Chagas disease: current epidemiological trends after the interruption of vectorial and transfusional transmission in the Southern Cone countries

Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 98(5): 577-591, July 2003 577 Chagas Disease: Current Epidemiological Trends after the Interruption of Vectorial and Transfusional Transmission in the Southern Cone Countries Alvaro Moncayo Universidad de los Andes, Calle 70, no. 5-60, (204) Bogotá, Colombia Chagas disease, named after Carlos Chagas who first described it in 1909, exists only on the American Continent. It is caused by a parasite, Trypanosoma cruzi, transmitted to humans by blood-sucking triatomine bugs and by blood transfusion. Chagas disease has two successive phases, acute and chronic. The acute phase lasts 6 to 8 weeks. After several years of starting the chronic phase, 20% to 35% of the infected individuals, depending on the geographical area will develop irreversible lesions of the autonomous nervous system in the heart, esophagus, colon and the peripheral nervous system. Data on the prevalence and distribution of Chagas disease improved in quality during the 1980’s as a result of the demographically representative cross-sectional studies carried out in countries where accurate information was not available. A group of experts met in Brasília in 1979 and devised standard protocols to carry out countrywide prevalence studies on human T. cruzi infection and triatomine house infestation. Thanks to a coordinated multi-country program in the Southern Cone countries the transmission of Chagas disease by vectors and by blood transfusion has been interrupted in Uruguay in1997, in Chile in 1999, and in 8 of the 12 endemic states of Brazil in 2000 and so the incidence of new infections by T. cruzi in the whole continent has decreased by 70%. Similar control multi-country initiatives have been launched in the Andean countries and in Central America and rapid progress has been recorded to ensure the interruption of the transmission of Chagas disease by 2005 as requested by a Resolution of the World Health Assembly approved in 1998. The cost-benefit analysis of the investments of the vector control program in Brazil indicate that there are savings of US$17 in medical care and disabilities for each dollar spent on prevention, showing that the program is a health investment with good return. Since the inception in 1979 of the Steering Committee on Chagas Disease of the Special Program for Research and Training in Tropical Diseases of the World Health Organization (TDR), the objective was set to promote and finance research aimed at the development of new methods and tools to control this disease. The well known research institutions in Latin America were the key elements of a world wide network of laboratories that received – on a competitive basis – financial support for projects in line with the priorities established. It is presented the time line of the different milestones that were answering successively and logically the outstanding scientific questions identified by the Scientific Working Group in 1978 and that influenced the development and industrial production of practical solutions for diagnosis of the infection and disease control. Key words: Chagas disease - Trypanosoma cruzi infection - control - interruption of transmission Chagas disease, named after Carlos Chagas who first described it in 1909, exists only on the American Continent (Chagas 1909). It is caused by a flagellate parasite, Trypanosoma cruzi transmitted to humans by bloodsucking triatomine bugs and by blood transfusion. The author was Secretary of the TDR Steering Committee on Chagas Disease from 1979-1997; Chief, Control of Trypanosomiasis and Leishmaniasis 1990-1998; and Manager of the TDR Task Force on Intervention Research on Chagas Disease from 1998 to 2001 at the World Health Organization, Geneva, Switzerland. Currently he is an Associate Researcher at the Universidad de los Andes, Bogotá, Colombia. Fax: +57-1-332.4540. E-mail: Received 10 June 2003 Accepted 26 June 2003 Chagas disease has two successive phases, acute and chronic. The acute phase lasts 6 to 8 weeks. Once the acute phase subsides, most of the infected patients recover an apparent healthy status, where no organ damage can be demonstrated by the current standard methods of clinical diagnosis. The infection can only be verified by serological or parasitological tests. This form of the chronic phase of Chagas disease is called indeterminate form. Most patients remain in this form of the disease. However, after several years of starting the chronic phase, 20% to 35% of the infected individuals, depending on the geographical area will develop irreversible lesions of the autonomous nervous system in the heart, esophagus, colon and the peripheral nervous system. The chronic phase lasts the rest of the life of the infected individual. Chagas disease represents the first cause of cardiac lesions in young, economically productive adults in the endemic countries in Latin America. 578 Chagas Disease, Interruption of Transmission • Alvaro Moncayo Thanks to a coordinated multi-country program in the Southern Cone countries the transmission of Chagas disease by vectors and by blood transfusion has been interrupted in Uruguay in1997, Chile in 1999, and in 8 of the 12 endemic states of Brazil in 2000 and so the incidence of new infections by T. cruzi in the whole continent has decreased by more than 70%. Similar control multi-country initiatives have been launched in the Andean countries and in Central America and rapid progress has been recorded to ensure the interruption of the transmission of Chagas disease by 2005 as requested by a Resolution of the World Health Assembly approved in 1998. MODES OF TRANSMISSION Transmission through vectors Chagas disease is a zoonosis transmitted in natural foci or ecological units within a well-defined geographical environment. The ecological unit is composed of sylvan or domestic mammals and of sylvan Triatoma bugs, both infected with T. cruzi. Continuous transmission is assured with or without the involvement of human beings. These conditions of transmission are present from latitude 42°N to latitude 40°S and so T. cruzi infection occurs from the South of the United States to the South of Argentina. There are two stages of the human disease: the acute stage, which appears shortly after the infection; and the chronic stage, which may last several years and after several years of a silent asymptomatic period, 25% of those infected develop cardiac symptoms that may lead to chronic heart failure and sudden death, 6% develop digestive damage, mainly mega-colon and mega- esophagus, and 3% will suffer peripheral nervous involvement (Coura 1983, 1985, Pereira 1985). Transmission via blood transfusion The rural-to-urban migration movements that occurred in Latin America in the decades of the1970’s and 1980’s changed the traditional epidemiological pattern of Chagas disease as a rural condition and transformed it into an urban infection that can be transmitted by blood transfusion. In most coun (...truncated)