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Chapter 1 : Overview of Tick-Borne Infections of Humans
Tick-borne diseases, long known but historically underappreciated, are increasingly recognized as important threats to public health. Tick-borne infections of humans are zooanthroponoses, or diseases of animals transmissible to humans in which humans are incidental, dead-end hosts. Tick bites are the sole or principal means by which most of these diseases are acquired by humans. Usually, persons become infected with tick-borne diseases when they intrude into an established natural focus (biocenose) where the disease agent is quietly cycling between vertebrate reservoir hosts and their tick vectors. This intersection is increasingly frequent as human populations grow in number and mobility; as more persons reside, work, or recreate in tick-infested habitats; and as changing environments favor ticks and increase their range, density, and likelihood of human interaction. Further, evolving socioeconomic factors and human behaviors can increase the risk that humans will come into contact with ticks and the disease agents they carry. Although students of medicine and public health are usually taught the basics of the more important tick-borne diseases, the emphasis is on clinical diagnosis and management, with less attention paid to epidemiology and to ticks’ fascinating but sometimes complex biology and ecology. Very little, if anything, is taught about tick vectors themselves. Biologists, on the other hand, may learn little about the medical and epidemiological aspects of vector-borne pathogens. This overview of the tick-borne diseases attempts to give a more balanced view and to provide key information in an easy access format.