Tick-borne Diseases: New Territory, New Agents

Importance: The incidence of tick-borne diseases is on the rise across North America as the ranges of tick vectors, such as the blacklegged or deer tick and the lone star tick, expand. In addition, 8 new agents of human tick-borne disease have been discovered in North America in the past few decades. Objective: Our objective is to provide a current overview of tick-borne diseases, including recently described pathogens, in North America for public health professionals, researchers, and clinicians. Our focus is on the importance of regional epidemiology and the clinical spectrum of tick-borne diseases to increase their recognition. Review: We summarize key aspects of the epidemiology, clinical presentation, diagnosis, and treatment of major tick-borne diseases encountered in North America, but we do not provide in-depth descriptions of the diseases or their management. Although not a formal literature review, selected articles are referenced to provide more detailed information on disease epidemiology and specific tick-borne diseases. Findings: Geography determines the likelihood of exposure to different tick-borne diseases, but known regions of risk have changed substantially during the past few decades. Lyme disease remains the most common tick-borne disease, with its highest incidence in the northeast and upper Midwest United States. The erythema migrans rashes of Lyme disease have a wider spectrum of morphology than the textbook “bull’s eye” pattern. Standard or modified 2-tier antibody testing is recommended to aid in diagnosing extra-cutaneous Lyme disease, but the results of this test are often negative during the first few weeks of illness when erythema migrans presents. Many tick-borne diseases, except Lyme disease, present with non-specific febrile illness accompanied by thrombocytopenia and/or leukopenia and elevated hepatic transaminases. Rarely, tick-borne disease may present as fever with cutaneous ulcers or eschars, or with isolated severe neurologic disease, such as encephalitis. Conclusions: Clinicians need to be familiar with the regional epidemiology and clinical presentation of tick-borne diseases. In addition, due to travel to other regions by many North Americans, clinicians also need to be aware of the common tick-borne diseases that may be acquired across our continent.