The genus Borrelia (arthropod-associated spirochaetes responsible for zoonosis) was originally divided into numerous species according to the arthropod vector of the disease. The species transmitted by Ornithodoros and by lice which cause Relapsing Fever Borreliosis (RFB) in humans are more or less uncultivable, while those causing Lyme Borreliosis, transmitted by hard ticks, can be cultivated. Borrelia species were named according to their natural vector and its geographical location. However, some Borrelia species were successfully transmitted experimentally by unusual vectors. Therefore, a co-speciation based on the taxonomy system for Borrelia is controversial. This was demonstrated by our group with B. burgdorferi, the agent of Lyme disease whose taxonomy and geographic locations depend upon several vectors species. Our objectives are to evaluate different models of Borrelia evolution and migration ways. Phylogenies of strains from both RFB and LB group will be inferred from : - fingerprinting techniques for cultivable Borrelia (LB) - sequencing of conserved or semi-conserved genes among both cultivable (LB) and uncultivable (RFB) Borrelia.