Dr. Walker's research interests are broadly in the area of obligately intracellular bacteria that are transmitted by arthropod vectors focused on immune mechanisms against rickettsiae, ehrlichiae and Orientia tsutsugamushi and identification of the protein antigens that stimulate immunity. Although the diseases caused by rickettsiae include many long known and feared life threatening infections such as Rocky Mountain spotted fever and epidemic typhus, elucidation of their molecular composition and effector immune mechanisms remains productive lines of investigation. In contrast, human ehrlichioses are truly emerging infectious diseases that are causing increasingly prevalent, severe infections. Ehrlichial pathogenesis and immunity are in the process of being discovered and investigated at present for these novel organisms. His focus has also added the neglected tropical rickettsial disease, scrub typhus.