Progress towards the elimination of transmission of Chagas disease in Latin America / Alvaro Moncayo

Progress towards the elimination of transmission of Chagas disease in Latin America Alvaro Moncayoa Chagas disease, named after the Brazilian physician Carlos Chagas who first described it in 1909, exists only on the American Continent. It is caused by a flagellate protozoan parasite, Trypanosoma cruzi, transmitted to humans by triatomine insects known popularly in the different countries as "vinchuca", "barbeiro", "chipo" etc. The geographical distribu- tion of the human T. cruzi infection extends from Mexico to the south of Argentina. The disease affects 16-18 million people and some 100 million, i.e. about 25% of the population of Latin America, is at risk of acquiring Chagas disease. There are two stages of the human disease: the acute stage which appears shortly after the infec- tion and the chronic stage which appears after a silent period that may last several years. The lesions of the chronic phase irreversibly affect internal organs namely the heart, oesophagus and colon and the peripheral nervous system. After several years of an asymptomatic period, 27% of those infected develop cardiac symptoms which may lead to sudden death, 6% develop digestive damage - mainly megaviscera, and 3% will present peripher- al nervous involvement. The risk of infection with Chagas disease is directly related to poverty: the blood-sucking tri- atomine bug which transmits the parasite finds a favourable habitat in crevices in the walls and roofs of poor houses in rural areas and in the peripheral urban slums. The rural/urban migration move- ments that occurred in Latin America in the 1970s and 1980s changed the traditional epidemiological pattern of Chagas disease, transforming it into an urban infection that can be transmitted by blood transfusion. The rates of infection of blood in blood banks in some selected cities of the conti- nent vary between 3% and 53% thus showing that the prevalence of T. cruzi-infected blood is higher than that of HIV infection and hepatitis B and C. From a global perspective, Chagas disease rep- resents the third largest tropical disease burden after malaria and schistosomiasis. According to the UNDP Human Development Report (1), the esti- mated average annual per capita gross domestic product in Latin America, is US$ 2 966. Thus, the economic loss for the continent due to early mor- tality and disability by this disease in economically a Chief, Trypanosomiasis and Leishmaniasis control, Division of Control of Tropical Diseases, World Health Organization, Geneva. Wld hlth statist. quart., SD (1997) most productive young adults currently amounts to US$ 8 156 millions which is equivalent to 2.5% of the external debt of the whole continent in 1995. Southern Cone Initiative In 1991, the Ministers of Health of Argentina, Bolivia, Brazil, Chile, Paraguay and Uruguay, launched the "Southern Cone Initiative for elimina- tion of transmission of Chagas disease". The progress towards elimination of vectorial and transfusional transmission ofChagas disease in U ru- guay, Chile, Argentina and Brazil has been exten- sively documented ( 2-5). Current data on disinfect- ing of houses, coverage of screening in blood banks and serology in children and young adults indicate that the interruption of the vectorial and transfu- sional transmission of Chagas disease will be achieved in these countries as follows: Uruguay and Chile in 1999, Brazil and Argentina in 2003. By eliminating the transmission of Chagas disease in the above countries, the incidence of the disease in the whole of Latin America will be reduced by more than 70% (see Figs. 1 & 2). Fig.1 Southern Cone Initiative for the elimination of transmission of Chagas disease: house infestation by triatomines, 1982-1996 Initiative du cone Sud pour !'elimination de la transmission de la maladie de Chagas : infestation des habitations par des triatomes, 1982-1996 35~~~~~~~~~~~~~~~~~~ 30 25 ::,!:! ~20 ::, ~ I ll'l 15 1;j a: 10 5 1980 Argentina - Argentine Brazil - Bresil Chile-Chili - Uruguay 1985 1990 1995 Year-Annee Source: Reports from national Chagas disease control programmes, 1993-1996. - Rapports des programmes nationaux de lutte contre la maladie de Chagas, 1993-1996. 2000 195 Fig. 2 Southern Cone Initiative for the elimination of transmission of Chagas disease: incidence of infections 1980-1996 Initiative du cone Sud pour 1'61imination de la transmission de la maladie de Chagas : incidence des infections, 1980-1996 6-.-~~~~~~~~~~~~~~~~~-, 5 -4 c x ::, ~3 I (I) "' ;;; a: 2 1980 1985 1990 Year-Annee 1995 Argentina (18 years)-Argentine (18 ans) Brazil (7-14 years)- Brasil (7·14 ans) Chile ( <10 years) - Chili ( moins de 1 O ans) - Uruguay (<12 years)-(moins de 12 ans) Source: Reports from national Chagas disease programmes, 1993·1997. - Rapports des programmes nationaux de lutte contre la maladie de Chagas, 1993·1997. 2000 Control activities are progressing as scheduled in Bolivia and Paraguay, but at this stage there are no entomological or epidemiological data avail- able to assess the impact of the control pro- grammes in these two countries and to estimate a date for achievement of interruption of transmis- sion. These data should be available in 1999, after 4-5 years of continued control activities and com- pletion of cross-sectional entomological and sero- logical surveys. Peru joined in March 1997 as the southern area of this country is also infested by T. infestans. The detailed epidemiological situa- tion, country by country is as follows: Argentina The area of transm1ss10n of Chagas disease in Argentina includes the zones north of latitude 44° 45', covering about 60% of the territory of the country. The main vector is Triatoma infestans which is a domiciliated species. The cumulative number of houses sprayed be- tween 1992 and 1996 completed the attack phase of the control strategy. This has led to important 196 reductions in the house infestation rates from 24% in 1983 to 4% in 1996- equivalent to 84% decrease in the period. As a consequence, there was a reduc- tion of80% in the incidence of human infection in the group of 18 year old males between 1983 and 1996. To prevent the transfusional transmission of Chagas disease, the screening of T. cruzi-infected blood is compulsory since 1983 and the coverage of the screening in the blood banks of the country was 98% in 1996. Brazil In 1970, the endemic area included over 36% of the country, with 2 493 municipalities being in- fested by T. infestans, the main vector of the dis- ease. A total of 49 million persons lived in the endemic zone, 53% of whom in rural areas. T. infestans, the most important species responsible for the vectorial transmission of the disease, is ex- clusively domestic. In 1983, there were 711 municipalities infested by T. infestans in the endemic states, while in 1995 only 75 municipalities were infested, representing a 90% reduction. In 8 of the 11 endemic states, a reduction of house infestation rates of 71 % is ob- served. Focal areas still infested with T. infestans remain only in the states of Bahia, Tocantins and Rio Grande do Sul, which gives a house infestation rate of 2. 7% for the whole country. Seroepidemiologi,cal surveys carried out be- tween 1994 and 1996 in 10 endemic states among population samples of individuals 7-14 years old showed that the incidence of infections in this age group is 0.23% in the country as a whole, indicat- ing a reduction of 95% as compared to the 1981 rates. Similar trends are observed in relation with the decreasing proportion of T. cruzi-infected blood in blood banks between 1982 and 1995. A proportion of 6.5% of infected blood was found in the whole country in 1982, whereas in 1995 this proportion was only 0. 7%. The coverage of screening in blood banks reached 98% in 1995. Chile Chile has a population of 13 380 OOO, including 1 654 OOO who live in the endemic rural area from parallel 18° 30' to parallel 34° 35' and hence are at risk of contracting the infection and further evolve to chronic myocardiopathy or megaviscera. The main species of triatomines responsible for the vectorial transmission of Chagas disease in Chile is T. infestans, a domestic insect. In 1981, the proportion of infected persons in all age groups in the country was 17% and the average house infestation rate was 29%. The countrywide prevalence of infected subjects among blood donors in 1984 was 3.6%. Rapp. trimest. statist. sanit. mond., 50 (1997) The vector control operations with residual ac- tivity insecticides carried out between 1982 and 1996 have reduced the house infestation rates by T. infestans to 1.6%, which is equivalent to a de- crease of95%. Transmission through blood trans- fusion is under control due to the 100% coverage since compulsory blood screening in the endemic regions was introduced in 1995. A countrywide seroepidemiological study, com- pleted in 1996, showed a prevalence rate of 1.4% in the age group <10 years as compared to 5.4% in the same age group in 1990, indicating the advanced degree of control and imminent interruption of vectorial transmission in Chile (6). Uruguay Chagas disease is endemic in Uruguay where vecto- rial domiciliary transmission is effected through the triatomine insect T. infestans. In 1983, this in- sect infested human dwellings and their perido- mestic annexes in 80% of the national territory. Sustained spraying helped eliminate the infesta- tion by T. infestans in Artigas, Colonia, Durazno and Soriano, and markedly decreased the rate of house infestation in the remaining areas to the current figure of0.3% for the entire country. In 1985, a countrywide serological survey to detect human T. cruzi infection, showed a preva- lence rate of 3.4% for the total population, and of 2.4% for the school-age group of <~2 years old. A seroepidemiological survey carried out in 1995 in different rural areas of the endemic depart- ments in children <12 years old showed 0-0.1 % infection rates in this age group. This could be interpreted as the confim1ation of the interruption of the vectorial transmission of Chagas disease in Uruguay. In addition, there is 100% coverage of compulsory blood screening in the country. Summary From a global perspective, Chagas disease represents the third largest tropical disease burden after malaria and schistosomiasis. The estimated average annual per-capita gross domestic product in Latin America is US$ 2 966. The economic loss for the continent due to early mortality and disability by this disease in econom- ically most productive young adults currently amounts to US$ 8 156 million which is equivalent to 2.5% of the external debt of the whole continent in 1995. In 1991, the Ministers of Health of Argentina. Bolivia, Brazil, Chile, Paraguay and Uruguay, launched the Southern Cone Initiative for elimination of transmission of Chagas disease. The progress towards elimination of vectorial and transfusional transmission of Chagas dis- ease in Uruguay, Chile, Argentina and Brazil has been Wld hlth statist. quart., 50 (1997) documented by reports from the national control pro- grammes of the above countries. Current data on disin- festation of houses, coverage of screening in blood banks and serology in children and young adults indi- cate that the interruption of the vectorial and transfusion- al transmission of Chagas disease will be achieved in these countries as follows: Uruguay and Chile in 1999, Brazil and Argentina in 2003. By eliminating the trans- mission of Chagas disease in the above countries, the incidence of the disease in the whole of Latin America will be reduced by more than 70%. Resume Progres sur la voie de /'elimination de la transmission de la maladie de Chagas en Amerique latine O'un point de vue mondial, la maladie de Chagas est la troisieme maladie tropicale par son importance, apres le paludisme et la schistosomiase. Le produit national brut moyen par habitant et par an de l'Amerique latine est estime a US $2 966. Les pertes economiques pour le continent dues a la mortalite precoce et aux incapa- cites provoquees par cette maladie chez des jeunes adultes economiquement les plus productifs s'elevent a l'heure actuelle a US $8 156 millions, soit !'equivalent de 2,5% du montant de la dette exterieure de !'ensemble du continent en 1995. En 1991, les Ministres de la Sante de !'Argentine, de la Bolivie, du Bresil, du Chili, du Paraguay et de !'Uruguay ant lance !'initiative du Cane Sud pour !'elimination de la transmission de la maladie de Chagas. Les progres accomplis sur la voie de !'elimination de la transmission vectorielle et transfusionnelle de la maladie de Chagas en Uruguay, au Chili, en Argentine et au Bresil ant ete attestes dans des rapports publies par les programmes nationaux de lutte des pays concernes. Les donnees actuelles concernant la desinsectisation des habita- tions. le depistage par les banques de sang et la serologie chez l'enfant et le jeune adulte indiquent que la transmission vectorielle et transfusionnelle de la ma- ladie de Chagas sera interrompue en Uruguay et au Chili d'ici 1999, et au Bresil et en Argentine en 2003. L'elimination de la transmission de la maladie de Cha- gas dans les pays susmentionnes permettra de reduire !'incidence de la maladie dans !'ensemble de l'Ameri- que latine de plus de 70%. References 1. UNDP Human Development Repmt 1996. New York, Oxford University Press, p 211. 2. Chagas disease. Elimination of transmission, Uruguay. Weekly epidemio/,ogical record, 59 ( 6): 38-40 (1994). Maladie de Chagas. Elimination de la transmission, Uruguay. &l£ue epidimiologique hebdomadaire, 69 ( 6): 38-40 (1994). 3. Chagas disease. Interruption of transmission, Chile. We,kly epidemiological record, 70(3): 13-16 (1995). 197 Maladie de Chagas. [nterruption de la transmission, Chili. RP/,eve epidimiowgique hebdomadaire, 70(3): 13-16 (1995). 4. Chagas disease. Progress towards elimination of trans- mission, Argentina. WeeklyEpidemiowgical&cord, 71(2): 12-15 (1996). 198 Maladie de Chagas. Progres realises vers !'elimination de la transmission, Argentine. R.e/,eve epidimiowgique hebdomadaire, 71(2): 12-15 (1996). 5. Chagas disease. [nte1Tuption of transmission, Brazil. Weekly epidemiological record, 72(1/2): 1-5 (1997). Maladie de Chagas. Interruption de la transmission, Bresil. RP/,eve epidimiowgique hebdomadaire, 72(1/2): 1-5 (1997). 6. Lorca, M. etal. Evaluacion de los programas de erradicacion de la enfermedad de Chag-as en Chile mediante estudio serologico de ninos menores de 10 anos. Boletin chileno de parasitowgia,, 5 l : 80-85 ( 1996) . Rapp. trimest. statist. sanit. mond., 50 (1997)