The inventive subject matter relates to a recombinant 110 kDa protein from O. tsutsugamuchi, Karp, Kato and Gilliam strains and for a DNA expression system containing DNA encoding the 110 kDa protein of O. tsutsugamuchi. The invention also relates to the use of these recombinant contructs in a formulation for the induction of a protective immune response against O. tsutsugamuchi invection using. The inventive subject matter also relates to a recombinant 110 kDa O. tsutsugamuchi protein or 110 kDa fragments for the production of antigen for use in immunodiagnosistic asssays for scrub typhus.