Ticks can transmit numerous bacterial, parasitic, and viral pathogens to humans, and the secretions of some species can induce allergic reactions or cause paralysis. This chapter aims to provide a broad overview of tick-borne infections endemic to North America and to discuss general principles regarding their epidemiology, therapy, and prevention. Details about each of these infections are provided in their respective chapters.

Epidemiology

Tick-borne infections occur most often in the spring and summer, when ticks are most active, but are reported in colder months as well. Some patients with tick-borne infections will recall a recent tick bite, and many, but not all, report having spent time in a rural or wooded area within 2 to 4 weeks before the onset of illness. Frequently, however, patients are unaware of their recent tick exposure, for several reasons: Tick bites are usually painless, ticks may attach in sites covered by hair or clothing, and ticks in their larval and nymphal stages are very small but still capable of transmitting infection. Tick-borne infections have been reported in urban areas and, in endemic areas, among patients whose only outdoor exposures occurred in their own backyards. Thus the historical findings of tick bite or outdoor exposure may provide useful diagnostic clues, but their absence never excludes the possibility of a tick-borne illness.