I trace the development of the concept of sylvatic plague – the first sylvatic disease – examining its invention by Ricardo Jorge to describe a global phenomenon of plague reservoirs among wild rodents, and its circulation. The concept implied a space where plague was enzootic, and relied on a division between inhabited and uninhabited spaces and between domestic rats and wild rodents. Some of the characteristics of this space varied, but it always referred to places imagined as empty of humans and rats. In 1927, it designated ambiguously deserts, in 1935, uninhabited regions in general, and in Brazil, it referred to the jungle.