Lyme disease (LD) is the leading arthropod-borne disease in North America with 300-600,000 cases each year. There are currently no approved human LD vaccines. Outer surface protein C (OspC) has emerged as a leading vaccine candidate and an attractive diagnostic marker due to its antigenicity and expression early in infection. Several chimeric, epitope based OspC derived proteins were generated. The constructs were found to be highly immunogenic in mice and vaccination induced complement-dependent bactericidal antibodies. These results suggest that a broadly protective polyvalent OspC epitope based vaccine can be produced. Currently, LD diagnostic approaches are unreliable and unable to differentiate between early and late stage disease. An Ab response to OspE family proteins occurs later in infection. The two-Ag diagnostic assay using chimeric OspC proteins and a site-directed mutant of an OspE paralog, accurately differentiated between early and late infection in experimentally infected canines and humans.