I evaluated the genetic structure of the leptospirosis transmitting rat population of Salvador, Brazil, in order to determine more effective eradication unit sizes. The genetic makeup of the rat population is linked to eradication efforts because knowing the makeup will define strategies that are empirically based. I describe the background of leptospirosis, from its disease agent, settings and modes of infection, and then lay out my research. I determined that there are distinct populations of rats in the Pau da Lima favela, different from the results of the Kajdacsi et al (2013), but that more sampling locations are needed to determine how rat migration works in Salvador. I conclude that the advanced eradication unit sizes are a start to limiting the spread of leptospirosis, but must be coupled with changes in the sanitation infrastructure of Salvador to provide long-term success.