Ticks and tickborne bacterial diseases in humans: An emerging infectious threat

Ticks are currently considered to be second only to mosquitoes as vectors o f human infectious diseases in the world. Each tick species has preferred e nvironmental conditions and biotopes that determine the geographic distribu tion of the ticks and, consequently, the risk areas for tickborne diseases. This is particularly the case when ticks are vectors and reservoirs of the pathogens. Since the identification of Borrelia burgdorferi as the agent o f Lyme disease in 1982, 15 ixodid-borne bacterial pathogens have been descr ibed throughout the world, including 8 rickettsiae, 3 ehrlichiae, and 4 spe cies of the Borrelia burgdorferi complex. This article reviews and illustra te various aspects of the biology of ticks and the tickborne bacterial dise ases (rickettsioses, ehrlichioses, Lyme disease, relapsing fever borreliose s, tularemia, Q fever), particularly those regarded as emerging diseases. M ethods are described for the detection and isolation of bacteria from ticks and advice is given on how tick bites may be prevented and how clinicians should deal with patients who have been bitten by ticks.