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.
