The invention provides methods, kits, compositions, and devices useful for detection of antibodies that bind to Ehrlichia antigens and/or for differentiation of certain Ehrlichia species from others. In particular, the invention provides methods and kits useful for identifying species of Ehrlichia using populations of isolated peptides.

Disclosed are vaccines containing one or more immunogenic polypeptides derived from an EtpE protein from an Ehrlichia sp. or nucleic acid encoding these polypeptides. Also disclosed is a method for vaccinating a subject against Ehrlichia sp. that involves administering to the subject a composition comprising any of the disclosed vaccines. Also disclosed is a method for diagnosing and/or monitoring the treatment of Ehrlichiosis in a subject that comprising assaying a biological sample (e.g., blood, serum, or plasma sample) from the subject for the presence of an antibody that specifically binds an EtpE polypeptide. Also disclosed are methods for delivering a therapeutic or diagnostic agent to a cell in a subject that involves conjugating the agent, or a delivery vehicle comprising the agent, to polypeptide containing the C-terminal domain of an EtpE protein.

The present invention provides compositions and methods that can be used to determine a peptide signature for an antibody repertoire in a sample comprising multiple antibodies. The method can be used to characterize a phenotype in a sample, such as providing a diagnosis, prognosis or theranosis of a medical condition.

Immunoreactive engineered polypeptides are provided. The engineered polypeptides can be used to diagnose or induce an immune response against E. chaffeensis or E. canis.

Provided herein are compositions and methods for detection and treatment of Rocky Mountain spotted fever (RMSF). The compositions specifically detect Rickettsia rickettsii and do not cross-react with other Rickettsia species providing rapid and accurate detection and diagnosis of RMSF.

Disclosed herein is use of a Rickettsia OmpB -peptide epitope that binds host immune IgM as a specific diagnostic substrate for detecting patient immune IgM antibody to both spotted fever group and typhus group Rickettsia.

Methods and compositions for diagnosing and vaccinating against Ehrlichia chaffeensis are provided.

Provided herein are chimeric polypeptides that may be used, e.g., for the diagnosis of or vaccination against Ehrlichia chaffeensis and/or Ehrlichia canis.