Ecology of Borreliae and Their Arthropod Vectors
Joseph Piesman and Tom G. Schwan
from: Borrelia: Molecular Biology, Host Interaction and Pathogenesis (Edited by: D. Scott Samuels and Justin D. Radolf). Caister Academic Press, U.K. (2010)
Borreliae are unique among the pathogenic spirochetes by requiring obligate blood-feeding arthropods for their transmission and maintenance in susceptible vertebrate host populations. With one exception, ticks transmit all borreliae and nearly all species are maintained in enzootic foci with humans being only accidental victims to infection. The true relapsing fever spirochetes are transmitted by many species of soft (Argasidae) ticks in the genus Ornithodoros and in many geographic areas, specific species of ticks transmit only one species of spirochete. Specific tick-spirochete associations range from near-desert conditions to high elevation coniferous forests. The four principal hard tick (Ixodidae) species that transmit Lyme disease spirochetes (Borrelia burgdorferi sensu lato) include Ixodes scapularis in eastern North America, I. pacificus in western North America, I. persulcatus in Asia and I. ricinus in Europe. These ticks are basically forest dwellers, spending most of their time hiding in the leaf litter of the forest floor, where humidity is high and the risk of desiccation is low. B. burgdorferi sensu stricto, B. garinii and B. afzelii are the principal genospecies causing human disease. Of these three genospecies, B. burgdorferi sensu stricto is unique in that it has a Holarctic distribution, spanning both the Old World (Palearctic Region) and the New World (Nearctic Region) in the northern hemisphere. Specific rodents were originally identified as the principal reservoirs of B. burgdorferi sensu stricto, including the white footed mouse (Peromyscus leucopus) in North America and the wood mouse (Apodemus sylvaticus), yellow-necked mouse (Apodemus flavicollis) and bank vole (Clethrionomys glareolus) in Europe. Birds also have been identified as reservoirs of B. burgdorferi sensu stricto on both sides of the Atlantic. Since the discovery of the Lyme borreliosis spirochete in 1982, a plethora of knowledge concerning the ecology of the spirochete, its tick vectors and vertebrate hosts has been brought forth through an incredible focus of research efforts. The task before the public health research community is not solely producing more ecological knowledge regarding the Lyme borreliosis spirochetes cycle in nature. Clearly, our immediate challenge is to synthesize and harness available knowledge of spirochete-tick-host interactions to develop ecologically-based interventions to combat Lyme borreliosis read more ...