ABSTRACT
Campaigns against transmissible diseases conducted in ex-colonial countries such as Brazil were similar attempts to regulate the uncontrollable universe of the tropics. On the other hand, making transmissible diseases visible was often an ambivalent endeavor. It displayed the "backwardness" of societies that aspired to present themselves as progressive and enlightened. Efforts to make visible an invisible agent in three "tropical plagues" that show the specificity of each enterprise when it was conducted in the framework of colonial or postcolonial medicine. The methods employed to make pathogenic agents visible were very different in each case, as was the ultimate fate of the disease studied. Once the omnipresence of transmissible diseases became visible, sanitarians and politicians immediately perceived the practical solution to the problem and began to implement solutions. In colonial and postcolonial situations, epidemiologists are not always obliged to follow infinitesimal traces to make visible a hidden reality.
