Technical Abstract: Pathogenic leptospires cause leptospirosis, one of the most widespread diseases transmitted from animals to humans. This disease has a significant impact on the economics of animal agriculture. Current leptospiral vaccines provide limited protection against a small number of strains. Promising targets for future vaccine development are outer membrane proteins. The current study examined genetic variability among diverse leptospiral strains in three important outer membrane proteins. One of these proteins shows little variation between strains, while the other two were quite varied. To account for these differences, a model was constructed that suggests DNA from an unknown Leptospira species has helped contribute to genetic variation among known species. These findings are critical to our understanding of how Leptospira changes, and will aid in the development of vaccines that can protect against a broad variety of Leptospira strains.