from 3.2% in 1994 to 0.14% in 1999, a reduction of 99.8%. In 1999 there were just 26 T. infestans insects were captured in the interior of dwellings of the endemic areas in the whole country which represents 2.5 insects in every 1000 houses, an infestation rate far below the threshold required for effective transmission of the parasite to new persons.

The infection rate in the age group 0—4 years in 1999 was 0.016% which represents a reduction of 98.5% as compared to 1.12% that was found in the same age group in 1995.

The screening in blood banks in the endemic areas has been mandatory since 1996 and the prevalence of infected samples has been reduced to 0.5%.

An independent commission visited the endemic areas of the country in November 1999 and based on the above data certified the interruption of vectorial

transmission.44,45

Paraguay

The main vector is T. infestans. Chagas disease is endemic in all rural areas of the country and the house infestation rate in 1982 varied from 10% in the Department of Misiones to 20% in Cordillera.

In a serological survey carried out in 1997 in a representative sample (940 individuals) of children less than 13 years old in marginal areas of the capital city of Asuncion a significant decrease of prevalence rates was observed in all age groups when compared with data of 1972.

Rural/urban migration to these marginal areas of Asuncion comes mainly from Paraguari, Cordillera, and Central which have the highest domiciliary infestation rates by triatomines. However, the fact of the 0 prevalence rate in the age group of less than 4-years-old indicate interruption of transmission by triatomines in the

urban areas of the capital.53,54

Uruguay

T. infestans was the only intradomicile vector. Since 1997 this species has been eliminated from the intradomiciles in the whole country. In 1975 the endemic area comprised the Departments of Artigas, Cerro Largo, Colonia, Durazno, Flores, Florida, Paysandu, Rio Negro, Rivera, Salto, San Jose, Soriano, and Tacuarembo.

The house infestation rate dropped from 5.65% in 1983 to 0.30% in 1997.

The interruption of vectorial and transfusional transmission was certified in 1997 and the whole country is under surveillance. There is 100% coverage of blood screening in blood banks.

The incidence of infection in the age group of 0—12 years was 0%, which confirms the interruption of vectorial and transfusional transmission of Chagas disease in Uruguay since 1997.43

 
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