The article explores the relation between the debate on Chagas' disease, discovered in 1909, and Brazil's 1916-1920 rural sanitation campaign. It argues that the political planks of the sanitary movement were intimately bound up with the definition and legitimization of this illness as a scientific fact and social issue. Presented as emblematic of rural endemic disease, this 'new tropical ailment' was characterized as 'the disease of Brazil', symbol of a 'sickly country'. The sanitary campaign was in turn a decisive element of the 1919-1923 polemic surrounding the disease. This is an exemplary case of how Brazilian scientists used theories from European tropical medicine to produce original knowledge in the field, basing themselves on meanings specific to the national context of their day.