A method for diagnosing Lyme disease status in a mammal is provided. The method entails, in a biological sample obtained or derived from a mammal, determining antibodies to Borrelia burgdorferi (B. burgdorferi) outer surface proteins (Osp) OspA, OspC, and OspF. Based upon determining the OspA, OspC, and OspF antibodies, the mammal can be diagnosed as vaccinated, not vaccinated, infected or not infected with B. burgdorferi. Mammals that have early, intermediate or chronic B. burgdorferi infection can also be identified. The method is particularly suited for use with horses and dogs. Isolated or recombinant B. burgdorferi antigens and compositions that contain them are also provided.