A state-by-state survey of ticks recorded from humans in the United States

Abstract

Based on tick specimens accessioned into the U.S. National Tick Collection, the species of ticks recorded as ectoparasites of humans are documented and compared for 49 U.S. states. A total of 44 tick species was recorded as parasites of humans, consisting of 11 species of soft ticks (Argasidae) and 33 species of hard ticks (Ixodidae). Four of the hard tick species are not native to the U.S. and were removed from travelers returning from foreign destinations. Therefore, we record 40 of the 84 species of U.S. ticks as ectoparasites of humans. Predictably, in the southern U.S. and Atlantic states, all active stages of the lone star tick, Amblyomma americanum (L.), were common ectoparasites of humans. Also, in the eastern U.S., adults of the American dog tick, Dermacentor variabilis (Say), and all active stages (especially adults) of the blacklegged tick, Ixodes scapularis (Say), were commonly recorded. In certain Rocky Mountain and western states, all active stages of the Rocky Mountain wood tick, Dermacentor andersoni (Stiles), predominated, whereas, in most far western states, adults of the western blacklegged tick, Ixodes pacificus Cooley and Kohls, were relatively common parasites of humans. Parasitism by Ornithodoros spp. soft ticks was mainly recorded in the western U.S. These findings, together with records of human parasitism by other tick species in the U.S., are briefly discussed with respect to tick-borne disease risk.