Group discussion: epidemiological and social determinants of Chagas disease and its control in the Amazon countries

Abstract

The emergence of Chagas disease transmission in theAmazon region is a new challenge for controlling thedisease. It takes on special importance, considering that:(i) vector transmission in homes in many other areas hasnow been brought under control, or at least that the tech-nology available for control presents proven efficiency;(ii) the transmission patterns are different; (iii) some ofits epidemiological and social determinants or risk con-ditions are unknown.The enzootic transmission cycle of Trypanosomacruzi has long been known in the Amazon region. CarlosChagas himself already recognized flagellates isolated frommonkeys of the species Saimiri scirius as T. cruzi, in theyear 1924 (Chagas 1924). Following this, many other ani-mal reservoirs were identified (Deane 1961, 1964). Thetriatomine fauna is also very diversified and natural infec-tion has been observed in several of the species present(Barret 1988, Coura et al. 1994, Schofield 2002).However, the domestic transmission cycle has notbecome established in an evident manner or on a largescale. With the progressive human occupation of the re-gion, introduction of non-autochthonous species or colo-nization by native species as a result of human predatoryaction on the natural environment were considered likely(Silveira et al. 1984, Barret 1988, Silveira 1997). So far, ithas not been possible to confirm this. Nonetheless, au-tochthonous cases started to be recognized in the Ama-zon region, including in countries without a history ofoccurrences of this disease (Shaw 1969, Rambajan 1984,Beauder 1985). Moreover, increasing numbers of suchcases have been found over recent years (Valente 2005).On the one hand, this may be ascribed to possible newevents or environmental changes. On the other hand, thisis certainly due to the greater attention that has been givento studying the disease and performing disease surveil-lance in this region, even if done non-systematically.The means of transmission in the Amazon region donot correspond to those that are recognized as charac-teristic of the endemic disease, with “installation andpermanence” of the vector in the home. The known au-tochthonous cases are produced by the following meansof transmission: (i) oral transmission, which indirectlyor passively may be understood as vectorial, providedthat it only occurs by means of contamination of foodsby the feces of infected triatomines; (ii) vectorial trans-mission in the home, without colonization, by meansof periodic or regular incursions by specimens that in-vade the home; (iii) vectorial transmission outside ofthe home, by means of frequent human entry into for-ests and contact with wild triatomines, as occurs withRhodnius brethesi in the case of extraction activitiesrelating to the piacaba palm tree.The peculiarities of Chagas disease in the Amazonregion require the adoption of a surveillance model dif-fering from what has been followed in historically en-demic areas, in which it is fundamentally centered onentomological surveillance.Likewise, in conceptualizing a surveillance and con-trol model for the disease in this region, the followingmust be considered: (i) the extent of the Amazon terri-tory and the operational difficulties implied; (ii) the factthat it is not recognized as a public health problem inthat region; (iii) the resources already installed in the re-gion that mat serve for preventing endemic Chagas disease.