Epizootiology of Lyme disease-causing borreliae

Otto Obermeier first observed helical-shaped bacteria, now called borreliae, in the blood of patients diagnosed with epidemic relapsing fever in 1867. 1 The association of borreliae with arthropods was probably first documented in 1903 with the transmission of Borrelia anserina to chickens following bites by soft-bodied ticks. 2 Thereupon, the transmission of endemic relapsing fever-causing borreliae to humans following bites by soft-bodied ticks was reported. 3 Thus, the serial transfer of borreliae from animals to ticks and then to humans was documented. Although erythema migrans in Europe was recognized to be associated with hard-bodied tick bites, 4 to be caused by a bacterium susceptible to penicillin, 5 and to be transmissible from human to human by skin grafts, 6 its spirochetal etiology remained unknown until Willy Burgdorfer observed borreliae in the hard-bodied tick Ixodes dammini and, with Allan Barbour, cultured the spirochetes. 7 The ability to culture borreliae 8 from tissues taken from ticks, 7 humans, 9,10 and wild animals 11,12 in a cell-free medium enabled scientists in both the New and Old Worlds to assemble considerable knowledge on the ecology of this illness now known as Lyme disease or Lyme borreliosis. In this article, the interactions of the causative agent, Borrelia burgdorferi, 13 with its tick vectors, with animal reservoir hosts, and with human disease are reviewed.