The forces that lead to the emergence of Trypanosoma cruzi, the etiologic agent of Chagas disease, are often distinct from those that maintain its transmission, and these are distinct again from those that allow the parasite to persist over decades. Just as kindling, logs, and coals all play discrete roles in the growth of a fire, a myriad of mammalian hosts contribute differently to epidemics of Trypanosoma. cruzi. Chagas disease affects millions of people in the Americas, and, through migration, thousands more on other continents. The agent of the disease, Trypanosoma cruzi, is a slender, highly-motile, unicellular parasite. T. cruzi does not migrate to the salivary glands of its insect vector–the blood-sucking triatomine insects–as many other vector-borne parasites do.