© International Epidemiological Association 2001
International Journal of Epidemiology 2001;30:894–895
Printed in Great Britain
Commentary: Control of Chagas’ disease: let’s put people before vectors Juan Carlos Villar
Chagas’ disease (CHAD), the result of the human infection by Trypanosoma cruzi remains a major disease burden in Latin America. A relatively high proportion (30%) of the 16–18 million infected individuals in the so-called indeterminate phase tend to progress to the chronic phase, mainly a dilated cardiomyopathy, which appears as early as in the third or fourth decade of life.1 Chagas’ disease contributes to approximately 2 740 000 disabilityadjusted life years lost, four times the overall burden of malaria, schistosomiasis, leprosy and leishmaniasis in the continent.2 In the absence of suitable vaccination, chemoprophylaxis or specific treatment, the only strategy for control of CHAD has been based on vector control. Having launched the ‘southern cone initiative’ in 1991, the transmission of CHAD has already been declared interrupted in southern South America and the World Health Organization expects this task to be completed in the continent by 2010.3 In this issue of the International Journal of Epidemiology Lima e Costa et al. present evidence of a cohort effect in a region in which transmission of CHAD has been interrupted.4 The authors show how, in the town of Bambuí, Brazil, the infection has virtually disappeared in individuals younger than 40, a result attributable to vector control campaigns started in the 1950s and reinforced in the 1970s. In addition, using a health status survey in an urban population older than 60 years, the authors demonstrate poorer health indicators among seropositive subjects, such as higher rates of hospitalizations, use of medications, time in bed and lower self-rated general health status. Based on these findings, the authors claim that among elderly people, in whom it is believed that its main impact on human health declines, T. cruzi infection remains a public health concern in endemic (or formerly endemic) areas. This well-conducted and informative study demonstrates how the epidemiology of CHAD may unfold over the coming decades in these areas, provided control of transmission remains successful. While this research emphasizes the continuing burden of CHAD among elderly people in endemic regions, this does not diminish the importance of CHAD, or imply that its control is straightforward. Rather, these data reflect a tangential aspect of the burden of CHAD, which Latin America will, in general, continue to face for the next three or four decades, at best. This survey did not capture the substantial part of the burden of CHAD for two main reasons. Participants were both older than 60 and lifelong residents in Bambuí. Once symptomatic in midlife, the reported 10-year survival is only 20%.5 Thus, the Facultad de Medicina, Universidad Autónoma de Bucaramanga, Bucaramanga, Colombia. Population Health Institute, McMaster University, 237 Barton St East, Hamilton, Ontario L9H 6L7, Canada. E-mail:
[email protected]
surveyed population represents only mild cases or cases not affected at all by Chagas cardiomyopathy. Indeed, the authors found that seropositive participants were more likely to be female, a fact that indirectly reflects the excess morbidity and/or mortality of infected males, as previously reported.6 In addition, while these vector control campaigns took place, huge waves of migration to urban centres changed simultaneously the demography of Latin America and therefore, the epidemiology of CHAD as the urban population in the region has increased from 25% 50 years ago to a projected 80% by the year 2015.7 In sum, these data reflect branches, rather than the mainstream, of the burden of CHAD and the past, rather than the current epidemiological scenario of CHAD. The authors document the interruption of the transmission attained by vector-based control programmes.8,9 However, even achieving this key goal will not prevent the burden of CHAD continuing for several decades while the cohort effect depicted in this paper is completed. Sustainable success of the vector control is a pre-requisite, but it relies on the extinction of some Reduvidae species, the consequences of which, for both the chain of transmission and the ecosystem, are not fully understood yet. Warning signals about the design, feasibility and sustainability of these campaigns in the northern countries of South America and Central America, where vectors behave differently, have been already issued, and should be heeded until the migration pathways of non-domiciliary vectors are better understood.10 Moreover, the persistence of poverty, violence and internal migrations in rural areas of Latin American countries11,12 are constant threats for the emergence or re-emergence of areas of active transmission, as happened with malaria and sleeping sickness, which again became public health threats after initial successes in their control.13,14 Governments and decisionmakers should not forget that improving the living conditions of these communities is, in the end, the key for long-term control. The other theoretical approach for control, successful primary prevention (i.e. chemoprophylaxis or vaccination) requires sound patient-based research. Unlike vector control, it would have both short- and long-term impacts on morbidity and mortality and would also target urban settings, where the disease has tended to move. Over the years, patients and health professionals dealing with the burden of CHAD have had only few therapeutic tools gathered from a weak, inadequately supported clinical research base. Of 1223 new drugs introduced for clinical use between 1975 and 1996, only 3 were designed for trypanosoma-caused diseases, and only 2 approved for CHAD.15 Only four randomized controlled trials testing the efficacy of trypanocidal therapy have been published16–19 and no vaccines have been developed. Control agencies continue to focus on vector-based research20 and the construction of evidence-based
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health care for CHAD, based on studies answering the questions that matter for infected individuals will have to wait still longer. For now, both resources and victory have gone to vectorbased research. This victory may not last long if control and granting agencies fail to assign, increase, or re-allocate resources for complementary and much needed patient-based research. The victory is also questionable, since focusing solely on the transmission of infection leaves people already infected still suffering the natural history of the disease. The control of CHAD requires a re-evaluation of research priorities and a consideration of both population and patient needs.
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transmission through vector elimination [letter]. Lancet 1996;348:1171. 9 Pan American Health Organization. Chagas’ disease interruption of
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Lancet 2000;355:236. 11 CEPAL—ONU. Pobreza y vulnerabilidad social Panorama social la
américa latina. In: Comision Económica para la America Latina (CEPAL)—Naciones Unidas (ed.). Panorama social la américa latina 1999–2000. Santiago: CEPAL, 2001, pp.35–57. 12 CEPAL—ONU. Boletin Demográfico No. 63. America Latina: Tasa de
Crecimiento de la Población Total, Urbana y Rural. CEPAL website 2000. 13 Martens P, Hall L. Malaria on the move: human population move-
ment and malaria transmission. Emerg Infect Dis 2000;6:103–09.
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Chagas’ Disease Elimination. Burden and Trends. WHO web.page www. who.int/ctd./html./chagburtre.html. 2000. 4 Lima e Costa MFF, Barreto SM, Guerra HL, Firmo JOA, Uchoa E,
Vidigal PG. Ageing with Trypanosoma cruzi infection in a community where the transmission has been interrupted: the Bambuí Health and Ageing Study (BHAS). Int J Epidemiol 2001;30:887–93. 5 Pugliese C, Lessa I, Santos FA. Estudo da sobrevida na miocardite
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14 Smith DH, Pepin J, Stich AH. Human African trypanosomiasis:
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