Tickborne Coinfections in the United States

Unlike mosquitoes, ticks transmit the broadest range of pathogens, including bacteria, viruses, and parasites. Ticks have capitalized on many competitive advantages offered to them by changes in climate and human lifestyle and a greater abundance of wild animal reservoir hosts no longer effectively controlled. As a result, tick-transmitted coinfections are increasing today with both recognized and newly discovered pathogens that complicate differential diagnosis and antimicrobial treatment. Without the support of immunological and molecular diagnostic techniques, usually only available at federal and some state laboratories, the initial differential diagnosis of tickborne coinfections is complicated and antimicrobial therapy may not cover coinfections. Therefore, the objectives of this review were to identify the newly emerging tickborne pathogens in the United States, to describe the evolving epidemiology of tick-transmitted coinfections, to design a decision tree analysis approach to the clinical diagnosis and management of tickborne coinfections, and to recommend effective strategies for the control and personal prevention of tickborne diseases. Clinicians should suspect tickborne coinfections in returning travelers and vacationers with clinical and immunological evidence of multiple infecting agents, especially in cases of unusual presentation or severity, prolonged duration, or nonresponse to single antibiotic therapy, typically with doxycycline. Decision tree models based on pathogen prevalence rates in ticks and their zoonotic reservoirs may assist clinicians in diagnosing tickborne coinfections and guiding initial antimicrobial therapy.