Tick-borne bacterial pathogens of humans cause significant morbidity and mortality throughout the United States and abroad. Lyme disease, caused by Borrelia burgdorferi, is the most prevalent arthropod-borne disease of humans in the United States and many other countries throughout Europe and Asia. Tick-borne relapsing fever, caused by Borrelia hermsii, is endemic in scattered foci throughout many regions of higher elevation in the western United States. Rocky Mountain spotted fever, caused by Rickettsia rickettsii, kills more people every year in the United States than any other vector-borne disease. Our work has focused in two areas: 1) to improve on the serodiagnosis of Lyme disease and tick-borne relapsing fever by using recombinant DNA technology to clone genes of spirochetes that express proteins that induce specific and detectable antibody responses in; 2) to examine how spirochetes and rickettsiae adapt to their tick and mammalian hosts. This work requires that we maintain colonies of Ixodes scapularis and Ornithodoros hermsi, the respective tick vectors of Lyme disease and relapsing fever spirochetes, and infect these ticks via a laboratory mouse - tick cycle. Wood ticks, Dermacentor andersoni, are colonized for the rickettsial work.Efforts toward improving serodiagnosis during the past year have been directed at cloning and expressing the internal, hypervariable regions of 26 major outer surface protein genes of Borrelia hermsii. Each of these proteins will be used with other antigens (GlpQ, flagellin, Vmp33) to test antiserum from relapsing fever patients and experimentally infected mice. Our studies on the interaction of spotted fever rickettsiae in wood ticks ended this year (see below). Our spirochete studies have continued by examining the temporal changes in outer surface proteins of both B. burgdorferi and B. hermsii during tick infection and transmission by tickbite. Unpublished observations to date suggest that both OspC of B. burgdorferi and Vmp33 of B. hermsii are required for mammalian infection when spirochetes are delivered by tickbite. This year we began producing monoclonal antibodies to different types of Vmp33 (the tick associated proteins) of B. hermsii. These antibodies will allow us to examine multiple infections in ticks using phylogenetically different spirochetes. Our studies investigating the pathogenesis of relapsing fever using a murine model has advanced using biotelemetry to monitor body temperature, heart rate and activity of animals infected either by needle inoculation or tickbite. - Tick-borne diseases, Lyme disease, relapsing fever, spotted fever, serodiagnosis